sam user guide

System Advisor Model (SAM)

User Guide

Version 2011.5.23Manual Release Date 5/23/2011

This user guide is a copy of SAM's Help system. To see the Help system,click Help, Contents in SAM, or press the F1 key (command-? in Mac OS)from any page in SAM.

The System Advisor Model ("Model") is provided by the National Renewable Energy Laboratory ("NREL"), which isoperated by the Alliance for Sustainable Energy, LLC ("Alliance") for the U.S. Department Of Energy ("DOE") andmay be used for any purpose whatsoever.

The names DOE/NREL/ALLIANCE shall not be used in any representation, advertising, publicity or other mannerwhatsoever to endorse or promote any entity that adopts or uses the Model. DOE/NREL/ALLIANCE shall notprovide any support, consulting, training or assistance of any kind with regard to the use of the Model or anyupdates, revisions or new versions of the Model.

YOU AGREE TO INDEMNIFY DOE/NREL/ALLIANCE, AND ITS AFFILIATES, OFFICERS, AGENTS, ANDEMPLOYEES AGAINST ANY CLAIM OR DEMAND, INCLUDING REASONABLE ATTORNEYS' FEES, RELATED TOYOUR USE, RELIANCE, OR ADOPTION OF THE MODEL FOR ANY PURPOSE WHATSOEVER. THE MODEL ISPROVIDED BY DOE/NREL/ALLIANCE "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING BUTNOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULARPURPOSE ARE EXPRESSLY DISCLAIMED. IN NO EVENT SHALL DOE/NREL/ALLIANCE BE LIABLE FOR ANYSPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER, INCLUDING BUT NOTLIMITED TO CLAIMS ASSOCIATED WITH THE LOSS OF DATA OR PROFITS, WHICH MAY RESULT FROM ANYACTION IN CONTRACT, NEGLIGENCE OR OTHER TORTIOUS CLAIM THAT ARISES OUT OF OR INCONNECTION WITH THE USE OR PERFORMANCE OF THE MODEL.

Microsoft and Excel are registered trademarks of the Microsoft Corporation.

While every precaution has been taken in the preparation of this document, the publisher and the author assumeno responsibility for errors or omissions, or for damages resulting from the use of information contained in thisdocument or from the use of programs and source code that may accompany it. In no event shall the publisher andthe author be liable for any loss of profit or any other commercial damage caused or alleged to have been causeddirectly or indirectly by this document.

Produced: May 2011

© 2011 National Renewable Energy Laboratory

Solar Advisor Model 2011.5.23 May 2011

2

3Contents


Table of Contents

1 Introduction 8

...........................................................................................................................81.1 About SAM

...........................................................................................................................101.2 User Support

...........................................................................................................................111.3 Keep SAM Up to Date

2 Getting Started 12

...........................................................................................................................122.1 Start a Project

...........................................................................................................................162.2 Welcome Page

...........................................................................................................................182.3 Main Window

...........................................................................................................................192.4 Input Pages

...........................................................................................................................212.5 Run Simulations

...........................................................................................................................222.6 Results Page

...........................................................................................................................242.7 Export Data and Graphs

...........................................................................................................................272.8 Manage Cases

...........................................................................................................................282.9 Menus

...........................................................................................................................322.10 Notes

...........................................................................................................................332.11 File Formats

3 Systems 34

...........................................................................................................................343.1 Overview

...........................................................................................................................393.2 Climate

...........................................................................................................................513.3 Photovoltaic Systems

............................................................................................................................51Getting Started with PV

............................................................................................................................55Array

............................................................................................................................70PVWatts Solar Array

............................................................................................................................71Shading

............................................................................................................................82Module

............................................................................................................................99Inverter

...........................................................................................................................1043.4 Generic System

............................................................................................................................104Generic System Overview

............................................................................................................................104Generic Plant

...........................................................................................................................1053.5 Dish Stirling

............................................................................................................................106System Library

............................................................................................................................106Solar Field

SAM Help4


............................................................................................................................109Collector

............................................................................................................................110Receiver

............................................................................................................................113Stirling Engine

............................................................................................................................115Parasitics

............................................................................................................................116Reference Inputs

...........................................................................................................................1173.6 Parabolic Trough Empirical

............................................................................................................................118Solar Field

............................................................................................................................128SCA / HCE

............................................................................................................................135Power Block

............................................................................................................................140Thermal Storage

............................................................................................................................148Parasitics

...........................................................................................................................1503.7 Parabolic Trough Physical

............................................................................................................................152Solar Field

............................................................................................................................169Collectors (SCAs)

............................................................................................................................172Receivers (HCEs)

............................................................................................................................176Power Cycle

............................................................................................................................180Thermal Storage

............................................................................................................................188Parasitics

...........................................................................................................................1903.8 Generic Solar System

............................................................................................................................190Solar Field

............................................................................................................................191Power Block

............................................................................................................................191Thermal Storage

...........................................................................................................................1913.9 Power Tower

............................................................................................................................192Heliostat Field

............................................................................................................................197Optimization Wizard

............................................................................................................................202Tower and Receiver

............................................................................................................................207Power Cycle

............................................................................................................................210Thermal Storage

............................................................................................................................217Parasitics

...........................................................................................................................2193.10 Solar Water Heating

............................................................................................................................219SWH System

...........................................................................................................................2233.11 Geothermal Power

............................................................................................................................224Resource

............................................................................................................................225Plant and Equipment

...........................................................................................................................2273.12 Geothermal Co-production

............................................................................................................................227Resource and Power Generation

5Contents


...........................................................................................................................2303.13 Small Scale Wind

............................................................................................................................230Small Scale Wind Overview

............................................................................................................................230Wind Climate

............................................................................................................................242Small Scale Wind System

...........................................................................................................................2443.14 Utility Scale Wind

............................................................................................................................244Utility Scale Wind Overview

............................................................................................................................244Wind Resource

............................................................................................................................248Wind Farm Specifications

4 Costs and Financing 251

...........................................................................................................................2514.1 Financing Overview

...........................................................................................................................2554.2 System Summary

...........................................................................................................................2564.3 Utility Rate

...........................................................................................................................2704.4 Financing

...........................................................................................................................2854.5 Tax Credit Incentives

...........................................................................................................................2884.6 Payment Incentives

...........................................................................................................................2914.7 Annual Performance

...........................................................................................................................2934.8 System Costs

............................................................................................................................293PV System Costs

............................................................................................................................298Trough System Costs

............................................................................................................................304Tower System Costs

............................................................................................................................309Dish System Costs

............................................................................................................................314Generic Solar System Costs

............................................................................................................................317Generic System Costs

............................................................................................................................321SWH System Costs

............................................................................................................................326Small Scale Wind Capital Costs

............................................................................................................................328Wind Farm Costs

............................................................................................................................331Geothermal System Costs

............................................................................................................................331Co-Production Costs

...........................................................................................................................3324.9 Energy Payment Dispatch

...........................................................................................................................3344.10 Electric Load

5 Results 339

...........................................................................................................................3395.1 Metrics Table

............................................................................................................................341Annual Energy

............................................................................................................................341Annual Water Usage

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............................................................................................................................342Capacity Factor

............................................................................................................................342Costs

............................................................................................................................342Debt Fraction

............................................................................................................................343First year kWhac/kWdc

............................................................................................................................343First Year PPA Price

............................................................................................................................345Gross to Net Conv Factor

............................................................................................................................345Internal Rate of Return

............................................................................................................................346Levelized Cost of Energy (LCOE)

............................................................................................................................352Minimum DSCR

............................................................................................................................353Net Present Value

............................................................................................................................354Payback Period

............................................................................................................................354PPA Escalation

............................................................................................................................355System Performance Factor

............................................................................................................................355Total Land Area

............................................................................................................................355Year 1 Revenues

...........................................................................................................................3565.2 Graphs and Charts

...........................................................................................................................3595.3 Base Case Cash Flow

............................................................................................................................360Residential and Commercial

............................................................................................................................367IPP and Commercial PPA

............................................................................................................................371New Utility Structures (Draft)

...........................................................................................................................3745.4 Tabular Data Browser

...........................................................................................................................3765.5 Sliders

...........................................................................................................................3775.6 Case Summary

...........................................................................................................................3795.7 Hourly Results

............................................................................................................................379Hourly Pricing Data

............................................................................................................................381PV Component Hourly Data

............................................................................................................................383PVWatts Hourly Data

............................................................................................................................384Physical Trough Hourly Data

............................................................................................................................386Empirical Trough Hourly Data

...........................................................................................................................3885.8 Simulation Results File

............................................................................................................................388PV Component Simulation

............................................................................................................................390Physical Trough Simulation

............................................................................................................................395Empirical Trough Simulation

6 Time Series Data Viewer (DView) 399

7Contents


7 Advanced Topics 401

...........................................................................................................................4017.1 Parametric Analysis

...........................................................................................................................4067.2 Sensitivity Analysis

...........................................................................................................................4107.3 Optimization

...........................................................................................................................4147.4 Statistical

...........................................................................................................................4197.5 Multiple Systems

...........................................................................................................................4217.6 Excel Exchange

...........................................................................................................................4237.7 Simulator Options

...........................................................................................................................4247.8 User Variables

...........................................................................................................................4247.9 SamUL

............................................................................................................................428Data Variables

............................................................................................................................431Flow Control

............................................................................................................................435Arrays of Data

............................................................................................................................438Function Calls

............................................................................................................................441Input, Output, and System Access

............................................................................................................................443Interfacing with SAM Analyses

............................................................................................................................446Case Study

............................................................................................................................451Library Reference

...........................................................................................................................4647.10 Generating Code

...........................................................................................................................4667.11 Libraries

8 References 474

SAM Help8

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1 Introduction

1.1 About SAMSAM is a performance and economic model designed to facilitate decision making for people involved in therenewable energy industry, ranging from project managers and engineers to incentive program designers,technology developers, and researchers. SAM makes performance predictions for grid-connected solar,solar water heating, wind, and geothermal power systems and makes economic calculations for bothprojects that buy and sell power at retail rates, and power projects that sell power through a power purchaseagreement.

The model calculates the cost of generating electricity (or the value of energy saved by a solar water heatingsystem) based on information you provide about a system's physical configuration, its location, and thecost of installing and operating the system. SAM's financial model accounts for different financingstructures, taxes, and incentives.

SAM consists of a performance model and financial model. The performance model calculates a system'senergy output on an hourly basis (sub-hourly simulations are available for some technologies). The financialmodel calculates annual project cash flows over a period of years for a range of financing structures forresidential, commercial, and utility projects.

The user interface provides access the input assumptions and displays results in tables and graphs, whichrange from a table of basic metrics such as levelized cost of energy and total annual output, to tables ofdetailed hourly simulation results, and a cash flow table showing project income, expenses, financingcosts, incentive payments and other details on a year-by-year basis over the analysis period.

All graphs and tables in SAM can easily be exported to word processing, spreadsheet, and presentationsoftware. The Excel-exchange feature also makes it possible to use Excel to calcualte values that SAMcan automatically use to populate input variables.

Advanced modeling options allow for parametric studies, optimization, sensitivity and other statisticalanalyses, optimization, and statistical analyses to investigate impacts of variations and uncertainty inperformance, cost, and financial parameters on model results.

SAM models system performance using the TRNSYS software developed at the University of Wisconsincombined with customized components. TRNSYS is a validated, time-series simulation program that cansimulate the performance of photovoltaic, concentrating solar power, water heating systems, and otherrenewable energy systems using hourly resource data. TRNSYS is integrated into SAM so there is no needto install TRNSYS software or be familiar with its use to run SAM.

The Department of Energy's Solar Energy Technologies Program (SETP) initially developed SAM foranalysis to support the implementation of the SETP Systems Driven Approach. The model also hasapplications for the solar industry for planning research and development programs, and developing projectcost and performance estimates. SAM is being used as part of the solicitation and evaluation process forSETP funding programs.

SAM also includes a simple model of fuel-based electric generation that can be used to model baselinesystems for comparison with the solar technologies.

For help getting started using SAM, see Start a Project.

About SAM 9

Solar Advisor Model 2011.5.23

Model Structure

SAM consists of a user interface, calculation engine, and programming interface. The user interface is thepart of SAM that you see, and provides access to input variables and simulation controls, and displaystables and graphs of results. SAM's calculation engine performs a time-step-by-time-step simulation of apower system's performance, and a set of annual financial calculations to generate a project cash flow andfinancial metrics. The programming interface allows external programs to interact with SAM.

The user interface performs three basic functions:

1. Provide access to input variables, which are organized into input pages. The input variables describethe physical characteristics of a system, and the cost and financial assumptions for a project.

2. Allow you to control how SAM runs simulations. You can run a basic simulation, or more advancedsimulations for optimization and sensitivity studies.

3. Provide access to output variables in tables and graphs on the Results page, and in files that you canaccess in a spreadsheet program or graphical data viewer.

SAM's scripting language SamUL allows you to automate certain tasks. If you have some experiencewriting computer programs, you can easily learn to write SamUL scripts to set the values of input variablesby reading them from a text file or based on calculations in the script, run simulations, and write values ofresults to a text file. You can also use SamUL to automatically run a series of simulations using differentweather files.

Excel Exchange allows you to use Microsoft Excel to calculate values of input variables. With ExcelExchange, each time you run simulations, SAM opens a spreadsheet and, depending on how you'veconfigured Excel Exchange, writes values from SAM input pages to the spreadsheet, and reads values fromthe spreadsheet to use in simulations. This makes it possible to use spreadsheet formulas to calculatevalues of SAM input variables.

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Calculation Engine

Each renewable energy technology in SAM has a corresponding performance model that performscalculations specific to the technology. Similarly, each financing option in SAM is also associated with aparticular financial model with its own set of inputs and outputs. The financial models are as independentas possible from the performance models to allow for consistency in financial calculations across thedifferent technologies.

A performance simulation consists of a series of many calculations to emulate the performance of thesystem over a one year period in time steps of one hour for most simulations, and shorter time steps forsome technologies.

A typical simulation run consists of the following steps:

1. After starting SAM, you select a combination of technology and financing options for a case in the userinterface.

2. Behind the scenes, SAM chooses the proper set of simulation and financial models.

3. You specify values of input variables in the user interface. Each variable has a default value, so it notnecessary to specify a value for every variable.

4. When you click the Run button, SAM runs the simulation and financial models. For advanced analyses,you can configure simulations for optimization or sensitivity analyses before running simulations.

5. SAM displays graphs and tables of results in the user interface's Results page.

1.2 User SupportFor information about any page in the software, do one of the following:

Press the F1 key (Command-? on a Mac).

Click the help button at the top right corner of each input page.

Click Help Contents from the Help menu.

In secondary windows, click the Help button for information about thewindow.

For additional help, try:

Click User Guide on the Help menu to open a user guide in PDF format.

For general information about the model, including a discussion of projectcosts, references to related publications and a list of frequently askedquestions, and other information visit the SAM website: https://www.nrel.gov/analysis/sam/.

https://www.nrel.gov/analysis/sam/

https://www.nrel.gov/analysis/sam/

User Support 11


To participate in the SAM discussion board, join Google Groups using youremail address (a Gmail account is not required) at http://groups.google.com/group/sam-user-group.

If you have questions comments about the software, please send an emailto the support team at [email protected]. You can also usethe User Support command on the Help menu to contact the supportteam.

1.3 Keep SAM Up to DateThe SAM team releases new versions of SAM periodically. To find out if your version of SAM is the latestversion, check the SAM website. SAM's welcome page also displays news from the SAM team, includingannouncements of new versions.

SAM displays the version number in the title bar of the Main window:

You can also find the SAM version number along with version numbers of other components of the softwareby clicking About on the Help menu:

Checking for Updates

Updates may be available before a new release is available to address minor issues with the software.

http://groups.google.com/group/sam-user-group

http://groups.google.com/group/sam-user-group

mailto:[email protected]

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To check for updates:

On the Help menu, click Check for updates to this version.

2 Getting Started

2.1 Start a ProjectThe following procedure describes the basic steps to run a simulation of a project based on photovoltaic orparabolic trough technology using default input assumptions to help you get started using SAM.

See also:

Financing Overview

Getting Started with PV

A. Create a project

Type a name for your project and click Create.

For details, see Options for Starting a Project.

B. Choose a technology

For photovoltaic systems, choose Component-based Models if you want to choose a specific module and

Start a Project 13


inverter from a list.

Choose PVWatts System Model if you want to model the entire system using a single derate factor.

For parabolic trough systems, choose Physical Trough System under Concentrating Solar Power. Ifyou are modeling a system with a configuration similar to the SEGS plants choose Empirical TroughSystem.

For other technologies, choose the appropriate option.

For descriptions of the technology options, see Technologies.

C. Choose a financing option

For projects that buy and sell electricity at retail rates, choose either Residential or Commercial.

For power projects that sell power at a price negotiated through a power purchase agreement, choose either Commercial PPA or one of the options under Utility Market.

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To model the performance of a system without the financial model, choose No Financials. Note that thePower Tower model requires that you choose a financial model because the performance model includes anoptimization algorithm that requires information about equipment costs.

Start a Project 15


For a description of the financing options, see Financing Options.

D. Review inputs

After creating your file, open each input page and review the default assumptions.

See Input Pages for details.

E. Run simulations

To run simulations, click the Run button.

See Run Simulations for details.

F. Review results

When simulations are complete, SAM displays a summary of results in the Metric table.

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You can display graphs and tables of detailed results data on the Results page.

2.2 Welcome PageWhen you start SAM, it displays a Welcome window with three options for starting a project.

Create a new file to start a project. Type the project name and click Create to display the Technologyand Market window where you choose a technology and financing option before creating a new zsamfile for your project.

Open a sample file. The sample files illustrate how to model some common types of projects and howto use some of SAM's more advanced modeling techniques.

Open a recent file. The Recent Files list contains project files that were saved during previous SAMsessions.

Welcome


Note. When you install SAM, it creates the SAM Projects folder in your default documents folder anduses this as the default location for storing project files. You can change the default project file locationby clicking Preferences in the File Menu.

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2.3 Main WindowThe main window gives you access to the input pages for each of the cases in the project:

The case tabs display different cases in the project. A project may consist of a single case, or maycontain more than one case. Click a tab to display the case. Click the 'x' on a tab to delete the case.

The navigation menu displays a list of input pages available for the technology and market of the currentcase. Click an item in the navigation menu to display an input page. The active input page is indicatedon the menu in blue. When the menu is too long to fit in the window, use the vertical scroll bar to movethrough the menu, or resize the Main window to make the entire menu visible. Each item on thenavigation menu also displays key data the input pages. For example, the system costs item in thenavigation menu shows the system's total installed cost.

Input Pages 19


2.4 Input Pages

SAM's input pages provide access to the input variables and options that define the assumptions of youranalysis. When you start a project, whether from a sample file, by creating a new project, or opening anexisting project, SAM populates all of the input variables with default values. This means that you can getstarted with your analysis even before you have final values for all of the input variables.

Note. To see a list of all input variables and their values for a case, on the Results menu, click CaseSummary, Send To Excel. SAM creates a workbook with a worksheet listing the input variables.

Colors of Input Variables

The text and data box colors on the input pages indicate the kind of information they contain:

Note. The appearance of text and text boxes depends on whether you are running SAM on Windows orMac OS. The screenshots below are for Windows.

White data boxes display input variables that you can modify by typing values in the box:

Blue data boxes are for reference values that SAM either displays from other input pages, or calculatesfrom other input variables. Data in blue cannot be modified. Press the F1 key on your keyboard(Command-? on a Mac) to see the Help topic with descriptions of the equations SAM uses to calculatethese values:

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Gray data boxes show values for your reference. For example, these input variables on the Climatepage show annual averages calculated from data stored in the weather file. You cannot modify data ingray:

Blue underlined text indicates links to websites with useful information related to the input page:

Informational text describing the input variables appears in orange font:

Library buttons populate input variables with values from a library of stored parameters. Modifying avalue on an input page does not change the value stored in the library. See Working with Libraries for tolearn more about libraries:

Run Simulations 21


2.5 Run SimulationsAfter reviewing and modifying inputs on the input pages, click the Run all Simulations button to runsimulations:

SAM runs simulations based on the values of input variables that appear on the input pages and reportsthose values as "base case" results.

In addition to the base case, SAM runs simulations for any additional simulations you may have set up onthe Configure Simulations pages, such as parametric or sensitivity analyses.

You can also run simulations from the Case menu (See Menus for a description of menu commands):

Run All Simulations

Runs all of the simulations configured in the current case. Equivalent to clicking the Run button. Thisoption does not save hourly results.

Run Base Case Only

Runs a single simulation based on the input values shown on the input pages, ignoring any parametric,sensitivity, optimization or other configurations requiring multiple simulation runs, and does not savehourly results.

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2.6 Results PageWhen you run simulations based on inputs you specify on the Systems pages in SAM, the performancemodel creates a file of hourly data called the simulation results file. There are several options in SAM forviewing data from this file:

The Metrics table displays key metrics that summarize the performance model results, such as totalannual electrical output, capacity factor, etc.

Graphs and charts display monthly electrical output and an annual energy flow graph.

The Tabular Data Browser allows you to build a custom table of hourly, monthly, and annual results onthe Results page.

The Case Summary workbook includes a worksheets of hourly, monthly, and annual data.

The Time Series Data Viewer (DView) displays time series and statistical graphs of hourly data from the simulation output file.

SAM's financial model uses the sum of the performance model's 8,760 hourly output values in kWh as aninput representing the system's total annual electrical output in kWh. The financial model then calculatesthe project's cash flow based on the inputs you specify on the Costs and Financing pages. SAM displaysfinancial model results in the following places:

The Metrics table displays key metrics including the LCOE, PPA price, IRR, payback period, etc.

The Base Case Cash Flow table shows details of the project's cash flow.

The Tabular Data Browser allows you to build a custom table of cost and cash flow data along withmetrics. shows data from the cash flowAfter running simulations, SAM displays the Results page,which provides access to many graphs and tables of output data.

Results


Simulation Warning Messages

Under some conditions, SAM displays simulation warnings. When there are simulation warnings, thesimulation warning button appears at the top right corner of the Results page. Click the Show SimulationWarnings button to view warning messages:

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2.7 Export Data and GraphsSAM provides a several options for exporting images of graphs and results data to other applications forfurther analysis or inclusion in reports and other documents.

Results Page View Graphs and Charts

When the Results page is in the View Graphs and Charts mode, you can export the data in the graphsusing one of the following methods:

Click Copy Graph Data to copy data from the graph to your computer's clipboard. You can then pastethe data into a spreadsheet or other program.

Right-click the graph to copy either data from the graph or an image of the graph to the clipboard, orexport it to a file:

On the Results menu, click Graph Data to view a list of options for exporting graph data:

Export Data and Graphs 25


Results Page Cash Flow and Tabular Data Browser

The base case cash flow table and tabular data browser provide three options for exporting data shown inthe tables:

Copy to clipboard

Copies the table to your clipboard. You can paste the entire table into a word processing document,spreadsheet, presentation or other software.

Save as CSV

Saves the table in a comma-delimited text file that you can open in a spreadsheet program or texteditor.

Send to Excel (Windows only)

Saves the table in an Excel file.

Case Summary and Hourly Results

The case summary contains data for the current case. To open the case summary, either click the Exportand view data button to display the options in the Export Data window:

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Or, click an option on the Results menu to display a the same list of export options in menus.

Note for Mac users. The Send to Excel and View Hourly Time Series (DView) options are not availableon Mac computers. DView does not run on Mac OS, and SAM cannot control Microsoft Excel on MacOS. For details on options for viewing data on a Mac, see Data Viewer (DView).

Graph Data

Exports data from all graphs currently visible on the Results page.

Cashflow

Exports data from the cash flow table. The exported data is the same as the data shown in the basecase cash flow table on the Results page.

Case Summary

Exports hourly performance data with monthly and annual averages and the cash flow table for thecurrent case.

The Send to Excel option (Windows only) exports the data to separate worksheets in an Excelworkbook, and includes a list of input variables.

The Save as CSV and To Clipboard options exports some of the case summary data as comma-separated values in a single file.

See Case Summary for details.

Save as CSV

Exports data to a comma-separated text file.

To Clipboard

Exports data to your computer's clipboard. Use the Paste command to copy the data to a spreadsheet

Export Data and Graphs 27


or other file.

Send to Excel

For Windows computers with Microsoft Excel installed only. Exports data to an Excel workbook andopens the file in Excel.

View Hourly Times Series (DView)

For Windows computers only. Opens the hourly results file in DView, which displays graphs of hourlydata. See Data Viewer (DView) for details.

2.8 Manage CasesA case is a complete set of input data and results. A project file contains at least one case. SAM usestabs to display each case in the project, analogous to the way Excel displays worksheets in a workbook.

SAM indicates the active case name in bold type:

Note. The number of cases that a project file can contain depends on the storage and computingresources available on your computer. SAM displays a warning if you try to add more than six cases toyour project. Your computer may be able to handle projects with more than six cases, but for the modelto run efficiently, it is best to keep the number of cases to less than seven.

Why Use Cases?

By creating more than one case in a file, you can easily compare the assumptions and results of differentanalysis scenarios. For example, you could use cases to compare the cost and performance of aresidential photovoltaic system in several locations by defining a separate case for each location, or youcould compare a utility-scale photovoltaic and concentrating solar power systems.

Creating and Deleting Cases

To add, remove, and rename cases, used the four commands on the Case menu:

Create Case

Adds a new case to the project file. SAM displays the Technology and Market window for you tochoose options for the case.

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Rename Case

Change the label identifying the case that appears on the case tab.

Duplicate Case

Creates a copy of the active case, with a duplicate set of input parameters and results.

Delete Case

Deletes the active case. You can also delete a case by clicking the 'x' on the case's tab.

For projects with more cases than can be displayed on tabs, the scroll and list controls allow you to accessall of the cases in the project.

2.9 MenusSAM's menus provide access to commands for managing projects, running simulations, exporting results,and getting more information about the model.

Contents

File menu commands allow you to manage files, access component libraries, clearthe simulation cache (advanced feature) and close SAM

Case menu commands apply to the current case, which indicated by the activecase tab in the main window.

Results menu commands allow you to export results for the current case

Developer commands for managing SamUL scripts.

Help for accessing help and version information.

Menus 29


File

NewCreate a new file using default input values. SAM creates a zsam file with a single case and no results.

OpenOpen an existing zsam file.

Open Sample FileOpen a sample file that contains a complete set of inputs and results. The submenu lists the availablesample files. SAM creates a zsam file with inputs and results for one or more cases.

Open SCIF FileOpen a SCIF file created in Version 3.0 or 2.5 of the model. Contact SAM Support at [email protected] for help with files from old versions of SAM.

Import one or more cases from another zsam file.

SaveSave the project as a zsam file in its current location.

Save AsSave the project as a zsam file in a different location or with a new name.

CloseClose the zsam file without exiting SAM.

Clear Cached SimulationsClears stored results and other data from computer memory. Use this command if the programbecomes sluggish after running a very large number of simulations, or if you are setting up very complexsimulations and want to clear the cache before running them.

LibrariesOpen the library editor to view or modify component libraries. See Libraries for details.

PreferencesOpen the Preferences window.

Recent FilesOpen a zsam file from the recent files list.

QuitClose the zsam file and exit SAM.

Case

Create CaseCreate a new case in the project. SAM opens the Technology and Market window where you chooseoptions for the case. The new case will open with default input values and no results.

Rename CaseChange the name of the current case.



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Duplicate CaseCreate a copy of the current case.

Delete CaseDelete the current case. You can also delete a case by clicking the 'x' in the case's tab.

Run All SimulationsRuns all of the simulations configured in the current case. Equivalent to clicking the Run button.

Run Base Case OnlyRuns a single simulation based on the input values shown on the input pages, ignoring any parametric,sensitivity, optimization or other configurations requiring multiple simulation runs, and does not savehourly results.

Reset to Tech/Market Default InputsReplaces all values on input pages with default values.

Clear Case ResultsClears results from the current case. SAM removes any graphs and sliders you may have created forthe case.

AdvancedThe advanced options create lines of code in Excel VBA, ANSI C, or for MATLAB that you can use inyour own programs to call SAM. See Generating Code for details.

ResultsThe Results menu commands allow you to export results for the current case to:

The clipboard for pasting into documents.

Comma-delimited text files.

Excel files (PC computers running Windows only).

The built-in DView data viewer for graphing hourly data (PC computers running Windows only).

Note. If the current case includes simulations that involve multiple input values, such as for parametricand sensitivity analyses, SAM only exports results for input values shown on the input pages, not forranges of values defined in simulation configurations.

Graph Data

Exports data from the graphs currently displayed on the Results page.

Cashflow

Exports cash flow data for the current case.

Case Summary

Exports all performance and cash flow data for the current case. If you choose the Send to Exceloption, SAM creates a workbooks that includes a worksheet listing all of the input variables with theirvalues.

View Hourly Time Series (DView)

Opens the DView data viewer and displays graphs of hourly data. See Time Series Data Viewer (DView)

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for details.

Simulations

ParametricsDisplays the parametric analysis page allowing you to assign multiple values to input variables forparametric studies and optimization. See Parametric Analysis for details.

SensitivityDisplays the sensitivity analysis page allowing you to specify a range of values to input variables forsensitivity analyses. See Sensitivity Analysis for details.

OptimizationDisplays the optimization page allowing you to specify an objective function and find the optimal value ofinput variables. See Optimization for details.

StatisticalDisplays the statistical analysis page allowing you to explore uncertainty in input variables. SeeStatistical Analysis for details.

Multiple SystemsDisplays the multiple systems page where you can build a system as a set of subsystems. SeeMultiple Systems for details.

Excel ExchangeDisplays the excel exchange page where you can set up a data exchange between SAM and Excelwhen you want to use Excel to calculate values of SAM input variables. See Excel Exchange fordetails.

Simulator OptionsDisplays the simulator options page where you can specify the simulation time step and to configureSAM to run custom TRNSYS decks. See Simulator Optionsfor details

Developer

New SAMUL ScriptOpens the script editor to create a program in SAM User Language (SamUL) to automate SAMmodeling tasks. See SamUL for details.

Help

Help ContentsOpens SAM's help system.

User GuideOpens the user guide, which is a version of the help system in PDF format.

SamUL GuideOpens the instructions in PDF format for using the SAM User Language, a scripting language thatallows you to automate SAM modeling tasks.

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Release NotesDisplays SAM's version history.

Web SiteOpens the SAM website in your computer's default browser. (Requires an internet connection.)

User GroupOpens the SAM discussion board on the Google Groups website in your computer's default browser.(Requires an internet connection.)

User SupportOpens your computer's default email program to compose an email that you can send to the SAMsupport team at [email protected]. (Requires an internet connection.)

Financial SpreadsheetsDisplays a list of Excel workbooks that mimic SAM's financial model using Excel formulas that you canuse to learn more about how the financial model works.

Download New Versions of SAMOpens the SAM website's download page. See Keep SAM Up to Date for details.

Check for updates to this versionChecks for updates to the SAM, component libraries, and help system, and allows you to update yoursoftware when updates are available. (Requires an internet connection.)

AboutDisplays the legal disclaimer and information about the version of your copy of the software.

2.10 NotesThe Notes feature allows you to store text associated with each input page and with the Results page.

To create notes:

1. From any input page or the Results page, click the Show Notes button at the top right of thewindow.

2. Type your text in the notes window.

3. Click the Notes window's close button to hide the window and save your notes.

For input page notes, SAM displays a Notes icon in the navigation menu indicating that there arenotes associated with the input page.


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For Results page notes, SAM opens the notes whenever you navigate to the page and after runningsimulations.

To delete notes:

1. Open the Notes window containing the notes you want to delete.

2. Select all text in the Notes window and press the Delete key.

3. Close the Notes window. SAM will remove the appropriate Notes icon from the navigation menu.

2.11 File FormatsSAM uses the following types of files to store and transfer data. The file formats are listed below by fileextension in alphabetical order.

Contact [email protected] for more information.

BAS is a text file containing VBA code for use with Excel.

BMP is a graphics file format used to export graph images.

C is a text file containing ANSI C code for use in a C program.

CSV is a text file containing a table comma-delimited columns that the model uses to export resultsdata from graphs and tables. Weather files in TMY3 format also use the CSV extension.

DVIEW is a file format used by SAM's time series data viewer, DView.

EPW is a weather file format that SAM can read directly.

M is a text file containing MATLAB code.

OUT is a text file format generated by SAM's simulation engine (TRNSYS) to store hourly performancedata.

SAMLIB is a text file used to store data for a SAM library.

SCIF (SAM compressed inputs file) is an obsolete compressed file format used in SAM versions 2.5through 3.0. The current version of SAM can open SCIF files created by older versions of the model.

SUL is a text file containing SamUL script for automating SAM analyses.

TM2 and TM3 are weather file formats that SAM can read directly.

XLS are Excel files used to export data from SAM and to exchange data between the model and Excel.Note that Excel files must be in Excel 2003-2007 XLS format, and not in the newer XLSX format.

ZSAM files store project data, which includes inputs and results for one or more cases.


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3 Systems

3.1 OverviewEach renewable energy technology in SAM has a corresponding performance model that performscalculations specific to the technology. Most of the models perform hourly simulations to calculate the totalannual electric output of the system, which is then used by the financial model to calculate project theproject cash flow and financial metrics.

Notes.

The solar water heating model calculates the thermal output of the system, assuming that it displaceselectricity that would normally heat water in a conventional water heating system.

Because of the nature of the technology, the geothermal model calculates system performance over aperiod of years rather than hours.

SAM can perform sub-hourly simulations for advanced analyses, but relies on interpolation to determinethe solar resource based on hourly weather data.

Photovoltaic Systems: Component-based Models

SAM models grid-connected photovoltaic systems that consist of a photovoltaic array and inverter. Thearray can be made up of flat-plate or concentrating photovoltaic (CPV) modules with one-axis, two-axis, orno tracking. The current version of the software includes simple models of loads and storage for grid-connected systems with electric storage batteries.

The Component-based Models option represents the performance of a photovoltaic system using separatemodels to represent the performance of the module and inverter. This is in contrast with the PVWattsSystem Model, which represents the entire system using a single model.

The SAM Performance Models option allows you to choose between the Sandia, CEC, and single-pointefficiency models for photovoltaic modules, and between the Sandia and single-point efficiency models forinverters.

ModulesEach of the four available module performance models uses a different algorithm to predict moduleperformance:

The Sandia PV Array Performance Model calculates hourly efficiency values based on data measuredfrom modules and arrays in realistic outdoor operating conditions. The Sandia model tends toproduce more accurate predictions of module performance than the CEC model. However, because ofthe time and effort required to make the field measurements, the Sandia module database is less up-to-date than the CEC database.

The California Energy Commission (CEC) Performance Model predicts module performance based ona database of module characteristics determined from module ratings. Like the Sandia model, theCEC model calculates hourly efficiency values, and allows you to select from a list of a commercially-

Overview 35


available modules. The CEC module database tends to be more up-to-date than the Sandia database.For some types of modules, the CEC model predictions may be less accurate than the Sandiamodel.

The Simple Efficiency Module model is a simple representation of module performance that requiresyou to provide the module area, a set of conversion efficiency values, and temperature correctionparameters. The simple efficiency model is the least accurate of the three models for predicting theperformance of specific modules. It is useful for preliminary performance predictions before you haveselected a specific module, and allows you to specify a module efficiency and temperatureperformance parameters, which is useful for analyses involving sensitivity or parametric analysis.

For concentrating photovoltaic (CPV) modules, use the Concentrating PV Module model unless youare modeling a CPV module available in the Sandia model, in which case, you can choose themodule from the database in the Sandia model. The concentrating PV module model is similar to thesimple efficiency model, except that it uses only the direct normal component of the incident solarradiation instead of the total radiation for performance predictions.

InvertersThe Sandia Performance Model for Grid-Connected PV Inverters is an empirically-based performancemodel that uses parameters from a database of commercially available inverters maintained by SandiaNational Laboratory. The parameters are based on manufacturer specifications and laboratorymeasurements for a range of inverter types.

The Sandia model consists of a set of equations that SAM uses to calculate the inverter's hourly ACoutput based on the DC input (equivalent to the derated output of the photovoltaic array) and a set ofempirically-determined coefficients that describe the inverter's performance characteristics. Theequations involve a set of coefficients that have been empirically determined based on data frommanufacturer specification sheets and either field measurements from inverters installed in operatingsystems, or laboratory measurements using the California Energy Commission (CEC) test protocol.

Because SAM does not track voltage levels in the system, it assumes that for each hour of thesimulation, the inverter operates at the photovoltaic array's maximum power point voltage, given thesolar resource data in the weather file for that hour.

The inverter single-point efficiency model calculates the inverter's AC output by multiplying the DC input(equivalent to the array's derated DC output) by a fixed DC-to-AC conversion efficiency that you specifyon the Inverter page. Unlike the Sandia inverter model, the single-point efficiency model assumes thatthe inverter's efficiency does not vary under different operating conditions.

Photovoltaic Systems: PVWatts System Model

The PVWatts System Model represents the entire photovoltaic system using a single model. This is incontrast with the Component-based Models option, which uses separate models to represent theperformance of the module and inverter.

Parabolic Trough

A parabolic trough system is a type of concentrating solar power (CSP) system that collects direct normalsolar radiation and converts it to thermal energy that runs a power block to generate electricity. Thecomponents of a parabolic trough system are the solar field, power block, and in some cases, thermalenergy storage and fossil backup systems. The solar field collects heat from the sun and consists ofparabolic, trough-shaped solar collectors that focus direct normal solar radiation onto tubular receivers.Each collector assembly consists of mirrors and a structure that supports the mirrors and receivers, allowsit to track the sun on one axis, and can withstand wind-induced forces. Each receiver consists of a metal

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tube with a solar radiation absorbing surface in a vacuum inside a coated glass tube. A heat transfer fluid(HTF) transports heat from the solar field to the power block (also called power cycle) and othercomponents of the system. The power block is based on conventional power cycle technology, using aturbine to convert thermal energy from the solar field to electric energy. The optional fossil-fuel backupsystem delivers supplemental heat to the HTF during times when there is insufficient solar energy to drivethe power block at its rated capacity.

Physical Trough ModelThe physical trough system model is a new parabolic trough model for SAM introduced in March 2010.The model approaches the task of characterizing the performance of the many of the systemcomponents from first principles of heat transfer and thermodynamics, rather than from empiricalmeasurements as in the empirical trough system model. The physical model uses mathematicalmodels that represent component geometry and energy transfer properties, which gives you theflexibility to specify characteristics of system components such as the absorber emissivity or envelopeglass thickness. The empirical model, on the other hand, uses a set of curve-fit equations derived fromregression analysis of data measured from real systems, so you are limited to modeling systemscomposed of components for which there is measured data. While the physical model is more flexiblethan the empirical model, it adds more uncertainty to performance predictions than the empirical model.In a physical model, uncertainty in the geometry and property assumptions for each system componentresults in an aggregated uncertainty at the system level that tends to be higher than the uncertainty inan empirical model. We've included both models in SAM so that you can use both in your analyses.

The following are some key features of the physical model:

Includes transient effects related to the thermal capacity of the heat transfer fluid in the solar fieldpiping, headers, and balance of plant.

Allows for flexible specification of solar field components, including multiple receiver and collectortypes within a single loop.

Relatively short simulation times to allow for parametric and statistical analyses that require multiplesimulation runs.

As with the other SAM models for other technologies, the physical trough model makes use of existingmodels when possible:

Collector model adapted from NREL's Excelergy model.

Receiver heat loss model by Forristall (2003).

Field piping pressure drop model by Kelley and Kearney (2006).

Power cycle performance model by Wagner (2008) for the power tower (also known as a centralreceiver) CSP system model in SAM.

Empirical Trough ModelThe empirical parabolic trough model uses a set of equations based on empirical analysis of datacollected from installed systems (the SEGS projects in the southwestern United States) to representthe performance of parabolic trough components. The model is based on Excelergy, a model initiallydeveloped for inernal use at at the National Renewable Energy Laboratory.

Power Tower

A power tower system (also called a central receiver system) is a type of concentrating solar power (CSP)system that consists of a heliostat field, tower and receiver, power block, and optional storage system. Thefield of flat, sun-tracking mirrors called heliostats focus direct normal solar radiation onto a receiver at the

Overview 37


top of the tower, where a heat-transfer fluid is heated and pumped to the power block. The power blockgenerates steam that drives a conventional steam turbine and generator to convert the thermal energy toelectricity.

SAM's power tower performance model uses TRNSYS components developed at the University ofWisconsin and described in Simulation and Predictive Performance Modeling of Utility-Scale CentralReceiver System Power Plants, Wagner (2008) http://sel.me.wisc.edu/publications/theses/wagner08.zip (32MB). For a description of the type of system the power tower model can represent, see About SAM.

The solar field optimization algorithm is based on the DELSOL3 model developed at Sandia NationalLaboratory, and described in A User's Manual for DELSOL3: A Computer Code for Calculating the OpticalPerformance and Optimal System Design for Solar Thermal Central Receiver Plants, Kistler (1986),(SAND86-8018) http://www.prod.sandia.gov/cgi-bin/techlib/access-control.pl/1986/868018.pdf (10 MB).

Dish Stirling

A dish-Stirling system is a type of concentrating solar power (CSP) system that consists of a parabolicdish-shaped collector, receiver and Stirling engine. The collector focuses direct normal solar radiation on thereceiver, which transfers heat to the engine's working fluid. The engine in turn drives an electric generator. Adish-Stirling power plant can consist of a single dish or a field of dishes.

SAM's dish-Stirling performance model uses the TRNSYS implementation of the energy prediction modeldescribed in the thesis Stirling Dish System Performance Prediction Model (Fraser 2008) https://www.nrel.gov/analysis/sam/pdfs/thesis_fraser08.pdf (4.1 MB). For a description of the type of system the dish-Stirlingmodel can represent, see About SAM.

Generic Solar

The generic solar model allows you to model a system that consists of a solar field, power block with aconventional steam turbine, and optional thermal energy storage system. The model represents the solarfield using a set of optical efficiency values for different sun angles and can be used for any solar technologythat uses solar energy to generate steam for electric power generation.

Generic System

The generic system model is a basic representation of a conventional fossil-fuel power plant. The Generictechnology option makes it possible to compare analyses of renewable energy project to a base caseconventional fossil fuel plant using consistent financial assumptions.

The generic system model allows you to characterize the plant's performance either using one of twooptions:

Specify a nameplate capacity and capacity factor value: Assumes that the plant generates power at aconstant rate over the year.

Specify an hourly our sub-hourly generation profile: Assumes that the plant generates power accordingto the generation profile you specify.

Solar Water Heating

SAM's Solar Water Heating model was developed at the National Renewable Energy Laboratory and modelsresidential or commercial solar water heating systems.

Simple Glycol and Tank Sytem

The simple model represents a two-tank glycol system with an auxiliary electric heater and storage

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tank for residential or commercial applications. The model allows you to vary the location, hot waterload profiles, and characteristics of the collector, heat exchanger, and solar tanks.

Detailed System

The detailed model includes options for direct, drainback, and glycol systems, and can model either anelectric or gas auxiliary water heater. The financing models are not available for the detailed systemmodel -- it does not calculate levelized cost of energy and other economic or financial metrics.

Wind

SAM's two wind models allow you to model the performance of small wind turbines for residential orcommercial applications, or of large wind turbines for a utility-scale wind farm project.

Small Scale WindThe small-scale wind model can model one or a few small wind turbines for residential or commercialapplications.

Utility Scale WindThe utility-scale wind model can model a single large wind turbine, or a wind farm of large wind turbinesthat sells power to the grid.

Geothermal

Geothermal PowerThe geothermal power plant model calculates the output of a power plant that uses heat from below thesurface of the ground to drive a steam electric power generation plant. SAM analyzes the plant'sperformance over its lifetime, assuming that changes in the resource and electrical output occurmonthly over a period of years, rather than over hours over a period of one year as in the solar and othertechnologies modeled by SAM.

SAM can be used to answer the following kinds of questions:

What is the levelized cost of a geothermal power plant, given a known configuration and resource?

How does changing the design of the plant affect its output and levelized cost of energy?

What plant size is required to meet an electric capacity requirement?

Given a known number of wells, what would the plant's electric capacity be?

SAM models the following types of systems:

Hydrothermal resources, where the underground heat reservoir is sufficiently permeable and containssufficient groundwater to make the resource useful without any enhancements.

Enhanced geothermal systems (EGS) that pump water or steam underground to collect heat storedin rock. These systems involve drilling or fracturing the rock to improve heat transfer. Over time(typically years), as heat is collected from the rock, its the temperature decreases, and more drillingis required. SAM's recapitalization cost accounts for the cost of these improvements to reach newresources.

Both flash and binary conversion plants.

Geothermal Co-ProductionThe co-production model is for relatively small commercial-scale projects that generate electricity froma geothermal resource available at the site of an oil or gas well.

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3.2 ClimateTo view the Climate page, click Climate in the main window's navigation menu.

The Climate page allows you to choose a weather file in TMY3, TMY2 or EPW format, download satellite-derived weather data from the Internet, create your own weather file in TMY3 format, and review yourweather data.

Note. This topic describes the Climate page for solar power systems. For small scale wind systemssee the Wind Resource page. For geothermal systems, see the geothermal Resource page.

Contents

Overview of the Climate Page describes the options for choosing weather data andthe variables displayed on the Climate page.

Input Variable Reference describes the variables and buttons on the Climate page.

Adding and Removing Weather File Search Paths explains how to add your ownweather files to the Location list.

Copying Weather Data to a Project explains how to embed weather data in yourproject file for sharing with other people.

Creating a Weather File from Your Own Data describes SAM's TMY3 weather filecreator to use your own weather data in SAM.

Using Location Lookup explains how to automatically download satellite-deriveddata for any location in the United States using a street address, zip code, orlatitude and longitude.

Downloading Weather Files from the Internet explains how to download TMY3,EPW, and satellite-derived data from the internet.

OverviewThe Climate page allows you to choose the weather file that SAM uses for simulations in the current case.The Climate page displays a summary of the weather data, and also allows you to view the actual data inthe time series data viewer (DView). The weather files are text files, so you can also examine the data usinga text editor, a spreadsheet program, or other software.

Weather Data Guidelines

For U.S. locations, use the Best weather data for the U.S. web link on the Climate page to downloada TMY3 file. If the TMY3 database does not include a file for a location at or very near your project site,try to find TMY3 files for locations near the site. You can run simulations for the different locations andcompare them to get a sense of what the resource might be at the project site. See DownloadingWeather Files from the Internet for instructions.

SAM comes with the complete set of the 239 TMY2 weather files. To use a TMY2 file, simply choose itfrom the Location list. See instructions below.

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If no TMY3 or TMY2 data is available for your project site, you can download typical year data fromNREL's Solar Prospector website using SAM's Location Lookup feature. The Solar Prospector websiteprovides access to satellite-derived weather data for the entire U.S. at a 10-km geographic resolution infiles using the TMY2 format. See Using Location Lookup for details.

For locations outside of the U.S., EPW files are available for over 1000 locations in 100 countries. SeeDownloading Weather Files from the Internet for instructions.

If you have weather data from a resource measurement program or from meteorological weather station,you can use SAM's TMY3 creator to create a TMY3 formatted file with the data. See Creating aWeather File from Your Own Data for details.

Some companies sell weather data and weather data processing software. For example, see WeatherAnalytics TMY Anywhere http://weatheranalytics.com/globaltmy.html, or http://www.meteonorm.com/pages/en/meteonorm.php.

To choose a weather data file from the Location list:

1. Download the weather file from the Internet. See Downloading Weather Files from the Internet fordetails

2. Place the file in your weather file folder. See Adding and Removing Weather File Search Paths fordetails.

Or, you can use one of the TMY2 files included with SAM. See below for a description of fileformats and guidelines for specifying weather data.

3. In the Location list, click the weather file's name.

If you cannot find a file for your project site on the Internet, or have data from another source that isnot in one of the file formats SAM recognizes, See Specifying Weather Data below for a list ofoptions.

Note. You can compare results for a system using more than one weather file in a single case by usingSAM's parametric simulation option.

File Formats

A SAM weather file is a file that contains hourly data describing the solar resource, wind speed,temperature, and other weather characteristics at a particular location in one of three text formats:

TMY3 comma-delimited text file format (.csv), http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/

TMY2 non-delimited text file format (.tm2), http://rredc.nrel.gov/solar/old_data/nsrdb/tmy2/

EPW comma-delimited text file format (.epw), http://www.eere.energy.gov/buildings/energyplus/weatherdata_format_def.html

The National Renewable Energy Laboratory's typical year data represents average weather data over arange of years: 1961-1990 for TMY2 data, and 1991-2005 for TMY3 data. Each typical year file may containdata from different years within the range, for example a TMY3 file might contain 1995 data for the month ofFebruary, 2001 data for March, 1998 data for April, etc. The NREL typical year data is based on analysis ofweather data measured at each location and is appropriate for economic and performance predictions of a

http://weatheranalytics.com/globaltmy.html

http://www.meteonorm.com/pages/en/meteonorm.php


http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/


http://rredc.nrel.gov/solar/old_data/nsrdb/tmy2/

http://www.eere.energy.gov/buildings/energyplus/weatherdata_format_def.html


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project over a long analysis period. The EPW data was developed for the U.S. Department of Energy'sEnergyPlus building simulation model, and is a source of non-U.S. weather data for SAM. The EPW dataon the EnergyPlus website is also typical year data.

TMY3 files are available for 1020 U.S. locations, and are based on more recent data and better modelingtechniques than the TMY2 data. However, the TMY3 data was developed using data from a shorter timeperiod than the TMY2 data, so may be less representative of the resource over the long term. (Although theTMY2 data includes effects from the Mt Pinatubo volcanic eruption, which may distort solar energy outputpredictions based on the data.) If both TMY2 and TMY3 files are available for your project site, you maywant to run SAM with both sets of data to compare results.

SAM will read a weather file containing data from any source, as long as it is correctly formatted. You cancreate your own weather file with data collected from a resource measurement program, or frommeteorological stations. SAM may not be able to read weather files that contain formatting errors orerroneous data elements. In some cases, you can use a text editor to compare a problematic file with onein the same format that works correctly in SAM to find problems with the file. Refer to the documentationavailable in the websites listed above for each file format for details.

Single Year Weather Data

Single year data represents the weather at a location for a specific year. Single year data is appropriate foranalysis of a project's economics and performance in a particular year, and for analyses involving time-dependent electricity pricing or electric loads for a given year. Single-year weather data can be developedfrom on-site measurements or from satellite-derived measurements. Single-year data for U.S. locations isavailable from NREL's Solar Prospector website, follow the link on the Climate page under Web Links. TheSolar Prospector data is satellite-derived data formatted using the TMY2 file format, so SAM can read thedata directly. NREL also publishes the specific-year data used to develop the TMY2 and TMY3 data sets onthe websites listed above, but that data must be formatted to work with SAM, either using external softwareor SAM's TMY3 Creator feature.

Time Convention

The time convention of the weather data determines the time convention of SAM's simulations. Forexample, TMY2 and TMY3 data both use local standard time, and the radiation data values represent thetotal energy received during the 60 minutes preceding the indicated hour. The global horizontal radiationshown for hour 1 represents the total radiation incident on a horizontal surface between midnight and 1:00am of the first hour of the year. Both data sets assume that there are 8,760 hours in one year and do notaccount for leap years. SAM assumes that the solar angle at the middle of the hour (at 30 minutes past thehour) applies to the entire hour.

Weather Data Elements

SAM uses the following data from the weather file:

Atmospheric pressure: CSP, wind

Dew point temperature: CSP

Diffuse horizontal radiation: PV

Direct normal radiation: PV, CSP

Dry bulb temperature: All technologies

Global horizontal radiation: PV, CSP

Hour of the day: All technologies

http://maps.nrel.gov/node/10/




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Latitude: All technologies

Longitude: All technologies

Percent relative humidity: CSP, wind

Site elevation: All technologies

Wet bulb temperature: CSP

Wind direction: Wind

Wind velocity: All technologies

Note. For the component-based PV model, you can specify the solar radiation elements from theweather file that SAM uses on the Array page. By default, SAM uses the global horizontal and directnormal radiation values and ignores the diffuse horizontal radiation from the weather file.

Input Variable Reference

Choose Climate/Location

Location

The name of the weather file. A filename preceded by "SAM/" is a standard weather data file includedwith SAM and stored in the \exelib\climate_files folder. A filename preceded by "USER/" is a file in afolder that you have added to the weather file search path list.

Add/Remove

Add or remove a folder on your computer from the list of folders SAM searches for files with the TMY2,TMY3, or EPW file extension. SAM will list all weather files in folders that you add to the search list inthe location list. See Adding and Removing Weather File Search Paths for details.

Refresh List

Refreshes the list of files in the location list. SAM automatically refreshes the list each time you visitthe Climate page. If you add a weather file to one of the folders in the search list, you may need torefresh the list for the file to be visible in the location list.

Copy to project

Embeds the data from a weather file to the project (.zsam) file. This useful when you share your projectfile with another person and do not want to send the weather file separately. Embedding weather data ina project increases the size of the project file. When you copy data to a project, SAM indicates thedata with "USER/" in the location list. See Copying Weather Data to a Project for details.

Remove from project

Remove embedded weather data. The button is only active when the active location in the location list ispreceded by "USER/."

Create TMY3 file

Use the TMY3 Creator to convert your own weather data into the TMY3 format. See Creating a TMY3file From Your Own Data for details.

Location Lookup

Type an address or coordinates for a U.S. location to download specific-year satellite-derived data fromthe Solar Prospector website. See Using Location Lookup for details.

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Location Information

The location information variables display data from the weather file header that describes the location. Anempty variable indicates that the information does not exist in the weather file's header. The locationinformation variables cannot be edited.

City

The name of the city.

When you use Location Look up to download weather data, SAM displays "satellitedata" in the Cityfield because the database does not provide a city name with the weather data.

State

The state abbreviation.

When you use Location Look up to download weather data, SAM displays "??" in the State fieldbecause the database does not provide a state name with the weather data.

Timezone

The location's time zone, relative to Greenwich Mean Time (GMT). A negative number indicates thenumber of time zones west of GMT. A positive number indicates the number of time zones east ofGMT.

Elevation (m)

The location's elevation above sea level in meters.

Latitude (degrees)

The location's latitude in degrees. A positive number indicates a location north of the equator.

Longitude (degrees)

The location's longitude in degrees. A negative number indicates the number of degrees west of thePrime Meridian.

Weather Data Information (Annual)

SAM calculates and displays the annual totals and averages of four of the hourly data columns from theweather file in the weather data information variables. Weather data information variables cannot be edited.

Direct Normal (kWh/m2)

The sum of the 8,760 hourly values of the direct normal radiation data in the weather file, expressed inkWh per square meter. Direct normal radiation is solar energy that reaches the ground in a straight linefrom the sun.

To convert this number to kWh per square meter per day, divide it by 365 days/yr.

Global Horizontal (kWh/m2)

The sum of the 8,760 hourly values of the global horizontal radiation data in the weather file, expressedin kWh per square meter. The global horizontal radiation is the total amount of direct and diffuse solarradiation incident on a horizontal surface over the period of one year.

To convert this number to kWh per square meter per day, divide it by 365 days/yr.

Dry-bulb Temp (°C)

The annual average of the ambient temperature data in the weather file in degrees Celsius.

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Wind Speed (m/s)

The annual average wind speed in meters per second.

For NREL TMY2 and TMY3 data, and EPW from the EnergyPlus website, wind speed data is at 10meters above the ground.

View hourly data

Displays graphs of data from the weather file in SAM's built-in data viewer, DView. See Viewing Graphsof Time Series Data (DView) for details.

Web Links

Links to websites with weather files on the internet. Each link opens one of three website in your computer'sdefault web browser:

Best weather data for the U.S. (1200 + locations in TMY3 format) takes you to NREL's NationalSolar Radiation Data Base (NSRDB) page for the Typical Meteorological Year 3 data.

Best weather data for international locations (in EPW format) takes you to the EnergyPlusweather file page.

U.S. satellite-derived weather data (10 km grid cells in TMY2 format) takes you to NREL's SolarPower Prospector website.

Adding and Removing Weather File Search PathsSAM allows you to use weather files that you download from the Internet or generate from another source.Weather files must meet the following requirements:

Be stored in a folder on your computer that you have specified in SAM as containing weather files.

Be in TMY2, TMY3, or EPW format.

To specify a folder as containing weather files:

1. On the Climate page, click Add/Remove.

2. In the Library Settings window, click Add.

3. Navigate to the folder on your computer that contains the weather file.

You can add as many file search paths as you wish.

4. Click Close to return to the Climate page.

SAM displays the search paths you added in the Location list.

To remove a search path from the list, click Add/Remove to open the Library Settings window,select the search path and then click Remove. Note that removing a search path does not deleteany weather files.

The default path for the complete set of TMY2 weather files included with SAM is \exelib\climate_files in theSAM installation folder. SAM can read weather files stored in any folder on your computer. Because thedefault location can be difficult to find, if you plan to use weather files other than the default TMY2 files, werecommend that you create an easy-to-find folder to store your weather files. You can then add the locationto the weather file search path using the instructions below, and SAM will automatically find all weather filesthat you add to the folder.

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Copying Weather Data to a ProjectWhen you want to share a SAM project with another person, and the project uses one or more weather filesthat the other person does not have, you can include a copy of the data from the weather files in the SAMfile. Including weather data in a SAM file increases the size of the file, but also makes it more portable. Forexample, the size of the photovoltaic sample file with no weather files is 35 kB, with one weather file 274kB, and with two weather files is 503 kB.

To copy data from a weather file to the project file:

1. On the Climate page, choose the weather file from the Location list.

2. Click Copy to project.

SAM adds the file to the location list with the "USER/" prefix, indicating that the data is included inthe SAM project file. To remove a file from the list, select it, and click Remove from project.

Creating a TMY3 File from Your Own DataIf you have hourly weather data that is not in one of the three formats (TMY3, TMY2, EPW) that SAM canread, you can use the Create TMY3 File feature to create your own weather file in the TMY3 format. TMY3files are comma-separated text files and use the csv extension, e.g., my_weather_file.csv.

Note. Unless you have a complete set of weather data for your location that you can use withconfidence, using your own data introduces uncertainty into your analysis, and may result in inaccurateresults or simulation errors.

To use the feature, you must have the following:

A "base" TMY3 file, which is an existing file in TMY3 format that SAM modifies by replacing only thecolumns that SAM needs for simulations with your data. If you have a complete data set that includesall of the columns shown in the table below, then you can use any TMY3 file as a base file. If you do nothave data for all of the categories listed in the table below, you may want to use a base file with data forthe same or a nearby location with similar weather characteristics. For a link to the TMY3 website anddocumentation, see the link on the Climate page under Web Links.

Hourly data (8,760 rows) for each of the data columns shown in the table below. If you do not have datafor one or more of the columns, you can choose to not replace data for those columns, and instead usedata from the base file. This will result in a data set that SAM can read but with mismatched elementsthat may cause inaccurate results or errors in the simulation.

To create a TMY3 weather file:

1. If you do not have a TMY3 file to use as the base file, download a TMY3 file to use at the base filefrom the NREL TMY3 website. You can do so by clicking the appropriate link on the Climate pageunder Web Links.

2. Open the file or files containing your weather in a text editor, spreadsheet program, or any softwarethat allows you to copy columns of 8,760 rows to your computer's clipboard.

3. On the Climate page, click Create TMY3 file.

4. In the TMY3 Creator window, click Open base TMY3 file, and navigate to the folder containing thebase file.

5. Type values in the header fields as appropriate, using the table below for reference.

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6. In your weather data file, copy the column of global horizontal radiation data. Be sure to copy all8,760 rows of data, but do not include the row header. The column should contain 8,760 rows ofnumbers.

7. In the TMY3 Creator window, click the GHI (W/m^w) column heading. SAM should highlight theentire column in dark gray.

8. Click Paste.

9. Repeat the copy and paste procedure for each column until you have pasted all of your data intothe table.

10. Click Save as new TMY3 file. Save the file in a folder that you have included in the weather filesearch list (see Adding and Removing Weather File Search Paths).


12. Click Refresh list. SAM may take a moment or two to refresh the location list.

13. In the Location list, select the new TMY3 file. You should find it toward the end of the list.

14. Click View Hourly Data to open the DView data viewer and visually inspect the data. See ViewingGraphs of Time Series Data (DView) for details.

After creating and loading your weather file, run some test simulations and examine the hourly results in the tabular data browser or DView to see if there are any problems with the data.

Header Data

Site Identifier Code

A number identifying the location. This element is not required.

Station Name

A text description identifying the location. This element is not required.

Station State

A two-letter text abbreviation for the location's state. This element is not required.

Site Time Zone (GMT)

The location's time zone offset from Greenwich Mean Time (GMT) with no daylight savings adjustment.A positive value indicates a time zone east of the Prime Meridian. Decimals indicate fractions of hours.A negative value indicates a time zone west of the prime meridian. For example, Chicago is -6; India is5.5.

Latitude

Location's latitude in decimal degrees. A positive value between zero and 90 indicates a latitude north ofthe equator. A negative value between 0 and -90 indicates a latitude south of the equator. For example,Durban (South Africa) is -29.97; New York City is 40.71.

Longitude

Location's longitude in decimal degrees. A positive value between zero and 180 indicates a longitudeeast of the Prime Meridian. A negative value between zero and -180 indicates a longitude west of thePrime Meridian. For example, Durban (South Africa) is 30.95; New York City is -74.01.

Elevation

Location's height above sea level in meters.

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Hourly Data

GHI (W/m^2)

Global horizontal irradiance: Total amount of direct and diffuse solar radiation received on a horizontalsurface for the hour in Watt-hours per square meter.

DNI (W/m^2)

Direct normal irradiance: Amount of solar radiation received in one hour within a limited field of viewcentered on the sun in Watt-hours per square meter.

DHI (W/m^2)

Diffuse horizontal irradiance: Amount of solar radiation received in one hour from the sky, excluding thesolar disk on a horizontal surface in Watt-hours per square meter.

Dry-bulb (C)

Average dry bulb temperature for the hour in degrees Celsius..

Dew-point (C)

Average dew point temperature for the hour in degrees Celsius.

RHum (%)

Average relative humidity for the hour.

Pressure (mbar)

Station pressure or measured atmospheric pressure in millibars corrected for temperature and humidityfor the hour.

Wspd (m/s)

Average speed of the wind for the hour in meters per second.

Albedo

Ratio of reflected solar radiation to global horizontal radiation. Use -99 for null.

Using Location LookupSAM's Location Lookup feature allows you to type an address, zip code, or latitude and longitude todownload a typical year data weather file for any location in the United States. Location Lookup uses theGoogle Maps API Geocoding Service service to identify the geographic coordinates of a location, anddownloads data from NREL's Solar Power Prospector database. To use the Location Lookup feature, yourcomputer must be connected to the Internet.

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Notes.

When you download weather data with Location Lookup, SAM displays "satellitedata" for the city and"??" for the state because the Solar Prospector database does not include city and state names.

Location Lookup downloads typical year data, representing the typical solar resource over the period1998-2005. To download specific-year data within that range, visit the Solar Power Prospector site athttp://maps.nrel.gov/prospector.

For information about downloading TMY3 and EPW files from the internet, see Downloading WeatherFiles from the Internet.

To download data from Solar Power Prospector:

1. On the Climate page, click Location Lookup.

2. Type a street address zip code, or latitude and longitude. Any of the following will return results forthe same location:

1617 Cole Boulevard, Golden CO

80401

39 44 N 105 09 W

39.75 -105.15

SAM searches the Solar Power Prospector database for a weather file and download it to the weather filefolder specified on the Preferences page.

To change the default weather file folder for downloaded files:

1. On the File menu, Click Preferences.

2. Under Folder for automatically downloaded weather files, type a path name or click tonavigate to the folder.

Note that the folder for automatically downloaded weather files is different from the weather filesearch path.

3. On the Climate page click Add/Remove.

4. In the Library Settings window, click Add to add the folder to the weather file search path list.


Sources of Weather Data on the InternetThe three links on the Climate page under Web Links to open websites where you can download and findmore information about weather data in TMY3, TMY2, and EPW formats.

Note. If you cannot find weather data for your location on one of those websites, you may want to tryusing data from either of the following companies, who provide data and software for a fee: WeatherAnalytics (TMY Anywhere) at http://weatheranalytics.com/globaltmy.html, or Meteonorm at http://www.meteonorm.com.

http://maps.nrel.gov/prospector


http://www.meteonorm.com

http://www.meteonorm.com

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NSRDB Typical Meteorological Year 3 (TMY3) data: Best data for U.S. Locations

The NSRDB maintains two sets of TMY data. The TMY2 data represent data from 1961 to 1990. Thecomplete TMY2 data is included with SAM: To use TMY2 data, you simply select a location from the list onthe Climate page.

The updated TMY3 data set is based on data from 1991 to 2005. To use TMY3 data in SAM, you mustdownload the data from the NSRDB website. For information about the TMY3 data, see:


To download a TMY3 file:

1. Click the Best weather data for the U.S. (1200 + locations in TMY3 format) link to open theNSRDB TMY3 database page.

2. On the NSRDB website, click the In alphabetical order by state and city link.

3. Scroll to the state and city at or nearest your location.

4. Click the identification code link for the location to download the TMY3 file.

5. Save the file in your SAM weather file folder. If you do not have a SAM weather file folder, seeAdding and Removing Weather Files for instructions.

6. In SAM, on the Climate page, click Refresh.

The weather file should appear in the Location list, toward the bottom of the list.

EnergyPlus Weather (EPW) files: Data for locations outside the United States

You can download weather data in EPW format for locations around the world at no cost from theEnergyPlus weather data website at the following website:

http://www.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm.

For information about the EPW weather files, see the following websites:

For a description of the file format: http://apps1.eere.energy.gov/buildings/energyplus/weatherdata_format.cfm

For a description of data sources: http://apps1.eere.energy.gov/buildings/energyplus/weatherdata_sources.cfm

To download an EPW file:

1. Click Best weather for international locations (in EPW format) and navigate to the region andlocation you want to model.

2. Download the EPW file for the location you are modeling.

If there is not an EPW file for the location, download the ZIP file and extract the EPW file.




For some regions, you can download an EPW file directly for a location. For example, for Bangladesh, youcan download the data for Dhaka by right-clicking the blue square next to the word EPW for Dhaka. Be sureto save the file with the .epw extension.


http://www.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm

http://apps1.eere.energy.gov/buildings/energyplus/weatherdata_format.cfm


http://apps1.eere.energy.gov/buildings/energyplus/weatherdata_sources.cfm


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For other regions, you must first download a zip file containing the EPW file and then extract the EPW file.For example, for Malaysia, you can download the data for Kuala Lumpur by right-clicking the red squarenext to the word ZIP for Kuala Lumpur. After downloading the zip file, you can extract the EPW file.

Satellite-derived (NREL Solar Prospector) Weather Data: Data for locations in thecontinental United States

The NREL Solar Prospector website provides access to satellite-derived files in TMY2 format for specificyears between 1998 and 2005, and in typical year data for locations in the U.S. at a geographical resolutionof 10 km.

For information about the Solar Power Prospector website, see:


For a description of the data used for the Solar Prospector website, see:

http://www.asrc.cestm.albany.edu/perez/publications/Solar%20Resource%20Assessment%20and%20Modeling/Papers%20on%20Resource%20Assessment%20and%20Satellites/A%20New%20Operational%20Satellite%20irradiance%20model-02.pdf

Although the files you download from the Solar Power Prospector website are in TMY2 format, you candownload files containing either specific year data or typical year data from the website.

The easiest way to use typical year data from Solar Power Prospector in SAM is to use Location Lookup.To download single year data, you can use the Solar Prospector map at http://maps.nrel.gov/prospector.

To download data from the NREL Solar Prospector Website:

1. Visit the Solar Prospector website at http://maps.nrel.gov/prospector.

2. Use the map to find your location.

3. Click Download in the toolbar above the map.

4. Choose a year for specific year data, or "TDY" for typical year data.










Photovoltaic Systems 51


3.3 Photovoltaic Systems

3.3.1 Getting Started with PV

SAM models grid-connected photovoltaic systems that consist of a photovoltaic array and inverter. Thearray can be made up of flat-plate or concentrating photovoltaic (CPV) modules with one-axis, two-axis, orno tracking.

The procedure below describes the basic steps to get started modeling a project based on photovoltaictechnology. For general getting started topics, see Getting Started.

For more detailed information about the photovoltaic model input pages, see the following topics:

PV System Costs

Array

PVWatts Solar Array

Shading

Module

Inverter

For photovoltaic systems with residential or commercial financing, SAM also makes the Electric Loadpage available. You only need to specify load data if you model a project with a utility rate structurethat includes different buy and sell rates for energy charges, demand charges, or tiered rates.

For systems with Utility Market financing, SAM makes the Energy Payment Dispatch page available.You only need to use this page for for projects that specify a power purchase price using a set ofpayment allocation factors.

The User Variables page is for analyses involving Excel Exchange or custom TRNSYS decks.

A. Choose a photovoltaic model

When you create a new file or case, SAM offers two options for modeling PV systems: Component-basedModels models and PVWatts System Model.

Component-based Models

The Component-based Models option represents the performance of a photovoltaic system usingseparate models to represent the performance of the module and inverter. You specify the module and

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inverter characteristics, array layout, derating factors, and optional shading, temperature correction, and backtracking parameters. Component-based Models calculates and reports detailed results, includingthe array's DC output, system's AC output, cell temperature, and the hourly efficiency of the array andinverters.

Use the Component-based models to model crystalline or thin-film modules, and for arrays with openrack, flush, gap, or building-integrated mounting.

The SAM Performance Models option allows you to choose between the Sandia, CEC, and single-pointefficiency models for photovoltaic modules, and between the Sandia and single-point efficiency modelsfor inverters.

PVWatts System Model

The PVWatts System Model represents the entire photovoltaic system using a single derate factor andaccounts for the effects of temperature on the system's performance. The PVWatts model isappropriate for modeling rack-mounted systems with crystalline silicon modules. The PVWatts modelcalculates and reports the array DC output, system AC output (based on a fixed derate factor), and celltemperature.

The following table summarizes the two options:

Component-basedModels

PVWatts SystemModel

Array output (DC) • •

Inverter output (AC) •

Temperature effects • •

Array shading • •

Row-to-row shading •

Backtracking •

Mounting options •

Tracking options • •



B. Choose a financing option

Note. SAM does not impose a size limit based on the financing option you choose. You can use anyfinancing option with any size of system.

For a project on the customer side of a utility meter that buys and sells power at retail rates, choose eitherResidential or Commercial financing:

Commercial allows you to model depreciation as a tax deduction (MACRS or custom).

Residential allows you to choose between a standard loan in which interest payments are not taxdeductible, and mortgage, in which interest payments are tax deductible.

For a power generation project that sells electricity at a negotiated price, choose either Commercial PPA orone of the Utility Market options:

Commercial PPA calculates a power purchase price (PPA price) based on a target internal rate ofreturn (IRR) that you specify. You can either specify a debt fraction and annual PPA price escalationrate, or allow SAM to find optimal values.

The Utility Market Options allow you to either specify a target IRR (SAM calculates a PPA price), orspecify a PPA price (SAM calculates the IRR). The Independent Power Producer option is similar toCommercial PPA, but allows you to add constraints for minimium debt-service coverage ratio (DSCR)and positive cash flow. The other Utility Market options allow you to model projects with a single owner,or with two parties with different structures for sharing project costs and revenues.

Note. The Commercial PPA and Utility Indepdendent Power Producer financing options are legacyoptions to allow you to model projects consistently with older versions of SAM. The parnership flip, saleleaseback, and single owner options are more representative of actual financing structures for renewableenergy projects.

See Financing Options for details.

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C. On the Climate page, choose a weather file to represent the solar resource atthe project location.

SAM offers four weather data options. You can:

Choose a location from the list at or near your project site. SAM will simulate the system using a filefrom NREL's TMY2 database.

Use Location Lookup to download data for your site from the online database. SAM will simulate thesystem using a file from NREL's database of satellite-derived solar resource data.

Download a file from NREL's TMY3 database.

Create a weather file in TMY3 format with your own data

For preliminary analyses in the United States either use a TMY2 file if there is a file in the database withsimilar weather to the project site, or use Location Lookup to find satellite-derived data for the site location.

For more robust analysis, download TMY3 data, or use your own data. You may also want to analyze yourproject using weather data from different sources to develop an understanding of how uncertainty in theweather data affects the metrics of interest for your project.

See Climate for details.

D. For Component-based models:

1. On the Array page, specify the system's size and tracking options.

Enter the system's DC nameplate capacity for Desired Array Size. After you choose modules andinverters, SAM will display the number of modules and inverters required for the system size youspecified under Actual Layout.

2. Under Tracking and Orientation, choose a tracking option and specify the array tilt angle.

3. On the Inverter page, choose an inverter.

4. On the Module page, choose a model option and module.

For the PVWatts System model

1. On the PVWatts Solar Array page, enter the system's DC nameplate capacity for NameplateCapacity.

2. Choose a tracking option and specify the tilt angle.

E. On the PV System Costs page, specify the project costs.

The capital costs (direct and indirect) are construction and installation costs that SAM applies to year zeroof the cash flow.

The operation and maintenance costs apply in years one and later of the cash flow.

See PV System Costs for details.

F. Run a simulation and review results.



See Results Page for details.

3.3.2 Array

The Array page displays variables and options that specify the number of modules and inverters in thesystem, derate factors, array tracking and orientation, and allows you to choose from several radiationmodel options. SAM uses the array properties to calculate the array's DC output and the system's ACoutput.

To view the Array page, click Array on the main window's navigation menu. Note that for the Array page tobe available, the technology option in the Technology and Market window must be Photovoltaics - SAMPerformance Models.

Contents

Overview explains how to specify the photovoltaic array.

Input Variable Reference describes the input variables and options on the Arraypage.

Specifying the Array Size describes how to choose values for the Modules perString, Strings in Parallel and Number of Inverters variables to avoid mismatchingthe array and inverter.

About Array Sizing Error Messages describes the pre- and post-simulation errorchecking and warning messages.

Specifying Array Tracking and Orientation describes the four tracking options andarray angles.

About Derate Factors describes how SAM uses the derate factors in calculations,and provides guidelines for choosing appropriate values.

OverviewThe Array page is where you build the photovoltaic system from the module and inverter you specify on theModule page and Inverter page. SAM provides two options for sizing the array: You can specify thesystem's rated DC capacity and let SAM calculate an appropriate number of modules and inverters for you,or you can specify the values yourself. See Specifying the Array Size for details.

Note. Before specifying parameters on the Array page, you should specify the module characteristicson the Module page, and the inverter characteristics on the Inverter page.

The Tracking and Orientation options are where you specify whether modules in the array move to track themotion of the sun across the sky, and at what angle from the horizontal modules are mounted in the array.See Specifying Array Tracking and Orientation for details.

The Land Area variables are for reference only and do not affect results. You can ignore the Packing Factorvariable unless you are interested in knowing how much land your array requires. See Input Variable

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Reference for a description of the two Land Area variables.

The Radiation Model and Tilt Radiation Type options allow you to choose how SAM calculates the solarradiation incident on the array from the data in the weather file. For most analyses, you can use the defaultvalues of Total and Beam and Perez Model 1990. For a description of the different options, see InputVariable Reference.

SAM uses the derate factors to adjust the DC electric input to the inverter model, and the inverter model'sAC electric output to account for losses in the system that the module and inverter models do not accountfor. For example, the module and inverter models do not account for losses in the DC and AC wiring thatconnects modules in the array, and that connects the inverter output to the grid and any external powerconditioning equipment. See About Derate Factors for details.


Layout

Array Sizing

The array sizing variables determine the number of modules in the array. SAM uses the modulenumbers under Actual Layout, which may be different from values that you type.

Mode

The two layout modes allow you to choose from either specifying an array size in DC kilowatts so thatSAM calculates the number modules and inverters in the system, or specifying those values yourself.See Specifying the Array Size for details.

Desired Array Size

When the mode is Specify desired array size, type the array DC rated capacity in kilowatts. Thearray's DC rating should be based on the same reference conditions used to specify the module powerrating on the Module page.

The desired array size variable is inactive when the mode is Specify number of modules andinverters. In that case, you must type values for the number of modules per string, strings in parallel,and inverters.

Modules per String

Modules per string is the number of modules connected in series in a single string. SAM assumes thatall strings in the array have the same number of modules connected in series.

The number of modules per string determines the array's open circuit voltage (Voc). For most analyses,you should ensure that the array Voc is less than the inverter's maximum input voltage, shown asMPPT_hi on the Inverter page. If the inverter does not have a value for MPPT_hi, you can find the valueon inverter manufacturer's specification sheet, which you may be able to find on the manufacturer orequipment supplier website. See Specifying the Array Size for more information.

Note. If you are using a module from the Sandia database on the Module page with the word "array" inits name, the module represents an array, so the Modules per String variable represents the number ofarrays in the system rather than number of modules.

The modules per string variable is inactive when the layout mode is Specify desired array size. In thatcase, SAM uses the value shown in the Actual Layout column. If you want to change the value,change the mode to Specify numbers of modules and inverters and type a value for the number of



modules in each string.

Strings in Parallel

Strings in parallel is the number of strings of modules connected in parallel to form the array. A string ofmodules is a number of modules connected in series. Once you specify the number of modules perstring to determine the array's open circuit voltage, the number of strings in parallel determines thearray's rated DC power. SAM displays a warning message if the array's rated DC power is either greaterthan the total inverter capacity, or less than about 75% of the system's total inverter capacity. You canrun simulations with values that fall outside of these guidelines; the warning message is intended tohelp you ensure that the array and inverter sizes are matched. See Specifying the Array Size for moreinformation.

The strings in parallel variable is inactive when the layout mode is Specify desired array size. In thatcase, SAM uses the value shown in the Actual Layout column. If you want to change the value,change the mode to Specify numbers of modules and inverters and type a value for the number ofparallel strings in the array.

Number of Inverters

Number of inverters is the total number of inverters in the system and determines the total invertercapacity.

The number of inverters variable is inactive when the layout mode is Specify desired array size. Inthat case, SAM uses the value shown in the Actual Layout column. If you want to change the value,change the mode to Specify numbers of modules and inverters and type a value for the number ofinverters in the system.

Note. If you are modeling a system with microinverters, see Modeling Microinverters for instructions.

Actual Layout

These calculated values are the values that SAM uses for simulations.

The variables listed below the Array Sizing group are calculated values or values from other pages that SAMdisplays for reference.

Total Modules

The number of modules in the array:

Total Modules = Modules per String × Strings in Parallel

The numbers of modules and strings are the values listed under Actual Layout under Array sizing.

Total Area, m2

The array's total area in square meters, not including space between modules:

Total Area = Module Area × Total Modules

The module area is shown on the Module page. The number of modules is the value listed under ActualLayout under Array sizing.

Nameplate Capacity (at reference conditions), Wdc

The maximum DC power output of the array at the reference conditions shown on the Module page:

Nameplate Capacity = Module Maximum Power × Total Modules

The module's maximum power rating is from the Module page. The number of modules is the valuelisted under Actual Layout under Array sizing.

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Voc (String, at 1000 W/m2 Tc=25'C), Vdc

The open circuit DC voltage of each string of modules:

Voc = Module Open Circuit Voltage × Modules per String

The module open circuit voltage and reference conditions are from the Module page. The number ofmodules per string is the value listed under Actual Layout under Array sizing.

For the Sandia and CEC model, the open circuit voltage is assumed to be for 1,000 W/m2 incidentradiation and 25 ºC cell temperature. For the simple efficiency model, SAM displays a zero becausethe model does not include voltage ratings.

Vmp (String, at reference conditions), Vdc

The maximum power point DC voltage of each string of modules:

Vmp = Module Max Power Voltage × Modules per String

The module's maximum power point voltage is at reference conditions as specified on the Module page.The number of modules per string is the value listed under Actual Layout under Array sizing.

SAM displays a maximum power point voltage of zero for the simple efficiency module performancemodel because the model does not include voltage ratings.

Vdco (dc-inverter), Vdc

The inverter's rated input DC voltage displayed from the Inverter page. SAM assumes that inverters areconnected in parallel so that the rated voltages of the inverter bank are the same as those of a singleinverter.

SAM displays an inverter voltage of zero for the single-point efficiency inverter performance modelbecause the model does not include voltage ratings.

Total Inverter Capacity, kWac

The total inverter capacity in AC kilowatts:

Total Inverter Capacity = Inverter Power ACo × Number of Inverters

The inverter's nominal AC power rating is from the Inverter page. The number of inverters is the valuelisted under Actual Layout under Array sizing.

Tracking and Orientation

The tracking and orientation options determine whether the system is modeled with a tracking system thatallows modules in the array to follow the sun's movement across the sky. See Choosing a Tracking Optionfor details.

Notes.

The tracking and orientation options apply to all modules in the array. To model a system that consistsof sub-arrays with different tracking and orientations, use the Multiple Systems option. This option doesnot allow you to model sub-arrays connected to a single inverter.

The current version of SAM does not allow you to limit the tracking angle. SAM assumes that trackerscan follow the full movement of the sun from sunrise to sunset.

Fixed

The array is fixed at the tilt and azimuth angles defined by the values of Tilt and Azimuth and does not



follow the sun's movement.

1 Axis

The array is fixed at the angle from the horizontal defined by the value of Tilt and rotates about the tiltedaxis from east in the morning to west in the evening to track the daily movement of the sun across thesky. Azimuth determines the array's orientation with respect to a line perpendicular to the equator.

2 Axis

The array rotates from east in the morning to west in the evening to track the daily movement of the sunacross the sky, and north-south to track the sun's seasonal movement throughout the year.

Azimuth Axis

The array rotates in a horizontal plane to track the daily movement of the sun.

Force Tilt = Latitude

Assigns the array tilt value with the latitude value stored in the weather file and displayed on the Climatepage. Note that SAM does not display the tilt value on the Array page, but does use the correct valueduring simulations.

Tilt (degrees)

Applies only to fixed arrays and arrays with one-axis tracking. The array's tilt angle in degrees fromhorizontal, where zero degrees is horizontal, and 90 degrees is vertical. As a rule of thumb, systemdesigners often use the location's latitude (shown on the Climate page) as the optimal array tilt angle.The actual tilt angle will vary based on project requirements.

Azimuth (degrees)

Applies only to fixed arrays with no tracking. The array's east-west orientation in degrees. An azimuthvalue of zero is facing the equator in both the northern and southern hemispheres. Positive 90 degreesis facing due west and negative 90 degrees is facing due east in both hemispheres. As a rule of thumb,system designers often use an array azimuth of zero, or facing the equator.

Max/Min Rotation

The maximum and minimum allowable rotation angle for one-axis tracking. The default value of 360degrees allows the tracker to follow the full movement of the sun from horizon to horizon.

Max/Min Tilt

The maximum and minimum allowable tilt angle for two-axis tracking. The default value of 360 degreesallows the tracker to follow the full movement of the sun from horizon to zenith.

Max/Min Azimuth

The maximum and minimum allowable azimuth angle for two-axis tracking. The default value of 360degrees allows the tracker to follow the full movement of the sun.

System Derates

SAM uses the derate factors to adjust the array's hourly DC output value before passing it to the invertermodel, and to adjust the inverter model's AC electric output to calculate the system's AC output. The deratefactors account for losses in the system that the module and inverter models do not account for, such aslosses in the DC wiring that connects modules in the array, and AC wiring that connects the inverter to thegrid and any external power conditioning equipment.

SAM only uses the total pre-inverter derate factor and the total post-inverter derate factor in calculations.The derate factor categories (mismatch, diodes and connections, AC wiring, etc) are to help you keep track

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of factors influencing the total derate factor. Each total derate factor is the product of the DC or AC deratecategories, as appropriate. See About Derate Factors for details.

You can see the effect of the derate factors in the hourly results (and in the monthly and annual averages) inthe tabular data browser on the Results page: The derated DC output is the product of the gross DC outputand the pre-inverter derate factor, and the derated AC output is the product of the gross AC output and thepost-inverter derate factor.

Note. SAM applies additional factors to the derated AC output to calculate the system's net annualoutput based on the values you specify on the Annual Performance page.

Total Pre-Inverter Derate

The total pre-inverter derate factor is the product of the six DC derate factors. In the hourly simulation,SAM calculates the DC power at the inverter's input for each hour by multiplying the array's DC outputby the total pre-inverter derate factor. A derate factor of 100% is equivalent to no derating. A deratefactor of 75% would reduce the calculated array DC output by 25%.

Total Post-Inverter Derate

The total pre-inverter derate factor is the product of the two AC derate factors. In the hourly simulation,SAM calculates the derated AC power at the inverter's output for each hour by multiplying the inverter'sAC output by the total post-inverter derate factor. A derate factor of 100% is equivalent to no derating. Aderate factor of 75% would reduce the calculated inverter AC output by 25%.

Total Derate Factor

The product of the pre- and post-inverter derate factors. This value is useful for comparing to hand-calculated performance estimates, but SAM does not use the value in calculations.

Radiation Model

Note. The radiation model and tilt radiation type options are for advanced users. Use the default Totaland Beam and Perez Model 1990 options unless you have a reason to change them.

The radiation model options determine how SAM uses the global horizontal radiation, direct normalradiation, and diffuse horizontal radiation data in the weather file in radiation calculations.

Beam and Diffuse

SAM reads the direct normal radiation (beam) and diffuse horizontal radiation data, and to ignore theglobal horizontal radiation data from the weather file. SAM calculates the global incident radiation.

Total and Beam

This is the default option, and is best for most analyses. SAM reads the global horizontal radiation(total) and direct normal radiation (beam) data, and to ignore the diffuse horizontal radiation from the

weather file. SAM calculates the diffuse incident radiation.

Total and Diffuse

SAM reads the global horizontal radiation (total) and diffuse horizontal radiation, and ignores the directnormal radiation from the weather file. SAM calculates the direct incident radiation.



Tilt Radiation Type

Note. The radiation model and tilt radiation type options are for advanced users. Use the default Totaland Beam and Perez Model options unless you have a reason to change them.

SAM allows you to choose the method it uses to convert global horizontal solar radiation data to globalsolar radiation incident on the array. Each method uses information about the global horizontal solarradiation and either the direct normal or diffuse solar radiation, and about the sun's position and orientationof the array. The four methods differ in how they estimate the diffuse radiation incident on the array.

The isotropic sky model tends to under-predict the global radiation on a tilted surface, and is included as anoption for analysis wanting to compare SAM results with those from other models using this approach. Theremaining three methods provide comparable estimates of the incident global radiation.

For references describing the different radiation models, see References, Weather Data.

Isotropic Sky Model

Assumes that diffuse radiation is uniformly distributed across the sky, called isotropic diffuse radiation.

Hay and Davies Model

Accounts for the increased intensity of diffuse radiation in the area around the sun, called circumsolardiffuse radiation, in addition to isotropic diffuse radiation.

Reindl Model

Accounts for the effect of horizon brightening, in addition to circumsolar diffuse radiation.

Perez Model 1988 and 1990

The Perez 1990 method is the default value and is best for most analysis.

Accounts for horizon brightening, circumsolar and isotropic diffuse radiation using a more complexcomputational method than the Reindl and Hay and Davies methods. The 1990 method is an updatedversion of the 1988 method.

Land Area

Note. The land area variables are for reference only and do not affect results. You can ignore thepacking factor variable unless you are interested in knowing how much land your array requires. SAMdoes not use the land area variable to account for land costs. You must specify any land costs explicitlyon the PV System Costs page.

Packing Factor

The packing factor is a multiplier that makes it possible to estimate the land area required by a projectbased on the array's total area. SAM multiplies the array area (Total Area) by the packing factor tocalculate the total land area. Note that the array area is simply the module area multiplied by thenumber of modules in the array: Use the packing factor to account for spacing between modules in thearray, and for the module tilt angle.

Total Land Area

The total land area is an estimate of the land area required by the PV system: Total Land Area =Module Area from Module page × Total Modules on the Array page × Packing Factor.

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Ground Reflectance

Ground Reflectance

The ground reflectance value for hours when the weather data indicate that there is no snow on theground. A value of zero means that the ground is completely non-reflective, and a value of 1 means thatit is completely reflective. A typical value for grassy ground is 0.2.

Ground Reflectance with Snow

The ground reflectance value for hours when the weather data indicate that there is snow on the ground.A value of zero means that the ground is completely non-reflective, and a value of 1 means that it iscompletely reflective. A typical value for snowy ground is 0.6.

Backtracking

The backtracking options allow you to specify parameters for an array consisting of multiple rows ofmodules wth one-, two-, or azimuth-axis trackers programmed to adjust the tracker angle to minimize self-shading. See Backtracking Overview for a general description.

Note. SAM's backtracking and self-shading models are independent. If you run simulations with bothmodels, SAM will calculate self-shading losses even with backtracking.

Subarrays per Row

Number of subarrays in one row of the total array layout. An array is normally made up of many rows,and each row may have multiple sections. The number of sections in each row is represented by thisnumber. For a two-axis tracking situation, this number specifies the number of 2 axis tracking units inthe vertical (North-South) direction.

Number of Rows

The number of rows in the total array layout. A row is considered to run North-South, so the number ofrows represents an East-West dimension. For a one axis tracking system, this is the number ofmodule rows that track together. For a two axis tracking system, this is the number of tracking units inthe horizontal (East-West) direction.

Subarray Spacing

The physical distance between the centers of the subarrays in the vertical (North-South) direction inmeters. SAM only allows for fixed spacing on a grid-type layout.

Row Spacing

The physical distance between the row centers in the horizontal (East-West) direction, in meters. SAMonly allows for fixed spacing on a grid-type layout.

Row Offset

The subarrays in each row can be horizontally offset by this amount, specified in meters. An offset ofzero will result in a rectangular grid of subarrays.

Offset Type

The row offset (above) can be applied to each row (resulting in a parallelogram-like subarray layout, or toevery other row, resulting in a staggered layout.

Row Orientation

The overall array rotation (from a birds-eye view), specified in degrees.



Subarray Length

The vertical (North-South) dimension of a subarray. This dimension is parallel to the primary axis ofrotation, hence N-S for a one axis tracking system.

Subarray Width

The horizontal (East-West) dimension of a subarray. This dimension is perpendicular to the primaryaxis of rotation, hence E-W for a one axis tracking system.

Specifying the Array SizeThe three array sizing variables, Modules per String, Strings in Parallel, and Number of Invertersdetermine the system's rated capacity in kilowatts. SAM considers the array's rated capacity in DCkilowatts to be the system's rated capacity for capacity-related calculations.

SAM uses the following sizing rules when possible (see below for details):

Voc < Vdcmax: The array's maximum rated open circuit DC voltage (Voc) is less than the inverter'smaximum rated DC voltage (Vdcmax).

MPPT_low < Vmp < MPPT_hi: The array's rated maximum power point DC voltage (Vmp) is less thanthe inverter's maximum operating DC voltage (MPPT_hi), but greater than the inverter's minimumoperating DC voltage (MPPT_low).

Total Inverter Capacity ~ Array Power: The inverter and array capacities are matched to avoid situationswhere either the array generates more power than the inverter can handle, or the inverter is oversized.

SAM provides two modes for specifying the array size:

Specify desired array size: SAM's array sizing calculator allows you to specify the array's DCcapacity in kilowatts, and SAM automatically calculates the number of modules per string and stringsin parallel in the array, and the number of inverters. The Modules per String, Strings in Parallel, andNumber of Inverters variables are inactive. Use this option unless you have a reason to specify thenumbers of modules and inverters by hand.

Specify numbers of modules and inverters: You specify the values of Modules per String, Stringsin Parallel, and Number of Inverters by hand. The Desired Array Size variable is inactive.

Specify a desired array capacity (array sizing calculator):

1. Choose an inverter for the system on the Inverter page.

2. Choose a module on the Module page.

3. On the Array page, for Mode, choose Specify desired array size for Mode.

4. Type a DC capacity value in kilowatts for the array in Desired Array Size. SAM disables the threearray sizing variables because it will calculate those values automatically.

5. Press the Enter key.

SAM calculates values for Modules per String, Strings in Parallel, and Number of Inverters,and displays them in the Actual Layout column.

6. Verify that Array Power is acceptably close to the desired array capacity value you specified.SAM will never choose array sizing values that result in an array capacity greater than the desiredarray capacity value. In some cases, if the array power value is significantly less than the desiredvalue, you may want to change the values by hand to specify an array capacity slightly greater thanthe desired value. See below for instructions on specifying the array size by hand.

7. Specify the tracking and orientation and system derate factors as appropriate. See SpecifyingArray Tracking and Orientation for details.

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8. When you run simulations, SAM will check the system sizing variables and display a message ifthere appear to problems. See About Array Sizing Error Messages for details.

Notes for Array Sizing Calculator.

For some of the inverters in the Sandia inverter database, the Vdcmax, MPPT_low, and MPPT_hi valuesare not included in the database, and SAM displays zeros for those variables on the Inverter page. Forthose inverters, there is insufficient information for SAM to determine whether the array rated voltagesare within the acceptable ranges for the inverter. To properly size the array, you must refer to the invertermanufacturer specifications outside of SAM, and manually size the array by choosing the Specifynumbers of modules and inverters mode.

Similarly, the single-point efficiency inverter model, simple efficiency module model, and concentratingphotovoltaic model, do not include information about rated voltage levels, so there is insufficientinformation for SAM to determine whether the array rated voltages are within the acceptable ranges forthe inverter. SAM assigns 1 to Module per String, and chooses a number of inverters and strings inparallel that results in matching array and inverter capacities. This approach is suitable for basicanalyses that do not involve the shading model.

Specify numbers of modules and inverters by hand:

1. Choose an inverter for the system on the Inverter page.

2. Choose a module on the Module page.

3. On the Array page, for Mode, choose Specify numbers of modules and inverters.

4. Type a number of inverters that results in a total inverter DC capacity close to the system's DCcapacity.

SAM displays the total inverter AC capacity on the Array page. To see the rated DC capacity of asingle inverter, see the Inverter page: Power DCo for the Sandia model or Power (DC) for thesingle-point efficiency model. The total inverter rated DC capacity is the product of the inverter's DCcapacity from the Inverter page and the number of inverters from the Array page.

5. Type a number of modules per string that results in an array maximum power rated DC voltage(Vmp) less than the inverter's maximum operating DC voltage level (MPPT_hi) shown on the Inverterpage, but greater than the inverter's minimum operating DC voltage level (MPPT_low) so thatMPPT_low < Vmp < MPPT_hi.

6. If the array open circuit rated DC voltage (Voc) on the Array page is greater than the inverter'smaximum rated DC voltage (Vdcmax) from the Inverter page, reduce the number of modules perstring so that Voc < Vdcmax.

7. Type a number of strings in parallel that results in a total array DC power value close to thesystem's rated DC capacity.

8. Specify the tracking and orientation and system derate factors as appropriate. See SpecifyingArray Tracking and Orientation for details.

9. When you run simulations, SAM will check the system sizing variables and display a message ifthere appear to problems with the sizes you specified. See About Array Sizing Error Messages fordetails.



Notes for Specifying Array Size by Hand.

For some of the inverters in the Sandia inverter database, the Vdcmax, MPPT_low, and MPPT_hi valuesare not included in the database, and SAM displays zeros for those variables on the Inverter page. Forthose inverters, there is insufficient information for you to determine whether the array rated voltages arewithin the acceptable ranges for the inverter. To properly size the array, you must refer to the invertermanufacturer specifications outside of SAM to find the voltage ratings.

Similarly, the single-point efficiency inverter model, simple efficiency module model, and concentratingphotovoltaic model, do not include information about rated voltage levels, so there is insufficientinformation for you to determine whether the array rated voltages are within the acceptable ranges for theinverter. In that case, you can only ensure that the array and inverter rated capacities are matched.

About Array Sizing Error Messages

Pre-simulation Size Checking and Error Messages

When you run simulations, before starting the simulations, SAM does a series of checks to make sure thatthe array sizing variable values meet a set of rules based on the module and inverter ratings. If it finds anyproblems with the array sizing variables, it displays a warning message. You can either go back to theArray page and change values of the array sizing variables, or ignore the warnings and continue with thesimulations.

If you chose either the the Sandia or CEC model option on the Module page, SAM checks for the followingbefore starting simulations:

Voc < Vdcmax: Array open circuit voltage (Voc String) is less than the inverter maximum rated DCvoltage (Vdcmax on the Inverter page).

Vmp > MPPT_low: Array rated voltage at maximum power (Vmp String) is greater than the inverterminimum rated operating DC voltage (MPPT_low on the Inverter page).

Vmp < MPPT_hi: Array rated voltage at maximum power (Vmp String) is less than the invertermaximum rated operating DC voltage (MPPT_hi on the Inverter page).

Array Power ~ Desired Array Size: Array rated capacity (Array Power) in DC kilowatts is as close aspossible to the desired array capacity in DC kilowatts. (The actual array capacity must be an integermultiple of the module's rated power (Pmp on the Module page.) The sizing calculator will not allow thearray capacity to be greater than the desired array capacity.

Total Inverter Capacity ~ Array Power: Inverter rated capacity (Total Inverter Capacity) in AC kilowattsis as close as possible to the array capacity in DC kilowatts (Array Power).

Note. For some of the inverters in the Sandia inverter database, the Vdcmax, MPPT_low, and MPPT_hivalues are not included in the database, and SAM displays zeros for those variables on the Inverter page. For those inverters, SAM cannot ensure that the array's rated voltages are within the acceptableranges for the inverter. To properly size the array, you must refer to the inverter manufacturerspecifications, and manually size the array by choosing the Specify numbers of modules andinverters mode.

If you chose the simple efficiency model or concentrating photovoltaics model on the Module page, SAMdoes not have enough information to determine the array's open circuit and maximum power DC voltagelevels, so it only performs last two checks listed above to ensure that the array and inverter rated capacities

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are as close as possible.

Post-simulation Size Checking and Error Messages

After completing simulations, SAM does another series of checks to see whether the inverter is over- orunder-sized based on the actual output of the array. If it finds any problems, SAM displays the ShowSimulation Warnings button in the notification area at the top right corner of the main window. Click thebutton to display the warning message.

Post-simulation checks include:

Array output greater than inverter rated capacity: SAM counts the number of hours that the array'ssimulated DC output is greater than the inverter's AC rated capacity, and displays a simulation warningif the number of hours is greater than zero.

Inverter output less than 75 percent of inverter rated capacity: SAM also compares the inverter'smaximum AC output to the total inverter AC capacity and displays a simulation warning if the inverter'smaximum AC output is less than 75% of the total inverter rated AC capacity.

Specifying Array Tracking and OrientationThe tracking options allow you to choose from one of four options for specifying whether and how moduleson the array follow the movement of the sun across the sky.

Fixed: The array is fixed at the tilt and azimuth angles defined by the values of Tilt and Azimuth anddoes not follow the sun's movement.

1 Axis: The array is fixed at the angle from the horizontal defined by the value of Tilt and rotates aboutthe tilted axis from east in the morning to west in the evening to track the daily movement of the sunacross the sky. Azimuth determines the array's orientation with respect to a line perpendicular to theequator.

2 Axis: The array rotates from east in the morning to west in the evening to track the daily movement ofthe sun across the sky, and north-south to track the sun's seasonal movement throughout the year.

Azimuth Axis: The array rotates in a horizontal plane to track the daily movement of the sun.

Note. SAM does not adjust installation or operating costs on the System Costs page based on thetracking options you specify. Be sure to use appropriate costs for the type of tracking system youspecify.

To specify array tracking and orientation:

1. Choose a tracking option: Fixed, 1 axis, 2 axis, or azimuth tracking.

If you use a tracking system, be sure that the Balance of System cost category on the PV SystemCosts page includes the cost of installing the tracking system, and that the Operation andMaintenance cost includes the cost of maintaining the system.

2. Type a value for the array tilt angle in degrees from horizontal. Zero degrees is horizontal, 90degrees is vertical.

If you are unsure of a value, use the location's latitude (displayed in the navigation menu underClimate and on the Climate page), or check Force Tilt = Latitude if you want SAM toautomatically assign the value of the latitude from the weather file to the array tilt angle. Note thatSAM does not display the tilt angle when you choose this option, but it does use the correct valuein simulations.



3. If the array is oriented away from due south in the northern hemisphere (or oriented away from duenorth in the southern hemisphere), change the default azimuth angle to the desired value. Anazimuth angle of 0 (facing the equator) normally maximizes energy production. For the northernhemisphere, increasing the azimuth angle favors afternoon energy production, and decreasing theazimuth angle favors morning energy production. The opposite is true for the southern hemisphere.

About Derate FactorsAn AC photovoltaic system typically consists of a DC side that includes modules, diodes, and DC wiringand fuses, and an AC side that includes AC wiring, fuses, and transformers. SAM allows you to enter twoderate factors, a pre-inverter derate factor to account for electrical losses on the DC side of the system, andpost-inverter derate factor to account for losses on the AC side.

Derate Factors in Performance Simulation Calculations

SAM calculates hourly conversion efficiency values for the module and inverter types included in the systemusing the hourly simulation models that you specify on the Module page and Inverter page. The deratefactors allow you to account for losses outside of the modules and inverters. During simulation, SAMcalculates the solar radiation incident on the array for each hour, and calculates the array DC output usingequations in the Module model. For each hour in the simulation, SAM applies the pre-inverter derate factorto the array's DC output before passing it to the inverter model. SAM calculates the inverter's AC outputusing equations in the Inverter model, and applies the post-inverter derate factor to the inverter's AC outputto calculate the derated AC power.

The total array power shown on the Array page is the array's rated power based on the module's power fromthe Module page and the number of modules shown on the Array page. SAM does not apply the deratefactor to this rated capacity value.

During simulations, SAM multiplies the array's DC power output by the pre-inverter derate factor to calculatethe inverter's DC input power for each hour of the simulation:

Similarly, to calculate the system's gross hourly output, it multiplies the inverter's output by the post-inverterderate factor:

You can see these values in the hourly results.

To calculate the system's net annual energy output, SAM adds up the 8,760 hourly gross system outputvalues and adjusts this gross annual energy output value using the degradation and availability factors fromthe Annual Performance page.

Choosing Derate Factors

One source of information on derate factors is the website for NREL's PVWatts model, which includes atable of derate factor components for various sources of losses. Because SAM's performance model alreadyaccounts for some of the losses listed in the PVWatts table, it is not appropriate to use some of thePVWatts derate factor components in your SAM analysis.

Note. The PVWatts derate factors are described at http://www.nrel.gov/rredc/pvwatts/changing_parameters.html

http://www.nrel.gov/rredc/pvwatts/changing_parameters.html


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If you are in doubt about the value to use for the derate factors, you can use the default values supplied withthe SAM sample files. The following information is based on the information provided on the PVWattswebsite, and can be used as a reference for choosing values for the derate factors in SAM.

The total pre-inverter derate factor is the product of the six DC derate factor categories.

The following derate factor components described on the PVWatts website are accounted for by SAM andshould not be included in the pre- or post-inverter derate factors.

Inverter and Transformer: SAM's inverter performance models calculate the inverter output based on theoutput of the module (as determined by the performance model) and parameters defined on the Inverterpage, and not based on a derate factor.

System availability: The system availability is an input variable on the Annual Performance page, andshould not be included as a derate factor.

Shading: SAM accounts for shading based on the parameters specified on the Shading page.

Age: SAM's degradation factor on the Annual Performance page accounts for performance losses overtime due to aging of modules.

The following derate factor components described on the PVWatts website are not accounted for by SAM.

Table 1. Pre-inverter (DC) derate factors not accounted for by the module performancemodel.

Derate FactorComponent Cause of Loss

PVWattsDefaultValue

PVWattsRange

Mismatch Slight differences in performance of different modules in thearray.

98.0 97.0 - 99.5

Diodes andConnections

Voltage drops across blocking diodes and electricalconnections.

99.5 99.0 - 99.7

DC Wiring Resistive losses in wiring on the DC side of the system. 98.0 97.0 - 99.0

Soiling Dirt, snow, or other matter on the module surface blockingsolar radiation from reaching cells.

95.0 30.0 - 99.5

Sun Tracking Inaccuracies in the tracking mechanisms ability to keep thearray oriented toward the sun. The default value of 100%assumes a fixed array with no tracking. Applies only tosystems with one- or two-axis tracking arrays.

100.0 95.0 - 100.0

Nameplate Accounts for accuracy of the manufacturer's nameplaterating, often for the performance degradation modules mayexperience after being exposed to light.

0.95 0.80-1.05

Table 2. Post-inverter (AC) derate factors not accounted for by the inverter performancemodel.

Derate FactorComponent Cause of Loss

PVWattsDefaultValue

PVWattsRange

AC wiring Resistive losses in wiring on the AC side of the system. 99.0 98.0 - 99.3



Transformer Transformer efficiency. If you use the Sandia inverter model,then the transformer losses are accounted for by the modelparameters and you should set the Transformer derate factorto 100%. If you use the simple efficiency inverter model, youcan specify a value to account for transformer losses if yourinverter efficiency value does not include transformer losses.The PVWatts model combines the inverter and transformerderate factor into a single value.

100% --

Backtracking OverviewBacktracking is a PV array tracking strategy that attempts to avoid row-to-row shading of modules in anarray. Without backtracking, a tracking array typically points the modules directly at the sun. However, foran array with closely spaced rows, modules in adjacent rows may shade each other at certain sun anglesangles, which can dramatically reduce the array's power output. With backtracking, under these conditions,the tracker will orient the modules away from the sun to avoid shading.

SAM's backtracking algorithm divides the array into subarrays. Each subarray has the same orientation asall the others, meaning that the entire array is driven by a single tracking scheme. Each subarray has aphysical location (origin: x, y, z) and a length l and width w. The length is parallel to the axis of rotation. Fora typical one-axis tracking system, the length represents the north-south dimension of each trackingsubarray, and the width represents the east-west dimension.

Note. The subarray layout for backtracking is not linked to the modules per string and strings in parallelvalues you specify under Layout on the Array page. SAM uses the subarray layout values forbacktracking calculations, but not for array sizing calculations.

The backtracking algorithm is an iterative process that determines whether a subarray is shaded, andsubsequently adjusts the angle of rotation until there is no more array shading. Once a suitable angle isfound, the module power output is calculated for the array at the given rotation angle and known sunposition.

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3.3.3 PVWatts Solar Array

The PVWatts Solar Array page displays variables for SAM's implementation of NREL's PVWatts model.

SAM includes an implementation of NREL's PVWatts model to facilitate comparing results calculated bySAM's three other photovoltaic module performance models with PVWatts results, and to generate resultsbased on the PVWatts performance model but using SAM's cost and financial model and assumptions.

Note. NREL's PVWatts model is a web-based simulation model for grid-connected photovoltaicsystems. To use the model or find out more about it, visit the PVWatts website at http://www.nrel.gov/rredc/pvwatts/. The model is also described in Marion W et al, 2002. PVWatts Version 2: EnhancedSpatial Resolution for Calculated Grid-Connected PV Performance. http://rredc.nrel.gov/solar/codes_algs/PVWATTS/pvwatts2.pdf.

To view the PVWatts Solar Array page, click PVWatts Solar Array on the main window's navigation menu.Note that for the PVWatts Solar Array page to be available, the technology option in the Technology andMarket window must be Photovoltaics - PVWatts Performance Model.

PVWatts System Inputs

The system inputs define the size of the system, derate factor, and the array orientation. For informationabout choosing values for the PVWatts input variables, see the PVWatts website at http://www.nrel.gov/rredc/pvwatts/changing_parameters.html.

DC Rating

The array's nameplate DC power rating in kilowatts under standard test conditions (STC). The DC ratingis equal to a single module's DC power rating in watts at 25°C and 1,000 W/m2 multiplied by thenumber of modules in the array divided by 1,000.

http://www.nrel.gov/rredc/pvwatts/

http://www.nrel.gov/rredc/pvwatts/

http://rredc.nrel.gov/solar/codes_algs/PVWATTS/pvwatts2.pdf

http://rredc.nrel.gov/solar/codes_algs/PVWATTS/pvwatts2.pdf





DC to AC Derate Factor

A factor accounting for conversion of the array's DC nameplate capacity to the system's AC powerrating at STC. The default value is 0.77. For help calculating the derate factor, see the PVWatts deratefactor calculator at http://rredc.nrel.gov/solar/calculators/PVWATTS/derate.cgi.

Array Tracking Mode

The three array tracking modes are:

A fixed array is fixed at the tilt and azimuth angles defined by the Tilt and Azimuth variables.

A one-axis tracking array is fixed at the tilt angle defined by the Tilt variable and rotates from east inthe morning to west in the evening to track the daily movement of the sun across the sky.

A two-axis tracking array rotates from east in the morning to west in the evening to track the dailymovement of the sun across the sky, and from north to south to track the sun's seasonal movementthroughout the year.

Tilt (degrees)

Applies only to fixed arrays and arrays with one-axis tracking. The array's tilt angle in degrees fromhorizontal, where zero degrees is horizontal, and 90 degrees is vertical. As a rule of thumb, systemdesigners often use the location's latitude as the optimal array tilt angle. The actual tilt angle will varybased on project requirements.

Force Tilt = Latitude

Populates the array tilt value with the latitude value stored in the weather file and displayed on theClimate page. Note that SAM does not display the tilt value on the Array page, but does use the correctvalue during simulations.

Azimuth (degrees)

Applies only to fixed arrays with no tracking. The array's east-west orientation in degrees. An azimuthvalue of zero or 360 degrees is facing north, 90 degrees = east, 180 degrees = south, and 270 degrees= west, regardless of whether the array is in the northern or southern hemisphere. For systems north ofthe equator, a typical azimuth value would be 180 degrees. For systems south of the equator, a typicalvalue would be 0 degrees. Note that this convention is different from the convention for the other SAMphotovoltaic model options.

3.3.4 Shading

The Shading page provides access to options for modeling shading of the array using any of three shadingmodel options, or by importing shading data from SunEye shading device or PVsyst simulation software.

To view the Shading page, click Shading on the main window's navigation menu. Note that for the Shadingpage to be available, the technology option in the Technology and Market window must be Photovoltaics -SAM Performance Models.

Contents

Overview describes the Shading model and its limitations.

Enabling and Disabling Array Shading explains how to turn on and off array

http://rredc.nrel.gov/solar/calculators/PVWATTS/derate.cgi

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shading.

Defining the Shading Factors explains how to edit the shading factor matrix.

Importing and Exporting Shading Factor Data explains how to use text files to storeshading matrix data.

OverviewSAM models two types of shading: Shading that affects the entire array uniformly, and shading of moduleswithin the array by neighboring modules. To model the first kind of shading, SAM reduces the solar radiationincident on the array. To model self shading of modules within the array, SAM adjusts the array's DCoutput:

Beam Radiation Shading

Shading objects block the direct normal component of radiation incident on the entire array. You caneither specify your own shading factors, or import shading factors from the SunEye shading device orPVsyst simulation software. See Specifying Beam Shading Factors for details.

Sky Diffuse Shading

A reduction in the diffuse component of the radiation incident on the entire array for all hours of the year.You can either specify your own shading factor, or import the factor from the PVsyst simulationsoftware. See Specifying a Sky Diffuse Shading Factor for details.

Self Shading

Estimates the reduction in the array's DC output due to row-to-row shading of modules within the array.Unlike the beam radiation shading and sky diffuse shading models, which reduce the amount ofradiation incident on the array, the self-shading model reduces the DC output of the array. To use theself-shading model, you must describe the configuration of cells in modules and modules in the array.See Specifying Self Shading Parameters for details.

Notes.

The self-shading model only works when the model option on the Module page is either CECPerformance Model or Sandia PV Array Performance Model. If the Simple Efficiency Module orConcentrating PV Module option is active, the self-shading parameters on the Shading page have noeffect on simulation results.

The self shading model is disabled for the PVWatts modeling option.

Beam and Sky Diffuse Shading Factors

Each shading factor is a value between zero and one that represents the fraction of radiation (either beam ordiffuse) allowed to reach the array. A shading factor of one represents no shading. A shading factor of zerorepresents complete blockage of either the beam or sky diffuse radiation from the array.

The value of the shading factor in each hour depends on the method you use to specify the values on theShading page.

To calculate the effect of shading on the array, SAM adjusts the incident beam and diffuse radiation valuethat it calculates from the data in the weather file and solar angles in each hour as appropriate:



SAM multiplies the the incident normal radiation in each hour by the beam shading factor for that hour.The incident normal radiation is the solar radiation that reaches the array in a straight line from the sun.

SAM the incident sky diffuse radiation for each hour by the sky diffuse shading factor. Sky diffuseradiation is radiation that reaches the array from the sun indirectly after being reflected by clouds andparticles in the atmosphere. Sky diffuse radiation does not include diffuse radiation reflected from theground. Note that you can only specify a single value that applies to all hours of the year for the skydiffuse shading factor.

Enabling and Disabling Shading Models

SAM provides options for five different shading models. To enable a shading model, click its check box. Forexample, to enable the beam shading model using month-by-hour shading factors, enter values in the beamshading factor table and check Enable Month by Hour Beam Shading Factors.

Notes.

You must enable at least one shading option using one of the Enable checkboxes for SAM to includeshading.

SAM does not prevent you from enabling more than one shading option even if that results in anunrealistic shading model. Be sure to verify that you have enabled the set of options you intend beforerunning SAM.

Beam Radiation Shading FactorsSAM provides three options for specifying beam shading factors: Hourly 8760, Month by Hour, and Azimuthby Altitude. If you enable more than one option, SAM multiplies the shading factors to calculate the totalshading factor for each hour.

Hourly 8760

The Hourly 8760 option allow you to use a set of hourly (8,760 hours/year) beam shading factors for theproject location. You can cut and paste the data from a spreadsheet if the data is organized into a singlecolumn of 8,760 values, or you can import the data from a text file that contains a single column of data withno header in the first row. See Overview for a description of shading factors.

To specify hourly beam shading factors:

1. Check Enable Hourly 8760 Beam Shading Factors.

2. Click Edit Data.

3. To copy data from a spreadsheet, select and copy a column of 8,760 beam shading factors in thespreadsheet and click Paste in the Edit Data window.

To import data from a text file, click Import and navigate to the file. The file must contain a singlecolumn of 8,760 beam radiation values with a header in the first row.

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Month by Hour

To define the month-by-hour shading factor matrix, you assign a value to each cell in the matrix. Theshading factor in a cell applies to a given hour for an entire month. For example, a shading factor of 0.90 inthe 6 a.m. cell for May would mean that 90% of the beam radiation value in the weather file for each hourbeginning at 6 a.m. and ending at 7 a.m. in May would be used to calculate the global solar radiationincident on the array.

Note. The time convention for the matrix is determined by the convention used in your weather file. Forexample, TMY2 and TMY3 data use local standard time.

As you work with the shading factor matrix, keep the following in mind:

The first column in the matrix is for the hour beginning at 12:00 a.m. and ending at 1:00 a.m.

A red cell indicates a value of zero, or full shading (beam radiation completely blocked).

A white cell indicates a value of one, or no shading.

A dark shade of red indicates more shading (more beam radiation) than a light shade of red.

To define a shading factor for a single cell:

Click the cell and type the shading factor.

To replace the value in a cell, click the cell and type a replacement value.

To delete the value from a cell, double-click the cell and press the Delete key.

To define a single shading factor for multiple cells:

Select the cells to which you want to apply the shading factor.

Type a value between zero and one.

Press the Enter key or click Apply to selected cells.

To import or export month-by-hour beam shading factors:

Solar Advisor allows you to import and export the shading factor matrix as a comma-delimited text file thatcontains 12 rows of 24 hourly shading factors separated by commas. The file should not have row or columnheadings.

To export the shading matrix as a text file, click Export.

To import a data from a comma-delimited text file, click Import.

Azimuth by Altitude

The azmiuth-altitude shading factors for beam radiation are represented as a two-dimensional lookup table,where solar azimuth values are given across the top and solar altitude values are given along the side of thetable. Azimuth values must increase monotonically from left to right. Altitude values must increasemonotonically from bottom to top.

For each hour in the simulation, SAM calculates the position of the sun as a set of azimuth and altitudeangles. SAM uses a linear interpolation method to estimate the value of the beam shading factor for thehour based on the nearest values in the lookup table.

To define the azimuth-altitude shading factor table, first enter the number of rows and columns in the table.



The number of rows is one greater than the number of azimuth values specified. The number of columns isone greater than the number of altitude values specified. Second, enter the headings for the table, withazimuth values increasing along the top and altitude values decreasing down the left side. Finally, enter theshading factors for beam radiation.

Note: Azimuth values use the component based conventions. 0 = equator, 90 = west, -90 = east. Thisconvention is different from the convention used on the PVWatts Solar Array page.

Solar Advisor allows you to import and export the azimuth-altitude lookup table as a comma-delimited textfile that contains shading factors separated by commas. The file should have row or column headings.

To import or export azimuth-by-altitude beam shading factors:

To export the shading matrix as a text file, click Export.

To import a data from a comma-delimited text file, click Import.

Sky Diffuse Shading FactorA shading factor for sky diffuse radiation may be used. This factor is applied to every hour in the year. Thisvalue is considered to be the fraction of the sky that is obstructed, and is therefore constant.

Import from External SoftwareSAM allows you to import shading data from either PVPVsyst, photovoltaic system design software fromthe University of Geneva in Switzerland (http://www.pvsyst.com), or from the SunEye, an electronicshading analysis device from Solmetric (http://www.solmetric.com/).

Importing Data from PVsyst

You can import a "Near Shadings" table generated by PVsyst into SAM. SAM automatically imports datafrom the text file generated by PVsyst into the Azimuth-Altitude Shading Factors for Beam Radiationtable and Diffuse Shading Factor value.

Notes. We have tested the following procedure with Version 5 of PVsyst.

The "Near Shadings" table in PVsyst looks like this:

http://www.pvsyst.com)

http://www.solmetric.com/

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The "Near Shadings" data exported to a text file looks like this (in this example with semicolon delimiters):

To import a "Near Shadings" table from PVsyst:

1. In PVsyst, follow the procedure to create and export a "Near Shadings" table. The table in PVsystshould look similar to the one below. SAM will recognize any of the delimiter options: tab, comma,or semicolon.

2. In SAM, click the Import PVsyst Near Shading and navigate to the folder containing the shadingfile.

When SAM imports data from the file, it displays the message "Azimuth-Altitude Table and DiffuseFactor update" and populates the azimuth-altitude shading table, the sky diffuse shading factor,and enables both options.

3. Disable any shading options that do not apply to your analysis.

Importing Data from SunEye

The Solmetric SunEye software generates shading data in two formats: The obstruction table, whichcharacterizes shading using an altitude-azimuth angle table to indicate solar positions that are blocked bynearby obstructions, and the hourly shading file, which lists hourly beam radiation shading factors. SAMcan read data from both tables.

Use the obstruction table if you plan to model the system for different locations (assuming the sameshading obstructions). Use the hourly shading factor table if you plan to model the system for a singlelocation.

Note. If you use the hourly shading factor table, be sure that the weather data specified on the Climatepage is for the same location as the one where the SunEye measurements were made.

To import a SunEye obstruction table:

1. In the Solmetric SunEye software (not the PV Designer software), on the File menu, click ExportSession Report and Data.

The SunEye software creates a set of files, and assigns a default name likeSky01ObstructionElevations.csv to the obstruction data file. By default, the files are in a foldernamed ExportedFiles in the exported report folder.

2. In SAM, on the Shading page, click Import Suneye Obstruction File, and navigate to the foldercontaining the file you want to import.

3. Open the obstruction data file for any of the available skies (Sky01ObstructionElevations,Sky02ObstructionElevations, etc.).

If the average or worst case obstruction data from multiple skylines will be used, then an extra stepis required. In a spreadsheet program, open the ObstructionElevation file containing the averageand maximum values as well as all skylines in the SunEye session. Make sure that the desired



data (average or maximum) is in the third column, delete the other columns, and save the file as .csv with a name like ObstructionElevationsAVG.csv. Use this file as the obstruction data file inSAM.

SAM displays the message "Azimuth-Altitude Table updated," populates the azimuth-altitudeshading factor table, and enables the Enable Azimuth-Altitude Shading Factors for BeamRadiation option.

4. Be sure to enable and disable the other shading options as appropriate.

To import a SunEye hourly shading file:

1. In the Solmetric SunEye software (not the PV Designer software), on the File menu, click ExportSession Report and Data.

The SunEye software creates a set of files, and assigns a default name like Sky01Shading.csv tothe hourly shading file. By default, the files are in a folder named ExportedFiles in the exportedreport folder.

2. In SAM, on the Shading page, click Import Suneye Hourly Shading File, and navigate to thefolder containing the shading file.

3. Open the shading file for any of the the available skies (Sky01Shading, Sky02Shading, etc.). Touse average shading for multiple skylines, open AverageShading.csv.

SAM displays the message "Hourly Shading Factors for Beam Radiation updated," populates thehourly shading factor table, and enables the Enable Hourly Beam Shading Factors option.

4. To see the hourly data, click Edit Data under Hourly Shading Factors for Beam Radiation.

5. Be sure to enable and disable the other shading options as appropriate.

6. On the Climate page, choose a weather file for the same location represented by the SunEyeshading data.

Self Shading Calculator for Fixed Tilt Arrays

Overview and Requirements

The self-shading model calculates the effect of row-to-row shading in the array, where shadows frommodules in neighboring rows of the array block sunlight from parts of other modules in the array duringcertain times of day. The response of a real photovoltaic module to shading is complex, and depends onseveral factors including the cell material, shape and layout of cells in the module, and configuration ofbypass diodes in the module.

For a description of the effect of module shading on system performance, see Deline C, Partially ShadedOperation of a Grid-Tied PV System, NREL/CP-520-46001, June 2009: www.nrel.gov/docs/fy09osti/46001.pdf.

SAM's self-shading model has several limitations, and only works under the following conditions:

The performance model option on the Module page is either Sandia PV Array Performance model orCEC Performance Model. The self-shading model does not work for the simple efficiency model or theconcentrating PV model. The self-shading model is disabled for the PVWatts modeling option.

The cell material is crystalline silicon, either mono-crystalline or poly-crystalline. The self-shading modeldoes not work for modules with thin film cells. SAM indicates the cell material on the Module pageunder Physical Characteristics. See Module page for a list of abbreviations used to indicate cellmaterial.

http://www.nrel.gov/docs/fy09osti/46001.pdf


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Each module in the array consists of square cells arranged in a rectangular grid with one or morebypass diodes and can be described using the input variables described below. The self-shading modeldoes not work for modules with rectangular, circular, or triangular shaped cells.

The array uses fixed tracking, as specified on the Array page. The self-shading model does not work forone-axis, two-axis, or azimuth-axis tracking.

The the number of modules per string and strings in parallel specified on the Array page is consistentwith the array configuration specified on the Shading page.

Note. To use the self-shading model, you need information about the module's dimensions, cell layout,and number of bypass diodes. This information is not available in SAM, but you should be able to find iton the manufacturer's data sheet for the module.

SAM's Sandia and CEC photovoltaic performance models assume that modules operate at the maximumpower point for the level of incident radiation in each hour. The self-shading model calculates a singlederating factor that estimates the effect of shading on the array's output.The self-shading model calculatesand applies hourly DC derating factors to the entire array's output using the following algorithm:

1. Calculate the array's derated DC output at the maximum power point based (without shading) on theinputs you specify on the Module page and Array page.

2. Calculate the size and position of rectangles of shade on the array using information about the relativepositions of the sun and modules in the array.

3. Determine the reduction in output of each module in the array based on the number of shaded cells andbypass diodes.

4. Calculate an overall derate factor to apply to the array's maximum power point DC output thatrepresents the reduction of output caused by the shadows.

5. Recalculate the array's derated DC output.

Note. For hours when both 20% or more of module strings and 25% or more of all cell strings in thearray are shaded, the self-shading algorithm reduces the array DC output to near zero, whichexaggerates the impact of shading for those hours. This typically only occurs for arrays with closelyspaced rows, and could cause SAM to overestimate self-shading impacts. If this situation occurs, SAMreports the overestimated shading impacts in a simulation warning message on the Results page.

Module

The module input variables describe the properties of the module required by the self-shading model. Notethat the values of these variables should be consistent with those shown on the Module page.

Orientation

The module orientation determines whether the short or long side of the module is parallel to the groundor at the bottom of the module, assuming that all modules in the array are mounted at an angle from thehorizontal equal to the tilt angle specifed on the Array page.

Portrait orientation means the short end of the module is parallel to the ground, or at the bottom of themodule.

Landcape orientation means the long end of the module is parallel to the ground, or at the bottom of themodule.

Length

Long side of a module. SAM calculates this value based on the width (short side) you specify and area



from the Module page.

Length (m) = Module Area (m2) / Width (m)

Width

Short side of a module. The product of the width and length should be equal to the module area on theModule page.

Number of cells along length

The number of cells along the long side of the module. SAM calculates this value based on the numberof cells along width that you specify and the number of cells from the Module page.

Number of Cells Along Length = Number of Cells / Number of Cells Along Width

Number of cells along width

The number of cells along the short side of the module. The product of the number of cells along thelength and width should equal the total number of cells on the Module page.

Number of bypass diodes

The number of bypass diodes in each module.

The images below show examples of a module with four cells along its width and in portrait orientation.Because the module is in portrait orientation, SAM would consider it to have four cells along the bottomof the module, and would assume the diode connections shown in the diagrams for the module withtwo, four, and eight diodes.

Note. SAM only uses the diode connections to estimate the DC power output reduction of the array dueto shading. The model does not consider diode polarity or current flow through the modules.

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The number of diodes determines what portion of the module output is reduced. In the following images,the grey square indicates the shaded cell for each of the combinations of numbers of diodes, andrectangle with broken lines indicates the portion of the module affected by the shaded cell. Forexample, for a module with four cells along the bottom and two diodes, when any single cell is shaded,SAM reduces the module's power output by 50%.

Array

The array input variables describe how modules are oriented in the array, and should be consistent with thevalues specified on the Array page.



Note. The self-shading model assumes that the array consists of module strings that are bothelectrically connected in series and physically laid out in a single line.

String Wiring

Describes the orientation of strings of modules in the array.

Horizontal: Strings are parallel to the ground.

Vertical: Strings are inclined at the array's tilt angle.

Number of modules along bottom

The number of modules along the edge of the array parallel to the ground. This is a calculated value thatyou cannot edit.

Number of modules along side

The number of modules along the edge of the array perpendicular to the bottom of the array as definedabove.

Number of rows

One row consists of one or more strings and is inclined from the horizontal at the tilt angle specified onthe Array page.

Layout from Array Page

The Modules per String and Strings in Parallel values from the Array page for your reference tofacilitate calculating the correct shading layout values described below.

As you type values for the shading layout variables, SAM performs checks to ensure that the values meetthe criteria described below for horizontal and vertical string wiring. If they do not, SAM displays a messagebut does not prevent you from running simulations with the incorrect values.

For horizontal string wiring:

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For vertical string wiring:

Row spacing

The distance in meters between rows.

Slope E/W

The east-west ground slope in degrees, where zero is horizontal and 90 is vertical.

An east-west slope of 10 degrees would be inclined uphill from east to west at a 10 degree angle fromhorizontal. SAM assumes that the ground under the array is uniformly inclined.

Slope N/S

The north-south ground slope in degrees, where zero is horizontal and 90 is vertical.

3.3.5 Module

The Module page allows you to choose a photovoltaic module performance model and either choose amodule from a list or to specify module characteristics. SAM assumes that the system consists of one ormore of the same type of module. Specify the number of modules in the system on the Array page.

To view the Module page, click Module on the main window's navigation menu. Note that for the Modulepage to be available, the technology option in the Technology and Market window must be Photovoltaics -SAM Performance Models.

Contents

Overview describes the Module page options and general guidelines for choosing aphotovoltaic module model.

Choosing a Module Performance Model explains guidelines for choosing the bestperformance model for your analysis and for modeling thin-film modules.

Sandia PV Array Performance Model describes the Sandia model in more detail,explains the model parameters, and suggests resources for learning more aboutthe model.

CEC Performance Model describes the CEC model in more detail (including



temperature correction), explains the model parameters, and suggests resourcesfor learning more about the model.

Simple Efficiency Module describes the input variables and algorithms for thesimple efficiency model for flat-plate modules.

Concentrating PV Module describes the concentrating photovoltaic (CPV) model and itsinput variables and algorithms. It also explains how to use the Sandia model the CPVmodules included in the Sandia database.

Temperature Correction (Except CEC Model) describes how SAM calculatesmodule temperature and a temperature correction factor for the Sandia, simpleefficiency, and CPV moduel model.

OverviewThe Module page allows you to choose a photovoltaic module performance model from four options:

Simple Efficiency Module

CEC Performance Model

Sandia PV Array Performance Model

Concentrating PV Module

Note. To model a photovoltaic system using the PVWatts model, you must choose PVWatts SystemModel in the Technology and Market window.

To specify a photovoltaic module model:

1. Choose the model name from the list.

2. For the Sandia or CEC models, choose a module from the database of available models.

For the simple efficiency model and concentrating PV Module, specify the module characteristics.

Hourly Simulation

Each of the four module performance models calculates the hourly DC electrical output of a single modulebased on the hourly incident solar radiation (plane-of-array irradiance) calculated by the climate model usingdata in the weather file as specified on the Climate page and array orientation and tracking information fromthe Array page. The photovoltaic array output depends on the number of modules and the pre-inverter deratefactor specified on the Array page. SAM passes the array's hourly DC power output to the inverter model,whose characteristics appear on the Inverter page.

Note. SAM assumes that the array operates at its maximum power point. SAM does not track changesin voltage and current levels in the system.

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Choosing a Module Performance ModelEach of the four available module performance models uses a different algorithm to predict moduleperformance. In general, if you are modeling a system that uses a particular brand and type of flat-plate PVmodule, you should first look for the module in the Sandia database, and then in the CEC database. If youdo not find the module in either database, you can either choose a similar module, or use the simpleefficiency model.

The simple efficiency and concentrating PV models are ideal for analyses involving explorations of therelationship between module efficiency and the system's performance and cost of energy. Both modelsallow you to define a curve of the module's efficiency versus incident radiation. The Sandia and CEC modelsdo not allow you to modify module parameters such as efficiency, although advanced users with andunderstanding of the model algorithms can add their own modules to the database.

The Sandia PV Array Performance Model calculates hourly efficiency values based on data measuredfrom modules and arrays in realistic outdoor operating conditions. The Sandia model tends to producemore accurate predictions of module performance than the CEC model. However, because of the timeand effort required to make the field measurements, the Sandia module database is less up-to-date thanthe CEC database.

The California Energy Commission (CEC) Performance Model predicts module performance based on adatabase of module characteristics determined from module ratings. Like the Sandia model, the CECmodel calculates hourly efficiency values, and allows you to select from a list of a commercially-available modules. The CEC module database tends to be more up-to-date than the Sandia database.For some types of modules, the CEC model predictions may be less accurate than the Sandia model.

The Simple Efficiency Module model is a simple representation of module performance that requires youto provide the module area, a set of conversion efficiency values, and temperature correctionparameters. The simple efficiency model is the least accurate of the three models for predicting theperformance of specific modules. It is useful for preliminary performance predictions before you haveselected a specific module, and allows you to specify a module efficiency and temperature performanceparameters, which is useful for analyses involving sensitivity or parametric analysis.

For concentrating photovoltaic (CPV) modules, use the Concentrating PV Module model unless you aremodeling a CPV module available in the Sandia model, in which case, you can choose the module fromthe database in the Sandia model. The concentrating PV module model is similar to the simpleefficiency model, except that it uses only the direct normal component of the incident solar radiationinstead of the total radiation for performance predictions.

Table 3. Guidelines for choosing a photovoltaic module performance model.

Use this model... ...if your analysisinvolves...

Comments

SandiaModel based on field test data.

estimates of module performancefor crystalline or thin-filmmodules.

If your module is in both theSandia and CEC lists, use theSandia model.

CECModel based on module ratings.

estimates of module performancefor crystalline-silicon modules orfor new modules recentlyavailable on the market.

Use the CEC model when youranalysis involves a particularmodule that is not available in theSandia database.



Simple Efficiency ModuleSimple efficiency curve withtemperature correction.

sensitivity or parametric studieson module efficiency ortemperature coefficients, or forpreliminary analyses before youhave chosen a specific module.

Concentrating PV ModuleSimple efficiency curve withtemperature correction.

Modeling concentratingphotovoltaic modules.

See Modeling ConcentratingPhotovoltaic (CPV) Modules fordetails.

Modeling Thin-film Modules

For modules based on thin-film cell technology, including amorphous silicon, copper indium diselenide(CIS), cadmium telluride (CdTe), and heterojunction with intrinsic thin layer (HIT), the Sandia model mayprovide more accurate results than the CEC and simple efficiency models, which do not adequatelyrepresent module performance at low-light levels. For best results, if you are modeling a thin-film module,look for the module in the Sandia database. If the module is not available in the Sandia database, you maywant to use a module from the database with similar characteristics to the one you are modeling. Use thetable below to help identify the thin-film modules in the Sandia database.

Table 4. Thin-film module manufacturers and model numbers available in the Sandiamodule database.

Cell Type Manufacturer Model Series or Number

amorphous tandem junction (2-a-Si)

Solarex MST

amorphous silicon triple junction(3-a-Si)

Uni-Solar PVL, SHR, US, USF

cadmium telluride (CdTe) BP Solar BP980, BP990

First Solar FS

copper indium diselenide (CIS) Shell Solar ST

Siemens Solar ST

amorphous silicon heterojunction(HIT-Si)

Sanyo HIP

Sandia PV Array Performance ModelThe Sandia PV Array Performance model consists of a set of equations that provide values for five points ona module's I-V curve and a database of coefficients for the equations whose values are stored in the SandiaModules library. The coefficients have been empirically determined based on a set of manufacturerspecifications and measurements taken from modules installed outdoors in real, operating photovoltaicsystems.

Note. If you are a module manufacturer and would like to add your module to the Sandia database, youshould contact Sandia National Laboratories directly. See http://photovoltaics.sandia.gov/testing_eval.htm.

The Sandia model is described in King et al, 2004. Photovoltaic Array Performance Model. Sandia NationalLaboratories. SAND2004-3535. http://photovoltaics.sandia.gov/docs/PDF/King%20SAND.pdf

http://photovoltaics.sandia.gov/testing_eval.htm

http://photovoltaics.sandia.gov/testing_eval.htm

http://photovoltaics.sandia.gov/docs/PDF/King%20SAND.pdf

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To use the Sandia photovoltaic model:

1. On the Module page, choose Sandia PV Array Performance Model.

2. Choose a module from the list of available modules. SAM displays the module's characteristics andmodel coefficients.

When you choose a module from the list, SAM displays the module characteristics at referenceconditions on the Module page. Internally, the model applies a set of coefficients from the SandiaModules library to the simulation equations.

3. Choose a module structure from the three available options (displayed as front material / cell / backmaterial). See Temperature Correction for details. Module manufacturers typically include adescription of the front material, and frame or back material in a mechanical characteristics sectionof module specification sheets.

Notes.

The current version of the Sandia database contains a single concentrating PV module, listed as Entech22X Concentrator [1994].

The first several items in the module list are arrays instead of single modules. The arrays are indicatedby the word "Array" in the name. The array coefficients account for some losses not accounted for in thesingle module parameters, including module mismatch, diodes and connections, and DC wiring losses.When you use an array from the database, you should be sure that the Pre-Inverter derate factor on theArray page does not include these losses.

Module Characteristics at Reference Conditions

SAM displays the module characteristics so that you can compare modules in the database tomanufacturer specifications or to different modules in the database.

Reference Conditions

The reference conditions describe the incident solar radiation, air mass, ambient temperature, and windspeed that apply to the module characteristics. The module efficiency, power, current, voltage, andtemperature coefficients values are those for the module operating at the reference conditions.

Efficiency (%)

The module's rated efficiency at reference conditions. SAM displays this value for reference only. Duringsimulations, the model calculates an efficiency value for each hour, which you can see in the hourlyoutput data in the tabular data browser on the Results page.

Maximum Power (Pmp), Wdc

The module rated power in DC Watts. Equal to the product of the maximum power voltage andmaximum power current.

Maximum Power Voltage (Vmp), Vdc

Maximum power voltage in DC Volts under reference conditions.

Maximum Power Current (Imp), Adc

Maximum power current in DC Amps under reference conditions. Defines the maximum power point onthe module's I-V curve.



Open Circuit Voltage (Voc), Vdc

Open circuit voltage under reference conditions. Defines the open circuit point on the module's I-Vcurve.

Short Circuit Current (Isc), Adc

Short circuit current under reference conditions. Defines the short circuit point on the module's I-Vcurve.

Temperature Coefficients

SAM displays the temperature coefficients in %/°C and W/°C at the different points on the power curve.

Module Structure and Mounting

This option determines the coefficients that SAM uses to calculate the cell temperature in each hour ofthe simulation. The default option is User Database Values, which displays the coefficients from themeasured data at reference conditions. See Temperature Correction for details.

Physical Characteristics

Material

A description of the semiconductor technology used in the photovoltaic cells.

2-a-Si: dual-junction amorphous silicon

3-a-Si: triple-junction amorphous silicon

CdTe: cadmium telluride

CIS: copper indium diselenide

HIT-Si: amorphous silicon heterojunction

c-Si: single-crystal silicon

mc-Si: multi-crystalline silicon

Vintage

The year that module coefficients were added to the database.

The letter "E" indicates that the coefficients were estimated from a combination of publishedmanufacturer specifications and data from the outdoor testing of a similar module. Entries without an"E" are for modules whose coefficients were derived entirely from outdoor tests involving one more ormore modules of that type.

Because the tested modules (listed without an "E") may have had different average power ratings thanproduction versions of the same module, the database typically also includes an "E" entry for each ofthe tested modules that represents the average power rating specified by the manufacturer.

Module Area, m2

The total area of the module, including spaces between cells and the frame.

Number of Cells

Total number of cells in the module, equal to the product of the number of cells in series and number ofcell strings in parallel.

Number of Cells in Series

Number of cells connected in series per cell string.

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Number of Cell Strings in Parallel

Number of cell strings connected in parallel per module.

References

A link to King et al, 2004. Photovoltaic Array Performance Model. Sandia National Laboratories. SAND2004-3535 document describing the Sandia PV Array Performance Model in detail. You can find links to moredocuments in References.

CEC Performance ModelThe California Energy Commission (CEC) Performance Model uses the University of Wisconsin-MadisonSolar Energy Laboratory's five-parameter model with a database of module parameters for modules from thedatabase of eligible photovoltaic modules maintained by the California Energy Commission (CEC) for theCalifornia Solar Initiative.

The five-parameter model calculates a module's current and voltage under a range of solar resourceconditions (represented by an I-V curve) using an equivalent electrical circuit whose electrical properties canbe determined from a set of five reference parameters. These five parameters, in turn, are determined fromstandard reference condition data provided by either the module manufacturer or an independent testinglaboratory, such as the Arizona State University Photovoltaic Testing Laboratory.

Note. If you are a module manufacturer and would like to add your module to the CEC database, youshould contact the CEC directly. See http://www.gosolarcalifornia.ca.gov/equipment/add.php.

The five-parameter model is described in brief in De Soto 2003, "Improvement and Validation of a Model forPhotovoltaic Array Performance," Solar 2003 Conference Proceedings, American Solar Energy Society. Amore detailed description can be founcec cd in De Soto 2004, Improvement and Validation of a Model forPhotovoltaic Array Performance, Master of Science Thesis, University of Wisconsin-Madison. http://minds.wisconsin.edu/handle/1793/7602.

For information about the CEC list of eligible photovoltaic modules, see http://www.gosolarcalifornia.org/equipment/pvmodule.html.

Note. To make sure that you have the latest CEC module library, on the Help menu, click Check forupdates. SAM will connect to NREL servers on the Internet and, if a more recent version of the library isavailable, automatically update your current library. Updating the library only affects the standard CECmodule library, and will not affect any modules you may have added to the library.

To use the CEC photovoltaic model:

1. On the Module page, choose CEC Performance Model.

2. Choose a module from the list of available modules. SAM displays the model's characteristics andmodel coefficients.

When you select a module from the CEC database on the Module page, SAM displays module'sparameters. You can see the complete set of parameters in the Module library by using SAM'slibrary editor.

http://www.gosolarcalifornia.ca.gov/equipment/add.php

http://minds.wisconsin.edu/handle/1793/7602


http://www.gosolarcalifornia.org/equipment/pvmodule.html

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Module Characteristics at Reference Conditions

Efficiency, %

The module's rated efficiency at reference conditions. SAM displays this value for reference only. Duringsimulations, the model calculates an efficiency value for each hour, which you can see in the hourlyoutput data.


The module rated power. Equal to the product of the maximum power voltage and maximum powercurrent.

Maximum Power Voltage (Vmp), Vdc

Reference maximum power voltage at the reference conditions.

Maximum Power Current (Imp), Adc

Reference maximum power current at the reference conditions.

Open Circuit Voltage (Voc), Vdc

Reference open circuit voltage at the reference conditions.

Short Circuit Current (Isc), Adc

Reference short circuit current at the reference conditions.

Temperature Coefficients

SAM displays the temperature coefficients in %/°C and W/°C at maximum power, open circuit, andshort circuit.

The temperature coefficients are based on data collected from laboratory test results and may notmatch coefficients provided by the manufacturer on the module's data sheet.

Temperature Correction

The CEC model provides two options for modeling the effect of cell temperature on module performance.

The NOCT method determines the cell temperature based on the nominal operating cell temperature(NOCT) specified in the module parameters. In SAM 2010.11.9 and earlier versions, this was the onlyavailable temperature correction option for the CEC mode.

The mounting-specific method uses a steady state heat transfer model to calculate cell temperatures, andis described in Neises T, 2011. Development and Validation of a Model to Predict the Temperature of aPhotovoltaic Cell. Master of Science Thesis. University of Wisconsin-Madison. http://sel.me.wisc.edu/publications/theses/neises11.zip

http://sel.me.wisc.edu/publications/theses/neises11.zip


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Notes.

The temperature correction algorithms use wind speed and ambient temperature data from the weatherfile. SAM assumes that the ambient temperature and wind speed data in the weather file are mid-hourvalues and that the radiation values are end-of-hour values. SAM interpolates temperature and windspeed values by averaging the current hour value with the previous hour value.

When you specify a vertical or horizontal mounting structure option, SAM also uses wind direction datain the cell temperature calculation. Note that for the NREL TMY weather data files, the degree ofuncertainty in the wind direction data is high.

NOCT Temperature Correction

Choose this option to use the nominal operating cell temperature (NOCT) method from the original five-parameter model.

Mounting Specific Temperature Correction

Choose this option to use the steady state heat transfer model for calculating the cell temperature, andwhen you want to model different module mounting options.

Mounting Configuration

Describes how the module is installed. The mounting configuration affects the movement of air aroundthe module and the transfer of heat between the module and the building surface or ground. SAMassumes that all modules in the array use the same mounting configuration.

Rack: Modules are mounted on open racks that allow ambient air to flow freely over the front andback of the modules.

Flush: Modules are in direct contact with a roof or wall, preventing air from flowing over the back ofthe module.

Integrated: Modules form part of the roof or wall so that the back of the module is in contact with theindoor air. When you specify integrated mounting, you must also specify Temperature behind themodule.

Gap: Modules are mounted with a space between the module and building surface that allows limitedair flow over the back of each module. When you specify Gap mounting, you must also specify theMounting Structure Orientation and Gap Spacing.

Heat Transfer Dimensions

Module Dimensions: SAM calculates cell temperature using the module dimensions you specify.

Array Dimensions: SAM calculates cell temperature using the array dimensions you specify.

The Array Dimensions option assumes that modules in the array are in direct contact with each otherand results in a higher calculated cell temperatures than the Module Dimensions option. Use the ArrayDimensions option for more conservative array output estimates.

Mounting Structure Orientation

This option describes how the mounting structure interferes with airflow under the modules for the gapmounting configuration.

None: The mounting structure does not impede air flow over the back of the modules.

Vertical supporting structures: Mounting structures on module back are perpendicular to the roofridge and impede air flow parallel to the ridge.



Horizontal supporting structures: The mounting structures are parallel to the roof ridge and impede airflow perpendicular to the ridge.

Module Width

Length of side of module parallel to the ground.

Module Height

SAM calculates this value by dividing the module area from the parameter library by the module widththat you specify.

Rows of modules in array

Assuming a rectangular array, the number of rows of modules, where a row is parallel to the line definedby the Module Width variable.

Columns of modules in array

Assuming a rectangular array, the number of modules along the side perpendicular to the line definedby the module width variable.

Note. The rows and columns of modules variables are independent of the similar variables on the Arraypage and Shading page. Before running simulations, verify that the values on the different pages areconsistent.

Temperature behind the module

The indoor air temperature for the flush mounting configuration option. SAM assumes a constant indoorair temperature.

Gap spacing

The distance between the back of the modules and the roof or wall surface for the gap mountingconfiguration option.

Physical Characteristics

Material

A description of the semiconductor technology used in the photovoltaic cells.

1-a-Si: single-junction amorphous silicon

2-a-Si: dual-junction amorphous silicon

3-a-Si: triple-junction amorphous silicon

a-Si/nc: amorphous silicon - microcrystalline silicon tandem module

CdTe: cadmium telluride

CIGS: copper indium gallium sulfide

CIS: copper indium diselenide

HIT-Si: amorphous silicon heterojunction

Mono-c-Si: single-crystal silicon

Multi-c-Si: multi-crystalline silicon

Module Area

The total area of the module, including spaces between cells and the frame.

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Number of Cells

Number of cells per module.

Additional Parameters

T_noct

Nominal operating cell temperature

A_ref

Modified ideality factor at reference conditions

I_L_ref

Photocurrent at reference conditions

I_o_ref

Reverse saturation current at reference conditons

R_s

Series resistance (constant)

R_sh_ref

Shunt resistance at reference conditions

References

A link to De Soto W, 2004. Improvement and Validation of a Model for Photovoltaic Array Performance.Master of Science Thesis. University of Wisconsin-Madison. http://sel.me.wisc.edu/theses/desoto04.zip.You can find links to more documents in References.

Simple Efficiency ModuleThe flat-plate photovoltaic simple efficiency module model calculates the module's hourly DC outputassuming that the module efficiency varies with radiation incident on the module as defined by the radiationlevel and efficiency table. The model makes an adjustment for cell temperature, See Temperature Correctionfor details.

To use the simple efficiency module model:

1. On the Module page, choose Simple Efficiency Module.

2. Enter a temperature coefficient. This is the number typically reported on manufacturer specificationsheets as the maximum power coefficient. See Temperature Correction for suggested values.

3. Choose a module structure from the three available options (displayed as front material / cell / backmaterial). See Temperature Correction for details.

Module manufacturers typically include a description of the front material, and frame or backmaterial in a mechanical characteristics section of module specification sheets.

4. Enter the module's total cell area in square meters, equivalent to the product of the cell area andnumber of cells.

5. In the Radiation Level and Efficiency Table, enter an efficiency value for each of the five incidentglobal radiation reference values in increasing order. If you are defining the efficiency curve withfewer than five efficiency values, you must include five radiation values, but you can assign thesame efficiency value to more than one radiation value. For example, to represent a module with

http://sel.me.wisc.edu/theses/desoto04.zip



13.5% constant efficiency, you would assign the value 13.5 to each of the five radiation values 200,400, 600, 850, 1000.

6. Choose the radiation level that represents the reference value, often 1000 W/m2 for flat-platemodules.

SAM uses the reference value to calculate the module's rated power, displayed as the Powervariable on the Module page.

Characteristics

The module characteristics define the module's capacity, efficiency, and thermal characteristics.


The module's rated maximum DC power at the reference radiation indicated in the radiation level andefficiency table. SAM uses this value to calculate the array cost on the PV System Costs page, but notin simulation calculations. The module power is the product of the reference radiation, referenceefficiency, and area.

Temperature Coefficient (Pmp), %/C

The rated maximum-power temperature coefficient as specified in the module's technical specifications. See Temperature Correction for details.

Area, m2

The module collector area in square meters. To calculate the area for a given module power rating at agiven reference radiation level, divide the power rating by the module efficiency and radiation level. For

example, a module with a 100 W rating and 13.5% efficiency at 1000 W/m2 would requires an area of

100 W / (0.135 × 1000 W/m2) = 0.74074 m2.

Module Structure and Mounting

The module's front and back materials (front material/cell/back material) used in the temperaturecorrection algorithm described below. See Temperature Correction for details.

Radiation Level and Efficiency Table

Radiation (W/m2)

The incident global (beam and diffuse) radiation level at which the given efficiency value applies.

Efficiency (%)

The module conversion efficiency at a given incident global radiation level. SAM calculates an efficiencyvalue for each hour in the simulation using linear extrapolation to determine the value based on radiationdata from the weather file. The efficiency values represent the efficiency of conversion from incidentglobal radiation to DC electrical output.

Reference

Indicates the value to use for the reference calculations. SAM uses the reference values to calculate themodule's rated power on which module costs are based.

For each hour of the year, the flat-plate single-point efficiency model calculates the module DC output asthe product of the total incident global radiation, module area, and temperature correction factor:

Where,

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ETotalIncident

(W/m2) Total incident radiation from the Climate model.

AModule

(m2) The module area in square meters.

nModule

Module efficiency at a given incident global radiation level, calculated byextrapolating values from the Radiation Level and Efficiency Table.

FTempCorr

Temperature correction factor. See Temperature Correction for details.

Concentrating PV ModuleThe Concentrating PV Module model uses a simple algorithm that calculates the module's hourly DC outputby multiplying the hourly direct normal component of the solar radiation data from the weather file by themodule's area and efficiency as specified on the Module page, and makes a correction for the cell'stemperature.

Note. If you are modeling the Entech 22X Concentrator (c-Si), you can use the Sandia PV ArrayPerformance model instead of the Simple Efficiency model. The Entech module is modeled using a setof coefficients determined by analyzing field test measurements. To use the Entech module, choose the Sandia model option and select the Entech 22X Concentrator [1994] module from the list of availablemodules.

To use the Concentrating PV module model:

1. On the Module page, choose Concentrating PV Module.

2. Enter a temperature coefficient. This is the number typically reported on manufacturer specificationsheets as the maximum power coefficient. See Temperature Correction for suggested values.

3. Enter the module's total collector area in square meters.

4. If you have a set of temperature correction coefficients, enter values for a, b, and dT. If you do nothave a set of values, use the default values (click Default Temperature Inputs to populate thevariables with their default values). See Temperature Correction for details.

5. In the Radiation Level and Efficiency Table, enter an efficiency value for each of the five incidentglobal radiation reference values in increasing order. If you are defining the efficiency curve withfewer than five efficiency values, you must include five radiation values, but you can assign thesame efficiency value to more than one radiation value. For example, to represent a module with 20% constant efficiency, you would assign the value 20 to each of the five radiation values 200,400, 600, 850, 1000.

Concentrating PV Module Characteristics


The module's rated maximum DC power at the reference radiation value indicated in the efficiency tablebelow. SAM uses this value to calculate the array cost shown on the PV System Costs page, but notin simulation calculations. The rated module power is the product of the reference radiation, referenceefficiency and area.

Temperature Coefficient (Pmp), %/C

The rated maximum-power temperature coefficient as specified in the module's technical specifications.The default value is -0.15. See Temperature Correction for details.



Area, m2

The module collector area in square meters.

a, b, and dT

Temperature correction coefficients, a=-3.2, b=-0.09, dT=17 by default. See Temperature Correction fordetails.

Default Temperature Inputs

Resets the a, b, and dT coefficients to their default values.

Cell Temperature

The calculated cell temperature at the reference radiation level specified in the Radiation Level andEfficiency Table. See Temperature Correction for a description of the equations used for the calculation.

Radiation Level and Efficiency Table

Radiation (W/m2)

The incident beam radiation level at which the given efficiency value applies.

Efficiency (%)

The module conversion efficiency at a given incident global radiation level and cell temperature shownunder Concentrating PV Module Characteristics.

Duing simulations, SAM calculates an efficiency value for each hour in the simulation using linearextrapolation to determine the value based on radiation data from the weather file. The efficiency valuesrepresent the efficiency of conversion from incident global radiation to DC electrical output.

Reference

Indicates which value to use for the reference calculations.

The module's hourly DC output is the product of the hour's direct normal solar radiation from the weather fileas defined on the Climate page, collector area, and module efficiency from the Module page:

Where,

Pmp,CPVModule

(Wdc) The module's average DC electric output for the hour.

EDirectNormal

(W/m2) The direct normal solar radiation from weather processor.

ACollector

(m2) The collector area in square meters.

nModule

The module's conversion efficiency at the incident beam radiation for the currenthour, extrapolated from the efficiency curve defined by the table on the Modulepage.

FTempCorr

Temperature correction factor. See Temperature Correction for details.

Temperature Correction (Except CEC Model)The Sandia, Simple Efficiency, and Concentrating PV models all use the temperature correction algorithmoriginally developed for the Sandia model to calculate a temperature correction factor that accounts forefficiency losses due to heating of the module during the day when the sun is shining. The algorithm

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calculates an hourly module temperature as a function of the solar radiation, ambient temperature, and windspeed in a given hour, and a set of properties describing the thermal characteristics of the cell and module.

The CEC model provides two options for calculating cell temperature. See CEC Performance Model for moreinformation.

For more details about the algorithm, see King et al, 2004. Photovoltaic Array Performance Model. SandiaNational Laboratories. SAND2004-3535. http://photovoltaics.sandia.gov/docs/PDF/King%20SAND.pdf

The CEC model uses a different temperature correction algorithm. For a description of the CEC temperaturecorrection approach, see De Soto 2004, Improvement and Validation of a Model for Photovoltaic ArrayPerformance, Master of Science Thesis, University of Wisconsin-Madison. http://sel.me.wisc.edu/theses/desoto04.zip.

Note. The SAM temperature correction algorithms do not account for cooling strategies used in someinnovative photovoltaic systems.

Guidelines for choosing the Module Structure - Mounting (a, b, dT) parameters

The a, b, and dT parameters determine the relationship between ambient temperature and moduletemperature. See the equations below for details.

For the Sandia and Simple Efficiency models for flat-plate modules, you can choose from a set of pre-determined values of the parameters for different module mounting options, or specify your own values forthe parameters. For the Concentrating PV model, you can assign a set values to the parameters, or specifyyour own.

For most analyses involving flat-plate modules mounted on open racks, choose Use Database Values.These are the values determined empirically during testing of the module. Most of the modules in thedatabase were tested on open racks.

To see how a flat-plate module might perform under different mounting conditions, choose anappropriate option from the list. Be sure to choose an option that is consistent with the module you aremodeling. You may need to refer to the module's specification sheet for information about its structure.

For the Concentrating PV model, use the default values (click Default Temperature Inputs) unlessyou have a set of a, b, and dT values for your module. See the equations below for details.

If you understand the Sandia model well enough to generate your own temperature correctioncoefficients, choose User Defined, and type your own values for a, b, and dT. See the equations belowfor details.

Table 5. Description of the module structure and mounting options.

Module Structureand Mounting

Description

Glass/Cell/Polymer SheetOpen Rack

Solar cells are between a glass front and polymer back, and the moduleis mounted on an open rack allowing air to circulate freely around themodule.

Glass/Cell/Glass Open Rack

Solar cells are between a glass front and glass back, and the module ismounted on an open rack allowing air to circulate freely around themodule.

Polymer/Thin Film/SteelOpen Rack

Solar cells are between a transparent polymer front and steel back, andthe module is mounted on an open rack allowing air to circulate freelyaround the module.






Glass/Cell/Polymer SheetInsulated Back

Solar cells are between a glass front and polymer back, and the moduleis mounted directly to a building surface in a building-integrated PV(BIPV) application preventing air from flowing over the module back.

Glass/Cell/GlassClose Roof Mount

Solar cells are between a glass front and glass back, and the module ismounted on a rack with little clearance between the building surface andmodule back allowing little air to flow over the module back.

Temperature Correction for Sandia, Simple Efficiency, and Concentrating PVModels

SAM uses the method described below to calculate a module and cell temperature and temperaturecorrection factor for the Sandia, Simple Efficiency and Concentrating PV models. The model uses thetemperature correction factor to adjust each hour's module efficiency value: The higher the module'stemperature in a given hour, the lower the module's efficiency in that hour.

You can explore temperature effects on the array's performance in the hourly output data. The data showsthe hourly cell temperature, along with the solar radiation, wind speed, and ambient temperature.

The temperature correction equations use the following input values from the Module page:

Temperature coefficients. The Sandia model uses the four values listed in the Temperature Coefficientscolumn. The Simple Efficiency and Concentrating PV models use the single temperature coefficient ofpower value.

Temperature correction coefficients: a, b, and dT. For the Sandia and Simple Efficiency models, the

three values appear under the Module Structure - Mounting option. For the Concentrating PV model, thevalues appear below the temperature coefficient variable.

The equations use four hourly data sets from the weather file. You can see the hourly data by either viewingthe climate data from the Climate page, or viewing the hourly results data after running simulations:

Incident direct normal radiation

Incident diffuse radiation

Ambient temperature

Wind speed

Table 6. Empirically-determined coefficients from the Sandia database for each of themodule structure and mounting options available on the Module page.

Module Structureand Mounting a b

dTºC

Glass/Cell/Polymer SheetOpen Rack

-3.56 -0.0750 3

Glass/Cell/Glass Open Rack

-3.47 -0.0594 3

Polymer/Thin Film/SteelOpen Rack

-3.58 -0.113 3

Glass/Cell/Polymer SheetInsulated Back

-2.81 -0.0455 0

Glass/Cell/GlassClose Roof Mount

-2.98 -0.0471 1

Concentrating PV Module -3.2 -0.09 17

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User Defined -99 0 0

Note. The default values for the User Defined option effectively remove temperature correction from themodel so that the cell temperature is equal to the ambient temperature.

Table 7. Sample temperature coefficient values for different cell types based on aninformal survey of manufacturer module specifications.

Cell Type Maximum Power Temperature Coefficient (%/°C)

Monocrystalline Silicon -0.49

Polycrystalline Silicon -0.49

Amorphous Silicon -0.24

Amorphous Silicon Triple Junction -0.21

Copper Indium Gallium DiSelenide (CIGS) -0.45

Cadmium Telluride (CdTe) -0.25

Temperature Correction Equations

The temperature correction algorithm first calculates the module back temperature based on the incidentsolar radiation, a and b coefficients, and the ambient temperature and wind speed:

Note. SAM assumes that the ambient temperature and wind speed data in the weather file are mid-hourvalues and that the radiation values are end-of-hour values. SAM interpolates temperature and windspeed values by averaging the current hour value with the previous hour value.

Next, the cell temperature is calculated based on the module back temperature, incident radiation, and dT:

The temperature correction factor FTempCorr

is:

In general, the temperature corrected module power is the the product of the power calculated by themodule model and the temperature correction factor. Each module model (Sandia, Simple Efficiency,Concentrating PV) uses a different algorithm to calculate the module power before temperature correction:

Where,

EIncident

(W/m2) The sum of the direct normal and diffuse radiation for the current hour in theweather data. SAM determines this value based on the data in the weather file.

E0 (W/m2) The reference total incident radiation, equal to 1000 W/m2.



Tref

(°C) The reference temperature in degrees Celsius, equal to 25°C.

gamma (%/°C) The maximum power temperature coefficient from Module page.

a, b Values from the Module page. They are empirically-determined coefficientsaccounting for the effect of wind on the module temperature: a defines the module

temperature upper limit (at low wind speed and high solar radiation levels), and bdefines the rate at which module temperature decreases as wind speed increases.The values depend on the module's construction, which determines its ability toabsorb and shed heat. See the table above for typical values.

dT Value from the Module page. The temperature difference between the cell and

module back surface at the reference incident radiation of 1000 W/m2. The valuedepends on how the module is mounted in the system, which determines howmuch air comes into contact with the module back surface. See the table abovefor typical values.

vWind

(m/s) Wind speed from the weather file in meters per second.

TAmbient

(°C) Ambient temperature from weather file.

FTempCorr

Temperature correction factor

PBeforeTempCorr

Module power before temperature correction

PTempCorr

Temperature-corrected module power

3.3.6 Inverter

The Inverter page allows you to choose an inverter performance model and either choose an inverter from alist or to specify the inverter capacity and efficiency. SAM assumes that the system consists of one ormore of the same type of inverter. Specify the number of inverters in the system on the Array page.

To view the Inverter page, click Inverter on the main window's navigation menu. Note that for the Inverterpage to be available, the technology option in the Technology and Market window must be Photovoltaics -SAM Performance Models.

Contents

Overview describes the two inverter model options and how to choose one for youranalysis.

Sandia Inverter Performance Model describes the Sandia describes the model inmore detail and explains the meanings of the input variables.

Single-point Efficiency Inverter Model describes in the input variables andalgorithms for the single-point efficiency model for inverters.

Modeling Microinverters provides instructions for modeling systems withmicroinverters.

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OverviewThe Inverter page allows you to choose an inverter performance model from two options, and displays thecharacteristics of the of the inverter.

On the Inverter page, you specify the characteristics of a single inverter. To enter the number of inverters inthe system, use the input variables on the Array page. SAM calculates the AC output of the total number ofinverters in the system based on the DC output of the photovoltaic array calculated by the moduleperformance model.

The current version of SAM includes two inverter performance models, the Sandia Performance Model forGrid-Connected PV Inverters model and the single-point efficiency model. The Sandia model allows you tochoose an inverter from a list of commercially-available inverters. The single-point efficiency model allowsyou to model inverters that are not in the list.

To specify an inverter model:

1. Choose the model name from the list.

2. For the Sandia model, choose an inverter from the database of available models.

For the Single Point Efficiency Model, enter inverter characteristics.

Sandia Inverter Performance ModelThe Sandia Performance Model for Grid-Connected PV Inverters is an empirically-based performance modelthat uses parameters from a database of commercially available inverters maintained by Sandia NationalLaboratory. The parameters are based on manufacturer specifications and laboratory measurements for arange of inverter types.

The Sandia model consists of a set of equations that SAM uses to calculate the inverter's hourly AC outputbased on the DC input (equivalent to the derated output of the photovoltaic array) and a set of empirically-determined coefficients that describe the inverter's performance characteristics. The equations involve a setof coefficients that have been empirically determined based on data from manufacturer specification sheetsand either field measurements from inverters installed in operating systems, or laboratory measurementsusing the California Energy Commission (CEC) test protocol.

Because SAM does not track voltage levels in the system, it assumes that for each hour of the simulation,the inverter operates at the photovoltaic array's maximum power point voltage, given the solar resource datain the weather file for that hour.

Note. If you are an inverter manufacturer and would like to add your module to the Sandia database, youshould contact the California Energy Commission or Sandia National Laboratories directly.

The Sandia inverter model is described in King D et al, 2007. Performance Model for Grid-ConnectedPhotovoltaic Inverters. Sandia National Laboratories. SAND2007-5036. http://infoserve.sandia.gov/sand_doc/2007/075036.pdf

The CEC inverter test protocol is described in Bower W et al, 2004. Performance Test Protocol for

http://infoserve.sandia.gov/sand_doc/2007/075036.pdf




Evaluating Inverters Used in Grid-Connected Photovoltaic Systems. http://bewengineering.com/docs/index.htm

To use the Sandia inverter model:

1. On the Inverter page, choose Sandia Performance Model for Grid Connected PV Inverters.

2. Choose an inverter from the list of available inverters. SAM displays the inverter's characteristicsand model coefficients for your reference.

If you are modeling an inverter not included in the database and want to use the Sandia model, youcan try to find an inverter with similar characteristics to your inverter's specifications.

Each inverter listing shows the manufacturer name, model number and AC voltage rating, and information inbrackets about the organization responsible for generating the test data and the year the data wasgenerated. "CEC" indicates that test data was generated by the California Energy Commission.

Inverter Characteristics

When you select an inverter from the Sandia database on the Inverter page, SAM displays the inverter'sparameters for your reference. You can see the complete set of parameters in the Inverter library by usingSAM's library editor.

The Sandia inverter library includes parameters for modules that have been tested by Sandia NationalLaboratory. Manufacturers wishing to add their inverters to the Sandia database should contact SandiaNational Laboratory directly. Because the parameters involve data from field and test measurements, it isnot possible to generate parameters based only on manufacturer specifications.

The following table describes the parameters in the Sandia inverter library, which are explained in moredetail in the King 2004 reference cited above.

AC Voltage (Vac)

Rated output AC voltage from manufacturer specifications.

Power ACo (Wac)

Maximum output AC power at reference or nominal operating conditions. Available from manufacturerspecifications.

Power DCo (Wdc)

Input DC power level at which the inverter's output is equal to the maximum AC power level. Availablefrom manufacturer specifications.

PowerSo (Wdc)

DC power required for the inverter to start converting DC electricity to AC. Also called the inverter's self-consumption power. Sometimes available from manufacturer specifications, and not to be confused withthe nighttime AC power consumption.

PowerNTare (Wac)

AC power consumed by the inverter at night to operate voltage sensing circuitry when the photovoltaicarray is not generating power. Available from manufacturer specifications.

Vdcmax (Vdc)

The inverter's maximum DC input voltage.

Idcmax (Adc)

The maximum DC voltage input, typically at or near the photovoltaic array's maximum power point

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current.

Coefficient 0 (1/V)

Empirically-determined coefficient that defines the relationship between AC and DC power levels at thereference operating condition.

Coefficient 1 (1/V)

Empirically-determined coefficient that defines the value of the maximum DC power level.

Coefficient 2 (1/V)

Empirically-determined coefficient that defines the value of the self-consumption power level.

Coefficient 3 (1/V)

Empirically-determined coefficient that defines the value of Coefficient 0.

MPPT-low (Vdc)

Manufacturer-specified minimum DC operating voltage, as described in CEC test protocol (seereference above).

Vdco (Vdc)

The average of MPPT-low and MPPT-high, as described in the CEC test protocol (see reference above).

MPPT-hi (Vdc)

Manufacturer-specified maximum DC operating voltage, as described in CEC test protocol (seereference above). The test protocol specifies that the inverter's maximum DC voltage should not exceed80% of the array's maximum allowable open circuit voltage.

Single Point Efficiency Inverter ModelThe inverter single-point efficiency model calculates the inverter's AC output by multiplying the DC input(equivalent to the array's derated DC output) by a fixed DC-to-AC conversion efficiency that you specify onthe Inverter page. Unlike the Sandia inverter model, the single-point efficiency model assumes that theinverter's efficiency does not vary under different operating conditions.

To use the single-point efficiency inverter performance model:

On the Inverter page, choose Single Point Efficiency Inverter.

1. Enter the inverter's rated AC power output in Watts. This information is available on manufacturerspecifications sheets.

2. Enter the inverter's conversion efficiency as a percentage.

Note that manufacturer specifications may include both a peak efficiency, which is the inverter'smaximum efficiency; and a CEC weighted efficiency value, which is an average value that betterrepresents the efficiency over a range of operating conditions.

SAM calculates the inverter's rated DC power input using the following equation:

Power DC (Wdc) = Power AC (Wac) / Efficiency (%)

Modeling MicroinvertersThe Sandia inverter model's library includes measured coefficients for several Enphase microinverters.

A microinverter is an inverter designed to be connected to a single module. A PV system with



microinverters has a single inverter for each module, rather than the more traditional single inverterconnected to the array or to individual string of modules. Microinverters track each module’s maximumpower point independently, and minimize shading and module mismatch losses associated with stringinverters.

Notes.

SAM assumes that all modules in the array operate at their maximum power point. The derate factorassociated with module mismatch losses is an input on the Array page. When you model a system withmicroinverters, you should change the mismatch derate factor to 100% as described in the procedurebelow.

SAM's self shading model on the Shading page does not account for MPPT tracking of individualmodules and is not suitable for use with microinverters.

For an example of a PV system with microinverters, see the Sample PV Systems sample file, whichincludes a 3.22 kWdc residential system with the Enphase M210 microinverter paired with SunPower SPR-230 230 Wdc modules.

To model a system with using microinverters in SAM:

1. Choose an Enphase inverter from the Sandia Inverter list.

2. On the Module page, choose a module matched with the microinverter.

For the Enphase microinverters, choose a module with rated maximum DC power ratings (Pmp) inthe range of 200-240 Wdc, and a nominal maximum power DC voltage (Vmp) in the 30-60 Vdcrange.

Consult the Enphase datasheet for more specific details.

3. On the Array page, choose the Specify number of modules and inverters mode.

4. For Modules per String, enter 1.

5. To calculate the number of Strings in Parallel, divide the system's nameplate capacity by themodule maximum power rating (Pmp) from the Module page:

Strings in Parallel = System Nameplate Capacity (Wdc) / Module Maximum Power (Wdc)

6. For Number of Inverters, enter the value you calculated for the number of strings in parallel:

Number of Inverters = Strings in Parallel

7. Under System Derates, for Mismatch, enter 100.

Microinverters avoid system losses due to module-to-module mismatch.

8. On the PV System Costs, be sure that the inverter cost is appropriate for the microinverter.

9. On the Shading page, clear the Enable Self-Shading Calculator check box.

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3.4 Generic System

3.4.1 Generic System Overview

The generic system model is a basic representation of a conventional fossil-fuel power plant. The Generictechnology option makes it possible to compare analyses of photovoltaic and concentrating power systemsto a base case conventional fossil fuel plant in the residential, commercial and central generation markets.

This section describes the system input pages that are available when the technology option in theTechnology and Market window is Generic Fossil System.

Fossil System Costs

Fossil Plant

User Variables

3.4.2 Generic Plant

To view the Fossil Plant page, click Fossil Plant on the main window's navigation menu. Note that for thegeneric fossil system input pages to be available, the technology option in the Technology and Marketwindow must be Generic Fossil System.

The parameters for the generic fossil system are for a simple model of a fossil fuel power plant. Unlike thephotovoltaic and concentrating solar power models, the generic model is not based on an hourly simulationengine. The first year annual energy output of the generic plant is based on a simple equation using the fourSystem variables: Nameplate Capacity, Capacity Factor, Availability, and Derate.

The First Year Annual Generation is calculated using the following equation:

Where,

EFirstYearOutput

(kW) First Year Annual Generation: The generic system's total output in the first year,before annual degradation applies.

ENamePlate

(%) Nameplate Capacity: The rated capacity of the generic system.

FCapacityFactor

(%) Capacity Factor: The expected net generated electricity over one year (8760 hours)divided by the electricity that could have been generated at continuous full ratedpower over the year. Base load plants typically operate at capacity factors of about90%, with capacity factors of less than 100% due to curtailed output. Loadfollowing plants and peaking plants will have lower capacity factors.

FAvailability

(%) The Availability factor from the Annual Performance page: the number of hours peryear that the generic system is able to produce electricity divided by the number ofhours in one year (8760 hours). Availability factors of less than 100% are typicallydue to plant down time for maintenance and repair.

FDerate

(%) A derating factor applied to the generic system rated capacity to account foroutput reductions caused by inefficiencies in the system from wiring losses orother causes.

Generic System 105


SAM also applies the system degradation factor from the Annual Performance page to represent an annualreduction in system output due to equipment aging that applies to year two and subsequent years.

The heat rate determines the cost of fuel reported as Fuel O&M Expense in year one of the project cashflow, and accounted for in the output metrics reported on the Results page. SAM uses the heat rate tocalculate the first year fuel cost as follows:

Where,

CFirstYearFuel

($/yr) The total cost of fuel for year one of the project cash flow, shown as the FuelO&M Expense reported for Year 1 in the project cash flow.

CCostOfFuel

($/MMBtu) Cost of Fuel from the Fossil System Costs page.

FHeatRate

(MMBtu/MWh) The generic system's heat rate, or conversion efficiency, equivalent to thenumber of MMBtu of heat required to produce one MWh of electricity.

EFirstYearOutput

() The generic system's total electricity output in the first year.

3.5 Dish StirlingA dish-Stirling system is a type of concentrating solar power (CSP) system that consists of a parabolicdish-shaped collector, receiver and Stirling engine. The collector focuses direct normal solar radiation on thereceiver, which transfers heat to the engine's working fluid. The engine in turn drives an electric generator. Adish-Stirling power plant can consist of a single dish or a field of dishes.

SAM's dish-Stirling performance model uses the TRNSYS implementation of the energy prediction modeldescribed in the thesis Stirling Dish System Performance Prediction Model (Fraser 2008) https://www.nrel.gov/analysis/sam/pdfs/thesis_fraser08.pdf (4.1 MB).

This user guide describes the dish-Stirling system input variables and some basic calculations in SAM,and is intended to be used with the Fraser publication, which describes dish-Stirling systems and the modelalgorithms in more detail.

This section describes the system input pages that are available when the technology option in theTechnology and Market window is Concentrating Solar Power - Dish Stirling System.

For an example of a dish-Stirling system, open the sample file Sample Dish Stirling Systems: On the Filemenu, click Open Sample Template and select the file from the list. The file contains two cases. Thefirst case represents a 25 kW system consisting of a single collector-receiver-engine unit. The second caserepresents a 100 MW field of collector-receiver-engine units.

The dish-Stirling input pages are:

Dish System Costs

System Library

Solar Field

Collector

Receiver

Stirling Engine

Parasitics

https://www.nrel.gov/analysis/sam/pdfs/thesis_fraser08.pdf


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Reference Inputs

User Variables

3.5.1 System Library

To view the System Library page, click System Library on the main window's navigation menu. Note thatfor the dish input pages to be available, the technology option in the Technology and Market window mustbe Concentrating Solar Power - Dish Stirling System.

For dish-Stirling systems, a complete set of default values for the parameters on the system pages (exceptcosts) are stored in the system library. There is a set of default input values for two systems: SES andWGA-ADDS. When you choose one of these systems, SAM populates the input pages with parametersappropriate for the system. You can modify variable values on the input pages without affecting the valuesstored in the library.

Note: These systems are discussed in the thesis Stirling Dish System Performance Prediction Model(Fraser 2008) https://www.nrel.gov/analysis/sam/pdfs/thesis_fraser08.pdf (4.1 MB).

3.5.2 Solar Field

To view the Solar Field page, click Solar Field on the main window's navigation menu. Note that for thedish input pages to be available, the technology option in the Technology and Market window must beConcentrating Solar Power - Dish Stirling System.

Contents

Overview describes the Solar Field page and lists references for more detailedinformation.

Input Variable Reference describes the input variables on the solar field page.

Equations for Calculated Values describes the equations used to calculated thecalculated values on the Solar Field page.

OverviewThe parameters on the Solar Field page define the size of the solar field and the layout of the dish network.To explore the impact of these parameters on the system's costs and performance, change the value of theparameter.

The relevant sections of the thesis Stirling Dish System Performance Prediction Model (Fraser 2008)https://www.nrel.gov/analysis/sam/pdfs/thesis_fraser08.pdf (4.1 MB) are:

3.1 Parabolic Collector Model, p 63



Dish Stirling 107


Appendix A: TRNSYS Parabolic Collector Model, p 152


Field Layout

The solar field is assumed to be a rectangular field with collectors oriented north-south and east-west.

Number of Collectors North-South

Number of collectors oriented along north-south lines. Used to calculate the total number of collectors.

Number of Collectors East-West

Number of collectors oriented along east-west lines. Used to calculate the total number of collectors.

Number of Collectors

Total number of collectors in the field. Used to calculate the predicted system output, the shadingfactor, and piping distance for pumping loss calculation.

Collector Separation North-South (m)

Center-to-center distance between collectors along north-south lines. Used to calculate the solar fieldarea, shading factor, and piping distance for pumping loss calculation.

Collector Separation East-West (m)

Center-to-center distance between collectors along east-west lines. Used to calculate the solar fieldarea, shading factor, and piping distance for pumping loss calculation.

Total Solar Field Area (m2)

The total ground area occupied by the collectors. Used in area-related cost calculations.

System Properties

Wind Stow Speed (m/s)

When the wind velocity from the weather file for the current hour is greater than or equal to this value,the concentrator moves into stow position to prevent wind damage. The solar power intercepted by thereceiver is zero during this hour.

Total Solar Field Capacity (kWe)

Nominal electric output capacity of the solar field. Used in capacity-related cost calculations.

Array Shading Parameters

SAM uses the shading parameters to calculate the shading of the concentrator mirror by the dishcomponents and by neighboring dish systems. SAM's approach to modeling shading is different from theOsborn approach described in the Fraser thesis.

Ground Slope, North-South (%)

Slope of the ground in percent (rise over run) along a north-south line. A positive slope indicates that fortwo dishes aligned north-south, the dish to the south is lower than the dish to the north. Used tocalculate shading factor.

Ground Slope,East-West (%)

Slope of the ground in percent (rise over run) along a east-west line. A positive slope indicates that for

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two dishes aligned east-west, the dish to the east is lower than the dish to the west. Used to calculateshading factor.

Slot Gap Width (m)

Average width of the slot in the mirror perpendicular to the vertical support post. Used to calculateshading factor.

Slot Gap Height (m)

Average height of the slot in the mirror parallel to the vertical support post. Used to calculate shadingfactor.

Equations for Calculated Values


The total number of collectors is calculated based on the numbers of north-south and east-west orientedcollectors.

Where,

NColl Number of Collectors

NColl,N-S Number of Collectors North-South

NColl,E-W Number of Collectors East-West

Total Solar Field Area

The total solar field area is the product of the north-south and east west dish collector separation distancesand the number of collectors.

Where,

ASF

(m2) Total Solar Field Area

dCollSep,N-S

(m)Collector Separation North-South

dCollSep,E-W

(m)Collector Separation East-West


Total Capacity

The total solar field capacity is the product of the number of collectors and the engine nameplate capacityon the Stirling Engine page.

Where,

Dish Stirling 109


PSF

(W) Total Capacity

PEngine

(W) Singe Unit Nameplate Capacity from the Stirling Engine page.


3.5.3 Collector

To view the Collector page, click Collector on the main window's navigation menu. Note that for the dishinput pages to be available, the technology option in the Technology and Market window must beConcentrating Solar Power - Dish Stirling System

Contents

Overview describes the Collector page and lists references for more detailedinformation.

Input Variable Reference describes the input variables on the Collector page.

Default Parameter Values shows a table of default values for different systems.

OverviewThe collector consists of parabolic mirrors, a support structure, and two-axis tracking system. The mirrorsfocus direct normal solar radiation on the aperture of the receiver. The receiver aperture size is typicallyoptimized to maximize the quantity of reflected solar radiation that enters the receiver and minimizeconvection and radiation losses out of the aperture.


2.1 Parabolic Concentrator, p 7

3.1 Parabolic Collector Model, p 63

Appendix A: TRNSYS Parabolic Collector Model, p 150

Appendix A: TRNSYS Parasitic Power Model, p 158

Input Variable ReferenceThe parameters on the Collector page are used to calculate the power output of the collector. Theparameters are for a single dish collector, and are assumed to apply to each dish in the solar field.

Mirror Parameters

Projected Mirror Area (m2)

Area of one concentrator's mirror projected on the aperture plane. Used to calculated the solar powerintercepted by the receiver, and the shading factor.


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Total Mirror Area (m2)

Area of mirrored parabolic surface. Used to calculate collector diameter, which is used in the rim anglecalculation and in the shading factor calculation.

Mirror Reflectance

The mirror reflectance input is the solar weighted specular reflectance. The solar-weighted specularreflectance is the fraction of incident solar radiation reflected into a given solid angle about the specularreflection direction. The appropriate choice for the solid angle is that subtended by the receiver asviewed from the point on the mirror surface from which the ray is being reflected. For parabolic troughs,typical values for solar mirrors are 0.923 (4-mm glass), 0.945 (1-mm or laminated glass), 0..906(silvered polymer), 0.836 (enhanced anodized aluminum), and 0.957 (silvered front surface).

Performance

Insolation Cut In (W/m2)

Direct normal radiation value above which the cooling system fan operates. Used to calculated parasiticlosses.

Default Parameter Values

Table 8. Collector default parameter values.

Variable SES WGA SBP SAIC

Projected Mirror Area 87.7 41.2 56.7 113.5

Total Mirror Area 91.0 42.9 60 117.2

Insolation Cut In 200 275 250 375

Wind Stow Speed 16 16 16 16

Receiver Aperture Diameter for Reference Intercept Factor 0.184 0.14 0.15 0.38

Reference Intercept Factor 0.995 0.998 0.93 0.90

Reference Focal Length of Mirror 7.45 5.45 4.5 12.0

3.5.4 Receiver

To view the Receiver page, click Receiver on the main window's navigation menu. Note that for the dishinput pages to be available, the technology option in the Technology and Market window must beConcentrating Solar Power - Dish Stirling System.

Contents

Overview describes the Receiver page and lists references for more detailedinformation.

Input Variable Reference describes the input variables on the Receiver page.

Dish Stirling 111



OverviewThe receiver absorbs thermal energy from the parabolic concentrator and transfers the energy to the workingfluid of the Stirling engine. The receiver consists of an aperture and absorber. The receiver aperture islocated at the parabolic concentrator's focal point. The current version of SAM models one receiver type,direct illumination receivers, in which solar radiation is directly absorbed by absorber tubes containing theworking fluid. Direct illumination receivers are the receiver type most commonly used for dish-Stirlingsystems.


2.2 Receiver, p 14

6.1 Modifying the Receiver Aperture Diameter, p 133

6.2 Receiver Cover versus no Cover, p 134

Appendix A: TRNSYS Receiver Model, p 153

SAM uses the receiver parameters to calculate thermal losses from the receiver, which typically account forover 50% of the system's total losses. Other system losses include collector losses due to mirrorreflectivity, receiver intercept losses, and Stirling engine losses. Receiver thermal losses are due toconduction, convection, and radiation:

Conductive losses through the receiver housing.

Natural convection from the cavity in the absence of wind.

Forced convection in the presence of wind.

Emission losses due to thermal radiation emitted from the receiver aperture.

Radiation losses reflected off of the receiver cavity surfaces and out of the receiver through the aperture.


Aperture

Receiver Aperture Diameter (m)

Diameter of the opening in the receiver that allows solar radiation to reach the absorber, and radiationand convection losses to escape the receiver cavity. Typical values range from 0.14 m to 0.20 m.

Insulation

Thickness (m)

Thickness of the receiver housing insulation. Typically about 75 mm. Used to calculate conductionlosses.

Thermal Conductivity (W/m-K)

Thermal conductivity of the receiver cavity wall at 550 degrees Celsius. For high-temperature ceramicfiber, the value is 0.061 W/m-K. Used to calculate conduction losses.


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Absorber

The absorber is a component of the receiver that absorbs solar radiation and transfers thermal energy to theStirling engine.

Absorber Absorptance

The ratio of energy absorbed by the receiver absorber to the solar radiation reaching the absorber. Usedto calculate radiation losses.

Absorber Surface Area (m2)

Area of the absorber surface. Used to calculate the internal cavity area.

Cavity

The cavity parameters determine the cavity's geometry. The internal cavity area is the sum of the cavity wallsurface area and absorber area and is used to calculate radiation, conduction and convection losses.

Cavity Absorptance

The ratio of energy absorbed by the cavity wall to radiation reaching it. Used to calculated reflectedradiation losses.

Cavity Surface Area (m2)

Area of the cavity wall surface. Used to calculate the internal cavity area.

Internal diameter of the Cavity Perp. to Aperture (m)

Average diameter of the cavity perpendicular to the receiver aperture. Used to calculate the internalcavity area.

Internal Cavity Pressure with Aperture covered (kPa)

Applies only to receivers with a cover. Used to calculate convection losses.

Internal Depth of the Cavity Perpendicular to the Aperture (m)

Equivalent to the cavity's characteristic length, which is used to calculate convection losses.


Table 9. Receiver default parameter values.


Absorber Absorptance 0.90 0.90 0.90 0.90

Absorber Surface Area 0.6 0.15 0.15 0.8

Cavity Wall Absorptance 0.6 0.6 0.6 0.6

Cavity Wall Surface Area 0.6 0.15 0.15 0.8

Internal Diameter of the Cavity Perpendicular to the ReceiverAperture

0.46 0.35 0.37 0.5

Internal Depth of the Cavity Perpendicular to the Aperture 0.46 0.35 0.37 0.5

Receiver Insulation Thickness 0.075 0.075 0.075 0.075

Insulation Thermal Conductivity 0.06 0.06 0.06 0.06

Delta Temp. for DIR Receiver 90 70 70 90

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3.5.5 Stirling Engine

To view the Stirling Engine page, click Stirling Engine on the main window's navigation menu. Note that forthe trough input pages to be available, the technology option in the Technology and Market window must beConcentrating Solar Power - Dish Stirling System.

Contents

Overview describes the Stirling Engine page and lists references for more detailedinformation.

Input Variable Reference describes the input variables on the Stirling Engine page.


OverviewThe Stirling engine converts heat from the receiver's absorber to mechanical power that drives an electricgenerator.


2.3 Stirling Engine Design, p 29

2.4 Stirling Engine Analysis Methods, p 40

3.3 Stirling Engine/System Models, p 82

6 TRNSYS Model Performance Predictions, p 132

Appendix A: TRNSYS Stirling Engine and Generator Model, p 156

The Stirling engine model is based on the Beale curve-fit equation with temperature correction described inFraser (2008). The model calculates the average hourly engine power output in Watts as a function of theBeale curve-fit equation, pressure curve-fit equation, the engine displacement and operating speed, andexpansion space (heater head) temperatures. The Beale curve-fit equation calculates the engine's grossoutput power as a function of the input power calculated by the collector and receiver models. SAMdetermines the compression space temperature from the ambient temperatures in the weather data file.


Estimated Generation

Single Unit Nameplate Capacity (kW)

The nominal electrical power output of the engine-generator set for a single dish-Stirling unit. Used forcapacity-related cost calculations.

Engine Parameters

Heater Head Set Temperature (K)

Expansion space temperature set point.


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Heater Head Lowest Temperature

The expansion space temperature in an engine with multiple cylinders of the heater head with thelowest temperature. The heater head temperature is equivalent to the expansion space temperature.

Engine Operating Speed (rpm)

The rotational speed of the engine drive shaft. Used to calculate the engine output power.

Displaced Engine Volume (m3)

The volume displaced by the pistons. Used to calculate the engine output power.

Beale Curve Fit Coefficients

The Beale numbers are a set of coefficients for the Beale curve-fit equation that describes the engine'spower output as a function of its input power and the engine pressure.

Pressure Curve Fit Coefficients

The pressure curve-fit equation expresses the engine pressure as a function of engine input power for aconstant volume system.


Table 10. Stirling engine default parameter values.The following parameter values are based on values developed for the model. The SBP and SAIC enginesare not included in the SAM standard library and require a different set of equations (see Fraser 35).


Heater Head SetTemperature

993 903 903 993

Heater Head LowestTemperature

973 903 903 973

Engine OperatingSpeed

1800 1800 1800 2200

Displaced EngineVolume

3.80 × 10-4

1.60 × 10-4

1.60 × 10-4

4.80 × 10-4

Beale ConstantCoefficient

4.247 × 10-2

8.50686 × 10-2

-1,82451 × 10-3

-1.6 × 10-2

Beale First-orderCoefficient

1.682 × 10-5

1.94116 × 10-5

2.60289 × 10-5

1.5 × 10-5

Beale Second-orderCoefficient

-5.105 × 10-10

-3.18449 × 10-10

-4.68164 × 10-10

-3.50 × 10-10

Beale Third-orderCoefficient

7.07260 × 10-15 0 0 3.85 × 10

-15

Beale Fourth-orderCoefficient

-3.586 × 10-20 0 0 -1.6 × 10

-20

Pressure ConstantCoefficient

6.58769 × 10-1

-7.36342 × 10-1

-2.00284 × 10-2

3.47944 × 10-5

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Pressure First-orderCoefficient

2.34963 × 10-4

3.6416 × 10-4

3.52522 × 10-4

5.26329 × 10-9

3.5.6 Parasitics

To view the Parasitics Costs page, click Parasitics on the main window's navigation menu. Note that for thedish input pages to be available, the technology option in the Technology and Market window must beConcentrating Solar Power - Dish Stirling System.

Contents

Overview describes the Parasitics page and lists references for more detailedinformation.

Input Variable Reference describes the input variables on the Parasitics page.

OverviewThe input variables on the Parasitics page are used to calculate the compression space temperature andthe electrical power consumption of pumps, cooling fans, and tracking controls.


2.5 Cooling System, p 55

3.4 Cooling System Analysis for Total System Optimization, p 92

Appendix A: TRNSYS Parasitic Power Model, p 158


Parasitic Parameters

Control System Parasitic Power, Avg. (W)

Average power required by the tracking control system.

Cooling System Pump Speed (rpm)

Cooling fluid pump operating speed. Used to calculated parasitic losses due to cooling fluid pumping.

Cooling System Fan Speed 1 (rpm)

Fan operating speed when the cooling fluid temperature is less than the fan speed 2 cut-in temperaturebelow.


Fan operating speed when the cooling fluid temperature is greater than the fan speed 2 cut-in and lessthan fan speed 3 cut-in temperature below.


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Fan operating speed when the cooling fluid temperature is greater than fan speed 3 cut-in temperaturebelow.

Cooling Fluid Temp. for Fan Speed 2 Cut-In (°C)

Cooling fluid temperature set point. Used to determine fan operating speeds.

Cooling Fluid Temp. for Fan Speed 3 Cut-In (°C)

Cooling fluid temperature set point. Used to determine fan operating speeds.

Cooling Fluid Type

Fluid used in the cooling system. Options are water, 50% ethylene glycol (EG), 25% ethylene glycol,40% propylene glycol (PG), and 40% propylene glycol. Percentages are by volume.

Cooler Effectiveness

Used to calculate working fluid temperatures in the cooling system as part of the compression spacetemperature calculation.

Radiator Effectiveness

Used to calculate cooling fluid temperature at the cooling system outlet as part of the compressionspace temperature calculation.

3.5.7 Reference Inputs

To view the Reference Inputs page, click Reference Inputs on the main window's navigation menu. Notethat for the dish input pages to be available, the technology option in the Technology and Market windowmust be Concentrating Solar Power - Dish Stirling System.

Contents

Overview describes the Reference Inputs page and lists references for more detailedinformation.

Input Variable Reference describes the input variables on the Reference Inputspage.

Parasitic Variable Reference Conditions lists the reference conditions for differentsystems.

OverviewSAM uses the reference condition parameters in an iterative process to calculate the total collector error fora given set of values for the aperture diameter, focal length, and collector diameter. Once the collector erroris calculated, that value can be used to calculate a new intercept factor for different aperture diameters (SeeFraser, p 150-151).

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Collector Reference Condition Inputs

Intercept Factor

Fraction of energy reflected from the parabolic mirror that enters the receiver aperture. The interceptfactor can be increased by increasing the concentration ratio or by increasing the size of the aperture.Intercept factors typically range between 0.94 and 0.99.

Focal Length of Mirror (m)

Parabolic mirror focal length.

Parasitic Variable Reference ConditionsThe reference condition parameters given in the table below and as user inputs in SAM are used in thepump law calculations that are part of the parasitic loss equations.


Pump ParasiticPower

150 100 175 300

Pump Speed (rpm) 1800 1800 1800 1800

Cooling Fluid Type 50% EG 50% EG water 50% EG

Cooling FluidTemperature (K)

288 288 288 288

Cooling FluidVolumetric FlowRate (gal/min)

9 7.5 7.5 12

Cooling System FanTest Power (W)

1000 410 510 2500

Cooling System FanTest Speed (rpm)

890 890 890 850

Fan Air Density (kg/m3)

1.2 1.2 1.2 1.2

Fan Volumetric FlowRate (CFM)

6000 4000 4500 10000

3.6 Parabolic Trough EmpiricalA parabolic trough system is a type of concentrating solar power (CSP) system that collects direct normalsolar radiation and converts it to thermal energy that runs a power block to generate electricity. Thecomponents of a parabolic trough system are the solar field, power block, and in some cases, thermalenergy storage and fossil backup systems. The solar field collects heat from the sun and consists ofparabolic, trough-shaped solar collectors that focus direct normal solar radiation onto tubular receivers.

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Each collector assembly consists of mirrors and a structure that supports the mirrors and receivers, allowsit to track the sun on one axis, and can withstand wind-induced forces. Each receiver consists of a metaltube with a solar radiation absorbing surface in a vacuum inside a coated glass tube. A heat transfer fluid(HTF) transports heat from the solar field to the power block (also called power cycle) and othercomponents of the system. The power block is based on conventional power cycle technology, using aturbine to convert thermal energy from the solar field to electric energy. The optional fossil-fuel backupsystem delivers supplemental heat to the HTF during times when there is insufficient solar energy to drivethe power block at its rated capacity.

The empirical parabolic trough model uses a set of equations based on empirical analysis of data collectedfrom installed systems (the SEGS projects in the southwestern United States) to represent the performanceof parabolic trough components. The model is based on Excelergy, a model initially developed for inernaluse at at the National Renewable Energy Laboratory. For information about the physical parabolic troughmodel, see Parabolic Trough Physical.

Note. Many of the input variables in the parabolic trough model are interrelated and should be changedtogether. For example, the storage capacity, which is expressed in hours of thermal storage, should notbe changed without changing the tank heat loss value, which depends on the size of the storagesystem. Some of these relationships are described in this documentation, but not all. If you havequestions about parabolic trough input variables, please contact SAM Support at [email protected].

To use the parabolic trough empirical model:

Open the sample parabolic trough sample file: On the File menu, click Open Sample Templateand choose Sample Parabolic Trough Systems from the list, or

In the Technology and Market window, choose Concentrating Solar Power, Empirical TroughSystem.

The sample file contains four cases. The first three cases use the physical trough model, and the fourthcase uses the empirical model. The fourth case represents a 100 MW baseline system with a mediumtemperature heat-transfer fluid and an indirect 2-tank thermal energy storage system.

The parabolic trough input pages for this option described in this section are:

Trough System Costs

Solar Field

SCA / HCE (solar collector assembly / heat collection element)

Power Block

Thermal Storage

Parasitics

User Variables

3.6.1 Solar Field

To view the Solar Field page, click Solar Field on the main window's navigation menu. Note that for theempirical trough input pages to be available, the technology option in the Technology and Market windowmust be Concentrating Solar Power - Empirical Trough System.



Parabolic Trough Empirical 119


Contents

Overview describes the Solar Field page and where to find more information aboutthe solar field model.

Input Variable Reference describes the input variables and options on the SolarField page.

Choosing the Field Layout Mode explains the two field layout options: Solarmultiple and solar field area.

About the Solar Multiple Reference Conditions explains how to choose anappropriate reference direct normal radiation value for a given location.

About the Heat Transfer Fluid Properties explains the role of the heat transfer fluidin the system and describes the properties of the HTFs available in the defaultlibrary.

Equations for Calculated Values describes the equations used to calculated thecalculated values on the Solar Field page.

OverviewThe Solar Field page displays variables and options that describe the size and properties of the solar field,properties of the heat transfer fluid, reference design specifications of the solar field, and collectororientation.

For a more detailed description of the model, please download the CSP trough reference manual from theSAM website's support page: https://www.nrel.gov/analysis/sam/support.html.


Field Layout

Option 1: Solar Multiple and Option 2: Solar Field Area

For option 1, (solar multiple mode), SAM calculates the solar field area and displays it in Solar FieldArea (calc). For option 2 (solar field area mode), SAM calculates the solar multiple and displays it inSolar Multiple (calc). Note that SAM does not use the value that appears dimmed for the inactiveoption.

Distance Between SCAs in Row (m)

The end-to-end distance in meters between SCAs (solar collection elements, or collectors) in a singlerow, assuming that SCAs are laid out uniformly in all rows of the solar field. SAM uses this value tocalculate the end loss. This value is not part of the SCA library on the SCA / HCE page, and should beverified manually to ensure that it is appropriate for the SCA type that appears on the SCA / HCE page.

Row spacing, center-to-center (m)

The centerline-to-centerline distance in meters between rows of SCAs, assuming that rows are laid outuniformly throughout the solar field. SAM uses this value to calculate the row-to-row shadowing lossfactor. This value is not part of the SCA library, and should be verified manually to ensure that it is

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appropriate for the SCA type that appears on the SCA / HCE page.

Number of SCAs per Row

The number of SCAs in each row, assuming that each row in the solar field has the same number ofSCAs. SAM uses this value in the SCA end loss calculation.

Deploy Angle (degrees)

The SCA angle during the hour of deployment. A deploy angle of zero for a northern latitude is verticalfacing due east. SAM uses this value along with sun angle values to determine whether the current hourof simulation is the hour of deployment, which is the hour before the first hour of operation in themorning. SAM assumes that this angle applies to all SCAs in the solar field.

Stow Angle (degrees)

The SCA angle during the hour of stow. A stow angle of zero for a northern latitude is vertical facingeast, and 180 degrees is vertical facing west. SAM uses this value along with the sun angle values todetermine whether the current hour of simulation is the hour of stow, which is the hour after the finalhour of operation in the evening.

Heat Transfer Fluid

Solar Field HTF Type

Name of the heat transfer fluid type. The Minimum HTF Temp value depends on the HTF type. Theavailable fluid types are limited to those described in the HTF Properties section.

Property table for user-defined HTF

When the Solar Field HTF type is "User-defined," click Edit to enter properties of a custom HTF.

Solar Field Inlet Temp (ºC)

Design temperature of the solar field inlet in degrees Celsius used to calculate design solar fieldaverage temperature, and design HTF enthalpy at the solar field inlet. SAM also limits the solar fieldinlet temperature to this value during operation and solar field warm up, and uses this value to calculatethe actual inlet temperature when the solar field energy is insufficient for warm-up.

Solar Field Outlet Temp (ºC)

Design temperature of the solar field outlet in degrees Celsius, used to calculate design solar fieldaverage temperature. It is also used to calculate the design HTF enthalpy at the solar field outlet,which SAM uses to determine whether solar field is operating or warming up. SAM also uses this valueto calculate the actual inlet temperature when the solar field energy is insufficient for warm-up.

Solar Field Initial Temp (ºC)

Initial solar field inlet temperature. The solar field inlet temperature is set to this value for hour one of thesimulation.

Piping Heat Losses @ Design Temp (W/m2)

Solar field piping heat loss in Watts per square meter of solar field area when the difference between theaverage solar field temperature and ambient temperature is 316.5ºC. Used in solar field heat losscalculation. See Equations for Calculated Values for details.

Piping Heat Loss Coeff (1-3)

These three values are used with the solar field piping heat loss at design temperature to calculate solarfield piping heat loss. See Equations for Calculated Values for details.



Solar Field Piping Heat Losses (W/m2)

Design solar field piping heat losses. This value is used only in the solar field size equations. Thisdesign value different from the hourly solar field pipe heat losses calculated during simulation. SeeEquations for Calculated Values for details.

Minimum HTF Temp (ºC)

Minimum heat transfer fluid temperature in degrees Celsius. SAM automatically populates the valuebased on the properties of the solar field HTF type, i.e., changing the HTF type changes the minimumHTF temperature. The value determines when freeze protection energy is required, is used to calculateHTF enthalpies for the freeze protection energy calculation, and is the lower limit of the average solarfield temperature.

HTF Gallons Per Area (gal/m2)

Volume at 25°C of HTF per square meter of solar field area, used to calculate the total mass of HTF inthe solar field, which is used to calculate solar field temperatures and energies during hourlysimulations. The volume includes fluid in the entire system including the power block and storagesystem if applicable. Example values are: SEGS VI: 115,000 gal VP-1 for a 188,000 m2 solar field is0.612 gal/m2, SEGS VIII 340,500 gal VP-1 and 464,340 m2 solar field is 0.733 ga/m2.

Solar Multiple (Design Point)

Note. The ambient temperature, direct normal radiation, and wind velocity reference variables differ fromthe hourly weather data that SAM uses for system output calculations. SAM uses the reference ambientcondition variables to size the solar field. Hourly data from the weather file shown on the Climate pagedetermine the solar resource at the site.

Solar Multiple (calc)

The solar field area expressed as a multiple of the exact area (see "Exact Area" below). SAM uses thecalculated solar multiple value to calculate the design solar field thermal energy and the maximumthermal energy storage charge rate.

Solar Field Area (calc) (m2)

The solar field area expressed in square meters. SAM uses this value in the delivered thermal energycalculations. The solar field area is the total collection aperture area, which is less than the mirror area.The solar field area does not include space between collectors or the land required by the power block.

Ambient Temp (ºC)

Reference ambient temperature in degrees Celsius. Used to calculate the design solar field pipe heatlosses.

Direct Normal Radiation (W/m2)

Reference direct normal radiation in Watts per square meter. Used to calculate the solar field area thatwould be required at this insolation level to generate enough thermal energy to drive the power block atthe design turbine thermal input level. SAM also uses this value to calculate the design HCE heatlosses displayed on the SCA / HCE page. The appropriate value depends on the system location. Forexample, 950 W/m2 is an appropriate value for the Mohave Desert and typical locations underconsideration for development in the U.S., and 800 W/m2 is appropriate for southern Spain. See belowfor more information.

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Wind Velocity (m/s)

Reference wind velocity in meters per second. SAM uses this value to calculate the design HCE heatlosses displayed on the SCA / HCE page.

Exact Area (m2)

The solar field area required to deliver sufficient solar energy to drive the power block at the designturbine gross output level under reference weather conditions. It is equivalent to a solar multiple of one,and used to calculate the solar field area when the Layout mode is Solar Multiple.

Exact Num. SCAs

The exact area divided by the SCA aperture area. SAM uses the nearest integer greater than or equalto this value in the solar field size equations to calculate value of the Solar Field Area (calc) variabledescribed above. The exact number of SCAs represents the number of SCAs in a solar field for a solarmultiple of one.

Aperture Area per SCA (m2)

SCA aperture area variable from the SCA / HCE page. SAM uses this value in the solar field sizeequations to calculate the value of the Solar Field Area (calc) variable described above.

HCE Thermal Losses (W/m2)

Design HCE thermal losses based on the heat loss parameters from the SCA / HCE page. SAM usesthis value only in the solar field size equations. This design value is different from the hourly HCEthermal losses calculated during simulation.

Optical Efficiency

Weighted optical efficiency variable from the SCA / HCE page. SAM uses this design value only in thesolar field size equations. This design value is different from SCA efficiency factor calculated duringsimulations.

Design Turbine Thermal Input (MWt)

Design turbine thermal input variable from the Power Block page. Used to calculate the exact areadescribed above.

Orientation

Collector Tilt (degrees)

The collector angle from horizontal, where zero degrees is horizontal. A positive value tilts up the end ofthe array closest to the equator (the array's south end in the northern hemisphere), a negative value tiltsdown the southern end. Used to calculate the solar incidence angle and SCA tracking angle. SAMassumes that the SCAs are fixed at the tilt angle.

Collector Azimuth (degrees)

The azimuth angle of the collector, where zero degrees is pointing toward the equator, equivalent to anorth-south axis. Used to calculate the solar incidence angle and the SCA tracking angle. SAMcalculates the SCAs' tracking angle for each hour, assuming that the SCAs are oriented 90 degreeseast of the azimuth angle in the morning and track the daily movement of the sun from east to west.

Choosing the Field Layout ModeSAM provides two options for defining the size of the solar field: Solar Multiple (Option 1) and Solar FieldArea (Option 2).



Note. The field layout mode options are similar to the options for the physical trough model. For detailsabout choosing between the two options, and optimizing the solar multiple for systems with and withoutstorage, see Sizing the Solar Field for the physical trough model.

In Solar Multiple mode, SAM calculates the solar field area based on the solar multiple, the power block'srated thermal input capacity, reference weather conditions, and design heat loss parameters. For a solarmultiple of one, SAM calculates the solar field area that, under reference weather conditions and accountingfor heat losses from the field, generates a thermal energy amount equal to the design turbine thermal inputvalue from the Power Block page.

In Solar Field Area mode, SAM uses the user-defined solar field area, and calculates the equivalent solarmultiple.

The solar multiple mode is useful for determining the optimal solar field area for a given location. By varyingthe solar multiple, you can find the value that minimizes the levelized cost of energy for a given power blockcapacity. The levelized cost of energy metric captures the tradeoff between the benefit of higher annualelectricity output and the cost of increased capital expenditures associated with increasing the solar fieldarea.

Using the Solar Multiple mode is best for analyses involving a known or fixed power block capacity becauseSAM automatically calculates the solar field area based on the power block capacity. The Solar Field Areamode is best for analyses involving a known or fixed solar field area, but requires that the power blockcapacity be manually adjusted to match the solar field output.

The third case in the Sample Parabolic Trough System file "Phys Trough - Parameterized Storage,"illustrates this approach using the physical trough model. The case compares the levelized cost of energyfor systems with different solar multiple values with and without storage. You can use the same approachwith the empirical model. For a description of the approach, see Sizing the Solar Field.

About the Solar Multiple Reference ConditionsThe three reference condition variables, ambient temperature, direct normal radiation, and wind velocity, arethe ambient conditions at which the solar field thermal output is equal to the power block's design thermalinput multiplied by the solar multiple. In other words, under reference conditions, the system operates at thesystem's design capacity. Note that these reference condition variables are system design parameters, anddo not describe the weather conditions at the project site. Weather conditions are determined by the data inthe weather file shown on the Climate page.

The reference ambient temperature and reference wind velocity variables are used to calculate the designheat losses, and do not have a significant effect on the solar field sizing calculations. Reasonable values forthose two variables are the average annual measured ambient temperature and wind velocity at the projectlocation.

The reference direct normal radiation value, on the other hand, does have a significant impact on the solar

field size calculations. For example, a system with reference conditions of 25°C, 950 W/m2, and 5 m/s(ambient temperature, direct normal radiation, and wind speed, respectively), a solar multiple of 2, and a

100 MWe power block, requires a solar field area of 871,940 m2. The same system with reference direct

normal radiation of 800 W/m2 requires a solar field area of 1,055,350 m2. Note that with a solar multiple of 2,both systems would produce two times the thermal energy required to drive the power block at its ratedcapacity during hours in which the direct normal radiation, temperature, and wind speed from the weatherfile are equal to the reference conditions.

For systems in the Mohave Desert of the United States, a value of 950 W/m2 is reasonable, and for

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southern Spain, a value of 800 W/m2 is reasonable.

Four factors affect the choice of a reference direct normal radiation value for a given system:

Location defined on the Climate page.

Storage capacity defined on the Thermal Storage page.

Maximum storage charge rate defined on the Thermal Storage page.

Variability of the solar resource over the year, determined by the weather data as defined on the Climatepage.

Using too low of a reference direct normal radiation value results in excessive dumped energy: The actualdirect normal radiation from the weather data is frequently greater than the reference value so that the solarfield sized for the low reference radiation value often produces more energy than required by the powerblock, and excess thermal energy is either dumped or put into storage. On the other hand, using too high ofa reference direct normal radiation value results in an undersized solar field that produces sufficient thermalenergy to drive the power block at its design point only during the few hours when the actual direct normalradiation is at or greater than the reference value.

Method 1 for Choosing the Reference Direct Normal Radiation Value

The first approach to choosing a value for the reference direct normal radiation value is to set the value tothe maximum value of the incident direct normal radiation (Q_nipCosTh) reported in the hourly simulationresults.

To display the cumulative distribution function for the direct normal radiation data:

1. On the Solar Field page, choose the collector tilt and azimuth values you plan to use for youranalysis.

2. Click Run. The values you use for the other inputs are not important at this stage, so you can usedefault or preliminary values.

3. On the Results menu, click View Hourly Time Series.

4. In the data viewer (DView), click the CDF tab and choose Q_nipCosTh in the variable list to displaythe "CDF of Q_nipCosTh" graph.

You can either read the maximum value off of the graph as the right-most value on the x-axis, orright-click the graph to export values to a text file and read the maximum value there.

You can also find the maximum Q_nipCosTh in the simulation output file (.out) as described inViewing Hourly Output Data. Use this option if you are running SAM on a Mac.

Method 2 for Choosing the Reference Direct Normal Radiation Value

Another approach to determine the reference direct normal radiation value for a given location is to find thevalue that minimizes the amount of thermal energy that the system dumps.

To minimize dumped thermal energy:

1. Use Option 1 (Solar Multiple) for the field layout option and set the value to one.

2. Enter an arbitrary value for the reference direct normal radiation, such as 950 W/m2.

3. Run a simulation.

4. In the hourly simulation results, examine the amount of dumped thermal energy QDump. You canview the variable's hourly values either in the time series data viewer or in Excel.

5. If the amount of dumped thermal energy is excessive, try a lower value for the reference direct



normal radiation value and repeat the above steps.

To determine the reference solar radiation value based on dumped thermal energy:

1. On the Solar Field page use the Solar Multiple option under Layout and set its value to one.

2. Enter an arbitrary value for the reference solar radiation value.

3. Run a simulation.

4. In the hourly simulation results, examine the amount of dumped thermal energy QDump. You canview the variable's hourly values by clicking either Spreadsheet or Time Series Graph.

5. If the amount of dumped thermal energy is excessive, try a lower value for the reference solarradiation and repeat the above steps.

About the Heat Transfer Fluid PropertiesThe solar field heat transfer fluid (HTF) absorbs heat as it circulates through the heat collection elements inthe solar field and transports the heat to the power block where it is used to run a turbine. Several types ofheat transfer fluid are used for trough systems, including hydrocarbon (mineral) oils, synthetic oils, siliconeoils and nitrate salts.

When you choose a heat transfer fluid, SAM populates the minimum HTF temperature variable with that oil'sminimum operating temperature value. SAM will not allow the system to operate at a temperature below theminimum HTF temperature. Electric heaters in the system maintain the fluid temperature. SAM accountsfor the electric power requirement for heating on the Parasitics page.

The remaining heat transfer fluid parameters describe characteristics of the solar field that affect theperformance of the heat transfer fluid. The two area-related parameters refer to square meters of solar fieldarea. If you are unsure of what values to use for these parameters, refer to the Solar Field page for the casein Sample Parabolic Trough Systems.zsam.

Note. Solar field outlet temperature and solar field area data for U.S. parabolic trough power plants areavailable on the Troughnet website at http://www.nrel.gov/csp/troughnet/power_plant_data.html.

Table 11. Heat transfer fluids.

Name TypeMin HTF Temp

ºC

Max OperatingTemp

ºC Freeze Point Comments

Solar Salt Salt 260 600 220

Caloria mineralhydrocarbon oil

-20 300 -40 used in first Luztrough plant,SEGS I

Hitec XL Nitrate salt 150 500 120 New generation

Therminol VP-1 mixture ofbiphenyl anddiphenyl oxide

50 400 12 Standard forcurrentgeneration oilHTF systems

Hitec Nitrate salt 175 500 140 For high-temperaturesystems

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Dowtherm Q Synthetic oil -30 330 -50 New generation

Dowtherm RP Synthetic oil -20 350 -40 New generation

To define a custom heat transfer fluid:

1. In the Field HTF fluid list, click User-defined.

2. In the Edit Material Properties table, change Number of data points to 2 or higher. The numbershould equal the number of temperature values for which you have data.

3. Type values for each property in the table.

You can also import data from a text file of comma-separated values. Each row in the file shouldcontain properties separated by commas, in the same the order that they appear in the EditMaterial Properties window. Do not include a header row in the file.

Keep the following in mind when you define a custom heat transfer fluid:

Each row in the materials property fluid table must be for a set of properties at a specific temperature.No two rows should have the same temperature value.

SAM calculates property values from the table using linear interpolation.

The rows in the table must sorted by the temperature value, in either ascending or descending order.

Equations for Calculated ValuesCalcualted values appear on the Solar Field page in blue type with blue backgrounds.

Solar Multiple and Solar Field Area

When the Layout option is Solar Multiple (Option 1), SAM calculates the solar field area based on the valueyou enter for the solar multiple:

When the Layout option is Solar Field Area (Option 2), SAM calculates the solar multiple based on thevalue you enter for the solar field area:

Where,

AExactArea

(m2) Exact Area

ASolarField

(m2) Solar Field Area

ASolarFieldCalculated

(m2) Solar Field Area (calc)

FSolarMultiple

Solar Multiple

FSolarMultipleCalculated

Solar Multiple (calc)

Exact Area and Exact Number of SCAs

The exact area is the solar field area for a solar multiple of one calculated as follows:



The values used for these equations are displayed under Solar Multiple Reference Conditions and ValuesFrom Other Pages, except for the five F

ET factors, which are on the Power Block page.

Where,

AExactArea

(m2) Exact Area

FET0

...FET4

Turb. Part Load Elec to Therm from the Power Block page

OpticalEfficiencyOptical Efficiency from the SCA / HCE page

QDesignTurbineThermalInput

(W) Design Turbine Thermal Input from the Power Block page

QDirectNormalRadiation

(W/m2) Direct Normal Radiation

QHCEThermalLosses

(W/m2) HCE Thermal Losses from the SCA / HCE page

QSolarFieldPipingHeatLosses

(W/m2) Solar Field Piping Heat Losses

Note. Direct Normal Radiation does not represent weather conditions at the site, but is the referenceradiation value used to calculate the solar field area when the solar multiple is one.

Where,

AApertureAreaPerSCA

(m2) Aperture Area per SCA, equivalent to SCA Aperature Area on SCA / HCEpage

AExactArea

(m2) Exact Area

NExactNumberOfSCAs

Exact Number of SCAs

Solar Field Piping Heat Losses

SAM uses the design solar field piping heat losses QsolarFieldPipeHeatLosses

value reported on the Solar Field

page to calculate the solar field area for Field Layout Option 1, when you specify the solar field area usingthe solar multiple:

Where,

QSolarFieldPipeHeatLosses

(W/m2) Solar Field Piping Heat Losses

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FPHL1

... FPHL3

Piping Heat Loss Temp Coeff 1 through 3. The default values (.001693, -1.683e-005, 6.78e-008) result in a scaling factor of one when Delta T =316.5ºC.

QSFPipeHLDesign

(W/m2) Solar Field Piping Heat Losses @ Design T, equivalent to the solar fieldpiping heat losses when the difference between the average solar fieldtemperature and ambient temperature is 316.5ºC.

TAmbient

(°C) Ambient Temperature at reference conditions, 25ºC by default.

TSFinDesign

(°C) Solar Field Inlet Temperature, 293ºC by default

TSFoutDesign

(°C) Solar Field Outlet Temperature, 391ºC by default.

3.6.2 SCA / HCE

To view the SCA / HCE page, click Solar Field on the main window's navigation menu. Note that for theempirical trough input pages to be available, the technology option in the Technology and Market windowmust be Concentrating Solar Power - Empirical Trough System.

Contents

Overview describes the SCA and HCE components and where to find moreinformation about the components.

Input Variable Reference describes the input variables and options on the SCA /HCE page.

About the SCA Parameters describes the physical charateristics of the four SCAsincluded in the default library.

About the HCE Parameters describes the four HCE (receiver) types and five HCEconditions included in the default library.

Equations for Calculated Values describes the equations used to calculated thecalculated values on the SCA / HCE page.

OverviewThe SCA / HCE page displays the characteristics of the solar collector assembly (SCA) and heat collectionelements (HCE) in the solar field. Note that the SCA is often referred to as the collector. The HCE is oftenreferred to as the receiver.

A solar collector assembly (SCA) is an individually tracking component of the solar field that includesmirrors, a supporting structure, and heat collection elements or receivers.

A heat collection element (HCE) is a metal pipe contained in a vacuum within glass tube that runs throughthe focal line of the trough-shaped parabolic collector. Seals and bellows ensure that a vacuum ismaintained in each tube. Anti-reflective coatings on the glass tube maximize the amount of solar radiationthat enters the tube. Solar-selective radiation absorbing coatings on the metal tube maximize the transfer ofenergy from the solar radiation to the pipe.



Note. See http://www.nrel.gov/csp/troughnet/solar_field.html for more information on solar collectorassemblies and heat collection elements. Also see relevant articles in the list of publications on theTroughnet website.



Solar Collector Assembly (SCA)

The solar collector assembly (SCA) input variables describe the dimensions and optical characteristicsof the SCA or collector.

Current SCA inputs

The name of the collector in the SCA library

SCA Length (m)

The total length of a single SCA. Used in SCA end loss calculation.

SCA Aperture (m)

The structural width of a single SCA, including reflective area and gaps. Used in the row-to-rowshadowing loss factor and HCE thermal loss calculations.

SCA Aperture Area (m2)

The reflective area of a single SCA, not including gaps. Used in the solar field size calculations.

Average Focal Length (m)

Average trough focal length. Used in end gain and end loss factor calculations.

Incident Angle Mod Coeff (1-3)

Incident angle modifier coefficients. Used to calculate the incident angle modifier factor, which is usedto calculate the HCE absorbed energy and the solar field optical efficiency.

Tracking Error and Twist

Accounts for errors in the SCA's ability to track the sun. Sources of error may include poor alignment ofsun sensor, tracking algorithm error, errors caused by the tracker drive update rate, and twisting of theSCA end at the sun sensor mounting location relative to the tracking unit end. A typical value is 0.985.Used to calculate SCA field error factor.

Geometric Accuracy

Accounts for SCA optical errors caused by misaligned mirrors, mirror contour distortion caused by thesupport structure, mirror shape errors compared to an ideal parabola, and misaligned or distorted HCE.A typical range of values is between 0.97 and 0.98. Used to calculate SCA field error factor.

Mirror Reflectance

The mirror reflectance input is the solar weighted specular reflectance. The solar-weighted specularreflectance is the fraction of incident solar radiation reflected into a given solid angle about the specularreflection direction. The appropriate choice for the solid angle is that subtended by the receiver asviewed from the point on the mirror surface from which the ray is being reflected. For parabolic troughs,typical values for solar mirrors are 0.923 (4-mm glass), 0.945 (1-mm or laminated glass), 0..906

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(silvered polymer), 0.836 (enhanced anodized aluminum), and 0.957 (silvered front surface).

Mirror Cleanliness Factor (avg)

Accounts for dirt and dust on the mirrors that reduce their effective reflectivity. Typically, mirrors arecontinuously cleaned, but a single mirror may be cleaned once each one or two weeks. The expectedoverall effect on the total solar field would be an average loss of between one and two percent. A typicalvalue would be 0.985. Used to calculate SCA field error factor.

Dust on Envelope (avg)

Accounts for dust on the HCE envelope that affects light transmission. A typical value would be 0.99.Used to calculate HCE heat loss.

Concentrator Factor

A additional error factor to make it possible to adjust the SCE performance without modifying the othererror factors. Useful for modeling an improved or degraded SCE. The default value is 1. Used tocalculate SCA field error factor.

Solar Field Availability

Accounts for solar field down time for maintenance and repairs. Used to calculate absorbed energy.

Heat Collection Element (HCE)

The HCE variables describe the properties of up to four HCE types that can make up the solar field. Thismakes it possible to model a solar field with HCEs in different states. Each set of properties applies to oneof the HCE types. The Fraction of Field variable determines what portion of the solar field is made up of agiven HCE type.

Current HCE inputs

The name of the receiver and its condition. Vacuum refers to an HCE in good condition, lost vacuum,broken glass, and hydrogen refer to different problem conditions. You can define up to four HCE(receiver) conditions.

Fraction of Field

Fraction of solar field using this HCE type and condition. Used to calculate HCE field error factor andHCE heat loss.

Bellows Shadowing

The portion of the HCE tube that does not absorb solar thermal radiation. Used to calculate HCE fielderror factor.

Envelope Transmissivity

Used to calculate HCE field error factor.

Absorber Absorption

Accounts for inefficiencies in the HCE black coating. Used to calculate HCE field error factor.

Unaccounted

Allows for adjustment of the HCE performance to explore effect of changes in performance of the HCEwithout changing the values of other correction factors. A typical value is 1. Used to calculate HCE fielderror factor.

Optical Efficiency (HCE)

The design optical efficiency of each of the four receiver type and condition options. SAM uses the



values to calculate the design weighted optical efficiency.

Optical Efficiency (Weighted)

The design weighted optical efficiency, representing the average optical efficiency of all receivers in thefield (see equation for calculated values below). SAM uses the value to calculate the solar field area.Note that SAM also calculates a separate HCE optical efficiency value for each hour during simulationthat counts for the loss factors on the SCA / HCE page that also accounts for the incident anglemodifier factor, which depends on the time of day and collector orientation.

Heat Loss Coefficient A0...A6

Used to calculate the HCE heat loss. The default values are based on NREL modeling and test results.(See Forristall R, 2003. Heat Transfer Analysis and Modeling of a Parabolic Trough Solar ReceiverImplemented in Engineering Equation Solver. National Renewable Energy Laboratory NREL/TP-550-34169. http://www.nrel.gov/csp/troughnet/pdfs/34169.pdf., and Burkholder F et al, 2009, Heat LossTesting of Schott's 2008 PTR70 Parabolic Trough Receiver. National Renewable Energy LaboratoryNREL/TP-550-45633. http://www.nrel.gov/csp/troughnet/pdfs/45633.pdf)

Heat Loss Factor

The design heat loss factor that applies to the active HCE type and condition. Used to calculate designHCE heat loss that is part of the solar field area equation. The heat loss factor scales the heat lossequation and can be used to fine tune the results when measured heat loss data are available. Thedefault value of 1.0 is valid for the current version of SAM using the default heat loss coefficients.

Min windspeed (m/s)

Used to calculated the HCE heat loss for hours when the wind speed from the weather file is lower thanthe minimum wind speed.

HCE Heat Losses (W/m), Thermal Losses (Weighted W/m), Thermal Losses (Weighted W/m2)

These values are provided for reference. SAM calculates the HCE heat loss for each hour duringsimulation based on the loss factor coefficients on the SCA / HCE page and other values from theweather data.

About the SCA ParametersThe default SCA library includes a set of parameters for four types of SCAs described in the table below.These SCA types are either installed in currently operating systems, or were used in past system designs.See Working with Libraries for information about managing libraries.

Table 12. Default collector types.

Name Description Location

Euro Trough ET150 Torque box, galvanized steel SEGS V, Kramer Junction, California

Luz LS-2 Torque-tube, galvanized steel SEGS I - VII, Kramer Junction, California

Luz LS-3 Bridge truss, galvanized steel SEGS VII - IX, Kramer Junction, California

Solargenix SGX-1 Organic hubbing structure,extruded aluminum

Nevada Solar One, Boulder City, Nevada

The values of input variables on the SCA / HCE page are stored in libraries. See Working with Libraries forinformation about managing libraries.

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About the HCE ParametersThe HCE library includes four HCE types, and for each HCE type, five HCE conditions. See Working withLibraries for information about managing libraries.

For each HCE type and condition, you can assign a Percent of Field value. For example, in the figurebelow, the receiver type is Schott PTR70, and 98.5% percent of the HCEs are in normal condition, 1.0%have lost vacuum, 0.5% have glass damage, and 0% have allowed hydrogen to enter the tube.

When you select a name from the Receiver Type and Condition list, SAM populates the optical and heatloss parameters using values stored in the library. When you change one or more of these values, SAMcreates a copy of the parameter set and adds it to the library under the name "CUSTOM CUSTOM."

The four HCE types are described in the table below.

Table 13. Default HCE types.

HCE Type Description

Luz Cermet Original HCE design. Low reliability of seals.

Schott PTR70 Vacuum Newer design with improved reliability. Two versions are available.

Solel UVAC2 Newer design with improved reliability.

Solel UVAC3 The newest HCE available as of May 2008.

The performance of the HCE is highly dependent on the quality of the vacuum in the glass tube. SAMmodels the HCE under the five conditions described in the following table.

Table 14. HCE conditions.

HCE Condition Description

Broken glass Glass tube is damaged, increasing heat transfer between tube and atmosphere.

Fluorescent Selective coating on metal tube is compromised, reducing absorption of solarradiation

Hydrogen Hydrogen from hydrocarbon-based heat transfer fluid (e.g., mineral oil) haspermeated through metal tube into the vacuum, increasing heat transfer betweenmetal tube and glass.

Lost vacuum Glass-to-metal seal is compromised

Vacuum HCE is not damaged and is operating as designed.


Optical Efficiency (HCE)

The design optical efficiency of each receiver type and condition option is a function of the efficiency andloss factors for each option.

Where,

FOptEffD,n

Optical Efficiency (HCE) for each of the four receivers types.



FSCAFieldError,n

The SCA field error factor, which is the product of Tracking Error and Twist, GeometricAccuracy, Mirror Reflectivity, Mirror Cleanliness Factor and Concentrator Factor. (Notethat the Dust on Envelope factor is used for the HCE field error calculation above, nothere.)

FDustEnvelope,n

Dust on Envelope (avg) specified in the SCA parameters above. The same value appliesto each of teh four receiver types.

FBellows,n

Bellows Shadowing for the receiver type n.

FTransmissivity,n

Envelope Transmissivity for the receiver type n.

FAbsorption,n

Absorber Absorption for the receiver type n.

FUnaccounted,n

Unaccounted for the receiver type n.

n The receiver type number (1 through 4)


The design weighted optical efficiency is a design value that SAM uses to calculate the solar field area.Note that the design optical efficiency equations differ from the optical efficiency factor equations used inthe hourly simulation. It is a function of the four design optical efficiency factors and fraction of field valuesfor each receiver type option:

Where,

FOptEffD


FOptEffD,n

Optical Efficiency (HCE) for each of the four receivers

FPercentOfField,n

Percent of Solar Field for each of the four receivers

n Receiver number (1 through 4)

HCE Heat Losses (W/m)

The heat loss for each of the four HCE types (Receiver 1 through 4) depends on the value of the six heatloss coefficients and heat loss factor for each HCE type, and on the design parameters specified on theSolar Field page:

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Where,

QHCEHLD,n

(W/m) HCE heat losses for HCE type n expressed in thermal Watts per meter

FHeatLoss,n

Heat Loss Factor for HCE type n

FA0

... FA6

A0 Heat Loss Coefficient through A6 Heat Loss Coefficient

TSFin

(°C) Solar Field Inlet Temperature from the Solar Field page

TSFout

(°C) Solar Field Outlet Temperature from the Solar Field page

TAmb

(°C) Reference ambient temperature from the Solar Field page

QDNIRef

Reference direct normal radiation from the Solar Field page

Wind (m/s) Reference wind velocity from the Solar Field page

Thermal Losses (Weighted W/m)

The total HCE losses are expressed in Watts per meter of SCA length:

Where,

QHCELossD(W/m)

(W/m) Thermal Losses per SCA aperture length.

QHCELosses,n

(W/m) Receiver Heat Losses for receiver number n

FPercentOfField,n

Percent of Solar Field for each of the four receivers

Thermal Losses (Weighted W/m2)

The total HCE losses are also expressed in Watts per square meter (the product of the aperture length(SCA Length) and aperture width (SCA Aperture):

Where,



QHCELossD

(W/m2) Thermal losses per square meter

QHCELossD(W/m)

(W/m) Thermal losses per SCA aperture length (described above)

DSCAAperture

(m) SCA Aperture (structural width of SCA)

3.6.3 Power Block

To view the Power Block page, click Power Block on the main window's navigation menu. Note that for theempirical trough input pages to be available, the technology option in the Technology and Market windowmust be Concentrating Solar Power - Empirical Trough System.

Contents

Overview describes the Power Block page and where to find more information aboutthe power block model.

Input Variable Reference describes the input variables and options on the PowerBlock page.

Power Cycle Library Options describes the reference steam turbines included in thedefault power block library.

Equations for Calculated Values describes the equations used to calculated thecalculated values on the Power Block page.

OverviewThe Power Block parameters describe the equipment in the system that converts thermal energy from thesolar field or thermal energy storage system into electricity. The power block is based on a steam turbinethat runs on a conventional Rankine power cycle and may or may not include fossil fuel backup. Powerblock components include a turbine, heat exchangers to transfer heat from the solar field or thermal energystorage system to the turbine, and a cooling system to dissipate waste heat. SAM considers the thermalenergy storage system to be a separate component, which is described on the Thermal Storage page.

The input variables on the Power Block page are divided into two groups. The turbine ratings groupdetermines the capacity of the power block, and the power cycle group defines the performance parametersof the reference turbine.



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Plant Characteristics

Design Turbine Gross Output (MWe)

The power cycle's design output, not accounting for parasitic losses. SAM uses this value to sizesystem components, such as the solar field area when you use the solar multiple tospecify the solar field size.

Estimated Gross to Net Conversion Factor

An estimate of the ratio of the electric energy delivered to the grid to the power cycle's gross output.SAM uses the factor to calculate the system's nameplate capacity for capacity-related calculations,including the estimated total cost per net capacity value on the System Costs page, capacity-basedincentives on the Payment Incentives page, and the capacity factor reported in the results.

Estimated Net Output at Design (MWe)

The power cycle's nominal capacity, calculated as the product of the design gross output andestimated gross to net conversion factor. SAM uses this value to calculate the system's rated capacityfor capacity-related calculations, including the estimated total cost per net capacity value on theSystem Costs page, capacity-based incentives on the Payment Incentives page, and the capacityfactor reported in the results.

Power Cycle

The variables in the power cycle group describe a reference steam turbine. SAM uses the reference turbinespecifications to calculate the turbine output, and then scales the actual output based on the turbine ratingvariables. Each set of reference turbine specifications is stored in the reference turbine library.

Current power block

Name of the reference turbine. Selecting a reference system determines the values of the other powercycle variables.


The thermal energy required as input to the power block to generate the design turbine gross (electric)output. SAM uses the design turbine thermal input to calculate several power block capacity-relatedvalues, including the solar field size, power block design point gross output, and parasitic losses.

Design Turbine Gross Efficiency

Total thermal to electric efficiency of the reference turbine. Used to calculate the design turbine thermalinput.

Max Over Design Operation

The turbine's maximum output expressed as a fraction of the design turbine thermal input. Used by thedispatch module to set the power block thermal input limits.

Minimum Load

The turbine's minimum load expressed as a fraction of the design turbine thermal input. Used by thedispatch module to set the power block thermal input limits.

Turbine Start-up Energy

Fraction of the design turbine thermal input required to bring the system to operating temperature after a



period of non-operation. Used by the dispatch module to calculate the required start-up energy.

Boiler LHV Efficiency

The back-up boiler's lower heating value efficiency. Used by the power block module to calculate thequantity of gas required by the back-up boiler.

Max Thermal Input (MWt)

The maximum thermal energy that can be delivered to the power block by the solar field, thermal energystorage system or both.

Min Thermal Input (MWt)

The minimum thermal energy that can be delivered to the power block by the solar field, thermal energystorage system or both.

Turb. Part Load Therm to Elec

Factors for the turbine thermal-to-electric efficiency polynomial equation. Used to calculate the designpoint gross output, which is the portion of the power block's electric output converted from solar energybefore losses.

Turb. Part Load Elec to Therm

Factors for turbine's part load electric-to-thermal efficiency polynomial equation. Used to calculate theenergy in kilowatt-hours of natural gas equivalent required by the backup boiler. SAM dispatches thebackup boiler based on the fossil-fill fraction table in the thermal storage dispatch parameters on theThermal Storage page.

Cooling Tower Correction

Cooling tower correction factor. Used to calculate the temperature correction factor that representscooling tower losses. To model a system with no cooling tower, set F0 to 1, and F1 = F2 = F3 = F4 =0.

Temperature Correction Mode

In the dry bulb mode, SAM calculates a temperature correction factor to account for cooling towerlosses based on the ambient temperature from the weather data set. In wet bulb mode, SAM calculatesthe wet bulb temperature from the ambient temperature and relative humidity from the weather data.

Power Cycle Library OptionsThe power cycle library includes six reference turbines. See Working with Libraries for information aboutmanaging libraries.

The reference turbines include five conventional Rankine-cycle steam turbines in a range of sizes, and oneorganic Rankine-cycle turbine. Conventional Rankine-cycle turbines are similar to those used in coal,nuclear, or natural gas power plants. A heat exchanger transfers energy from the solar field's heat transferfluid to generate steam that drives the turbine. The organic Rankine-cycle turbine operates on the sameprinciple as the conventional turbine, but uses an organic fluid, typically butane or pentane, to run theturbine instead of water.

Table 15. Power cycle reference systems.

Reference System

Approximate SolarField Size Range

m2

Approximate OperatingTemperature

ºCSuggested Modeling

Application

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APS Ormat 1 MWe 300C 10,000 300Organic Rankine-cyclepower block

Nexant 450C HTF - 450High-temperature heattransfer fluid (molten salt)

Nexant 500C HTF - 500High-temperature heattransfer fluid (molten salt)

SEGS 30 MWe Turbine 180,000 - 230,000 300 - 400 Typical applications

SEGS 80 MWe Turbine 460,000 - 480,000 400 Typical applications

Siemens 400C HTF 400High-temperature heattransfer fluid

When you choose a turbine from the reference system library, SAM changes the values of the Power Cyclevariables. The following table shows the power cycle parameters for the standard reference systems. Notethat you can use any value for the Rated Turbine Net Capacity and Design Turbine Gross Output variables,SAM will use the reference system parameters with the rated and design turbine parameters.

Table 16. Reference system parameters.

Parameter Name SEGS 30 SEGS 80 APS ORC Nexant450

Nexant500

Siemens400

Rated Turbine Net Capacity 30 80 1 100 100 50

Design Turbine Gross Output 35 89 1.160 110 110 55

Design Turbine Thermal Input 93.3 235.8 5.600 278.0 269.9 147.2

Design Turbine Gross Efficiency 0.3749 0.3774 0.2071 0.3957 0.4076 0.3736

Max Over Design Operation 1.15 1.15 1.15 1.15 1.15 1.15

Minimum Load 0.15 0.15 0.15 0.15 0.15 0.15

Turb. Part Load Therm to Elec F0 -0.0571910 -0.0377260 -0.1593790 -0.0240590 -0.0252994 -0.0298

Turb. Part Load Therm to Elec F1 1.0041000 1.0062000 0.9261810 1.0254800 1.0261900 0.7219


Turb. Part Load Therm to Elec F3 -0.0724470 -0.0447750 -1.3605660 0.0000000 0.0000000 -0.5518


Turb. Part Load Elec to Therm F0 0.0565200 0.0373700 0.1492050 0.0234837 0.0246620 0.044964


Turb. Part Load Elec to Therm F2 -0.0982950 -0.0649910 -0.3247150 0.0000000 0.0000000 -0.563880


Turb. Part Load Elec to Therm F4 0.0000000 0.0000000 -0.1256020 0.0000000 0.0000000 -0.130090

You can use any of the the built-in power cycle options to model most systems expected to run at or nearthe power block's design point for most operating hours. You can specify your own power cycle if you havea set of part load coefficients from the manufacturer, or if you have calculated coefficients using power plantsimulation or equation solving software. The part load equation is a fourth-order or lower polynomial equationthat describes the relationship between power cycle efficiency and operating load.




Design Turbine Thermal Input

Where,

DesignTurbineGrossDesign Turbine Gross Efficiency

QDesignTurbineGross

(W) Design Turbine Gross Output

QDesignTurbineThermalInput

(W)


Max Thermal Input

Where,

QtoPBMax

(W) Max Thermal Input

QPBDesign

(W)


FET(0-4) Turbine Part Load Elec To Therm coefficients

FPBMax Max Over Design Operation

Min Thermal Input

Where,

QtoPBMin

(W) Min Thermal Input

QPBDesign

(W) Design Turbine Thermal Input

FET(0-4) Turbine Part Load Elec To Therm coefficients

FPBMax Minimum Load

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3.6.4 Thermal Storage

To view the Thermal Storage page, click Thermal Storage on the main window's navigation menu. Notethat for the empirical trough input pages to be available, the technology option in the Technology and Marketwindow must be Concentrating Solar Power - Empirical Trough System.

Contents

Overview describes thermal energy storage systems and explains where find moreinformation about them.

Input Variable Reference describes the input variables and options on the ThermalStorage page.

Estimating Tank Heat Loss Values describes how to choose values for the tankheat loss variable for different thermal energy storage capacities.

Storage and Fossil Backup Dispatch Controls describes the dispatch controls thatdetermine the timing of energy releases from the storage and fossil back upsystems.

Defining Dispatch Schedules explains how to assign dispatch periods to weekdayand weekend schedules.

Equations for Calculated Values describes the equations used to calculated thecalculated values on the Thermal Storage page.

OverviewA thermal energy storage system (TES) stores heat from the solar field in a liquid medium. Heat from thestorage system can drive the power block turbine during periods of low or no sunlight. A TES is beneficial inmany places where the peak demand for power occurs after the sun has set. Adding TES to a parabolictrough system allows the collection of solar energy to be separated from the operation of the power block.For example, a system might be able to collect energy in the morning and use it to generate electricity lateinto the evening.

In direct systems, the heat transfer fluid itself serves as the storage medium. In indirect systems, aseparate fluid is the storage medium, and heat is transferred from the HTF to the storage medium throughheat exchangers. The TES system consists of one or two tanks, pumps to circulate the liquids, anddepending on the design, heat exchangers. A thermocline system stores both the hot and cold storagemedium in one tank. The zone in the tank where hot and cold fluids meet is called a thermocline. Thestorage tank in a thermocline system contains low-cost filler materials such as sand and rock. A two-tanksystem consists of a hot tank to store heat from the solar field, and a cold tank to store the cooled storagemedium after the power block has extracted its energy.

Note. For more information on thermal energy storage systems for parabolic trough systems, see http://www.nrel.gov/csp/troughnet/thermal_energy_storage.html.

The user inputs on the Thermal Storage page are divided into two groups. The thermal energy storage (TES)group defines the thermal energy storage capacity and type along with some efficiency parameters. The

http://www.nrel.gov/csp/troughnet/thermal_energy_storage.html




thermal storage dispatch controls group variables determine the the operation of the storage and fossil backup systems.



Thermal Energy Storage (TES)

Equiv Full Load Hours of TES hours

The thermal storage capacity expressed in number of hours of thermal energy delivered at the powerblock's design thermal input level. The physical capacity is the number of hours of storage multiplied bythe power block design thermal input. Used to calculate the TES maximum storage capacity.

Storage System Configuration

The current version of SAM models a two-tank TES consisting of a cold storage tank and hot storagetank.

Storage Fluid Type

The Storage fluid used in the TES. When the storage fluid and solar field heat transfer fluid (HTF) aredifferent, the system is an indirect system with a heat exchanger. When the storage fluid and solar fieldHTF are the same, the system is a direct system that uses the solar field HTF as the storage medium. Used to calculate the heat exchanger duty.

Turbine TES Adj Efficiency

SAM applies the TES efficiency adjustment factor to the turbine efficiency for trough systems withstorage to account for the lower steam temperature that results from imperfect heat exchange in thestorage system. Used to calculate maximum TES discharge rate. Also used to calculate a TEScorrection factor.

Turbine TES Adj Gross Output

Efficiency adjustment factor. Used to calculate maximum TES discharge rate.

Initial Thermal Storage (MWht)

The amount of energy in storage when the simulation starts, at midnight on January 1. The default valueis zero.

Tank Heat Losses (MWht)

Storage tank thermal losses. SAM subtracts value from the total energy in storage at the end of eachsimulation hour. See the table below for suggested values.

Maximum Energy Storage (MWht)

The maximum thermal energy storage capacity of the TES.


The thermal input requirement of the power block to operate at its design point. Used to calculate thefollowing dispatch parameters: power block input limits, power block load requirement, TES maximumstorage capacity, and the start-up requirement

Max Power to Storage (MWt)

Maximum TES charge rate. Used in the dispatch calculation when energy from the solar field exceeds


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the power block load requirement.

Max Power From Storage (MWt)

Maximum TES discharge rate. Used in the dispatch calculation when energy from the solar field is lessor equal to than the power block load requirement.

Heat Exchanger Duty

Applies only to indirect thermal storage systems that use a different storage fluid and solar field HTF.Used to calculate the maximum TES charge rate.

Thermal Storage Dispatch Control

The storage dispatch control variables each have six values, one for each of six possible dispatch periods.They determine how SAM calculates the energy flows between the solar field, thermal energy storagesystem, and power block. The fossil-fill fraction is used to calculate the energy from a backup boiler.

Storage Dispatch Fraction with Solar

The fraction of the TES maximum storage capacity (see table above) required for the system to startwhen the solar field energy is greater than zero. A value of zero will always dispatch the TES in anyhour assigned to the given dispatch period; a value of one will never dispatch the TES. Used tocalculate the storage dispatch levels.

Storage Dispatch Fraction without Solar

The fraction of the TES maximum storage capacity (see table above) required for the system to startwhen the solar field energy is equal to zero. A value of zero will always dispatch the TES in any hourassigned to the given dispatch period; a value of one will never dispatch the TES. Used to calculate thestorage dispatch levels.

Turbine Output Fraction

A fraction of the design turbine thermal input adjusted by the turbine part load electric-to-thermalefficiency factors. Used to calculate the power block load requirement.

Fossil Fill Fraction

A fraction of the power block design turbine gross output from the Power Block page that can be met bythe backup boiler. Used by the power block module to calculate the energy from the backup boiler.

Payment Allocation Factor

The energy payment allocation factors are a set of multipliers that SAM uses to adjust the electricityprice based on time of day and month of year for utility projects. The allocation factors work inconjunction with the assumptions on the Financing page.

Estimating Tank Heat Loss ValuesAn increase in the hours of thermal storage requires a both an increase in the solar field size to minimizethe levelized cost of energy for the system, and an increase in the tank heat losses to account for the largertank. The "100 MW Baseline - Parameterized Storage" case in Sample Parabolic Trough Systems.zsamillustrates these relationships. See Sizing the Solar Field for a discussion of an approach to optimize thesolar field for system with storage.

The following table shows suggested tank heat loss values for three sample systems over a range ofthermal storage capacities. The relationship between tank heat losses and hours of thermal storage islinear, so you can extrapolate to estimate values for storage capacity values not on the table.



Table 17. Suggested Tank Heat Losses (MWt) values for different thermal storagecapacities (hours).

System Description

Hours of Thermal Storage

0 3 6 9 12 15

100 MW Two Tank IndirectVP-1/Nitrate Salt

0 0.62 0.96 1.23 1.56 1.87

200 MW Two Tank IndirectVP-1/Nitrate Salt

0 1.0 1.61 2.21 2.81 3.56

200 MW Two Tank DirectHitec Salt

0 0.34 0.64 0.93 1.24 1.52

Storage and Fossil Backup Dispatch ControlsThe thermal storage dispatch controls determine the timing of releases of energy from the thermal energystorage and fossil backup systems to the power block. When the system includes thermal energy storageor fossil backup, SAM can use a different dispatch strategy for up to six different dispatch periods.

Storage Dispatch

SAM decides whether or not to operate the power block in each hour of the simulation based on how muchenergy is stored in the TES, how much energy is provided by the solar field, and the values of the thermalstorage dispatch controls parameters. You can define when the power block operates for each of the sixdispatch periods. For each hour in the simulation, if the power block is not already operating, SAM looks atthe amount of energy that is in thermal energy storage at the beginning of the hour and decides whether itshould operate the power block. For each period, there are two targets for starting the power block: one forperiods of sunshine (w/solar), and one for period of no sunshine (w/o solar).

The turbine output fraction for each dispatch period determines at what load level the power block runs usingenergy from storage during that period. The load level is a function of the turbine output fraction, designturbine thermal input, and the five turbine part load electric to thermal factors on the Power Block page.

For each dispatch period during periods of sunshine, thermal storage is dispatched to meet the power blockload level for that period only when the thermal power from the solar field is insufficient and available storageis equal to or greater than the product of the storage dispatch fraction (with solar) and maximum energy instorage. Similarly, during periods of no sunshine when no thermal power is produced by the solar field, thepower block will not run except when the energy available in storage is equal to or greater than the productof storage dispatch fraction (without solar) and maximum energy in storage.

By setting the thermal storage dispatch controls parameters, you can simulate the effect of a clear daywhen the operator may need to start the plant earlier in the day to make sure that the storage is not filled tocapacity and solar energy is dumped, or of a cloudy day when the operator may want to store energy forlater use in a higher value period.

Fossil Backup Dispatch

When the fossil fill fraction is greater than zero for any dispatch period, the system is considered to includefossil backup. The fossil fill fraction defines the solar output level at which the backup system runs duringeach hour of a specific dispatch period. For example, a fossil fill fraction of 1.0 would require that the fossilbackup operate to fill in every hour during a specified period to 100% of design output. In that case, during

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periods when solar is providing 100% output, no fossil energy would be used. When solar is providing lessthan 100% output, the fossil backup operates to fill in the remaining energy so that the system achieves100% output. For a fossil fill fraction of 0.5, the system would use energy from the fossil backup only whensolar output drops below 50%.

The boiler LHV efficiency value on the Power Block page determines the quantity of fuel used by the fossilbackup system. A value of 0.9 is reasonable for a natural gas-fired backup boiler. SAM includes the cost offuel for the backup system in the levelized cost of energy and other metrics reported in the results, andreports the energy equivalent of the hourly fuel consumption in the hourly simulation results. The cost of fuelfor the backup system is defined on the Trough System Costs page.


The energy payment allocation factors are a set of multipliers that SAM uses to adjust the electricity pricebased on time of day and month of year for utility projects. The allocation factors work in conjunction withthe assumptions on the Financing page.

For utility dispatch and utility bid price projects, SAM calculates a first year PPA price or bid price thatcovers project installation, operating, and financing costs (accounting for any tax credits or incentivepayments), given time-of-use adjustments specified by the payment allocation factors.

When you choose a dispatch schedule from SAM's dispatch schedule library, SAM populates the paymentallocation factors with values appropriate for the schedule you choose.

Note. For utility bid price projects with no energy payment allocation factors, set the value for all periodsto one.

Defining Dispatch SchedulesThe storage dispatch schedules determine when each of the six periods apply during weekdays andweekends throughout the year. You can either choose an existing schedule from one of the schedules inthe CSP trough TES dispatch library or define a custom schedule. For information about libraries, seeWorking with Libraries.

The TES dispatch library only assigns period numbers to the weekday and weekend schedule matrices.The dispatch fractions assigned to each of the six periods are not stored in the library.

To choose a schedule from the library:

1. Click Dispatch schedule library.

2. Choose a schedule from the list of four schedules. The schedules are based on time-of-use pricingschedules from four California utilities.

3. Click OK.

You can modify a schedule using the steps described below. Modifying a schedule does not affectthe schedule stored in the library.

4. For each of the up to six periods used in the schedule, enter values for the dispatch fractionsdescribed above. Use the period number and color to identify the times in the schedule that eachperiod applies.

To specify a weekday or weekend schedule:

1. Assign values as appropriate to the Storage Dispatch, Turbine Output Fraction, Fossil Fill Fraction,



and Payment Allocation Factor for each of the up to nine periods.


3. Choose a Uniform Dispatch.

4. Click OK.

5. Use your mouse to draw a rectangle in the matrix for the first block of time that applies to period 2.

6. Type the number 2.

7. SAM shades displays the period number in the squares that make up the rectangle, and shadesthe rectangle to match the color of the period.

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8. Repeat Steps 2-4 for each of the remaining periods that apply to the schedule.


Maximum Energy Storage

Where,

QMaximumStorage

(Wh)

Maximum Energy Storage

QDesignTurbineInput

(W)


NHoursOfStorage

(hours)

Equiv. Full Load Hours of TES


The thermal energy required by the power block to operate at its rated capacity, described on the PowerBlock page.

Maximum Power To and From Storage

The maximum power to and from storage depends on whether the TES includes a heat exchanger. Whenthe TES fluid is different from the solar field fluid, the TES includes a heat exchanger. When the fluids arethe same, there is no heat exchanger.

For a TES with heat exchanger (TES fluid and solar field fluid are different):



For a TES with no heat exchanger (TES fluid and solar field fluid are the same):

Where,

FHeatExchangerDuty

Heat Exchanger Duty

FSolarMultiple

Solar Multiple from Solar Field page

FTESAdjustEfficiency

Turbine TES Adj. - Efficiency

FTESAdjustOutput

Turbine TES Adjustment - Gross Output

FTurbineMaximumOverDesign

Max Over Design Operation from Power Block page

NHoursOfStorage

Equiv. Full Load Hours of TES

PMaximumFromStorage

(W) Maximum Power From Storage

PMaximumToStorage

(W) Maximum Power To Storage

QDesignTurbineInput

(W) Design Turbine Thermal Input from Power Block page

QMaximumStorage

(W) Maximum Energy Storage

Heat Exchanger Duty

The heat exchanger duty depends on the value of the solar multiple. When the solar multiple is greater thanone:

When the solar multiple is equal to or less than one:

Where,

FHeatExchangerDuty

Heat Exchanger Duty

FSolarMultiple

Solar Multiple from Solar Field page

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3.6.5 Parasitics

To view the Parasitics page, click Parasitics on the main window's navigation menu. Note that for theempirical trough input pages to be available, the technology option in the Technology and Market windowmust be Concentrating Solar Power - Empirical Trough System.

Contents

Input Variable Reference describes the input variables and options on the Parasiticspage.

Equations for Calculated Values describes the equations used to calculated thecalculated values on the Parasitics page.

OverviewThe Parasitics page displays parameters describing losses due to parasitic electrical loads, such as drivemotors, electronic circuits, and pump motors. SAM includes a set of default parasitic parameters for arange of solar trough power systems. Choose a reference parasitic system option that is the same orsimilar to the system you are modeling. SAM will automatically adjust the total parasitic load to match thesize of the solar field and power block in the system you are modeling.

The design point parasitic values are the maximum possible values for each parasitic loss category. SAMcalculates the hourly parasitic loss value for each category during simulation based on the design point, thePF and F0-F2 coefficients, and the solar field thermal output and power block load in each hour, and reportsthem in the hourly simulation results. The calculated parasitic loss values are never as high as the totaldesign point parasitic losses.


Input Variable ReferenceThe values of input variables on the Parasitics page are stored in a library of reference solar fields. You canchange the parameter values without changing the values stored in the library. For information aboutlibraries, See Working with Libraries.

Parasitic Electric Energy Use

Current reference parasitic system

The reference system from the CSP trough parasticis library. SAM stores a set of parasitic parametersfor reference systems.

Solar Field Area (m2)

The calculated solar field area from the Solar Field page. Used to calculate parasitic losses that are

based on the solar field size with units of MWe/m2.




Gross Turbine Output (MWe)

The design turbine gross output value from the Power Block page. Used to calculate parasitic lossesthat are based on the power block capacity with units of MWe/Mwe.

SCA Drives and Electronics (MWe)

Electrical losses from electric or hydraulic SCA drives that position the collector to track the sun andfrom electronic SCA tracking controllers and alarm monitoring devices. Calculated as a function of thesolar field area.

Solar Field HTF Pumps

Electrical losses from cold HTF pumping in the solar field. Calculated as a function of the solar fieldarea. These losses are calculated only in hours when the solar field is operating, which is defined aswhen the solar field load is greater than zero.

TES Pumps

Electrical losses from pumps in the TES system. Calculated as a function of the design turbine grossoutput.

Antifreeze Pumping (MWe)

Electrical losses from HTF pumps in the solar field. Calculated as a function of the solar field area.These losses are used only in hours when the solar field is not operating, which is defined as when thesolar field load is zero.

Power Block Fixed (MWe)

These fixed losses apply 24 hours per day, for all of the 8,760 hours of the year.

Balance of Plant (MWe)

Electrical losses that apply in hours when the power block operates at part or full load.

Heater and Boiler (MWe)

Losses that apply only when the back-up boiler is in operation.

Cooling Towers (MWe)

The cooling tower parasitic losses are electrical losses that occur when the power block operates atpart or full load. Calculated either as a function of power block load or at a fixed 50% or 100% of thedesign cooling tower parasitic losses.

Cooling Tower Operation Mode

Determines how cooling tower parasitic losses are calculated. For "Cooling Tower at 50% or 100%,"parasitic losses are calculated as 50% of the design cooling tower parasitic losses when the powerblock load is 0.5 or less, and as or 100% of the design parasitic losses when the power block load isgreater than 0.5. For "Cooling Tower parasitics a function of load," cooling tower parasitic losses arecalculated as a function of power block load.

Total Design Parasitics (MWe)

The sum of collector drives and electronics, solar field HTF pump, night circulation pumping, powerblock fixed, balance of plant, heater/boiler, and cooling towers design loss values. This value representsthe maximum possible value if all parasitic losses were to occur simultaneously in a given hour, and istypically greater than the actual parasitic losses. SAM displays the value for reference only, and doesnot use it in simulation calculations.

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Equations for Calculated ValuesEach parasitic loss type has a set of parameters that includes a factor, PF and F0, F1, and F2 coefficient.The design point values are maximum values and are calculated using the factor and PF coefficient. SAMuses the F0-F2 coefficients in calculations for the hourly simulations, which are described in the referencemanual.

Table . Design point parasitic loss equations for each parasitic loss category.

Source of Parasitic Loss Equation

SCA Drives and Electronics Factor x PF x Solar Field Area

Solar Field HTF Pumps Factor x PF x Solar Field Area

TES Pumps Factor x PF x Gross Turbine Output

Antifreeze Pumping Factor x Solar Field HTF Pump losses

Power Block Fixed Factor x Gross Turbine Output

Balance of Plant Factor x PF x Gross Turbine Output

Heater and Boiler Factor x PF x Gross Turbine Output

Cooling Towers Factor x PF x Gross Turbine Output

The Total Design Point Parasitics is the sum of the the design point parastic loss categories:

SCA Drives and Electronics

Solar Field HTF Pumps

TES Pumps

Power Block Fixed

Balance of Plant

Heater and Boiler

Cooling Towers

3.7 Parabolic Trough PhysicalA parabolic trough system is a type of concentrating solar power (CSP) system that collects direct normalsolar radiation and converts it to thermal energy that runs a power block to generate electricity. Thecomponents of a parabolic trough system are the solar field, power block, and in some cases, thermalenergy storage and fossil backup systems. The solar field collects heat from the sun and consists ofparabolic, trough-shaped solar collectors that focus direct normal solar radiation onto tubular receivers.Each collector assembly consists of mirrors and a structure that supports the mirrors and receivers, allowsit to track the sun on one axis, and can withstand wind-induced forces. Each receiver consists of a metaltube with a solar radiation absorbing surface in a vacuum inside a coated glass tube. A heat transfer fluid(HTF) transports heat from the solar field to the power block (also called power cycle) and othercomponents of the system. The power block is based on conventional power cycle technology, using aturbine to convert thermal energy from the solar field to electric energy. The optional fossil-fuel backupsystem delivers supplemental heat to the HTF during times when there is insufficient solar energy to drivethe power block at its rated capacity.

Parabolic Trough Physical 151


The physical trough system model is a new parabolic trough model for SAM introduced in March 2010. Themodel approaches the task of characterizing the performance of the many of the system components fromfirst principles of heat transfer and thermodynamics, rather than from empirical measurements as in theempirical trough system model. The physical model uses mathematical models that represent componentgeometry and energy transfer properties, which gives you the flexibility to specify characteristics of systemcomponents such as the absorber emissivity or envelope glass thickness. The empirical model, on theother hand, uses a set of curve-fit equations derived from regression analysis of data measured from realsystems, so you are limited to modeling systems composed of components for which there is measureddata. While the physical model is more flexible than the empirical model, it adds more uncertainty toperformance predictions than the empirical model. In a physical model, uncertainty in the geometry andproperty assumptions for each system component results in an aggregated uncertainty at the system levelthat tends to be higher than the uncertainty in an empirical model. We've included both models in SAM sothat you can use both in your analyses.

The following are some key features of the physical model:

Includes transient effects related to the thermal capacity of the heat transfer fluid in the solar fieldpiping, headers, and balance of plant.

Allows for flexible specification of solar field components, including multiple receiver and collector typeswithin a single loop.

Relatively short simulation times to allow for parametric and statistical analyses that require multiplesimulation runs.

As with the other SAM models for other technologies, the physical trough model makes useof existing models when possible:

Collector model adapted from NREL's Excelergy model.

Receiver heat loss model by Forristall (2003).

Field piping pressure drop model by Kelley and Kearney (2006).

Power cycle performance model by Wagner (2008) for the power tower (also known as a centralreceiver) CSP system model in SAM.

For publications describing the subcomponent models, see References, Parabolic Trough Technology andModeling.

To use the parabolic trough physical model:

Open the sample parabolic trough sample file: On the File menu, click Open Sample Templateand choose Sample Parabolic Trough Systems from the list, or

In the Technology and Market window, choose Concentrating Solar Power, Physical TroughSystem.

The sample file contains four cases. The first three cases use the physical trough model, and the fourthcase uses the empirical model. The first case represents a 100 MW baseline system with a mediumtemperature heat-transfer fluid and an indirect 2-tank thermal energy storage system. The second caserepresents a similar 100 MW system with dry cooling. The third case shows how to optimize the solar fieldthermal energy storage system size to minimize the system levelized cost of energy, as described inSizing the Solar field.

The parabolic trough input pages for this option described in this section are:

Trough System Costs

Solar Field

Collectors (SCAs)

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Receivers (HCEs)

Power Cycle

Thermal Storage

Parasitics

User Variables

3.7.1 Solar Field

To view the Solar Field page, click Solar Field on the main window's navigation menu. Note that for thephysical trough input pages to be available, the technology option in the Technology and Market windowmust be Concentrating Solar Power - Physical Trough System.

Contents

Overview describes the Solar Field page.

Input Variable Reference describes the input variables and options on the SolarField page.

Sizing the Solar Field describes how to choose between Option 1 and Option 2,choose a field layout, choose an irradiation at design value, and optimize the solarmultiple for systems with and without storage.

Specifying a Custom Heat Transfer Fluid describes the steps for creating your ownheat transfer fluid

Specifying the Loop Configuration describes the single loop configuration diagramand how to specify collector-receiver assemblies in the loop.

Defining Collector Defocusing describes the collector defocusing options

Equations for Calculated Values describes the equations used to calculate valueson the Solar Field page.

OverviewThe Solar Field page displays variables and options that describe the size and properties of the solar field,properties of the heat transfer fluid. It also displays reference design specifications of the solar field. SeeInput Variable Reference for a description of the solar field input variables.

SAM provides two options for specifying the size of the solar field: Option 1 specifies the field area as amultiple of the area required to drive the power cycle at its rated capacity under design conditions, andOption 2 specifies the field area as an explicit value in square meters. See Sizing the Solar Field for details.

You can specify the heat transfer fluid by choosing from a list of pre-defined fluids, or by creating your ownfluid. See Specifying a Custom Heat Transfer Fluid for details.

SAM assumes that all collectors in the field use single-axis tracking with the collector tilt and azimuthdefined by the collector orientation input variables. See the variable descriptions in Input Variable Referencefor details.



The mirror washing variables determine the quantity of water required for mirror washing. See the variabledescriptions in Input Variable Reference for details.


Solar Field Parameters

Option 1 and Option 2

For Option 1 (solar multiple mode), SAM calculates the total required aperture and number of loopsbased on the value you enter for the solar multiple. For option 2 (field aperture mode), SAM calculatesthe solar multiple based on the field aperture value you enter. Note that SAM does not use the valuethat appears dimmed for the inactive option. See Sizing the Solar Field for details.

Solar multiple

The field aperture area expressed as a multiple of the aperture area required to operate the power cycleat its design capacity. See Sizing the Solar Field for details.

Field aperture

The total solar energy collection area of the solar field in square meters. Note that this is less than thetotal mirror surface area.

Row spacing (m)

The centerline-to-centerline distance in meters between rows of collectors, assuming that rows are laidout uniformly throughout the solar field.

Stow angle (degrees)

The collector angle during the hour of stow. A stow angle of zero for a northern latitude is vertical facingeast, and 180 degrees is vertical facing west.

Deploy angle (degrees)

The collector angle during the hour of deployment. A deploy angle of zero for a northern latitude isvertical facing due east. Default is 10 degrees.

Solar Field

The two solar field layout options describe the location and shape of header piping that delivers heattransfer fluid to the power block. The "I" layout represents a field where two headers emerge from thepower block in opposite directions, shown at left below. The "H" layout represents a system where tworunner pipes emerge from the power block in opposite directions and feed into two headers each, whereeach header feeds one quarter of the total loops in the field, shown at right:

Header pipe roughness (m)

The header pipe roughness is a measure of the internal surface roughness of the header and runnerpiping. SAM uses this value in calculation of the shear force and piping pressure drop in the headers.

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Surface roughness is important in determining the scale of the pressure drop throughout the system.As a general rule, the rougher the surface, the higher the pressure drop (and parasitic pumping powerload). The surface roughness is a function of the material and manufacturing method used for the piping.A conservative roughness value for extruded steel pipe (the type often used for the absorber pipe) isabout 3e-6 meters. The default value of 4.5e-5 m is based on this value and the absorber tube innerdiameter value of 0.066 m: 3e-6 m / 6.6e-2 m = 4.5e-5.

HTF pump efficiency

The electrical-to-mechanical energy conversion efficiency of the field heat transfer fluid pump. This valueaccounts for all mechanical, thermodynamic, and electrical efficiency losses.

Freeze protection temp (ºC)

The minimum temperature that the heat transfer fluid is allowed to reach in the field. The temperature atwhich freeze protection equipment is activated. The fluid temperature is maintained at this value duringhours that freeze protection is operating.

Irradiation at design (W/m2)

The design point direct normal radiation value, used in solar multiple mode to calculate the aperturearea required to drive the power cycle at its design capacity. Also used to calculate the design massflow rate of the heat transfer fluid for header pipe sizing. See Sizing the Solar Field for details.

Allow partial defocusing

Partial defocusing assumes that the tracking control system can adjust the collector angle in responseto the capacity of the power cycle (and thermal storage system, if applicable). See Defining CollectorDefocusing for details.

Heat Transfer Fluid

Field HTF fluid

The heat transfer fluid (HTF) used in the heat collection elements and headers of the solar field. SAMincludes the following options in the HTF library: Solar salt, Caloria, Hitec XL, Therminol VP-1, Hitecsalt, Dowtherm Q, Dowtherm RP. You can also define your own HTF using the user-defined HTF fluidoption

User-defined HTF fluid

To define your own HTF, choose User-defined for the Field HTF fluid and specify a table of materialproperties for use in the solar field. You must specify at least two data points for each property:temperature, specific heat, density, viscosity, and conductivity. See Specifying a Custom Heat TransferFluid for details.

Design loop inlet temp (ºC)

The temperature of HTF at the loop inlet under design conditions. The actual temperature duringoperation may differ from this value. SAM sets the power cycle's design outlet temperature equal to thisvalue.

Design loop outlet temp (ºC)

The temperature of the HTF at the outlet of the loop under design conditions. During operation, theactual value may differ from this set point. This value represents the target temperature for control of theHTF flow through the solar field and will be maintained when possible.

Min single loop flow rate (kg/s)

The minimum allowable flow rate through a single loop in the field.



Max single loop flow rate (kg/s)

The maximum allowable flow rate through a single loop in the field.

Min field flow velocity (m/s)

The minimum allowable HTF flow velocity through the field.

Max field flow velocity (m/s)

The maximum allowable HTF flow velocity through the field.

Header design min flow velocity (m/s)

A calculated value that indicates the minimum flow velocity in the field corresponding to the specifiedminimum single loop flow rate. This value is calculated using the density of the HTF at the design inlettemperature and the maximum specified receiver diameter.

Header design max flow velocity (m/s)

A calculated value that indicates the maximum flow velocity in the field corresponding to the specifiedmaximum single loop flow rate. This value is calculated using the density of the HTF at the designoutlet temperature and the minimum specified receiver diameter.

Initial field temperature (ºC)

Temperature of the HTF in the solar field in the first time step of the simulation (Hour one, typically thehour beginning at midnight on January 1). The value affects the system's performance in the first hoursof the simulation, but typically has little impact on subsequent hours and total annual plantperformance.

Design Point

Single loop aperture (m2)

The aperture area of a single loop of collectors, equal to the product of aperture width, reflective area,times the structure length times the number of collector assemblies per loop according to thedistribution of the up to four collector types in the field. This area does not include non-reflective surfaceon the collector or non-reflective space between collectors.

Loop optical efficiency

The optical efficiency when incident radiation is normal to the aperture plane, not including end lossesor cosine losses. This value does not include thermal losses from piping and the receivers.

Total loop conversion efficiency

The total conversion efficiency of the loop, including optical losses and estimated thermal losses. Usedto calculate the required aperture area of the solar field.

Total required aperture, SM=1 (m2)

The exact mirror aperture area required to meet the design thermal output for a solar multiple of 1.0.SAM uses the required aperture to calculate the actual aperture. The actual aperture may be slightlymore or less than the required aperture, depending on the collector dimensions you specify on theCollectors page.

Required number of loops, SM=1

The exact number of loops required to produce the total required aperture at a solar multiple of 1.0. Thisnumber may be a non-integer value, SAM rounds this value to the nearest integer to caculate the valueof the actual number of loops variable.

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Actual number of loops

The actual number of loops in the field, equal to the solar multiple times the required number of loops ata solar multiple of 1.0. The required number of loops is rounded to the nearest integer to represent arealistic field layout.

Actual aperture (m2)

The actual aperture area based on the actual number of loops in the field, equal to the single loopaperture times the actual number of loops.

Actual solar multiple

For Option 1 (solar multiple mode), the calculated solar multiple based on the actual (rounded) numberof loops in the field. For Option 2 (field aperture mode), the solar multiple value corresponding to thethermal output of the field based at design point: The actual aperture divided by the field thermal output.

Field thermal output (MWt)

The thermal energy delivered by the solar field under design conditions at the actual solar multiple.

Collector Orientation

Collector tilt (degrees)

The angle of all collectors in the field in degrees from horizontal, where zero degrees is horizontal. Apositive value tilts up the end of the array closest to the equator (the array's south end in the northernhemisphere), a negative value tilts down the southern end. SAM assumes that the collectors are fixedat the tilt angle.

Collector azimuth (degrees)

The azimuth angle of all collectors in the field, where zero degrees is pointing toward the equator,equivalent to a north-south axis. West is 90 degrees, and east is -90 degrees. SAM assumes that thecollectors are oriented 90 degrees east of the azimuth angle in the morning and track the dailymovement of the sun from east to west.

Land Area

Note. SAM does not use the land area variables in any calculations. The values are presented for yourreference.

Solar Field Area (m2)

The land area required for solar collectors, including space between the collectors.

Non-Solar Field Land Area Multiplier

Land area required for the system excluding the solar field land area, expressed as a fraction of thesolar field land area.

Total Land Area (m2)

Land area required for the entire system including the solar field land area.

Mirror Washing

SAM reports the water usage of the system in the results based on the mirror washing variables. Theannual water usage is the product of the water usage per wash and 365 (days per year) divided by the



washing frequency.

Water usage per wash

The volume of water in liters per square meter of solar field aperture area required for periodic mirrorwashing.

Washing frequency

The number of days between washing.

Single Loop Configuration

Number of SCA/HCE assemblies per loop

The number of individual solar collector assemblies (SCAs) in a single loop of the field. Computationally,this corresponds to the number of simulation nodes in the loop. See Specifying the Loop Configurationfor details.

Edit SCAs

Click Edit SCAs to assign an SCA type number (1-4) to each of the collectors in the loop. Use yourmouse to select collectors, and type a number on your keyboard to assign a type number to theselected collectors. SAM indicates the SCA type by coloring the rectangle representing the collector inthe diagram, and displaying the type number after the word "SCA." See Specifying the LoopConfiguration for details.

Edit HCEs

Click Edit HCEs to assign a receiver type number (1-4) to each of the collectors in the loop. Use yourmouse to select collectors, and type a number on your keyboard to assign a type number. SAMindicates the HCE type by coloring the line representing the receiver, and displaying the type numberafter the word "HCE." See Specifying the Loop Configuration for details.

Edit Defocus Order

Click Edit Defocus Order to manually define the defocus order of the collectors in the field. Click anassembly to assign the defocus order. You should assign each collector a unique defocus ordernumber. See Defining Collector Defocusing for details.

Reset Defocus

Click to reset the defocus order to the default values, starting at the hot end of the loop and proceeding

sequentially toward the cold end of the loop. See Defining Collector Defocusing for details.

Sizing the Solar FieldSizing the solar field of a parabolic trough system in SAM involves determining the optimal solar fieldaperture area for a system at a given location. In general, increasing the solar field area increases thesystem's electric output, thereby reducing the project's LCOE. However, during times there is enough solarresource, too large of a field will produce more thermal energy than the power block and other systemcomponents can handle. Also, as the solar field size increases beyond a certain point, the higherinstallation and operating costs outweigh the benefit of the higher output.

An optimal solar field area should:

Maximize the amount of time in a year that the field generates sufficient thermal energy to drive thepower block at its rated capacity.

Minimize installation and operating costs.

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Use thermal energy storage and fossil backup equipment efficiently and cost effectively.

The problem of choosing an optimal solar field area involves analyzing the tradeoff between a larger solarfield that maximizes the system's electrical output and project revenue, and a smaller field that minimizesinstallation and operating costs.

The levelized cost of energy (LCOE) is a useful metric for optimizing the solar field size because it includesthe amount of electricity generated by the system, the project installation costs, and the cost of operatingand maintaining the system over its life. Optimizing the solar field involves finding the solar field aperturearea that results in the lowest LCOE. For systems with thermal energy storage systems, the optimizationinvolves finding the combination of field area and storage capacity that results in the lowest LCOE.

Option 1 and Option 2

SAM provides two options for specifying the solar field aperture area: Option 1 (solar multiple) allows you tospecify the solar field area as a multiple of the power block's rated capacity (design gross output), andOption 2 (field aperture) allows you to specify the solar field aperture area as an explicit value in squaremeters.

Option 1: You specify a solar multiple, and SAM calculates the solar field aperture area required tomeet power block rated capacity.

Option 2: You specify the aperture area independently of the power block's rated capacity.

If your analysis involves a known solar field area, you should use Option 2 to specify the solar field aperturearea explicitly.

If your analysis involves optimizing the solar field area for a specific location, or choosing an optimalcombination of solar field aperture area and thermal energy storage capacity, then you should chooseOption 1, and follow the procedure described below to size the field.

Solar Multiple

The solar multiple makes it possible to represent the solar field aperture area as a multiple of the powerblock rated capacity. A solar multiple of one (SM=1) represents the solar field aperture area that, whenexposed to solar radiation equal to the design radiation value (irradiation at design), generates the quantityof thermal energy required to drive the power block at its rated capacity (design gross output), accountingfor thermal and optical losses.

Because at any given location the number of hours in a year that the actual solar resource is equal to thedesign radiation value is likely to be small, a solar field with SM=1 will rarely drive the power block at itsrated capacity. Increasing the solar multiple (SM>1) results in a solar field that operates at its design pointfor more hours of the year and generates more electricity.

For example, consider a system with a power block design gross output rating of 111 MW and a solarmultiple of one (SM=1) and no thermal storage. The following frequency distribution graph shows that thepower block never generates electricity at its rated capacity, and generates less than 80% of its ratedcapacity for most of the time that it generates electricity:



For the same system with a solar multiple chosen to minimize LCOE (in this example SM=1.5), the powerblock generates electricity at or slightly above its rated capacity almost 15% of the time:

Adding thermal storage to the system changes the optimal solar multiple, and increases the amount of timethat the power block operates at its rated capacity. In this example, the optimal storage capacity (full loadhours of TES) is 3 hours with SM=1.75, and the power block operates at or over its rated capacity over 20%of the time:

Note. For clarity, the frequency distribution graphs above exclude nighttime hours when the gross poweroutput is zero.

Irradiance at Design

The irradiance at design value is a reference value that represents the solar resource at a given location forsolar field sizing purposes. The value is necessary to establish the relationship between the field aperturearea and power block rated capacity for solar multiple (SM) calculations:

Total Required Aperture SM 1 = Design Gross Output ÷ (Irradiation at Design x Rated CycleConversion Efficiency x Total Loop Conversion Efficiency)

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The total loop efficiency conversion accounts for collector optical and thermal losses.

Note. The irradiance at design value is different from the solar radiation data in the weather file. SAMuses the design value to size the solar field, but not in hourly simulations.

The irradiance at design value should be close to the maximum direct radiation incident on the fieldexpected for the location. For trough systems with horizontal collectors and a field azimuth angle of zero inthe Mohave Desert of the United States, we suggest a design irradiance value of 950 W/m2. For southernSpain, a value of 800 W/m2 is reasonable for similar systems. However, for best results, you should choosea value for your specific location as described below.

Parabolic trough collectors typically track the sun by rotating on a single axis, which means that the directsolar radiation rarely (if ever) strikes the collector aperture at a normal angle. Consequently, the total energyper square meter incident on the solar field in any given hour will always be less than the direct normalradiation (DNI) value in the resource data for that hour. The cosine-adjusted DNI value is a measure of theincident irradiance. One method for choosing a design irradiation value involves finding the maximum cosine-adjusted direct normal irradiation (DNI) given a field orientation and weather data set.

In order to determine the maximum cosine-adjusted DNI for a particular location in SAM, you choose theweather file on the Climate page, run a test simulation to generate a list of hourly cosine-adjusted DNIvalues, and find the maximum value in the list. To ensure that the values are appropriate for your system,you should set the collector orientation variables on the Solar Field page (collector tilt and azimuth) to thevalues you plan to use for your analysis. For this test simulation, the only important variables are:

Location on the Climate page.

Collector tilt on the Solar Field page.

Collector azimuth on the Solar Field page.

To find the maximum cosine-adjusted annual direct normal irradiation value:

1. On the Climate page, choose a location for your system. See Climate page for details.

2. On the Solar Field page, enter values of collector tilt and azimuth for the system. See InputVariable Reference for descriptions of the input variables. You can use default values for theremaining inputs.

3. Click run all simulations, or press Ctrl-G.

4. On the Results menu, choose View Hourly Time Series (DView), or press Ctrl-T.

5. On the Boxplot tab, choose Collector_DNI-x-CosTh.

6. Read the maximum annual value from the graph. If you want to use an exact value, right-click thegraph and click Export Data to export of values to a text file, which you can open in a text editor.

Optimizing the Solar Multiple

Representing the solar field aperture area as a solar multiple (Option 1) makes it possible to run parametricsimulations in SAM and create graphs of LCOE versus solar multiple like the ones shown below. You canuse this type of graph to find the optimal solar multiple.



For a parabolic trough system with no storage, the optimal solar multiple is typically between 1.4 and 1.5.

The graph shown below is for a system with no storage in Blythe, California, the optimal solar multiple is 2,meaning that the solar field aperture area should be chosen to be twice the area required to drive the powercycle at its rated capacity:

Because the optimal solar multiple depends on the LCOE, for accurate results, you should specify all of theproject costs, financing, and incentive inputs in addition to the inputs specifying the physical characteristicsof the solar field, power cycle and storage system before the optimization. However, for preliminary results,you can use default values for any variables for which you do not have values.

The following instructions describe the steps for optimizing the solar multiple for a preliminary systemdesign that mostly uses default values except for a few key variables. This example is for a 50 MW system,but you can use the same procedure for a system of any size.

To optimize the solar field with no storage:

1. Create a new physical trough project with Utility IPP financing.

2. On the Climate page, choose a location.

3. Follow the instructions above to find an appropriate irradiation at design value for your weather data.Use zero for both the collector tilt and azimuth variables.

4. On the Power Cycle page, for Design gross output, type 55 to specify a power block with a ratednet electric output capacity of 50 MW (based on the default net conversion factor of 0.9).

5. On the Thermal Storage page, for Full load hours of TES, type 0 to specify a system with nostorage.

6. On the Solar Field page, under Solar Field Parameters, choose Option 1 (solar multiple) if it isnot already active.

7. Click Configure simulations.

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8. Click Parametrics.

9. Click Add Parametric Simulation.

10. Click Add to open the Choose Parametrics window.

11. Double-click the Physical Trough Solar Field category to show the list of solar field variables.

12. Check Solar Multiple.

Note. Do not check Actual solar multiple. The actual solar multiple is a calculated value on the solarfield page whose value you cannot change.

13. Click Edit to open the Edit Parametric Values window.

14. Type the following values: Start Value = 1, End Value = 2, Increment = 0.25.

15. Click Update. The parametric simulation setup options should look like this:

16. Click OK.

17. Click Run all simulations. SAM will run a simulation for each of the 5 solar multiple values youspecified. The simulations may take a few minutes to run.

18. On the Results page, click Add a new graph.

19. Choose the following options: Choose Simulation = Parametric Set 1, X Value = {Solar Multiple}, Y1 Values = LCOE Nominal, Graph Type = Line Plot

20. Click Accept. SAM should display a graph that looks similar to the "Nominal LCOE vs SolarMultiple (No Storage)" graph above.



21. On the graph, find the solar multiple value that results in the lowest LCOE. If the minimum LCOEoccurs at either end of the graph, you may need to add more values to the solar multiple parametricvariable to find the optimal value.

Optimal Solar Multiple for a System with Storage

Adding storage to the system introduces another level of complexity: Systems with storage can increasesystem output (and decrease the LCOE) by storing energy from an larger solar field for use during timeswhen the solar field output is below the design point. However, the thermal energy storage system's costand thermal losses also increase the LCOE.

To find the optimal combination of solar multiple and storage capacity for systems with thermal storage, runa parametric analysis as described above, but with two parametric variables instead of one: Solar multipleand Full load hours of TES (storage capacity). The parametric setup options should look similar to this:

After running simulations, you will be able to create a graph like the one below that allows you to choosethe combination of solar multiple and storage capacity that minimizes the LCOE. For example, the followinggraph shows that for a system in Blythe, California, the optimal combination of solar multiple and thermalstorage capacity is SM = 1.75 and Hours of TES = 3.

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Each line in the graph represents a number of hours of thermal energy storage from the list we saw in thelist of parametric values for the Equivalent Full Load Hours of TES variable: 0, 3, 6, 9, and 12 hours ofstorage.

For the no storage case (the dark green line, zero hours of storage), the lowest levelized cost of energyoccurs at a solar multiple of 1.25. For a given storage capacity, as the solar multiple increases, both thearea-dependent installation costs electricity output increase. The interaction of these factors causes thelevelized cost of energy to decrease as the solar multiple increases from 1, but at some point the costincrease overwhelms the benefit of the increased electric energy output, and the levelized cost of energybegins to increase with the solar multiple.

Simplified Steps for Optimizing the Solar Field

If you are performing a preliminary analysis or learning to use SAM, you can use the following simplifiedsteps, using default values for most of the inputs:

1. Choose a location on the Climate page.

2. Specify the power cycle capacity on the Power Cycle page.

3. Choose an irradiation at design value on the Solar Field page.

4. Optimize the solar field aperture area using Option 1.

Overall Steps for Optimizing the Solar Field

1. Choose a location on the Climate page.

2. Specify the power cycle capacity and other characteristics on the Power Cycle page.

3. Specify characteristics of the solar field components on the Receivers (HCEs) and Collectors (SCAs)pages.

4. If the system includes thermal energy storage, specify its characteristics on the Thermal Storage page.(Note. For systems with storage, use the optimization process in Step 8 below to find the optimalstorage capacity.)

5. Define the project costs on the Trough System Costs page.



6. Configure a single loop and specify solar field heat transfer fluid (HTF) properties on the Solar Fieldpage.

7. Specify the collector orientation on the Solar Field page.

8. Choose an irradiation at design value on the Solar Field page.

9. Either optimize the solar field aperture area using Option 1, or specify the solar field area explicitlyusing Option 2 on the Solar Field page.

10.Refine your analysis by adjusting other model parameters.

Specifying a Custom Heat Transfer FluidIf the heat transfer fluid you want to use in the solar field is not included in the Field HTF Fluid list, you candefine a custom heat transfer fluid using the User-defined option in the list. To define a custom fluid, youneed to know the specific heat, density, viscosity, kinematic viscosity, conductivity, and enthalpy of thefluid for at least two temperatures.

Table 18. Heat transfer fluids on the Field HTF Fluid list.

Name TypeMin HTF Temp

ºC

Max OperatingTemp

ºC Freeze Point Comments

Solar Salt Salt 260 600 220

Caloria mineralhydrocarbon oil

-20 300 -40 used in first Luztrough plant,SEGS I

Hitec XL Nitrate salt 150 500 120 New generation

Therminol VP-1 mixture ofbiphenyl anddiphenyl oxide

50 400 12 Standard forcurrentgeneration oilHTF systems

Hitec Nitrate salt 175 500 140 For high-temperaturesystems

Dowtherm Q Synthetic oil -30 330 -50 New generation

Dowtherm RP Synthetic oil -20 350 -40 New generation

To define a custom heat transfer fluid:

1. In the Field HTF fluid list, click User-defined.

2. In the Edit Material Properties table, change Number of data points to 2 or higher. The numbershould equal the number of temperature values for which you have data.

3. Type values for each property in the table.

You can also import data from a text file of comma-separated values. Each row in the file shouldcontain properties separated by commas, in the same the order that they appear in the EditMaterial Properties window. Do not include a header row in the file.

Keep the following in mind when you define a custom heat transfer fluid:

Each row in the materials property fluid table must be for a set of properties at a specific temperature.

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No two rows should have the same temperature value.

SAM calculates property values from the table using linear interpolation.

The rows in the table must sorted by the temperature value, in either ascending or descending order.

The physical trough model uses the temperature, specific heat, density, viscosity, and conductivityvalues. It ignores the enthalpy and kinematic viscosity values (the empirical trough model does usethose values).

Specifying the Loop ConfigurationThe solar field consists of loops of collector-receiver assemblies. On the Solar Field page, you specify thecharacteristics of a single loop in the field.

When you configure a loop, you specify the following characteristics using the single loop configurationdiagram:

Number of assemblies in a single loop.

Collector (SCA) type of each assembly in the loop.

Receiver (HCE) type of each assembly in the loop.

Collector defocusing order, if applicable.

Each rectangle in the diagram represents a collector-reciever assembly. SAM allows you to specify a singleloop of up to 35 collector-receiver assemblies, and up to four different receiver and collector types.

Note. In the current version of SAM, it is not possible to specify more than one loop. If your fieldconsists of different types of collectors and receivers, you must represent the proportion of differenttypes in a single loop.

Assembly #1, at the cold end of the loop, appears at the top left corner of the diagram. Depending on thecollector defocusing option you use, you may need to know each assembly's number to assign a collectordefocusing order. See Defining Collector Defocusing for details.



The color of the rectangle and SCA number indicates the collector type of each assembly. Similarly, thecolor of the line representing the receiver and the HCE number indicates the receiver type. The "DF" numberindicates the collector defocusing order:

The characteristics of each collector type are defined on the Collectors page, and of each receiver type onthe Receivers page.

To specify the loop configuration:

1. In Number of SCA/HCE assemblies per loop, type a number between 1 and 32. SAM displays arectangle for each assembly in the loop.

2. If the loop has more than one type of collector, define each of up to four collector types on theCollectors page. At this stage in your analysis, you can simply make note of the type number foreach collector type you plan to include in the loop and define its characteristics on the Collectorspage later.

3. Click Edit SCAs.

4. Use your mouse to select all of the collectors to which you want to assign a type number. You canuse the Ctrl key to select individual collectors.

5. Use your keyboard to type the number corresponding to the collector's type number as defined onthe Collectors page. SAM displays the collector (SCA) type number and color in the rectanglerepresenting the collector type.

6. Repeat Steps 4-5 for each collector type in the loop.

7. If the loop includes more than one receiver type, click Edit HCEs, and follow Steps 4-6 for each

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receiver (HCE) type. You can define up to four receiver types on the Receivers page.

Defining Collector DefocusingDuring hours when the solar field delivers more thermal energy than the power cycle (and thermal storagesystem, if available) can accept, or when the mass flow rate is higher than the maximum single loop flowrate defined on the Solar Field page, SAM defocuses collectors in the solar field to reduce the solar fieldthermal output. Mathematically, the model multiplies the radiation incident on the collector by a defocusingfactor. In a physical system, the collector tracker would adjust the collector angle to reduce the amount ofabsorbed energy.

SAM provides three defocusing options:

Option 1. No partial defocusing allowed: Collectors are either oriented toward the sun or in stowposition. Collectors defocus in the order you specify. You should define a defocusing order as describedbelow for this option.

Option 2. Partial defocusing allowed with sequenced defocusing: Collectors can partially defocus bymaking slight adjustments in the tracking angle. Collectors defocus in the order you specify. Youshould define a defocusing order as described below for this option.

Option 3. Partial defocusing allowed with simultaneous defocusing: Collectors can partially defocus bymaking slight adjustments in the tracking angle. All of the collectors in the field defocus by the sameamount at the same time. You do not need to define a defocusing order for this option.

To define collector defocusing option:

In the Solar Field Parameters options, choose a defocusing option (see descriptions above):

Option 1: Clear Allow partial defocusing.

Option 2: Check Allow partial defocusing, and choose Sequenced.

Option 3: Check Allow partial defocusing, and choose Simultaneous.

If you choose Option 1 or Option 2, you should define the defocus order as described in the next procedure.If you choose Option 3, SAM ignores the defocusing order displayed in the single loop diagram.

To define the defocus order:

1. If you choose Option 1 or 2 for the defocusing option, under Single Loop Configuration, click EditDefocus Order.

2. Click each collector-receiver assembly in the loop, and type a number in the Defocus Orderwindow. Assemblies are numbered starting at the top right corner of the diagram, at the cold end ofthe loop. Be sure to assign a unique defocus order number to each assembly.

Click Reset Defocus if you want the defocus order to start at the hot end of the loop and proceedsequentially to the cold end of the loop.

Equations for Calculated ValuesThis section will describe equations for the calculated values on the Solar Field page. It is currently underdevelopment. For general descriptions of the variables, see Input Variable Reference.

Min field flow velocity, Max field flow velocity

The minimum and maximum solar field HTF flow velocity depend on the minimum and maximum HTF massflow rates, HTF density at the design loop inlet temperature, and the absorber tube inner diamater specified



on the Receivers page. SAM calculates the field HTF flow velocity for the receiver type with the smallestdiameter.

Single loop aperture

Loop optical efficiency

Total loop conversion efficiency

Total required aperture, SM=1

Required number of loops, SM=1

Actual number of loops

Actual aperture

Actual solar multiple

Field thermal output

3.7.2 Collectors (SCAs)

To view the Collectors page, click Collectors (SCAs) on the main window's navigation menu. Note that forthe physical trough input pages to be available, the technology option in the Technology and Market windowmust be Concentrating Solar Power - Physical Trough System.

Contents

Overview describes the Collectors page.

Input Variable Reference describes the input variables and options on the Collectorspage.

Equations for Calculated Values describes the equations used to calculate valueson the Collectors page.

OverviewA collector (SCA, solar collector assembly) is an individually tracking component of the solar field thatincludes mirrors, a supporting structure, and receivers.

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Note. See the Troughnet website at http://www.nrel.gov/csp/troughnet/solar_field.html for moreinformation about collectors.

On the Collectors page, you can define the characteristics of up to four collector types. On the Solar Fieldpage, you specify how the different collector types are distributed in each loop of the field, assuming thatthe field consists of identical loops. SAM only uses data for collector types that you have included in thesingle loop specification on the Solar Field page


Collector Type and Configuration Name

Collector Type

Choose the active SCA type (1-4). SAM displays the properties of the active SCA type on theCollectors page. You can assign different properties to each of the up to four collector types. SeeSpecifying the Loop Configuration for details on including different SCA types in the solar field.

Configuration Name

The name of library entry for the receiver type.

Collector Geometry

Reflective aperture area (m2)

The total reflective area of a single collector, used to calculate the loop aperture area of a loop, andnumber of loops required for a solar field with the aperture area defined on the Solar Field page.

Aperture width, total structure (m)

The structural width of the collector, including reflective and non-reflective area. SAM uses this value tocalculate row-to-row shadowing and blocking effects.

Length of collector assembly (m)

The length of the collector assembly, used to calculate the length of a single assembly, and for a solarfield with an "H" layout, the length of runner pipes.

Number of modules per assembly

The number of individual collector-receiver sections in a single collector.

Average surface-to-focus path length (m)

The average distance between the collector surface and the focus of the parabola. This value is notequal to the focal length of the collector. To calculate the value when you know the focal length andaperture width, use the following equation, where F

avg is the average surface-to-focus path length:

Where a is the focal length at the vertex, and w is the aperture width




Piping distance between assemblies (m)

Length of pipes and hoses connecting collectors in a single row, not including the length of crossoverpipes.

Length of single module (m)

The length of a single collector-receiver module, equal to the collector assembly length divided by thenumber of modules per assembly.

Optical Parameters

Incidence angle modifier coeff 1-3

Coefficients for a polynomial equation defining the Incidence Angle Modifier equation. The equationcaptures the degradation of collector performance as the incidence angle (theta) of the solar radiationincreases.

Tracking error

Accounts for reduction in absorbed radiation error in collectors tracking caused by poor alignment ofsun sensor, tracking algorithm error, errors caused by the tracker drive update rate, and twisting of thecollector end at the sun sensor mounting location relative to the tracking unit end.

Geometry effects

Accounts for errors in structure geometry caused by misaligned mirrors, mirror contour distortioncaused by the support structure, mirror shape errors compared to an ideal parabola, and misaligned ordistorted receiver.

Clean mirror reflectance

The mirror reflectance input is the solar weighted specular reflectance. The solar-weighted specularreflectance is the fraction of incident solar radiation reflected into a given solid angle about the specularreflection direction. The appropriate choice for the solid angle is that subtended by the receiver asviewed from the point on the mirror surface from which the ray is being reflected. For parabolic troughs,typical values for solar mirrors are 0.923 (4-mm glass), 0.945 (1-mm or laminated glass), 0.906 (silveredpolymer), 0.836 (enhanced anodized aluminum), and 0.957 (silvered front surface).

Dirt on mirror

Accounts for reduction in absorbed radiation caused by soiling of the mirror surface. This value is notlinked to the mirror washing variables on the Solar Field page.

General optical error

Accounts for reduction in absorbed radiation caused by general optical errors or other unaccountederror sources.

Optical Calculations

Incidence angle modifier

The incidence angle modifier equation calculated as a reference for the location in question at noon onthe summer solstice. This value is not used in determining the design of the solar field.

End loss at design

Optical end loss at noon on the summer solstice due to reflected radiation spilling off of the end of thecollector assembly. This value is provided as a reference and is not used in determining the design ofthe solar field.

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Optical efficiency at design

The collector's optical efficiency under design conditions.

Equations for Calculated ValuesThis section will describe equations for the calculated values on the Collectors page. It is currently underdevelopment. For general descriptions of the variables, see Input Variable Reference.

Incidence angle modifier

Where,

IAM incidence angle modifier

F0-2

incidence angle modifier coefficients that you specify on the Collectors page

Theta solar incidence angle (zero at normal incidence)

End loss at design

Optical efficiency at design

3.7.3 Receivers (HCEs)

To view the Receivers page, click Receivers (HCEs) on the main window's navigation menu. Note that forthe physical trough input pages to be available, the technology option in the Technology and Market windowmust be Concentrating Solar Power - Physical Trough System.

Contents

Overview describes the Receivers page.

Input Variable Reference describes the input variables and options on the Receiverspage.

Specifying Receiver Type Variations describes an example of using variantweighting fraction values and different receiver types.

Equations for Calculated Values describes the equations used to calculate valueson the Receivers page.

OverviewA receiver (HCE, heat collection element) is a metal pipe contained in a vacuum within glass tube that runs



through the focal line of the trough-shaped parabolic collector. Seals and bellows ensure that a vacuum ismaintained in each tube. Anti-reflective coatings on the glass tube maximize the amount of solar radiationthat enters the tube. Solar-selective radiation absorbing coatings on the metal tube maximize the transfer ofenergy from the solar radiation to the pipe.

Note. See the Troughnet website at http://www.nrel.gov/csp/troughnet/solar_field.html for moreinformation about receivers.

On the Receivers page, you define the characteristics of up to four receiver types. On the Solar Field page,you specify how the different receiver types are distributed in each loop of the field, assuming that the fieldconsists of identical loops. SAM only uses data for receiver types that you have included in the single loopspecification on the Solar Field page.

For each receiver type, you also specify up to four variations. You can use the variations to describedifferent conditions of the receiver type. For example, you may use one variation to describe the receivertype in good condition, and another to describe the receiver type with a damaged glass envelope.


Receiver Type and Configuration Name

Receiver Type

Choose the active receiver type (1-4). SAM displays the properties of the active receiver.

Configuration Name

The name of library entry for the receiver type.

Choose receiver from library

Allows you to choose a receiver from the library of available receivers.

Receiver Geometry

Absorber tube inner diameter (m)

Inner diameter of the receiver absorber tube, this surface in direct contact with the heat transfer fluid.

Absorber tube outer diameter (m)

Outer diameter of the receiver absorber tube, the surface exposed to the annular vacuum.

Glass envelope inner diameter (m)

Inner diameter of the receiver glass envelope tube, the surface exposed to the annular vacuum.

Glass envelope outer diameter (m)

Outer diameter of the receiver glass envelope tube, the surface exposed to ambient air.

Absorber flow plug diameter (m)

A non-zero value represents the diameter of an optional plug running axially and concentrically withinthe receiver absorber tube. A zero value represents a receiver with no plug. The plug allows for anincrease in the receiver absorber diameter while maintaining the optimal heat transfer within the tubeheat transfer fluid. For a non-zero value, be sure to use annular flow for the absorber flow pattern option.


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Internal surface roughness

The surface roughness of the inner receiver pipe surface exposed to the heat transfer fluid, used todetermine flow shear force and the corresponding pressure drop across the receiver.

Surface roughness is important in determining the scale of the pressure drop throughout the system.As a general rule, the rougher the surface, the higher the pressure drop (and parasitic pumping powerload). The surface roughness is a function of the material and manufacturing method used for the piping.A conservative roughness value for extruded steel pipe (the type often used for the absorber pipe) isabout 3e-6 meters. The default value of 4.5e-5 m is based on this value and the absorber tube innerdiameter value of 0.066 m: 3e-6 m / 6.6e-2 m = 4.5e-5.

Absorber flow pattern (m)

Use standard tube flow when the absorber flow plug diameter is zero. Use annual flow with a non-zeroabsorber flow plug diameter.

Absorber material type

The material used for the absorber tube. Choose from stainless steel or copper.

Parameters and Variations

Variant weighting fraction

The fraction of the solar field that consists of the active receiver variation. For each receiver type, thesum of the four variations should equal one. See Specifying Receiver Type Variations for details.

Absorber absorptance

The ratio of radiation absorbed by the absorber to the radiation incident on the absorber.

Absorber emittance

The energy radiated by the absorber surface as a function of the absorber's temperature. You can eitherspecify a table of emittance and temperature values, or specify a single value that applies at alltemperatures.

Envelope absorptance

The ratio of radiation absorbed by the envelope to the radiation incident on the envelope, or radiationthat is neither transmitted through nor reflected from the envelope. Used to calculate the glasstemperature. (Does not affect the amount of radiation that reaches the absorber tube.)

Envelope emittance

The energy radiated by the envelope surface.

Envelope transmittance

The ratio of the radiation transmitted through the glass envelope to the radiation incident on theenvelope, or radiation that is neither reflected nor refracted away from the absorber tube.

Broken glass

Option to specify that the envelope glass has been broken or removed, indicating that the absorber tubeis directly exposed to the ambient air.

Annulus gas type

Gas type present in the annulus vacuum. Choose from Hydrogen, air, or Argon.



Annulus pressure (torr)

Absolute pressure of the gas in the annulus vacuum, in torr, where 1 torr = 133.32 Pa

Estimated avg. heat loss (W/m)

An estimated value representing the total heat loss from the receiver under design conditions. SAMuses the value to calculate the total loop conversion efficiency and required solar field aperture area forthe design point values on the Solar Field page. It does not use the value in simulation calculations.

Bellows shadowing

An optical derate factor accounting for the fraction of radiation lost after striking the mechanical bellowsat the ends of the receiver tubes.

Dirt on receiver

An optical derate factor accounting for the fraction of radiation lost due to dirt and soiling on thereceiver.

Total Weighted Losses

The total weighted losses are used in the solar field sizing calculations as an estimate of the optical andthermal losses in the solar field at the design point. SAM does not use the weighted loss variables in hourlysimulations.

Heat loss at design

The total thermal loss expected from the active receiver type under design conditions accounting for theweighting fraction of the four receiver variations. SAM uses the value to calculate the design point totalloop conversion efficiency and the solar field aperture area shown on the Solar Field page.

Optical derate

Represents the total optical losses expected from the active receiver type under design conditionsaccounting for the weighting fraction of the four receiver variations. SAM uses the value to calculate thedesign point total loop conversion efficiency and the solar field aperture area shown on the Solar Fieldpage.

Specifying Receiver Type VariationsYou can use the receiver variations to model a solar field with receivers in different conditions. If you want allof the receivers in the field to be identical, then you can use a single variation and assign it a variantweighting fraction of 1.

When you use more than one receiver variation, be sure that the sum of the four variant weighting fractionsis 1.

Here's an example of an application of the receiver variations for a field that consists of a two receiver types.The first type, Type 1, represents receivers originally installed in the field. Type 2 represents replacementreceivers installed as a fraction of the original receivers are damaged over time.

Over the life of the project, on average, 5 percent of the Type 1 receivers have broken glass envelopes, andanother 5 percent have lost vacuum in the annulus. We'll also assume that degraded receivers are randomlydistributed throughout the field -- SAM does not have a mechanism for specifying specific locations ofdifferent variations of a given receiver type. To specify this situation, we would start with Type 1, and useVariation 1 to represent the 90 percent of intact receivers, assigning it a variant weighting fraction of 0.90.We'll use Variation 2 for the 5 percent of receivers with broken glass envelopes, giving it a weighting fractionof 0.05, and Variation 3 for the other 5 percent of lost-vacuum receivers with a weighting fraction of 0.05.

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We'll assign appropriate values to the parameters for each of the two damaged receiver variations.

Next, we'll specify Type 2 to represent intact replacement receivers. We will us a single variation for theintact Type 2 receivers.

On the Solar Field page, we'll specify the single loop configuration (assuming a loop with eight assemblies),using Type 2 for the first and second assembly in the loop, and Type 1 receivers (with the variant weightingwe assigned on the Receivers page) for the remaining six assemblies in the loop.

Equations for Calculated ValuesThis section will describe equations for the calculated values on the Receivers page. It is currently underdevelopment. For general descriptions of the variables, see Input Variable Reference.

Heat loss at design

Optical derate

3.7.4 Power Cycle

To view the Power Cycle page, click Power Cycle on the main window's navigation menu. Note that for thephysical trough input pages to be available, the technology option in the Technology and Market windowmust be Concentrating Solar Power - Physical Trough System.

Contents

Overview describes the power cycle model and where to find more information aboutthe model.

Input Variable Reference describes the input variables and options on the PowerCycle page.

Modeling a Fossil-fired Backup Boiler describes the steps for including a backupboiler in the system.

Equations for Calculated Values describes the equations used to calculate valueson the Power Cycle page.

OverviewThe power cycle model represents a power block that converts thermal energy delivered by the solar fieldand optional thermal energy system to electric energy using a conventional steam Rankine cycle powerplant.

The power cycle can use either an evaporative cooling system for wet cooling, or an air-cooled system fordry cooling.

The power cycle may include a fossil-fired backup boiler that heats the heat transfer fluid before it enters the



power cycle during times when there is insufficient solar energy to drive the power cycle at its design load.

The power cycle model for the SAM physical trough model is the same as that used for the power towermodel. For a detailed description of the power cycle model, see Chapter 4 of Wagner M, 2008. Simulationand Predictive Performance Modeling of Utility-Scale Central Receiver System Power Plants. Master ofScience Thesis. University of Wisconsin-Madison. http://sel.me.wisc.edu/theses/wagner08.zip.


Plant Capacity

Design gross output (MWe)

The power cycle's design output, not accounting for parasitic losses. SAM uses this value to sizesystem components, such as the solar field area when you use the solar multiple to

specify the solar field size.

Estimated gross to net conversion factor

An estimate of the ratio of the electric energy delivered to the grid to the power cycle's gross output.SAM uses the factor to calculate the power cycle's nameplate capacity for capacity-relatedcalculations, including the estimated total cost per net capacity value on the Trough System Costspage, capacity-based incentives on the Payment Incentives page, and the capacity factor reported inthe results.

Estimated net output design (nameplate) (MWe)

The power cycle's nameplate capacity, calculated as the product of the design gross output andestimated gross to net conversion factor.

Power Block Design Point

Rated cycle conversion efficiency

The thermal to electric conversion efficiency of the power cycle under design conditions.

Design inlet temperature (ºC)

The heat transfer fluid temperature at the power cycle inlet under design conditions.

Design outlet temperature (ºC)

The heat transfer fluid temperature at the power cycle outlet under design conditions.

Boiler operating pressure (bar)

The steam pressure in the main Rankine cycle boiler at design, used to calculate the steam saturationtemperature in the boiler, and thus the driving heat transfer temperature difference between the inletheat transfer fluid and the steam in the boiler.

Boiler LHV efficiency

The back-up boiler's lower heating value efficiency, used to calculate the quantity of gas required by theback-up boiler. See Storage and Fossil Backup Dispatch Controls for details.

Heat capacity of balance of plant (kWht/ºC-MWhe)

A term to introduce additional thermal capacity into the solar field to account for thermal inertia effects

http://sel.me.wisc.edu/theses/wagner08.zip

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not directly linked to the mass of heat transfer fluid in the solar field. The units for this value are thermalkilowatt-hours per megawatt of gross electric output capacity needed to raise the balance of planttemperature one degree Celsius.

Steam cycle blowdown fraction

The fraction of the steam mass flow rate in the power cycle that is extracted and replaced by freshwater. This fraction is multiplied by the steam mass flow rate in the power cycle for each hour of plantoperation to determine the total required quantity of power cycle makeup water. The blowdown fractionaccounts for water use related directly to replacement of the steam working fluid. The default value of0.013 for the wet-cooled case represents makeup due to blowdown quench and steam cycle makeupduring operation and startup. A value of 0.016 is appropriate for dry-cooled systems to account foradditional wet-surface air cooling for critical Rankine cycle components.

Plant Control

Fraction of thermal power needed for standby

The fraction of the power cycle's design thermal input required from storage to keep the power cycle instandby mode. This thermal energy is not converted into electric power. SAM does not calculatestandby energy for systems with no storage.

Power block startup time (hr)

The time in hours that the system consumes energy at the startup fraction before it begins producingelectricity. If the startup fraction is zero, the system will operate at the design capacity during thestartup time.

Fraction of thermal power needed for startup

The fraction of the turbine's design thermal input energy required during startup. This thermal energy isnot converted to electric power.

Min required startup temp (ºC)

The temperature at which heat transfer fluid circulation through the power cycle heat exchangersbegins, typically near the power block design heat transfer fluid outlet temperature.

Max turbine over design operation

The maximum allowable power cycle output as a fraction of the electric nameplate capacity. Wheneverstorage is not available and the solar resource exceeds the irradiation at design value from the SolarField page, some collectors in the solar field are defocused to limit the power block output to themaximum load.

Min turbine operation

The fraction of the nameplate electric capacity below which the power cycle does not generateelectricity. Whenever the power block output is below the minimum load and thermal energy is availablefrom the solar field, the field is defocused. For systems with storage, solar field energy is delivered tostorage until storage is full before the field is defocused.

Cooling System

Condenser type

Choose either an air-cooled condenser (dry cooling), evaporative cooling (wet cooling), or hybrid coolingsystem.

In hybrid cooling a wet-cooling system and dry-cooling share the heat rejection load. Although there are



many possible theoretical configurations of hybrid cooling systems, SAM only allows a parallel coolingoption.

Hybrid Dispatch

For hybrid cooling, the hybrid dispatch table specifies how much of the cooling load should be handledby the wet-cooling system for each of 6 period in the year. The periods are specified in the matrices onthe Thermal Storage page. Each value in the table is a fraction of the design cooling load. For example,if you want 60% of heat rejection load to go to wet cooling in Period 1, type 0.6 for Period 1. Directingpart of the heat rejection load to the wet cooling system reduces the total condenser temperature andimproves performance, but increases the water requirement. SAM sizes the wet-cooling system tomatch the maximum fraction that you specify in the hybrid dispatch table, and sizes the air-coolingsystem to is sized to meet the full cooling load.

Ambient temp at design (ºC)

The ambient temperature at which the power cycle operates at its design-point-rated cycle conversionefficiency. For the air-cooled condenser option, use a dry bulb ambient temperature value. For theevaporative condenser, use the wet bulb temperature.

Ref. Condenser Water dT (ºC)

For the evaporative type only. The temperature rise of the cooling water across the condenser underdesign conditions, used to calculate the cooling water mass flow rate at design, and the steamcondensing temperature.

Approach temperature (ºC)

For the evaporative type only. The temperature difference between the circulating water at thecondenser inlet and the wet bulb ambient temperature, used with the ref. condenser water dT value todetermine the condenser saturation temperature and thus the turbine back pressure.

ITD at design point (ºC)

For the air-cooled type only. Initial temperature difference (ITD), difference between the temperature ofsteam at the turbine outlet (condenser inlet) and the ambient dry-bulb temperature.

Condenser pressure ratio

For the air-cooled type only. The pressure-drop ratio across the air-cooled condenser heat exchanger,used to calculate the pressure drop across the condenser and the corresponding parasitic powerrequired to maintain the air flow rate.

Min condenser pressure

The minimum condenser pressure in inches if mercury prevents the condenser pressure from droppingbelow the level you specify. In a physical system, allowing the pressure to drop below a certain pointcan result in physical damage to the system. For evaporative (wet cooling), the default value is 1.25inches of mercury. For air-cooled (dry cooling), the default is 2 inches of mercury. For hybrid systems,you can use the dry-cooling value of 2 inches of mercury.

Cooling system part load levels

The cooling system part load levels tells the heat rejection system model how many discrete operatingpoints there are. A value of 2 means that the system can run at either 100% or 50% rejection. A valueof three means rejection operating points of 100% 66% 33%. The part load levels determine how theheat rejection operates under part load conditions when the heat load is less than full load. The defaultvalue is 2, and recommended range is between 2 and 10. The value must be an integer.

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Modeling a Fossil-fired Backup BoilerTo model a system with a fossil-fired backup boiler, set the boiler LHV efficiency input variable value to anappropriate value, and define the boiler's operating schedule on the Thermal Storage page. See Storage andFossil Backup Dispatch Controls for details.

Equations for Calculated ValuesThis section will describe equations for the calculated values on the Power Cycle page. It is currently underdevelopment. For general descriptions of the variables, see Input Variable Reference.

Estimated net output at design (nameplate)

Design inlet temperature

Design outlet temperature


To view the Thermal Storage page, click Thermal Storage on the main window's navigation menu. Notethat for the physical trough input pages to be available, the technology option in the Technology and Marketwindow must be Concentrating Solar Power - Physical Trough System.

Contents

Overview describes the thermal storage model.

Input Variable Reference describes the input variables and options on the ThermalStorage page.

Storage and Fossil Backup Dispatch Controls describes the storage dispatchoptions, and the control parameters for a fossil-fired backup boiler.

Defining Dispatch Schedules explains how to assign times to the six dispatchperiods using the weekday and weekend schedules.

Equations for Calculated Values describes the equations used to calculate valueson the Thermal Storage page.

OverviewA thermal energy storage system (TES) stores heat from the solar field in a liquid medium. Heat from thestorage system can drive the power block turbine during periods of low or no sunlight. A thermal storagesystem is beneficial in many locations where the peak demand for power occurs after the sun has set.Adding thermal storage to a parabolic trough system allows the collection of solar energy to be separated



from the operation of the power block. For example, a system might be able to collect energy in themorning and use it to generate electricity late into the evening.

In direct storage systems, the solar field's heat transfer fluid itself serves as the storage medium. In indirectsystems, a separate fluid is the storage fluid, and heat is transferred from the solar field's heat transfer fluidto the storage fluid through heat exchangers. The thermal storage system consists of one or more tankpairs, pumps to circulate the liquids, and depending on the design, heat exchangers. Each tank pairconsists of a hot tank to store heat from the solar field, and a cold tank to store the cooled storage mediumafter the power block has extracted its energy.

Note. For more information on thermal energy storage systems for parabolic trough systems, see http://www.nrel.gov/csp/troughnet/thermal_energy_storage.html.

The storage system variables describe the thermal energy storage system. The thermal storage dispatchcontrol variables determine when the system dispatches energy from the storage system, and from a fossil-fired backup system if the system includes one.


Storage System

Full Load Hours of TES (hours)

The thermal storage capacity expressed in number of hours of thermal energy delivered at the powerblock's design thermal input level. The physical capacity is the number of hours of storage multiplied bythe power cycle design thermal input. Used to calculate the system's maximum storage capacity.

Storage volume (m3)

SAM calculates the total heat transfer fluid volume in storage based on the storage hours at full loadand the power block design turbine thermal input capacity. The total heat transfer fluid volume is dividedamong the total number of tanks so that all hot tanks contain the same volume of fluid, and all coldtanks contain the same volume of fluid.

TES Thermal capacity (MWt)

The equivalent thermal capacity of the storage tanks, assuming the thermal storage system is fullycharged. This value does not account for losses incurred through the heat exchanger for indirect storagesystems.

Parallel tank pairs

The number of parallel hot-cold storage tank pairs. Increasing the number of tank-pairs also increasesthe volume of the heat transfer fluid exposed to the tank surface, which increases the total tank thermallosses. SAM divides the total heat transfer fluid volume among all of the tanks, and assumes that eachhot tank contains an equal volume of fluid, and each cold tank contains and equal volume.

Tank height (m)

The height of the cylindrical volume of heat transfer fluid in each tank.

Tank fluid min height (m)

The minimum allowable height of fluid in the storage tank(s). The mechanical limits of the tankdetermine this value.



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Tank diameter (m)

The diameter of a storage tank, assuming that all tanks have the same dimensions. SAM calculatesthis value based on the specified height and storage volume of a single tank, assuming that all tankshave the same dimensions.

Min fluid volume (m3)

The volume of fluid in a tank that corresponds to the tank's minimum fluid height specified above.

Tank loss coeff (W/m2-K)

The thermal loss coefficient for the storage tanks. This value specifies the number of thermal watts lostfrom the tanks per square meter of tank surface area and temperature difference between the storagefluid bulk temperature and the ambient dry bulb temperature.

Estimated heat loss (MWt)

The estimated value of heat loss from all storage tanks. The estimate assumes that the tanks are 50%charged, so that the storage fluid is evenly distributed among the cold and hot tanks, and that the hottank temperature is equal to the solar field hot (outlet) temperature, and the cold tank temperature isequal to the solar field cold (inlet) temperature.

Tank heater set point (ºC)

The minimum allowable storage fluid temperature in the storage tanks. If the fluid temperature fallsbelow the set point, the auxiliary heaters deliver energy to the tanks, attempting to increase thetemperature to the set point.

Aux heater outlet set temp (ºC)

The temperature set point for the auxiliary heaters, assumed to be electric heaters.

Tank heater capacity (MWt)

The maximum rate at which heat can be added by the auxiliary electric tank heaters to the storage fluidin the tanks.

Tank heater efficiency

The electrical to thermal conversion efficiency of the auxiliary electric tank heaters.

Hot side HX approach temp (ºC)

Applies to systems with a heat exchanger only (indicated by a heat exchanger derate value of less thanone). The temperature difference on the hot side of the solar-field-to-thermal-storage heat exchanger.During charge cycles, the temperature is the solar field hot outlet temperature minus the storage hottank inlet temperature. During discharge cycles, it is defined as the storage hot tank temperature minusthe power cycle hot inlet temperature.

Cold side HX approach temp (ºC)

Applies to systems with a heat exchanger only (indicated by a heat exchanger derate value less thanone). The temperature difference on the cold side of the solar field-to-thermal-storage heat exchanger.During charge cycles, the temperature is the storage cold temperature (storage outlet) minus the heatexchanger cold temperature. During discharge cycles, it is the heat exchanger cold temperature minusthe storage cold temperature (storage inlet).

Heat exchanger derate

A calculated value indicating the temperature derate caused by the heat exchanger approachtemperatures. The derate factor is for reference only and not used in performance calculations. Thederate is defined as the temperature difference between the hot and the cold field design temperatures



minus the heat exchanger approach temperatures all divided by the difference between the hot and coldfield design temperatures. A derate of one indicates a system that uses the same fluid for the solar fieldheat transfer fluid and for the storage fluid and therefore does not require a heat exchanger between thesolar field and storage system.

Initial TES Fluid temp (ºC)

The temperature of the storage fluid in the thermal energy storage system in the first time step of thesimulation.

Storage HTF fluid

The storage fluid used in the thermal energy storage system. When the storage fluid and solar field heattransfer fluid (HTF) are different, the system is an indirect system with a heat exchanger (heatexchanger derate is less than one). When the storage fluid and solar field HTF are the same, thesystem is a direct system that uses the solar field HTF as the storage medium (heat exchanger derateequals one).

User-defined HTF fluid

When you choose user-defined from the Storage HTF fluid list, you can specify a table of materialproperties of a storage fluid. You must provide values for two temperatures (two rows of data) of specificheat, density, viscosity, and conductivity values. See Specifying a Custom Heat Transfer Fluid fordetails.

Fluid Temperature (ºC)

A reference value indicating the temperature at which the substance properties are evaluated for thermalstorage.

TES fluid density (kg/m3)

The density of the storage fluid at the fluid temperature, used to calculate the total mass of thermal fluidrequired in the storage system.

TES specific heat (kJ/kg-K)

The specific heat of the storage fluid at the fluid temperature, used to calculate the total energy contentof the fluid in the storage system.




The fraction of the maximum storage capacity (TES thermal capacity) required for the system to startwhen the solar field energy is greater than zero. A value of zero will always dispatch stored energy inany hour assigned to the given dispatch period; a value of one will never dispatch energy from storage.Used to calculate the storage dispatch levels.


The fraction of the maximum storage capacity (TES thermal capacity) required for the system to startwhen the solar field energy is equal to zero. A value of zero will always dispatch stored energy in anyhour assigned to the given dispatch period; a value of one will never dispatch energy from storage. Usedto calculate the storage dispatch levels.

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The fraction of the power cycle design gross output from the Solar Field page at which energy from thestorage system can drive the power cycle. See Storage and Fossil Backup Dispatch Controls fordetails.


Determines how much energy the backup boiler delivers during hours when there is insufficient energyfrom the solar field (and storage system, if available) to drive the power cycle at its design outputcapacity. A value of one for a given dispatch period ensures that the power cycle operates at its designoutput for all hours in the period: The boiler "fills in" the energy not delivered by the solar field or storagesystem. For a fossil fill fraction less than one, the boiler supplies enough energy to drive the powercycle at a fraction of its design point. To define a system with no fossil backup, use a value of zero forall six dispatch periods. See Storage and Fossil Backup Dispatch Controls for details.




When you choose a dispatch schedule from SAM's dispatch schedule library, SAM populates thepayment allocation factors with values appropriate for the schedule you choose.



Storage Dispatch

SAM decides whether or not to operate the power cycle in each hour of the simulation based on how muchenergy is available in storage, how much energy is delivered by the solar field, and the values of the thermalstorage dispatch control parameters. You can define a different dispatch strategy for each of six dispatchperiods for weekdays and weekends. See Defining Dispatch Schedules for details.

For each hour in the simulation, SAM looks at the amount of energy in storage at the beginning of the hourand decides whether or not to operate the power cycle in that hour. For each dispatch period, there are twodispatch targets for starting or continuing to run the power cycle: one for periods of sunshine (storagedispatch fraction w/solar), and one for periods of no sunshine (storage dispatch fraction w/o solar).The dispatch target for each dispatch period is the product of the storage dispatch fraction for that periodand the thermal storage capacity defined by the TES thermal capacity input variable.

During periods of sunshine when there is insufficient energy from the solar field to drive the power cycle atits load requirement, the system dispatches energy from storage only when energy in storage is greaterthan or equal to the dispatch target.



During periods of no sunshine, the power cycle will not run unless energy in storage is greater than or equalto the dispatch target.

The turbine output fraction for each dispatch period determines the power cycle output requirement forhours that fall within the dispatch period. A turbine output fraction of one defines an output requirementequivalent to the power cycle's design gross output defined on the Power Cycle page. For hours when thesolar field energy is insufficient to drive the power cycle at the output requirement, the power cycle runs onenergy from both the solar field and storage system. For hours when the solar field energy exceeds theoutput requirement, the power block runs at the required output level, and any excess energy goes tostorage. If the storage system is at capacity, the collectors in the field defocus as specified on the SolarField page to reduce the field's thermal output.

By setting the thermal storage dispatch control parameters, you can simulate a dispatch strategy for cleardays when storage is at capacity that allows the operator to start the plant earlier in the day to avoiddefocusing collectors in the field, for cloudy days that allows the operator to store energy for later use in atime period when the value of power is higher.


When the fossil fill fraction is greater than zero for any dispatch period, the system is considered toinclude a fossil-fired boiler that heats the heat transfer fluid before it is delivered to the power cycle. Thefossil fill fraction defines the backup boiler output as a function of the thermal energy from the solar field(and storage, if applicable) in a given hour and the power cycle design gross output defined on the PowerCycle page. For example, for an hour with a fossil fill fraction of 1.0 when solar energy delivered to the powercycle is less than that needed to run at the power cycle design gross output, the backup boiler wouldsupply enough energy to "fill" the missing heat, and the power cycle would operate at the design grossoutput. If, in that scenario, solar energy (from either the field or storage system) is driving the power cycle atfull load, the boiler would not operate. For a fossil fill fraction of 0.75, the boiler would only be fired whensolar output drops below 75% of the power cycle's design gross output.

The boiler LHV efficiency value on the Power Cycle page determines the quantity of fuel used by thebackup boiler. A value of 0.9 is reasonable for a natural gas-fired backup boiler. SAM includes the cost offuel for the backup system in the levelized cost of energy and other metrics reported in the results, andreports the energy equivalent of the hourly fuel consumption in the hourly simulation results. The cost of fuelfor the backup boiler is defined on the Trough System Costs page.






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Defining Dispatch SchedulesThe weekday and weekend dispatch schedules determine when each of the six dispatch periods applyduring throughout the year. You can either choose an existing schedule from one of the schedules in thedispatch schedule library or define a custom schedule. For information about libraries, see Working withLibraries.

The dispatch schedule library only assigns period numbers to the weekday and weekend schedulematrices. The dispatch fractions that you specify are not stored in the library.

Note. SAM also uses the dispatch schedules when you choose Hybrid Cooling on the Power Cyclepage to assign hybrid dispatch fractions to the periods specified in the dispatch schedules..




3. Click OK.


4. For each of the up to six periods used in the schedule, enter values for the dispatch fractions (seeStorage and Fossil Backup Dispatch Controls) described above. Use the period number and colorto identify the times in the schedule that each period applies.


1. Assign values as appropriate to the Storage Dispatch, Turbine Output Fraction, Fossil Fill Fraction,and Payment Allocation Factor for each of the up to nine periods.



4. Click OK.







Equations for Calculated ValuesThis section will describe equations for the calculated values on the Thermal Storage page. It is currentlyunder development. For general descriptions of the variables, see Input Variable Reference.

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Storage volume

TES thermal capacity

Tank diameter

Min fluid volume

Estimated heat loss

Heat exchanger derate

Fluid temperature

TES fluid density

TES specific heat

3.7.6 Parasitics

To view the Parasitics page, click Parasitics on the main window's navigation menu. Note that for thephysical trough input pages to be available, the technology option in the Technology and Market windowmust be Concentrating Solar Power - Physical Trough System.

Contents

Overview describes the purpose of the variables on the Parasitics page.

Input Variable Reference describes the input variables and options on the Parasiticspage.

Equations for Calculated Values describes the equations used to calculate valueson the Parasitics page.

OverviewThe variables on the Parasitics page define electrical loads in the system. For each hour of the simulation,SAM calculates the parasitic load and subtracts it from the power cycle's gross electrical output tocalculate the net electrical output.




Parasitics

Piping thermal loss coefficient (W/m2-K)

The thermal loss coefficient that is used to calculate thermal losses from piping between receivers,crossover piping, header piping, and runner piping. The coefficient specifies the number of thermalwatts lost from the system per pipe surface area, square meter of aperture area and temperaturedifference between the fluid in the piping and the ambient air (dry bulb temperature). The length ofcrossover piping depends on the row spacing variable on the Solar Field page, and the piping distancebetween assemblies on the Collectors page.

Tracking power (W per collector)

The amount of electrical power consumed by a single collector tracking mechanism. SAM onlycalculates tracking losses during hours when collectors are actively tracking the sun. The total fieldtracking power is calculated by multiplying this value by the number of loops in the field and number ofassemblies per loop specified on the Solar Field page.

Required pumping power for HTF through power block (kJ/kg)

A coefficient used to calculate the electric power required to pump heat transfer fluid through the powercycle. SAM applies the coefficient to all heat transfer fluid flowing through the power cycle. Thecoefficient can alternatively be defined as the pumping power divided by the mass flow rate kW/kg-s,which is equivalent to the units kJ/kg.

Required pumping power for HTF through storage (kJ/kg)

A coefficient used to calculate the electric power consumed by pumps to move heat transfer fluidthrough the storage heat exchanger on both the solar field side and the storage tank side (for caseswhere a heat exchanger exists, specified on the Thermal Storage page). This coefficient is appliedseparately to the solar field flow and the tank flow.

Fraction of rated gross power consumed at all times

A fixed electric load applied to all hours of the simulation, expressed as a fraction of rated gross powerat design from the Power Cycle page.

Balance of plant parasitic (MWe/MWcap)

A parasitic load that is applied as a function of the thermal input to the power cycle.

Aux heater, boiler parasitic (MWe/MWcap)

A parasitic load that is applied as a function of the thermal output of the auxiliary fossil-fired heaters.Applies only when the system includes fossil backup. See Modeling a Fossil-fired Backup Boiler fordetails.

Design Point Total Tracking (W)

A value displayed for reference indicating what the total tracking parasitic load would be if all collectorsin the field were actively tracking simultaneously.

Design Point Total Fixed (MWe)

The value of the fixed parasitic load applied at all times.

Design Point Total BOP (MWe)

The value of the balance-of-plant parasitic load assuming design-point operation.

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Design Point Total Aux (MWe)

The value of the auxiliary heater (for the backup gas boiler) parasitic load assuming the auxiliary heateris providing 100% of the thermal load required for the power cycle.

Equations for Calculated ValuesThis section will describe equations for the calculated values on the Parasitics page. It is currently underdevelopment. For general descriptions of the variables, see Input Variable Reference.

Tracking

Fixed

BOP

Aux

3.8 Generic Solar System

This topic is under construction.If you have questions about this topic, please contact user support:

[email protected].

This topic will describe the inputs on the Generic Solar System pages.

3.8.1 Solar Field


[email protected].

This topic will describe the inputs on the Generic Solar System Solar Field page.



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3.8.2 Power Block


[email protected].

This topic will describe the inputs on the Generic Solar System Power Block page.



[email protected].

This topic will describe the inputs on the Generic Solar System Thermal Storage page.

3.9 Power TowerA power tower system (also called a central receiver system) is a type of concentrating solar power (CSP)system that consists of a heliostat field, tower and receiver, power block, and optional storage system. Thefield of flat, sun-tracking mirrors called heliostats focus direct normal solar radiation onto a receiver at thetop of the tower, where a heat-transfer fluid is heated and pumped to the power block. The power blockgenerates steam that drives a conventional steam turbine and generator to convert the thermal energy toelectricity.

SAM's power tower performance model uses TRNSYS components developed at the University ofWisconsin and described in Simulation and Predictive Performance Modeling of Utility-Scale CentralReceiver System Power Plants, Wagner (2008) http://sel.me.wisc.edu/publications/theses/wagner08.zip (32MB).

The solar field optimization algorithm is based on the DELSOL3 model developed at Sandia NationalLaboratory, and described in A User's Manual for DELSOL3: A Computer Code for Calculating the OpticalPerformance and Optimal System Design for Solar Thermal Central Receiver Plants, Kistler (1986),(SAND86-8018) http://www.prod.sandia.gov/cgi-bin/techlib/access-control.pl/1986/868018.pdf (10 MB).

This user guide describes the power tower system input variables and some basic calculations in SAM,and is intended to be used with the two publications, which describes power tower systems and the modelalgorithms in more detail.

For an example of power tower systems, open the sample file Sample Power Tower System: On the Filemenu, click Open Sample Template and select the file from the list. The file contains three cases



http://sel.me.wisc.edu/publications/theses/wagner08.zip

http://www.prod.sandia.gov/cgi-bin/techlib/access-control.pl/1986/868018.pdf

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representing a 100 MW field of collector-receiver-engine units with and without thermal energy storage, andsample SamUL script for relative density calculation. For information about SamUL, on the Help menu, click SamUL Guide.

This section describes the system input pages that are available when the technology option in theTechnology and Market window is Concentrating Solar Power - Power Tower System.

Tower System Costs

Heliostat Field

Tower and Receiver

Power Cycle

Thermal Storage

Parasitics

User Variables

3.9.1 Heliostat Field

To view the Heliostat page, click Heliostat Field on the main window's navigation menu. Note that for thepower tower input pages to be available, the technology option in the Technology and Market window mustbe Concentrating Solar Power - Power Tower System.

Contents

Overview describes the Heliostat Field page and explains where to find moreinformation about the variables on the page.

Input Variable Reference describes the input variables on the Heliostat Field page.

Specifying the Field describes how to specify the number of heliostats and theirlocations in the field using either x-y coordinates, radial sections, or theoptimization wizard.

Working with Heliostat Field Files explains how to import heliostat location datafrom a text file, and how to export data to a text file.

OverviewThe Heliostat Field page displays the variables that specify the position of the heliostats in the solar fieldalong with the heliostat geometry and optical properties. Unlike parabolic trough and dish system designs,which can be based on modular designs of individual components, power tower system designs typicallyrequire optimization of the tower height, receiver geometry, and distribution of heliostats around the receiveras a complete system.

Page numbers relevant to this section from the Wagner (2008) and Kistler B (1986) references are:

Wagner p 10, 23-42, 49

Kistler p 25-37, 39-47, 74-75

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You can define the heliostat field layout in two ways: If you have a field layout in mind, you can enter valuesby hand. Or, you can use SAM's optimization wizard to determine the optimal layout for you.


Heliostat Properties

The heliostat properties define the area of a single heliostat mirrored surface, shape of the heliostat, and theboundaries of the solar field area. Note that SAM assumes that each heliostat employs a two-axis drivesystem with a pivot at the center of the mirrored surface.

Heliostat Width (m)

The width of the heliostat surface in meters, including the mirrored surface, edge supports and anycutouts or slots.Sandia 44

Heliostat Height (m)

The height of the heliostat surface in meters, including the mirrored surface, edge supports and anycutouts or slots.

Ratio of Reflective Area to Profile

The fraction of the area defined by the heliostat width and height that actually reflects sunlight. Thisvalue determines the ratio of reflective area on each heliostat to the total projected area of the heliostaton a plane normal to the heliostat surface. The ratio accounts for non-reflective area on the heliostatthat may cause shading of neighboring heliostats.

Use Round Heliostats (D=W)

Check the box to use round heliostats in place of the standard rectangular shape. For round heliostats,the heliostat diameter is equal to the value of the Heliostat Width variable.

Heliostat Area (m2)

The area of the heliostat mirrored area. For rectangular heliostats, the area is the product of theheliostat width and height (or the product of the square of half the width and pi for round heliostats) andthe ratio of reflective area to heliostat profile.

Mirror Reflectance and Soiling

The mirror reflectance input is the solar weighted specular reflectance. The solar-weighted specularreflectance is the fraction of incident solar radiation reflected into a given solid angle about the specularreflection direction. The appropriate choice for the solid angle is that subtended by the receiver asviewed from the point on the mirror surface from which the ray is being reflected. For parabolic troughs,typical values for solar mirrors are 0.923 (4-mm glass), 0.945 (1-mm or laminated glass), 0..906(silvered polymer), 0.836 (enhanced anodized aluminum), and 0.957 (silvered front surface).

Heliostat Availability

An adjustment factor that accounts for reduction in energy output due to downtime of some heliostats inthe field for maintenance and repair. A value of 1 means that each heliostat in the field operateswhenever sufficient solar energy is available. SAM multiplies the solar field output for each hour by theavailability factor.

Image Error (radians)

A measure of the deviation of the actual heliostat image on the receiver from the expected or idealimage that helps determine the overall shape and distribution of the reflected solar flux on the receiver.

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This value specifies the total conical error distribution for each heliostat at one standard deviation inradians. SAM applies the value to each heliostat in the field regardless of its distance from the tower.The image error accounts for all error sources, including tracking imprecision, foundation motion, mirrorwaviness, panel alignment problems, atmospheric refraction and tower sway.

Heliostat Stow Deploy Angle (degrees)

Solar elevation angle below which the heliostat field will not operate.

Wind Stow Speed (m/s)

Wind velocity from the weather file at which the heliostats defocus and go into stowed position toprotect them from possible wind damage.Wagner, 10 and 68. Mentions "ground level."

Circular Field Optimization Wizard

When the you are specifying the heliostat field using radial sections, SAM can find the optimal number ofheliostats for each section automatically. See Optimization Wizard for more information.

Note. The optimization wizard will not work if you are specifying the solar field using x-y coordinates.

Field Parameters

Total Reflective Area (m2)

Total mirrored area of the heliostat field, equal to the heliostat reflective area multiplied by the number ofheliostats. SAM uses the total field area to calculate the site improvements and heliostat costs on theTower System Costs page.

Number of Heliostats

The total number of individual heliostats in the field. SAM displays the number of heliostats based eitheron the results of the optimization wizard, or based on the data in the heliostat layout file when theheliostat locations are loaded from a text file.

Radial Step Size for Layout (m)

The radial distance between centers of heliostat field zones. The zone centers are indicated by thesymbol + in the zone layout sample diagram shown on the Heliostat Field page.

In the x-y coordinate mode, SAM disables the radial step size variable.

When you define the number of heliostats per zone by entering values in the field layout table by handor by loading a file, the radial step size is the difference between the initial maximum distance from thetower and initial minimum distance from the tower divided by the number of radial zones.

When you use the optimization wizard to specify the field, SAM calculates the radial step size as afunction of the initial minimum and maximum distances from the tower, which it in turn calculates as afunction of the ratio of the optimized tower height to the minimum and maximum tower height specifiedon the Receiver/Tower Sizing tab of the optimization wizard.

Solar Field Layout Constraints

Max Heliostat Distance to Tower Height Ratio and Min Heliostat Distance to Tower Height Ratio

The maximum and minimum ratio of the distance from the heliostat furthest and closest from the towerto the tower height.

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Max Distance to Tower and Min Distance from Tower (m)

The maximum and minimum allowable radial distances in meters between the center of the tower baseand heliostats furthest from the tower. Under certain conditions, SAM uses this value to calculate theradial step size. (See radial step size variable description below.)

Tower Height (m)

The height of the tower in meters. Specify this value on the Tower and Receiver page.

Mirror Washing

SAM reports the water usage of the system in the results based on the mirror washing variables. Theannual water usage is the product of the water usage per wash and 365 (days per year) divided by thewashing frequency.

Water usage per wash

The volume of water in liters per square meter of solar field aperture area required for periodic mirrorwashing.

Washes Per Year

Number of times per year that heliostats mirrors are washed.

Land Area

Note. SAM does not use the land area variables in any calculations. The values are presented for yourreference.

Non-Solar Field Land Area

Land area in acres required for components other than solar field components, such as the powercycle, storage, buildings, etc.

Solar Field Land Area Multiplier

The ratio of the total solar field land area to land occupied by heliostats.

Calculated Total Land Area

The total land area required for the system.

Specifying the FieldSAM allows the heliostat locations in the field to be specified either by a set of rectangular coordinates (x-y)or as a number of heliostats per radial section of the field (number of radial and azimuthal zones).

Span Angle

For external receivers the span angle should be 360 degrees. For a cavity receiver, specify a span angleless than 180 degrees. The default value for cavity receivers is 120 degrees. Specify the receiver type on the Tower and Receiver page.

Radial and Azimuthal Zones

To specify the field as a number of heliostats per radial zone enter the number of radial zones and azimuthalzones to divide the heliostat field into radial zones shown in the field diagram. You can then specify the field

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manually or automatically. To specify the field manually, either type values in the Number of Heliostats PerZone table or import the data as a text file. To specify the field automatically, use the optimization wizard tospecify a set of optimization parameters and allow SAM to optimize the heliostat field design and calculatethe optimal number of heliostats per zone, receiver tower height, receiver height and diameter, and othervariables.

The solar field is divided into evenly distributed sections of a circle called zones, as shown in the samplediagram on the Heliostat Field page. The rows of the table specify the radial position if each zone relative tothe tower located at the center of the field. The zone closest to the tower is assigned the number one, witheach successively farther zone incrementing by one. The columns specify the position of the zone's centerin degrees east of due north, where zero is north, 90 degrees is east, 180 degrees is south, and 270degrees is west. The number of heliostats per zone can be a non-integer value because SAM converts thevalue to a mirror surface area for each zone that is equivalent to the total mirrored surface of all heliostats inthe zone.

Rectangular (x-y) Coordinates

To specify the field as a set of rectangular coordinates, change the value of Azimuthal Zones to 2, and enterthe number of heliostats for # of Heliostats. You can then either type the x-y coordinates of each heliostat inthe field, or import a text file of x-y coordinates. SAM displays the location of each heliostat on the fielddiagram. It models the system based on the heliostat locations specified by the set of x-y locations, andbased on the values you specify for the tower height, receiver height, receiver diameter, and other inputvalues. This approach is appropriate for predicting the output of a system with a known design. Theoptimization wizard does not work in the x-y coordinate mode.

Each row specifies the position of an individual heliostat relative to the tower. The first column in the tablespecifies the x-coordinate along the east-west axis of the field, with negative values indicating positionswest of the tower, and positive values indicating positions east of the tower. The second column specifiesthe y-coordinate along the north-south axis, with positive values indicating positions north of the tower, andnegative values indicating positions south of the tower. The tower is assumed to be at 0,0. Note that thisconvention also applies to systems in the southern hemisphere. In the x-y coordinate mode, SAM requiresthat the field be symmetric about the north-south axis.

Working with Heliostat Field FilesSAM allows you to use text files to save and load field layout data when you specify the field layout by handinstead of relying on the optimization wizard to calculate the optimal layout.

For radial zone data, each row in the file represents a radial step (distance away from the center of thecircle), and each column represents an azimuthal division (distance clockwise around the circle from thezero degree line pointing north), as shown on the sample layout diagram. The first row must contain data forthe radial step closest to the center of the field, and subsequent rows should be in consecutive order awayfrom the center. The first column of each row must contain data for the azimuthal division containing thenorth line at zero degrees, and the second column the next division moving counterclockwise from the firstcolumn, and so on. Zones with no heliostats should be indicated by a zero. Each column in the file shouldbe separated by a space, and each row by a new line. For example, a text file with the following contentswould describe a field with three radial steps and four azimuthal divisions:

9.0 10.0 9.0 10.0

15.5 15.5 15.5 15.5

22.5 18.0 18.5 22.5

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For rectangular coordinate data, each row represents an individual heliostat position in the field, with the xcoordinate in the first column and the y coordinate in the second column. A positive x value is east, and apositive y value is north of the tower. Use negative values for positions west and south of the tower. Theheliostat coordinates do not have to be in a particular order in the file. Each column in the file should beseparated by a space, and each row by a new line. A file with the following contents would describe a solarfield with three heliostats at (x = 0.0, y = 75.0), (x = 7.5, y = 70.0), and (x = 15.0, y = 65.0):

0.0 75.0

7.5 70.0

15.0 65.0

3.9.2 Optimization Wizard

To start the power tower optimization wizard, first click Heliostat Field on the main window's navigationmenu to view the Heliostat Field page, and then follow the instructions below. Note that for the power towerinput pages to be available, the technology option in the Technology and Market window must beConcentrating Solar Power - Power Tower System.

Contents

Overview describes the optimization wizard.

Input Variable Reference describes the input variables on the Optimization Wizardwindow.

Overview of the Optimization Process explains how SAM searches for the optimalsolution and lists the input variables that are affected by the optimization.

Guidelines for Choosing Variable Ranges for Optimization explains how to choosevalues for the variables in the Optimization Wizard window.

OverviewThe power tower optimization wizard simplifies the task of choosing values for the relatively large number ofinput parameters required to specify the power tower solar field and receiver. Because the heliostat field istypically the most capital intensive part of a power tower project, often accounting for 30-40% of the totalinstallation cost, optimizing the heliostat field size is a critical step in minimizing overall project cost.

The optimization wizard searches for a set optimal system parameter values, where the optimal system isdefined as the one that results in the lowest levelized cost of energy. Note that the optimization process isseparate from the simulation process. When you run the wizard, it populates some of the input variables inthe SAM input pages (listed below) with optimal values. Before running simulations, you can choose toeither keep the values generated by the wizard or modify them.

The wizard's underlying code is based on the DELSOL3 code from Sandia National Laboratory (Kistler

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1986, see References), and is implemented in SAM through the PTGen program described in the thesisSimulation and Predictive Performance Modeling of Utility-Scale Central Receiver System Power Plants(Wagner 2008) http://sel.me.wisc.edu/theses/wagner08.zip (33 MB).

To use the optimization wizard:

1. On the Tower System Costs page, enter values for the capital costs.

2. On the Heliostat Field page, click Start Wizard to start the wizard.

SAM initially populates the variables in the wizard with values from the Heliostat Field, Tower andReceiver, and Power Cycle pages. SAM assigns values to variables that don't appear elsewhere,such as Minimum Tower Height and Maximum Tower Height, using either default values or valuesbased on the last time the wizard ran.

3. Enter values to define the parameters of the optimization.

4. Click Optimize Solar Field.

5. After the wizard finishes running, click Close.

6. Review the variables on the input pages. Modify any values as needed, and then configure and runsimulations to simulate the system(s) and display annual production, levelized cost of energy, andother results on the Results page.


Solar Field

Solar Multiple

The ratio of of the receiver's design thermal output to the power block's design thermal input. Forsystems with no storage, the solar multiple should be close to or equal to one.

Receiver and Tower

The receiver and tower optimization variables determine the optimization search range and step size forthe receiver and tower dimensions.

External Receiver and Tower

Note. The external receiver and tower variables are active when you specify External Receiver on theTower and Receiver page.

Min Receiver Diameter (m)

The minimum value for the range of receiver diameter values that the wizard will search for an optimalsolution.

Max Receiver Diameter (m)

The maximum value for the range of receiver diameter values that the wizard will search for an optimalsolution.

Optimization Levels for Receiver Diameter

The number of receiver diameter values to evaluate in the search for an optimal solution. The maximumallowed number of optimization levels is 10.

http://sel.me.wisc.edu/theses/wagner08.zip

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Min Receiver Height / Diameter Ratio

The minimum receiver height to receiver diameter ratio for the range of values that the wizard will searchfor the optimal solution.

Max Receiver Height / Diameter Ratio

The maximum receiver height to receiver diameter ratio for the range of values that the wizard willsearch for the optimal solution.

Optimization Levels for Receiver H/D Ratio

The number of receiver height to diameter ratio values to evaluate in the search for an optimal solution.The maximum allowed number of optimization levels is 10.

Min Tower Height (m)

The minimum value for the range of tower height values that the wizard will search for an optimalsolution.

Max Tower Height (m)

The maximum value for the range of tower height values that the wizard will search for an optimalsolution.

Optimization Levels for Tower Height

The number of tower height values to evaluate in the search for an optimal solution. The maximumallowed number of optimization levels is 10.

Cavity Receiver and Tower

Note. The cavity receiver and tower variables are active when you specify Cavity Receiver on the Towerand Receiver page.

Min Aperture Width (m)

The minimum value for the range of receiver aperture width values that the wizard will search for anoptimal solution.

Max Aperture Width (m)

The maximum value for the range of receiver aperture width values that the wizard will search for anoptimal solution.

Optimization Levels for Aperture H/W Ratio

The number of aperture height to width ratio to evaluate in the search for an optimal solution. Themaximum allowed number of optimization levels is 10.

Min Aperture Height / Width Ratio

The minimum aperture height to width ratio for the range of values that the wizard will search for theoptimal solution.

Max Aperture Height / Width Ratio

The maximum aperture height to width ratio for the range of values that the wizard will search for theoptimal solution.

Optimization Levels for Receiver H/D Ratio

The number of receiver height to diameter ratio values to evaluate in the search for an optimal solution.

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The maximum allowed number of optimization levels is 10.

Min Tower Height (m)

The minimum value for the range of tower height values that the wizard will search for an optimalsolution.

Max Tower Height (m)

The maximum value for the range of tower height values that the wizard will search for an optimalsolution.

Optimization Levels for Tower Height

The number of tower height values to evaluate in the search for an optimal solution. The maximumallowed number of optimization levels is 10.

Overview of the Optimization ProcessFor each variable that is specified as a range in the optimization wizard, the wizard searches for the valuewithin the range that meets the performance requirements at the lowest levelized cost of energy. The wizardsearches discrete combinations of options based on the "optimization level" of each optimized variable. Forexample, if the minimum tower height is specified as 150 m and the maximum 250 m, and the tower heightoptimization level is 10, the wizard will simulate 10 systems with unique tower heights evenly incrementedbetween 150 m and 250 m. Be sure to choose reasonable ranges and step sizes to minimize the number ofcalculations the wizard must perform.

The solar multiple is the ratio of of the receiver's design thermal output to the power block's design thermalinput. The optimization wizard uses the solar multiple to calculate the receiver's thermal rating, which isequal to the solar multiple multiplied by the power cycle nameplate electric capacity divided by the ratedcycle conversion efficiency, both of which are on the Power Cycle page.

The wizard holds the following variables constant as it searches for the optimal system:

Solar Multiple on the Optimization Wizard window.

Nameplate Capacity on the Power Cycle page.

Heliostat Width on the Heliostat Field page.

Heliostat Height on the Heliostat Field page.

Maximum Receiver Flux on the Tower and Receiver page.

The wizard searches within the specified ranges to find optimal values of the following variables on the Towerand Receiver page.When the wizard finishes running, SAM populates the variables with the optimal values.

Receiver Diameter

Receiver Height (calculated as a function of the receiver height to the receiver diameter ratio)

Tower Height

SAM also populates the following variables on the Heliostat Field page with values from the wizard:

Radial Step Size for Layout

Total Reflective Area

Number of Heliostats

Number of heliostats per radial zone in the field layout table

The optimization wizard uses the following values from the input pages, but does not change their values.

From the Heliostat Field page:

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Heliostat Width

Heliostat Height

Ratio of Reflective Area to Profile

Mirror Reflectivity and Soiling

Use Round Heliostats

Max Distance from Tower

Min Distance from tower

Image Error

Number of Radial Zones

Number of Azimuthal Zones

From the Tower and Receiver page:

Coating Absorptivity

Max Receiver Flux

From the Power Cycle page:

Nameplate Capacity

Rated Cycle Conversion Efficiency

It is possible that the wizard will not find an optimal field layout given a set of values that you provide.Finding an optimal set of input parameters is often an iterative process that may require you to run theoptimization wizard and adjust input value ranges several times until the wizard finds a reasonable fieldlayout for your analysis. When the wizard cannot find an optimal layout, it displays a message withsuggestions for adjustments. Typically, the suggestions include adjusting the upper or lower limits ofoptimization variables, and ensuring that the minimum and maximum heliostat distance from tower valuesare reasonable. Keep in mind that because the wizard uses capital costs from the Tower System Costspage in the optimization process, unreasonable cost values may also prevent the wizard from finding anoptimal field layout. In some cases, wizard will fail to find an optimal design and exit without notice. Whenthat happens, check to see if the values of optimized variables shown on the input pages are outside of therange specified for those variables in the wizard, and try adjusting the ranges you specified and rerunningthe wizard.

Guidelines for Choosing Variable Ranges for OptimizationThe optimization wizard does its best to find parameter values for an optimal system within the searchranges you specify on the wizard input tabs. Because the wizard searches a discrete number of valueswithin the range for each parameter, defining too broad of a range increases the chances that the optimalvalue lies between the values included in the search. On the other hand, defining too narrow a rangeincreases the chances that the optimal value lies outside of the search range.

The ability of the optimization wizard to find an optimal system is sensitive to the following variable ranges:

Receiver diameter range, defined by Minimum Receiver Diameter and Maximum Receiver Diameter.

Receiver height to diameter ratio range, defined by Minimum Receiver Height/Diameter Ratio andMaximum Receiver Height/Diameter Ratio.

Tower height range, defined by Minimum Tower Height and Maximum Tower Height.

Heliostat distance from tower range, defined by Maximum Distance from Tower and Minimum Distancefrom Tower values on the Heliostat Field page.

The following rules of thumb may be helpful in choosing search ranges for these variables, although they

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may not apply to some systems.

Tower height: The tower height typically falls between 15 m for very small systems (5 MWe) and 300 mfor very large systems (150 MWe). For example, a reasonable range for a 30 MWe system with a solarmultiple of 1.0 would be between 40 m and 120 m.

Receiver diameter: The optimization wizard searches for a receiver diameter value that maximizesabsorbed radiation from the heliostat field within the flux limit defined by the maximum value on theReceiver/Tower page. Like the tower height, the receiver area typically scales with system's designthermal power. For very small systems, the optimal receiver diameter is typically between 1 m and 3 m,while very large systems may require a diameter of 25 m.

Receiver height to diameter ratio: This ratio should generally fall between 0.5 and 2.0.

Heliostat distance from tower: If the minimum distance is too small, the inner zones in the heliostat willcontain no heliostats (the first rows in the field layout table on the Heliostat Field page contain zeros),which will cause the simulation to fail. If the maximum distance is too large, the outer zones willcontain no heliostats. On the other hand, if the maximum distance is too small, all of the outer zoneswill contain heliostats. For very small systems, the maximum distance might be set to 300 m, and forvery large systems, a distance of 2000 m might be appropriate.

3.9.3 Tower and Receiver

To view the Tower and Receiver page, click Tower and Receiver on the main window's navigation menu.Note that for the power tower input pages to be available, the technology option in the Technology andMarket window must be Concentrating Solar Power - Power Tower System.

Contents

Overview describes the Tower and Receiver page and where to find additionalinformation about the tower and receiver model.

Input Variable Reference describes the input variables on the Tower and Receiverpage.

OverviewThe Tower and Receiver page displays variables that specify the geometry of the heat collection system.The receiver model uses semi-empirical heat transfer and thermodynamic relationships to determine thethermal performance of the receiver. This allows the model to represent a wide array of geometries withoutdeviating from a hypothetical reference system.


Wagner p 43-47, 68-71

The model makes several assumptions about the system geometry for external receivers:

The receiver consists of a discrete number of panels.

Each panel in the receiver consists of a set of parallel tubes in thermal contact that share a common

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heat transfer fluid (HTF) header.

The panel tubing is vertical and the heat transfer fluid flows through each sequential panel in aserpentine pattern (up one panel and down the adjacent panel).

The number of tubes per panel is a function of the Number of Panels, Receiver Diameter, and TubeOuter Diameter variables.

The model varies the heat transfer fluid mass flow rate through the receiver to maintain the required outletheat transfer fluid temperature. The model includes several practical safeguards to ensure realistic behaviorin the receiver. For example, the mass flow rate through the receiver is limited to the value of the Max FlowRate to Receiver variable, and the maximum receiver heat transfer fluid inlet temperature is kept at a valuebelow the value of the Max Temp to Receiver variable.

SAM allows several options for the heat transfer fluid flow patterns through the receiver as indicated by thediagrams on the Receiver / Tower page. The Flow Pattern variable specifies the path taken by the fluid as itpasses through the receiver. Options include a full circle around the receiver, a split path around thereceiver, and a split pass with a single cross-over.


Receiver Options

SAM models power tower systems with either an external receiver or cavity receiver. When you change thereceiver option, you should run the optimization wizard to optimize the field for the new receiver type.

External Receiver

Note. The external receiver parameters are only active when you select External Receiver.

For analyses involving the optimization wizard to optimize the heliostat field layout, SAM populates thesevariables with optimal values. You can change the values after running the optimization wizard, but resultswill no longer be for the optimal system.

Receiver Height (m)

Height in meters of the receiver panels.

Receiver Diameter (m)

Total diameter in meters of the receiver.The distance from center of the receiver to center of a receiverpanel. The width of a single panel is the circumference of receiver divided by number of panels.

Number of Panels

Number of vertical panels in the receiver.

Coating Emittance

The emissivity of the receiver coating, assumed to be black-body emissivity constant over the range ofwavelengths.

Enable Night Recirculation through Receiver

With night circulation enabled, whenever the radiation incident on the receiver is zero, hot heat transferfluid circulates through the receiver to prevent fluid in the receiver from freezing. For systems withstorage, the system pumps heat transfer fluid from hot storage. For systems with no storage, or whenthere is insufficient energy in storage, the circulating fluid is heated with an electric heater. The heat

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transfer fluid is assumed to enter the receiver at the temperature required for it to exit the receiver at therequired outlet temperature, accounting for thermal losses. SAM ajdusts the heat transfer fluid massflow rate accordingly.

Recirculation Heater Efficiency

With night circulation enabled, the electric-to-thermal conversion efficiency of the heater used to supplythermal energy for preventing the receiver heat transfer fluid from freezing. SAM calculates the heaterelectricity based on the required thermal recirculation energy and the heater efficiency, and reports thehourly electricity required by the heater as Par_recirc_htr in the hourly results.

Cavity Receiver

SAM assumes that the cavity receiver consists of four panels arranged at the circumference of a semicircle:

Where:

HL: Lip height

HA: Aperture height

HP: Internal panel height

WA: Aperture width

Notes.

The cavity receiver parameters are only active when you select Cavity Receiver.

If you run the optimization wizard, SAM automatically populates the cavity receiver values. If you modifythese values, they will be inconsistent with other values calculated by the wizard.

Aperture Width

The width of the rectangle in the plane of the cavity opening.

Aperture Height To Width Ratio

The ratio of aperture height to aperture width.

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Aperture Height

The height of the rectangle in the plane of the cavity opening: Aperture Height = Aperture Width ×Aperture Height to Width Ratio. Note that the receiver height may be greater than the aperture height.

Lip to Height Ratio

The "lip" is the difference between the aperture height and receiver height.

Internal Panel Height

The internal height of the panel: Internal Height = Aperture Height × (1 + Lip to Height Ratio).

Aperture Lip Height

The height of the aperture lip: Aperture Lip Height = Internal Panel Height × Lip to Height Ratio

Receiver Thermodynamic Characteristics

Tube Outer Diameter (mm)

The outer diameter in millimeters of the tubing that carries the heat transfer fluid through the receiverpanels. Typical values range from 25 mm to 50 mm.

Tube Wall Thickness (mm)

The thickness in millimeters of the individual receiver panel tube walls.

Required Outlet HTF Temp (°C)

The temperature set point in degrees Celsius for the heat transfer fluid at the receiver outlet.

Max Temp to Receiver (°C)

The maximum allowable temperature of the heat transfer fluid at the receiver inlet.

Coating Absorptance

Absorptance fraction of receiver tube coating. Typical values are 0.91 to 0.95.

Heat Loss Factor

A receiver heat loss adjustment factor that can be used when the calculated heat loss value deviatesfrom an expected value. The default value is 1, corresponding to no heat loss correction. The calculatedreceiver heat loss is the sum of convection and radiation losses from the receiver, reported in the hourlyresults as Rec_conv_loss and Rec_rad_loss, respectively.

Max Flow Rate to Receiver (kg/s)

The maximum heat transfer fluid flow rate at the receiver inlet. SAM calculates this value as a functionof the maximum heat transfer fluid velocity in the receiver.

Max Receiver Flux (kW/m2)

The upper limit of solar radiation incident on the receiver allowed to be reflected from the heliostat field.SAM ensures that the optimal receiver size and heliostat positions do not result in a receiver flux thatexceeds this value.

Materials and Flow

HTF Type

One of two types of solar salt used for the heat transfer fluid, also called the working fluid. You can alsoadd a user defined HTF by choosing the user defined option and clicking the Edit button to open theHTF properties editor.

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Property table for user-defined HTF

When the HTF type is "user defined," the Edit button provides access to the HTF properties editor.

Material Type

The material of the receiver panel tubes, typically a stainless-steel alloy. The current version of SAMallows only one material type.

Flow Pattern

One of eight heat available transfer fluid flow configurations shown in the diagram.

For an external receiver, the views are from the top of the receiver, assuming that panels are arranged ina circle around the center of the receiver. Arrows show the direction of heat transfer fluid flow into,through, and out of the receiver.

For a cavity receiver SAM assumes four panels, and one of eight available flow patterns through thepanels.

Design Operation

Solar Multiple

This value is populated by the optimization wizard, but you can modify it to use a different value thanthe one calculated by the wizard. If you modify the solar multiple without running the optimizationwizard, the receiver design thermal power will change, but the solar field will not. The solar multiple isthe ratio of of the receiver's design thermal output to the power block's design thermal input. Forsystems with no storage, the solar multiple should be close to or equal to one.

Min receiver turndown fraction

The minimum allowable fraction of the maximum flow rate to receiver.

Max receiver operation fraction

The maximum allowable fraction of the maximum flow rate to receiver. SAM removes heliostats fromoperation if the HTF mass flow rate exceeds the maximum allowable value.

Receiver design thermal power

Product of solar multiple and power cycle design thermal power on the Power Cycle page.

Receiver startup delay time

The time in hours required to start the receiver. The receiver starts whenever the radiation incident onthe field in the previous hour is zero, and there is sufficient thermal energy in the current hour to meetthe thermal design requirement. SAM calculates the start up energy as the product of the availablethermal energy, startup delay time, and startup delay energy fraction.

Receiver startup delay energy fraction

Fraction of receiver design thermal power required by the receiver during the startup period.

Tower Dimension

Tower Height (m)

Height in meters of the tower structure from the ground, equal to the vertical distance between theheliostat pivot points and the vertical center of receiver.

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3.9.4 Power Cycle

To view the Power Cycle page, click Power Cycle on the main window's navigation menu. Note that for thepower tower input pages to be available, the technology option in the Technology and Market window mustbe Concentrating Solar Power - Power Tower System.

Contents

Overview describes the Power Cycle page and where to find additional informationabout the power cycle model.

Input Variable Reference describes the input variables on the Power Cycle page.

OverviewThe power cycle converts thermal energy to electric energy. The power cycle is assumed to consist of aRankine-cycle steam engine, two open feed-water heaters, and a pre-heater, boiler and super-heater.

The parameters on the Power cycle page describe the steam turbine size and other properties.


Wagner 83, 86, 114, 164

Kistler 224

The power cycle page displays variables that specify the design operating conditions for the steam Rankinecycle used to convert thermal energy to electricity.


Plant Capacity

Design Turbine Gross Output (MWe)

The power cycle's design output, not accounting for parasitic losses.

Estimated Gross to Net Conversion Factor

An estimate of the ratio of the electric energy delivered to the grid to the power cycle's gross output.SAM uses the factor to calculate the power cycle's nameplate capacity for capacity-relatedcalculations, including the estimated total cost per net capacity value on the System Costs page, andthe capacity factor reported in the results.

Estimated Net Output design (nameplate) (MWe)

The power cycle's nameplate capacity, calculated as the product of the design gross output andestimated gross to net conversion factor.

Power Block Design Point

Rated Cycle Conversion Efficiency

The thermal to electric conversion efficiency of the power cycle under design conditions.

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Design Thermal Power (MWt)

The turbine's design thermal input. It is the thermal energy required at the power block inlet for it tooperate at its design point, as defined by the value of the nameplate electric capacity and an estimateof the parasitic losses: Design thermal power = nameplate electric capacity + total parasitic lossestimate. (See the Parasitics page for a description of the total parasitic loss estimate.)

Design HTF Inlet Temp (°C)

The design temperature in degrees Celsius of the hot heat transfer fluid at the power block inlet.p 114.design htf inlet temperature can be different from receiver outlet temperature when power block designspecifications require a different inlet temperature for maximum efficiency. The design values are theoperating conditions at which the power block operates at its nameplate capacity.

Design HTF Outlet Temp (°C)

The design temperature in degrees Celsius of the cold heat transfer fluid at the power block outlet.p 114The design values are the operating conditions at which the power block operates at its nameplatecapacity.

Boiler Operating Pressure (Bar)

The saturation pressure of the steam as it is converted from liquid to vapor in the boiler or steamgenerator. SAM uses this value to determine the steam's saturation temperature and thus thesuperheating capability of the heat exchangers. The temperature difference that drives the steam massflow rate in the Rankine cycle is the difference between the hot heat transfer fluid inlet temperature andthe saturation temperature of the steam boiler pressure.

Fossil Backup Boiler LHV Efficiency

The backup boiler's lower heating value efficiency, used to calculate the quantity of gas required by theboiler.

Steam cycle blowdown fraction

The fraction of the steam mass flow rate in the power cycle that is extracted and replaced by freshwater. This fraction is multiplied by the steam mass flow rate in the power cycle for each hour of plantoperation to determine the total required quantity of power cycle makeup water. The blowdown fractionaccounts for water use related directly to replacement of the steam working fluid. The default value of0.013 for the wet-cooled case represents makeup due to blowdown quench and steam cycle makeupduring operation and startup. A value of 0.016 is appropriate for dry-cooled systems to account foradditional wet-surface air cooling for critical Rankine cycle components.

Plant Control

Min Required Temp for Startup (°C)

The temperature at which heat transfer fluid circulation through the power cycle heat exchangersbegins, typically near the power block design heat transfer fluid outlet temperature. Default is 500degrees.

Low-Resource Standby Period (hours)

During periods of insufficient flow from the heat source due to low thermal resource, the power blockmay enter standby mode. In standby mode, the cycle can restart quickly without the startup periodrequired by a cold start. The standby period is the maximum number of hours allowed for standbymode. This option is only available for systems with thermal storage. Default is 2 hours.

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Fraction of Thermal Power Needed for Standby

The fraction of the turbine's design thermal input required from storage to keep the power cycle instandby mode. This thermal energy is not converted into electric power. Default is 0.2.

Power Block Startup Time (hours)

The time in hours that the system consumes energy at the startup fraction before it begins producingelectricity. If the startup fraction is zero, the system will operate at the design capacity over the startuptime. Default is 0.5 hours.

Fraction of Thermal Power Needed for Startup

The fraction of the turbine's design thermal input required by the system during startup. This thermalenergy is not converted to electric power. Default is 0.75.

Min Turbine Operation

The fraction of the nameplate electric capacity below which the power block does not generateelectricity. Whenever the power block output is below the minimum load and thermal energy is availablefrom the solar field, the field is defocused. For systems with storage, solar field energy is delivered tostorage until storage is full. Default is 0.25.

Max Turbine Over Design Operation

The maximum allowable power block output as a fraction of the electric nameplate capacity. Wheneverstorage is not available and the solar resource exceeds the design value of 950 W/m2, some heliostatsin the solar field are defocused to limit the power block output to the maximum load. Default is 1.05.

Cooling System

Condenser type

Choose either an air-cooled condenser (dry cooling), evaporative cooling (wet cooling), or hybrid coolingsystem.

In hybrid cooling a wet-cooling system and dry-cooling share the heat rejection load. Although there aremany possible theoretical configurations of hybrid cooling systems, SAM only allows a parallel coolingoption.

Hybrid Dispatch

For hybrid cooling, the hybrid dispatch table specifies how much of the cooling load should be handledby the wet-cooling system for each of 6 period in the year. The periods are specified in the matrices onthe Thermal Storage page. Each value in the table is a fraction of the design cooling load. For example,if you want 60% of heat rejection load to go to wet cooling in Period 1, type 0.6 for Period 1. Directingpart of the heat rejection load to the wet cooling system reduces the total condenser temperature andimproves performance, but increases the water requirement. SAM sizes the wet-cooling system tomatch the maximum fraction that you specify in the hybrid dispatch table, and sizes the air-coolingsystem to is sized to meet the full cooling load.

Ambient temp at design (ºC)

The ambient temperature at which the power cycle operates at its design-point-rated cycle conversionefficiency. For the air-cooled condenser option, use a dry bulb ambient temperature value. For theevaporative condenser, use the wet bulb temperature.

Ref. Condenser Water dT (ºC)

For the evaporative type only. The temperature rise of the cooling water across the condenser underdesign conditions, used to calculate the cooling water mass flow rate at design, and the steam

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condensing temperature.

Approach temperature (ºC)

For the evaporative type only. The temperature difference between the circulating water at thecondenser inlet and the wet bulb ambient temperature, used with the ref. condenser water dT value todetermine the condenser saturation temperature and thus the turbine back pressure.

ITD at design point (ºC)

For the air-cooled type only. Initial temperature difference (ITD), difference between the temperature ofsteam at the turbine outlet (condenser inlet) and the ambient dry-bulb temperature.

Condenser pressure ratio

For the air-cooled type only. The pressure-drop ratio across the air-cooled condenser heat exchanger,used to calculate the pressure drop across the condenser and the corresponding parasitic powerrequired to maintain the air flow rate.

Min condenser pressure

The minimum condenser pressure in inches if mercury prevents the condenser pressure from droppingbelow the level you specify. In a physical system, allowing the pressure to drop below a certain pointcan result in physical damage to the system. For evaporative (wet cooling), the default value is 1.25inches of mercury. For air-cooled (dry cooling), the default is 2 inches of mercury. For hybrid systems,you can use the dry-cooling value of 2 inches of mercury.

Cooling system part load levels

The cooling system part load levels tells the heat rejection system model how many discrete operatingpoints there are. A value of 2 means that the system can run at either 100% or 50% rejection. A valueof three means rejection operating points of 100% 66% 33%. The part load levels determine how theheat rejection operates under part load conditions when the heat load is less than full load. The defaultvalue is 2, and recommended range is between 2 and 10. The value must be an integer.


To view the Thermal Storage page, click Thermal Storage on the main window's navigation menu. Notethat for the power tower input pages to be available, the technology option in the Technology and Marketwindow must be Concentrating Solar Power - Power Tower System.

Contents

Overview describes the Thermal Storage page.

Input Variable Reference describes the input variables on the Thermal Storagepage.

Storage and Fossil Backup Dispatch Controls describes the dispatch controls thatdetermine the timing of energy releases from the storage and fossil back upsystems.

Defining Dispatch Schedules explains how to assign dispatch periods to weekdayand weekend schedules.

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OverviewThe parameters on the Thermal Storage page describe the properties thermal energy storage system andthe storage dispatch controls.

The power tower storage model uses storage tank geometry, which requires that the heat transfer fluidvolume, tank loss coefficients, and tank temperatures be specified. SAM calculates the storage tankgeometry to ensure that the storage system can supply energy to the power block at its design thermalinput capacity for the number of hours specified by the Full Load TS Hours variable.

Note. Because the storage capacity is not tied to the solar multiple on the Heliostat Field page, becareful to choose a storage capacity that is reasonable given the system's thermal capacity.Mismatched storage and solar thermal capacities will result in high levelized cost of energy values.


Storage System

Storage Type

SAM models only two-tank storage systems for power towers. A two-tank system consists of separatehot and cold storage tanks.

Full Load Hours of TES (hours)

The storage capacity expressed in hours at full load: The number of hours that the storage system cansupply energy at the power block design turbine input capacity. Note that SAM displays the equivalentstorage capacity in MWht on the Tower System Costs page.

Storage HTF Volume (m3)

SAM calculates the total heat transfer fluid volume in storage based on the storage hours at full loadand the power block design turbine thermal input capacity. The total heat transfer fluid volume is dividedamong the total number of tanks so that all hot tanks contain the same volume of fluid, and all coldtanks contain the same volume of fluid.

Tank Diameter (m)

The diameter of the cylinder-shaped heat transfer fluid volume in each storage tank.

Tank Height (m)

The height of the cylinder-shaped heat transfer fluid volume in each tank. SAM calculates the heightbased on the diameter and storage volume of a single tank.

Tank Fluid Min Height (m)

The minimum allowable height of fluid in the storage tank(s). The mechanical limits of the tankdetermine this value.

Parallel Tank Pairs

The number of parallel hot-cold storage tank pairs. Increasing the number of tank-pairs also increasesthe volume of the heat transfer fluid exposed to the tank surface, which increases the total tank thermallosses. SAM divides the total heat transfer fluid volume among all of the tanks, and assumes that each

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hot tank contains an equal volume of fluid, and each cold tank contains and equal volume.

Min Fluid Volume (m3)

The minimum storage heat transfer fluid volume allowed in each storage tank. The usable fluid volume isequal to the total volume minus the minimum fluid volume. Calculated based on the minimum tankvolume fraction, the total volume, and the number of parallel tank pairs.

Min Tank Volume Fraction

The minimum allowed fraction of the total storage heat-transfer fluid volume of each storage tank.

Max Fluid Volume (m3)

The maximum usable heat transfer fluid volume allowed in each storage tank. The maximum volume isless than the total volume when the minimum tank volume is greater than zero, or the number of paralleltank pairs is greater than 1.

Wetted Loss Coefficient (W/m2-K)

The thermal loss coefficient that applies to the portion of the storage tank holding the storage heattransfer fluid.

Dry Loss Coefficient (W/m2-K)

The thermal loss coefficient that applies to the portion of the storage tank that contains storage heattransfer fluid.

Initial Hot HTF Temp (°C)

The temperature of the storage heat transfer fluid in the hot storage tank at the beginning of thesimulation.

Initial Cold HTF Temp (°C)

The temperature of the storage heat transfer fluid in the cold storage tank at the beginning of thesimulation.

Initial Hot HTF Percent (%)

The fraction of the storage heat transfer fluid in the hot storage tank at the beginning of the simulation.

Initial Hot HTF Volume (m3)

The volume of the storage heat transfer fluid in the hot storage tank at the beginning of the simulation.

Initial Cold HTF Volume (m3)

The volume of the storage heat transfer fluid in the cold storage tank at the beginning of the simulation.

Cold Tank Heater Temp Set-Point (°C)

The minimum allowed cold tank temperature. Whenever the heat transfer fluid temperature in storagedrops below the set-point value, the system adds sufficient thermal energy from an electric heater tostorage to reach the set-point.

Cold Tank Heater Capacity (MWe)

The maximum electric load of the cold tank electric heater.

Hot Tank Heater Temp Set-Point (°C)

The minimum allowed hot tank temperature. Whenever the heat transfer fluid temperature in storagedrops below the set-point value, the system adds sufficient thermal energy from an electric heater tostorage to reach the set-point.

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Hot Tank Heater Capacity (MWe)

The maximum electric load of the hot tank electric heater.

Tank Heater Efficiency

The electric-to-thermal conversion efficiency of the hot- and cold-tank heaters.

Enable storage bypass valve

When the storage bypass valve is disabled, all of the HTF from the tower is delivered to storage beforebeing delivered to the power block. Enabling the storage bypass valve allows the HTF to be deliveredfrom the tower either to the power block or storage system. When the bypass valve is enabled, SAMonly calculates hot HTF storage pumping power losses when the storage system is running. Withoutthe bypass valve, storage pumping losses apply whenever HTF is circulating in the system.




The fraction of the maximum storage capacity (TES thermal capacity) required for the system to startwhen the solar field energy is greater than zero. A value of zero will always dispatch stored energy inany hour assigned to the given dispatch period; a value of one will never dispatch energy from storage.Used to calculate the storage dispatch levels.


The fraction of the maximum storage capacity (TES thermal capacity) required for the system to startwhen the solar field energy is equal to zero. A value of zero will always dispatch stored energy in anyhour assigned to the given dispatch period; a value of one will never dispatch energy from storage. Usedto calculate the storage dispatch levels.


The fraction of the receiver design thermal power from the Tower and Receiver page at which energyfrom the storage system can drive the power cycle. See Storage and Fossil Backup Dispatch Controlsfor details.


Determines how much energy the backup boiler delivers during hours when there is insufficient energyfrom the solar field (and storage system, if available) to drive the power cycle at its design outputcapacity. A value of one for a given dispatch period ensures that the power cycle operates at its designoutput for all hours in the period: The boiler "fills in" the energy not delivered by the solar field or storagesystem. For a fossil fill fraction less than one, the boiler supplies enough energy to drive the powercycle at a fraction of its design point. To define a system with no fossil backup, use a value of zero forall six dispatch periods. See Storage and Fossil Backup Dispatch Controls for details.



For utility dispatch and utility bid price projects, SAM calculates a first year PPA price or bid price thatcovers project installation, operating, and financing costs (accounting for any tax credits or incentive

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payments), given time-of-use adjustments specified by the payment allocation factors.

When you choose a dispatch schedule from SAM's dispatch schedule library, SAM populates thepayment allocation factors with values appropriate for the schedule you choose.



Storage Dispatch

SAM decides whether or not to operate the power block in each hour of the simulation based on how muchenergy is stored in the TES, how much energy is provided by the solar field, and the values of the thermalstorage dispatch controls parameters. You can define when the power block operates for each of the sixdispatch periods. For each hour in the simulation, if the power block is not already operating, SAM looks atthe amount of energy that is in thermal energy storage at the beginning of the hour and decides whether itshould start the power block. For each period, there are two targets for starting the power block: one forperiods of sunshine (w/solar), and one for period of no sunshine (w/o solar).

The turbine output fraction for each dispatch period determines at what load level the power block runs usingenergy from storage during that period. The load level is a function of the turbine output fraction, designturbine thermal input, and the five turbine part load electric to thermal factors on the Power Cycle page.

For each dispatch period during periods of sunshine, thermal storage is dispatched to meet the power blockload level for that period only when the thermal power from the solar field is insufficient and available storageis equal to or greater than the product of the storage dispatch fraction (with solar) and maximum energy instorage. Similarly, during periods of no sunshine when no thermal power is produced by the solar field, thepower block will not run except when the energy available in storage is equal to or greater than the productof storage dispatch fraction (without solar) and maximum energy in storage.

By setting the thermal storage dispatch controls parameters, you can simulate the effect of a clear daywhen the operator may need to start the plant earlier in the day to make sure that the storage is not filled tocapacity and solar energy is dumped, or of a cloudy day when the operator may want to store energy forlater use in a higher value period.


When the fossil fill fraction is greater than zero for any dispatch period, the system is considered to includefossil backup. The fossil fill fraction defines the solar output level at which the backup system runs duringeach hour of a specific dispatch period. For example, a fossil fill fraction of 1.0 would require that the fossilbackup operate to fill in every hour during a specified period to 100% of design output. In that case, duringperiods when solar is providing 100% output, no fossil energy would be used. When solar is providing lessthan 100% output, the fossil backup operates to fill in the remaining energy so that the system achieves100% output. For a fossil fill fraction of 0.5, the system would use energy from the fossil backup only whensolar output drops below 50%.

The tank heater efficiency determines the quantity of fuel used by the fossil backup system. SAM includesthe cost of fuel for the backup system in the levelized cost of energy and other metrics reported in the

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results, and reports the energy equivalent of the hourly fuel consumption in the hourly simulation results.The cost of fuel for the backup system is defined on the Tower System Costs page.






Defining Dispatch SchedulesThe storage dispatch schedules determine when each of the six periods apply during weekdays andweekends throughout the year. You can either choose an existing schedule from one of the schedules inthe CSP Tower TES dispatch library or define a custom schedule. For information about libraries, seeWorking with Libraries.

The TES dispatch library only assigns period numbers to the weekday and weekend schedule matrices.The dispatch fractions assigned to each of the six periods are not stored in the library.




3. Click OK.


4. For each of the up to six periods used in the schedule, enter values for the dispatch fractionsdescribed above. Use the period number and color to identify the times in the schedule that eachperiod applies.


1. Assign values as appropriate to the Storage Dispatch, Turbine Output Fraction, Fossil Fill Fraction,and Payment Allocation Factor for each of the up to nine periods.



4. Click OK.


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Power Tower 217



3.9.6 Parasitics

To view the Parasitics page, click Parasitics on the main window's navigation menu. Note that for the powertower input pages to be available, the technology option in the Technology and Market window must beConcentrating Solar Power - Power Tower System.

Contents

Overview describes the Parasitics page and where to find additional informationabout the parasitics model.

Input Variable Reference describes the input variables on the Parastics page.

Estimated Parasitic Losses explains the parasitic loss estimate SAM uses tocalculate the plant capacity displayed on the Power Cycle page.

Hourly Parasitic Losses describes the hourly parasitic losses reported in hourlyresults.

OverviewThe parameters on the Parasitics page describe parasitic electrical loads and other losses in the powertower system.


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The parasitic loss variables are factors that SAM uses to calculate the estimated total parasitic loss and

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hourly parasitic losses, which are described in more detail below.

SAM calculates two types parasitic loss values. The first is an estimate of the total parasitic losses used tocalculate the power block design thermal input, and the second are the hourly values calculated duringsimulation of the system's performance.

Note. Parasitic losses from components that do not exist in the system should be set to zero.


Parasitic Energy Consumption

Startup Energy of a Single Heliostat (kWe-hr)

The electric energy in kilowatt-hours required to move each heliostat into position. Applies during hourswhen the heliostat is starting up.

Tracking Power for a Single Heliostat (kWe)

The electric power in kilowatts required by the tracking mechanism of each heliostat in the field duringhours of operation.

Receiver HTF Pump Efficiency

The electro-mechanical efficiency of the receiver heat transfer fluid pump.

Storage Pump Power (MWe/MWt)

The ratio of the electric power in kilowatts required by the storage pumps to the thermal power passingthrough the storage system.

Fraction of rated gross power consumed at all times

Piping Loss Coefficient (Wt/m)

Thermal loss per meter of piping. Includes piping throughout the system.

Piping Length Constant (m)

Piping Length Multiplier

Total Piping Length (m)

Length of piping throughout the system: From the receiver to power block, power block to process heat,etc. The piping loss varies with output produced by turbine.

Balance of Plant Parasitic (MWe/MWcap)

Losses as a fraction of the power block nameplate capacity that apply in hours when the power blockoperates.

Cooling Tower Parasitic Power (MWe/MWcap)

The cooling tower parasitic losses as a fraction of power block nameplate capacity are electrical lossesthat occur when the power block operates at part or full load.

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3.10 Solar Water Heating

3.10.1 SWH System

To view the SWH System page, click SWH System on the main window's navigation menu. Note that forthe solar water heating system input pages to be available, the technology option in the Technology andMarket window must be Solar Water Heating.

SAM's Solar Water Heating model was developed at the National Renewable Energy Laboratory.

The current version of the model represents a two-tank glycol system with an auxiliary electric heater andstorage tank for residential applications. The model allows you to vary the location, hot water load profiles,and characteristics of the collector, heat exchanger, and solar tanks.

Contents

Overview describes the SWH System page and provides some guidelines for usingthe model.

Input Variable Reference describes the input variables.

Specifying the Hot Water Draw explains how to define the hourly load profiles forthe hot water draw.

OverviewThe SWH system page displays characteristics of the solar water heating system and allows you to definethe hourly hot water draw of the system.

Keep the following in mind as you use SAM's solar water heating model:

SAM calculates the water mains inlet temperature is based on the correlation to local air temperatureused in the Building America Benchmark.

The flow rate is assumed constant over each hour, using values from the hourly hot water draw profilethat you specify. SAM calculates the flow rate in kg/hr as the draw volume in kg for a given hour dividedby one hour.

Collectors are assumed to be flat plate collectors plumbed in parallel, with uniform flow through eachcollector at the tested flow rate.

Collectors are characterized by the linear form of the collector efficiency and IAM (incident anglemodifier) equations, with parameters available from test data (e.g., www.solar-rating.org), or by externalcalculation for untested collectors.

The collector loop is assumed to be charged with glycol having Cp = 3.4 kJ/kG-ºC, with no correction to

the collector parameters.

The heat exchanger is external to the solar tank, has no thermal losses, and is assumed to have theconstant effectiveness that you specify on the SWH system page.

A standard differential controller controls the solar and storage tank loop pumps. Pump power is 40Wfor both solar loop and storage loop pumps, and pump energy is assumed totally lost.

Tanks are modeled with a finite difference approach. The solar and auxiliary storage tanks each are

http://www.solar-rating.org

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modeled with 3 nodes, accommodating modest stratification. The solar tank loss coefficient is the TankU Value specified on the SWH system page. The auxiliary tank loss coefficient is calculated from thewater heater energy factor specified on the SWH system page. The model assumes a single electricelement located at the bottom node of the auxiliary tank, witha maximum capacity of 4.5 kW. Atempering valve is placed at the outlet of the auxiliary tank, with setpoint equal to the water heater settemperature on the SWH System page.


Hourly Hot Water Draw

You must specify a set of 8,760 hourly values representing the hot water system's heating load. You caneither import values from a text file, paste values from a spreadsheet or other file using your computer'sclipboard, or type a set of 24-hour load profiles for each of the twelve months of the year, with the option ofspecifying separate profiles for weekdays and weekends.

See Specifying the Hot Water Draw for details.

Water Draw (kg/hr)

The mass of hot water drawn over an hour. Click Edit to specify the hot water draw.

The mean, min, and max values displayed in the small box next to the Edit button display the mean,minimum and maximum values in the current data set.

Solar Array


The number of collectors in the system.

Collector Tilt (degrees)

The array's tilt angle in degrees from horizontal, where zero degrees is horizontal, and 90 degrees isvertical. As a rule of thumb, system designers often use the location's latitude (shown on the Climatepage) as the optimal array tilt angle. The actual tilt angle will vary based on project requirements.

Collector Azimuth (degrees)

The array's east-west orientation in degrees. An azimuth value of zero is facing south in the northernhemisphere. Positive 90 degrees is facing due west and negative 90 degrees is facing due east. As arule of thumb, system designers often use an array azimuth of zero, or facing the equator.

Nameplate Capacity

The system's nominal capacity in thermal kilowatts, used to in capacity based cost and financingcalculations, and to calculate the system capacity factor reported in results:

Nameplate Capacity = Total Collector Area × FRta - FRUL × 30/1000

Total Collector Area (m2)

Total area of all collectors. :

Total Collector Area = Single Collector Area × Number of Collectors



Collector Specifications

Choose from library

Use this option to choose a collector from the collector library. SAM applies parameters from the libraryto model the collector.

The collector library contains parameters for collectors certified by the Solar Rating and CertificationCorporation (SRCC): http://www.solar-rating.org.

User Specified

Choose this option to specify your own collector parameters.

SRCC#

The collector's SRCC number.

Type

The collector's optic type.

Fluid

The solar system's heat transfer fluid.

Test flow

Fluid flow rate used to generate test data.

The User Specified Collector variables are active for the User Specified option. SAM ignores thesevalues for the Choose From Library option:

Area

Area of a single collector. Choose a value consistent with the area convention used in the collectorefficiency equation. For example, use gross area for all SRCC data.

FRta

Optical gain a in Hottel-Whillier-Bliss (HWB) equation hcoll

= a – b × dT

FRUL (W/m2-°C)

Thermal loss coefficient b in the Hottel-Whillier-Bliss (HWB) equation hcoll

= a – b × dT

IAM

The incident angle modifier coefficient: The constant b0 in the equation IAM = 1 – b

0 × (1/cos(q) – 1)

The Values Used in Simulation variables show parameters from either the collector library or user-specified variables that SAM uses to simulate the system's performance:

Single Collector Area

The area of one collector.

FRta

Optical gain

FRUL

Thermal loss coefficient.

http://www.solar-rating.org

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Incident Angle Modifier

Incident angle modifier coefficient.

Solar Tank and Pump

Solar Tank Storage Volume (m3)

The actual volume of the solar storage tank. Note that the actual volume may be different from the ratedvolume.

Solar Tank Height/Diameter Ratio

Defines the solar storage tank geometry, and by extension its geometry.

Solar Tank U Value (kJ/h-m2-ºC)

the solar storage tank loss coefficient. Note that 1 kJ/h-m2-C = 3.6 W/m2-C).

Pump and Heat Exchanger

Circulation Pump Power (W)

The pump's peak power rating in Watts.

Heat Exchanger Efficiency

Heat exchanger effectiveness, where the effectiveness e, is defined as e = (Tcold-out

– Tcold-in

) / (Thot-in

- Tcold-in

)

Specifying the Hot Water DrawThe hot water draw represents the solar water heating system's hourly thermal load over the period of oneyear.

A load data file is a text file with 8,761 rows: The first row is a text header that SAM ignores, and theremaining 8,760 rows must contain average hourly electric demand data in kilowatts. The first data elementrepresents the hour beginning at midnight and ending at 1 a.m. on January 1.

To import load data from a properly formatted text file:

1. On the SWH System page, click Edit.

2. In the Edit Hourly Data window, click Import.

3. Navigate to the folder containing the load data file and open the file.

SAM displays the data in the data table. Use the scroll bars to see all of the data.

4. Click OK to return to the SWH System page.

To import load data from a spreadsheet or other file:


2. Open the spreadsheet containing the load data. The data must be in a single column of 8,760 rows,and expressed in kg.

3. In the spreadsheet, select the load data and copy it.

4. In the Edit Hourly Data window, click Paste.



5. You can also copy data from the Edit Hourly Data window by clicking Copy, or export the data to atext file by clicking Save.

If you do not have a complete 8,760 set of load data, you can use a set of daily load profiles for each month,and use SAM to create a set of 8,760 values.

To create a load data set using daily load profiles:


2. In the Edit Hourly Data window, check Use monthly grid to generate 8760 data.

3. For each month of the year, define a daily load profile by typing a kg hot water draw value for eachof the 24 hours of the day. The first column represents the first hour of the day, beginning atmidnight and ending at 1:00 a.m.

If you want to specify separate load profiles for weekdays and weekends, click Weekend Values todefine profiles that apply to two days each week. SAM arbitrarily assumes that the first day in thedata set is a Monday, and that weekends fall on Saturday and Sunday.

If you do not specify separate weekend profiles, SAM applies the weekday profile to all days of theweek.

4. When you have specified all of the daily load profiles, click To 8760 to transfer the data to the UserSpecified data table. You must complete this step for SAM to use the profile data in simulations.

When you define a load with daily load profiles, SAM assumes that all days in a given month haveidentical load profiles.

5. If you want to export the 8,760 data to a text file, click Save. You can also copy the data to aspreadsheet or other file by clicking Copy, and then pasting the data in to the file.

3.11 Geothermal Power

Note. This topic is still under development.

For more details, about SAM's geothermal model, please refer to the documentation for the U.S.Department of Energy's Geothermal Electricity Technology Evaluation Model (GETEM), which you candownload from http://www1.eere.energy.gov/geothermal/getem_manuals.html

If you have questions about SAM's geothermal model, please contact [email protected]'s geothermal power systems model is based on the U.S. Department of Energy's GeothermalElectricity Technology Evaluation Model (GETEM), http://www1.eere.energy.gov/geothermal/getem.html.The model calculates the annual and lifetime electrical output of a utility-scale geothermal power plant,and the levelized cost of energy and other economic metrics for the plant.

The geothermal power plant model calculates the output of a power plant that uses heat from below thesurface of the ground to drive a steam electric power generation plant. SAM analyzes the plant'sperformance over its lifetime, assuming that changes in the resource and electrical output occur monthlyover a period of years, rather than over hours over a period of one year as in the solar and other technologiesmodeled by SAM.

SAM can be used to answer the following kinds of questions:

http://www1.eere.energy.gov/geothermal/getem_manuals.html


http://www1.eere.energy.gov/geothermal/getem.html

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What is the levelized cost of a geothermal power plant, given a known configuration and resource?

How does changing the design of the plant affect its output and levelized cost of energy?

What plant size is required to meet an electric capacity requirement?

Given a known number of wells, what would the plant's electric capacity be?

SAM models the following types of systems:

Hydrothermal resources, where the underground heat reservoir is sufficiently permeable and containssufficient groundwater to make the resource useful without any enhancements.

Enhanced geothermal systems (EGS) that pump water or steam underground to collect heat stored inrock. These systems involve drilling or fracturing the rock to improve heat transfer. Over time (typicallyyears), as heat is collected from the rock, its the temperature decreases, and more drilling is required.SAM's recapitalization cost accounts for the cost of these improvements to reach new resources.

Both flash and binary conversion plants.

3.11.1 Resource



If you have questions about SAM's geothermal model, please contact [email protected].

Resource Characterization

The resource characterization inputs describe the energy available in the underground geology at the projectsite.

Resource Type

For Hydrothermal resources, the rocks have enough permeability, heat, and water to be usefulimmediately.

For Enhanced Geothermal System (EGS) resources, there is heat, but either water, or permeability,or both are missing and must be added during the project development and operation.

Total Resource Potential

The total resource potential is an estimate of the total size of the energy available in the undergroundthermal reservoir. SAM uses the value to calculate the number of times over the project life that newdrilling would be required to renew the resource based on the reduction of the reservoir's temperatureover time. As the system operates and draws heat from the reservoir, the reservoir temperature drops.After a number of years, there may be insufficient heat to maintain the steam temperature required todrive the plant, and new wells may need to be drilled to renew the resource by reaching another sectionof the reservoir where there is sufficient heat. Eventually, the reservoir may cool to the point that it isimpossible to find more heat by drilling from the plant location. Total resource potential is meant to be ameasure of how many times the reservoir can be renewed. For example, a 210 MW reservoir divided by30 MW plant capacity could support up to seven renewals (210 ÷ 30 = 7).



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Resource Temperature

The temperature of the reservoir at the depth given by the resource depth.

Resource Depth

The depth below ground at which the temperature specified by the resource temperature exists.

In general, the higher the temperature of the resource, the lower the cost of energy generated by the plant.That is true to a certain point, but SAM won’t handle the case of the steam being so hot that specialequipment is necessary to deal with it.

For a description of the resource characterization inputs, see page 2 of the "Revisions to GETEMSpreadsheet (Version 2009-A15)" document available at http://www1.eere.energy.gov/geothermal/getem_manuals.html.

Reservoir Parameters

The reservoir parameters describe the geologic formation. SAM provides three options for calculating thechange in reservoir pressure. The option you choose affect the plant's overall efficiency, which depend onthe design parameters that SAM displays under Calculated Design. The design value determine thepumping power or parasitic load required by the plant.

For a description of the reservoir parameters, see page 6 of the "Revisions to GETEM Spreadsheet (Version2009-A15)" document available at http://www1.eere.energy.gov/geothermal/getem_manuals.html.

3.11.2 Plant and Equipment



If you have questions about SAM's geothermal model, please contact [email protected].

Plant Configuration

The plant configuration describes the plant's conversion technology and how SAM models it.

Specify plant output

The Specify Plant Output option allows you to specify the plant's electrical capacity in kilowatts. SAMcalculates the plant size required to ensure that the plant's net output meets this output requirement,with enough extra power to supply parasitic load defined by the Calculated Design values on theResource page.

Use exact number of wells

When you choose Use Exact Number of Wells, you specify the number of wells, and SAM, calculatesthe plant's gross capacity based on the energy available from the wells, and the plant net output bysubtracting the parasitic load from the gross output. The parasitic load is defined by the CalculatedDesign values on the Resource page.






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Conversion Plant Type

The Conversion Plant Type determines the plant's steam-to-electricity conversion efficiency, also called"brine effectiveness.” The plant efficiency is different from the system efficiency, which also accounts forpumping losses from the parasitic load.

Binary

When you choose the Binary option, you can specify the plant efficiency.

Plant Efficiency

The steam-to-electricity conversion efficiency, expressed as a percentage of the theoretical maximumconversion efficiency.

Flash

The Flash option allows you to choose from four subtypes that determine the plant efficiency.

For a description of the conversion system inputs see pages 12-16 of the "Revisions to GETEMSpreadsheet (Version 2009-A15)" document available at http://www1.eere.energy.gov/geothermal/getem_manuals.html.

Temperature Decline

The temperature decline parameters determine when and how often the project will require that new wells bedrilled, and are related to the total resource potential specified on the Resource page.

For a description of the temperature decline inputs, see page 9 of the "Revisions to GETEM Spreadsheet(Version 2009-A15)" document available at http://www1.eere.energy.gov/geothermal/getem_manuals.html.

Flash Technology

The two flash technology inputs impact the plant conversion efficiency for the flash conversion type.

Pumping Parameters

The Production Well Flow Rate and resource temperature specified on the Resource page dictate howmuch energy is available to the plant for conversion into electricity. The higher the flow rate, the more steam(or hot water) moves through the system, making thermal energy available for conversion, which, in turn,means fewer wells have to be drilled and therefore a lower capital expense.

The remaining inputs impact the parasitic load for pumping. The Injection Well Diameter applies onlywhen the resource type on the Resource page is EGS.

For a description of pumping, see Section 5.7 of the GETEM Technical Reference Manual (Volume I)available at http://www1.eere.energy.gov/geothermal/getem_manuals.html.

For a description of EGS pumping, see Section 6.1.a of the GETEM User's Manual (Volume II), and page 4of "Revisions to GETEM Spreadsheet (Version 2009-A15)" both available at http://www1.eere.energy.gov/geothermal/getem_manuals.html.







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3.12 Geothermal Co-production

3.12.1 Resource and Power Generation

The Co-Production in SAM model estimates power output from co-production resources based on theresource temperature and flow rate and the power plant model chosen. The power plant model calculatesthe plant net power output based on either the thermal efficiency or utilization efficiency assumed for thepower plant.

Thermal Efficiency

The thermal or “First Law” efficiency is defined as the ratio of the net rate of work output of the power plantto the net rate of heat input into the power plant:

Where,

ηth = thermal efficiency

W dot = rate of net work/power output from power plant, kJ/s

Q dot = rate of net heat input to power plant, kJ/s

The thermal efficiency represents the amount of thermal energy input into the power plant that is convertedto useful work. The rate of heat input to the power plant is calculated from the change in enthalpy of theresource fluid between the inlet and outlet of the power plant:

Where,

Q dot= mass flow rate of co-production resource (water from well), kg/s

H(T) = specific enthalpy of fluid at temperature T, kJ/kg

Tin = temperature of resource fluid into power plant in degrees Celsius. SAM assumes that thetemperature into the power plant is the same as the resource temperature entered under the “specifyresource” section

Tout = plant outlet temperature in degrees Celsius.

When calculating enthalpy, SAM assumes that the co-production resource is pure water and pressureeffects are ignored so that enthalpy is a function of temperature only. The correlation for enthalpy is thesame as that used in the Geothermal Energy Technology Evaluation Model (GETEM) (http://www1.eere.energy.gov/geothermal/getem.html). The correlation used is a 6th order polynomial of form:

Where,

c6 = 1.0122595469E-14

c5 = -1.8805783302E-11

c4 = 1.4924845946E-08

c3 = -5.9760546933E-06

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c2 = 0.0013462856545

c1 = 0.83827719984

c0 = -24.113934502

Utilization Efficiency

The utilization or “Second Law” efficiency is defined as the ratio of the work output of the power plant to thetheoretical maximum power that could be extracted from the resource relative to the ambient or dead state,defined by its exergy:

Where,

S(T) = specific entropy of fluid at temperature T, kJ/(kg-ºC)

Tambient = ambient temperature, degrees Celsius

The utilization efficiency is then defined as:

Where:

ηu = utilization efficiency

Like with the enthalpy of the fluid, when calculating entropy, SAM assumes that the co-production resourceis pure water and pressure effects are ignored so that entropy is a function of temperature only. Thecorrelation for enthalpy is the same as that used in the Geothermal Energy Technology Evaluation Model(GETEM) (http://www1.eere.energy.gov/geothermal/getem.html). The correlation used is a 6th orderpolynomial of form:

Where,

c6 = 7.39915E-18

c5 = -1.29452E-14

c4 = 8.84301E-12

c3 = -0.00000000184191

c2 = -0.00000120262

c1 = 0.002032431

c0 = -0.060089552

Choose how to model geothermal production

You can model your system using either a theoretical model or a model based on the performance curves ofexisting commercial power plants to calculate the plant power output.

Theoretical Model

Thermal efficiency - MIT Report

Power output is based on the specified resource temperature (assumed to be plant input temperature),specified plant output temperature, and the thermal efficiency defined in Equation 7.1 of the “Future of

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Geothermal Energy” report published in 2006 by MIT:

ηth = 0.0935*T(oC) - 2.3266

This correlation is based on existing binary hydrothermal power plants with operating temperaturesbetween roughly 100-200 degrees Celsius.

Thermal Efficiency – User Defined

Power output is based on a user defined thermal efficiency curve for the power plant, the specifiedresource temperature (assumed to be plant input temperature), and specified plant output temperature. The user creates the thermal efficiency curve using the “Enter curve efficiency” button to inputtemperature/thermal efficiency data. The thermal efficiency curve is created from the data pointsentered by using linear interpolation to estimate the curve between points. Performance beyond themaximum and minimum temperatures is determined by linear extrapolation.

Entering a single temperature/efficiency data point results in a power plant with constant thermalefficiency at all temperatures. Entering two data points gives a linear thermal efficiency curve similar inshape to the MIT correlation described above. More complex curves can be created by entering a largenumber of data points that approximate the shape of the user defined curve. In this way, the user candefine a curve of any shape desired. Data can be input by cutting and pasting values into the“Efficiency Curve” columns.

Utilization Efficiency – User Defined

Power output is based on a user defined utilization efficiency curve for the power plant, the specifiedresource temperature (assumed to be plant input temperature), and specified ambient temperature. Theuser creates the utilization efficiency curve in the same manner as for the thermal efficiency curvedescribed above.

Existing Systems

PureCycle

Thermal efficiency curves for the PureCycle system are based on performance curves published by UTCat (http://www.pratt-whitney.com/StaticFiles/Pratt%20&%20Whitney%20New/Media%20Center/Press%20Kit/1%20Static%20Files/pwps_orc_brochure.pdf). The thermal efficiency curves assume a net powerplant output of 260 kW. It is assumed that cooling water is available. The user can specify coolingwater temperatures from 50-80 oF, consistent with the published performance curves.

Size plant based on resource power potential

You can also specify whether you want to use the system design power output of 260 kW, or to sizethe power plant specifically to the resource. This is identical to having a power plant that has similarperformance characteristics of the PureCycle system but is sized specifically to the defined resource. Such systems are hypothetical and are not actually available commercially, but are included to allowthe user to determine how having a system with performance similar to available commercial systemsbut more-closely sized to their resource would affect the economics of their projects.

Specify the number of units

Plant output for each unit is assumed to be the same as that advertised for the commercially availablesystem. If the resource power potential is greater than the design output of the specified units, then theresource is under-utilized and the power output is limited by the number of units. If the resource powerpotential is less than the design output of the specified units, then the power plant is under-utilized andthe power output from the plant will not reach its maximum, but will be limited by the resource. Thecapital costs for the project will still be based on the plant’s design power output. In this way, the usercan explore how a power plant vs. resource power potential mismatch affects the economics of the

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system.

A similar comparison can be done with theoretical plants by choosing whether to specify the plant designnet output or size it to match the resource power potential.

3.13 Small Scale Wind

3.13.1 Small Scale Wind Overview

The Small Scale Wind system models a wind system with one or more wind turbines for a residential orcommercial project.

The model uses wind speed and direction data from weather files in TMY2, TMY3, or EPW format.

Wind Resource

Small Scale Wind Capital Costs

Small Scale Wind System

Electric Load

3.13.2 Wind Climate

To view the Wind Climate page, click Wind Climate in the main window's navigation menu. The WindClimate page is available for the Small Scale Wind model. Note that the Utility Scale Wind model uses adifferent set of inputs on the Wind Resource page.

The Wind Resource page allows you to choose a weather file in TMY3, TMY2 or EPW format, downloadsatellite-derived weather data from the Internet, create your own weather file in TMY3 format, and reviewyour weather data.

Note. This topic describes the Wind Resource page for small wind power systems. In the currentversion of SAM, the page has been adapted from the Climate page for solar power systems, and someof the variables displayed on the page are not appropriate for wind systems. The page will be updated infuture versions of SAM. Please contact [email protected] with any questions or commentsabout the Wind Resource page.

Contents

Overview of the Wind Resource Page describes the options for choosing weatherdata and the variables displayed on the Wind Resource page.

Input Variable Reference describes the variables and buttons on the Wind Resourcepage.

Adding and Removing Weather File Search Paths explains how to add your own


Small Scale Wind 231


weather files to the Location list.


Creating a Weather File from Your Own Data describes SAM's TMY3 weather filecreator to use your own weather data in SAM.


Downloading Weather Files from the Internet explains how to download TMY3,EPW, and satellite-derived data from the internet.

Wind Resource Details describes the variables required for modeling small scalewind systems.

OverviewThe Wind Climate page allows you to choose the weather file that SAM uses for simulations in the currentcase. The Wind Climate page displays a summary of the weather data, and also allows you to view theactual data in the time series data viewer (DView). The weather files are text files, so you can also examinethe data using a text editor, a spreadsheet program, or other software.

Weather Data Guidelines

For U.S. locations, use the Best weather data for the U.S. web link on the Wind Climate page todownload a TMY3 file. If the TMY3 database does not include a file for a location at or very near yourproject site, try to find TMY3 files for locations near the site. You can run simulations for the differentlocations and compare them to get a sense of what the resource might be at the project site. SeeDownloading Weather Files from the Internet for instructions.

SAM comes with the complete set of the 239 TMY2 weather files. To use a TMY2 file, simply choose itfrom the Location list. See instructions below.

If no TMY3 or TMY2 data is available for your project site, you can download typical year data fromNREL's Solar Prospector website using SAM's Location Lookup feature. The Solar Prospector websiteprovides access to satellite-derived weather data for the entire U.S. at a 10-km geographic resolution infiles using the TMY2 format. See Using Location Lookup for details.

For locations outside of the U.S., EPW files are available for over 1000 locations in 100 countries. SeeDownloading Weather Files from the Internet for instructions.

If you have weather data from a resource measurement program or from meteorological weather station,you can use SAM's TMY3 creator to create a TMY3 formatted file with the data. See Creating aWeather File from Your Own Data for details.

Some companies sell weather data and weather data processing software. For example, see WeatherAnalytics TMY Anywhere http://weatheranalytics.com/globaltmy.html, or http://www.meteonorm.com/pages/en/meteonorm.php.

To choose a weather data file from the Location list:

1. Download the weather file from the Internet. See Downloading Weather Files from the Internet for




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details

2. Place the file in your weather file folder. See Adding and Removing Weather File Search Paths fordetails.

Or, you can use one of the TMY2 files included with SAM. See below for a description of fileformats and guidelines for specifying weather data.

3. In the Location list, click the weather file's name.

If you cannot find a file for your project site on the Internet, or have data from another source that isnot in one of the file formats SAM recognizes, See Specifying Weather Data below for a list ofoptions.

Note. You can compare results for a system using more than one weather file in a single case by usingSAM's parametric simulation option.

File Formats

A SAM weather file is a file that contains hourly data describing the solar resource, wind speed,temperature, and other weather characteristics at a particular location in one of three text formats:

TMY3 comma-delimited text file format (.csv), http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/

TMY2 non-delimited text file format (.tm2), http://rredc.nrel.gov/solar/old_data/nsrdb/tmy2/

EPW comma-delimited text file format (.epw), http://www.eere.energy.gov/buildings/energyplus/weatherdata_format_def.html

The National Renewable Energy Laboratory's typical year data represents average weather data over arange of years: 1961-1990 for TMY2 data, and 1991-2005 for TMY3 data. Each typical year file may containdata from different years within the range, for example a TMY3 file might contain 1995 data for the month ofFebruary, 2001 data for March, 1998 data for April, etc. The NREL typical year data is based on analysis ofweather data measured at each location and is appropriate for economic and performance predictions of aproject over a long analysis period. The EPW data was developed for the U.S. Department of Energy'sEnergyPlus building simulation model, and is a source of non-U.S. weather data for SAM. The EPW dataon the EnergyPlus website is also typical year data.

TMY3 files are available for 1020 U.S. locations, and are based on more recent data and better modelingtechniques than the TMY2 data. However, the TMY3 data was developed using data from a shorter timeperiod than the TMY2 data, so may be less representative of the resource over the long term. (Although theTMY2 data includes effects from the Mt Pinatubo volcanic eruption, which may distort solar energy outputpredictions based on the data.) If both TMY2 and TMY3 files are available for your project site, you maywant to run SAM with both sets of data to compare results.

SAM will read a weather file containing data from any source, as long as it is correctly formatted. You cancreate your own weather file with data collected from a resource measurement program, or frommeteorological stations. SAM may not be able to read weather files that contain formatting errors orerroneous data elements. In some cases, you can use a text editor to compare a problematic file with onein the same format that works correctly in SAM to find problems with the file. Refer to the documentationavailable in the websites listed above for each file format for details.



http://rredc.nrel.gov/solar/old_data/nsrdb/tmy2/





Single Year Weather Data

Single year data represents the weather at a location for a specific year. Single year data is appropriate foranalysis of a project's economics and performance in a particular year, and for analyses involving time-dependent electricity pricing or electric loads for a given year. Single-year weather data can be developedfrom on-site measurements or from satellite-derived measurements. Single-year data for U.S. locations isavailable from NREL's Solar Prospector website, follow the link on the Wind Climate page under Web Links. The Solar Prospector data is satellite-derived data formatted using the TMY2 file format, so SAM can readthe data directly. NREL also publishes the specific-year data used to develop the TMY2 and TMY3 datasets on the websites listed above, but that data must be formatted to work with SAM, either using externalsoftware or SAM's TMY3 Creator feature.

Time Convention

The time convention of the weather data determines the time convention of SAM's simulations. Forexample, TMY2 and TMY3 data both use local standard time, and the radiation data values represent thetotal energy received during the 60 minutes preceding the indicated hour. The global horizontal radiationshown for hour 1 represents the total radiation incident on a horizontal surface between midnight and 1:00am of the first hour of the year. Both data sets assume that there are 8,760 hours in one year and do notaccount for leap years. SAM assumes that the solar angle at the middle of the hour (at 30 minutes past thehour) applies to the entire hour.


Choose Climate/Location

Location

The name of the weather file. A filename preceded by "SAM/" is a standard weather data file includedwith SAM and stored in the \exelib\climate_files folder. A filename preceded by "USER/" is a file in afolder that you have added to the weather file search path list.

Add/Remove


Refresh List

Refreshes the list of files in the location list. SAM automatically refreshes the list each time you visitthe Wind Climate page. If you add a weather file to one of the folders in the search list, you may needto refresh the list for the file to be visible in the location list.

Copy to project


Remove from project






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Create TMY3 file

Use the TMY3 Creator to convert your own weather data into the TMY3 format. See Creating a TMY3file From Your Own Data for details.

Location Lookup


Location Information

The location information variables display data from the weather file header that describes the location. Anempty variable indicates that the information does not exist in the weather file's header. The locationinformation variables cannot be edited.

City

The name of the city.

State

The state abbreviation.

Timezone

The location's time zone, relative to Greenwich Mean Time (GMT). A negative number indicates thenumber of time zones west of GMT. A positive number indicates the number of time zones east ofGMT.

Elevation (m)

The location's elevation above sea level in meters.

Latitude (degrees)

The location's latitude in degrees. A positive number indicates a location north of the equator.

Longitude (degrees)

The location's longitude in degrees. A negative number indicates the number of degrees west of thePrime Meridian.

Weather Data Information (Annual)

SAM calculates and displays the annual totals and averages of four of the hourly data columns from theweather file in the weather data information variables. Weather data information variables cannot be edited.

Direct Normal (kWh/m2)

The sum of the 8,760 hourly values of the direct normal radiation data in the weather file, expressed inkilowatt-hours per square meter. Direct normal radiation is solar energy that reaches the ground in astraight line from the sun.

Diffuse Horizontal (kWh/m2)

The sum of the 8,760 hourly values of the diffuse horizontal radiation data in the weather file, expressedin kilowatt-hours per square meter. Diffuse radiation is solar energy that reaches a horizontal planealong the ground after reflecting from clouds and particles in the atmosphere. Note that the annualaverage global horizontal radiation is the sum of the direct normal and diffuse horizontal components.



Dry-bulb Temp (°C)

The annual average of the ambient temperature data in the weather file in degrees Celsius.

Wind Speed (m/s)

The annual average wind speed in meters per second. For NREL TMY2 and TMY3 data, and EPW fromthe EnergyPlus website, wind speed data is at 10 meters above the ground.

View hourly data

Displays graphs of data from the weather file in SAM's built-in data viewer, DView. See Viewing Graphsof Time Series Data (DView) for details.

Web Links

Links to websites with weather files on the internet. Each link opens one of three website in your computer'sdefault web browser:

Best weather data for the U.S. (1200 + locations in TMY3 format) takes you to NREL's NationalSolar Radiation Data Base (NSRDB) page for the Typical Meteorological Year 3 data.

Best weather data for international locations (in EPW format) takes you to the EnergyPlusweather file page.

U.S. satellite-derived weather data (10 km grid cells in TMY2 format) takes you to NREL's SolarPower Prospector website.

Wind Resource Details

The wind resource details group only appears if you have specified Small Scale Wind as the technology inthe Technology and Market window. SAM uses these values to estimate the characteristics of the wind atthe turbine's hub height.

Shear Coefficient

The power law coefficient characterizes the wind shear, or relationship between height above the groundand wind speed. At most locations, the wind speed increases with height above the ground. The defaultvalue of 0.14 is appropriate for flat terrain free of obstructions.

Turbulence Coefficient

The turbulence coefficient characterizes the stability of the air. The default value is 0.1.

Height at which Wind was Measured

The height above the ground in meters of the anemometer used to measure the wind data in theweather file. For the NREL TMY3, TMY2, and the EPW files, the measurement height is 10 meters.





1. On the Wind Climate page, click Add/Remove.

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4. Click Close to return to the Wind Climate page.






1. On the Wind Climate page, choose the weather file from the Location list.



Creating a TMY3 File from Your Own DataIf you have hourly weather data that is not in one of the three formats (TMY3, TMY2, EPW) that SAM canread, you can use the Create TMY3 File feature to create your own weather file in the TMY3 format. TMY3files are comma-separated text files and use the csv extension, e.g., my_weather_file.csv.

Note. Unless you have a complete set of weather data for your location that you can use withconfidence, using your own data introduces uncertainty into your analysis, and may result in inaccurateresults or even simulation errors.

To use the feature, you must have the following:

A "base" TMY3 file, which is an existing file in TMY3 format that SAM modifies by replacing only thecolumns that SAM needs for simulations with your data. If you have a complete data set that includesall of the columns shown in the table below, then you can use any TMY3 file as a base file. If you do nothave data for all of the categories listed in the table below, you may want to use a base file with data forthe same or a nearby location with similar weather characteristics. For a link to the TMY3 website anddocumentation, see the link on the Wind Climate page under Web Links.



Hourly data (8,760 rows) for each of the data columns shown in the table below. If you do not have datafor one or more of the columns, you can choose to not replace data for those columns, and instead usedata from the base file. This will result in a data set that SAM can read but with mismatched elementsthat may cause inaccurate results or errors in the simulation.

To create a TMY3 weather file:

1. If you do not have a TMY3 file to use as the base file, download a TMY3 file to use at the base filefrom the NREL TMY3 website. You can do so by clicking the appropriate link on the Wind Climatepage under Web Links.

2. Open the file or files containing your weather in a text editor, spreadsheet program, or any softwarethat allows you to copy columns of 8,760 rows to your computer's clipboard.

3. On the Wind Climate page, click Create TMY3 file.

4. In the TMY3 Creator window, click Open base TMY3 file, and navigate to the folder containing thebase file.

5. Type values in the header fields as appropriate, using the table below for reference.

6. In your weather data file, copy the column of global horizontal radiation data. Be sure to copy all8,760 rows of data, but do not include the row header. The column should contain 8,760 rows ofnumbers.

7. In the TMY3 Creator window, click the GHI (W/m^w) column heading. SAM should highlight theentire column in dark gray.

8. Click Paste.

9. Repeat the copy and paste procedure for each column until you have pasted all of your data intothe table.

10. Click Save as new TMY3 file. Save the file in a folder that you have included in the weather filesearch list (see Adding and Removing Weather File Search Paths).


12. Click Refresh list. SAM may take a moment or two to refresh the location list.

13. In the Location list, select the new TMY3 file. You should find it toward the end of the list.

14. Click View Hourly Data to open the DView data viewer and visually inspect the data. See ViewingGraphs of Time Series Data (DView) for details.

After creating and loading your weather file, run some test simulations and examine the hourly simulationresults to see if there are any problems with the data.

Table 19. Header data for TMY3 weather files

Data Element Name Description Units

Site Identifier Code A number identifying the location. This element is notrequired.

--

Station Name A text description identifying the location. This elementis not required.

--

Station State A two-letter text abbreviation for the location's state.This element is not required.

--

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Site Time Zone (GMT) The location's time zone offset from Greenwich MeanTime (GMT) with no daylight savings adjustment. Apositive value indicates a time zone east of the PrimeMeridian. A negative value indicates a time zone west ofthe prime meridian. For example, Chicago is -6; India is5.5.

decimal time

Latitude Location's latitude in decimal degrees. A positive valuebetween zero and 90 indicates a latitude north of theequator. A negative value between 0 and -90 indicates alatitude south of the equator. For example, Durban(South Africa) is -29.97; New York City is 40.71.

decimal degrees

Longitude Location's longitude in decimal degrees. A positivevalue between zero and 180 indicates a longitude eastof the Prime Meridian. A negative value between zeroand -180 indicates a longitude west of the PrimeMeridian. For example, Durban (South Africa) is 30.95;New York City is -74.01.

decimal degrees

Elevation Location's height above sea level in meters. m

Table 20. Hourly data used for different technologies.


GHI (W/m 2̂) Global horizontal irradiance: Total amount of direct anddiffuse solar radiation received on a horizontal surface for thehour.

Wh/m2

DNI (W/m 2̂)Direct normal irradiance: Amount of solar radiation receivedin one hour within a limited field of view centered on the sun.

Wh/m2

DHI (W/m 2̂)Diffuse horizontal irradiance: Amount of solar radiationreceived in one hour from the sky, excluding the solar diskon a horizontal surface.

Wh/m2

Dry-bulb (C) Average dry bulb temperature for the hour. °C

Dew-point (C) Average dew point temperature for the hour. °C

RHum (%) Average relative humidity for the hour. %

Pressure (mbar) Station pressure or measured atmospheric pressurecorrected for temperature and humidity for the hour.

mbar

Wspd (m/s) Average speed of the wind for the hour. m/s

Albedo Ratio of reflected solar radiation to global horizontalradiation. Use -99 for null.

--

Using Location LookupSAM's Location Lookup feature allows you to type an address, zip code, or latitude and longitude todownload a typical year data weather file for any location in the United States. Location Lookup uses theGoogle Maps API Geocoding Service service to identify the geographic coordinates of a location, and



downloads data from NREL's Solar Power Prospector database. To use the Location Lookup feature, yourcomputer must be connected to the Internet.

Notes.

Location Lookup downloads typical year data, representing the typical solar resource over the period1998-2005. To download specific-year data within that range, visit the Solar Power Prospector site athttp://maps.nrel.gov/prospector.

For information about downloading TMY3 and EPW files from the internet, see Downloading WeatherFiles from the Internet.


1. On the Wind Climate page, click Location Lookup.



80401

39 44 N 105 09 W

39.75 -105.15






3. On the Wind Climate page click Add/Remove.



Downloading Weather Files from the InternetYou can click the links under Web Links to open websites where you can download and find moreinformation about weather data in TMY3, TMY2, and EPW formats.

NSRDB Typical Meteorological Year 3 (TMY3) data: Best data for U.S. Locations

The NSRDB maintains two sets of TMY data. The TMY2 data represent data from 1961 to 1990. Thecomplete TMY2 data is included with SAM: To use TMY2 data, you simply select a location from the list onthe Wind Climate page.

The updated TMY3 data set is based on data from 1991 to 2005. To use TMY3 data in SAM, you mustdownload the data from the NSRDB website. For information about the TMY3 data, see:


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To download a TMY3 file:

1. Click the Best weather data for the U.S. (1200 + locations in TMY3 format) link to open theNSRDB TMY3 database page.

2. On the NSRDB website, click the In alphabetical order by state and city link.

3. Scroll to the state and city at or nearest your location.

4. Click the identification code link for the location to download the TMY3 file.


6. In SAM, on the Wind Climate page, click Refresh.


EnergyPlus Weather (EPW) Files

You can download weather data in EPW format for locations around the world at no cost from theEnergyPlus weather data website at the following website:

http://www.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm.

For information about the EPW weather files, see the following websites:

For a description of the file format: http://apps1.eere.energy.gov/buildings/energyplus/weatherdata_format.cfm

For a description of data sources: http://apps1.eere.energy.gov/buildings/energyplus/weatherdata_sources.cfm

To download an EPW file:

1. Click Best weather for international locations (in EPW format) and navigate to the region andlocation you want to model.

2. Download the EPW file for the location you are modeling.

If there is not an EPW file for the location, download the ZIP file and extract the EPW file.




For some regions, you can download an EPW file directly for a location. For example, for Bangladesh, youcan download the data for Dhaka by right-clicking the blue square next to the word EPW for Dhaka. Be sureto save the file with the .epw extension.

For other regions, you must first download a zip file containing the EPW file and then extract the EPW file.For example, for Malaysia, you can download the data for Kuala Lumpur by right-clicking the red squarenext to the word ZIP for Kuala Lumpur. After downloading the zip file, you can extract the EPW file.


http://www.eere.energy.gov/buildings/energyplus/cfm/weather_data.cfm







Satellite-derived (NREL Solar Prospector) Weather Data

The NREL Solar Prospector website provides access to satellite-derived data in TMY2 format for specificyears between 1998 and 2005 for locations in the U.S. at a geographical resolution of 10 km.

For information about the Solar Power Prospector website, see:


For a description of the data used for the Solar Prospector website, see:


Although the files you download from the Solar Power Prospector website are in TMY2 format, you candownload files containing either specific year data or typical year data from the website.

The easiest way to use typical year data from Solar Power Prospector in SAM is to use Location Lookup.To download single year data, you can use the Solar Prospector map at http://maps.nrel.gov/prospector.

To download data from the NREL Solar Prospector Website:

1. Visit the Solar Prospector website at http://maps.nrel.gov/prospector.

2. Use the map to find your location.

3. Click Download in the toolbar above the map.

4. Choose a year for specific year data, or "TDY" for typical year data.




Specifying Wind Resource ParametersIf you are modeling a small scale wind system, you must specify the three parameters describing additionalcharacteristics of the wind resource. SAM uses these parameters to calculate the wind speed at the turbinehub height, assuming that the wind resource data was measured at a different height, typically just 10meters above the ground.

To specify wind resource parameters:

1. On the Wind Climate page, scroll down to the bottom of the page if the parameters are not visibleon your screen.

2. For Shear Coefficient, type a value between 0 and 1. The default value of 0.14 is appropriate forturbines on flat land with little vegetation.

3. For Height at which Wind was Measured, type the height above the ground at which the windspeeds in the weather file were measured. For the NREL TMY3, TMY2, and the EPW data, themeasurement height is 10 meters.







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3.13.3 Small Scale Wind System

The Small Scale Wind System page allows you to choose a wind turbine from a list, and to specify thelocations of turbines for a project with more than one wind turbine.

Wind Turbine

The wind turbine parameters specify the turbine power curve and hub height of a single turbine. For a projectwith multiple turbines, SAM assumes that the project consists of turbines with the same parameters. It isnot possible to specify turbines with different power curves, cut-in speeds, or hub heights.

Model Name

Choose a turbine from the list.

You can add turbines to the Small Scale Wind Turbine Library list by creating a user library with theLibrary Editor.

Nameplate Capacity

The turbine's rated capacity from the turbine database. You cannot edit this value. SAM uses this valuefor capacity-related cost calculations.

Rotor Diameter

The turbine's rotor diameter from the turbine database. You cannot edit this value.

Cut-in Wind Speed

The minimum wind speed at which the turbine generates power.

During simulations, SAM sets the turbine's output to zero for hours with an average wind speed belowthe cut in speed.

The default value is 4 m/s, which is appropriate for many of the turbines in the library.

Hub Height

The hub height is distance between the ground and the turbine's hub at the center of the rotor.

System Size

SAM calculates the system size by multiplying the turbine nameplate capacity by the number of turbines inthe project.

Use more than one wind turbine

Check this option if you want to model a project with two or more turbines. SAM assumes that theproject consists of turbines with the same power curve, cut-in speed, and hub height.

To model a project with one turbine, clear the checkbox. SAM disables the Turbine Farm Layoutoptions when the checkbox is cleared.

Number of Turbines

Number of turbines in the project specified in the Turbine Farm Layout options.

System Nameplate Capacity

Total capacity of the project in AC kilowatts, equal to the product of the number of turbines and thenameplate capacity of a single turbine.



Turbine Farm Layout

The Turbine Farm Layout options allow you to specify the parameters of a project with two or more turbines.You must check Use more than one wind turbine to make the parameters active.

The best way to see how the parameters work is to change values and see how the turbine layout mapchanges.

Turbine Layout Map

A diagram showing the locations of turbines in the field. Each blue dot in the map represents a turbine.

Shape

Choose the shape defined by a set of lines connecting outermost turbines in the project.

Turbines per Row / Turbines in First Row

For the Square / Rectangle / Parallelogram shape, the number of turbines in each row.

For the Triangle / Trapezoid shape, the number of turbines in the row closest to the bottom of theturbine layout map.

Number of Rows

Number of rows of turbines in the field.

Turbines in Layout

Product of turbines per row and number of rows.

Turbine Spacing

Distance in meters between turbines in each row.

Row Spacing

Distance in meters between rows.

Offset for Rows

The distance in meters between a line drawn through a turbine perpendicular to its row, and a similarline drawn through a turbine in the nearest neighboring row.

Offset Type

Every Other Row applies the offset distance to alternating rows. Each Row applies the distance toevery row.

Row Orientation

The angle west of north of a line perpendicular to the rows of turbines.

You can set the value by either typing a number or dragging the slider with your mouse.

The compass rose indicates the cardinal directions. SAM uses this information with wind direction datafrom the weather file and the distance between turbines to estimate the effect of wind shadowing byneighboring turbines.

Wind Farm Losses

Expected power losses as a percentage of the wind farm's total output due to wake effects and otherlosses due to wind farm layout.

Losses per turbine

Losses in kilowatts per turbine. SAM multiplies this value by the number of turbines to calculate the

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total turbine losses.

3.14 Utility Scale Wind

3.14.1 Utility Scale Wind Overview

The Utility Scale Wind model is for projects involving one or more large-scale turbines with one of the UtilityMarket financing options.

SAM's utility scale wind uses weather data from a database for United States locations.

Wind Resource

Wind Farm Specifications

Wind Farm Costs

3.14.2 Wind Resource

The Wind Resource page allows you to download a wind resource data file from the internet by typinglocation coordinates or an address.

The data is from NREL's Western Wind Dataset, which covers the western United States:

For information about the dataset, see http://www.nrel.gov/wind/integrationdatasets/western/methodology.html.

The Utility Scale Wind model uses wind resource data from files in the .swrf format, which is a tab-delimitedtext format. To see examples of the files, search your computer for "swrf", or look for files with the .swrfextension in the \exelib\climate_files folder in your SAM installation folder, which is \SAM\2011.4.27 by

http://www.nrel.gov/wind/integrationdatasets/western/methodology.html

http://www.nrel.gov/wind/integrationdatasets/western/methodology.html

Utility Scale Wind 245


default.

To download wind resource data:

1. Click Location Lookup. See Using Location Lookup for details.

2. Type a latitude and longitude, street address, or zip code.

3. Click OK.

Contents

Input Variable Reference describes the variables and buttons on the Wind Resourcepage.


Adding and Removing Weather File Search Paths explains how to add your ownweather files to the Location list.



Wind Resource Location

Wind Data File

The name of the file downloaded from the database.

Data Source

The URL pointing to the data used to create the wind data file.

Date Created

The date the wind data was downloaded and the weather file created.

Latitude Requested

The latitude requested in Location Lookup.

Longitude Requested

The longitude requested in Location Lookup.

Latitude

The latitude from the database, which may differ from the requested latitude.

Longitude

The longitude from the database, which may differ from the requested longitude.

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Distance from request

The distance between the requested point in Location Lookup and the point in the database.

Elevation

The locations height above sea level.

Click here to view map of (R)equested and (A)ctual locations

Displays a map in your browser showing the location of the requested point from Location Lookup andthe actual point in the database.

Location Lookup


Add/Remove


Refresh List

Refreshes the list of files in the location list. SAM automatically refreshes the list each time you visitthe Wind Climate page. If you add a weather file to one of the folders in the search list, you may needto refresh the list for the file to be visible in the location list.

Copy to project


Remove from project


Annual Average Data

SAM displays annual averages of the wind speed data in the weather file, which contains data for fourheights above the ground.

SAM also displays the annual average temperature at 10 meters. The weather file contains temperaturedata at each wind speed height.

A green check mark indicates the height that SAM will use for simulations, which is based on the turbine'shub height that you specify on the Wind Farm Specifications page.

Wind Resource Details

The wind resource details group only appears if you have specified Small Scale Wind as the technology inthe Technology and Market window. SAM uses these values to estimate the characteristics of the wind atthe turbine's hub height.

Shear Coefficient

The power law coefficient characterizes the wind shear, or relationship between height above the ground



and wind speed. At most locations, the wind speed increases with height above the ground. The defaultvalue of 0.14 is appropriate for flat terrain free of obstructions.

Turbulence Coefficient

The turbulence coefficient characterizes the stability of the air. The default value is 0.1.

Height at which Wind was Measured

The height above the ground in meters of the anemometer used to measure the wind data in theweather file. For the NREL TMY3, TMY2, and the EPW files, the measurement height is 10 meters.

Using Location LookupSAM's Location Lookup feature allows you to type an address, zip code, or latitude and longitude todownload a wind resource data file. Location Lookup uses the Google Maps API Geocoding Service toidentify the geographic coordinates of a location. To use the Location Lookup feature, your computer mustbe connected to the Internet.


1. On the Wind Climate page, click Location Lookup.



80401

39 44 N 105 09 W

39.75 -105.15






3. On the Wind Climate page click Add/Remove.






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1. On the Wind Climate page, click Add/Remove.










1. On the Wind Climate page, choose the weather file from the Location list.



3.14.3 Wind Farm Specifications

The Wind Farm Specifications page allows you to choose a wind turbine from a list, and to specify thelocations of turbines for a project with more than one wind turbine.

Wind Turbine

The wind turbine parameters specify the turbine power curve and hub height of a single turbine. For a projectwith multiple turbines, SAM assumes that the project consists of turbines with the same parameters. It isnot possible to specify turbines with different power curves, cut-in speeds, or hub heights.

Model Name

Choose a turbine from the list.



You can add turbines to the Large Scale Wind Turbine Library list by creating a user library with theLibrary Editor.

Nameplate Capacity

The turbine's rated capacity from the turbine database. You cannot edit this value. SAM uses this valuefor capacity-related cost calculations.

Rotor Diameter

The turbine's rotor diameter from the turbine database. You cannot edit this value.

IEC Class

The turbine's International Electrotechnical Commission wind turbine classification.

Cut-in Wind Speed

The minimum wind speed at which the turbine generates power.

During simulations, SAM sets the turbine's output to zero for hours with an average wind speed belowthe cut in speed.

The default value is 4 m/s, which is appropriate for many of the turbines in the library.

Hub Height

The hub height is distance between the ground and the turbine's hub at the center of the rotor.

Closest available resource ht

During simulation, SAM uses wind resource data for the height indicated. For example, if the ClosestAvailable Resource Ht value is 100 m, SAM uses wind resource data measured at 100 m. The annualaverage wind speed at this height is indicated by a green check mark under Annual Average Data onthe Wind Resource page.

System Size

SAM calculates the system size by multiplying the turbine nameplate capacity by the number of turbines inthe project.

Use more than one wind turbine

Check this option if you want to model a project with two or more turbines. SAM assumes that theproject consists of turbines with the same power curve, cut-in speed, and hub height.

To model a project with one turbine, clear the checkbox. SAM disables the Turbine Farm Layoutoptions when the checkbox is cleared.

Number of Turbines

Number of turbines in the project specified under Turbine Farm Layout.

System Nameplate Capacity

Total capacity of the project in AC kilowatts, equal to the product of the number of turbines and thenameplate capacity of a single turbine.

Turbine Farm Layout

The Turbine Farm Layout options allow you to specify the parameters of a project with two or more turbines.You must check Use more than one wind turbine to make the parameters active.

The best way to see how the parameters work is to change values and see how the turbine layout map

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changes.

Turbine Layout Map

A diagram showing the locations of turbines in the field. Each blue dot in the map represents a turbine.

Shape

Choose the shape defined by a set of lines connecting outermost turbines in the project.

Turbines per Row / Turbines in First Row

For the Square / Rectangle / Parallelogram shape, the number of turbines in each row.

For the Triangle / Trapezoid shape, the number of turbines in the row closest to the bottom of theturbine layout map.

Number of Rows

Number of rows of turbines in the field.

Turbines in Layout

Product of turbines per row and number of rows.

Turbine Spacing

Distance in meters between turbines in each row.

Row Spacing

Distance in meters between rows.

Offset for Rows

The distance in meters between a line drawn through a turbine perpendicular to its row, and a similarline drawn through a turbine in the nearest neighboring row.

Offset Type

Every Other Row applies the offset distance to alternating rows. Each Row applies the distance toevery row.

Row Orientation

The angle west of north of a line perpendicular to the rows of turbines.

You can set the value by either typing a number or dragging the slider with your mouse.

The compass rose indicates the cardinal directions. SAM uses this information with wind direction datafrom the weather file and the distance between turbines to estimate the effect of wind shadowing byneighboring turbines.

Wind Farm Losses

Expected power losses as a percentage of the wind farm's total output due to wake effects and otherlosses due to wind farm layout.

Losses per turbine

Losses in kilowatts per turbine. SAM multiplies this value by the number of turbines to calculate thetotal turbine losses.

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4 Costs and Financing

4.1 Financing OverviewThe financial model provides options for projects in the residential, commercial, and utility markets, andaccount for a wide range of incentive payments and tax credits.

Tax Credits and Incentive Payments

For all of the financing options in SAM, you can include benefits in the form of tax credits or incentivepayments. SAM assumes that a project may pay both federal and state income taxes, and that incentivepayments may be available from government, utility, or other entities.

Tax credits are reductions in a projects tax payment specified on the Tax Credit Incentives page, and mayinclude:

Investment tax credits (ITC) based on the cost of installing equipment.

Production tax credits (PTC) based on the amount of electricity generated by the project.

Incentive payments are cash payments to the project specified on the Payment Incentives page, and mayinclude:

Investment-based incentives (IBI) based on the cost of installing equipment.

Capacity-based incentives (CBI) based on the size of the system.

Production-based incentives (PBI) based on the amount of electricity generated by the project.

For commercial and utility projects, SAM also models accelerated depreciation (including MACRS),specified on the Financing page.

Residential and Commercial Projects

In SAM, residential and commercial projects buy and sell power at retail rates. They may be financedthrough either a loan or cash payment (0% debt fraction). These projects recover investment costs byselling electricity at rates established by the electricity service provider.

For residential and commercial projects, SAM calculates the project's levelized cost of energy, whichrepresents the cost of installing and operating the system, including debt and tax costs, and accounting forincentives. The model also calculates the net present value of the after tax cash flow and a payback periodrepresenting the number of years required for the cumulative after tax cash flow to cover the initial equityinvestment in the project.

Commercial projects may qualify for tax deductions under the Modified Accelerated Depreciation Schedule(MACRS) described in the United States tax code. SAM provides options for specifying customdepreciation schedules in addition to the MACRS mid-quarter and half-year schedules on the Financingpage.

Residential and commercial projects are typically smaller than 500 kW, although SAM does not restrictsystem sizes, so it is possible to model any size system using either the residential or commercialfinancing option.

SAM's Utility Rate page provides a range of options for specifying the utility rate structure for a project. The

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rate structure may include any of the following:

Flat buy and sell rates (with or without net metering)

Time-of-use energy charges

Monthly demand charges (either fixed or time-of-use)

Tiered rates

Fixed monthly charges

Adjustment fees

For projects with demand charges and tiered rates, SAM requires electric load data, which is specified onthe Electric Load page.

A Note About the Old and New Financing Options

The "old" financing options, Commercial PPA and Independent Power Producer, available in the currentversion of SAM, are based on the financing options available in SAM 2010.11.9 and older versions. They areincluded in the current version to allow for comparison of results with older versions of SAM:

Commercial PPA in the current version is equivalent to Commercial Third Party in previous versions.

Independent Power Producer in the current version combines the Independent Power Producer, Time ofDispatch, and First Year Bid Price options from previous versions into a single model.

The "new" Utility Market options (All Equity Partnership Flip, Leveraged Partnership Flip, Sale Leaseback,and Single Owner) are based on a new financial model developed for SAM and better represent actualproject financing structures for renewable energy projects.

The following list summarizes some of the differences between the old and new financing options:

Debt fraction is an input for the Commercial PPA and Independent Power Producer (old) options. Forthe new options that involve debt (see table below), SAM calculates the debt fraction as a result basedon the debt service coverage requirements you specify as an input on the Financing page, and theavailable cash in the project cash flow.

The new financing options include structures with two partners, and report IRRs, NPVs, and cash flowsfor each partner. The old financing options report only the total project IRR, NPV, and cash flow.

The new Single Owner and old Independent Power Producer options model the same financingstructure: A project financed with debt and involving a single entity that develops and operates theproject and receives all project income and benefits. The Single Owner option is more representative ofactual projects. The Independent Power Producer option may be suitable for basic preliminary analysesbefore some of the details required by the Single Owner option are known.

The new Utility Market financing options allow you to specify a reserve account for major equipmentreplacement that is not available in the Commercial PPA and Independent Power Producer options.

The new Utility Market financing options include options for bonus depreciation and more sophisticatedhandling of depreciation with tax credits and payment incentives than the Commercial PPA andIndependent Power Producer options.

The Commercial PPA and Independent Power Producer models have been updated since SAM 2010.11.9.Improvements include:

You specify whether the PPA price is an input and IRR a result, or IRR is an input and PPA price aresult using the Solution Mode option on the Financing page.

The Independent Power Producer model allows you to model a PPA price with energy paymentallocation factors, where the negotiated power price varies based on a pre-determined time-of-dayschedule. (Energy payment allocation factors were available for the Time of Dispatch and Bid Price

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options in previous versions.) For the concentrating solar power technologies, you specify the energypayment allocation factors on the Thermal Energy Storage page. For other technologies, see theEnergy Payment Dispatch page.

The construction period financing cost includes the option to specify an up-front fee based on theapproach used in the new financing models. See Financing, Construction Period for details.

The property tax calculation allows you to specify the property's assessed value as a percentage of thetotal installed cost, and to specify an annual rate of decline in the assessed value. Previous versionsassumed that the assessed value was equal to the total installed cost throughout the analysis period.

Commercial PPA

Commercial PPA projects sell electricity at a price negotiated through a power purchase agreement (PPA).SAM calculates a power purchase price given a target minimum IRR, with options for optimizing the debtfraction and PPA escalation rate to minimize the PPA price.

For commercial PPA projects, SAM calculates an electricity sales price (PPA price), and IRR and NPV forthe project as a whole, assuming that a single entity participates in the project and has sufficient taxliability to absorb tax credits and depreciation benefits.

Commercial PPA projects are typically larger than 500 kW, although SAM does not restrict system sizes,so it is possible to model any size system using either the residential or commercial financing option.

Utility Market

Utility projects sell electricity at a price negotiated through a power purchase agreement (PPA) to meet aset of equity returns requirements, and and may involve one or two parties.

SAM provides options for calculating a power purchase price given a target internal rate of return, or forcalculating the rate of return given a power purchase price. An optional annual escalation rate allows forpricing that varies annually, and optional payment allocation factors allow for pricing that varies with time ofday.

For utility projects, SAM calculates an electricity sales price (PPA price), and IRRs and NPVs for theproject as a whole and, as appropriate for each equity participant.

The utility market structures is typically used for large-scale projects because of the costs associated withfinancial customization, developers of smaller commercial projects are experimenting with lower costapproaches, such as using standardized versions of some of the financing structures, financing projects onan aggregated basis, seeking corporate financing rather than project-level financing, and partering withcommunity-based lending institutions and investors. Because SAM does not restrict the size of the system,it is possible to use these financing structures with any size of system.

SAM provides five options for modeling Utility Market projects:

All Equity Partnership Flip and Leveraged Partnership FlipThe All Equity Partnership Flip and Leveraged Partnership Flip options are two-party projects thatinvolve equity investments by a project developer and a third party tax investor. The tax investor hassufficient tax liability from its other business operations to utilize any tax benefits (tax credits anddepreciation deductions) fully in the years in which the project generates the benefits. The project setsup a limited liability entity, and once the project begins generating and selling electricity, all of theproject’s net cash flows and tax benefits are passed through this entity to its owners. The projectallocates a majority of the cash and tax benefits to the tax investor when the project begins operationand until the tax investor receives a pre-negotiated after-tax IRR, also known as the flip target. Once theflip target is reached, a majority of the cash and any remaining tax benefits are allocated to the

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developer.

Sale LeasebackThe Sale Leaseback option is another two-party structure that involves a tax investor purchasing 100%of the project from the developer and then leasing it back to the developer. This structure differs fromthe partnership flip structures in that the tax investor and the developer do not share the project cashand tax benefits (or liability). Instead, each party has its own separate cash flow and taxable income.The purchase price paid by the tax investor is equal to the total project cost, less a lease payment andthe value of working capital reserve accounts. The developer typically funds the reserve accounts toensure it has some financial exposure. The tax investor receives lease payments from the developerand any ownership-related incentives such as the tax credits, incentive payments, and the depreciationtax deductions. The developer operates the project and keeps any excess cash flow from operations,after payment of all operating expenses and the lease payments. This provides the developer with anincentive to operate the project as efficiently as possible.

Note. SAM assumes that the tax investor receives the ITC in the sale leaseback structure. SAM doesnot model alternative lease structures that treat the ITC differently.

Single Owner and Independent Power ProducerIn the Single Owner and Independent Power Producer options, one entity owns the project and hassufficient tax liability to utilize the tax benefits. This structure is less complicated than the PartnershipFlip and Sale Leaseback structures because there is no need to allocate cash and tax benefits todifferent partners. The owner may be either the original developer or a third-party tax investor thatpurchases the project from the developer. (See above for a discussion of the differences between theSingle Owner and Independent Power Producer options.)

Below is a table summarizing the five structures.

All EquityPartnership Flip

LeveragedPartnership Flip Sale Leaseback

Single Owner /Independent

Power Producer

Equity Owners Tax investorDeveloper

Tax investorDeveloper

Tax investor(Lessor)

Developer(third party if sold)

Project Debt No Yes No Optional (ownerchoice)

Return Target Tax investor after-tax IRR(Flip Target)

Tax investor after-tax IRR(Flip Target)

Lessor after-tax IRR Owner after-tax IRR

Cash Sharing Pre-Flip: BifurcatedPost-Flip: Primarilydeveloper

Pre-Flip: Pro rataPost-Flip: Primarilydeveloper

Lessor: LeasepaymentLessee: Projectmargin

Owner receives100% of projectcash

Tax BenefitSharing

Pre-Flip: Primarilytax investor Post-Flip: Primarilydeveloper

Pre-Flip: Primarilytax investor Post-Flip: Primarilydeveloper

Tax investor anddeveloper havedifferent taxableincomesITC andDepreciation goes totax investor

Owner receives100% of project taxbenefits

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4.2 System SummaryTo view the System Summary page, click System Summary in the main window's navigation menu.

The System Summary page displays variables that describe the system's capacity and capital costs. SAMdisplays the variables so that you can quickly see some key properties of the system.

SAM displays the same set of summary variables for all of the technologies to facilitate quick comparisonsof different cases using different technologies.

Note. The values shown on the System Summary page are copies of values from other input pages asdescribed below. You cannot change values on the System Summary page.

System Summary

System Nameplate Capacity (kW)

The nameplate capacity is the system's rated or nominal capacity in kilowatts. It is the value that SAMuses to calculate cost per kilowatt values displayed on the cost pages and used for economicmodeling.

For photovoltaic systems, the value is equivalent to the total array power in DC kilowatts calculated onthe Array page.

For concentrating solar power systems, the value is equivalent to the power block's rated capacity inAC kilowatts, which is an input on the Power Block or Power Cycle, Power Cycle, or Stirling Enginepage for trough, tower, or dish systems, respectively.

For wind systems, the value is equal to the product of a single turbine's nameplate capacity in ACkilowatts the and number of turbines in the system.

For geothermal systems, the value is the the net plant output in AC megawatts on the Plant andEquipment page converted to AC kilowatts.

Total Direct Cost ($)

The total cost of installation equipment and services, calculated on the system cost page.

Total Installed Cost ($)

The project's total capital cost, including direct and indirect costs, calculated on the system cost page.

Total Installed Cost per Capacity ($/kW)

The total installed cost divided by the system nameplate capacity, also displayed on the system costpage.

Analysis Period (years)

Number of years covered by the analysis. Typically equivalent to the project or investment life, alsodisplayed on the Financing page.

Inflation Rate (%/year)

Annual rate of change of prices, typically based on a price index. SAM uses the inflation rate tocalculate costs in the cash flows for years after year one, also displayed on the Financing page.

Real Discount Rate (%/year)

A measure of the time value of money expressed as an annual rate. SAM uses the real discount rate tocalculate the present value (value in year one) of cash flows over the analysis period and to calculate

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annualized costs, also displayed on the Financing page.

4.3 Utility RateTo view the Utility Rate page, open a case with residential or commercial financing, and then click UtilityRate in the main window's navigation menu.

The Utility Rate page displays options for specifying a wide range of utility rate structures for projects withResidential and Commercial financing, from flat rates with net metering to complex time-of-use rates withdemand charges and tiered rates.

Contents

Overview defines the utility rate options and how to view the impact of rates onresults.

Input Variable Reference describes each of the input variables on the Utility Ratepage.

Specifying a Flat Rate with or without Net Metering explains how to set up a ratestructure that uses a single rate for buying and selling electricity that does not varywith time.

Specifying Time of Use Energy Charges explains how to set up a rate structurewith different buy and sell rates at different times of day and year.

Specifying Peak Demand Charges explains how to assign charges that apply to thehour of maximum electric demand in each month.

Specifying a Tiered Rate Structure explains how to set up a rate structure withelectricity prices that vary with the amount of electricity purchased over a month.

Importing Rate Structure Data explains how to download rate structure data fromNREL's OpenEI database.

Specifying Escalation Rates describes escalation rates and explains how tospecify them.

Defining Weekday and Weekend Schedules explains how to use the weekend andweekday matrices to define the times when charges apply.

OverviewThe Utility Rate page allows you to specify a rate schedule for residential and commercial projects. The rateschedule defines the prices of electricity purchased and sold by the project under an agreement with anelectric service provider. For some service providers in the United States, you can download the ratestructure from the internet.

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Notes.

The Utility Rate page is available only for projects with residential or commercial financing. For projectswith utility or commercial PPA financing, the electricity sales price is a result instead of an input. Forthose projects, SAM reports the electricity sales price as the first year power purchase price.

A project's financing type is defined in the Technology and Market window.

You can specify an electric rate structure with any level of complexity, from a simple flat rate with netmetering to a complex schedule with time-of-use rates that change with time, demand charges, and tieredrates:

Flat rate: A fixed rate in dollars per kilowatt-hour that does not vary with time or with the amount ofelectricity the project purchases.

Fixed monthly charge: A fixed amount in dollars that the project pays each month.

Time-of-use (TOU) rate: Rates in dollars per kilowatt-hour that vary with time of day and month of year.

Net metering: The project buys and sells electricity at the same rate. Net metering can apply to flatrates or time-of-use rates. Note that SAM calculates net metering on an hourly basis, not on a monthlyor annual basis.

Peak demand charges: Monthly fees in dollars per kilowatt paid by the project for the maximummonthly electric demand. You can specify demand charges as fixed monthly charges or as chargesthat vary with time of use.

Tiered rates: Rates in dollars per kilowatt-hour that vary with the amount of electricity purchased by theproject in a month.

You can also specify an escalation rate if you expect electricity prices to increase from year to year at arate above inflation.

Utility Rates and Results

After you specify the rate schedule and run simulations, you can see the resulting hourly pricing data in thetabular data browser on the Results page, and the total annual revenue from electricity sales in the projectcash flow. SAM reports revenues from electricity sales in the metrics table. Note that the electricity buy andsell rates do not affect the project's levelized cost of energy (LCOE), because for residential and commercialprojects, the LCOE value is independent of project revenue. The electricity rates do affect the project netpresent value and payback period.


OpenEI Online Utility Rate Database

NREL's Open Energy Information initiative (OpenEI) hosts a database of electric rate structures for aselection of U.S. electric service providers. SAM allows you to search the database and upload ratestructures from the database directly from the Utility Rate page.

Search for Rates

Search the OpenEI database for a rate structure and import the structure into SAM. This featurerequires a web connection. See Importing Rate Structure Data for details.

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Go to website

Open the OpenEI website (http://en.openei.org/wiki/Gateway:Utilities) in your computer's default Webbrowser.

Description

These variables help you identify the rate structure. These are optional variables and do not affect results. Ifyou download rate structure data from the internet, SAM populates the variables automatically.

Name

The name or title of the rate structure.

Description

Text describing the rate structure.

Schedule

The schedule name, often an alphanumeric designation used by the electric service provider.

Source

A document reference or website link for the rate sheet, tariff book, or other document containing therate information.

Rate Escalation

The escalation rate is an annual percentage increase that applies to all of the rates you specify on theUtility Rates page. SAM uses the sum of the escalation rate and inflation rate specified on the Financingpage to calculate utility rates in years 2 and later of the analysis period (also specified on the Financingpage). If you specify an escalation rate of zero, then SAM will use only the inflation rate to calculate out-year values. See Specifying Escalation Rates for details.

Out-years escalation rate(s)

SAM adds the escalation rate to the inflation rate specified on the Financing page to calculate values inthe project cash flow for years 2 and later. You can specify the escalation rate as either a single annualvalue, or specify a different escalation rate for each year in the project cash flow. See SpecifyingEscalation Rates for details.

Net Metering

With net metering, the project purchases and sells electricity at the same price. See Specifying a SimpleFlat Rate with or without Net Metering for details.

Enable net metering (buy=sell)

Check the box for a rate structure with net metering to set the sell rate equal to the buy rate for flatrates and time-of-use rates. Checking the box disables all Sell input variables in the rate structure.

Fixed Monthly Charges

A fixed charge is a fee that the project pays each month to the electric service provider that does notdepend on the quantity of electricity consumed or generated by the project.

Fixed Charge

A fixed dollar amount that applies to all months. Because SAM tracks project sales and purchases on

http://en.openei.org/wiki/Gateway:Utilities

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an hourly basis, it must assign the monthly fixed charge on an hourly basis. SAM arbitrarily applies thefixed charge to the final hour of each month. For example, SAM applies the charge for January to hour744 (for a month with 31 days, 24 hours/day × 31 days/month = 744 hours/month).

Flat Rate

A flat rate is an energy charge in dollars per kilowatt-hour that does not vary with the amount of electricitypurchased or sold by the project. See Specifying a Simple Flat Rate with or without Net Metering for details.

Notes.

If you specify different buy and sell rates, you should also specify load data on the Electric Load page.SAM compares the renewable energy system's output to the load data in each hour to determinewhether to buy or sell electricity in that hour.

If you specify both a flat rate and time-of-use rates, SAM adds the two rates to calculate the electricityprice in each hour.

Enable Flat Rates

Check the box for a rate structure with flat rates. If you clear the checkbox, SAM will ignore any flat ratevalues that you may have specified.

Flat Buy Rate

The fixed energy charge in dollars per kilowatt-hour for a simple flat rate structure with no time-of-use ortiered rates. This is the price that the project pays to purchase electricity from the electric serviceprovider. If you check the Enable net metering (buy=sell) box, SAM assumes that the flat buy rateand flat sell rates are equal.

Flat Sell Rate

The price in dollars per kilowatt-hour paid by the electric service provider to the project for electricitydelivered to the grid by the project. If you check the Enable net metering (buy=sell) box, SAMassumes that the flat buy rate and flat sell rates are equal and disables the flat sell rate variable. Thesell rate applies in each hour to the difference between the energy generated by the system and theload requirement specified on the Electric Loads page.

Flat Fuel Adjustment

A charge in dollars per kilowatt-hour paid by the project to the service provider for a fuel adjustment feeor any other riders or fees. SAM adds the adjustment charge to the flat buy rate to calculate the totalelectricity purchase price.

Time of Use Rate (Energy Charge)

Time of use rates are energy charges in dollars per kilowatt-hour that vary with the time of day, month ofyear, or both. See Specifying a Time-of-use Rate Structure for details.

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Notes.

If you specify time of use rates, you should also specify load data on the Electric Load page. SAMcompares the renewable energy system's output to the load data in each hour to determine whether tobuy or sell electricity in that hour.

If you specify both a flat rate and time-of-use rates, SAM adds the two rates to calculate the electricityprice in each hour.

Enable TOU Rates

Check the box to apply the time of use rate schedule specified by the time-of-use (TOU) rates for theperiods shown the weekday and weekend schedule matrices. You can disable the TOU rates withoutlosing the rate and schedule data by clearing the checkbox.

Period (1-9)

The buy, sell, and adjustment rates in dollars per kilowatt-hour for each of up to nine periods. Assign aperiod number to the weekday or weekend matrices by using your mouse to select a block in thematrix and typing the period number on your keyboard. See Defining Weekday and Weekendschedules for details.

Buy $/kWh

The price paid by the project in dollars per kilowatt-hour to purchase electricity from the electric serviceprovider.

Sell $/kWh

The price paid to the project in dollars per kilowatt-hour by the electric service provider for electricitydelivered by the project to the grid. The sell rate applies in each hour to the difference between theenergy generated by the system and the load requirement specified on the Electric Loads page.

Adj. $/kWh

Any additional charge paid by the project in dollars per kilowatt-hour to the service provider for fuel feesor other fees or riders. SAM adds the adjustment charge to the flat buy rate to calculate the totalelectricity purchase price.

Weekday

The time-of-day and month-of-year matrix that assigns a period representing set of time-of-use rates tothe five working days of the week: Monday through Friday. SAM assumes that the year begins onMonday, January 1, in the hour ending at 1:00 a.m. See Defining Weekday and Weekend schedules fordetails.

Weekend

The time-of-day and month-of-year matrix that assigns time-of-use periods to the two weekend days ofthe week: Saturday and Sunday. SAM assumes that the year begins on Monday, January 1, in thehour ending at 1:00 a.m.

Peak Demand Charges

A peak demand charge is a fee that the project pays to the electric service provider that depends on theload data you specify on the Electric Load page. The electric demand in a given hour is the differencebetween the load in that hour and the electricity generated by the system in that hour. See Specifying PeakDemand Charges for details.

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SAM arbitrarily applies the monthly demand charge to the final hour of each month. For example, SAMapplies the charge for January to hour 744 (for a month with 31 days, 24 hours/day × 31 days/month = 744hours/month).

Enable Demand Charges

Check the box to apply peak demand charges. You can disable demand charges without losing the rateand schedule data by clearing the checkbox.

Monthly fixed demand charge ($/kW,peak)

An amount in dollars per kilowatt to be paid by the project each month of the year for the maximumaverage hourly electric demand in the month.

Monthly time-of-use demand charge

An amount in dollars per kilowatt to be paid the project each month for the maximum hourly averageelectric demand in each of up to nine periods. See Specifying Peak Demand Charges for details.

Period (1-9)

The amount and adjustment rates in dollars per peak average hourly kilowatt for each of up to nineperiods. See Specifying Peak Demand Charges for details. Assign a period number to the weekday orweekend matrices by using your mouse to select a block in the matrix and typing the period number onyour keyboard. See Defining Weekday and Weekend schedules for details.

Amount ($/kW,peak)

An amount in dollars per kilowatt that the project pays for the peak average demand in kilowatts overthe period specified in the weekday and weekend schedule matrices.

Adj ($/kW)

An adjustment fee for fuel or other fees and adjustments in dollars per kilowatt that the project pays forthe peak average demand in kilowatts over the period specified in the weekday and weekend schedulematrices.

Weekday

The time-of-day and month-of-year matrix that assigns a set of peak demand charge rates to the fiveworking days of the week: Monday through Friday. SAM assumes that the year begins on Monday,January 1, in the hour ending at 1:00 a.m. See Defining Weekday and Weekend schedules for details.

Weekend

The time-of-day and month-of-year matrix that a set of peak demand charge rates to the two weekenddays of the week: Saturday and Sunday. SAM assumes that the year begins on Monday, January 1, inthe hour ending at 1:00 a.m.

Tiered Rates (Energy Charge)

Tiered rates are energy charges in dollars per kilowatt-hour that depend on the amount of electricity theproject purchases over a specified period. See Specifying a Tiered Rate Structure for details.

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Notes.

If you specify tiered rates, you should also specify load data on the Electric Load page. SAM uses theload data to determine the tier rates to apply to a given hour.

In SAM, a "tier structure" is a set of tiered rates. In most cases you will use a single tier structure. Formore complex structures with different tiered rates for different months, you can assign tiered rates tomore than one tier structure. You can define up to six tiers in each tiered structure.

Enable Tiered Rates

Check the box to apply tiered rates. You can disable tiered rates for a model run without losing the ratedata by clearing the checkbox.

Sell at Tiered Sell Rate

Assigns the rate specified by the Tiered Sell Rate variable to the sell rate.

Tiered Sell Rate

Specify the sell rate only when you choose the "sell at tiered sell rate" option. SAM ignores this valuewhen you choose either the "sell at tier 1" or "sell at lowest rate" options.

Sell at Tier 1 rate for each Tiered Structure

Assigns the rate specified by the Tier 1 buy rate to the sell rate for each of the up to six tier structures.

Sell at lowest rate for each Tiered Structure

Assigns the minimum of the up to six tier buy rates to the sell rate for each of the tier structures.

kWh Use

The maximum amount of electricity that can be purchased at the electricity charge rate and adjustmentrate for each of the up to six tiers that you can specify for each tier structure. A tier with the defaultvalue of 1e+099 would account for all of the electricity purchased over the amount of the next lowesttier. For example, for a two-tier structure with one price for all electricity purchased up to 1,000 kWhand a second price for electricity purchased over 1,000 kWh for a given month, you would specify Tier1's kWh use at 1,000 kWh and Tier 2's kWh use at 1e+099.

Rate $/kWh

The buy rate in dollars per kilowatt-hour that applies to each of up to six tiers per tier structure.

Adj $/kWh

Any additional fee in dollars per kilowatt-hour that applies to the tier.

Monthly Schedule

Choose the tier structure that applies for each month. If the same tier structure applies to all months ofthe year, use Tier Structure 1.

Specifying a Flat Rate with or without Net MeteringThe flat rate option is appropriate when a project buys and sells electricity at a fixed price that does not varywith time of day or month of year.

SAM determines whether the project buys or sells electricity on an hourly basis by comparing therenewable energy system's output with the load for each hour. This approach does not accurately model net

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metering calculated on a monthly or annual basis.

SAM assumes that the electricity price increases from year to year at the rate of inflation specified on theFinancing page. You can specify an additional annual escalation rate if you want the price to increase at arate above the inflation rate. See Specifying Escalation Rates for details.

Note. Be sure to express all rates in dollars per kilowatt-hour. Some electricity service providers mayexpress rates in cents per kilowatt-hour that you will need to convert to dollars.

A flat rate with net metering means that the project buys and sells electricity at the same price through anet metering agreement with the electric service provider. A flat rate without net metering means that theproject buys electricity at one rate, and sells it at another rate.

Note. If you specify both a flat rate and time-of-use rates, SAM adds the two rates to calculate theelectricity price in each hour.

To specify a flat rate with net metering:

1. Under Flat Rate, check Enable Flat Rates.

2. Under Net Metering, click Enable net metering (buy=sell). SAM will disable the variables forspecifying electricity sell rates.

3. In Flat Buy Rate, type the electricity purchase price in dollars per kilowatt-hour.

4. If the electricity service provider charges any additional fees in dollars per kilowatt-hour, such as afuel adjustment fee, type the value of the fee in Adjustment.

5. SAM assumes that electricity prices increase from year to year at the inflation rate specified on the Financing page. If you expect the electricity rate to increase at a rate higher than inflation, type theadditional rate of increase in Out-years escalation rate(s). See Specifying Escalation Rates fordetails.

6. Disable any rate options that do not apply to your project by clearing the following checkboxes asappropriate: Enable TOU Rates, Enable Demand Charges, Enable Tiered Rates.

To specify a flat rate without net metering:

1. Under Flat Rate, check Enable Flat Rates.

2. Under Net Metering, clear Enable net metering (buy=sell).

3. In Flat Buy Rate, type the price in dollars per kilowatt-hour at which the project will purchaseelectricity from the service provider.

4. In Flat Sell Rate, type the price in dollars per kilowatt-hour at which the project will sell electricityto the service provider.

5. If the electricity service provider charges any additional fees in dollars per kilowatt-hour, such as afuel adjustment fee, type the value of the fee in Adjustment. SAM will add this value to the flat buyrate, but not to the sell rate.

6. SAM assumes that electricity prices increase from year to year at the inflation rate specified on theFinancing page. If you expect the electricity rate to increase at a rate higher than inflation, type theadditional rate of increase in Out-years escalation rate(s). See Specifying Escalation Rates fordetails.


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Specifying Time of Use Energy ChargesA time-of-use rate (TOU) schedule is appropriate for a project that buys and sells electricity according to aprice schedule that varies with time of day and month of year. A TOU agreement may include net metering,in which case the project buys and sells electricity at the same price.

If you are modeling a project that has an agreement with a particular electricity service provider in the UnitedStates, you may be able to download the rate schedule from the OpenEI database. Follow the instructionsin Importing Rate Structure Data to see if the database includes rate structures for your provider. Theinstructions below explain how to specify a TOU rate structure by hand.

You can specify a buy rate, sell rate, and adjustment rate in dollars per kilowatt-hour for up to nine TOUperiods. You must assign a block defining time of day and month of year to each period in the weekday andweekend matrices.

Notes.

If you specify both time-of-use rates and a flat rate, SAM adds the two rates to calculate the electricityprice in each hour.

Be sure to express all rates in dollars per kilowatt-hour. Some electricity service providers may expressrates in cents per kilowatt-hour that you will need to convert to dollars.

To specify a time-of-use schedule:

1. If your project buys and sells electricity at the same price under a net metering agreement, checkEnable net metering (buy=sell) under Net Metering. Otherwise, disable net metering by clearingthe checkbox.

2. Under Time of Use Rate (Energy Charge), check Enable TOU Rates to include the TOU ratestructure in simulations. You can disable the TOU rates without losing the TOU rate data byclearing the checkbox.

3. Type appropriate prices in dollars per kilowatt-hour in the Buy $/kWh, Sell $/kWh, and Adj $/kWhcolumns for each of up to nine periods. If the rate uses net metering, you only need to specify abuy rate because SAM assumes that the sell rate is equal to the buy rate.

4. In the Weekday matrix, use your mouse to draw a rectangle representing the block of time thatapplies to Period 2, and press the 2 key on your keyboard. SAM highlights the block in the color forPeriod 2 and displays the number 2 in square the block.

5. Repeat Step 3 for each time block in the rate schedule until the weekday matrix shows all of theTOU periods you specified with the appropriate time blocks.

6. Repeat Steps 3-5 for the weekend matrix. See Defining Weekday and Weekend Schedules formore detailed instructions.

7. If the rate structure includes peak demand charges, see Specifying Peak Demand Charges.

8. If the rate structure includes tiered rates, see Specifying a Tiered Rate Structure.


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Specifying Peak Demand ChargesA peak demand charge is a monthly price paid by the project in dollars per kilowatt for the maximum powerit consumes from the grid over each month of the year.

Note. In SAM, the units for energy quantities such as hourly AC output of the system, hourly electricitypurchased from the grid, and hourly load are all given in kWh and represent a total energy quantity overthe hour. (That is assuming that hourly solar radiation data determined from the weather file representsthe total solar radiation that reaches the solar collector over each hour.) Each hourly quantity is thereforealso effectively a power quantity (rate of generating or consuming energy per unit of time) value inkilowatt-hours per hour (kWh/h), equivalent to kilowatt (kW).

SAM calculates the peak demand charge for each month by first determining the maximum demand inkilowatts for the month, and then determining what charge to apply to that kilowatt value based on thedemand charges you specify. (See instructions below.)

The demand in a given hour is the load in that hour from the load data specified on the Electric Load pageminus the AC output of the system in that hour calculated during simulation. The maximum demand in amonth is the highest demand value that occurs over the period of a month.

f you only specify monthly fixed demand charges, then the demand charge would be the value you specifiedfor the month in question. For example, if for the month of May, SAM finds that the maximum demandoccurs on the weekday May 12th at 3 pm, SAM would apply the May demand charge specified underMonthly fixed demand charge. If you specify a monthly time-of-use (TOU) demand charge, then would applythe weekday TOU demand charge for 3 pm in May specified on the Weekday schedule matrix. Note thatyou can specify both a monthly demand charge and a monthly TOU demand charge, SAM simply adds thetwo charges to calculate the total demand charge.

Note. The demand charge calculation requires that you specify an electric load for your project. SeeElectric Load for details.

To specify peak demand charges:

1. Under Peak Demand Charges, check Enable Demand Charges. You can always disabledemand charges without losing the rate data by clearing the checkbox.

2. If the rate structure includes a fixed monthly demand charge that does not vary with time of day,under Monthly fixed demand charge ($/kW,peak) type the charge in dollars per kilowatt thatapplies to each month.

3. If the demand charge varies with time of day and year, type the demand charge and any additionaladjustment fee in dollars per kilowatt for each of up to nine TOU periods. The total demand chargefor each period is the sum of the values in the Amount and Adj columns.

You can specify both a monthly fixed demand charge and a monthly TOU demand charge if that isappropriate for your rate schedule. SAM will add the two values when it calculates the total demandcharge.

4. In the Weekday matrix, use your mouse to draw a rectangle representing the block of time thatapplies to Period 2, and press the 2 key on your keyboard. SAM highlights the block in the color forPeriod 2 and displays the number 2 in square the block.

5. Repeat Steps 3-4 for each time block in the rate schedule until the weekday matrix shows all of theTOU periods you specified with the appropriate time blocks.

6. Repeat Steps 3-5 for the weekend matrix. See Defining Weekday and Weekend Schedules for

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more detailed instructions.

7. If the rate structure includes time-of-use energy charges, see Specifying Time of Use EnergyCharges.

8. If the rate structure includes tiered rates, see Specifying a Tiered Rate Structure.


Specifying a Tiered Rate StructureIn a tiered rate structure, different electricity prices apply as the amount of electricity purchases increasesover time in a given month. Each tier represents a monthly quantity of purchased electricity, a purchaseprice, and optional adjustment fee. For example, in a three-tier structure, one price might apply to electricitypurchased up 100 kWh (Tier 1) in a given month. If the project purchases more than 100 kWh in that month,then a second price might apply for electricity purchased between 100 kWh and up to 150 kWh (Tier 2). Ifthe project purchases more than 150 kWh, a third price might apply to electricity purchased over 150 kWh(Tier 3). In this three-tier example, if the project only purchases 75 kWh in a month, then it would purchaseall of its electricity at the Tier 1 rate for that month.

SAM allows you to specify both a buy rate, or price paid by the project to purchase electricity from theelectric service provider, and a sell rate, or price paid to the project for electricity it sells to the provider.There are three options for defining the sell rate:

As a fixed price that you specify,

as a price equal to the Tier 1 rate you specify, or

as a price equal to the lowest of the up to six tiers that you specify.

SAM also allows you to specify more than one set of tiered rates. Each set of tiered rates is called a tierstructure, and applies to one or months of the year as specified under Monthly Schedule. You might usemore than one tier structures to specify different tiered rates for different seasons of the year.

To specify a tiered rate structure:

1. Under Tiered Rates (Energy Charge), check Enable Tiered Rates. You can always disabletiered rates without losing rate data by clearing the checkbox.

2. Under Sell Rate, choose one of the three options available for specifying the sell rate. See abovefor descriptions.

3. If you specify Sell at Tiered Sell Rate, type a value for Tiered Sell Rate in dollars per kilowatt-hour. If you choose one of the other two options, SAM ignores this value.

4. Under Tier Structure 1, type the maximum amount of electricity in kilowatt-hours in the kWh Usecolumn for Tier 1 that the project is allowed to purchase at the Tier 1 rate in a single month.

5. In the Rate $/kWh column, type the purchase price that applies to Tier 1.

6. In the Adj $/kWh column, type the additional fee in dollars per kilowatt-hour that applies to the tier.SAM adds the rate and adjustment values to calculate the total energy price for the tier.

7. Repeat Steps 4-6 for each of the up to six tiers in Tier Structure 1.

8. Repeat Steps 3-7 for each of the up to six tier structures.

9. Under Monthly Schedule, for each month of the year, choose the tier structure that applies to themonth.

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Importing Rate Structure DataIf your computer is connected to the internet, you can download rate structure data from the OpenEIdatabase for a selection of electricity service providers in the United States. You can find out more aboutthe database on the OpenEI website: http://en.openei.org/wiki/Gateway:Utilities.

Note. When you import data from the OpenEI website, SAM imports the appropriate rates and scheduledata, but does not check the appropriate boxes to enable the rate options that apply to the ratestructure. Be sure to very that the appropriate options are enabled as described in the instructionsbelow.

To import rate structure data:

1. Click Search for rates.

2. In the OpenEI Utility Rate Database window, locate your electric service provider in the list by eithertyping some letters in the provider's name and clicking Refresh, or by scrolling through thealphabetical list.

3. Click the provider's name to populate the Available rate schedules list. If nothing appears in thelist, there is no data available for the service provider in the database.

4. In the Available rate schedules list, click the rate schedule you want to import into SAM. SAMdisplays information about the rate schedule under Rate Information. You cannot change thisinformation.

To see the database entry on the OpenEI website using your computer's web browser, click Go torate page on OpenEI.org. You can also right-click the link to copy the URL to your computer'sclipboard.

To open a copy of the database file, click JSON. You can also right-click the link to copy the URLto your computer's clipboard. The database file is a text file that you can view in a web browser andedit in a text editor.

5. Click Download and apply utility rate to download the rate structure data into SAM, or clickClose to return to the Utility Rate page without downloading the data.

After you import the data, SAM displays the appropriate rates and schedules on the Utility Ratespage.

6. Verify that the appropriate options for the rate structure are checked: Enable net metering(buy=sell), Enable Flat Rates, Enable TOU Rates, Enable Demand Charges, Enable TieredRates.

Specifying Escalation RatesWhen you specify electricity prices and rates, SAM assumes that those values apply in Year 1 of theproject cash flow. To calculate dollar values in Year 2 and later, SAM increases the Year 1 values using theinflation rate specified on the Financing page. If you specify an escalation rate, SAM uses the sum of theescalation rate and inflation rate to calculate the out-year values.

In some cases, it may be useful to assign a different escalation rate to each year in the analysis periodusing an annual schedule. (The analysis period is defined on the Financing page.) For example, you could

http://en.openei.org/wiki/Gateway:Utilities

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model an escalation rate that increases every five years by assigning one value to years 1 through 5, asecond one to years 6 through 10, and so on.

To enter the escalation rate as an annual schedule:

1. Under Rate Escalation, look at the grey and blue button next to Out-years escalation rate(s). Bydefault, the "Value" label is blue indicating that the single value mode is active for the variable.

2. Click the button with the "Sched" label to change the mode to schedule and activate the Editbutton.

3. Click Edit. The Edit Schedule window displays a table with each row representing a year in theanalysis period.

4. If you want to limit the number of values in the schedule, type a number in # Values. Typically, youshould type a number equal to or greater than the analysis period specified on the Financing page.SAM ignores any data for years greater than the analysis period. For example, if the schedule has50 rows, but the analysis period is 30 years, SAM ignores any values in rows 31 and above.

5. In the Edit Schedule window, type an escalation rate for each year in the analysis period. Use thevertical scroll bar to move through the years.

To delete a value, select it and press the Delete key on your keyboard.

Note. You must type a value for each year. If you delete a value, SAM will clear the cell, and you musttype a number in the cell or SAM will consider the schedule to be invalid and display the error message"Bad numeric format in column xx: Edit canceled."

6. When you have finished editing the schedule, click Accept.

Defining Weekday and Weekend SchedulesThe weekday and weekend matrices allow you to associate a period with a time of day and month of year.To use the matrices, you draw rectangles on the matrix with your mouse, and type a number with yourkeyboard for the period that applies to the times represented by the rectangles.

SAM arbitrarily defines the first day of time series data (the first 24 hours for hourly data) to be Monday onJanuary 1, and assigns the remaining days of the year accordingly. SAM assumes that weekdays includeMonday through Friday, and that weekends include Saturday and Sunday. SAM does not account forholidays or other special days. It also does not account for leap years, and does not include a day forFebruary 29.


1. Assign values as appropriate to each of the up to nine periods.


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The following example shows a complete schedule for a TOU rate structure with five periods. In this case,

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the schedule only uses Periods 1,2 and 4-6.

4.4 FinancingThe Financing page displays the variables that SAM uses to calculate the project cash flow and otherrelated financial metrics that appear on the Results page.To view the Financing page, click Financing inthe main window's navigation menu. The Financing page allows you to specify the analysis period, inflationand discount rates, and loan parameters for the project. For projects with utility financing, it also allows youto specify rate-of-return targets.

Note. If the Financing page is not available, check that the No Financials option is not the active optionon the Technology and Market window. The Financials page is available only for projects with an activefinancing option.

The input variables that appear on the Financing page depend on the project financing option that youspecify in the Technology and Market window. SAM displays the project financing option in square bracketsdirectly below the tabs at the top left corner of the Main window. For example, the image below is from aproject with the Residential financing option:

To change the project financing type, click Select Technology and Market, and click a button under theheading "Select a financing option" in the Technology and Market window.

For a general description of the financing options, see Financing Overview.

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General

Applies to: All financing options (see Financing Overview for descriptions)

Analysis Period

Number of years covered by the analysis. Typically equivalent to the project or investment life. Theanalysis period determines the number of years in the project cash flow.

Inflation Rate

Annual rate of change of costs, typically based on a price index. SAM uses the inflation rate tocalculate the value of costs in years two and later of the project cash flow. Note that many of the coststhat you specify on the System Costs page, Financing page, Utility Rate page, Tax Credit Incentives, orPayment Incentives page are in year one dollars.

Real Discount Rate

A measure of the time value of money expressed as an annual rate. SAM uses the real discount rate tocalculate the present value (value in year one) of dollar amounts in the project cash flow over theanalysis period and to calculate annualized costs.

Nominal Discount Rate

SAM calculates the nominal discount based on the values of the real discount rate and the inflationrate:

Nominal Discount Rate = (1 + Real Discount Rate)(1 + Inflation Rate) - 1

Taxes and Insurance


Federal Tax, State Tax

The annual federal and state income tax rate applies to taxable income and is used to calculate taxbenefits or liabilities. Taxable income can include incentive payments for all projects, if specified by theuser, and incentive payments and revenues from electricity sales for utility and commercial third partyprojects. Note that for residential and commercial systems, electricity sales offset payments to theelectric service provider, and are not considered taxable income.

Sales Tax

The sales tax is a one-time tax that SAM includes in the project's total installed cost. SAM calculatesthe sales tax amount by multiplying the sales tax rate on the Financing page by the rate you specifyunder Indirect Capital Costs and the Total Direct Cost on the System Costs page.

Insurance

The annual insurance rate applies to the total Pre-Financing Installed cost of the project. SAM treatsinsurance as an operating cost for each year. The insurance cost in year one of the project cash flow isthe insurance rate multiplied by the Pre-Financing Installed Costs. The first year cost is then increasedby inflation in each subsequent year. For commercial and utility projects, the insurance cost is anoperating expense and therefore reduces federal and state taxable income.

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Salvage Value

Applies to: Commercial PPA, Independent Power Producer (see Financing Overview for descriptions)

SAM considers the salvage value to be taxable income of the project in the final year of the project cashflow, and calculates the value as a percentage of the total Pre-Financing Installed cost from the SystemCosts page. For example, if you specify a 10% salvage value for a 30-year project with an inflation rate of2.5% and total installed cost of $1 million, SAM will include income of $204,640.74 in year 30: $1,000,000 ×0.10 × (1 + 0.025) ̂(30 - 1).

For residential projects, the salvage value has no effect on federal and state income tax. For commercialand utility projects, the salvage value is treated as a source of pre-tax revenue in the final year of theanalysis period, increasing the federal and state taxable income. For details, see Base Case Cashflow.

Net Salvage Value

The salvage value as a percentage of the project's total Pre-Financing Installed cost.

End of Analysis Period Salvage Value

Property Tax


Assessed Percent

The assessed value of property subject to property taxes as a percentage of the system total installedcost specified on the System Costs page. SAM uses this value to calculate the assessed propertyvalue in year one of the project cash flow.

Assessed Value

The assessed property value in year one of the project cash flow. SAM calculates this value as theproduct of the Assessed Percent and the total installed cost specified on the System Costs page, andreports it in the Property Tax Net Assessed Value row of the cash flow.

Assessed Value Decline

The annual decline in the assessed property value. SAM uses this value to calculate the propertyassessed value in years two and later of the project cash flow. For an assessed value that does notdecrease annually, specify a value of zero percent per year.

Property Tax

The annual property tax rate applies to the assessed value of the project, which is a user definedpercentage of Pre-Financing Installed Costs. In addition to specifying the property tax rate, the useralso can define an annual change in the assessed value of the project. SAM treats property tax as atax-deductible operating expense for each year. In each year of the project cash flow, the property taxcost is the property tax rate multiplied by the assessed value for that year. For residential projects, theproperty tax amount is the only operating cost that can be deducted from state and federal income tax.

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Loan Type

Applies to: Residential (see Financing Overview for descriptions)

Standard Loan

For the standard loan option, loan interest payments are not tax deductible.

Mortgage

For the mortgage option, loan interest payments are tax deductible.

Loan or Financing Parameters

Applies to: Residential, Commercial, Commercial PPA, Independent Power Producer (see FinancingOverview for descriptions)

Installed Cost (Commercial PPA, Independent Power Producer)

The total installed cost from the System Costs page.

Construction Financing Cost (Commercial PPA, Independent Power Producer

The total construction financing cost shown under Construction Period.

Principal Amount

The loan principal amount. This is a calculated value and cannot be edited. To change the value, eitherchange the value of the debt fraction, or change the value of cost variables on the System Costs page.

For Residential and Commercial financing:

Principal Amount ($) = Total Installed Cost ($) × Debt Fraction (%)

For Commercial PPA and Independent Power Producer financing:

Principal Amount ($) = (Installed Cost ($) + Construction Financing Cost ($)) × Debt Fraction (%)

Debt Fraction

Percentage of the total installed cost to be borrowed.

For example, specifying a debt fraction of 25% means that the project borrows 25% of the TotalInstalled Cost amount shown on the system costs page for a 25/75 debt-equity ratio.

Note. For projects with Independent Power Producer or Commercial PPA financing, if you check AllowSAM to pick a debt fraction to minimize the LCOE, SAM disables the Debt Fraction input variable.

Loan Term

Number of years required to repay a loan. Note that this value is different than the analysis period.

Loan Rate

Annual loan interest rate.

WACC

The Weighted Average Cost of Capital (WACC) is defined as the minimum return that the project mustearn to cover financing costs. This is calculated value that you cannot directly edit. To change its value,change one of the parameters described in the following equations:

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WACC = Return on Equity × (1 - Debt Fraction) + (1 - Effective Tax Rate) × Loan Rate × DebtFraction

The effective tax rate is a single number that includes both the federal income tax rate and state incometax rate. SAM uses the effective tax rate for several calculations requiring a total income tax value:

Effective Tax Rate = Federal Tax Rate × (1 - State Tax Rate) + State Tax Rate

For residential and commercial projects, the return on equity is equal to the discount rate, which is aninput on the Financials page:

Return on Equity = Real Discount Rate

For Independent Power Producer and Commercial PPA projects, the return on equity is the requiredinternal rate of return

Return on Equity = Mininimum Required IRR

Note. If you choose the Specify First Year PPA Price solution mode option, SAM uses the MinimumRequire IRR value visible in the inactive variable for the WACC calculation.

Federal and State Depreciation

Applies to: Commercial, Commercial PPA, all Utility Market options (see Financing Overview fordescriptions)

No Depreciation

The project does not claim a depreciation tax deduction.

MACRS Mid-Quarter Convention

Modified Accelerated Cost Recovery System depreciation schedule offered by the Federal governmentand some states. This tax deduction, expressed as a percentage of the total installed cost, applies tothe first years of the project life as follows: 35%, 26%, 15.6%, 11.01%, 11.01%, and 1.38%.

MACRS Half-Year Convention

Modified Accelerated Cost Recovery System depreciation schedule offered by the Federal governmentand some states. This tax deduction, expressed as a percentage of the total installed cost, applies tothe first years of the project life as follows: 20%, 32%, 19.2%, 11.52%, 11.52%, and 5.76%.

Straight Line (specify years)

A depreciation schedule offered by the Federal government and some states. This tax deduction is 20%of the of total installed cost and applies to the number of years you specify, starting with year one of theproject life.

Custom (specify percentages)

Allows you to assign a depreciation deduction as a percentage of the total installed cost for each yearin the project life. Click Edit to assign the values, and see Editing Annual Schedules for details onentering the values.

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Construction Period

Applies to: Commercial PPA, all Utility Market options (see Financing Overview for descriptions)

SAM allows you to specify parameters for up to five construction loans to approximate interest duringconstruction (IDC) that SAM considers to be a cost to the project.

SAM assumes that 100% of the construction balance is outstanding for half of the construction period,which is equivalent to an even monthly draw schedule with an average loan life of half of the constructionperiod. To approximate a different draw schedule, you could adjust the loan's interest rate accordingly.

Note. To model a project with no construction period loans, set the Percent of Installed Costs value foreach of the five loans to zero.

For the Commercial PPA and Independent Power Producer options, SAM includes the total constructionfinancing cost in the project loan principal amount shown on the Financing page.

For the partnership flip, sale leaseback, and single owner options, SAM includes the total constructionfinancing cost in the issuance of equity value reported in the project cash flow.

Loan

SAM allows you to specify up to five construction loans. You can type a name describing each loan oruse the default names.

Percent of Installed Costs

The amount borrowed for the construction loan as a percentage of the total installed cost, assumingthat all construction costs are included in the installation costs you specify on the System Costs page.Specify a non-zero percentage for each construction period loan you want to include in the analysis.

The sum of the up to five percentage values you specify for each construction loan must be 100%.

Up-front Fee

A percentage of the principal amount, typically between 1% and 3% that SAM adds to the interestamount for each construction loan to calculate the total construction financing cost. Note that nointerest applies to the up-front fee.

Up-front Fee Amount ($) = Principal Amount ($) × Up-front Fee Percentage (%)

Months Prior to Operation

The loan period for the construction loan in months.

Interest Rate (Annual)

The construction loan interest rate as an annual percentage.

Principal Amount

The amount borrowed for each construction period loan:

Principal Amount ($) = Total Installed Cost ($) × Percent of Installed Costs (%)

Interest

The total interest payment due for each construction period loan, assuming that 100% of theconstruction balance is outstanding for half of the construction period.

Interest ($) = Principal Amount ($) × Loan Rate (%/yr) / 12 (mos/yr) × 0.5

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Total Construction Financing Cost

SAM includes the total construction financing cost included in the project cost.

Total Construction Financing Cost ($) = Interest ($) + Up-front Fee Amount ($)

Solution Mode

Applies to: Commercial PPA, all Utility Market options (see Financing Overview for descriptions)

The solution mode determines whether SAM calculates a PPA price based on IRR targets that you specify,or an IRR based on a PPA price that you specify.

SAM uses a different set of equations to calculate the PPA price or IRR for different financing options:

The utility market options (Leveraged Partnership Flip, All Equity Partnership Flip, Sale Leaseback, andSingle Owner) use a new financial model developed for the April 2011 version of SAM.

The Commercial PPA and Independent Power Producer options use a simpler financial model that wasused in SAM 2010.11.9 and older versions.

See Financing Overview for a description of the Financing options.

Utility Market Options (except Independent Power Producer)

SAM offers two solution modes for the Leveraged Partnership Flip, All Equity Partnership Flip, SaleLeaseback, and Single Owner financing options:

Specify First Year PPA Price allows you to specify the PPA price as an input, and SAM calculates theresulting IRR.

Specify IRR Target allows you to specify the IRR as an input, and SAM uses a search algorithm to findthe PPA price required to meet the target IRR.

Solution Mode 1: Specify First Year PPA Price

The Specify PPA Price option allows you to specify a first year power purchase price and optional annualescalation rate:

For All Equity and Leveraged Partnership Flip options, and Sale Leaseback option that involve twoparties, SAM calculates the investor and developer IRR.

For the Single Owner option, SAM calculates the project IRR.

After running simulations, SAM shows the IRR values in the Metrics table.

Note. For the Specify PPA Price option, the IRR target year, IRR target, IRR actual year, and IRR intarget years shown in the Metrics table are not valid results because these values do not apply to theoption.

PPA Price

The power purchase price in cents per kWh.

If an annual escalation rate applies to the power purchase price, enter it under Power PurchaseAgreement.

Note. If you choose the Specify IRR Target option, SAM ignores the value of the PPA Price variable.

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Solution Mode 2: Specify Investor IRR Target

The Specify Investor IRR Target option allows you to specify a desired IRR target and the year you wouldlike the IRR to be achieved. SAM finds the PPA price required to meet the target given the financingassumptions and system costs you specify.

SAM uses an iterative algorithm to search for the PPA price that meets the IRR target in the year youspecify. If it cannot find a solution, it finds the PPA price that result in an IRR and year as close as possibleto the target values, and reports the IRR and year as "actual" values.

Note. In some cases, the actual values may differ significantly from the target values. If you are notsatisfied with the actual values, you can adjust your assumptions and rerun simulations until the actualand target values match.

After running simulations, SAM shows both the target values and the actual values in the Metrics table. Forfinancing options involving both a tax investor and developer, SAM shows the IRR for both partners.

IRR Target

The desired IRR target as a percentage:

For the All Equity and Leveraged Partnership Flip options and Sale Leaseback option, the target IRRis the tax investor IRR. SAM calculates the developer IRR as a function of the value in excess of thetax investor IRR.

For the Single Owner option the required IRR is the project IRR.

Tip. SAM assumes a default tax equity return rate of 8.5% for the All Equity PartnershipFlip option and a default rate of 10.5% for the Leveraged Partnership Flip option. Inpractice, tax investors may accept lower or require higher returns for specific projectsthan these rates, depending on project size, market conditions, and perceived projectrisks.The solution mode determines whether SAM calculates a first year PPA price based on an IRRthat you specify or whether SAM calculates IRR values based on a PPA price that you specify.

IRR Target Year

The year in which the target IRR will be achieved.

Commercial PPA and Independent Power Producer

SAM offers two solution modes for the Commercial PPA and Independent Power Producer financingoptions:

Specify First Year PPA Price allows you to specify the PPA price as an input, and SAM calculates theresulting IRR.

Specify IRR Target allows you to specify the IRR as an input, and SAM uses a search algorithm to findthe PPA price required to meet the target IRR.

Solution Mode 1: Specify IRR Target

Choose this option when you have an IRR in mind and want SAM to calculate the PPA price required toachieve the IRR.

SAM uses an iterative algorithm to search for the PPA price that meets the IRR target. If it cannot find asolution, it finds the PPA price that results in an IRR as close as possible to the target.

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After simulations, SAM shows the first year PPA price that it calculated in the Metrics table and theproject's after-tax IRR required associated with the PPA price.

Minimum Required IRR

The project's minimum internal rate of return target. SAM uses an iterative algorithm to calculate a PPAprice that results in an IRR no less than the target you specify.

PPA Escalation Rate

An escalation rate applied (above inflation) to the first year PPA price to calculate the electricity salesprice in years two and later in the project cash flow. When the financial optimization option is checked,the PPA escalation rate is a result instead of an input variable.

Constraint: Require a Minimum DSCR

A requirement that the debt-service coverage ratio not be allowed to fall below the specified level.

Minimum Required DSCR

The lowest value of the DSCR required for the project to be financially feasible. The DSCR is the ratio ofoperating income to costs in a given year.

Constraint: Require a positive cashflow

A requirement that the annual project cash flow be positive throughout the project life.

The financial optimization options allow you to automatically optimize the debt fraction and PPA escalationrate to minimize the levelized cost of energy. When you optimize the value of these variables, SAM findsthe debt fraction and PPA escalation rates that result in the lowest levelized cost of energy. Thisoptimization is often necessary to minimize project costs when you specify constraints on the internal rateof return (IRR), debt-service coverage ratio (DSCR), and positive cash flow (See Wiser 1996 in References).

Allow SAM to pick a debt fraction to minimize the LCOE

Check this option instead of entering a value for Debt Fraction to allow SAM to find the debt fractionvalue that results in the lowest levelized cost of energy. When you check this option, SAM disables thedebt fraction input variable and reports it as a result in the Metrics table on the Results page.

Allow SAM to pick a PPA escalation rate to minimize the LCOE

Check this option instead of entering a value PPA Escalation Rate to allow SAM to find the PPAescalation rate value that results in the lowest levelized cost of energy. When you check this option,SAM disables the PPA escalation rate input variable and reports it as a result in the Metrics table onthe Results page.

Solution Mode 2: Specify First Year PPA Price

Choose this option when you want SAM to calculate the IRR based on a PPA price that you specify.

After simulations, SAM shows the project IRR that it calculated in the Metrics table, along with the first yearPPA price you specify.

First Year PPA Price

The first year PPA price in dollars per kilowatt-hour.

PPA Escalation Rate

An optional annual power price escalation rate.

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Power Purchase Agreement

Applies to: Commercial PPA, all Utility Market options except Independent Power Producer (seeFinancing Overview for descriptions)

For the Utility Independent Power Producer option, the PPA escalation rate variable is under SpecifyMinimum Required IRR or Specify First Year PPA Price. See Solution Mode for details.

PPA Escalation Rate

An escalation rate applied to the first year PPA price to calculate the electricity sales price in years twoand later in the project cash flow.

Constraining Assumption

Applies to: Commercial PPA (see Financing Overview for descriptions)

Minimum Required IRR

The project's minimum target internal rate of return. SAM uses an iterative algorithm to calculate a PPAprice that results in an internal rate of return no less than the target you specify.

Reserves

Applies to: All Utility Market options except Independent Power Producer (see Financing Overview fordescriptions)

Interest on Reserves

Annual interest rate earned on funds in reserve accounts. The different financing options have differentreserve accounts, and the interest on reserves rate applies to all of the accounts available for a givenoption:

Working capital reserve account, specified under Cost of Acquiring Financing.

Major equipment reserve account, specified under Major Equipment Replacement Reserves.

Debt service reserve account (Leveraged Partnership Flip, Single Owner), specified under DebtService.

Lessee reserve account (Sale Leaseback), specified under Sale Leaseback.

Tax Investor

Applies to: Leveraged Partnership Flip, All Equity Partnership Flip (see Financing Overview fordescriptions)

The Tax Investor parameters determine the tax investor's share of the project investment, revenue, and taxbenefits.

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Initial Capital Contribution

The tax investor's share of the project equity requirement as a percentage of:

For Leveraged Partnership Flip, the total installed cost less the debt amount.

For All Equity Partnership Flip, the total installed cost.

Share of Project Cash, Pre-flip

The percentage of annual project cash returns allocated to the tax investor in years before the flip targetis reached.

Share of Project Cash, Post-flip

The percentage of annual project cash returns allocated to the tax investor in years after the flip targetis reached.

Share of Tax Benefits, Pre-flip

The percentage of taxable income and any tax benefits, including depreciation-related tax losses andITC-related tax credits, allocated to the tax investor before the flip target is reached.

Share of Tax Benefits, Post-flip

The percentage of taxable income and any tax benefits, including depreciation-related tax losses andITC-related tax credits, allocated to the tax investor after the flip target is reached.

Developer

Applies to: All Equity Partnership Flip, Leveraged Partnership Flip (see Financing Overview fordescriptions)

The developer's initial capital contribution and share of cash and tax flows are based on the tax investorquantities.

SAM calculates these values by subtracting the tax investor quantities from 100%. You cannot directly editthese values. To change the values, edit values under Tax Investor.

Developer Capital Recovery

Applies to: All Equity Partnership Flip (see Financing Overview for descriptions)

The Developer Capital Recovery options determine the timing of cash flows to the developer.

During the capital recovery period, the developer cannot receive an amount of cash greater than its initialinvestment.

Time

Choose this option to specify the duration of the developer's capital recovery period.

Full Capital Recovery

Choose this option to allocate 100% of the project cash flow to the developer until the developerrecovers its investment. Note that there is no return on investment, just a return of investment.

Duration

The number of years during which the developer receives 100% of the project cash flow. If the number of

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years exceeds the time required for full capital recovery the developer only receives 100% of the projectcash for years up to the year the developer recovers its investment.

Debt Terms

Applies to: Leveraged Partnership Flip, Single Owner (see Financing Overview for descriptions)

The Debt Terms input variables determine the quantity and cost of of debt.

SAM calculates the debt fraction as a result based on the debt terms you specify here, the Debt Serviceparameters, and the project costs and revenues shown in the cash flow.

All-In Interest Rate

Annual loan interest rate.

Tenor

The loan period in years.

Debt Closing Costs

You can specify debt closing costs as a dollar amount, percentage of the debt amount, or both. Closingcosts are costs associated with securing financing, and may include fees paid to consultants, legalcounsel, or the lender.

SAM considers debt closing costs to be part of the project's total installed cost.

Debt Closing Costs

A dollar amount representing debt closing costs.

Debt Closing Fee

A percentage of the total debt representing debt closing costs.

Debt Service

Applies to: Leveraged Partnership Flip, Single Owner (see Financing Overview for descriptions)

The Debt Service input variables determine the quantity of cash available to service debt for each year of theanalysis period.

SAM assumes that the debt service coverage ration remains constant over the analysis period.

Debt Service Coverage Ratio (DSCR)

The ratio of annual cash available for debt service to the sum of the annual principal and interestpayment.

Annual cash available for debt service is equal to Earnings Before Interest Taxes Depreciation andAmortization (EBITDA) shown in the cash flow less cash used to fund the major equipment replacementreserves.

Tip. DSCRs generally range between 1.40 and 1.50 for proven wind technology. For solar, the ratios areslightly lower: In the 1.30 to 1.40 range for PV, and perhaps slightly lower for CSP and CPVtechnologies.

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Debt Service Reserve Account

A debt service reserve account is a fund that may be required by the project debt provider. The account isfunded in Year 0 and earns interest in Years 1 and later at the reserve interest rate specified under Reserves. Once debt has been repaid, the funds in the account are released to the project cash flow.

Debt Service Reserve Account

The number of months of principal and interest payments in Year 1 whose value is equivalent to the sizeof the debt reserve account in Year 0.

SAM calculates the reserve account size in Year 0 based on the principal and interest amounts in Year 1:

Year 0 Debt Service Reserve Amount ($) = [ Year 1 Principal ($/yr) + Year 1 Interest ($/yr) ] × DebtService Reserve Account (months) / 12 (months/yr)

Tip. Debt Service Reserve Accounts for utility-scale projects are typically sized to cover 6 to 12 monthsof principal and interest payments.

Production Based Incentives (PBI) Available for Debt Service

If you specified one or more production-based incentives on the Payment Incentives page, and theincentives can be used to service debt, check the box for the incentive.

For example, if you specified a Utility PBI on the Payment Incentives page that can be used to servicedebt, check the Utility box.

Sale Leaseback

Applies to: Sale Leaseback (see Financing Overview for descriptions)

The Sale Leaseback input variables determine the developer's operating margin and size of the leasepayment reserve account. SAM includes the developer's margin as a project expense in the cash flow.

Lessee Operating Margin

The developer's margin in dollars per kilowatt of system nameplate capacity.

Lessee Margin Escalation

An annual escalation rate that applies to the developer's margin. The inflation rate does not apply to thedeveloper's margin.

Lessor Required Lease Payment Reserve

The size of the lease payment reserve account in months. (In some cases, the tax investor may requirethat the developer fund a reserve account.)

Lease Reserve Amount ($) = Lessor Required Lease Payment Reserve (months) / 12 (months/yr) ×Year 1 Pre-tax Operating Cash Flow ($/yr)

Amount

This amount of the developer's margin.

Amount ($) = Lessee Operating Margin ($/kW) × System Nameplate Capacity (kW)

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Cost of Acquiring Financing

Applies to: All Utility Market financing options, except Independent Power Producer (see FinancingOverview for descriptions)

The available variables depend on the financing option as indicated in parentheses below.

The Cost of Acquiring Financing input values represent the cost of securing debt or the participation of taxinvestors.

Financing Cost (Single Owner)

The dollar amount associated with acquiring financing.

Development Fee (All options except Single Owner)

A fee paid to the developer in Year 0, specified as a percentage of the total installed cost on theSystem Costs page.

Development Fee ($) = Development Fee (%) × Total Installed Cost ($)

Equity Closing Cost (All options except Single Owner)

A dollar amount representing costs associated with securing participation of a tax investor, such asconsulants and legal fees.

Other Financing Costs (All options except Single Owner)

A dollar amount for financing costs not included in the equity closing cost or development fee.

Working Capital Reserve Account Sizing - Months of Operating Costs (All options)

The size of the working capital reserve in months.

Work ing Capital Reserve Amount ($) = Months of Operating Costs (months) / 12 months/yr × Year1 Total Expenses ($/yr)

Depreciation

Applies to: All Utility Market options, except Independent Power Producer (see Financing Overview fordescriptions)

The Depreciation options allow you to specify how SAM calculates the depreciation tax deduction and tospecify an optional bonus depreciation.

SAM makes the following simplifying assumptions:

To represent depreciation of assets with different classes or service lives, you can specify an allocationas a percentage of the total installed cost to each of up to six different depreciation methods.

State and federal depreciable bases are the same, except for bonus depreciation.

Investment-based incentives (IBI) and capacity-based incentives (CBI) reduce the depreciation basisproportionally.

Allocation

You can allocate a percentage of the total project cost to each of the following deprecation methods: 5-Yr Modified Accelerated Cost Recovery System (MACRS), 15-Yr MACRS, 5-year straight line (SL), 15-Yr SL, 20-Yr SL, 39-Yr SL.

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SAM assumes the half-year convention for all depreciation methods.

To model a project with no depreciation, enter zero for all depreciation methods.

Note. SAM allows you to specify allocations that total more than 100%. A negative Non-depreciablevalue indicates total allocations greater than 100%.

Bonus Depreciation

The bonus depreciation applies in Year 1 as a percentage of the allocations that you specify for thestandard depreciation.

Specify a percentage and check the box for each depreciation allocation that qualifies for the bonusdepreciation.

For example, for a federal bonus depreciation that is 100% of the 5 yr MACRS depreciation class, if youspecified the following depreciation allocations: 80% 5 yr MACRS, 1.5% 15 yr MACRS, and 3% 15 yrStraight Line, you would enter 100% for Federal, check the 5-yr MACRS box, and clear the remainingboxes.

Tip. The Tax Relief, Unemployment Insurance Reauthorization, and Jobs Creation Act of 2010 extendedthe bonus depreciation incentive through 2010. Projects placed in service in 2011 qualify for 100% bonusdepreciation, while projects placed in service in 2012 qualify for 50% bonus depreciation. Note thatthese bonus depreciation provisions are temporary.

ITC Qualification

Check the box for each depreciation allocation that qualifies for investment tax credits (ITC) specified onthe Tax Credit Incentives page.

Major Equipment Replacement Reserves

Applies to: All Utility Market options, except Independent Power Producer (see Financing Overview fordescriptions)

Major equipment replacement reserves are funds that the project sets aside to cover the cost of replacingequipment during the analysis period. You can specify up to three replacement reserve accounts.

SAM assumes that the cost of each major equipment replacement is capitalized rather than expensed. Youcan specify a depreciation schedule for each the major equipment replacement cost.

SAM calculates the inflation-adjusted cost of each major equipment replacement and funds a reserveaccount in each of the replacement cycle. At the time of the major equipment replacement, funds arereleased from the reserve account in an amount sufficient to cover the expense.

Reserve Account

The name of the reserve account for your reference. SAM reports value associated with each account inthe cash flow and other graphs and tables using the name Reserve Account 1, 2, and 3, regardless ofthe name you enter.

Replacement Cost

The cost in Year 1 dollars per kW of nameplate capacity.

Replacement Cost ($) = Replacement Cost (Year 1 $/kW) × Nameplate Capacity

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Replacement Frequency

The frequency in years that the replacement cost occurs.

For example, a replacement cost of $10,000 and frequency of 5 years results in an inflation-adjustedmajor equipment capital spending amount of $10,000 occurring in Years 5, 10, 15, 20, etc.

Depreciation Treatment For All Capital Expenditure

Specify a federal and state depreciation method for the major equipment replacement cost.

4.5 Tax Credit IncentivesTo view the Tax Credit Incentives page, click Tax Credit Incentives in the main windows navigation menu.The Tax Credit Incentives page allows you to specify parameters of income tax deductions, includinginvestment tax credits or production tax credits.

The Tax Credit Incentives page allows you to define the parameters of investment tax credits (ITC) orproduction tax credits (PTC) provided by either the federal government, a state government, or both. Foreach tax credit that you define, you can specify whether the tax credit amounts are taxable, and how thetax credits affect the depreciation basis.

A tax credit is an amount that is deducted from the project's income tax. SAM displays tax credits andincome tax payments in the project cash flow and in results graphs and tables.

For a description of tax credits and incentives available to solar and other renewable energy projects in theUnited States, see the Database of State Incentives for Renewables and Efficiency at http://dsireusa.org.

Contents

Input Variable Reference describes the input variables on the Tax Credit Incentivespage.

Using Annual Schedules to Specify Incentives explains how to assign incentivevalues to individual years instead of using a single value for all years.

Viewing Tax Credits in Results explains where to find results that show the effect oftax credits on the project metrics and cash flow.


Investment Tax Credit (ITC)

An investment tax credit reduces the project's annual tax liability in year one of the project cash flow. SAMallows the ITC to be expressed either as a fixed amount or as a percentage of the project's total installedcost with a maximum limit.

Amount ($)

The fixed dollar amount of the tax credit. A zero indicates no tax credit. A value of zero indicates no taxcredit.

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Percentage (%)

The amount of the tax credit expressed as a percentage of the total installed cost displayed on thesystem costs page. A value of zero indicates no tax credit.

Maximum ($)

The upper limit of the tax credit in dollars. For tax credits with no limits, type the value 1e+099.

Reduces Depreciation Basis

Applies only to commercial and utility projects when one of the depreciation options is active on theFinancing page.

The check boxes determine whether the basis used to calculate federal depreciation, statedepreciation, or both should be reduced by the tax credit payment amount.

SAM reduces the depreciable base by 50% of the present value of the tax credits over the analysisperiod defined on the Financing page.

Production Tax Credit (PTC)

A production tax credit reduces the project's annual tax liability in year one of the cash flow and subsequentyears up to and including the year specified in the term variable. The PTC is a dollar amount per kilowatt-hour of annual electric output. If you specify an escalation rate, SAM increases the annual tax creditamount in years 2 and later in the cash flow by a percentage of the previous year's payment.

Amount ($/kWh)

The amount of the production tax credit as a function of the system's total electrical output in the firstyear expressed in dollars per kilowatt-hour of AC output. A zero indicates no tax credit.

Term (years)

The number of years, beginning with year 1 on the project cash flow, that the tax credit applies. Forexample, a credit with a 10-year term would apply to years 1 through 10 of the project cash flow. A zeroindicates no tax credit.

Escalation (%/year)

The annual escalation rate that applies to the tax credit. SAM applies the escalation rate to years 2 andlater in the cash flow. For example, for a tax credit with a ten year term and two percent escalation rate,the tax credit in year 2 would be 2% greater than in year 1, and in year 3, 2% greater than in year 2,and so on.

Using Annual Schedules to Specify IncentivesYou can specify each incentive as either a single value (amount or percentage) that applies to all years inthe analysis period defined on the Financing page, or you can assign a different value to each year in theanalysis period using an annual schedule.

To specify an incentive using an annual schedule:

1. Note the blue "Value" label on the blue and gray button next to the input variable indicating that thesingle value mode is active for the variable.

2. Click the button to change the mode to schedule and activate the Edit button. The button will show

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"Sched" in blue indicated that the schedule mode is active for the variable.

3. Click Edit.

4. In the Edit Schedule window, type values for each year in the analysis period. Use the horizontalscroll bar to move through the years.

SAM will ignore any values for years after the end of the analysis period. You can change the valuein Number of values to a number less than or equal to the analysis period to shorten the length ofthe table.


You can use the Copy and Paste buttons to copy values from the table to your clipboard, or pastethem into the table from the clipboard.

Note. You must type a value for each year. If you delete a value, SAM will clear the cell, and you musttype a number in the cell or SAM will consider the schedule to be invalid.


Viewing Tax Credits in ResultsThe options you select on the Tax Credit Incentives page affect the financial metrics displayed in theresults, including the levelized cost of energy, net present value, and payback.

You can see the tax credit amounts and their impact on income tax and depreciation in graphs on theResults page and in the project cash flow.

To display tax credit amounts in a graph:

1. After running simulations, click the Graph button.

2. On the Graphing tab, click Add.

3. Choose the simulation for which you want to see tax credit amounts.

4. For X Value, choose Single Value.

5. For Y1 Values, check the name of each tax credit you want to display in the graph.

6. Clear the LCOE check boxes.

SAM displays the graph as you choose graphing options. You can adjust the properties of thegraph as needed.

7. Click Accept to return to return to the main window.

To display tax credit amounts in the project cash flow:


2. Click the Base Case Cashflow tab to display the cash flow in a table.

3. Either drag the graph area border up or scroll down until the tax credits are visible in the table.

You can also export the base case cash flow to a csv file or to Excel by clicking the Export button.

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4.6 Payment IncentivesTo view the Payment Incentives page, click Payment Incentives in the main windows navigation menu.The Payment Incentives page allows you to specify payments made to the project and calculated based onthe total installed cost, system rated capacity, or the system's electricity output.

The Payment Incentives page allows you to define the parameters of investment based incentives (IBI),capacity based incentives (CBI), or production based incentives (PBI) provided by either the federal or stategovernment, an electric utility, or other institution.

An incentive payment is an amount paid to the project that contribute's to the projects annual income in oneor more years of the cash flow. SAM displays payment incentives in the project cash flow and in graphs onthe Results page.

For each payment incentive that you define, you can specify whether the incentive payments are taxable,and how the payments affect the depreciation basis.

For a description of incentives available to solar and other renewable energy projects in the United States,see the Database of State Incentives for Renewables and Efficiency at http://dsireusa.org.

Contents

Input Variable Reference describes the input variables on the Tax Credit Incentivespage.

Using Annual Schedules to Specify Incentives explains how to assign incentivevalues to individual years instead of using a single value for all years.

Viewing Tax Credit Incentives in Results explains where to find results that showthe effect of tax credits on the project metrics and cash flow.


Investment Based Incentive (IBI)

An investment-based incentive reduces the project's annual expenditures in year one of the project cashflow. SAM allows the IBI to be expressed either as a fixed amount or as a percentage of the project's totalinstalled cost with a maximum limit.

Note that if you specify two incentives from the same source (federal, state, utility, other) as both a fixedamount and a percentage of the total installed cost, SAM includes both amounts in the total incentiveamount.

Amount ($)

The fixed dollar amount of the incentive. A zero indicates no incentive.

Percentage (%)

The amount of the investment tax credit expressed as a percentage of the total installed cost displayedon the system costs page. A zero indicates no incentive.

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Maximum ($)

The upper limit of the incentive in dollars. For incentives with no limits, type the value 1e+099.

Capacity Based Incentive (CBI)

A capacity-based incentive reduces the project's annual expenditures in year one of the project cash flow.SAM allows the CBI to be expressed as a function of the system's rated capacity in watts. The system'srated capacity depends on the technology:

Photovoltaic systems: DC watts of array capacity.

Concentrating solar power systems: AC watts of power block nameplate capacity.

Generic fossil: AC watts of power block nameplate capacity.

Check an option for each capacity based incentive that applies to the project, and enter values to specifythe credit amount, percentage, term, and annual escalation rate as applicable.

Amount ($/W)

The amount of the incentive as a function of the system's nameplate electric capacity expressed indollars per watt. A zero indicates no incentive.

Maximum ($)

The upper limit of the incentive in dollars. For incentives with no limits, type the value 1e+099.

Production Based Incentive (PBI)

A production-based incentive reduces the project's annual tax liability in year one of the cash flow andsubsequent years up to and including the year specified in the term variable. The PBI is a dollar amount perkilowatt-hour of annual electric output. If you specify an escalation rate, SAM increases the annual incentivepayment amount in years two and later in the cash flow by a percentage of the previous year's payment.

Amount ($/kWh)

The amount of the incentive as a function of the system's total electrical output in the first yearexpressed in dollars per kilowatt-hour of AC output. A zero indicates no incentive.

Term (years)

The number of years, beginning with year one of the project cash flow, that the incentive applies. Forexample, an incentive with a 10-year term would apply to years one through 10 of the project cash flow. A zero indicates no incentive.

Escalation (%/year)

The annual escalation rate that applies to the incentive. SAM applies the escalation rate to years twoand later in the cash flow. For example, for an incentive with a ten year term and two percent escalationrate, the incentive in year two would be two percent greater than in year one, and in year three, twopercent greater than in year two, and so on.

Tax Implications

The check boxes in the Taxable Incentive, Reduces ITC Basis, and Reduces Depreciation Basis columnsdetermine whether each incentive qualifies as income for tax purposes, reduces the basis used to calculatethe ITC, or reduces the basis used to calculate the depreciation amount, respectively.

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Taxable Incentive

Determines whether the incentive payment is subject to federal or state income tax.

When you check a Taxable Incentives check box for an incentive, SAM multiplies the applicable federaland state tax rate by the incentive amount and adds it to the income tax amount in the appropriateyears of the project cash flow.

The state and federal tax rates are inputs on the Financing page.

Reduces ITC Basis

This option applies only to projects with one or more ITCs specified on the Tax Credit Incentives page.

When you check a Reduces ITC Basis check box for an incentive, SAM subtracts the amount of theincentive payment from the total installed cost shown on the system costs page before calculating theITC amount.

Reduces Depreciation Basis

This option applies only to projects with commercial or utility financing with one or more depreciationoption selected on the financials page.

When you check a Reduces Depreciation Basis check box for an incentive, SAM subtracts 50 percentof the tax credit amount from the depreciation basis in each applicable year of the project life.

Using Annual Schedules to Specify IncentivesYou can specify each incentive as either a single value (amount or percentage) that applies to all years inthe analysis period defined on the Financing page, or you can assign a different value to each year in theanalysis period using an annual schedule.

To specify an incentive using an annual schedule:

1. Note the blue "Value" label on the blue and gray button next to the input variable indicating that thesingle value mode is active for the variable.

2. Click the button to change the mode to schedule and activate the Edit button. The button will show"Sched" in blue indicated that the schedule mode is active for the variable.

3. Click Edit.

4. In the Edit Schedule window, type values for each year in the analysis period. Use the horizontalscroll bar to move through the years.

SAM will ignore any values for years after the end of the analysis period. You can change the valuein Number of values to a number less than or equal to the analysis period to shorten the length ofthe table.


You can use the Copy and Paste buttons to copy values from the table to your clipboard, or pastethem into the table from the clipboard.

Note. You must type a value for each year. If you delete a value, SAM will clear the cell, and you musttype a number in the cell or SAM will consider the schedule to be invalid.

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Viewing Incentives in ResultsThe options you select on the Payment Incentives page affect the financial metrics displayed in the results,including the levelized cost of energy, net present value, and payback.

You can see the incentive amounts and their impact on income tax and depreciation in graphs on theResults page and in the project cash flow.

To display incentive amounts in a graph:


2. On the Graphing tab, click Add.

3. Choose the simulation for which you want to see investment amounts.

4. For X Value, choose Single Value.

5. For Y1 Values, check the name of each incentive you want to display in the graph.

6. Clear the LCOE check boxes.

SAM displays the graph as you choose graphing options. You can adjust the properties of thegraph as needed.

7. Click Accept to return to return to the main window.

To display incentive amounts in the project cash flow:


2. Click the Base Case Cashflow tab to display the cash flow in a table.

3. Either drag the graph area border up or scroll down until the incentive payments are visible in thetable.

You can also export the base case cash flow to a csv file or to Excel by clicking the Export button.

4.7 Annual PerformanceTo view the Annual Performance page, click Annual Performance in the main windows navigation menu.The Annual Performance page displays input variables that impact the system's total annual electric output.

The two annual performance variables are used by SAM's financial model. The performance modelcalculates the hourly system electrical output (thermal output for solar water heating systems) over a singleyear and passes the sum of the hourly values to the financial model. The financial model then applies theavailability factor to this total to determine the total annual output for Year one of the project cash flow, andapplies the degradation rate to that value to calculate the Year two output. See below for details.

You can enter the annual performance factors either as a single value, or as a series of values that apply toeach year in the project life. If you assign values to specific years, SAM applies the degradation rate oravailability factor to the year 1 annual output value, not to the previous year's value. See below for details.

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Notes.

The simulation output data does not take into consideration the system degradation or availability factoron the Annual Performance page.

The annual energy quantity value reported in the metrics table and graphs is the Year one value, whichtakes the availability factor into account.

Annual System Performance

System Degradation (%)

The system degradation rate can be used to account for annual reduction in electrical output due toaging system components. SAM applies the degradation rate to the system's total annual electric ACoutput in year 2 and later. For example, the default value of 1% for photovoltaic systems results in fulloutput in year 1, 99% of the year 1 output in year 2, 99% of the year 2 output in year 3, and so on.

If you assign values to specific years using an annual schedule, SAM applies the degradation rate tothe year 1 annual output value, not to the previous year's value.

Availability (%)

The availability factor accounts for downtimes due to forced and scheduled outages. SAM multiplieseach hour's calculated electrical AC output by the system availability factor. The default value of 100%for photovoltaic systems results in no reduction in output. The default value of 96% for concentratingsolar power systems results in a 4% reduction in output.

If you assign values to specific years using an annual schedule, SAM applies the availability factor tothe year 1 annual output value. See below for details.

Some input variables allow you to enter either a single value, or a series of values for each year in theanalysis period defined on the Financing page. Examples of these variables are the System Degradationand Availability variables on the Annual Performance page, operation and maintenance costs on the systemcosts pages for each technology, and tax credit and incentives on the Tax Credit Incentives and PaymentIncentives pages.

Annual Schedules

Variables with an annual schedule option have a small Value / Sched button next to the variable label. Thevariable's current mode is indicated in blue.

When the word "Value" is highlighted in blue, you define the variable's value as a single number.

You can use an annual schedule to enter annual values either by hand, typing values or pasting values froma spreadsheet or text file. You can also exchange data from an annual schedule with an Excel worksheet,see Excel Exchange for details.

Note. When you specify rates using an annual schedule, SAM applies the rate to the year one value.For example, a degradation rate of 0.5% in year five would result in SAM assigning a value 0.5% greaterthan the year one value to year five.

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To enter year-by-year values by hand:

1. Click Sched to change the variable's mode from a single value to annual schedule mode. SAMdisplays the Edit button.

2. Click Edit to open the Edit Schedule window.

3. In Number of values, type the number of years for which you want to assign values. Typically, thisnumber should be equal to or less than the number of years in the Analysis Period defined on theFinancing page.

Important Note. If you specify a number greater than the number of years in the analysis period, SAMignores any values in the table for years after the end of the analysis period, which does not affectanalysis results. However, if you specify a number less than the analysis period, SAM assigns a zero toeach year after the number of years you specify, which may cause unexpected results.

4. For each year in the schedule, type a value. The value should be in the same units as the variable'svalue.

You can also copy a row of values from Excel, or a line of comma separated values from a text fileand click Paste to enter a series of values.

5. Click Accept to return to the Costs page.

4.8 System Costs

4.8.1 PV System Costs

The PV System Costs page provides access to variables that define the installation and operating costs ofa photovoltaic project. Debt-related and tax costs are specified on the Financing page.

To view the PV System Costs page, select a photovoltaic technology, and click PV System Costs on themain window's navigation menu. Note that for the PV System Costs page to be available, the technologyoption in the Technology and Market window must be Photovoltaics - SAM Performance Models orPhotovoltaics - PVWatts Performance Model, and the financing option must be something other than NoFinancials.

SAM uses the variables on the PV System Costs page to calculate the project investment cost and annualoperating costs reported in the project cash flow and used to calculate cost metrics.

Variable values in boxes with white backgrounds are values that you can edit. Boxes with blue backgroundscontain calculated values or values from other pages that SAM displays for your information.

SAM provides the categories under Direct Capital Costs and Indirect Capital Costs for your convenienceto help keep track of project installation costs. Only the Total Installed Cost value affects the cash flowcalculations, so you can assign capital costs to the different cost categories in whatever way makes sensefor your analysis. For example, you could assign the cost of designing the array to the module costcategory or to the engineering category with equivalent results. After you assign costs to the categories,you should verify that the total installed cost value is what you expect. SAM accounts for the total installedcost in Year 0 of the project cash flow.

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The Operation and Maintenance Costs categories are where you specify recurring project costs. SAMreports these annual costs in the project cash flow under the Operating Expenses heading.

Note: The cost values in the sample files are intended to illustrate SAM's use. The cost data are meantto be realistic, but not to represent actual costs for a specific project. For more information see the SAMwebsite, https://www.nrel.gov/analysis/sam/cost_data.html.

Direct Capital Costs

A direct capital cost represents an expense for a specific piece of equipment or installation service thatapplies in year zero of the cash flow.

Note: Because SAM uses only the Total Installed Cost value in cash flow calculations, how youdistribute costs among the different direct capital cost categories does not affect the final results.

Module ($/Wdc or $/Unit)

For the Component-based Photovoltaic model, the module cost is expressed per unit or per DC Watt:

Dollars per DC watt multiplied by Nameplate Capacity (at reference conditions) on the Arraypage, or

Dollars per unit multiplied by Total Modules on the Array page.

For the PVWatts System Model, the module cost is expressed per unit or per DC Watt:

Dollars per watt multiplied by Nameplate Capacity on the PVWatts Solar Array page, or

Dollars per unit, where the number of modules is assumed to be one.

Inverter ($/Wac or $/Unit)

For the Component-based Photovoltaic model, the cost of inverters in the system is expressed indollars per AC Watt or dollars per inverter:

Dollars per AC watt multiplied by Total Inverter Capacity on the Array page, or

Dollars per unit multiplied by Number of Inverters in the Actual Layout column on the Array page.

For the PVWatts System Model, the inverter cost is either dollars per watt or dollars per inverter:

Dollars per watt multiplied by the product of DC Rating and DC to AC Derate Factor on thePVWatts Solar Array page, or

Dollars per unit where the number of inverters is assumed to be one.

The three other direct capital cost categories, Balance of system, equipment, Installation labor, andInstaller margin and overhead can be specified using three units. SAM calculates the total amount foreach category as shown below.

$

A fixed cost in dollars.

$/Wdc

A cost proportional to the system's DC nameplate capacity, equal to the Nameplate Capacity on theArray page for the component-based model, or the DC Rating on the PVWatts Solar Array page for thePVWatts model.

https://www.nrel.gov/analysis/sam/cost_data.html

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$/m2

Applies only to the component-based model. A cost proportional to the total module area of the array insquare meters, equal to the Total Area on the Array page. This option is not active for the PVWattsmodel.

Total

For each category, the total is the sum of the three units: Total = $ + $/Wdc × Nameplate Capacity(Wdc) + $/m2 × Total Area (m2)

Contingency (%)

A percentage of the sum of the module, inverter, balance of system, installation labor, and installermargin and overhead costs that you can use to account for expected uncertainties in direct costestimates.


The sum of module, inverter, balance of system, installation labor, installer margin and overhead costs,and contingency costs.

Indirect Capital Costs

An indirect cost is typically one that cannot be identified with a specific piece of equipment or installationservice.

Note: Because SAM uses only the total installed cost value in cash flow calculations, how youdistribute costs among the different indirect capital cost categories does not affect the final results.

The five indirect cost categories, Permitting, Environmental Studies, Engineering, Gridinterconnection, Land, and Land preparation are each calculated as the sum of the three valuesexpressed with the following units:

% of Direct Cost

A percentage of the Total Direct Cost value shown under Direct Capital Costs.

Cost $/Wdc

A cost proportional to the system's DC nameplate capacity, equal to the Nameplate Capacity on theArray page for the component-based model, or the DC Rating on the PVWatts Solar Array page for thePVWatts model.

Fixed Cost

A fixed cost in dollars.

Total

For each category, the total is the sum of the three units: Total = % of Direct Cost × Total DirectCost ($) + Cost $/Wdc × Nameplate Capacity (Wdc) + Fixed Cost ($).

Sales Tax (%)

The sales tax percentage is the percentage of the total direct cost that is subjected to sales tax.

SAM calculates the total sales tax by multiplying the sales tax rate specified on the Financing page bythe percentage of direct costs you specify on the System Costs page: Total Sales Tax = Sales TaxRate × Percentage of Direct Cost × Direct Cost.

The total sales tax is a cost included in the total installed cost, which applies in Year 0 of the project

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cash flow. For projects with commercial and utility financing, the sales tax amount is deducted fromfederal and state income tax in Year 1.

Total Indirect Cost ( $)

The sum of the five indirect cost categories and the sales tax.

Total Installed Cost

The total installed cost is the project's investment cost that applies in year zero of the project cash flow.SAM uses this value to calculate loan amounts and debt interest payments based on inputs on theFinancing page, and to calculate tax credit and incentive payment amounts for incentive based tax creditsand incentives defined on the Tax Credit Incentives page and Payment Incentives pages.


The sum of total direct cost and total indirect cost.

Total Installed Cost per Capacity ($/Wdc or $/kW)

Total installed cost divided by the total system rated or nameplate capacity. This value is provided forreference only. SAM does not use it in cash flow calculations.

Operation and Maintenance Costs

Operation and Maintenance (O&M) costs represent annual expenditures on equipment and services thatoccur after the system is installed. SAM allows you to enter O&M costs in three ways: Fixed annual, fixedby capacity, and variable by generation. O&M costs are reported on the project cash flow in Years 1 andlater..

For each O&M cost category, you can specify an optional annual Escalation Rate to represent anexpected annual increase in O&M cost above the annual inflation rate specified on the Financing page. Foran escalation rate of zero, the O&M cost in years two and later is the year one cost adjusted for inflation.For a non-zero escalation rate, the O&M cost in years two and later is the year one cost adjusted forinflation plus escalation.

For expenses such as component replacements that occur in particular years, you can use an annualschedule to assign costs to individual years. See below for details.

Fixed Annual Cost ($/yr)

A fixed annual cost that applied to each year in the project cash flow.

Fixed Cost by Capacity ($/kW-yr)

A fixed annual cost proportional to the system's rated or nameplate capacity.

Variable Cost by Generation ($/MWh)

A variable annual cost proportional to the system's total annual electrical output in AC megawatt-hours.The annual energy output depends on either the performance model's calculated first year value and thedegradation rate specified on the Annual Performance page, or on an annual schedule of costs,depending on the option chosen.

Fossil Fuel Cost ($/MMBtu)

The cost per million British thermal units for fuel. SAM uses the conversion factor 1 MWh = 3.413MMBtu.

The fuel cost only applies to generic fossil, parabolic trough, and power tower systems. When the fossilfill fraction variable on the Thermal Storage page is greater than zero, the systems may consume fuel

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for backup energy.

Although the photovoltaic and dish-Stirling models ignore the fuel cost input variable, you should specifya value of zero for the variable to avoid confusion.

Specifying O&M Costs in Specific Years

SAM allows you to specify any of the four operation and maintenance (O&M) cost categories on theSystem Costs page either as a single annual cost, or using a table of values to specify an annual scheduleof costs. An annual schedule makes it possible to assign costs to particular years in the analysis period.Annual schedules can be used to account for component replacement costs and other periodic costs thatdo not recur on a regular annual basis.

You choose whether to specify an O&M cost as a single annual value or an annual schedule with the greyand blue button next to each variable. SAM uses the option indicated by the blue highlight on the button: Ablue highlighted “Value” indicates a single, regularly occurring annual value. A blue highlighted “Sched”indicates that the value is specified as an annual schedule.

For example, to account for component replacement costs, you can specify the fixed annual cost categoryas an annual schedule, and assign the cost of replacing or rebuilding the component to particular years. Fora 30-year project using a component with a seven-year life, you would assign a replacement cost to yearsseven, 14, and 21. Or, to account for expected improvements in the component's reliability in the future, youcould assign component replacement costs in years seven, 17, and 27. After running simulations, you cansee the replacement costs in the project cash flow in the appropriate column under Operating Expenses.SAM accounts for the operating costs in the other economic metrics including the levelized cost of energyand net present value.

Notes.

If you use the annual schedule option to specify equipment replacement costs, SAM does not calculateany residual or salvage value of system components based on the annual schedule. SAM calculatessalvage value separately, using the salvage value you specify on the Financing page.

Dollar values in the annual schedule are in nominal or current dollars. SAM does not apply inflation andescalation rates to values in annual schedules.

The following procedure describes how to define the fixed annual cost category as an annual schedule. Youcan use the same procedure for any of the other operation and maintenance cost categories.

To assign component replacement costs to particular years:

1. In the Fixed Annual Cost category, note that the "Value" label of the grey and blue button is blueindicating that the single value mode is active for the variable.

In this case, SAM would assign an annual cost of $284 to each year in the project cash flow.

2. Click the button so that "Sched" label is highlighted in blue. SAM replaces the variable's value withan Edit button.

3. Click Edit.

4. In the Edit Schedule window, use the vertical scroll bar to find the year of the first replacement, and

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type the replacement cost in current or constant dollars for that year.


Note. You must type a value for each year. If you delete a value, SAM will clear the cell, and you musttype a number in the cell or SAM will consider the schedule to be invalid. Type a zero for years with noannual costs.


Because you must specify an O&M cost category as either an annual cost or annual schedule, to assignboth a recurring annual fixed cost and periodic replacement cost, you must type the recurring cost in eachyear of the annual schedule, and for years with replacement costs, type the sum of the recurring andreplacement costs.

4.8.2 Trough System Costs

To view the Trough System Costs page, click Trough System Costs on the main window's navigationmenu. Note that for the empirical trough input pages to be available, the technology option in theTechnology and Market window must be Concentrating Solar Power - Empirical Trough System.

Contents

Overview describes the trough system costs.

Input Variable Reference describes the input variables on the Trough System Costspage.

Entering Periodic Operation and Maintenance Costs explains how to use annualschedules to assign operation and maintenance costs to particular years in theproject cash flow.

About the Trough System Default Cost Assumptions describes the assumptionsand sources of the default parabolic trough system costs.

OverviewSAM uses the variables on the Trough System Costs page to calculate the project investment cost andannual operating costs reported in the project cash flow and used to calculate cost metrics reported in theMetrics table on the Results page.

Because only the Total Installed Cost value affects the cash flow calculations, you can assign capital coststo the different cost categories in whatever way makes sense for your analysis. For example, you couldassign the cost of designing the solar field to the solar field cost category or to the engineer-procure-construct category with equivalent results. The categories are provided to help you keep track of thedifferent costs, but do not affect the economic calculations. After assigning costs to the categories, verifythat the total installed costs value is what you expect.

Variable values in boxes with white backgrounds are values that you can edit. Boxes with blue backgrounds

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contain calculated values or values from other pages that SAM displays for your information.

Note: The cost values in the sample files are intended to illustrate SAM's use. The cost data are meantto be realistic, but not to represent actual costs for a specific project. Actual costs will vary dependingon the market, technology and geographic location of a project. Because of price volatility in solarmarkets, the cost data in the sample files is likely to be out of date. For more information see the SAMwebsite, https://www.nrel.gov/analysis/sam/cost_data.html.





Site Improvements ($/m2)

A cost per square meter of solar field area to account for expenses related to site preparation and otherequipment not included in the solar field cost category.

Solar Field ($/m2)

A cost per square meter of solar field area to account for expenses related to installation of the solarfield, including labor and equipment.

HTF System ($/m2)

A cost per square meter of solar field area to account for expenses related to installation of the heattransfer fluid pumps and piping, including labor and equipment.

Storage ($/kWht)

Cost per thermal megawatt-hour of storage capacity to account for expenses related to installation ofthe thermal storage system, including equipment and labor.

Fossil Backup ($/kWe)

Cost per electric megawatt of power block nameplate capacity to account for the installation of a fossilbackup system, including equipment and labor.

Power Plant ($/kWe)

Cost per electric megawatt of power block nameplate capacity to account for the installation of thepower block, including equipment and labor.

Balance of Plant ($/kWe)

Cost per electric megawatt of power block nameplate capacity to account for additional costs.

Contingency (%)

A percentage of the sum of the site improvements, solar field, HTF system, storage, fossil backup, andpower plant costs to account for expected uncertainties in direct cost estimates.


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The sum of improvements, solar field, HTF system, storage, fossil backup, power plant costs, andcontingency costs.




EPC and Owner Costs (% and $)

Engineer-procure-construct costs, sometimes abbreviated as EPC costs, are costs associated with thedesign and construction of the project, which SAM calculates as the sum of a "non-fixed cost" and afixed cost.

% of Direct Cost is a value that you type as a percentage of Total Direct Cost (under Direct CapitalCost).

Non-fixed Cost is the product of % of Direct Cost and Total Direct Cost.

Fixed Cost is a value that you type as a fixed amount in dollars.

The total engineer-procure-construct cost is the sum of Non-fixed Cost and Fixed Cost.

Land (% and $)

Costs associated with land purchases, which SAM calculates as the sum of a "non-fixed cost" and afixed cost.

SAM does not use the land area value shown on the solar field page for trough and tower systems inthe land cost calculation.




The total project-land-miscellaneous cost is the sum of Non-fixed Cost and Fixed Cost.

Sales Tax (%)



The total sales tax is a cost included in the total installed cost, which applies in Year 0 of the projectcash flow. For projects with commercial and utility financing, the sales tax amount is deducted fromfederal and state income tax in Year 1.


The sum of engineer-procure-construct costs, project-land-miscellaneous costs, and sales tax.

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Operation and Maintenance (O&M) costs represent annual expenditures on equipment and services thatoccur after the system is installed. SAM allows you to enter O&M costs in three ways: Fixed annual, fixedby capacity, and variable by generation. O&M costs are reported on the project cash flow.










The cost per million British thermal units for fuel. SAM uses the conversion factor 1 MWh = 3.413MMBtu. The fuel cost only applies to generic fossil, parabolic trough, and power tower systems.Although the photovoltaic and dish-Stirling models ignore the fuel cost input variable, you should specifya value of zero for the variable to avoid confusion. (When the fossil fill fraction variable on the ThermalStorage page for either of the parabolic trough models or the power tower model is greater than zero,the systems may consume fuel for backup energy.)

Entering Periodic Operation and Maintenance CostsSAM allows you to specify any of the four operation and maintenance (O&M) cost categories on the

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System Costs page either as a single annual cost, or using a table of values to specify an annual scheduleof costs. An annual schedule makes it possible to assign costs to particular years in the analysis period.Annual schedules can be used to account for component replacement costs and other periodic costs thatdo not recur on a regular annual basis.



Notes.








3. Click Edit.

4. In the Edit Schedule window, use the vertical scroll bar to find the year of the first replacement, andtype the replacement cost in current or constant dollars for that year.



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About the Trough System Default Cost AssumptionsThe default values on the Trough System Costs page reflect the National Renewable Energy Laboratory'sbest estimate of representative system costs for the United States in the second quarter of 2009. Thevalues are based on a cost study for 100-MWe reference plant cost performed by the WorleyParsons Groupunder NREL contract KAXL-9-99205-00, and on conversations with developers and industry insiders. Thecosts are composite values and do not represent a specific location or market within the United States.

Note. Always review all of the inputs for your SAM project to determine whether they are appropriate foryour analysis.

Major points of note include:

Site improvement cost estimates have been increased from earlier estimates to better account for thecost of access roads, drainage, and land grading.

The HTF System category includes the cost of the heat transfer fluid (HTF) and header piping costs.The HTF and header piping account for most of the HTF System category.

The Power Plant cost for the dry-cooled case is higher than for the wet-cooled case to account for thehigher cost of an air-cooled condenser compared to a cooling tower.

The Storage cost estimate is based on a two-tank molten salt system, and accounts for the cost ofnitrate salts in 2009

Contingency has been rounded to 10%

The operation and maintenance cost category, Variable Cost by Generation includes the cost of waterfor wet-cooled case.

Table 21. Comparison of Trough System Costs in SAM versions 3.0 (June 2009) and 2009(October 2009).

Parabolic Trough Costs SAM 3.0 SAM 2009 units

Site Improvements 3 20 $/m2

Solar Field 300 350 $/m2

HTF System 150 ($/kWe)

50

($/m2)

Storage 40 70 $/kWht

Fossil Backup 0 0 $/kWe

Power Block (wet-cooled) 850 880 $/kWe

Power Block (dry-cooled) 850 960 $/kWe

Contingency 8.85 10 %

Engineer, procure,construct

16 15 %

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Project, land,management

3.5 3.5 %

Sales tax applies to 80 80 %

Fossil Fuel Cost 0 0 $/MMBTU

O&M Fixed Annual cost 0 0 $/yr

O&M Fixed cost bycapacity

50 80 $/kW-yr

O&M Variable cost bygen.

0.7 3 $/MWh

Note. SAM does not account for the capacity value of storage. Some utilities apply a capacity credit tosystems with storage that can affect overall project economics.

4.8.3 Tower System Costs

To view the Tower System Costs page, click Tower System Costs on the main window's navigation menu.Note that for the power tower input pages to be available, the technology option in the Technology andMarket window must be Concentrating Solar Power - Power Tower System.

Contents

Overview describes the Tower System Costs page.

Input Variable Reference describes the input variables on the Tower System Costspage.


OverviewSAM uses the variables on the Tower System Costs page to calculate the project investment cost andannual operating costs reported in the project cash flow and used to calculate cost metrics reported in theMetrics table on the Results page.

Because only the Total Installed Cost value affects the cash flow calculations, you can assign capital coststo the different cost categories in whatever way makes sense for your analysis. For example, you couldassign the cost of designing the solar field to the solar field cost category or to the engineer-procure-construct category with equivalent results. The categories are provided to help you keep track of thedifferent costs, but do not affect the economic calculations. After assigning costs to the categories, verifythat the total installed costs value is what you expect.


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A cost per square meter of total reflective area from the Heliostat Field page to account for expensesrelated to site preparation and other equipment not included in the heliostat field cost category.

Heliostat Field ($/m2)

A cost per square meter of total reflective area from the Heliostat Field page to account for expensesrelated to installation of the heliostats, including heliostat parts, field wiring, drives, labor, andequipment.


A cost per electric kilowatt of power cycle nameplate capacity from the Power Cycle page expensesrelated to installation of the balance-of-plant components and controls, and construction of buildings,including labor and equipment.

Power Block ($/kWe)

A cost per electric kilowatt of power cycle nameplate capacity from the Power Cycle page expensesrelated to installation of the power block components, including labor and equipment. The Power Blockand Balance of Plant costs are rolled together into a single number for calculation purposes.


Cost per electric kilowatt of power block nameplate capacity to account for the installation of a fossilbackup system, including equipment and labor.

Storage ($/kWht)

Cost per thermal megawatt-hour of storage capacity from the Thermal Storage page to account for theinstallation of a thermal energy storage system, including equipment and labor.

Fixed Solar Field Cost ($)

An additional fixed cost in dollars to include as a direct cost that is not accounted for by any of theabove categories.

Fixed Tower Cost ($)

A fixed cost to account for tower construction, materials and labor costs. The fixed tower cost servesas the multiplier in the tower cost scaling equation shown below.


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Tower Cost Scaling Exponent

SAM uses the tower cost in the optimization calculations. The tower cost scaling exponent defines thenonlinear relationship between tower cost and tower height. See Total Tower Cost below.

Total Tower Cost ($)

Total Tower Cost = Fixed Tower Costs x exp (Tower Height x Tower Cost Scaling Exponent)

Receiver Reference Cost ($)

The cost per receiver reference area to account for receiver installation costs, including labor andequipment.

Receiver Reference Area (m2)

The receiver area on which the receiver reference cost is based.

Receiver Cost Scaling Exponent

SAM uses the receiver cost in the optimization calculations. The receiver cost scaling exponent definesthe nonlinear relationship between receiver cost and receiver area based on the reference costconditions provided.

Total Receiver Cost ($)

Receiver Cost = Receiver Reference Cost x (Receiver Area / Receiver Reference Area ) ^ Receiver CostScaling Exponent.

Contingency (%)

A percentage of the sum of the site improvements, heliostat field, balance of plant, power block, storagesystem, fixed solar field, total tower, and total receiver costs to account for expected uncertainties indirect cost estimates.


The sum of improvements, site improvements, heliostat field, balance of plant, power block, storagesystem, fixed solar field, total tower, total receiver, and contingency costs.










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Land (% and $)







Sales Tax (%)















For expenses such as component replacements that occur in particular years, you can use an annual

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schedule to assign costs to individual years. See below for details.









Note. For information on water consumption and other operation and maintenance costs andrequirements for concentrating parabolic trough systems, see the Troughnet website: http://www.nrel.gov/csp/troughnet/power_plant_systems.html. For information on operation and maintenance costs forphotovoltaic systems, see the California Energy Commission's online Distributed Energy Resourceguide http://www.energy.ca.gov/distgen/economics/operation.html.

Entering Periodic Operation and Maintenance CostsSAM allows you to specify any of the four operation and maintenance (O&M) cost categories on theSystem Costs page either as a single annual cost, or using a table of values to specify an annual scheduleof costs. An annual schedule makes it possible to assign costs to particular years in the analysis period.Annual schedules can be used to account for component replacement costs and other periodic costs thatdo not recur on a regular annual basis.



http://www.nrel.gov/csp/troughnet/power_plant_systems.html

http://www.nrel.gov/csp/troughnet/power_plant_systems.html

http://www.energy.ca.gov/distgen/economics/operation.html

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Notes.








3. Click Edit.






4.8.4 Dish System Costs

To view the Dish System Costs page, click Dish System Costs on the main window's navigation menu.Note that for the dish input pages to be available, the technology option in the Technology and Marketwindow must be Concentrating Solar Power - Dish Stirling System.

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Contents

Overview describes the Dish System Costs page.

Input Variable Reference describes the input variables on the Dish System Costspage.


OverviewSAM uses the variables on the Dish System Costs page to calculate the project investment cost andannual operating costs reported in the project cash flow and used to calculate cost metrics reported in theMetrics table on the Results page.

Because only the Total Installed Cost value affects the cash flow calculations, you can assign capital coststo the different cost categories in whatever way makes sense for your analysis. For example, you couldassign the cost of designing the solar field to the site improvements cost category or to the engineer-procure-construct category with equivalent results. The categories are provided to help you keep track of thedifferent costs, but do not affect the economic calculations. After assigning costs to the categories, verifythat the total installed costs value is what you expect.









Collector Cost (Projected Area) ($/m2)

A cost per square meter of projected mirror area from the Collector page to account for expensesrelated to installation of the collectors, including labor and equipment.


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Receiver Cost ($/kW)

A cost per kW of engine rated capacity from the Stirling Engine page to account for expenses related toinstallation of the receiver, including labor and equipment.

Engine Cost ($/kW)

Cost per kW of engine rated capacity from the Stirling Engine page to account for expenses related toinstallation of the Stirling engine components, including labor and equipment.

Contingency (%)



The sum of site improvements, collector cost, receiver cost, engine cost, and contingency costs.










Land (% and $)







Sales Tax (%)


SAM calculates the total sales tax by multiplying the sales tax rate specified on the Financing page by

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the percentage of direct costs you specify on the System Costs page: Total Sales Tax = Sales TaxRate × Percentage of Direct Cost × Direct Cost.





















The cost per million British thermal units for fuel. SAM uses the conversion factor 1 MWh = 3.413MMBtu. The fuel cost only applies to generic fossil, parabolic trough, and power tower systems.

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Although the photovoltaic and dish-Stirling models ignore the fuel cost input variable, you should specifya value of zero for the variable to avoid confusion. (When the fossil fill fraction variable on the ThermalStorage page for either of the parabolic trough models or the power tower model is greater than zero,the systems may consume fuel for backup energy.)




Notes.








3. Click Edit.

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4.8.5 Generic Solar System Costs






Solar Field ($/m2)

A cost per square meter of solar field area to account for expenses related to installation of the solarfield, including labor and equipment.

Storage ($/kWht)

Cost per thermal megawatt-hour of storage capacity to account for expenses related to installation ofthe thermal storage system, including equipment and labor.


Cost per electric megawatt of power block nameplate capacity to account for the installation of a fossilbackup system, including equipment and labor.

Power Plant ($/kWe)

Cost per electric megawatt of power block nameplate capacity to account for the installation of thepower block, including equipment and labor.


Cost per electric megawatt of power block nameplate capacity to account for additional costs.

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Contingency (%)



The sum of improvements, solar field, HTF system, storage, fossil backup, power plant costs, andcontingency costs.










Land (% and $)







Sales Tax (%)




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4.8.6 Generic System Costs

To view the Fossil System Costs page, click Fossil System Costs on the main window's navigation menu.Note that for the generic fossil system input pages to be available, the technology option in the Technologyand Market window must be Generic Fossil System.

Contents

Overview describes the Fossil System Costs page and explains where to find moreinformation.

Input Variable Reference describes the input variables on the Fossil System Costspage.


OverviewSAM uses the variables on the Fossil System Costs page to calculate the project investment cost andannual operating costs reported in the project cash flow and used to calculate cost metrics reported in theMetrics table on the Results page.

Because only the Total Installed Cost value affects the cash flow calculations, you can assign capital coststo the different cost categories in whatever way makes sense for your analysis. For example, you couldassign the cost of designing the power plant to the direct plant cost category or to the engineer-procure-construct category with equivalent results. The categories are provided to help you keep track of thedifferent costs, but do not affect the economic calculations. After assigning costs to the categories, verifythat the total installed costs value is what you expect.







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System size (kW)

The Nameplate Capacity from the Generic Plant page.

Cost per watt ($/W)

A cost per Watt of nameplate capacity.

Fixed Plant Cost ($)

A fixed dollar amount.

Non-fixed System Cost ($)

The product of the Cost per Watt cost category and the nameplate capacity.

Contingency (%)

A percentage of the fixed plant cost and non-fixed system cost to account for expected uncertainties indirect cost estimates.


The sum of fixed plant cost, non-fixed system cost, and contingency costs.




Engineer, Procure, Construct (% and $)






Project, Land, Miscellaneous (% and $)

Costs associated with land purchases, permitting, and other costs which SAM calculates as the sumof a "non-fixed cost" and a fixed cost.




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Sales Tax (%)





















A variable annual cost proportional to the system's total annual electrical output in AC megawatt-hours.The annual energy output depends on either the performance model's calculated first year value and thedegradation rate specified on the Annual Performance page, or on an annual schedule of costs,

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depending on the option chosen.






Notes.







2. Click the button so that "Sched" label is highlighted in blue. SAM replaces the variable's value with

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an Edit button.

3. Click Edit.






4.8.7 SWH System Costs

To view the SWH System Costs page, click SWH System Costs on the main window's navigation menu.Note that for the solar water heating system input pages to be available, the technology option in theTechnology and Market window must be Solar Water Heating.

Contents

Overview describes the purpose of the SWH System Costs page and the costvariable categories.

Input Variable Reference describes the input variables on the SWH System Costspage.

Entering Periodic Costs explains how to use annual schedules to assign operationand maintenance costs to particular years in the project cash flow.

OverviewSAM uses the variables on the SWH System Costs page to calculate the project investment cost andannual operating costs reported in the project cash flow and used to calculate cost metrics.


The SWH System Costs page is divided into four main categories. The first two, Direct Capital Costs andIndirect Capital Costs, are summed in the third category, Total Installed Costs. Because only the TotalInstalled Cost value affects the cash flow calculations, you can assign capital costs to the different costcategories in whatever way makes sense for your analysis. For example, you could assign the cost of

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designing the collector to the collector cost category or to the engineer-procure-construct category withequivalent results. The categories are provided to help you keep track of the different costs, but do not affectthe economic calculations. After assigning costs to the categories, verify that the total installed costs valueis what you expect. The fourth category of costs covers Operation and Maintenance.

Note: The cost values in the sample files are intended to illustrate SAM's use. The cost data are meantto be realistic, but not to represent actual costs for a specific project. Actual costs will, of course, vary.Because of price volatility in solar markets, the cost data in the sample files is likely to be out of date.





Collector Cost ($/m2, $/Unit, or $/W)

The cost of collectors in the system. You can either include labor costs for collector installation in thecollector cost, or account for it separately using the installation cost category. The total collector costis calculated as either:

Dollars per square meter multiplied by collector area on the SWH System page, or

Dollars per unit, representing the total collector cost, or

Dollars per thermal watt of collector capacity multiplied by the nameplate capacity on the SWHSystem page.

Storage Cost ($/m3 or $/Unit)

The cost of the solar storage tanks. The total storage cost is either:

Dollars per cubic meters multiplied by the storage volume on the SWH System page, or

Dollars per unit, representing the total storage cost.

Balance of System ($)

A fixed cost that can be used to account for costs not included in the collector and storage costcategories, for example, the mounting racks and piping.

Installation Cost ($)

A fixed cost that can be used to account for labor or other costs not included in the other costcategories.

Contingency (%)

A percentage of the sum of the collector, storage, balance of system, and installation costs to accountfor expected uncertainties in direct cost estimates.


The sum of collector, storage, balance of system, installation, and contingency costs.

System Costs 323











Project, Land, Maintenance (% and $)







Sales Tax (%)







The total installed cost is the project's investment cost that applies in year zero of the project cash flow.SAM uses this value to calculate loan amounts and debt interest payments based on inputs on theFinancing page, and to calculate tax credit and incentive payment amounts for incentive based tax credits

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and incentives defined on the Tax Credit Incentives page and Payment Incentives pages.

















Entering Periodic CostsSAM allows you to specify any of the four operation and maintenance (O&M) cost categories on theSystem Costs page either as a single annual cost, or using a table of values to specify an annual scheduleof costs. An annual schedule makes it possible to assign costs to particular years in the analysis period.Annual schedules can be used to account for component replacement costs and other periodic costs thatdo not recur on a regular annual basis.

You choose whether to specify an O&M cost as a single annual value or an annual schedule with the grey

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and blue button next to each variable. SAM uses the option indicated by the blue highlight on the button: Ablue highlighted “Value” indicates a single, regularly occurring annual value. A blue highlighted “Sched”indicates that the value is specified as an annual schedule.


Notes.








3. Click Edit.






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4.8.8 Small Scale Wind Capital Costs




Cost of all Turbines

The number of turbines from the Small Scale Wind System page multiplied by the single turbine cost.

Installation

Installation labor or other costs calculated as the sum costs specified as a cost per unit cost in dollarsper turbine, cost per capacity cost in dollars per kilowatt of total rated capacity, and a fixed cost indollars. SAM assumes that the capacity is the value specified as the nameplate capacity on SmallScale Wind System page.

Balance of System

Costs not included in other categories calculated as the sum costs specified as a cost per unit cost indollars per turbine, cost per capacity cost in dollars per kilowatt of total rated capacity, and a fixed costin dollars. SAM assumes that the capacity is the value specified as the nameplate capacity on SmallScale Wind System page.

Single Turbine Cost

The cost of a single turbine. SAM uses this value to calculate the cost of all turbines.

Fixed Cost per Turbine

A cost specified in dollars per unit of a single turbine.

Cost by Capacity

A cost specified in dollars per kilowatt of rated capacity.

Single Turbine Cost

Sum of the cost per turbine and cost by capacity values, assuming the turbine capacity is the valueshown as the nameplate capacity on the Small Scale Wind System page.

Contingency (%)

A percentage of the sum of the cost of all turbines, installation, and balance of system costs that youcan use to account for expected uncertainties in direct cost estimates.


The sum of cost of all turbines, installation, balance of system, and contingency costs.



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Sales Tax (%)










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4.8.9 Wind Farm Costs




System Costs 329


Cost of all Turbines

The number of turbines from the Wind Farm Specifications page multiplied by the single turbine cost.

Installation

Installation labor or other costs calculated as the sum costs specified as a cost per unit cost in dollarsper turbine, cost per capacity cost in dollars per kilowatt of total rated capacity, and a fixed cost indollars. SAM assumes that the capacity is the value specified as the nameplate capacity on WindFarm Specifications page.

Balance of System

Costs not included in other categories calculated as the sum costs specified as a cost per unit cost indollars per turbine, cost per capacity cost in dollars per kilowatt of total rated capacity, and a fixed costin dollars. SAM assumes that the capacity is the value specified as the nameplate capacity on WindFarm Specifications page.

Single Turbine Cost

The cost of a single turbine. SAM uses this value to calculate the cost of all turbines.

Fixed Cost per Turbine

A cost specified in dollars per unit of a single turbine.

Cost by Capacity

A cost specified in dollars per kilowatt of rated capacity.

Single Turbine Cost

Sum of the cost per turbine and cost by capacity values, assuming the turbine capacity is the valueshown as the nameplate capacity on the Wind Farm Specifications page.

Contingency (%)

A percentage of the sum of the cost of all turbines, installation, and balance of system costs that youcan use to account for expected uncertainties in direct cost estimates.


The sum of cost of all turbines, installation, balance of system, and contingency costs.








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Sales Tax (%)














For each O&M cost category, you can specify an optional annual Escalation Rate to represent anexpected annual increase in O&M cost above the annual inflation rate specified on the Financing page. Foran escalation rate of zero, the O&M cost in years two and later is the year one cost adjusted for inflation.For a non-zero escalation rate, the O&M cost in years two and later is the year one cost adjusted for

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inflation plus escalation.










4.8.10 Geothermal System Costs

For descriptions of how geothermal system costs are specified in the GETEM model, see the followingsections of the GETEM User's Manual (Volume II), available at http://www1.eere.energy.gov/geothermal/getem_manuals.html:

Binary

Section 4.1.c on page A-11

Section 4.1.g on page A-15

Flash

Section 5.2.a on page A-20

4.8.11 Co-Production Costs

For questions about the Co-Production model please email SAM support at [email protected].




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4.9 Energy Payment DispatchThe Energy Payment Dispatch page allows you to specify a set of energy payment allocation factors forprojects with Independent Power Producer financing.


Energy Dispatch Schedule

You can either choose a pre-defined set of energy payment allocation factors from SAM's library of factors,or specify your own.

Current dispatch schedule

When you choose a set of factors from the library, the current dispatch schedule shows the name ofthe set of factors.

When you specify your own set of factors, it shows "No library match."

Dispatch schedule library

Click Dispatch schedule library to choose a set of energy payment allocation factors from SAM'slibrary of factors.


The energy payment allocation factors are a set of up to nine multipliers that SAM uses to adjust theelectricity price based on time of day and month of year for utility projects. Each factor is associatedwith a period number, which represents a time periods indicated on the weekday and weekendschedule matrices.


Weekday Schedule, Weekend Schedule

The weekday and weekend matrices allow you to associate a period with a time of day and month ofyear. To use the matrices, you draw rectangles on the matrix with your mouse, and type a number withyour keyboard for the period that applies to the times represented by the rectangles.

SAM arbitrarily defines the first day of time series data (the first 24 hours for hourly data) to be Mondayon January 1, and assigns the remaining days of the year accordingly. SAM assumes that weekdaysinclude Monday through Friday, and that weekends include Saturday and Sunday. SAM does notaccount for holidays or other special days. It also does not account for leap years, and does not includea day for February 29.


1. Assign values as appropriate to each of the up to nine periods.


Energy Payment Dispatch 333




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4.10 Electric LoadThe Electric Load page allows you to specify the electric load for systems with either the Residential orCommercial financing option. You only need to specify an electric load if you are modeling a residential orcommercial system with tiered rates or demand charges specified on the Utility Rate page.

To view the Electric Load page, click Electric Load on the main window's navigation menu. Note that forthe Electric Load page to be available, the technology option in the Technology and Market window must bePhotovoltaics - Component-based Models, Photovoltaics - PVWatts Performance Model, or Small ScaleWind.

Contents

Overview describes options for specifying the electric load.

Input Variable Reference describes the input variables on the Electric Load page.

Working with Time Series Load Data explains how to import load data from aproperly formatted text file, or how to paste load data from your computer'sclipboard.

Creating Load Data from Daily Profiles explains how to define daily load profiles foreach month of the year and use SAM to convert them to an 8,760 load data set.

OverviewThe Electric Load page allows you to specify the electric demand, or expected electricity consumption for a

Electric Load 335


grid-connected power system. The load data represents the electric demand of a building or other loadcenter over the period of a single year.

Note. You should only specify electric load data for residential or commercial projects that includedemand charges or tiered rates on the Utility Rate page. If your project does not use these ratestructures, choose the No load data option on the Electric Load page.

Energy values represent the electric energy required over a single time step and are expressed in kilowatt-hours. Peak load values represent the maximum electric power required in either a month or year and areexpressed in kilowatts.

If you have load data stored in a text file, spreadsheet file, or other file that allows you to copy columnsof data to your computer's clipboard, you can paste the data into SAM using the Edit Data window. See Working with Time Series Load Data for details.

You can also import load data from a properly formatted text file. See Working with Time Series LoadData for details.

You can specify load data using an hourly time step or sub-hourly time step. The load data time stepcan be different from the weather data time step. For example, you can use 10-minute load data withhourly weather data. See Working with Time Series Load Data for details.

If you do not have time series load data, SAM allows you to specify load data by typing a values fortwelve monthly 24-hour load profiles. See Creating Load Data from Daily Profiles for details.

You can scale the load upwards or downwards, or specify a load that increases from year to year. SeeInput Variable Reference for details.

SAM displays a load data summary table and allows you to view graphs of hourly load data. See InputVariable Reference for details.

SAM reports load data in the hourly results. See Tabular Data Browser for details.


Electric Load Data

No load data

Choose No load data for an analysis that does not require load data. You should choose this optionunless you are modeling a residential or commercial project with demand charges or tiered rates.

Monthly schedule

Choose Monthly schedule to specify the load using a set of monthly 24-hour load profiles. SeeCreating Load Data from Daily Profiles for details.

User entered data

Choose User entered data to specify the load by either cutting and pasting load data from an externalprogram, or by importing load data from a properly formatted text file. See Working with Time SeriesLoad Data for details.

Edit monthly schedule

Click Edit monthly schedule to specify 24-hour load profiles when you chose the monthly scheduleoption. Edit monthly schedule is inactive when you choose No load data or User entered data.

Edit data

Click Edit data to either cut and paste load data from another program or to import data from a properly

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formatted text file. Edit data is inactive when you choose No load data or Monthly schedule.

Adjustments

The load adjustment factors allow you to uniformly scale the load up or down, and to model a load profilethat increases from year to year. Scaling the load can be useful for scenario analyses where you want toinvestigate the effect of a higher or lower load than expected loads.

Escalation

The load escalation scales the load in years two an later by the percentage you specify. For example,if you specify a load escalation rate of 0.5% per year, for each year in the analysis period specified onthe Financing page, SAM would increase the load value in each time step by 0.5% of the previousyear's load value for the same time step.

You can also assign load escalation values to specific years using the annual schedule. When youspecify

Scaling factor

To calculate the load value during simulation, SAM multiplies the load value in each time step by thescaling factor that you specify. For example, if you specify a scaling factor of 1.5, and the hourlyaverage load at 2 p.m. on March 18th is 1.2 kWh, SAM would use a load value of 1.5 × 1.2 = 1.8 kWhfor that hour.

To see the effect of the scaling factor, try changing the value from the default of 1 to another value, andlook at how the values under Hourly Simulation Load Profile Data change.

Offset value

To calculate the load value during simulation, for each time step, SAM adds the offset value you specifyto the load value. For example, if you specify an offset value of 0.5 kWh, and the hourly average load at2 p.m. on March 18th is 1.2 kWh, SAM would use a load value of 1.2 + 0.5 = 1.7 kWh for that hour.

To see the effect of the offset value, try changing the value from the default of 1 to another value, andlook at how the values under Hourly Simulation Load Profile Data change.

Hourly Simulation Load Profile Data

SAM displays the table of monthly and annual averages to help you verify that the load data is correct. SAMalso allows you to view also graphs of the time series load data using the built-in data viewer.

Energy (kWh)

The Energy column displays the total amount of electricity required by the load for each month. SAMcalculates the value by adding the average hourly values for each month, or if you specify a differenttime step for the load data, the sum of average values over each time step for the month.

Peak (kW)

The maximum load value that occurs in each month. If you specify hourly load data, the monthly peakis equal to the maximum hourly load value in kWh/h. If you specify sub-hourly load data, the monthlypeak is equal to the maximum load value that occurs in the sub-hourly data.

Annual Total

The total amount of electricity required by the load over an entire year. SAM calculates the value byadding the average hourly values for the year, or if you specify a different time step for the load data, thesum of average values over each time step for the year.

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The annual total applies to year one of the analysis period. If you specify a load escalation rate underAdjustments, the annual total does not reflect load data in years two and later.

Annual Peak

The maximum load value that occurs in the year. If you specify hourly load data, the annual peak isequal to the maximum hourly load value in kWh/h. If you specify sub-hourly load data, the annual peakis equal to the maximum load value that occurs in the sub-hourly data.

Visualize load data

Click Visualize load data to display the time series data in SAM's built-in data viewer, DView. SeeViewing Graphs of Time Series Data (DView) for details.

Calculate Load Profiles

EnergyPlus is a building simulation model developed for the Department of Energy. You can use theEnergyPlus Example File Generator to generate a text file containing hourly load data for different buildingtypes and configurations for some locations in the United States. SAM includes a set of residential loadprofiles created by this web application in the \samples\Residential Load Data folder.

The EnergyPlus load data generator uses weather data from the TMY2 data set to generate the load data. Ifyou model a system in SAM using this load data, you may want to use the same weather file to ensure thatthe energy model results are consistent with the load data. Choose the weather file on the Climate page.

To visit the EnergyPlus file generator website, click EERE Building Technologies Program EnergyPlusLoad Calculator. The websites URL is http://apps1.eere.energy.gov/buildings/energyplus/cfm/inputs/.

Working with Time Series Load DataIf you have load data for an entire year in either hourly or sub-hourly time steps you can either import thedata from a properly formatted text file, or copy and paste the data from a spreadsheet program or othersoftware.

Data Sources

The following examples are some sources of electric load data:

Electrical measurements from a building or other load center. Some electricity service providers makeload data available to their customers.

Data generated by a building simulation model, such as the EnergyPlus Example File Generator, http://apps1.eere.energy.gov/buildings/energyplus/cfm/inputs/.

Some electric service area operators provide system-wide load data on their websites. For examples,see California ISO and Midwest ISO websites.

Sample residential load data generated by the EnergyPlus load data generator supplied with SAM in\samples\Residential Load Data folder.

Time Step and Convention

SAM requires load data in a single column of average kilowatt per time step values. The number of datarows depends on the time step.

For hourly data, SAM requires a column of 8,760 rows, where each row contains a value in kilowattsrepresenting the average power required by the load over the hour. For sub-hourly data, SAM requires acolumn of 8,760 ÷ Number of Times Steps per Hour rows, with kilowatt values representing the average

http://apps1.eere.energy.gov/buildings/energyplus/cfm/inputs/



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electric power over the period of a single time step.

The time convention must follow the time convention of the weather data specified on the Climate page. ForNREL typical meteorological year data (TMY2 and TMY3), the first row of data represents the time stepbeginning at midnight on January 1. SAM assumes that January first is a Monday.

When you use sub-hourly load data with hourly weather data, SAM uses hourly average load values to forthe energy charge calculations, and the sub-hourly data to determine the peak load for demand charges.

Importing Data from a File

SAM can import data from a text file that contains a single column of values representing the load in asingle year. SAM ignores the first row, so you can use that row to store text describing the data. Thenumber of rows depends on the number of time steps. For hourly data, the file should contain a total of8,761 rows: The first row for header information, and the remaining rows for the load data.

To import load data from a properly formatted text file:

1. Under Electric Load Data, click User entered data.

2. Click Edit Data.

3. In the Edit Data window, click Import.

4. Navigate to the folder containing the load data file and open the file.

SAM displays the data in the data table. Use the scroll bar to see all of the data.

5. Click OK to return to the Electric Load page.

SAM displays monthly and annual load data under Hourly Simulation Load Profile Data.

Pasting Load Data from your Computer's Clipboard

If you have load data in a spreadsheet or other program that allows you to copy columns of data to yourcomputer's clipboard, you can paste the data into SAM. The data should be a single column of values inkilowatt-hours representing the load in a single year. The number of rows depends on the number of timesteps. For hourly data, the column should contain 8,760 rows of load data.

To paste load data from your computer's clipboard:

1. Under Electric Load Data, click User entered data.

2. Click Edit Data.

3. Open the spreadsheet or other program containing the load data. The data must be in a singlecolumn with the appropriate number of rows for the data's time step.

4. Select the entire column of data and copy it.

5. In SAM's Edit Data window, click Paste.

SAM displays the data in the data table. Use the scroll bar to see all of the data.


SAM displays monthly and annual load data under Hourly Simulation Load Profile Data.

Creating Load Data from Daily ProfilesIf you do not have a complete 8,760 set of load data, you specify the load using a set of daily load profilesfor each month. SAM creates a set of 8,760 values representing the load for an entire year. When youdefine a load with daily load profiles, SAM assumes that the load for all days in a given month is identical.

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To create a load data set using daily load profiles:

1. Under Electric Load Data, click Monthly schedule.

2. Click Edit monthly schedule.

3. In the Edit Monthly Schedule window, click Weekday Values.

4. For each month of the year, define a daily load profile by typing a value in kilowatt-hours for each ofthe 24 hours of the day. The first column represents the first hour of the day, beginning at midnightand ending at 1:00 a.m. SAM assumes that January 1st is a Monday.

5. Click Weekend Values.

6. Repeat Step 4 to define the daily load profile for Saturdays and Sundays. SAM assumes thatJanuary 6 is a Saturday.


SAM displays monthly and annual load data under Hourly Simulation Load Profile Data..

5 Results

5.1 Metrics TableThe Metrics table displays a set of output variables for each case in the project file. SAM displays theMetrics table under the navigation menu when results are available for a case. The variables that appear inthe metrics table depend on the technology and financing options, which are defined in the Technology andMarket window.

Note. The annual energy quantity reported in the metrics table and graphs on the Results pageaccounts for the availability factor on the Annual Performance page, while the data reported in the hourlysimulation results and case summary workbook does not. The annual energy quantity in the metricstable is equal to the total annual energy output reported in the hourly results multiplied by the availabilityfactor.

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Table 22. Variables in the Metrics table for different financing types.

Metric Res ComComPPA

IPP LPF AEPF SL SO

Annual Energy • • • • • • • •

Nominal LCOE • • • •

Real LCOE • • • •

Year 1 Revenue without System • •

Year 1 Revenue with System • •

Year 1 Net Revenue • •

Net Present Value • • •

Payback Period • •

First year PPA price • • •

Internal Rate of Return •

Minimum DSCR •

PPA Escalation •

Debt Fraction •

IRR target year • • • • •

IRR target • • • • •

IRR actual year • • • • •

IRR in target year • • • • •

After-tax IRR • • •

After-tax NPV • • •

After-tax tax investor IRR • • •

After-tax tax investor NPV • • •

After-tax developer IRR • • •

After-tax developer NPV • • •

PPA price escalation • • • • • •

Debt fraction • • •

Direct Cost • • • •

Indirect Cost • • • •

Financing Cost • • • •

Total project cost • • • •

Total debt • •

Total equity • • • •

Metrics Table 341


For certain simulation configurations, SAM displays two columns of values for each output variable:

For model runs involving the Multiple Systems simulation configuration, SAM displays output variablesfor the active case in the Base column of the Metrics table, and output variables for the combinedsystem in the Combined column.

For model runs involving the Statistical simulation configuration, the values of mu, sigma are displayedin the second column of the Metrics table.

5.1.1 Annual Energy

SAM calculates and reports three annual energy values.

Annual Energy

The total annual AC electric output of the system in kWh, not accounting for the availability factor fromthe Annual Performance page.

Net Annual Energy

The total annual AC electric output of the system in kWh, accounting for the availability factor from theAnnual Performance page.

Energy (in the cash flow table)

The total annual AC electric output of the system in kWh, accounting for both the availability and thedegradation factor from the Annual Performance page.

Note. If you run simulations with no financing by choosing the No Financials option in the Technologyand Market window, SAM reports the annual energy value in the metrics table. If your analysis includesfinancing, then SAM reports the net annual energy value in the Metrics table.

5.1.2 Annual Water Usage

For CSP systems, the total annual water consumption in cubic meters for cooling and mirror washing. Thevalue is determined based on the cooling system options specified on the Power Block page, and the mirrorwashing options specified on the Solar Field page.

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5.1.3 Capacity Factor

The capacity factor is the ratio of the system's predicted electrical output in the first year of operation to theoutput had the system operated at its nameplate capacity.

Note. SAM only displays the capacity factor metric when you run simulations with a financing option.The metric is not available when you choose No Financials in the Technology and Market window.

Capacity Factor = Net Annual Energy (kWh) / System Capacity (kW) / 8760 (h/yr)

For PV systems, the capacity factor is an AC-to-DC value. For CSP systems, the capacity is an AC-to-ACvalue.

Net Annual Energy

The total annual electric generation in the first year of operation, accounting for the availability factorfrom the Annual Performance page.

System Capacity

The system's nameplate capacity (see table below). For PV systems the capacity is in DC kW, forCSP systems, the capacity is in AC kW.

The system capacity depends on technology being modeled. Note that SAM converts the capacity value tokW before using it in the calculation.

Table 23. Rated system capacity values for each technology.

Technology System Capacity Input Page

PV SAM Performance Models Total Array Power (Wdc) Array

PV PVWatts DC Rating (kW) PVWatts Solar Array

CSP Parabolic Trough Rated Turbine Net Capacity (MWe) Power Block

CSP Power Tower Nameplate Capacity (MWe) Power Cycle

CSP Dish Stirling Total Capacity (kW) Solar Field

Generic Fossil Nameplate Capacity (kWe) Fossil Plant

5.1.4 Costs

Enter topic text here.

5.1.5 Debt Fraction

The debt fraction is the percentage of the project total installed cost that is financed through a loan. Thevalue is reported as a result only for projects with Utility or Commercial - Third-Party Ownership financing asdefined in the Technology and Market window.

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For these types of projects, depending on the financial optimization option on the Financing page, the debtfraction is either a user-defined input on the Financing page, or a value that SAM calculates. When theAutomatically minimize LCOE with respect to Debt Fraction option is checked, SAM finds the debt fractionthat results in the lowest levelized cost of energy.

SAM uses the debt fraction to calculate the principal and interest payments shown in the project cash flow,and used in the iterative search algorithm described in 1st Year PPA Price.

5.1.6 First year kWhac/kWdc

For PV systems, SAM reports the ratio of the system's annual AC electric output in Year one to it'snameplate DC capacity.

Note. SAM only displays the First year kWhac/kWdc metric when you run simulations with a financingoption. The metric is not available when you choose No Financials in the Technology and Market window.

First year kWhac/kWdc = Net Annual Energy / Nameplate Capacity

Net Annual Energy

The total annual electric generation in the first year of operation, accounting for the availability factorfrom the Annual Performance page.

Nameplate Capacity

The system's DC nameplate capacity from the Array page for component-based model and thePVWatts Solar Array page for the PVWatts model.

5.1.7 First Year PPA Price

The first year PPA price is the electricity sales price for projects with Utility or Commercial - Third-PartyOwnership financing as defined in the Technology and Market window. SAM assumes that such projectssell electricity through a power purchase agreement (PPA) at a fixed price over the life of the project with anoptional annual escalation rate.

The first year PPA Price and annual escalation rate (PPA Escalation rate on the Financing page) determinethe project's annual revenues. SAM calculates the annual revenues to meet the minimum requirements ofthe internal rate of return (IRR), debt service coverage ratio (DSCR), and positive cash flow, which aredefined as constraining assumptions on the Financing page. Because of the way the first year PPA price,IRR, and minimum DSCR interact, SAM uses an iterative algorithm to determine the values of thesevariables.

For projects with utility financing, the constraining assumptions defined on the Financing page are theMinimum Required IRR and the Minimum Required DSCR, and a positive cash flow requirement:

Find First Year PPA such that

IRR >= Minimum Required IRR, and

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Min DSCR >= Minimum Required DSCR, andCash Flow in Year n > 0 (when the cash flow requirement is positive)

For projects with Third-Party Ownership financing, there is a single constraining assumption defined on theFinancing page, the Minimum Required IRR:

Find First Year PPA such that

Actual IRR >= Minimum Required IRR

The following equations show the calculations used in the iterative algorithm to determine the IRR andminimum DSCR, which are both reported as results with the 1st Year PPA Price in the Metrics table on the Results page.

The internal rate of return is the discount rate, IRR in the equation below, that corresponds to a project net

present value, NPV, of zero:

Where,

NPV ($) The net present value of the project over its life.

N The number of years in the project life, defined by the analysis period on the Financingpage.

Rn

($) The required revenue in year n, shown in the Revenues row of the cash flow. The revenue

in year 1 (Rn=1

) is equal to the first year PPA price. The revenue is subsequent years (R

1<n<=N) is equal to the first year PPA price adjusted by the PPA escalation rate defined

on the Financing page.

CAfterTax,n

($) The after tax cash flow in year n, equal to State Tax Savings + Federal Tax Savings + PBI

Incentives - Operating Costs - Debt Total Payment + Revenues in the project cash flow.

IRR Internal rate of return, calculated by systematically trying different values until the NPV isequal to zero.

The debt service coverage ratio in each analysis year (DSCRn) is the ratio of operating income to expenses

in that year:

Where,

DSCRn

Debt service coverage ratio in year n shown in the PreTax Debt Service Coverage Ratio

row of the cash flow.

Rn

($) The required revenue in year n, shown in the Revenues row of the cash flow table, equal to

the product of the electric output and electricity sales price in year n. Note that theelectricity sales price in year 1 is equal to the first year PPA price, and in subsequentyears (R

1<n<=N) is equal to the first year PPA price adjusted by the PPA escalation rate

defined on the Financing page.

COperating,n

($) The total operating costs in year n, shown in the Operating Costs row of the cash flow.

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CInterest,n

($) The loan interest payment in year n, shown in the Debt Interest Payment row of the cashflow.

CPrincipal,n

($) The loan principal payment in year n, shown in the Debt Repayment row of the cash flow.

The minimum DSCR is the lowest value of the project's debt-service coverage ratio that occurs in the life ofthe project:

Where,

minimum DSCR The minimum debt service coverage ratio, reported as a result in the Metrics table.

DSCRn

Debt service coverage ratio in year n shown in the PreTax Debt Service Coverage

Ratio row of the cash flow. (The symbol min represents the function that searches for

the minimum value of the DSCR in the cash flow.)

5.1.8 Gross to Net Conv Factor

For CSP systems, SAM displays the ratio of the system's annual AC electric output to the power block'sgross electric output. The difference between the two is due to parasitic losses from electric loads in thesolar field and power block for pumps, cooling equipment, etc.

Gross to Net Conv Factor = Annual Energy (kWh) / Gross Electric Output (kWh)

Annual Energy (kWh)

The system's total AC electrical output in year one, not accounting for the availability factor on theAnnual Performance page.

Gross Electric Output (kWh)

The power block's gross electrical output, reported under Metrics in the tabular data browser.

5.1.9 Internal Rate of Return

The internal rate of return is the discount rate that corresponds to a project net present value of zero forprojects with Utility or Commercial - Third-Party Ownership financing as defined in the Technology andMarket window.

Where Revenues and After Tax Cash Flow are rows in the project cash flow.

SAM calculates the internal rate of return using an iterative search algorithm described in 1st Year PPAPrice.

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5.1.10 Levelized Cost of Energy (LCOE)

Contents

Overview defines the levelized cost of energy in general terms.

LCOE for Residential and Commercial Projects describes how SAM calculates thelevelized cost of energy for systems with either residential market or commercialMarket financing.

LCOE for Commercial Third Party and Independent Power Producer Projectsdescribes the calculation of the levelized required revenue for projects with eithercommercial market - third-party ownership or utiltity and IPP financing.

Real and Nominal LCOE describes the difference between the two forms of LCOE.

Replicating LCOE Calculations in Excel explains how to use data from the cashflow table to calculate the LCOE valeus with Excel formulas.

LCOE without Incentives explains the two LCOE "w/o incentives" variables thatappear in some graphs.

OverviewThe levelized cost of energy (LCOE) in cents per kilowatt-hour accounts for a project's installation,financing, tax, and operating costs and the quantity of electricity it produces over its life. The LCOE makesit possible to compare alternatives with different project lifetimes and performance characteristics. Analystscan use the LCOE to compare the option of installing a residential or commercial project to purchasingelectricity from an electric service provider, or to compare utility and third-party ownership projects withinvestments in energy efficiency, other renewable energy projects, or conventional fossil fuel projects. TheLCOE captures the trade-off between typically higher-capital-cost, lower-operating-cost renewable energyprojects, and lower-capital-cost, higher-operating-cost fossil fuel-based projects.

SAM calculates the LCOE for residential and commercial projects differently than it does for utility andcommercial third-party ownership projects as described below. You can specify the project's financing type(residential, commercial, commercial third-party, and utility) in the Technology and Market window. SAMdisplays the financing type on the main window in the toolbar directly below the case tabs in the mainwindow.

For all projects, SAM calculates both a real and nominal LCOE value. The real LCOE accounts for the effectof inflation over the life of the project. The nominal LCOE excludes inflation from the calculation.

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Notes.

You can verify the SAM's LCOE calculation by exporting the cash flow table on the Results page toExcel and using the formulas described for each form of the LCOE below. See Replicating LCOECalculations in Excel for details.

You can also explore the LCOE methodology by downloading the spreadsheets on the Support page ofthe SAM website. Each of the five spreadsheets duplicates SAM's cash flow equations using Excelformulas.

For more information about the levelized cost of energy and other economic metrics for renewableenergy projects, see Manual for the Economic Evaluation of Energy Efficiency and Renewable EnergyTechnologies. (Short 1995) http://www.nrel.gov/docs/legosti/old/5173.pdf.

LCOE for Residential and Commercial ProjectsFor a project using one of the Residential Market or Commercial Market (except Commercial Third-PartyOwnership) financing options defined in the Technology and Market window, the LCOE is the cost offinancing, installing, and operating a system per unit of electricity it generates over the analysis period,accounting for tax credits and incentive payments.

SAM assumes that projects with residential or commercial financing are installed on a residential orcommercial property, and sell electricity at retail electricity rates specified on the Utility Rate page.

You specify the installation and operating costs on the System Costs page, financing assumptions on theFinancing page, tax credits on the Tax Credit Incentives page, and other incentives on the PaymentIncentives page.

For these projects, you you can compare a project's LCOE to the electricity rate that the residence orcommercial entity would pay to an electric service provider if the project were not installed.

SAM uses the real discount rate on the Financing page to calculate the present worth of future costs. Thediscount rate accounts for the time value of money and the relative degree of risk for alternative investments.

SAM uses the inflation rate on the Financing page to calculate year two and later costs in the cash flowbased on the cost input values that you specify in year one dollar values on the System Costs and otherinput pages. The inflation rate accounts for expected price increases over the project life for future operatingcosts.

SAM assumes that the project generates electricity in year one of the analysis period. It assigns capitalcosts to year zero of the project cash flow.

Note. You can calculate the real and nominal values of the LCOE yourself by exporting the cash flowtable to Excel. See Replicating LCOE Calculations in Excel for details.

For the real LCOE, the real discount rate appears in the denominator's total energy output term:



http://www.nrel.gov/docs/legosti/old/5173.pdf

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Similarly, for the nominal LCOE, the nominal discount rate appears in the denominator's total energy outputterm:

Qn (kWh) Electricity generated by the project in year n, calculated by the performance model based

on weather data and system performance parameters. The first year annual energy isreported in the Metrics table and in the year one column of the Energy row in the projectcash flow. Year two and subsequent output is the first year output reduced by the amountspecified for the degradation rate on the Annual Performance page.

N Analysis period in years as defined on the Financing page.

CAfterTax,n

($) The after tax cash flow in year n, equal to State Tax Savings + Federal Tax Savings +

PBI Incentives - Operating Costs - Debt Total Payment + Energy Value in the projectcash flow. The after tax cash flow in year zero is the equity portion of total installed costless any capital based incentives specified on the Payment Incentives page. The equityportion of the total installed cost is the total installed cost shown on the System Costspage minus the principal amount from the Financing page.

dreal

The real discount rate defined on the Financing page. This is the discount rate withoutinflation.

dnominal

The nominal discount rate, calculated as described below. This is the discount rate withinflation.

The nominal discount rate can be calculated based on the values of the real discount rate and the inflationrate on the Financing page:

dnominal

= (1 + dreal

)(1 + e) - 1

Where,

dnominal

Nominal discount rate expressed as a fraction.

dreal

Real discount rate defined on the Financing page expressed as a fraction.

e Inflation rate defined on the Financing page expressed as a fraction.

LCOE for Utility and Commercial Third Party ProjectsFor a project using either a Utility or Commercial Market - Third-Party Ownership financing option in theTechnology and Market window, the LCOE is the amount that the project must receive for each unit ofelectricity it sells to cover financing, installation, and operating costs, and to meet the financial constraintson the Financing page.

SAM assumes that utility and commercial third-party ownership projects are power generation projectsinstalled on the utility side of consumer power meters. These projects sell electricity at a price negotiatedby the project and electricity purchaser.

For these projects, the LCOE is effectively a levelized price of electricity because it is based on the presentworth of the project's revenue stream (which you can see in the Energy Value row of the project cash flow).SAM reports the revenue for each year of the analysis period as the Energy Value in the project cash flow,

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and the average annual electricity price in the Energy Price row. The Energy Price in year one is equal tothe first year power purchase price, which SAM reports as 1st Year PPA Price in the Metrics table.

Note. Because the LCOE for utility and commercial third party projects depends on the PPA price, itcan be very sensitive to the values that you specify for the minimum IRR, minimum DSCR, and positivecash flow. In some cases, it is possible to specify constraints that make the project capital investment arelatively insignificant factor in the LCOE calculation. For details on how SAM calculates the first yearPPA price, see 1st Year PPA Price.

SAM uses the real discount rate and inflation rate on the Financing page to calculate the present worth offuture costs. The discount rate accounts for the time value of money and the relative degree of risk foralternative investments.

SAM uses the inflation rate on the Financing page to calculate year two and later costs in the cash flowbased on the cost input values that you specify in year one dollar values on the System Costs and otherinput pages. The inflation rate accounts for expected price increases over the project life for future operatingcosts.

Note. You can calculate the real and nominal values of the LCOE yourself by exporting the cash flowtable to Excel. See Replicating LCOE Calculations in Excel for details.

For the real LCOE, the real discount rate appears in the denominator's total energy output term:

Similarly, for the nominal LCOE, the nominal discount rate appears in the total energy output term:

Where,

Qn (kWh) Electricity generated by the project in year n, calculated by the performance model based on

weather data and system performance parameters. The first year output is reported in theMetrics table on the Results page and in the year one column of the project cash flow. Yeartwo and subsequent output is the first year output reduced by the amount specified for thedegradation rate on the Annual Performance page.

N Analysis period in years as defined on the Financing page.

Rn

Project revenue from electricity sales in year n , equal to the annual electric output multiplied

by the annual electricity sales price. The required revenue in year one is equal to the product ofthe first year PPA price and Annual Energy values reported in the results. The required revenuein subsequent years is equal to the first year PPA price escalated by the PPA Escalation Rateshown on the Metrics table.

dreal

The real discount rate defined on the Financing page. This is the discount rate without inflation.

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dnominal

The nominal discount rate, calculated as described below. This is the discount rate withinflation.


dnominal

= (1 + dreal

)(1 + e) - 1

Where,

dnominal


dreal



Real and Nominal LCOESAM reports both a real LCOE and a nominal LCOE value in the Metrics table on the Results page. Theform of the discount rate used in the denominator's total energy output term of the equations describedabove determines the form of the LCOE.

The real LCOE is a constant dollar value that is adjusted for inflation. The real LCOE is lessthan the nominal LCOE whenever the inflation rate on the Financing page is greater thanzero. Because the nominal discount rate used to compute the nominal LCOE includesinflation, inflation is effectively factored out of the nominal LCOE. The nominal LCOE is acurrent dollar value. If the inflation rate on the Financing page is zero, the real and nominalLCOE are equal.

The choice of real or nominal LCOE depends on the analysis. Most long-term analyses are conducted inreal (constant) dollars to account for many years of inflation over the project life, whereas most short termanalyses use nominal (current) dollars. Some industries prefer to use one form over the other. For example,when discussing LCOE for parabolic trough projects, analysts tend to use the nominal LCOE, while the U.S. Department of Energy uses the real LCOE in its comparative analysis of photovoltaic project costs. Besure to use the same form of the LCOE when comparing costs for different alternatives: Never compare areal LCOE of one alternative with a nominal LCOE of another.


dnominal

= (1 + dreal

)(1 + e) - 1

Where,

dnominal


dreal



Replicating LCOE Calculations in ExcelIf you would like to better understand SAM's LCOE calculations, you can follow the procedures describedbelow to replicate the calculations using a spreadsheet program.

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Note for Mac users. SAM can not exchange data with Microsoft Excel on Mac computers. This meansthat the Excel Exchange feature is disabled on Mac versions of the software, and that SAM cannotdirectly export data to Excel workbooks.

To use the SAM data in Excel or another spreadsheet program, you can export the data to a comma-separated text file (CSV), and then import the CSV file to the spreadsheet program.

To replicate the residential or commercial LCOE calculation in Excel:

1. On the Results page, click Base Case Cashflow to display the project cash flow.

2. Click Send to Excel to export the cash flow table to an Excel worksheet, or click Save as CSV tosave the data as a text file then open it in Excel.

3. Type the project's discount rate and inflation rates as percentages into two blank cells in theworksheet. You can find these values on SAM's Financing page.

4. Type the following formula into a third empty cell to calculate the nominal discount rate:

=(1+[inflation rate])*(1+[real discount rate])-1

Replace the words in brackets with cell references to the appropriate values in the worksheet.

5. Type the following formula into a blank cell to calculate the real LCOE:

=(-[year zero after tax cost]-NPV([nominal discount rate],[after tax cost]))/NPV([real discount rate],[energy])

The year zero after tax cost flow is the value in the year zero column in the after tax cost rowtoward the bottom of the table. The after tax cost and energy are series of values from year 1 to thefinal year in the analysis period. The energy row is at the top of the table.

6. Use the following formula to calculate the nominal LCOE:

=(-[year zero after tax cost]-NPV([nominal discount rate],[after tax cost]))/NPV([nominal discountrate],[energy])

To replicate the utility or commercial third party LCOE calculation in Excel:

1. On the Results page, click Base Case Cashflow to display the project cash flow.2. Click Send to Excel to export the cash flow table to an Excel worksheet, or click Save as CSV to save

the data as a text file then open it in Excel.

3. Type the project's discount rate and inflation rates as percentages into two blank cells in the worksheet.You can find these values on SAM's Financing page.

4. Type the following formula into a third empty cell to calculate the nominal discount rate:

=(1+[inflation rate])*(1+[real discount rate])-1

Replace the words in brackets with cell references to the appropriate values in the worksheet.

5. Type the following formula into a blank cell to calculate the real LCOE:

=NPV([nominal discount rate],[energy value])/NPV([real discount rate],[energy])

The energy value and energy are series of values from year 1 to the final year in the analysis period.Energy is in the first row at the top of the table, and energy value is in the third row.

6. Use the following formula to calculate the nominal LCOE:

=NPV([nominal discount rate],[energy value])/NPV([nominal discount rate],[energy])

Note. You can also replicate the calculations in Excel using the summations shown in the equationsabove in place of the NPV formulas.

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LCOE without IncentivesSAM displays a value labeled LCOE (real-w/o incentives) on some graphs. This value of the LCOE iscalculated in the same way as the other forms of the LCOE, but excludes any tax credit incentives orpayment incentives that you specified on the Tax Credit Incentives page or Payment Incentives page.

If you remove all tax credits and payment incentives from your analysis, then the LCOE values with andwithout incentives are identical.

5.1.11 Minimum DSCR

The minimum DSCR is the minimum debt-service coverage ratio that SAM calculates for projects with Utilityor Commercial - Third-Party Ownership financing as defined in the Technology and Market window.

The debt-service coverage ratio in each year n is the ratio of operating income to expenses in that year

(SAM displays these values in the cash flow table):

Where,

DSCRn

Debt service coverage ratio in year n shown in the PreTax Debt Service Coverage Ratio

row of the cash flow.

Rn

($) The required revenue in year n, shown in the Revenues row of the cash flow table, equal to

the product of the electric output and electricity sales price in year n. Note that theelectricity sales price in year 1 is equal to the first year PPA price, and in subsequentyears (R

1<n<=N) is equal to the first year PPA price adjusted by the PPA escalation rate

defined on the Financing page.

COperating,n

($) The total operating costs in year n, shown in the Operating Costs row of the cash flow.

CInterest,n

($) The loan interest payment in year n, shown in the Debt Interest Payment row of the cashflow.

CPrincipal,n

($) The loan principal payment in year n, shown in the Debt Repayment row of the cash flow.

In SAM, the project's debt service coverage ratio (reported in results as the Minimum DSCR) is the lowestvalue of the DSCR that occurs in the life of the project N, equivalent to the Analysis Period on the Financing

page.

Where,

minimumDSCR

The minimum debt service coverage ratio, reported as a result in the Metrics table.

DSCRn

Debt service coverage ratio in year n shown in the PreTax Debt Service Coverage Ratio row

of the cash flow. (The symbol min represents the function that searches for the minimum

value of the DSCR in the cash flow.)

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SAM calculates the minimum debt-service coverage ratio to be greater than or equal to the minimumrequired DSCR target defined on the Financing page. The iterative algorithm used for the calculation isdescribed in 1st Year PPA Price.

5.1.12 Net Present Value

A project's net present value is a measure of a project's economic feasibility that includes both revenue andcost. In general, a positive net present value indicates an economically feasible project, while a negative netpresent value indicates an economically infeasible project, although this may not be true for all analyses.

For more information about using the net present value and other economic metrics to evaluate renewableenergy projects, see Short W et al, 1995. Manual for the Economic Evaluation of Energy Efficiency andRenewable Energy Technologies. National Renewable Energy Laboratory. NREL/TP-462-5173. http://www.nrel.gov/docs/legosti/old/5173.pdf

SAM only calculates the net present value for projects with residential or commercial (except third-partyownership) financing. These projects earn revenue through electricity sales at the retail rate specified as aninput on the Utility Rate page. For project with utility or commercial third-party ownership financing, SAMcalculates the electricity sales price as a result, and the project's levelized cost of energy accounts for bothrevenue and costs.

The net present value is the present value of the after tax cash flow discounted to year one using thenominal discount rate, plus the after-tax cash flow in year zero. The net cash flow for each year is thedifference between the revenue and cost in that year:

Where,

NPV ($) The net present value of the project over its life.

N The number of years in the project life, defined by the analysis period on the Financingpage.

CAfterTax,n

($) The after tax cash flow in year n, equal to State Tax Savings + Federal Tax Savings + PBI

Incentives - Operating Costs - Debt Total Payment + Revenues in the project cash flow.The after tax cash flow in year zero is the equity portion of total installed cost less anycapital based incentives specified on the Payment Incentives page. The equity portion ofthe total installed cost is the total installed cost shown on the System Costs pagemultiplied by 100% minus the debt fraction from the Financing page.

dnominal

The nominal discount rate, calculated as shown below.


dnominal

= (1 + dreal

)(1 + e) - 1

Where,

dnominal




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dreal



5.1.13 Payback Period

The payback period is a measure of the time it takes for project income from electricity sales, incentivepayments, and tax credits to "pay back" the initial project investment.

Note. SAM calculates the payback period for commercial and residential projects only.

For more information about using the net present value and other economic metrics to evaluate renewableenergy projects, see Short W et al, 1995. Manual for the Economic Evaluation of Energy Efficiency andRenewable Energy Technologies. National Renewable Energy Laboratory. NREL/TP-462-5173. http://www.nrel.gov/docs/legosti/old/5173.pdf

SAM calculates the payback period by determining the number of years that it takes for the values in theCumulative Payback Expenses Included row of the cash flow to switch from negative to positive.

If the cumulative payback cash flow amount is negative for all years in the cash flow, SAM displays thevalue 1e+99 for the payback, indicating that the payback period is greater than the analysis period.

Payback expenses included = After Tax Cashflow + Debt Interest Payment × (1 - Effective TaxRate) + Debt Repayment

Payback expenses excluded = Payback expenses included + Operating Costs + DeductibleExpenses × Effective Tax Rate

The cumulative cash flow for each year is the sum of the current year's payback amount and the previousyear's amount.

For a description of the cash flow calculations, see the residential and commercial cash flow details.

5.1.14 PPA Escalation

The PPA escalation rate is an annual escalation rate that SAM uses to calculate future electricity salesprices based on the first year PPA price. The value applies to projects with Utility or Commercial - Third-Party Ownership financing as defined in the Technology and Market window.

Depending on the financial optimization option on the Financing page, the PPA escalation rate is either auser-defined input on the Financing page, or a value that SAM calculates. When the Automatically minimizeLCOE with respect to PPA Escalation Rate option is checked, SAM finds the PPA escalation rate thatresults in the lowest levelized cost of energy.

SAM uses the PPA escalation rate in the iterative search algorithm described in 1st Year PPA Price.



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5.1.15 System Performance Factor

The system performance factor is a measure of a photovoltaic system's annual electric generation output inAC kWh compared to its nameplate rated capacity in DC kW, taking into account the solar resource at thesystem's location.

Note. SAM only calculates the system performance factor for the component-based photovoltaic model.It does not calculate the value for the PVWatts model or other technologies.

System Performance Factor = Annual Energy (kWh) / ( Nameplate Capacity (kW) × IncidentRadiation (kW/m2) / 1 Peak Sun Hour (h × kW/m2) )

Annual Energy

The system's total AC output in Year 1 in kWh reported in the Metrics table.

Nameplate Capacity

The system's DC rated capacity in kW from the Array page.

Incident Radiation

For flat-plate PV modules, the total (direct + diffuse) radiation incident on the array. This value isequivalent to the sum of the Radiation Total (kW/m2), Hourly values available on the tabular databrowser.

For concentrating PV (CPV) modules the direct radiation incident on the array. This value is equivalentto the sum of the Incident Beam, Shaded (kW/m2), Hourly values available on the tabular databrowser.

Peak Sun Hour

The equivalent number of hours in a year that the array receives 1 kW/m2.

5.1.16 Total Land Area

For the PV component-based and CSP models, the land area required for the project. SAM calculates thevalue based on the Land Area values you specify, and the array and collector area SAM calculates on theArray and Solar Field pages.

Note. SAM displays the total land area value for reference only. The value does not affect costcalculations, and is not affected by the land costs you specify on the System Costs page.

5.1.17 Year 1 Revenues

Enter topic text here.

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5.2 Graphs and ChartsSAM displays graphs on the Results page after running simulations. The standard graphs that appear bydefault show summaries of results from both the performance model and financial model. You can edit thestandard graphs and create your own graphs.

Related topics:

For detailed graphs of hourly results, see Time Series Data Viewer (DView).

For a description of how to use sliders with graphs, see Sliders.

To view the project cash flow, click Base Case Cashflow. See Base Case Cashflow for details.

To view a tables of results data, click Tabular Data Browser. See Tabular Data Browser fordetails.

To show and hide graphs:

1. Click View Graphs and Charts at the top of the Results page.

SAM displays a thumbnail of all of the graphs defined for the case. Some graphs are defaultgraphs, and others are graphs that you may have added or edited.

2. Click a thumbnail at the bottom of the page to display a graph. Hold down the Ctrl key and click upto four graphs to display multiple graphs on the page.

To hide a graph, hold down the Ctrl key and click its thumbnail on the Graphing tab.

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Manage Graphs

To create or modify graphs:

1. To add a graph to the list of available graphs, click Add a new graph.

To modify an existing graph, select the graph name in the available graphs and click Edit. You canalso modify a visible graph by right-clicking it.

2. In the Edit Graph window, choose data to graph and other graph properties.

Use the Properties options to assign graph labels, adjust line thickness, show and hide the legend,and change other properties.

To remove graphs:

1. Click the thumbnail for up to four graphs that you want to remove.

2. Click Remove.

To remove all graphs, including default graphs, click Remove All.

Data Tables for Graphs

You can view tables of data for graphs visible on the Results page and export the data to text files.

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To view the data tables:

1. On the Results page, click View Graphs and Charts.

2. Click the thumbnails at the bottom of the page to show up to four graphs. (Hold down the ctrl keywhile clicking the thumbnails to show more than one graph.)

3. Click Show Graph Data.

To export graph data:

To export data from a graph, right-click the graph and choose an export option:

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Tips for working with graphs

Use sliders to see the effect of changing input variables on the graph without changing input variablevalues on the input pages. See Working with Sliders for details.

Right-click a graph to hide the legend, change line thickness and colors, edit graph legends, and modifyother graph properties.

Click the Notes button above the top right corner of the Results page to display an editable text box tomake notes about a graph.

5.3 Base Case Cash FlowThe base case cash flow table displays the project cash flow calculated by the financial model. The cashflow table only displays data from the base case, which is the set of results calculated from the inputvariable values that are visible on the input pages. Use the tabular data browser to see cash flow data forresults from that involve multiple simulation runs for parametric, sensitivity, optimization, or statisticalanalyses.

For detailed descriptions of the cash flow for the different financing options, see:

Residential and Commercial

IPP and Commercial PPA

Leveraged Partnership Flip

All Equity Partnership Flip

Sale Leaseback

Single Owner

Related Topics:

You can also see the cash flow table in the tabular data browser and case summary workbook.

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If you want to see cash flow data for analyses involving multiple runs such as parametric analyses,use the Tabular Data Browser to display the cash flow.

To view the cash flow table:

On the Results page, click Base Case Cashflow at the top of the page.

If you have trouble seeing values in columns at the far right of the table, click a cell in the table anduse the right-arrow key to display the columns.

SAM offers three options for exporting the cash flow table:

Copy to clipboard copies the table to your clipboard. You can paste the entire table into a wordprocessing document, spreadsheet, presentation or other software.

Save as CSV saves the table in a comma-delimited text file that you can open in a spreadsheetprogram or text editor.

Send to Excel (Windows only) saves the table in an Excel file.

Note. When you export cash flow data to Excel, the worksheet contains values from the cash flow tablebut no formulas. This is because SAM calculates the values internally and does not rely on Excel tomake the calculations.

5.3.1 Residential and Commercial

Cash Flow Year

The cash flow year is displayed in the top row of the cash flow table. In the descriptions below, the letter nindicates the cash flow year, where n = 0 is Year zero of the cash flow, n = 1 is year one, n = 2 is year two,

Base Case Cash Flow 361


etc.

Energy (kWh)

For systems that generate electricity, Energy is the total amount of electricity generated by the system inAC kilowatt-hours for each year.

For solar water heating systems, Energy is the amount of electricity saved by the solar water heatingsystem in AC kilowatt-hours for each year.

For Year 1, the energy value is equal to the sum of the hourly values calculated by the performance modelmultiplied by the availability factor from the Annual Performance page.

For Years 2 and later, the energy value is the previous year's energy value adjusted by the annualdegradation rate (System Degradation) from the Annual Performance page:

Energy in Year n = Energy in Year n-1 * (1 - Degradation Rate)

Note. Some of the annual electric energy values reported elsewhere in the results are performancemodel results, and do not account for the availability factor and degradation rate.

Energy Value ($)

The energy value is the value of electricity that the project avoids purchasing because of the renewableenergy system.

SAM assumes that the project sells electricity only in hours when the renewable energy system's output isgreater than the electric load specified on the Electric Load page, and at the sell rate for each hour definedby the rate structure on the Utility Rate page.

The project buys electricity in hours when the electric load is less than the renewable energy system'soutput at the buy rate for each hour specified in the rate structure.

To determine the annual energy value, SAM calculates two "revenue" values:

"Revenue with system" represents the net value of electricity bought and sold (revenue = sales -purchases) by the project with the renewable energy system.

"Revenue without system" shows what it would cost to meet the load entirely with electricity purchasedfrom the utility at the buy rates specified in the rate structure.

The energy value is the difference between the two:

Energy Value ($) = Revenues with System ($) - Revenues without System ($)

The tabular data browser shows hourly values of revenues and other related values.

For a simple utility rate structure with net metering at a flat rate, the project buys and sells electricity at thesame rate (equal to the flat rate from the Utility Rate page), and the energy value is equivalent to the value ofthe energy from the renewable energy system:

Energy Value in Year n ($) = Energy in Year n ($) * Flat Rate ($/kWh)

Operation and Maintenance (O&M) Costs

The operation and maintenance (O&M) costs are defined on the system costs page and escalated in eachyear after year one using both the escalation rate for each O&M category on the system costs page andthe inflation rate value on the Financials page.

Fixed O&M Annual in Year n = Fixed Annual Cost ($/yr) * (1 + Inflation Rate + Escalation Rate) ^ n-

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1

Fixed O&M in Year n = Fixed Cost by Capacity ($/kW-yr) * System Capacity * (1 + Inflation Rate +Escalation Rate)^(n-1)

Variable O&M in Year n = Variable Cost by Generation ($/MWh) / 1000 (kWh/MWh) * AnnualOutput in Year n (MWh) * (1 + Inflation Rate + Escalation Rate)^(n-1)

The system capacity depends on technology being modeled. Note that SAM converts the capacity value tokW before using it in the calculation.

Table 24. Rated system capacity values for each technology.

Technology System Capacity Input Page

PV SAM Performance Models Total Array Power (Wdc) Array

PV PVWatts DC Rating (kW) PVWatts Solar Array

CSP Parabolic Trough Rated Turbine Net Capacity (MWe) Power Block

CSP Power Tower Nameplate Capacity (MWe) Power Cycle

CSP Dish Stirling Total Capacity (kW) Solar Field

Generic Fossil Nameplate Capacity (kWe) Fossil Plant

Fuel O&M

Parabolic trough, power tower, and generic fossil systems include an annual cost of fuel for the fossilbackup system in the total operating expense. (When the fossil fill fraction variable on the Thermal Storagepage for troughs or towers is greater than zero, the systems consume fuel for backup energy.) Forphotovoltaic and CSP dish systems, the fuel cost is always zero.

SAM reports the annual fuel usage in the hourly results. The total annual fuel usage in year 1 is reported onthe Annual Data spreadsheet in the Spreadsheet summary table.

Fuel O&M in Year n = Annual Fuel Usage in Year 1 (kWh) * 0.003413 MMBtu/kWh * Fossil FuelCost ($/MMBtu) * (1 + Inflation Rate + Escalation Rate)^(n-1)

Insurance

The insurance cost applies in year 1 and later of the cash flow, and depends on the insurance rate specifiedon the Financing page and the total installed costs on the System Costs page.

Insurance in Year n = Total Installed Costs ($) * Insurance (%) * (1 + Inflation Rate + EscalationRate)^(n-1)

Property Assessed Value

The property assessed value is the value SAM uses as a basis to calculate the annual property taxpayment. The value depends on the property tax variables on the Financing page.

The assessed value in Year 1 is shown on the Financing page, and is the product of the assessed percentand total installed cost from the System Costs page.

In Years 2 and later, the property assessed value is the Year 1 value adjusted by the assessed valuedecline value from the Financing page:

Property Assessed Value in Year n = Assessed Value ($) * (1 - Assessed Value Decline)^(n-1)



Property Taxes

Property taxes apply in Year 1 and later of the cash flow, and depend on the property tax rate specified onthe Financing page, and on the property assessed value:

Property Taxes in Year n = Property Assessed Value in Year n ($) * Property Tax (%)

Net Salvage Value

SAM calculates the net salvage value using the percentage you specify on the Financing page and the totalinstalled cost from the System Costs page. The salvage value applies in the final year of the project cashflow.

For example, if you specify a 10% salvage value for a 30-year project with an inflation rate of 2.5% and totalinstalled cost of $1 million, SAM includes income of $204,640.74 in year 30: $1,000,000 × 0.10 × (1 +0.025) ̂(30 - 1).

SAM adds the salvage value as income (a negative value) to the operating expenses in the cash flow in thefinal year of the analysis period. The salvage value therefore reduces the operating expenses in the finalyear of the analysis period

For residential projects, the salvage value has no effect on federal and state income tax because operatingexpenses are not taxable.

For commercial projects, because the salvage value reduces the operating expenses in the final year of theanalysis period, it increases the federal and state income tax payment because operating expenses aredeductible from federal and state income tax.

Operating Costs

The total operating expenses include operation and maintenance costs, and insurance and property taxpayments:

Operating Costs = Fixed O&M Annual + Fixed O&M + Variable O&M + Fuel O&M + Insurance +Property Taxes - Salvage Value

Deductible Expenses

The deductible expenses are project costs that can be deducted from federal and state income taxes.

For residential projects, the deductible expense amount equals the property tax amount:

Deductible Expenses = - Property Taxes

For commercial projects, all operating costs are deductible:

Deductible Expenses = - Operating Costs

Debt Balance

The debt balance in Year 1 represents the debt portion of the capital costs, adjusted for any investment-based incentives (IBI). The total installed cost is from the System Costs page, and total IBI is the sum of allIBIs specified on the Payment Incentives page, and debt fraction is the value specified on the Financingpage:

Debt Balance in Year 1 = (-Total Installed Costs + Total IBI) * Debt Fraction

In Years 2 and later, the debt balance is calculated from the previous year's debt balance and debt

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repayment amounts:

Debt Balance in Year n = Debt Balance in Year n-1 + Debt Repayment in Year n-1

Debt Interest Payment

The debt interest payment is the debt balance multiplied by the loan interest rate on the Financing page:

Debt Interest Payment in Year n = - Debt Balance in Year n * Loan Rate

Debt Repayment

The debt repayment amount is the annual payment on principal amount assuming constant payments overthe loan term defined on the Financials page and at the constant annual interest rate defined on theFinancials page. SAM calculates the amount using a methodology equivalent to Excel's PPMT function:

Debt Repayment in Year n = -PPMT(Loan Rate,n,Loan Term,Principal Amount,0,0)

Debt Total Payment

The total debt payment is the sum of interest and principal payments:

Debt Total Payment = Debt Interest Payment + Debt Repayment

Investment Based Incentives (IBI)

Each IBI applies in Year 0 of the project cash flow. SAM calculates the value of each investment-basedincentive (IBI) as either a fixed amount or percentage of the total installed cost that you specify on thePayment Incentives page. The total installed cost is from the System Costs page:

IBI in Year 0 = Amount ($)

IBI in Year 0 = Total Installed Cost ($) * Percentage (%), up to maximum value

Note. The IBI reduces the debt balance in Year 1.

Capacity Based Incentives (CBI)

Each CBI applies in Year 0 of the project cash flow, and is calculated based on the system's rated capacityand the incentive rate (Amount) from the Payment Incentives page. The rated capacity depends on thesystem type, as described above under "Operation and Maintenance Costs:"

CBI in Year 0 = System Capacty (W) * Amount ($/W), up to maximum value

Production Based Incentives (PBI)

The PBI apply in Years 1 and later of the project cash flow, up to the number of years specified by the Termvariable on the Payment Incentives page. The PBIs are calculated based on each year's annual outputdisplayed in the Energy row of the cash flow table and the incentive rate (Amount) from the PaymentIncentives page. The amount, term, and escalation rate are specified on the Payment Incentives page:

PBI in Year n = Amount ($/kWh) * Energy in Year n (kWh) * (1 + Escalation)^(n-1)

Note. If you specify a PBI amount on the Payment Incentives page, be sure to also specify the incentiveterm. If you specify a term of zero, the incentive will not appear in the cash flow table.



Federal PTC and State PTC

The PTC apply in Year 1 and later of the project cash flow, up to the number of years specified by the Termvariable on the Tax Credit Incentives page. The PTC are calculated based on each year's annual electricaloutput, displayed in the Energy row of the cash flow table, and the amount specified on the Tax CreditIncentives page:

PTC in Year n = Amount ($/kWh) * Energy in Year n (kWh) * (1 + Escalation)^(n-1)

Federal ITC and State ITC

The ITC apply only in Year 1 of the project cash flow. The ITC can be specified on the Tax Credit Incentivespage as a fixed amount, or as a percentage of the total installed cost with a maximum value. Thecheckboxes in the "Reduces Depreciation Basis" column determines whether the basis used to calculateaccelerated depreciation is reduced by the ITC amount.

ITC in Year 1 = Amount

ITC in Year 1 = ( Total Installed Cost ($) - Basis Reduction ($) ) * Percentage (%), up to maximumvalue

The "Basis Reduction" amount depends on whether the project includes any investment-based incentives(IBI) or capacity-based incentives (CBI) specified on the Payment Incentives page with checked boxes inthe "Reduces ITC Basis." For each checked incentive, SAM subtracts the IBI or CBI amount from the totalinstalled cost to calculate the ITC.

Sales Tax Deduction (Commercial Only)

SAM calculates the sales tax amount by multiplying the sales tax rate on the Financing page by the"percent of direct cost" rate from the System Costs page.

The sales tax amount is included the total installation cost and accounted for in the Year 0 after tax costvalue of the cash flow.

For commercial projects, SAM also deducts the sales tax amount from federal and state income taxpayment in Year 1. The sales tax deduction amount depends on the sales tax rate specified on theFinancing page, and the percentage of direct cost and total direct cost specified on the System Costspage:

Sales Tax Deduction = Sales Tax (%) * Percent of Direct Cost (%) * Total Direct Cost ($)

Depreciation Schedule (%) -- State and Federal (Commercial Only)

For commercial projects with a depreciation option defined on the Financing page, SAM displays thedepreciation percentage in the State Depreciation Schedule and Federal Depreciation Schedule rows of thecash flow table. SAM determines the depreciation schedule (percentage and applicable years) based on theoptions specified on the Financing page.

Depreciation -- State and Federal (Commercial Only)

The depreciation amount is the product of the percentage and the total installed costs on the System Costspage:

Depreciation = Depreciation Schedule (%) * Total Installed Costs

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Income Taxes -- State and Federal

The state and federal income tax amount is the taxable income multiplied by the tax rate on the Financingpage for the applicable tax:

Income Taxes = (Deductible Expenses + IBI + CBI + PBI - Interest Payment) × Tax Rate

Tax Savings -- State and Federal

For both federal and state taxes, a positive value of Tax Savings indicates a tax savings or cash inflow. Anegative value indicates a tax liability or cash outflow.

The tax savings amount is the income tax less PTC and ITC tax credit amounts:

Tax Savings = Income Taxes - PTC - ITC

The PTC and ITC are the production tax credit and investment tax credit, respectively:

The PTC, if it applies, is calculated for each year by multiplying the tax credit percentage from the TaxCredit Incentives page by the value electric output amount for that year.

When an ITC applies, it is subtracted only in year one of the project; it is not subtracted in year two andsubsequent years. The ITC is either equal to the fixed amount on the Payment Incentives page, orcalculated by multiplying the ITC percentage on the Incentives page by the applicable basis.

A note about incentives. Some incentives have caps that limit their maximum value, while others haveescalation rates that increase their value from year to year. Others have term limits that end paymentsafter a given number of years. In some cases the incentive income is taxable at the federal or state level,and in other cases it is not. Finally, investment and capacity based incentives may or may not reducethe basis on which the investment tax credit (ITC) is calculated. All of these factors are defined on thePayment Incentives page.

After Tax Cost

Year zero of the cash flows represents the project capital cost. The capital cost is equal to the totalinstalled cost displayed on the system costs page minus the loan principal amount from the Financing page, and any investment based incentives.

Year one is the first year that the project generates electricity. The cash flow for year one and subsequentyears accounts for project expenses, income from electricity sales, taxes, and incentive payments.

The after tax cost row represents the net income of the project after tax and debt payments are made,operating costs are paid, and any incentive payments are received. The after tax cost in year one andsubsequent years is:

After Tax Cost = State Tax Savings + Federal Tax Savings + PBI Incentives - Operating Costs -Debt Total Payment

Note. The cash flow table for utility projects does not include a row for the After Tax Cost flow.

After Tax Cashflow

The after tax cash flow for year one and subsequent years is given by:

After Tax Cashflow = After Tax Cost +



Residential Offset Electricity Payments

Commercial Offset Electricity Payments - Offset Electricity Payments × Effective Tax Rate

The effective tax rate is a single number that includes both the federal income tax rate and state income taxrate. SAM uses the effective tax rate for several calculations requiring a total income tax value.

The effective tax rate calculation is:

The federal and state tax rates are input variables on the Financing page.

Payback Cash Flows

SAM uses the payback cash flows to calculate the project payback period displayed in the Metrics table onthe Results page.

The payback period is the number of years that it takes for the cumulative payback expenses included cashflow to switch from negative to positive. If the cumulative payback cash flow amount is negative for all yearsin the cash flow, SAM displays the value 1e+99 for the payback, indicating that the payback period isgreater than the analysis period.

For Year 0, the payback cash flow is equal to the total installed cost from the System Costs page. Anegative value indicates an expenditure.

For Years 1 and later, the payback cash flow is:

Payback expenses included = After Tax Cashflow + Debt Interest Payment × (1 - Effective TaxRate) + Debt Repayment

Payback expenses excluded = Payback expenses included + Operating Costs + DeductibleExpenses × Effective Tax Rate

The cumulative payback cash flow for each year is the sum of the current year's payback amount and theprevious year's amount.

5.3.2 IPP and Commercial PPA

Cash Flow Year

The cash flow year is displayed in the top row of the cash flow table. In the descriptions below, the letter nindicates the cash flow year, where n = 0 is year zero of the cash flow, n = 1 is year one, n = 2 is year two,

etc.

Energy (kWh)

The energy quantity reported for year one is equal to the Annual Energy value displayed in the Metrics tableon the Results page. The quantities in year two and subsequent years is based on the year one valueadjusted for the degradation rate on the Annual Performance page:

Energy in Year n = Energy in Year One * (1 - Degradation Rate) ^ n-1

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Energy Price ($/kWh)

For residential and commercial projects, the energy price is determined by the rate structure you specify onthe Utility Rate page and does not appear in the cash flow table.

For utility and commercial third party projects, the energy price in year one is the 1st Year PPA price,which is a result displayed in the Metrics table on the Results page. The energy price represents theaverage annual electricity sales price.

For utility projects, the energy price in years two and later is the first year price adjusted by the PPAescalation rate displayed on the Metrics table.

Energy Price in Year n = Energy Price in Year n-1 * (1 + PPA Escalation Rate)^(n-1)

Energy Value ($)

For residential and commercial projects, the energy value represents total annual value of electricitygenerated by the system, assuming that the electricity is sold at prices specified by the rate structurespecified on the Utility Rate page. For solar hot water systems, the value represents the value of thethermal energy delivered to the thermal load.

For utility and commercial third party projects, the energy value represents annual income earned by theproject through electricity sales:

Energy Value = Energy (kWh) * Energy Price ($/kWh)

Recapitalization

The recapitalization cost applies only to geothermal projects and represents the cost required to drill newwells when the reservoir temperature drops below a certain level. The recapitalization cost is specified onthe Geothermal System Costs page.

Operation and Maintenance (O&M) Costs

The operation and maintenance (O&M) costs are defined on the system costs page and escalated in eachyear after year one using both the escalation rate for each O&M category on the system costs page andthe inflation rate value on the Financials page.

Fixed O&M Annual in Year n = Fixed Annual Cost ($/yr) * (1 + Inflation Rate + Escalation Rate) ^ n-1

Fixed O&M in Year n = Fixed Cost by Capacity ($/kW-yr) * System Rated Capacity * (1 + InflationRate + Escalation Rate)^(n-1)

Variable O&M in Year n = Variable Cost by Generation ($/MWh) * Annual Output in Year n (MWh) *(1 + Inflation Rate + Escalation Rate)^(n-1)

Fuel O&M

Parabolic trough, power tower, and generic fossil systems include an annual cost of fuel for the fossilbackup system in the total operating expense. (When the fossil fill fraction variable on the Thermal Storagepage for troughs or towers is greater than zero, the systems consume fuel for backup energy.) Forphotovoltaic and CSP dish systems, the fuel cost is always zero.

SAM reports the annual fuel usage in the hourly results. The total annual fuel usage in year 1 is reported onthe Annual Data spreadsheet in the Spreadsheet summary table.



Fuel O&M in Year n = Annual Fuel Usage in Year 1 (kWh) * 0.003413 MMBtu/kWh * Fossil FuelCost ($/MMBtu) * (1 + Inflation Rate + Escalation Rate)^(n-1)

Insurance

The insurance cost applies in year 1 and later of the cash flow, and depends on the insurance rate specifiedon the Financing page and the total installed costs on the System Costs page.

Insurance in Year n = Total Installed Costs ($) * Insurance (%) * (1 + Inflation Rate + EscalationRate)^(n-1)

Property Taxes

Property taxes apply in year 1 and later of the cash flow, and depend on the property tax rate specified onthe Financing page, and on the total installed costs on the System Costs page:

Property Taxes in Year n = Total Installed Costs ($) * Property Tax (%) * (1 + Inflation Rate +Escalation Rate)^(n-1)

Net Salvage Value

SAM calculates the net salvage value using the percentage you specify on the Financing page and the totalinstalled cost from the System Costs page. The salvage value applies in the final year of the project cashflow.

For example, if you specify a 10% salvage value for a 30-year project with an inflation rate of 2.5% and totalinstalled cost of $1 million, SAM includes income of $204,640.74 in year 30: $1,000,000 × 0.10 × (1 +0.025) ̂(30 - 1).

SAM adds the salvage value as income (a negative value) to the operating expenses in the cash flow in thefinal year of the analysis period.

For residential projects, the salvage value has no effect on federal and state income tax because operatingexpenses are not taxable.

For commercial and utility projects, the salvage value reduces the operating expenses in the final year ofthe analysis period, which effectively increases the federal and state income tax payment becauseoperating expenses are deductible from federal and state income tax.

Total Operating Expenses

The total operating expenses include operation and maintenance costs, and insurance and property taxpayments:

Total Operating Expenses = Fixed O&M Annual + Fixed O&M + Variable O&M + Fuel O&M +Insurance + Property Taxes - Salvage Value

Operating Income

For utility projects, the operating income is the difference between revenues and operating costs:

Operating Income = Energy Value - Operating Costs

Debt Balance

The debt balance in year one represents the debt portion of the capital costs, adjusted for any investment-based incentives (IBI). The total installed cost is from the System Costs page, total investment-based

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incentives is the sum of all IBIs specified on the Payment Incentives page, and debt fraction is the valuespecified on the Financing page:

Debt Balance = (-Total Installed Costs + Total Investment Based Incentives) * Debt Fraction

In years two and later, the debt balance is calculated from the previous year's debt balance and debtrepayment amounts:

Debt Balance = - Debt Balance (previous year) - Debt Repayment (previous year)

Debt Interest Payment

The debt interest payment is the debt balance multiplied by the loan interest rate on the Financing page:

Debt Interest Payment = Debt Balance * Loan Rate

Debt Repayment

The debt repayment amount is the annual payment on principal amount assuming constant payments overthe loan term defined on the Financials page and at the constant annual interest rate defined on theFinancials page. SAM calculates the amount using a methodology equivalent to Excel's PPMT function.

Debt Total Payment

The total debt payment is the sum of interest and principal payments:

Debt Total Payment = Debt Interest Payment + Debt Repayment

Investment Based Incentives (IBI)

Each IBI applies in year one of the project cash flow. SAM calculates the value of each investment-basedincentive (IBI) as either a fixed amount that you specify, or as a percentage of the total installed cost fromthe System Costs page:

IBI = Amount ($)

IBI = Total Installed Cost ($) * Percentage (%), up to maximum value

Capacity Based Incentives (CBI)

The CBI also apply in year one of the project cash flow, and are calculated based on the system's ratedcapacity. The rated capacity depends on the system type, as described in the capacity factor description:

CBI = System Rated Capacty (W) * Amount, up to maximum value

Production Based Incentives (PBI)

The PBI apply in years 1 and later of the project cash flow. The PBIs are calculated based on each year'sannual output, displayed in the Energy row of the cash flow table. The amount and escalation rate arespecified on the Payment Incentives page:

PBI = Amount ($/kWh) * Energy in Year n (kWh) * (1 + Escalation) ^(n-1)

Federal PTC and State PTC

The PTC apply in year 1 and later of the project cash flow, up to the number of years specified by the Termvariable on the Tax Credit Incentives page. The PTC are calculated based on each year's annual electricaloutput, displayed in the Energy row of the cash flow table, and the amount specified on the Tax Credit



Incentives page:

PTC = Amount ($/kWh) * Energy in Year n (kWh) * (1 + Escalation) ^ n-1

Federal ITC and State ITC

The ITC apply only in year 1 of the project cash flow. The ITC can be specified on the Tax Credit Incentivespage as a fixed amount, or as a percentage of the total installed cost with a maximum value. Thecheckboxes in the "Reduces Depreciation Basis" column determines whether the basis used to calculateaccelerated depreciation is reduced by the ITC amount.

ITC = Amount

ITC = ( Total Installed Cost ($) - Basis Reduction ($) )* Percentage (%), up to maximum value

The "Basis Reduction" amount depends on whether the project includes any investment-based incentives(IBI) or capacity-based incentives (CBI) specified on the Payment Incentives page with checked boxes inthe "Reduces ITC Basis." For each checked incentive, SAM subtracts the IBI or CBI amount from the totalinstalled cost to calculate the ITC.

Sales Tax Deduction

SAM calculates the sales tax amount by multiplying the sales tax rate on the Financing page by the"percent of direct cost" rate you specify under Indirect Capital Costs and the Total Direct Cost on theSystem Costs page. The sales tax amount is therefore included the total installation cost and accounted forin the year zero after tax cost in the project cash flow.

SAM also deducts the sales tax amount from federal and state income tax payment in year one of theproject cash flow. The sales tax deduction amount depends on the sales tax rate specified on the Financingpage, and the percentage of direct cost and total direct cost specified on the System Costs page:

Sales Tax Deduction = Sales Tax (%) * Percent of Direct Cost (%) * Total Direct Cost ($)

PreTax Debt Service Coverage RatioThe debt-service coverage ratio row in the cash flow table only applies to projects with utility andcommercial third-party financing. Solar Adviser displays the annual debt service coverage (DSCR) amountsfor utility and commercial third party ownership projects only. The minimum DSCR value displayed in theMetrics table is the minimum value in the row of the cash flow table.

PreTax DSCR = Operating Income ÷ Total Debt Payment

5.3.3 New Utility Structures (Draft)

This section describes the cash flow for the four new utility rate structures, Single Owner, All EquityPartnership Flip, Leveraged Partnership Flip and Sale Leaseback.

Note. This section is in draft form and will be updated soon after the release of SAM 0.0.1.

Partial Income Statement: Project

The first four rows of the cash flow table show values for the project as a whole.

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Net Energy (kWh)

The energy quantity reported for year one is equal to the Annual Energy value displayed in the Metricstable on the Results page. The quantities in year two and subsequent years is based on the year onevalue adjusted for the degradation rate on the Annual Performance page:

Energy in Year n = Energy in Year One * (1 - Degradation Rate) ^ n-1

PPA price (cents/kWh)

The PPA price year one is the 1st Year PPA price, which is a result displayed in the Metrics table onthe Results page. The energy price represents the average annual electricity sales price.

The PPA price in years two and later is the first year price adjusted by the PPA escalation ratedisplayed on the Metrics table.

Energy Price in Year n = Energy Price in Year n-1 * (1 + PPA Escalation Rate)^(n-1)

Salvage value ($)

SAM calculates the net salvage value using the percentage you specify on the Financing page and thetotal installed cost from the System Costs page. The salvage value applies in the final year of theproject cash flow.

For example, if you specify a 10% salvage value for a 30-year project with an inflation rate of 2.5% andtotal installed cost of $1 million, SAM includes income of $204,640.74 in year 30: $1,000,000 × 0.10 ×(1 + 0.025) ̂(30 - 1).

SAM adds the salvage value as income (a negative value) to the operating expenses in the cash flow inthe final year of the analysis period. The salvage value reduces the operating expenses in the final yearof the analysis period, which effectively increases the federal and state income tax payment becauseoperating expenses are deductible from federal and state income tax.

Total revenue ($)

Annual income earned by the project through electricity sales:

Total Revenue = Net Energy (kWh) * PPA Price ($/kWh)

Expenses

The eight expense rows are for annual project costs calculated from assumptions you specify on theFinancing and System Costs pages.

The four O&M expenses are based on the first year or annual schedule costs you specify under Operationand Maintenance Costs on the System Costs page, and are adjusted by the inflation rate from theFinancing page and optional escalation rate from the System Costs page.

O&M Fixed expense ($)

O&M Fixed Expense in Year n = Fixed Annual Cost ($/yr) * (1 + Inflation Rate + Escalation Rate) ^n-1

O&M Capacity-based expense ($)

O&M Capacity-based Expense in Year n = Fixed Cost by Capacity ($/kW-yr) * System RatedCapacity * (1 + Inflation Rate + Escalation Rate)^(n-1)

O&M Production-based expense ($)

O&M Production-based Expense in Year n = Variable Cost by Generation ($/MWh) * Annual Outputin Year n (MWh) * (1 + Inflation Rate + Escalation Rate)^(n-1)



O&M Fuel expense ($)

Parabolic trough, power tower, and generic fossil systems include an annual cost of fuel for the fossilbackup system in the total operating expense. (When the fossil fill fraction variable on the ThermalStorage page for troughs or towers is greater than zero, the systems consume fuel for backup energy.)For photovoltaic and CSP dish systems, the fuel cost is always zero.

SAM reports the annual fuel usage in the hourly results. The total annual fuel usage in year 1 isreported on the Annual Data spreadsheet in the Spreadsheet summary table.

Fuel Expense in Year n = Annual Fuel Usage in Year 1 (kWh) × 0.003413 MMBtu/kWh × FossilFuel Cost ($/MMBtu) × (1 + Inflation Rate + Escalation Rate)^(n-1)

The insurance and property tax expense amounts depend on the insurance and tax rates you specify on the Financing page.

Insurance expense ($)

The insurance cost applies in year 1 and later of the cash flow, and depends on the insurance ratespecified on the Financing page and the total installed costs on the System Costs page.

Insurance in Year n = Total Installed Costs ($) × Insurance (%) × (1 + Inflation Rate + EscalationRate)^(n-1)

Property tax net assessed value ($)

The first year property tax net assessed value is shown on the Financing page, and is based on theassessed percent value you specify and the total installed cost from the System Costs page.

Property Tax Net Assessed Value in Year 1 = Assessed Percent (%) × Total Installed Cost ($)

The assessed value in Years 2 and later is based on the assessed value decline value you specify onthe Financing page:

Property Tax Net Assessed Value in Year n = Property Tax Net Assessed Value in Year 1 × (1 -Assessed Value Decline)^(n-1)

Property tax expense ($)

The property tax expense depends on the assessed value and the property tax rate you specify on theFinancing page:

Property Tax Expense in Year n = Property Tax Net Assessed Value in Year n ($) × Property Tax(%/Year)

Total operating expense ($)

The total operating expense is the sum of O&M, insurance, and property tax expenses.

Total Operating Expense in Year n = O&M Fixed Expense ($) + O&M Capacity-based Expense ($)+ O&M Production-based Expense ($) + O&M Fuel Expense ($) + Insurance Expense ($) +Property Tax Expense ($) (all in Year n)

EBITDA ($)

Earnings before Interest, Taxes, Depreciation and Amortization (EBITDA) is a measure of the project'sannual net income:

EBITDA in Year n = Total Revenue in Year n ($) - Total Operating Expense in Year n ($)

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5.4 Tabular Data BrowserThe tabular data browser displays results in tabular form from both the base case simulation, which reflectsdata specified on the input pages, and from parametric analyses and other advanced analyses involvingmultiple simulations.

You can create custom tables of data in the tabular data browser and export them for use in anotherprogram.

To view the tabular data browser:

1. On the Results page, click Tabular Data Browser.

If you do not see the Hourly Data list, run simulations to generate the list.

2. If your analysis involved multiple simulations, such as for parametric analyses, choose a simulationin the Choose Simulation list. The list does not appear for results of single simulations.

3. In the navigation tree under Output Variables, check the box for each variable you want to displayin the table.

Tabular Data Browser Categories

The tabular data browser displays data in the following categories:

Metrics

Displays any results that consist of a single value, including:

Results from the Metrics table

Cost data from the System Costs page

Annual totals of energy output values from the hourly data.

Monthly Data

Displays results that consist of twelve monthly values:

Monthly averages of energy output values from the hourly data.

Weather and performance output data values are monthly totals of the hourly data.

For projects with Utility IPP financing, the "First Year TOD..." values show the total electrical outputand revenue by month at for each time of day period specified on the Thermal Energy Storage pagefor CSP systems and Energy Payment Dispatch page for other technologies.

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For projects with residential or commercial financing, the "First year..." values show monthly demandcharges and for rate structures with tiered rates, monthly energy charges under the tier structure.Rate structures are from the Utility Rate page.

Annual Data

Displays results that consist of values for each year in the analysis period:

Year-to-year quantities from the cash flow for each year of the analysis period.

Year-to-year cumulative kWh/kW value.

Hourly Data

Hourly values calculated by the performance model. For descriptions of the hourly data, see:

PV Component Hourly Data

PVWatts Hourly Data

Physical Trough Hourly Data

Empirical Trough Hourly Data

Hourly pricing data for projects with residential and commercial financing.

For for other models, contact SAM Support at [email protected].

Note. If you do not see the Hourly Data list, run simulations to generate the list. SAM deletes storedhourly data when you close the file to save storage space.

Exporting Data from the Tabular Data Browser

SAM offers three options for exporting the cash flow table:

Copy to clipboard copies the table to your clipboard. You can paste the entire table into a wordprocessing document, spreadsheet, presentation or other software.

Save as CSV saves the table in a comma-delimited text file that you can open in a spreadsheetprogram or text editor.

Send to Excel (Windows only) saves the table in an Excel file.

Tip. You can view graphs of hourly values from the tabular data browser in DView by first exporting it toa CSV file, and then opening the file in DView. To open DView, on the Results menu, click View HourlyTime Series (DView). Use a text editor to make sure that the first row of the file contains columnlabels separated by commas and the second row contains column units separated by commas.

Related topics:

Time Series Data Viewer (DView) for details about viewing hourly data in DView.

Base Case Cash Flow for information about financial model results.

Simulation Output File for details about viewing the raw hourly simulation data.

Case Summary for information about viewing the case summary spreadsheet, which includes datashown on the tabular data browser.


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5.5 SlidersA slider is a user interface element that allows you to dynamically change the value of an input variable andobserve the effects on tables and graphs displayed on the Results Summary page. For example, thefollowing group of three sliders would allow you to view the effect of changing operation and maintenancecosts (Fixed Cost by Capacity), inverter cost and module cost on the levelized cost of energy and othergraphs.

Note. Moving a slider only changes the graph. It does not change the stored inputs or results.

To use sliders:

To add a slider, click Choose base case sliders:

To change value of a slider, click and drag the blue slider button, which will turn yellow as you dragit. The button indicates the variable's current value, as does the number at the left end of the slider.The red line indicates the variable's base case value, which is the value from the variable's inputpage.

The buttons on the top right corner of the slider allow you to assign the current value to the basecase value, change the slider's range, and to remove the slider from the Results Summary page.

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Note. Assigning a slider's current value to the base case changes the variable's value on the input page.

5.6 Case SummaryThe case summary is a dataset that SAM generates input variables, the cash flow, hourly results, andaverages of hourly results.

The data included in the case summary is from "base case" input values, which are the values of inputvariables visible on the input pages. The case summary does not display data from additional simulationsfor parametric or other simulation configurations that require multiple simulations.

Note. The case summary is a report that contains values generated by SAM during simulations. Whenyou export the case summary to Excel (Windows only) the workbook contains values but no formulas.This is because SAM calculates the values internally and does not rely on Excel to make thecalculations.

To generate the case summary workbook:

1. On the Results page, click the Export and view data button

or, on the Results menu, click Case Summary.

2. Choose an option for exporting the data.

SAM provides three options for exporting case summary data:

To Clipboard (Windows and Mac)

Creates a copy of the case summary data as comma-separated values (CSV) in your computer'sclipboard. You can paste the data in a spreadsheet, word processing program, or other program. Thisoption does not save hourly output data.

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Save as CSV (Windows and Mac)

Saves the case summary data to a text file as comma-separated values (CSV). The comma-separatedversion of the case summary includes some of the data included in the case summary workbook in asingle file. The data is arranged in columns as follows: Monthly averages of some hourly variables,annual averages, cash flow table with years listed by row instead of by column, data from the Metricstable. This option does not save hourly output data.

Send to Excel (Windows only)

For Windows only. Creates and opens an Excel workbook containing several worksheets of data.

Case Summary Workbook in Excel (Windows Only)

The case summary workbook contains a worksheet for each of the following categories of output data:

Cashflow

Cash flow table showing project cost details for each year of the analysis period. This is the same datashown in the Base Case Cashflow table on the Results page.

Metrics

A copy of the data shown in the Metrics table on the Results page. See Metrics Table for details.

Graphs

Data from graphs visible on the Results page when you displayed the case summary workbook.

Inputs

A list of input variables and values.

Hourly Data

Hourly values calculated by the performance model. For descriptions of the hourly data, see:

PV Component Hourly Data

PVWatts Hourly Data

Physical Trough Hourly Data

Empirical Trough Hourly Data

For for other models, contact SAM Support at [email protected].

Monthly Data

Monthly averages of the hourly performance data.

Annual Data

Annual averages of the hourly performance data.

All Outputs

A single worksheet containing some data from the worksheets described above. This data is equivalentto the data exported using the To Clipboard or Save as CSV export options.

Data File

A blank worksheet.


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5.7 Hourly ResultsSAM displays hourly results in the tabular data browser and on the Hourly Data tab of the case summaryspreadsheet.

The variables that appear in the hourly results are different for different technologies, and are a subset of thehourly results stored in the simulation results file.

For descriptions of the hourly results by technology, see the relevant section below. For technologies notincluded in the list, contact SAM support at [email protected]:

Photovoltaic component-based model

PVWatts

Physical trough

Empirical trough

For projects with residential and commercial financing, SAM also displays hourly results for electricityprices, electric load, and energy to and from the grid:

Hourly Pricing Data

5.7.1 Hourly Pricing Data

For projects with residential and commercial financing, you specify electricity prices on the Utility Ratepage and an electric load on the Electric Load page. The electricity prices are retail prices set by theelectric service provider.

SAM reports the following hourly data in the tabular data browser on the Results page that you can use toexplore pricing data along with hourly energy quantities:

Electricity sold to and purchased from the grid in kWh

Electricity prices in $/kWh

Electric load in kWh

Revenue from electricity sales (sales - purchases) in $

To view hourly pricing data:

1. After running simulations, on the Results page, click Tabular Data Browser.

Note. To save disk space, SAM discards hourly data each time you close a file. To see the hourly dataafter opening a file, you must first run simulations.

2. Under Output Variables, click Hourly Data to expand the list of hourly variables.

3. Check a variable name to display the variable's hourly values.

You can export the data to Excel or another spreadsheet program using the buttons above thetable.


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Hourly Pricing Variables

System output, kWh

The electric output of the renewable energy system. The variable name differs for the differenttechnologies.

Electricity demand, kWh

Electricity required from the grid. For negative values, SAM sets the electricity demand to zero:

Electricity Demand = Electricity Load - System Output

Note that SAM reports the load as a negative number. The above equation is for positive load values.

Electricity Load, kWh

The electric load requirement defined on the Electric Load page.

Electricity Price with System, $/kWh

The price of electricity for the given hour using buy and sell rates specified on the Utility Rate page. Forhours when the project buys electricity, it is the buy rate specified for that hour. For hours when theproject sells electricity, it is the sell rate.

Electricity Price without System, $/kWh

The price of electricity for the given hour, assuming the renewable energy system does not exist, usingthe sell rates specified on the Utility Rate page.

Electricity to grid, kWh

Electricity delivered to the grid. A negative value indicates electricity purchased from the grid. A positivevalue indicates electricity sold to the grid.

Electricity to Grid = System Output - Electricity Load

Note that SAM reports the load as a negative number. The above equation is for positive load values.

Peak electricity demand, kW

Applies only when you specify sub-hourly load data on the Electric Load page. The maximum value ofthe sub-hourly electricity demand values for each hour.

Peak electricity load, kW

Applies only when you specify sub-hourly load data on the Electric Load page. The maximum value ofthe sub-hourly electricity load values for each hour. SAM determines the maximum monthly value tocalculate any monthly demand charges specified on the Utility Rate page.

Peak electricity to grid, kW

Applies only when you specify sub-hourly load data on the Electric Load page. The maximum value ofthe sub-hourly electricity to grid values for each hour.

Purchases with system, $

The value of electricity purchased from the grid at the applicable buy rate for each hour, includingmonthly charges and tiered rate energy charges.

Purchases with System = Electricity Price with System × Electricity Demand

SAM assigns monthly charges and tiered rate energy charges to the final hour of each month. Forexample, charges for January apply to Hour 744 (31 days/month × 24 hours/day = 744 hours/month),and charges for February apply to Hour 1416, assuming 28 days for February. For the final hour of each

Hourly Results 381


month:

Purchases with System = Electricity Price with System × Electricity Demand + Demand Charges +Tiered Rate Energy Charges

Purchases without system, $

The value of electricity that would be purchased to meet the load without the renewable energy systemat the buy rates specified on the Utility Rate page.

Purchases without System = Electricity Price without System × Electricity Load

SAM assigns monthly charges and tiered rate energy charges to the final hour of each month asdescribed above. For the final hour of each month:

Purchases without System = Electricity Price without System × Electricity Load + Demand Charges+ Tiered Rate Energy Charges

Revenue with system, $

The net value of sales to the grid.

Revenue with System = Sales with System - Purchases with System

Revenue without system, $

The value of electricity that would be purchased from the grid without the renewable energy system.

Revenue without System = Sales without System - Purchases without System

Because sales without the system are zero,

Revenue without System = - Purchases without System

Sales with system, $

The value of electricity sold to the grid at the applicable sell rate for each hour that the system output isgreater than the load.

Sales with System = Electricity Price with System × ( System Output - Electricity Load )

Note that SAM reports the load as a negative number. The above equation is for positive load values.For hours when the sales value is less than zero, SAM reports a value of zero.

Sales without system, $

Without a renewable energy system, no electricity is sold to the grid.

Sales without System = 0

5.7.2 PV Component Hourly Data

SAM displays hourly results for the photovoltaic component-based model in the following places:

Case summary workbook

Tabular data browser

DView

Simulation output file

The data in the different places is the same, but SAM uses slightly different names for the same values inthe different places. For some technologies, the hourly data in the case summary, tabular data browser and

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DView is a subset of the data in the simulation output file.

Case Summary Hourly Data for the Photovoltaic Component-based Model

Hour

Hour of the year. The time convention is determined by the convention used in the weather file. ForNREL's TMY format, Hour 1 represents the hour ending at 1 am on January 1, and February has 28days. For schedules used for utility rate structures and thermal energy storage dispatch, SAMassumes that January 1 is a Monday.

Global Horizontal (kW/m2), Hourly

Global horizontal radiation value from the weather file, which represents the radiation over the hour atthe end of the hour.

Incident Beam (kW/m2), Hourly

Incident beam radiation value from the weather file, which represents the radiation over the hour at theend of the hour.

Incident Beam, Shaded (kW/m2), Hourly

Incident beam radiation reduced by the beam shading factor (if any) specified on the Shading page.

Incident Diffuse (kW/m2), Hourly

Incident diffuse radiation value from the weather file, which represents the radiation over the hour at theend of the hour.

Incident Diffuse, Shaded (kW/m2), Hourly

The incident diffuse radiatin reduced by the sky diffuse shading factor (if any) specified on the Shadingpage.

Radiation Total (kW/m2), Hourly

Incident total radiation calculated by the weather processor based on solar angles determined from thelatitude and longitude values in the weather file and array orientation options specified on the Array page.

Incident Total (kWh), Hourly

The total average hourly incident global radiation absorbed by the array, the product of the incidentradiation in kilowatts per square meter and the array area in square meters from the Array page.

Module Eff. (%), Hourly

Module average efficiency by hour, equivalent to Gross DC Power / Incident Total.

Wind Speed (m/s), Hourly

The mid-hour wind speed calculated by the weather data processor by averaging the end-of-hour windspeed from the previous hour with the end-of-hour wind speed from the current hour in the weather file.

Ambient Temperature ('C), Hourly

The mid-hour ambient temperature calculated by the weather data processor by averaging the end-of-hour temperature from the previous hour with the end-of-hour temperature from the current hour in theweather file.

Cell Temperature ('C), Hourly

The cell temperature.

Hourly Results 383


Vmp (V), Hourly

The array's maximum power DC voltage.

Gross DC Output (kWh), Hourly

DC output of the array, not derated.

Derated DC Output (kWh), Hourly

DC output of the array, derated by the amount specified by the pre-inverter derate factor on the Arraypage.

Gross AC Output (kWh), Hourly

AC output of the inverter, not derated.

Derated AC Output (kWh), Hourly

AC output of the inverter, derated by the amount specified by the post-inveter derate factor on the Arraypage.

For simulations that involve retail pricing and a load (residential and commercial financing only), the hourlyresults includes additional variables showing the load, grid electricity, and prices. See Hourly Pricing Datafor details.

5.7.3 PVWatts Hourly Data

SAM displays hourly results for the PVWatts model in the following places:

Case summary workbookTabular data browser

DView


The data in the different places is the same, but SAM uses slightly different names for the same values inthe different places. For some technologies, the hourly data in the case summary, tabular data browser andDView is a subset of the data in the simulation output file.

Case Summary Hourly Data for the PVWatts Model

Hour

Hour of the year. The time convention is determined by the convention used in the weather file. ForNREL's TMY format, Hour 1 represents the hour ending at 1 am on January 1, and February has 28days. For schedules used for utility rate structures and thermal energy storage dispatch, SAMassumes that January 1 is a Monday.

Direct (kW/m2), Hourly

Incident direct radiation value from the weather file, which represents the radiation over the hour at theend of the hour.

Diffuse (kW/m2), Hourly

Incident diffuse radiation value from the weather file, which represents the radiation over the hour at theend of the hour.

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Plane of Array (kW/m2), Hourly

Incident total radiation calculated by the weather processor based on solar angles determined from thelatitude and longitude values in the weather file and array orientation options specified on the Array page.



Ambient Temp ('C), Hourly


Cell Temp ('C), Hourly


DC Output (kWh), Hourly

DC output of the array.

Hourly Energy (kWh)

AC output of the system.

Shading Factor for Beam Radiation, Hourly

The hourly beam shading factor specified on the Shading page.

For simulations that involve retail pricing and a load (residential and commercial financing only), the hourlyresults includes additional variables showing the load, grid electricity, and prices. See Hourly Pricing Datafor details.

5.7.4 Physical Trough Hourly Data

SAM displays hourly results for the physical trough model in the following places:


DView



Case Summary Hourly Data for the Physical Trough Model

Hour

Hour of the year

Hourly Energy (kWh)

AC electricity generated by the system.

Hourly Results 385


DNI (kW/m2-hr), Hourly

Direct normal irradiance

DNIxCosTH (W/m2), Hourly

Incident direct normal irradiance

Dry Bulb Temp (C), Hourly


Wet Bulb Temp (C), Hourly

The mid-hour wet bulb temperature calculated by the weather data processor by averaging the end-of-hour wet bulb temperature from the previous hour with the end-of-hour temperature from the current hourin the weather file.

Collector Optical Efficiency, Hourly

Collector efficiency

Available Flow From Field, Hourly

Mass flow rate at solar field outlet in kg/hr.

Flow to Power Block, Hourly

Mass flow rate at power block inlet in kg/hr.

Flow Discharge Collector Side, Hourly

Mass flow rate mass flow at solar side of storage loop in kg/hr.

Flow Discharge TES Side, Hourly

Mass flow rate at tank side storage loop in kg/hr.

Flow to Aux Heater, Hourly

Auxiliary heater mass flow rate in kg/hr.

Mass in Cold Tank, Hourly

Mass of fluid in cold tank in kg.

Mass in Hot Tank, Hourly

Mass of storage fluid in hot tank in kg.

Power Block Efficiency, Hourly

Thermal-to-electricy conversion efficiency of the power block.

Field Pumping Power, Hourly

Parasitic solar field pumping load in kWh/h.

Gross Electric Output (kWh), Hourly

System electric output.

Q Field Output, Hourly

Solar field thermal energy output in kWh.

Q Incident Total, Hourly

Total radiation incident on collector in kWh.

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Q Absorbed Total, Hourly

Total energy absorbed by the solar field in kWh.

Q to Power Block, Hourly

Thermal energy delivered to power block in kWh.

Q Dumped, Hourly

Thermal energy shed by defocusing collectors in kWh

Q Thermal Loss, Hourly

HCE thermal heat losses in kWh.

Q Aux. Fuel Usage

Auxiliary boiler fuel consumption in kWh.

Cold Header Inlet Temp (C), Hourly

HTF temperature at solar field inlet.

Hot Header Outlet Temp (C), Hourly

HTF temperature at solar field outlet.

Power Block HTF Inlet Temp (C), Hourly

HTF temperature at power block inlet.

Power Block HTF Outlet Temp (C), Hourly

HTF temperature at power block outlet.

Water Usage (m3), Hourly

Water usage for cooling and mirror washing.

5.7.5 Empirical Trough Hourly Data

SAM displays hourly results for the empirical trough model in the following places:


DView



Hour

Hour of simulation from the weather file. SAM assumes that Hour 1 ends at 1:00 a.m. on January 1,and that Hour 8,760 ending at midnight December 31.

DNI (kW/m2-hr), Hourly

Direct normal irradiance from weather file.

Hourly Results 387


DNIxCosTH (W/m2), Hourly

Incident direct normal irradiance.



Ambient Temp ('C), Hourly


Incident Solar Radiation, Hourly

Total direct radiation incident on the solar field in kWh, equal to the product of the direct normalirradiance and the actual solar field area from the Solar Field page.

Incidence Angle for Solar Field, Hourly

Total cosine-adjusted direct radiation incident on the solar field in kWh, equal to the product of theDNIxCosTh and the actual solar field area from the Solar Field page.

Solar Field Availability, Hourly

Total availability-adjusted field energy in kWh, equal to the product of the cosine-adjusted energy andthe Solar Availability factor from the SCA / HCE page.

Solar Field Optical Efficiency, Hourly

The availability-adjusted field energy value in kWh less optical efficiency-related losses.

Receiver Thermal Losses, Hourly

Thermal losses from the receiver in kWh.

Piping Thermal Losses, Hourly

Piping thermal losses in kWh.

Thermal Energy Delivered by Solar Field, Hourly

Thermal energy output of the solar field in kWh.

TES Full Losses, Hourly

Losses from the thermal energy storage system TES when the TES is at full capacity.

TES Thermal Losses, Hourly

Hourly losses from the thermal energy storage system, equal to the Tank Heat Loss value specified onthe Thermal Storage page.

Turbine Start Up, Hourly

Energy required to start up the power block.

Excess to PB,TES, Hourly

Thermal energy in kWh dumped when either the energy delivered to either the power block or TESexceeds the maximum allowed

Thermal Energy to Power Block, Hourly

Thermal energy in kWh delivered to the power block from the solar field an/or storage.

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Gross Electric Output (kWh), Hourly

Power block gross electric output before parasitic losses.

Hourly Energy (kWh)

System electric output after parasitic losses.

5.8 Simulation Results FileDuring simulations, SAM generates a set of hourly output data and stores them in the simulation output file.SAM stores the file in a temporary folder that is available until you close SAM.

SAM provides three options for viewing subsets of the data in the simulation output file. Each optiondisplays a different subset of the data in the simulation output file:

Tabular Data Browser (Windows and Mac) on the Results page allows you to choose the data todisplay and to export the data to the clipboard or to a text or Excel file.

Time Series Data Viewer (DView) (Windows only) displays the data in a graphical data viewing programthat shows the raw hourly data along with statistical summaries of the data, and allows graphs and datato be exported to the clipboard, image files, and text files.

Case Summary Workbook (Windows only) displays the data in an Excel workbook on the Hourly Dataspreadsheet.

Open the simulation output file (.out) directly (Windows and Mac) with a text-editor or spreadsheetprogram. Press the F9 key to open the temporary folder containing the file.

If you frequently work with hourly results, you can choose to save hourly output files in a folder of yourchoice in the Preferences window by checking the Save TRNYSYS hourly data, list, and log files infolder option and specifying a folder. Click Preferences on the File menu to open the window. SAM doesnot delete files from this folder. However, it uses the same file name each time it runs a simulation, so if youwant to save files from different simulations, you should manually rename the file after each simulation sothat SAM does not overwrite the data.

Hourly Simulation Data Descriptions

For descriptions of the hourly simulation data by technology, see the relevant section below. Fortechnologies not included in the list, contact SAM support at [email protected]:

Photovoltaic component-based models

Physical trough model

Empirical trough model

5.8.1 PV Component Simulation

SAM displays photovoltaic system hourly output data in the following places:

Simulation output file (described below)

Tabular data browser on the Results page


Simulation Results File 389



DView

Hourly Simulation Output Data for Photovoltaic Component-based Model

hour

Hour of simulation from the weather file. SAM assumes that Hour 1 ends at 1:00 a.m. on January 1,and that Hour 8,760 ending at midnight December 31.

GlobHozRad, kW/m2

Global horizontal radiation from weather file.

IncBeam, kW/m2

Incident beam radiation calculated by the weather data processor based on data from weather file andarray orientation specified on the Array page.

IncBeamShad, kW/m2

Incident beam radiation reduced by the beam shading factor specified on the Shading page.

IncDiff, kW/m2

Incident diffuse radiation calculated by the weather data processor based on data from the weather fileand array orientation specified on the Array page.

IncDiffShad

Incident diffuse radiation reduced by the sky diffuse shading factor specified on the Shading page.

IncTotRad, kW/m2

Incident total radiation calculated by the weather data processor based on data from the weather fileand array orientation specified on the Array page, and accounting for the shading factors on theShading page.

DCPower

The average DC power delivered by the array over the hour in kWh/h.

InvPartLoad

The ratio of the inverter's AC power to its rated AC power.

InvEff

The ratio of the inverter's AC output to its DC input.

ACPower, kW

The average AC power delivered by the system.

CellTemp, °C


AmbTemp, °C


Windspd, m/s

The mid-hour wind speed calculated by the weather data processor by averaging the end-of-hour wind

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speed from the previous hour with the end-of-hour wind speed from the current hour in the weather file.

Vmp, Vdc

The array's maximum power DC voltage.

InputRadiation, kWh

The total average hourly incident global radiation absorbed by the array, the product of the incidentradiation in kilowatts per square meter and the array area in square meters.

Gross_DCPower, kW

DC output of the array, not derated.

Derated_DCPower, kW

DC output of the array, derated by the amount specified by the total pre-inverter derate factor on theArray page.

Gross_ACPower, kW

AC output of the inverter, not derated.

Derated_ACPower, kW

AC output of the inverter, derated by the amount specified by the total post-inveter derate factor on theArray page

ModEff

Module average efficiency by hour, equivalent to Gross_DCPower / InputRadiation.

Beam_derate

The beam shading factor from the Shading page.

self_shad_nonlin

self_shad_lin

slope, deg

The array angle from horizontal, based on the tracking option and tilt angle from the Array page and thesun angle calculated by the weather processor.

azimuth, deg

The east-west orientation of the array, based on the tracking option and tilt angle from the Array pageand the sun angle calculated by the weather processor.

rotation, deg

5.8.2 Physical Trough Simulation

SAM displays physical trough simulation output data in the following places:




DView



Hourly Simulation Output Data for Physical Trough Model

TIME, hours

hour of the year

DNI, W/m2

direct normal irradiance

Hour_of_day, hours

hour of the day

P_atm, atm

atmospheric pressure

V_wind, m/s


Solar_azimuth, deg

solar azimuth

Solar_elevation, deg

solar elevation

T_dry_bulb, C


T_wet_bulb, C

The mid-hour wet bulb temperature calculated by the weather data processor by averaging the end-of-hour temperature from the previous hour with the end-of-hour temperature from the current hour in theweather file.

collector_opt_efficiency

collector efficiency

collector_Theta, deg

collector incidence angle (Theta)

collector_CosTheta

cosine of Theta

collector_IAM, none

incidence angle modifier

collector_Row-Shadow

row shadowing

collector_End-loss

end loss

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collector_DNI-x-CosTh, W/m2

CosTheta-adjusted incident radiation

collector_Qsf-x-CosTh, MW

CosTheta-adjusted field power

flow_available_from_field, kg/hr

mass flow rate

flow_within_field, kg/hr

Internal field mass flow rate

flow_to_power_block, kg/hr

flow to power block

flow_demand_power_block, kg/hr

demand mass flow rate

flow_store_disch-col-side, kg/hr

mass flow rate of solar side storage loop

flow_store_disch-TES-side, kg/hr

mass flow rate of tank side storage loop

flow_to_aux_heat, kg/hr

auxiliary heater mass flow rate

flow_in_loop, kg/s

flow in a single loop

flow_water_makeup, kg/hr

water makeup flow rate

Frac_focused_SCAs

fraction of all SCAS that are defocused

hx_effectiveness

hx effectiveness

mass_cold_tank, kg

cold tank available mass

mass_hot_tank, kg

hot tank available mass

mass_tanks_total, kg

total available storage HTF mass

Pressure_drop_field, bar

pressure drop across solar field

Efficiency_power_block

cycle thermal efficiency



power_field-pump_par, MW

required pumping power

power_PB-TES-pumps_par, MW

TES and PB HTF pumping power

power_drives-elec_par, MW

SCA drives and electronics parasitic power

power_BOP_par, MW

balance of plant parasitic load

power_fixed_par, MW

fixed parasitic load

power_htr-boiler_par, MW

auxiliary boiler parasitic load

power_cooling_par, MW

cooling parasitic power

power_gross, MW

cycle power output

E_net, MW

net electric power output

Q_field_out, MW

thermal power produced by the field

Q_inc_total, MW

total incident power on field

Q_abs_total, MW

total absorbed power

Q_to_pb, MW

thermal energy to the power block

Q_hdr_pipe_hl

MW, hot header and runner pipe heat losses

Q_dump, MW

dumped energy

Q_loss_tank, MW

tank thermal losses

Q_loss_therm, MW

HCE thermal losses

Q_loss_abstube_avg, W/m

average losses from absorber tube

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Q_aux_fluid, MW

auxiliary thermal energy delivered

Q_aux_fuel_hv, MMBTU

auxiliary fuel heat content required

Q_freeze_prot, MW

required freeze protection

Q_frzprot_tank, MW

total parasitic power for tank freeze protection

Q_startup, MW

energy used for startup

T_cold_header_in, C

system inlet temperature

T_hot_header_out, C

outlet temperature

T_collector_in, C

HCE inlet temperature

T_cold_tank_in, C

cold tank inlet temp

T_hot_tank_in, C

hot tank inlet temp

T_cold_tank, C

cold tank temperature

T_hot_tank, C

hot tank temperature

T_store_loop_in, C

fluid temp of hot HTF in solar loop

T_store_loop_out, C

cold side of storage, HTF temperature in solar loop

T_power_block_HTF_in, C

power block inlet HTF temperature

T_power_block_HTF_out, C

cold HTF outlet temp

Vol_cold_tank, m3

available cold htf volume

Vol_hot_tank, m3

available hot htf volume



Vol_tanks_tot, m3

total storage volume

5.8.3 Empirical Trough Simulation

SAM displays physical trough simulation output data in the following places:




DView

Hourly Simulation Output Data for Empirical Trough Model

TIME, HOURS

hour of year

Day_of_year, day

day of year

MONTH, month

month of year

Hour_of_month, hr

hour of month

Day_of_month, day

day of month

Hour_of_day, hr

hour of day

TOUPeriod, none

time-of-use period defined for storage dispatch

SolTime, hr

solar time

HrAngle, deg

hour angle

SolAz, deg

solar azimuth angle

SolAlt, deg

solar altitude

DNI, W/m2

direct normal irradiance from weather file

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T_dry_bulb, C


V_wind, m/s


Theta, deg

theta incidence angle

Costheta, none

cosine theta angle product

TrckAngl, deg

collector tracking angle

IAM, none

incident angle modifier

RowShadow, none

fraction of incoming radiation remaining after row shadowing is subtracted

Endloss, none

fraction of incoming radiation remaining after losses off end of collector

RecHtLoss, MW

receiver heat loss

QSF_HCE_HL, MW

energy lost by HCEs (receivers) in the solar field

SF_OptEff, none

total solar field optical efficiency

Q_nip, W/m2

direct normal radiation value read from the weather file

Q_nipCosTh, W/m2

cosine Theta-adjusted incident radiation

QSF_nipCosTh, MW

radiation in the solar field collector plane

Q_DNI_on_SF, MW

direct normal radiation incident on the solar field. Q_DNI_on_SF = Q_nip * Solar Field Area

Q_abs, W/m2

thermal energy absorbed by collectors

QSF_Abs, MW

thermal energy absorbed by the solar field accounts for optical losses but not thermal losses



Q_SF(MW), MW

thermal energy delivered by the solar field Q_SF = Q_abs - QSF_HCE_HL - QSF_Pipe_HL

SfPipeHL, kJ/hr.m2

energy lost by header piping in the solar field

QSF_Pipe_HL, MW

energy lost by header piping in the solar field

SF_Tin, C

solar field inlet temperature

SF_TOut, C

solar field outlet temperature

SF_MassFlow, kg/s

solar field outlet mass flow rate

SF_AveTemp, C

average solar field temperature

Q_col, W/m2

collected energy

ColOptEff, none

collector optical efficiency

QsfWarmUp, MW

power contributed to warming the field

Q_htf_FrPr, MW

energy used for freeze protection

Q_htf_FP_TES, MW.hr

energy supplied by the TES when the heat transfer fluid temperature falls below its freezing point

Q_htf_FP_Htr, MW.hr

energy supplied by the auxiliary heater when the heat transfer fluid temperature falls below its freezingpoint

Q_to_TES, MW

thermal energy to storage

Q_from_TES, MW

thermal energy from storage

E_in_TES, MW

thermal energy in storage

Q_TES_HL, MW

storage tank heat loss

Q_TES_Full, MW

thermal energy dumped because the thermal storage is full

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Q_to_PB, MW

thermal energy to the power block, may include energy from the solar field or energy from both thesolar field and thermal storage"

Q_turb_SU, MW

thermal energy needed to start the turbine

Q_min, none

Q_dump, MW

thermal energy dumped when either the energy delivered to either the power block or TES exceeds themaximum allowed

PBMode, none

zero indicates that power block is not generating electricity, one indicates that the power block is notgenerating electricity but is starting up, two indicates that the power block is generating electricity"

Turb_Su_Frac, none

zero indicates the power block is not starting, one indicates that the power block is starting

E_gross_solar, MW

gross solar electric generation

E_under_min, MW

gross solar output during hours when the solar energy is insufficient to drive the turbine does notcontribute to the electric output"

E_dump, MW

the difference between gross solar output and the design output for hours when E_gross_solar > DesignTurbine Gross Output, does not contribute to power output"

E_gross_fossil, MW

gross fossil electric generation

Q_gas, MW

thermal energy equivalent of the electric energy generated by the fossil fuel-fired backup boiler

E_gross, MW

electric output originating from both solar and fossil sources but not accounting for parasitic losses oravailability

E_net, MW

electric output from both solar and fossil sources accounting for parasitic losses but not for availability

E_parasit, MW

electric energy losses due to parasitic electrical loads in the system (pumps, control electronics, etc.)

E_par_SF, MW.hr

parasitics of the solar field

E_par_cHTF, MW

cold HTF pump parasitics (HTF flow to solar field)



E_par_hHTF, MW

hot HTF pump parasitic losses

E_par_Anti, MW.hr

antifreeze parasitics

E_par_Htr, MW

heater parasitic losses

E_par_PB, MW

fixed power block parasitics (24 hr)

E_par_BOP, MW

balance of plant parasitics

E_par_CT, MW

cooling tower parasitic loads

E_par_Offline, MW

parasitic losses that occur during hours when the power block is not generating electricity

E_par_Online, MW

parasitic losses that occur during hours when the power block is generating electricity

Ftrack, none

one indicates that collectors are tracking the sun zero indicates that trackers are stowed

6 Time Series Data Viewer(DView)

SAM displays graphs of hourly data for the current case in a built-in data viewer called DView. You can usethe viewer to display graphs of the following types of data:

Weather data: On the Climate page, click View hourly data.

Electric load data for systems with commercial or residential financing: On the Electric Load page, click Visualise load data.

Hourly simulation results: On the Results menu, click View Hourly Time Series (DView).

For a listing of the hourly output variables displayed in DView, see Simulation Output File. For a descriptionof weather data in the Climate file, see Climate.

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Note for Mac users. DView only runs on Windows. To view hourly output data on a Mac computer, youmust open the simulation output file directly in a text editor or spreadsheet program. See SimulationOutput File for details. To view weather data, weather files in the TMY3 format are comma-separated textfiles, so you can open them with a spreadsheet program. Files in TMY2 and EPW format use aconstant-width column format, and are more difficult to read without specialized software.

DView displays graphs of hourly data, monthly and annual averages of hourly data, and statistical graphs.DView allows you to export data from graphs to a tab-delimited text file, and to copy graph images for usein presentations and reports.

You can download the latest version of DView from http://www.mistaya.ca/software/dview.htm.

Tips for using DView:

For check box lists, checking a box in the left-hand column displays two graphs and displays thechecked variable in the upper graph. Checking a box in the right-hand column displays the graph in thelower graph, or in a single graph when no boxes are checked in the left-hand column.

Right-click a graph to export an image of the graph or a table of the data in the graph.

Change properties of a graph, such as the graph title and labels, line colors and style, and axis scaleby right-clicking a graph and choosing Properties.

When you display hourly output data in DView, SAM opens a temporary file. You can use DView tosave the file if you want to compare hourly results from different simulations.

Table 25. Data viewer graph formats.

Tab Name Graph Format Description

DMap 8,760 point data map showing entire year of hourly data in a single graph

Hourly Time series line graph, use scroll bars and zoom buttons to view entire data set

Daily Daily average line graph

Monthly Monthly average line graph

Boxplot Monthly average with daily and monthly minima and maxima

Profile Average daily profiles by month

PDF Probability distribution function

CDF Cumulative distribution function

DC Duration curve

http://www.mistaya.ca/software/dview.htm

Parametric Analysis 401


7 Advanced Topics

7.1 Parametric Analysis

Contents

Overview describes the parametric simulation option.

Page Reference describes the parametric simulation setup options.

Setting up a Parametric Analysis describes the steps for defining parametricvariables.

Working with Linkages explains how to set up a parametric analysis whenparametric variables have a dependent relationship.

Sample Parametric Results shows examples of the types of graphs that can becreated using parametric analyses.

OverviewA parametric analysis involves assigning multiple values to one or more input variables to explore therelationship between the input variables and results metrics. Examples of parametric analyses include:

For photovoltaic systems, exploring the effect of array orientation on system electricity output byassigning multiple values to the array tilt and orientation variables.

For CSP trough systems with thermal energy storage, exploring the effect of solar multiple and storagecapacity on the levelized cost of energy.

For any technology, exploring the effect of annual degradation rates on the system's annual energyoutput over the life of a project.

Configuring parametric variables makes it possible to plot graphs of performance or economic outputmetrics as a function of one or more input variables. For example, to plot a graph of the annual electricgeneration performance metric and the array tilt input variable, you would need to define the array tiltvariable as a parametric variable. Parametric variables also appear on sliders, allowing you to dynamicallychange graphs and tables on the Results page.

Note. Input variables that are not involved in the performance simulation calculations, such as those onthe financing, tax credit and payment incentives, and utility rate pages, are available as sliders withoutbeing defined as parametric variables.

To display the parametric simulation setup options:

1. On the Main window, click Configure Simulations to view the Configure Simulation page.

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2. On the Configure Simulations page, click Parametrics to display the Parametric simulation setupoptions.

3. Click Add Parametric Simulation to add a set of parametric simulation setup options. You canadd as many parametric simulations as your analysis requires.

Click Remove Simulation to delete a simulation option.

Click Clear All to remove all simulation options from the case.

Page ReferenceThe Parametric Simulation Setup options allow you to add and remove variables from the list of parametricvariables, assign values to and edit parametric variables, and to set up linkages between parametricvariables that have interdependent values.

Parametric Simulation Setup

Add

Add an input variable to the parametric variables list. You must add a variable before you can assign itmultiple values.

Remove

Remove a variable from the parametric variables list. When you remove a variable, SAM assigns thevalue from the variable's input page to the variable.

Setup Linkages

Create linkages between parametric variables when the values of one of the variables is dependent on



those of the other.

Edit

Assign values to or edit values of the variable highlighted in the parametric variables list.

Up

Move the highlighted value in the variable values list up one row.

Down

Move the highlighted value in the variable values list down one row.

Remove Simulation

Remove the parametric simulation setup and delete all parametric values. You can also clear theEnable this simulation checkbox to keep the setup options but exclude the parametric analysis fromsimulations.

Enable this simulation

This box must be checked for the parametric simulation setup to be included in simulations when yourun the model.

Setting up a Parametric AnalysisOnce you have added a parametric simulation, you must add one or more parametric variables to thesimulation, and assign multiple values to each variable.

After setting up the optimization, click the Run All Simulations button, or click Run All Simulations on theCase menu to run the optimization and any other enabled simulations.

To set up a parametric analysis:

1. Display the parametric simulation setup options as described above.

2. Click Add to choose variables to which you want to assign multiple values from a list of availableinput variables. SAM adds the variables to the parametric variables list.

3. Highlight each variable in the parametric variables list and click Edit to assign values to thevariables. See Working with Numeric Ranges for details.

4. Check Enable this simulation to include the parametric analysis in simulation runs. You can savethe parametric simulation setup options and exclude the analysis from simulations by clearing thecheckbox. Clearing the checkbox allows you to shorten simulation run times without losing thesetup configuration.

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Working with LinkagesIn some analyses, parametric variables may be interdependent. For example:

Tilt depends on location when an analysis assumes that the photovoltaic array or CSP collector tiltangle is equal to the location's latitude.

Thermal storage capacity depends on the solar multiple for a CSP trough analysis that assumes thatthe storage system capacity scales with the solar field area.

For these analyses, linking the interdependent parametric variables prevents SAM from simulatingcombinations of parametric variable values that are not relevant to the analysis. For example, linking thearray or collector tilt variable to the location variable ensures that SAM only simulates systems that use alocation's latitude as the tilt angle. Without linkages, SAM would simulate all combinations of locations andtilt values.

To setup a linkage between two parametric variables:

1. Add the two variables to the parametric variables list as described above. The parametric variableslist may include other variables.

2. Click Setup Linkages.

3. In the Choose Linked Parametric Variables window, check the variable names for each of the twolinked variables.

4. Click OK. SAM displays the word "Linked" in brackets next to the variable names in the parametricvariables list indicating the linked variables

5. Click the first linked variable. SAM displays the variable's values in the variable values list, andshows the value of the other linked variable in brackets.

6. Click Edit to assign multiple values to the first linked variable. See Working with Numeric Rangesfor details.

7. Click OK. SAM displays question marks in brackets next to the values of the second linkedvariable to which you have not yet assigned values.

8. In the parametric variables list, click the second linked variable.

9. Click Edit to assign multiple values to the variable. Note that you should assign the same numberof values to this variable as you did to the first linked variable.

10. Click OK. SAM displays the values of both variables in the variable values list. Check the list tomake sure that there are no question marks in brackets indicating a missing linked value and thatthe values are in correctly matched pairs.

Sample Parametric Analysis ResultsThe following graphs were created by setting up parametric analyses. You can use these examples tobetter understand how to use parametric analysis to create useful graphs.

The following graph shows how a photovoltaic system's first year annual electric output depends on thearray tilt. The tilt variable on the Climate page was defined as a parametric variable with ten values: 0, 10,



20, 30, 40, 50, 60, 70, 80, and 90 degrees from horizontal:

The next graph shows how the first year annual electric output depends on both the array tilt and azimuth.The tilt variable was assigned the same values as the previous graph, and the azimuth variable wasassigned values between -90 and 90 degrees west of south in increments of 15 degrees:

The third graph shows the relationship between the first year annual electric output and array azimuth forthree locations, assuming an array tilt equal to the location's latitude. The azimuth value was assignedranges between -90 and 90 degrees as above, and the tilt and location variables were linked as follows:Location = Boulder : Tilt = 40 degrees, Location = Los Angeles : Tilt = 34 degrees, Location = New YorkCity : Tilt = 41 degrees. Each cluster of bars in the graph shows the annual energy output for each azimuthvalue for Boulder, Los Angeles, and New York, respectively.

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7.2 Sensitivity Analysis

Contents

Overview describes the sensitivity simulation option.

Page Reference describes the sensitivity simulation setup options.

Setting up a Sensitivity Analysis describes the steps for defining sensitivityvariables.

Sample Sensitivity Results shows examples of tornado graphs that can be createdusing sensitivity analyses.

OverviewThe sensitivity analysis option allows you to specify a range of values as a percentage for one or more inputvariables to investigate how sensitive an output metric is to variations in the input variables' values.Examples of sensitivity analyses include:

Determining the sensitivity of the levelized cost of energy to different capital cost components.

Comparing the sensitivity of the levelized cost of energy to capital cost and financial assumptions.

Configuring sensitivity analyses makes it possible to plot tornado graphs on the Results page showing therange of an output metric values for one or more sensitivity variables.

Sensitivity Analysis 407


Note. SAM calculates results for each sensitivity variable independently. In some analyses, this maycause misleading results. This is especially true when the sensitivity variable is a performance inputvariable rather than a cost or financial input variable. For example, for CSP trough systems with storage,varying the thermal storage capacity independently of the tank heat loss variable to examine howsensitive the system's electrical output is to storage capacity would not accurately account for theexpected increase in heat loss for larger storage systems. Similarly, for photovoltaic systems, varyingthe number of modules per string independently of the inverter type or number of inverters might result ininaccurate system output calculations if the inverter is improperly sized for a number of modules withinthe range specified for the sensitivity analysis.

To display the sensitivity simulation setup options:


2. On the Configure Simulations page, click Sensitivity to display the Parametric simulation setupoptions.

3. Click Add Sensitivity Simulation to add a set of sensitivity simulation setup options. You can addas many sensitivity simulations as your analysis requires.



Page ReferenceThe Analysis Setup options allow you to choose an output metric, add and remove variables from the list ofsensitivity variables, assign values to and edit sensitivity variables, and assign ranges to each sensitivityvariable.

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Analysis Setup

Select an output metric

Choose an output metric for the sensitivity analysis. This metric will appear on tornado graphs in theresults.

Add

Add an input variable to the sensitivity variables list.

Edit

Assign a "custom" variation range to the variable highlighted in the sensitivity variables list. SAMassigns the default range to all sensitivity variables that do not have a different custom range. SAMindicates the custom range in parentheses next to the variable's name in the sensitivity variable list.

Remove

Remove a variable from the sensitivity variables list.

+/- Variation on inputs

The default range applied to all sensitivity variables that do not have a different custom range. For arange value of 10 %, SAM would calculate the range of values of an input variable between 10 % belowand 10 % above the variable's value on the input page.

Setting up a Sensitivity AnalysisOnce you have added a sensitivity simulation, you must add one or more sensitivity variables to thesimulation.


To set up a sensitivity analysis:

1. Display the sensitivity simulation setup options as described above.

2. Click Add to choose variables to which you want to assign a variation range from a list of availableinput variables. SAM adds the variables to the sensitivity variables list.

3. If you want to use a variation range value other than the default value displayed below the sensitivityvariables list, click Edit to assign a custom range value.

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4. Check Enable this simulation to include the sensitivity analysis in simulation runs. You can savethe sensitivity simulation setup options and exclude the analysis from simulations by clearing thecheckbox. Clearing the checkbox allows you to shorten simulation run times without losing thesetup configuration.

Sample Sensitivity Analysis ResultsThe following tornado graphs were created by setting up sensitivity analyses. You can use these examplesto better understand how to use parametric analysis to create useful graphs.

The following graph shows how sensitive a CSP trough project's levelized cost of energy is to four capitalcost categories. To create the graph, the following four variables were defined as sensitivity variables usingthe default variation range of 10 %: Power plant cost, solar field cost, HTF system cost, and storagesystem cost:

The next graph shows shows how sensitive the levelized cost of energy is to selected capital costcategories compared to selected financial assumptions for a CSP trough system. The solar field cost, loanrate, and PPA escalation rate were defined as sensitivity variables with a 10 % variation range. how the firstyear annual electric output depends on both the array tilt and azimuth. The tilt variable was assigned thesame values as the previous graph, and the azimuth variable was assigned values between -90 and 90degrees west of south in increments of 15 degrees:

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7.3 Optimization

Contents

Overview describes the optimization option.

Page Reference describes the optimization simulation setup options.

Setting up an Optimization describes the steps for defining optimization variables.

Sample Optimization Results shows examples of results from an optimizationanalysis.

OverviewAn optimization involves choosing an output metric that you would like to either maximize or minimize, andallowing SAM to find values of one or more input variables that result in the maximum or minimum outputmetric value. Examples of optimization include:

For photovoltaic systems, finding the array tilt and azimuth values that result in the lowest levelized costof energy to optimize the array orientation for lowest cost of energy.

For a photovoltaic system modeled using the PVWatts performance model, optimize the storagecapacity for minimum levelized cost of energy.

For a CSP trough system, find the optimal collector deploy and stow angle to maximize solar fieldthermal output.

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Note. When you optimize an input variable, be careful to choose one that is not interdependent on othervariables. For example, for a CSP trough system with storage, optimizing the solar multiple independentof storage capacity to minimize the levelized cost of energy could give misleading results. Similarly, forphotovoltaic systems, optimizing the number of modules per string independently of the inverter mightresult in a system with an improperly sized inverter. To find optimal values of interdependent variables,you can use parametric analysis.

One application of SAM's optimization capability is to help you find values of input variables to use for youranalysis. For example, for a photovoltaic system, you could use optimization to find the best array tilt andazimuth values to use on the Array page. Or, for a CSP trough system, you could use optimization to findthe deploy and stow angle to use on the Solar Field page.

To display the optimization setup options:


2. On the Configure Simulations page, click Optimization to display the optimization simulationsetup options.

3. Click Add Optimization Simulation to add a set of optimization setup options. You can add asmany parametric simulations as your analysis requires.



Page ReferenceThe Optimization Setup options allow you to select the output metric to maximize or minimize, add andremove variables from the list of optimization variables, and assign a range of values to optimizationvariables.

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Optimization Setup

Minimize / Maximize

Choose whether to maximize or minimize the output metric.


Choose the output metric to maximize or minimize.

Add

Choose one or more optimization variables from a list of available input variables.

Edit limits

Assign an upper and lower limit to the variable highlighted in the optimization variable list.

Remove

Remove the highlighted variable from the optimization variable list.

Advanced parameters

The advanced parameters affect the speed and resolution of the optimization. You can use the defaultvalues for most analyses, or experiment with the values for faster run times. You can also try adjustingthe values if SAM does not find an optimal solution.

Setting up an OptimizationOnce you have added an optimization simulation, you must choose an output metric to maximize orminimize, add one or more optimization variables to the simulation, and edit the limits of each variable.

After setting up the optimization, click the Run All Simulations button, or click Run All Simulations on the

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Case menu to run the optimization and any other enabled simulations.

To set up an optimization:

1. Display the parametric simulation setup options as described above.

2. Click Add to choose variables to which you want to assign multiple values from a list of availableinput variables. SAM adds the variables to the parametric variables list.

3. Highlight each variable in the parametric variables list and click Edit to assign an upper and lowerlimit to each variable.

4. Check Enable this simulation to include the optimization in simulation runs. You can save theoptimization setup options and exclude the analysis from simulations by clearing the checkbox.Clearing the checkbox allows you to shorten simulation run times without losing the setupconfiguration.

Sample Optimization ResultsThe following example illustrates the use of optimization for SAM analyses.

This example is for a CSP trough system, and finds the optimal collector deploy and stow angles defined onthe Solar Field page. Those angles determine the collector angle at which heat transfer fluid beginscirculating in the morning, and stops circulating in the evening, respectively. The system starts tracking themovement of the sun at sunrise, but deploying collectors too early results in wasted energy from operatingfluid pumps before there is sufficient energy to generate electricity. Similarly, continuing to operate the fluidpumps in the evening when the sun is below a certain point above the horizon wastes energy. Optimizingthe deploy and stow angles for maximum thermal energy delivered by the solar field ensures that thesystem does not waste energy by deploying the collectors too late or stowing them too early. In thisexample for a system in Dagget, California, SAM found an optimal deploy angle of 12 degrees, and anoptimal stow angle of 167 degrees. The optimization found the maximum value of the annual thermal energyfrom solar field output metric for deploy angle limits of 0 and 20 degrees, and stow angle limits of 160 to 180degrees:

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7.4 Statistical

Contents

Overview describes the statistical analysis simulation option.

Page Reference describes the statistical simulation setup options.

Input Distribution Options describes the distribution parameters that you specify foreach statistical variable.

Setting up a Statistical Analysis describes the steps for choosing an output metric,input variables, and distribution parameters for a statistical analysis.

Displaying Histograms for Statistical Variables describes the graphing options onthe Results page available for statistical analyses.

OverviewA statistical analysis allows you to examine the effect of uncertainty in the value of one or more inputvariables on an output metric. For example, you could use statistical analysis to explore how the degree ofuncertainty in the installation cost of one or more system components might affect the system's levelizedcost of energy over the project life.

In a statistical analysis, SAM runs several simulations for a distribution of values assigned to one or moreinput variables, and displays a histogram showing the frequency distribution of different output metric values

Statistical 415


over each input variable's distribution of values.

For an example of a SAM file with statistical analysis, open the sample file Statistical Analysis Sample: Onthe File menu, click Open Sample Template and select the file from the list.

To display the statistical simulation setup options:


2. On the Configure Simulations page, click Statistical to display the statistical simulation setupoptions.

3. Click Add Parametric Simulation to add a set of parametric simulation setup options. You canadd as many parametric simulations as your analysis requires.



Page ReferenceThe statistical Analysis Setup options allow you to select the output metric, add and remove variables fromthe list of statistiacl variables, and assign distribution parameters to the statistical variables.

Analysis Setup


Choose the output metric for the statistical analysis.

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Add

Choose one or more statistical variables from a list of available input variables.

Edit

Assign an input distribution for the analysis. See below for details.

Remove

Remove the highlighted variable from the statistical variable list.

Number of Monte Carlo Runs

Enter a value for the number of simulations to run for the analysis. The default value is 400.

Input Distribution OptionsThe edit distribution window allows you to define the type of distribution to use for the statistical analysisand to assign values to the statistical analysis parameters.

Choose an input distribution

Variable name

The name of the statistical variable. This the variable that was highlighted in the statistical variable listwhen you clicked Edit.

Current Value

The value of the statistical variable on the variable's input page.

Distribution list

Select from a list of distributions, and SAM displays a description of the distribution and parameters foryou to enter.

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Setting up a Statistical AnalysisOnce you have added a statistical simulation, you must choose an output metric for the analysis, add oneor more statistical variables to the simulation, and edit the distribution parameters of each variable.


To set up a statistical analysis:

1. Display the statistical simulation setup options as described above.

2. Click Add to choose variables to which you want to assign a distribution from a list of availableinput variables. SAM adds the variables to the parametric variables list.

3. Highlight each variable in the parametric variables list and click Edit to assign the distributionparameters.

4. Enter a number of simulations for Number of sampled values per variable. SAM will run thismany simulations using variable values based on the distribution parameters you specify.

5. Click Compute Samples to generate a table of values without running simulations.

6. Check Enable this simulation to include the optimization in simulation runs. You can save theoptimization setup options and exclude the analysis from simulations by clearing the checkbox.Clearing the checkbox allows you to shorten simulation run times without losing the setupconfiguration.

Displaying Histograms for Statistical VariablesAfter you run all simulations with one or more statistical simulations enabled, SAM allows you to view ahistogram for each statistical variable on the Results page. To display a histogram, SAM sorts the values ofthe simulations into bins. The number of bins is specified in the graph setup.

For example, in the Statistical Analysis Sample file, the Inverter Cost histogram shows the number ofoccurrences of inverter cost that fall into each of the equally spaced bins, whose center values are shownalong the x axis. The blue line is the estimated cumulative distribution function (CDF), labeled on the rightaxis from 0 to 1, and indicates the percentage of inverter cost values whose values fall below thecorresponding x value.

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The histogram graph can only plot a single variable. Instead of plotting the inverter cost values, you couldplot the levelized cost of energy, showing histogram of the 700 calculated LCOE values that correspond tothe random values chosen for the Inverter costs. This way, given different amounts of uncertainty in yourchosen inputs, you can visualize the effect and uncertainty on any of the single-valued output metrics.

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7.5 Multiple Systems

Contents

Overview describes the multiple systems simulation option.

Page Reference describes the multiple system analysis setup options.

Setting up a Multiple System Analysis describes the steps for combiningsubsystems into a combined system.

OverviewA multiple systems analysis allows you to model a power system as a combination of subsystems. Thismakes it possible to model a photovoltaic system consisting of separate subsystems with arrays orientedin different directions, or a CSP trough system consisting of two separate subsystems with differentcharacteristics. Each subsystem is a complete electricity generating system, which means that for a CSPsystem for example, each subsystem would include a solar field, storage system, and power generatingunit.

SAM applies a single set of financing, tax credit and payment incentives to a combined system, but appliesseparate performance and climate specifications to each subsystem.

The results such as levelized cost of energy and annual electric output displayed in graphs and tables onthe Results page are for the combined system rather than for the individual subsystems.

For an example of a SAM file with multiple systems, open the sample file Combined Multiple PV Systems:On the File menu, click Open Sample Template and select the file from the list.

To display the multiple system simulation setup options:


2. On the Configure Simulations page, click Multiple Systems to display the multiple systemanalysis setup options.

Page ReferenceThe multiple system setup options allow you to choose which cases in the project file to combine into asystem, and display the capacity and cost values for the combined system.

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Select Additional Performance Outputs

List of available cases

The list of available cases shows the cases in the project file that you can combine into a singlesystem. You must create a case for each subsystem to be combined into a single system. SAMincludes only checked cases in the combined system. The list of cases corresponds to the case tabsin the project file.


This box must be checked for the system to be modeled as a combined system.

Aggregate System Variables

The aggregate system variables display values for the combined system that SAM calculates by addingvalues from the individual subsystems.

Combined Nameplate Capacity (kW)

The sum of the subsystem nameplate capacities displayed on the System Summary page for eachsubsystem. For photovoltaic systems, the nameplate capacity is equivalent to the total array capacityin DC kW. For CSP systems, it is the nominal capacity of the power cycle in kW of electricity.

Combined Heat Rate (MMBtu/MWh)

This applies only to generic fossil systems and is the sum of each subsystem's heat rate from theFossil Plant page.


The sum of the total direct cost values displayed on each subsystem's costs page.


The sum of the total installed cost values displayed on each subsystem's costs page.

Total Direct Sales Tax ($)

The sum of the total sales tax values displayed on each subsystem's costs page.

O&M Annual Cost ($/yr)

The sum of the fixed annual operation and maintenance costs displayed on each subsystem's costspage.

O&M Annual Capacity Cost ($/kW-yr)


O&M Variable by Production ($/MWh)


Setting up a Multiple System AnalysisSetting up a multiple system analysis involves creating a case for each subsystem to be combined, andthen selecting the cases to be included in the multiple system analysis.

After setting up the analysis, click the Run All Simulations button, or click Run All Simulations on the

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Case menu to simulated the combined system..

To set up a multiple system analysis:

1. Create a case for each subsystem to be included in the combined system.

2. Display the case that you want to be the primary system.

SAM will apply the input variables on the Utility Rate, Financing, Tax Credit Incentives, andPayment Incentives pages from the primary system to the combined system. It will ignore inputvalues on those pages from the subsystems.

3. Display the multiple system analysis setup options as described above.

4. Under Select Additional Performance Outputs, check each case to include in the combinedsystem, including the current (primary) case indicated by "This case is required" in parenthesesnext to the case name.

SAM displays the combined system nameplate capacity and costs under Aggregate SystemVariables.

5. Check Enable this simulation to include the multiple system analysis in simulation runs. You cansave the parametric simulation setup options and exclude the analysis from simulations by clearingthe checkbox. Clearing the checkbox allows you to shorten simulation run times without losing thesetup configuration.

7.6 Excel ExchangeSAM allows you to connect any input variable in SAM to a cell or range of cells in a Microsoft Excelworkbook. This feature allows you to use external spreadsheet-based cost and performance models togenerate values for SAM input variables. Because SAM can both import values from workbooks and exportvalues to them, you can use the result of a spreadsheet calculation as the value of one input variable thatdepends on the value of other input variables. User variables are user-defined input variables that can alsoshare values with external workbooks.

Note for Mac users. SAM can not exchange data with Microsoft Excel on Mac computers. This meansthat the Excel Exchange feature is disabled on Mac versions of the software, and that SAM cannotdirectly export data to Excel workbooks.

To use the SAM data in Excel or another spreadsheet program, you can export the data to a comma-separated text file (CSV), and then import the CSV file to the spreadsheet program.

For an example of a SAM file with Excel Exchange, open the sample file Excel Sample: On the File menu,click Open Sample File and select the file from the list.

Note. When you run simulations with Excel Exchange, SAM opens a copy of the Excel file to read andwrite values but does not save the file. If you open the Excel file after running the simulations, you willnot see any values from the SAM in the Excel file.

To display the Excel data exchange setup options:


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2. On the Configure Simulations page, click Excel Exchange to display the Excel data exchangeoptions.

The Excel Data Exchange options allow you to add and remove SAM input variables to the list of variablesto exchange data with Excel, specify the Excel workbook with which to exchange data, and for each inputvariable, define the relationship with a cell or range of cells in the workbook.

Excel Data Exchange

Add

Add one or more input variable from the input pages. You can configure each variable to either send avalue to an Excel range, or "capture" a value from an Excel range.

Remove

Delete the highlighted variable from the list.

Clear All

Delete all variables from the list.

Browse

Browse your computer's folders to find the Excel workbook with which you want to exchange data. Theworkbook can be located in any folder on your computer.

Apply for all variables

When all of the variables are in a single Excel file, you can click this button to avoid having to retype thefile name for each variable.

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Send Variable Value to Excel Range

Configure the highlighted variable to send its value to the specified Excel range.

Capture Variable Value From Excel Range

Configure the highlighted variable to capture its value from the specified Excel range.

Excel Range

The range name or cell reference identifying the cell or range of cells in the Excel workbook with whichthe highlighted variable will exchange data.


This box must be checked for the analysis to exchange data with Excel.

7.7 Simulator OptionsThe Simulator Options are for advanced analyses that involve either changing the simulation time step, orworking with custom TRNSYS input decks.

TRNSYS Simulation Timestep

For some technologies, you can adjust the simulation time step from the default hourly (60 minute) timestep. Using a smaller time step than one hour is most appropriate for the physical trough model when youwant to explore the effects of sub-hourly changes in dispatch of energy from the solar field and thermalenergy storage system.

Note. Changing the simulation time step does not affect the weather data time step. When you use asmaller than hourly time step, SAM uses interpolation of the hourly weather data to estimate the solarresource and other weather parameters at the sub-hourly time points.

TRNSYS Executable and Input Deck

You can use these options to use custom TRNSYS components with SAM. Leave the values blank to useSAM's default TRNSYS comopnents.

Deck file name

The path and name of the TRNSYS deck file for your custom component

TRNSYS executable

The path and name of the TRNSYS executable file with arguments.

Arguments

Arguments for the TNRSYS executable you specify above.

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7.8 User VariablesThe User Variables page displays two types of special variables. SAM only uses these variables underspecial conditions -- you can ignore the user variables for most analyses.

To view the User Variables page, click User Variables on the main window's navigation menu. The uservariable input page is available for all technologies.

Note. The Name and units text boxes are ignored by SAM. You can use the boxes to help youremember what each user variable represents.

General Purpose User Variables

A general purpose user variable is a variable that you can create to store values in SAM for advancedanalyses. SAM stores values of user variables but does not use them in any internal calculations. You cancreate up to ten user variables.

One application of user variables is to enhance analyses that involve exchanging data with Excel. You canconnect user variables, like other input variables, to cells in an Excel workbook. For example, you coulduse a user variable to convert units using a formula in Excel. You can use the general purpose uservariables in parametric and sensitivity analyses.

TRNSYS System Simulation Input User Variables

The system variables are for TRNSYS programmers. You can use the system variables to store values inthe SAM user interface that interact with a customized TRNSYS input deck.

7.9 SamULThe SAM User Language (SamUL) is a built-in scripting language that allows a user to automate tasks andperform more complex analyses directly from within SAM. This guide assumes some rudimentary facilitywith basic programming concepts and familiarity with the SAM interface, capabilities, and general work flow.

Why use SamUL?

Suppose you are an energy analyst, and want to calculate the levelized cost of energy (LCOE) for severalhundred locations in the United States for a specific PV system of a given size, installation costs, andfinancial assumptions. You are familiar with the SAM, and have access to weather data for all the requestedlocations.

The first step would be to set up a case for the PV system with appropriate input values. Next, you couldrun a simulation for each weather file individually, and record the results in a spreadsheet. You could evenset up many locations in a parametric simulation. Either method would be tedious and error prone for theseveral hundred locations. Furthermore, if you decided to change even just one specification of the system,you would have to start all over. Automating the process would minimize errors and allow the flexibility ofmodifying inputs.

One option for automation would be to write a program or script in Python, C, or Excel VBA using SAM'scode generation feature. Your program would assign values to all of the inputs in the case, make a call

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SAM's simulation engine to run simulations, and then read the appropriate results and write them to a file.That option would work if you are handy with one of the languages, but involves working with large amountsof code.

SamUL, SAM's built in scripting language allows you to perform this task in just a few lines of code. Seethe SamUL case study for an example. Once you've written the script, you can easily make changes to theassumptions in the base case, or modify the script. Because the scripting language is built in to SAM youdo not need a software development environment or compiler to use it.

To get started using SamUL, see the Write a Simple SamUL Script section below. For a more detailedreference, see the following topics:

Data Variables

Flow Control

Arrays of Data

Function Calls

Input, Output, and System Access

Interfacing with SAM Analyses

Case Study: PV System with Multiple Locations

Library Reference

Why SamUL instead of VBA?

Since SamUL is so similar in functionality and syntax to Visual Basic, you might wonder why we didn'tsimply put a VBA engine behind SAM. Visual Basic for Applications (VBA) is a closed source Microsoftproduct that is very tightly integrated into the Office suite of applications, and while there are some freelyavailable interpreters for subsets of VB-like languages, we decided that engineering a simple scriptinglanguage would be straightforward enough. In the future, we might consider integrating other well knownlanguages, such as Lua.

In general, SamUL is close enough to VBA in syntax and structure to make it easily understandable bypeople familiar with VBA. By developing our own script engine, we have been able to integrate it very tightlyinto the SAM environment for maximum ease of use.

Some notable points distinctions include:

'for' loop syntax follows the C / Perl convention

Array arithmetic is automatically performed element by element

'elseif' statement formatting is similar to PHP

No distinction between functions and procedures

Write a Simple SamUL Script

A SamUL script is code that you write in a SAM file. SAM stores the script in the file along with casesrepresenting the power projects you are modeling. SAM creates a tab in the main window that gives youaccess to the script, in the same way that it creates tabs for cases in the file.

When you create a SamUL script in a SAM file, SAM adds a SamUL development environment to the filethat consists of a toolbar, editor, and console:

The toolbar provides controls for running and saving scripts, adding commands and variables, and forfinding text in the script.

The editor is where you write and edit the script.

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The console displays script outputs and error messages when you run the script.

When you create a script in a SAM file, you must also create at least one case the file. In the script, youspecify the name of a case, and write code to change values of inputs variables in the case, configure andrun simulations, and write simulation outputs to the console or a text file.

The following simple script displays the total annual output and levelized cost of energy of a PV system fora range of five array tilt values. The script uses an input prompt to get a latitude value.

To write and run a simple SamUL script:

1. Start SAM and create a case using the Photovoltaics, PVWatts option with Residential financing.Use the default case name "New PVWatts Case 1."

2. On the Developer menu, click New SamUL Script.

SAM adds a script and creates a tab for your script with the label Script1.

3. Click Browse Function Library, and from the SAM Functions list, choose Set Active Case.

The function library is a list of the SamUL functions.

4. Type an open parentheses immediately after the Set Act i veCase function to display the functionsyntax and a brief description.

5. Type the name of the case in quotations " New PVWat t s Case" and close the parentheses.

6. On the next line, use the function browser to add the Get I nput function to the script.

7. Type an open parenthesis, and use the input variable browser to find the c l i mat e. l ocat i onvariable.

8. Use the toolbar to find the functions and variables and to write the rest of the script shown below.

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9. Click Execute SamUL Script to run the script.

SAM displays the script output in the console, and a message in the status bar at the bottom ofthe window.

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7.9.1 Data Variables

General Syntax

In SamUL, a program statement is generally placed on a line by itself, and the end-of-line marks the end ofthe statement. Currently, there is no facility to split a long statement across multiple lines.

Blank lines may be inserted between statements. While they have no meaning, they can help make a scripteasier to read. Spaces can also be added or removed nearly anywhere, except of course in the middle of aword. The following statements all have the same meaning.

out ( " Hel l o 1\ n" )

out ( " Hel l o 2\ n" )

out ( " Hel l o 3\ n" )

Comments are lines in the program code that are ignored by SamUL. They serve as a form ofdocumentation, and can help other people (and you!) more easily understand what the script does.Comments begin with the single-quote ' character, and continue to the end of the line.

' t hi s pr ogr am cr eat es a gr eet i ng

out ( " Hel l o, wor l d! \ n" ) ' di spl ay t he gr eet i ng t o t he user

Variables

Variables store information while your script is running. SamUL variables share many characteristics withother computer languages.

Variables do not need to be declared in advance of being used

There is no distinction between variables that store text and variables that store numbers

Variable names may contain letters, digit, and the underscore symbol. A limitation is that variablescannot start with a digit. Unlike some languages such as C and Perl, SamUL does not distinguishbetween upper and lower case letters in a variable (or subroutine) name. As a result, the name myDat ais the same as MYdat a.

Values are assigned to variables using the equal sign =. Some examples are below:

Num_Modul es = 10

Ar r ayPower Wat t s = 4k

Ti l t = 18. 2

syst em_name = " Super PV Syst em"

Cost = " unknown"

COST = 1e6

cost = 1M

Assigning a value to a variable overwrites its previous value. As shown above, decimal numbers can bewritten using scientific notation or engineering suffixes. The last two assignments to Cost are the samevalue.

Recognized suffixes are listed in the table below. Suffixes are case-sensitive, so that SamUL candistinguish between m (milli) and M (Mega).

Name Suffix Multiplier

Tera T 1e12

Giga G 1e9

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Mega M 1e6

Kilo k 1e3

Milli m 1e-3

Micro u 1e-6

Nano n 1e-9

Pico p 1e-12

Femto f 1e-15

Atto a 1e-18

Arithmetic

SamUL supports the four basic operations +, - , * , and / . The usual algebraic precendence rules arefollowed, so that multiplications and divisions are performed before additions and subtractions. Parenthesesare also understood and can be used to change the default order of operations. Operators are left-associative, meaning that the expression 3- 10- 8 is understood as ( 3- 10) - 8.

More complicated operations like raising to a power and performing modulus arithmetic are possible usingbuilt-in function calls in the standard SamUL library.

Examples of arithmetic operations:

bat t er y_cost = cost _per _kwh * bat t er y_capac i t y

' mul t i pl i cat i on t akes pr ecedence

degr aded_out put = degr aded_out put - degr aded_out put * 0. 1

' use par ent heses t o subt r ac t bef or e mul t i pl i cat i on

cash_amount = t ot al _cost * ( 1 - debt _f r ac t i on/ 100. 0 )

Simple Input and Output

You can use the built-in out and outln functions to write data to the console window. The difference is thatoutln automatically appends a newline character to the output. To output multiple text strings or variables,use the + operator, or separate them with a comma.

ar r ay_power = 4. 3k

ar r ay_ef f = 0. 11

out l n( " Ar r ay power i s " + ar r ay_power + " Wat t s . " )

out l n( " I t i s " + ( ar r ay_ef f * 100) + " per cent ef f i c i ent . " )

out l n( " I t i s " , ar r ay_ef f * 100, " per cent ef f i c i ent . " ) ' same as above

The console output generated is:

Ar r ay power i s 4300 Wat t s .

I t i s 11 per cent ef f i c i ent .

Use the i n function to read input from the user. You can optionally pass a message to i n to display to theuser when the input popup appears. The user can enter either numbers or text, and SamUL will perform anytype conversions if needed (and if possible).

cost _per _wat t = i n( " Ent er cost per wat t : " ) ' Show a message. i n( ) al so i sf i ne.

not i ce( " Tot al cos t i s : " + cost _per _wat t * 4k + " dol l ar s" ) ' 4kW syst em

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The not i ce function works like out , except that it displays a pop up message box on the computerscreen.

Data Types and Conversion

SamUL supports four basic types of data, although most conversions between types happen automatically.Because of this, SamUL is generally a weakly typed language, meaning that you can add text variables tonumber variables, and SamUL with try to make a appropriate conversion in context.

Type Conversion Function Valid Values

Integer Number i nt eger ( ) +/- approx. 2 billion

Double-precision Decimal Number doubl e( ) 1e-308 to 1e308, with infinity

Boolean bool ean( ) true or false (1 or 0)

Text Strings s t r i ng( ) Any length text string

Sometimes you have two numbers in text strings that you would like to multiply. This can happen if youread data in from a text file on the computer, for example. Since it does not make sense to try to multiplytext strings, you need to first convert the strings to numbers. To convert a variable to a double-precisiondecimal number, use the double function, as below.

a = " 3. 5"

b = " - 2"

c1 = a* b ' t hi s wi l l cause an er r or when you c l i ck ' Run'

c2 = Doubl e( a) * Doubl e( b) ' t hi s wi l l ass i gn c2 t he number val ue of - 7

The assignment to c1 above will cause the error Error: Invalid string operator '*', while the assignment to c2makes sense and executes correctly.

You can also use integer to convert a string to an integer or truncate a decimal number, or the stringfunction to explicitly convert a number to a string variable.

If you need to find out what type a variable currently has, use the t ypeof function to get a description.

a = 3. 5

b = - 2

c1 = a+b ' t hi s wi l l set c1 t o - 1. 5

c2 = St r i ng( I nt eger ( a) ) + St r i ng( b ) ' c2 set t o t ex t " 3- 2"

out l n( t ypeof ( a) ) ' wi l l di spl ay " doubl e"

out l n( t ypeof ( c2) ) ' wi l l di spl ay " s t r i ng"

Special Characters

Text data can contain special characters to denote tabs, line endings, and other useful elements that arenot part of the normal alphabet. These are inserted into quoted text strings with escape sequences, whichbegin with the \ character.

Escape Sequence Meaning

\n New line

\t Tab character

\r Carriage return

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\" Double quote

\\ Backslash character

So, to print the text "Hi, tabbed world!", or assign c:\Windows\notepad.exe, you would have to write:

out l n( " \ " Hi , \ t t abbed wor l d! \ " " )

pr ogr am = " c : \ \ Wi ndows\ \ not epad. exe"

Note that for file names on a Windows computer, it is important to convert back slashes ('\') to forwardslashes (/). Otherwise, the file name may be translated incorrectly and the file won't be found.

7.9.2 Flow Control

Comparison Operators

SamUL supports many ways of comparing data. These types of tests can control the program flow withbranching and looping constructs that we will discuss later.

There are six standard comparison operators that can be used on most types of data. For text strings, "lessthan" and "greater than" are with respect to alphabetical order.

Comparison Operator

Equal ==

Not Equal !=

Less Than <

Less Than or Equal <=

Greater Than >

Greater Than or Equal >=

Examples of comparisons:

di v i sor ! = 0

s t at e == " or egon"

er r or <= - 0. 003

" pv" > " csp"

Single comparisons can be combined by boolean operators into more complicated tests.

The not operator yields true when the test is false. It is placed before the test whose result is to be notted:

not ( di v i sor == 0)

The and operator yields true only if both tests are true:

di v i sor ! = 0 and di v i dend > 1

The or operator yields true if either test is true:

st at e == ör egon" or s t at e == " col or ado"

The boolean operators can be combined to make even more complex tests. The operators are listed abovein order of highest precedence to lowest. If you are unsure of which test will be evaluated first, useparentheses to group tests. Note that the following statements have very different meanings.

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st at e_count > 0 and s t at e_abbr ev == " CA" or s t at e_abbr ev == " OR"

st at e_count > 0 and ( s t at e_abbr ev == " CA" or s t at e_abbr ev == " OR" )

Branching

Using the comparison and boolean operators to define tests, you can control whether a section of code inyour script will be executed or not. Therefore, the script can make decisions depending on differentcircumstances and user inputs.

if StatementsThe simplest branching construct is the if statement. For example:

i f ( t i l t < 0. 0 )

out l n( " Er r or : t i l t angl e must be 0 or gr eat er " )

end

Note the following characteristics of the i f statement:

The test is placed in parentheses after the if keyword.

The following program lines include the statements to execute when the i f test succeeds.

To help program readability, the statements inside the i f are usually indented.

The construct concludes with the end keyword.

When the i f test fails, the program statements inside the i f -end block are skipped.

else ConstructWhen you also have commands you wish to execute when the if test fails, use the else clause. Forexample:

i f ( power > 0 )

ener gy = power * t i me

oper at i ng_cost = ener gy * ener gy_cost

el se

out l n( " Er r or , no power was gener at ed. " )

ener gy = - 1

oper at i ng_cost = - 1

end

Multiple if TestsSometimes you wish to test many conditions in a sequence, and take appropriate action depending onwhich test is successful. In this situation, use the el sei f clause. Be careful to spell it as a single word,as both else if and el sei f can be syntactically correct, but have different meanings.

i f ( angl e >= 0 and angl e < 90)

t ex t = " f i r s t quadr ant "

el sei f ( angl e >= 90 and angl e < 180 )

t ex t = " second quadr ant "

el sei f ( angl e >= 180 and angl e < 270 )

t ex t = " t hi r d quadr ant "

el se

t ex t = " f our t h quadr ant "

end

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You do not need to end a sequence of el sei f statements with the else clause, although in most cases itis appropriate so that every situation can be handled. You can also nest if constructs if needed. Again, werecommend indenting each level of nesting to improve your script's readability. For example:

i f ( angl e >= 0 and angl e < 90 )

i f ( pr i nt _val ue == t r ue )

out l n( " f i r s t quadr ant : " + angl e )

el se

out l n( " f i r s t quadr ant " )

end

end

Single line ifsSometimes you only want to take a single action when an if statement succeeds. To reduce the amount ofcode you must type, SamUL accepts single line i f statements, as shown below.

i f ( az i mut h < 0 ) out l n( " War ni ng: az i mut h < 0, cont i nui ng. . . " )

i f ( t i l t > 90 ) t i l t = 90 ' set max i mum t i l t val ue

You can also use an el se statement on single line i f . Like the i f , it only accepts one programstatement, and must be typed on the same program line. Example:

i f ( val ue > aver age ) out l n( " Above aver age" ) el se out l n( " Not above aver age" )

Looping

A loop is a way of repeating the same commands over and over. You may need to process each line of afile in the same way, or sort a list of names. To achieve such tasks, SamUL provides two types of loopconstructs, the while and for loops.

Like if statements, loops contain a "body" of program statements followed by the end keyword to denotewhere the loop construct ends.

while LoopsThe whi l e loop is the simplest loop. It repeats one or more program statements as long as a logical testholds true. When the test fails, the loop ends, and the program continues execution of the statementsfollowing the loop construct. For example:

whi l e ( done == f al se )

' pr ocess some dat a

' check i f we ar e f i ni shed and updat e t he ' done' var i abl e

end

The test in a while loop is checked before the body of the loop is entered for the first time. In the exampleabove, we must set the variable done to false before the loop, because otherwise no data processing wouldoccur. After each iteration ends, the test is checked again to determine whether to continue the loop or not.

Counter-driven LoopsCounter-driven loops are useful when you want to run a sequence of commands for a certain number oftimes. As an example, you may wish to display only the first 10 lines in a text file.

There are four basic parts of implementing a counter-driven loop:

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Initialize a counter variable before the loop begins.

Test to see if the counter variable has reached a set maximum value.

Execute the program statements in the loop, if the counter has not reached the maximum value.

Increment the counter by some value.

For example, we can implement a counter-driven loop using the while construct:

i = 0 ' use i as count er var i abl e

whi l e ( i < 10)

out l n( " val ue of i i s " + i )

i = i + 1

end

for LoopsThe f or loop provides a streamlined way to write a counter-driven loop. It combines the counterinitialization, test, and increment statements into a single line. The script below produces exactly the sameeffect as the whi l e loop example above.

f or ( i = 0; i < 10; i = i +1 )

out l n( " val ue of i i s " + i )

end

The three loop control statements are separated by semicolons in the for loop statement. The initializationstatement (first) is run only once before the loop starts. The test statement (second) is run before enteringan iteration of the loop body. Finally, the increment statement is run after each completed iteration, andbefore the test is rechecked. Note that you can use any assignment or calculation in the incrementstatement.

Just like the i f statement, SamUL allows for loops that contain only one program statement in the body tobe written on one line. For example:

f or ( val =57; val > 1; val = val / 2 ) out l n( " Val ue i s " + val )

Loop Control StatementsIn some cases you may want to end a loop prematurely. Suppose under normal conditions, you woulditerate 10 times, but because of some rare circumstance, you must break the loop's normal path ofexecution after the third iteration. To do this, use the br eak statement.

val ue = doubl e( i n( " Ent er a s t ar t i ng val ue" ) )

f or ( i =0; i <10; i =i +1 )

out l n( " Val ue i s " + val ue )

i f ( val ue < 0)

br eak

end

val ue = val ue / 3. 0

end

In another situation, you may not want to altogether break the loop, but skip the rest of program statementsleft in the current iteration. For example, you may be processing a list of files, but each one is onlyprocessed if it starts with a specific line. The cont i nue keyword provides this functionality.

f or ( i =0; i <f i l e_count ; i =i +1 )

f i l e_header _ok = f al se

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' check i f whet her cur r ent f i l e has t he cor r ec t header

i f ( f i l e_header _ok == f al se)

cont i nue

end

' pr ocess t hi s f i l e

end

The br eak and cont i nue statements can be used with both f or and whi l e loops. If you have nestedloops, the statements will act in relation to the nearest loop structure. In other words, a br eak statement inthe body of the inner-most loop will only break the execution of the inner-most loop.

QuittingSamUL script execution normally ends when there are no more statements to run at the end of the script.However, sometimes you may need to halt early, if the user chooses not to continue an operation.

The ex i t statement will end the SamUL script immediately. For example:

i f ( yesno( " Do you want t o qui t ?" ) == t r ue )

out l n( " Abor t ed. " )

ex i t

end

The yesno function call displays a message box on the user's screen with Yes and No buttons, showingthe given message. It returns t r ue if the user clicked yes, or f al se otherwise.

7.9.3 Arrays of Data

Often you need to store a list of related values. For example, you may need to refer to the price of energy indifferent years. Or you might have a table of state names and capital cities. In SamUL, you can use arraysto store these types of collections of data.

Initializing and Indexing

An array is simply a list of variables that are indexed by numbers. Each variable in the array is called anelement of the array, and the position of the element within the array is called the element's index. Theindex of the first element in an array is always 0.

To access array elements, enclose the index number in square brackets immediately following the variablename. SamUL does not require you to declare or allocate space for the array data in advance.

names[ 0] = " Sean"

names[ 1] = " Wal t er "

names[ 2] = " Pam"

names[ 3] = " Cl ai r e"

names[ 4] = " Pat r i ck"

out l n( names[ 3] ) ' out put i s " Pat r i ck"

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my_i ndex = 2

out l n( names[ my_i ndex] ) ' out put i s " Pam"

You can also initialize a fixed array using the ar r ay command provided in SamUL. Simply separate eachelement with a comma. There is no limit to the number of elements you can pass to array.

names = ar r ay( " Sean" , " Wal t er " , " Pam" , " Cl ai r e" , " Pat r i ck" )

out l n( " Fi r s t : " + names[ 0] )

out l n( " Al l : " + names )

Note that calling the t ypeof function on an array variable will return "ärray" as the type description, not thetype of the elements. This is because SamUL is not strict about the types of variables stored in an array,and does not require all elements to be of the same type.

Array Length

Sometimes you do not know in advance how many elements are in an array. This can happen if you arereading a list of numbers from a text file, storing each as an element in an array. After the all the data hasbeen read, you can use the length function to determine how many elements the array contains.

count = l engt h( names )

Processing Arrays

Arrays and loops naturally go together, since frequently you may want to perform the same operation oneach element of an array. For example, you may want to find the total sum of an array of numbers.

number s = ar r ay( 1, - 3, 2. 4, 9, 7, 22, - 2. 1, 5. 8 )

count = l engt h( number s )

sum = 0

f or ( i =0; i <count ; i =i +1)

sum = sum + number s [ i ]

end

The important feature of this code is that it will work regardless of how many elements are in the array.

Multidimensional Arrays

As previously noted, SamUL is not strict with the types of elements stored in an array. Therefore, a singlearray element can even be another array. This allows you to define matrices with both row and columnindexes, and also three (or greater) dimensional arrays.

To create a multi-dimensional array, simply separate the indices with commas between the squarebrackets. For example:

dat a[ 0, 0] = 3

dat a[ 0, 1] = - 2

dat a[ 1, 0] = 5

dat a[ 2, 0] = 1

nr ows = l engt h( dat a) ' r esul t i s 4

ncol s = l engt h( dat a[ 0] ) ' r esul t i s 2

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r ow1 = dat a[ 0] ' ex t r ac t t he f i r s t r ow

x = r ow1[ 0] ' val ue i s 3

y = r ow1[ 1] ' val ue i s - 2

Managing Array Storage

When you define an array, SamUL automatically allocates sufficient computer memory to store theelements. If you know in advance that your array will contain 100 elements, for example, it can be muchfaster to allocate the computer memory before filling the array with data. Use the al l ocat e command tomake space for 1 or 2 dimensional arrays.

dat a = al l ocat e( 3, 2) ' a mat r i x wi t h 3 r ows and 2 col umns

dat a[ 2, 1] = 3

pr i ces = al l ocat e( 5 ) ' a s i mpl e 5 el ement ar r ay

As bef or e, you can ex t end t he ar r ay s i mpl y by us i ng hi gher i ndexes. However ,i f you know i n advance how many mor e el ement s you wi l l be addi ng, i t can bef as t er t o use t he r es i ze command t o r eal l ocat e comput er memor y t o s t or e t hear r ay . r es i ze pr eser ves any dat a i n t he ar r ay , or t r uncat es dat a i f t he newsi ze i s smal l er t han t he ol d s i ze.

dat a = al l ocat e( 5)

out l n( l engt h( dat a) )

r es i ze( dat a, 10)


r es i ze( dat a, 2, 4)


out l n( l engt h( dat a[ 0] ) )

Multiple Advance Declarations

You can also declare many variables and arrays in advance using the dec l ar e statement. For example:

dec l ar e r adi at i on[ 8760] , t emp[ 8760] , mat r i x [ 3, 3] , i =0

This statement will create the array variables radiation and temp, each with 8760 values. It will also setaside memory for the 3x3 matrix variable, and 'create' the variable i and assign it the value of zero. Thedeclare statement can be a useful shortcut to creating arrays and initializing many variables in a single line.The only limitation is that you cannot define arrays of greater than two dimensions using the declarecommand.

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7.9.4 Function Calls

It is usually good programming practice to split a larger program up into smaller sections, often calledprocedures, functions, or subroutines. A program may be easier to read and debug if it is not all throwntogether, and you may have common blocks of code that appear several times in the program.

User Functions

A function is simply a named chunk of code that may be called from other parts of the script. It usuallyperforms a well-defined operation on a set of variables, and it may return a computed value to the caller.

Functions can be written anywhere in your SAM script, including after they are called. If a function is nevercalled by the program, it has no effect.

Definition

Consider the very simple procedure listed below.

f unct i on show_wel come( )

out l n( " Thank you f or choos i ng SamUL. " )

out l n( " Thi s t ex t wi l l onl y be di spl ayed at t he s t ar t of t he scr i pt . " )

end

Notable features:

Use the function keyword to define a new function.

The function name is next, and follows the same rules as for variable names. Valid function names canhave letters, digits, and underscores, but cannot start with a digit.

The empty parentheses after the name indicate that this function takes no parameters.

The end keyword closes the function definition.

To call the function from elsewhere in the code, simply write the function's name, followed by theparentheses:

' show a message t o t he user

show_wel come( )

Returning a Value

A function is generally more useful if it can return information back to the program that called it. In thisexample, the function will not return unless the user enters ÿes" or "no" into the input dialog.

f unct i on r equi r e_yes_or _no( )

whi l e( t r ue )

answer = i n( " Dest r oy ever y t hi ng? Ent er yes or no: " )

i f ( answer == " yes" ) r et ur n t r ue

i f ( answer == " no" ) r et ur n f al se

out l n( " That was not an accept abl e r esponse. " )

end

end

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' cal l t he i nput f unct i on

r esul t = r equi r e_yes_or _no( ) ' r et ur ns t r ue or f al se

i f ( not r esul t )

out l n( " user sai d no, phew! " )

ex i t

el se

out l n( " dest r oy i ng ever y t hi ng. . . " )

end

The important lesson here is that the main script does not worry about the details of how the user isquestioned, and only knows that it will receive a true or false response. Also, the function can be reused indifferent parts of the program, and each time the user will be treated in a familiar way.

Parameters

In most cases, a function will accept arguments when it is called. That way, the function can change itsbehavior, or take different inputs in calculating a result. Analogous to mathematical functions, SamULfunctions can take arguments to compute a result that can be returned. Arguments to a function are givennames and are listed between the parentheses on the function definition line.

For example, consider a function to determine the minimum of two numbers:

f unct i on mi ni mum( a, b)

i f ( a < b) r et ur n a el se r et ur n b

end

' cal l t he f unct i on

count = 129

out l n( " Mi ni mum: " + mi ni mum( count , 77) )

In SamUL, changing the value of a function's named arguments will modify the variable in the callingprogram. Instead of passing the actual value of a parameter a, SamUL always passes a reference to thevariable in the original program. The reference is hidden from the user, so the variable acts just like anyother variable inside the function.

Because arguments are passed by reference (as in Fortran, for example), a function can "return" more thanone value. For example:

f unct i on sumdi f f mul t ( s , d, a, b)

s = a+b

d = a- b

r et ur n a* b

end

sum = - 1

di f f = - 1

mul t = sumdi f f mul t ( sum, di f f , 20, 7)

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out l n( " Sum: " + sum + " Di f f : " + di f f + " Mul t : " + mul t ) ' wi l l out put 27,13, and 140

Variable Scope

Generally, variables used inside a function are considered "local", and cannot be accessed from the callerprogram. For example:

f unct i on t r i pl e( x)

y = 3* x

end

t r i pl e( 4 )

out l n( y ) ' t hi s wi l l f ai l because y i s l ocal t o t he t r i pl e f unct i on

As we have seen, we can write useful functions using arguments and return values to pass data into and outof functions. However, sometimes there are some many inputs to a function that it becomes verycumbersome to list them all as arguments. Alternatively, you might have some variables that are usedthroughout your program, or are considered reference values or constants. For these situations, you candefine variables to be global in SamUL, and then they can be used inside functions and in the mainprogram. For example:

gl obal pi = 3. 1415926

f unct i on c i r cumf er ence( r )

r et ur n 2* pi * r

end

f unct i on deg2r ad( x )

r et ur n pi / 180* x

end

out l n( " PI : " + pi )

out l n( " CI RC: " + c i r cumf er ence( 3 ) )

out l n( " D2R: " + deg2r ad( 180 ) )

Common programming advice is to minimize the number of global variables used in a program. Sometimesthe are certainly necessary, but too many can lead to mistakes that are harder to debug and correct, andcan reduce the readability and maintainability of your script.

Built-in SamUL Functions

Throughout this guide, we have made use of built-in functions like in, out l n, and others. These functionsare included with SamUL automatically, and called in exactly the same way as user functions. Like userfunctions, they can return values, and sometimes they modify the arguments sent to them. Refer to theLibrary Reference for documentation on each function's capabilities, parameters, and return values.

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7.9.5 Input, Output, and System Access

SamUL provides a variety of standard library functions to work with files, directories, and interact with otherprograms. So far, we have used the in, out, and outln functions to accept user input and display programoutput in the runtime console window. Now we will learn about accessing files and other programs.

Working with Text Files

To write data to a text file, use the wr i t et ex t f i l e function. wr i t et ex t f i l e accepts any type ofvariable, but most frequently you will write text stored in a string variable. For example:

dat a = " "

f or ( i =0; i <10; i =i +1) dat a = dat a + " Text Dat a Li ne " + s t r i ng( i ) + " \ n"

ok = wr i t et ex t f i l e( " C: / t es t . t x t " , dat a )

i f ( not ok) out l n( " Er r or wr i t i ng t ex t f i l e. " )

Reading a text file is just as simple with the r eadt ex t f i l e function.

myt ext = " "

i f ( not r eadt ex t f i l e( " C: / t es t . t x t " , myt ex t ) )

out l n( " coul d not r ead t ex t f i l e. " )

el se

out l n( " t ex t dat a: " )

out ( myt ext )

end

While these functions offer an easy way to read an entire text file, often it is useful to be able to access itline by line. SamUL provides the open, c l ose, and r eadl n functions for this purpose.

f i l e = open( " c : / t es t . t x t " , " r " )

i f ( not f i l e)

out l n( " coul d not open f i l e" )

ex i t

end

dec l ar e l i ne

whi l e ( r eadl n( f i l e, l i ne ) )

out l n( " My Text Li ne=' " + l i ne + " ' " )

end

c l ose( f i l e)

In the example above, f i l e is a number that represents the file on the disk. The open function opens thespecified file for reading when the "r" parameter is given. The r eadl n function will return true as long asthere are more lines to be read from the file, and the text of each line is placed in the line variable.

Another way to access individual lines of a text file uses the split function to return an array of text lines.

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For example:

myt ext = " "

r eadt ex t f i l e( " C: / t es t . t x t " , myt ex t )

l i nes = spl i t ( myt ex t , " \ n" )

out l n( " Ther e ar e " + l engt h( l i nes) + " l i nes of t ex t i n t he f i l e. " )

i f ( l engt h( l i nes) > 5) out l n( " Li ne 5: ' " , l i nes [ 5] , " ' " )

File System Functions

Suppose you want to run SAM with many different weather files, and consequently need a list of all the filesin a folder that have the .tm2 extension. SamUL provides the directorylist function to help out in thissituation. If you want to filter for multiple file extensions, separate them with commas.

f i l e_names = di r ec t or y l i s t ( " C: / Wi ndows" , " dl l " ) ' coul d al so use " t x t , dl l "

out l n( " Found " + l engt h( f i l e_names) + " f i l es t hat mat ch. " )

out l n( unspl i t ( f i l e_names, " \ n" ) )

To list all the files in the given folder, leave the extension string empty or pass in "*".

Sometimes you need to be able to quickly extract the file name from the full path, or vice versa. Thefunctions filenameonly and dirnameonly extract the respective sections of the file name, returning the result.

To test whether a file or directory exist, use the di r ex i s t s or f i l eex i s t s functions. Examples:

pat h = " C: / SAM/ 2010. 11. 9/ samsi m. dl l "

di r = di r nameonl y( pat h )

name = f i l enameonl y( pat h )

out l n( " Pat h: " + pat h )

out l n( " Name: " + name + " Ex i s t s? " + f i l eex i s t s ( pat h) )

out l n( " Di r : " + di r + " Ex i s t s? " + di r ex i s t s ( di r ) )

Standard Dialogs

To facilitate writing more interactive scripts, SamUL includes various dialog functions. We have already usedthe not i ce and yesno functions in previous examples.

The choosef i l e function pops up a file selection dialog to the user, prompting them to select a file.choosefile will accept three optional parameters: the path of the initial directory to show in the dialog, awildcard filter like "*.txt" to limit the types of files shown in the list, and a dialog caption to display on thewindow. Example:

f i l e = choosef i l e( " c : / SAM" , " * . dl l " , " Choose a DLL f i l e" )

i f ( f i l e == " " )

not i ce( " You di d not choose a f i l e, qui t t i ng. " )

ex i t

el se

i f ( not yesno( " Do you want t o l oad: \ n\ n" + f i l e) ) ex i t

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' pr oceed t o l oad . dl l f i l e

out l n( " Loadi ng " + f i l e)

end

Calling Other Programs

Suppose you have a program on your computer that reads an input file, makes some complicatedcalculations, and writes an output file. For example, a program could read in some system specificationsand calculate its heat loss coefficients that could be used in a SAM analysis.

There are two very similar ways to call external programs: the system and shell functions. They areidentical except that shell pops up an interactive system command window and runs the program in it. Bothfunctions will wait until the called program finishes before returning to SamUL, so that the program runssynchronously. Examples:

syst em( " not epad. exe" ) ' r un not epad and wai t

shel l ( " i pconf i g / al l > c : / t es t . t x t " ) ' r un i n t he sys t em shel l

out put = " "

r eadt ex t f i l e( " c : / t es t . t x t " , out put )

out l n( out put )

Each program runs in a folder that the program refers to as the working directory. Sometimes you may needto switch the working directory to conveniently access other files, or to allow an external program to runcorrectly.

wor k i ng_di r = cwd( ) ' get t he cur r ent wor k i ng di r ec t or y

chdi r ( " C: / wi ndows" ) ' change t he wor k i ng di r ec t or y

out l n( " cwd=" + cwd( ) )

chdi r ( wor k i ng_di r ) ' change i t back t o t he or i gi nal one

out l n( " cwd=" + cwd( ) )

7.9.6 Interfacing with SAM Analyses

The SamUL language would be of little interest if it did not allow for direct manipulation and automation ofSAM analyses. To this end, there is a set of included function calls that can set SAM input variables,invoke a simulation, and retrieve output data.

All of the SamUL function calls involve only "base case" analysis. That is, the built-in parametrics,sensitivity, optimization, and statistical simulation types that are controlled from the user interface are notaccessible from SamUL. This is probably less of a hindrance than it sounds, as SamUL exists primarily toallow for specialized simulations that do not fall into one of those categories.

Getting Started

SamUL scripts are part of a SAM project file that can consist of multiple cases and scripts. The generalmethodology is to have a SAM case that more or less describes the system you want to investigate, and

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then create a SamUL script within the same project that can manipulate the case. A SamUL script can onlyoperate on one case at a time, and the active case is specified using the SetActiveCase function call. Forexample:

Set Act i veCase( " PV Syst em i n Ar i zona Case" )

Changing Input Values

Once an active case has been chosen, you can change base case input values using the Set I nputfunction. If an input affects other calculated variables, they are automatically recalculated, and the updatedvalues are shown on the case input page. Calling Set I nput causes the SAM interface to be updated justas if the user had changed the variable manually. Examples:

Set I nput ( " sys t em. degr adat i on" , 12. 5 ) ' set degr adat i on t o 12. 5 \ %/ year

Set I nput ( " pvwat t s . ar r ay_t ype" , 1 ) ' set s PVWat t s ar r ay t r ack i ng mode t o oneax i s

SamUL requires that you provide the internal names of variables to access them. These names can beaccessed from the third button on the SamUL toolbar. A dialog box will pop up, listing all SAM variablessorted by grouping and labels. The internal data type of a variable is also listed. Simply select the inputvariable from the hierarchical menu, and the internal name will be pasted into the SamUL script at thecursor position.

Unfortunately, because of the huge number of variables in SAM, there is no comprehensive referencemanual that describes each variable's values or any special formatting that may be required. For example,the PV shading derate factor matrix is actually stored in memory as a one-dimensional column-major array,with the first two elements indicating the number of rows and columns respectively. Supposing that you hadread in a 2D array from a text file into the shadi ng[ i , j ] variable, you must convert it to a singledimensional array representation as below:

shadar r = al l ocat e( 12* 24+2)

shadar r [ 0] = 12

shadar r [ 1] = 24

c=2

f or ( i =0; i <12; i =i +1)

f or ( j =0; j <24; j =j +1)

shadar r [ c ] = shadi ng[ i , j ]

c=c+1

end

end

Then you can write set i nput ( " pv . shadi ng. mxh. f ac t or s" , shadar r ) and it will assign the factorscorrectly. The same holds true for most 2D matrix representations in SAM.

One exception is the heliostat field layout matrix for CSP Power Towers. The matrix is also stored as a one-dimensional array as described above, but there is one more number attached to the end of the array tohold the span angle in degrees. Thus the total array length is nr ows* ncol s+3. In any situation, it isalways possible to call the GetInput with a variable to inspect how the data is stored.

set ac t i vecase( " New CSP Power Tower Case 1" )

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x = get i nput ( " csp. pt . s f . user _f i el d" )

out l n( " l en=" , l engt h( x) , " : " , x )

Simulating and Saving Output

To start a base case simulation, use the simulate function. It take a boolean parameter to specify whetherto save the hourly (8760) outputs from the simulation. After the simulation has finished, you can access theoutputs using the getoutput function.

set ac t i vecase( " Res i dent i al PV Syst em" )

set i nput ( " sys t em. degr adat i on" , 12. 5 ) ' set degr adat i on t o 12. 5 per cent

s i mul at e( )

l coe = get out put ( " sv . l coe_r eal " )

not i ce( " LCOE = " + l coe )

As with the input variables, the internal variable names of the available outputs are also accessible from theSamUL toolbar.

You can also save several outputs to a comma-separated value (CSV) file to work with in Excel or anotherprogram using the wr i t er esul t s function. The outputs variables are passed to the function separated bycommas in a single string, and each variable is dumped as a separate column in the CSV file.

set ac t i vecase( " Res i dent i al PV Syst em" )

set i nput ( " sys t em. degr adat i on" , 12. 5 ) ' set degr adat i on t o 12. 5 per cent

s i mul at e( )

wr i t er esul t s ( " c : / t es t . csv" , " sys t em. hour l y . e_net , sys t em. mont hl y . e_net , sv .l coe_nom" )

Batching Weather Files

Let's return to the original hypothetical example discussed in the introduction. You have directory of weatherfiles, and for each one you are asked to calculate the hourly generation and LCOE for the system.

The code addresses this need, and makes use of many SamUL language capabilities and built-in functioncalls.

' Set t he ac t i ve case f r om t he cur r ent ones

set ac t i vecase( " Si mpl e PV Syst em" )

' Spec i f y a di r ec t or y t o use f or weat her bat chi ng

di r = " c : / Document s and Set t i ngs/ Dav i d Smi t h/ Deskt op/ Weat her Fi l es"

' Li s t al l t he f i l es i n a di r ec t or y t hat have t he ex t ens i on " t m2"

f i l e_l i s t = Di r ec t or yLi s t ( di r , " t m2" )

' l oop t hr ough al l t he f i l es

count = l engt h( f i l e_l i s t )

f or ( i =0; i <count ; i =i +1)

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out ( " Weat her ( " , ( i +1) , " of " , count , " ) =" +Fi l eNameOnl y( f i l e_l i s t [ i ] ) +" \ n" )

' set t he c l i mat e var i abl e t o t he f i l e name

set i nput ( " c l i mat e. l ocat i on" , f i l e_l i s t [ i ] )

' r un t he base case

s i mul at e( )

' make t he out put f i l e name

out put _f i l e = di r + " / out put _" + Fi l eNameOnl y( f i l e_l i s t [ i ] ) + " . csv"

out ( " Wr i t i ng Out put Fi l e: " +Fi l eNameOnl y( out put _f i l e) +" \ n\ n" )

' dump t he needed r esul t s i nt o a CSV f i l e

Wr i t eResul t s ( out put _f i l e, " sys t em. hour l y . e_net , sv . l coe_nom" )

end

This example and several others are included in the standard SAM sample files.

7.9.7 Case Study

Problem Description

Suppose your supervisor sends you an Excel spreadsheet with a list of 30 photovoltaic systems at variouslocations. For each system, you are given a street address, system size in kW, capital cost, and a flatutility rate in cents/kWh for the location. You are asked to add additional columns to the spreadsheet toshow the levelized cost of electricity (LCOE) in both real and nominal terms, the total annual energyproduction, the payback period if the system were installed. For each system, the array tilt should equal thelocation's latitude. The spreadsheet may look something like:

Address PV System Size

300 West Second Street Little Rock Ar 72000 170

15902 Jamaica Ave Jamaica NY 700

125 South Grand Avenue Pasadena CA 91105 125

135 High Street Hartford CT 06103 355

333 Constitution Avenue NW Washington DC 20001 970

717 Madison Place NW Washington DC 20005 200

One approach would be to calculate all of the metrics by manually setting up each system in SAM. Anotherpossibility would be to set up a complicated linked parametric simulation for all the systems, after havingdownloaded the correct weather data for each location. Either way, the task would be at best cumbersomeand error prone. Worse, if your supervisor decides to change one or two inputs, or later wants additional

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output metrics, it would be a hassle to start all over again. SamUL provides all the tools you need toautomate this process in a flexible way.

Obtaining Latitudes and Longitudes

The first task is to determine the latitude and longitude of each address, so that we can find appropriatehourly weather data for each location. Google conveniently provides a simple web service for decoding astreet address into coordinates. We simply need a valid URL string to pass to Google, and it will return thelatitude and longitude in a string via the HTTP/GET method. SamUL has a built-in function ht t pget toprocess a GET request and returns the string data from the server.

We will code up this functionality in a SamUL function called addr2latlon that fills in latitude and longitudefrom an address. The first task is to normalize the address string to first remove multiple spaces, and thenreplace single spaces with the + sign to make a valid URL. The result of ht t pget is split at each commalocation, and the 3rd and 4th elements (latitude and longitude) are extracted and converted to doubleprecision numbers.

If the web service returned something strange, the latitude and longitude are set to -1 to signify an error. Thecomplete function is listed below.

f unct i on addr 2l at l on( addr ess, l at , l on )

addr = addr ess

s t r r epl ace( addr , " " , " " )

s t r r epl ace( addr , " " , " " )

s t r r epl ace( addr , " " , " +" )

quer y = " ht t p: / / maps. googl e. com/ maps/ geo?q=" + addr +" &out put =csv&key=mykey&sensor =f al se"

r esul t = ht t pget ( quer y )

par t s = spl i t ( r esul t , " , " )

i f ( l engt h( par t s ) == 4)

l at = doubl e( par t s [ 2] )

l on = doubl e( par t s [ 3] )

el se

l at = - 1

l on = - 1

end

end

Downloading Weather Data

Hourly TMY2 formatted weather data can be retrieved from the Mercator web service provided by NREL.Since we are not doing analysis for a particular year, we will write a function to download the typical (TDY)weather data for a location. The getweather function uses the addr2latlon function listed above to translatethe address to coordinates. Given a latitude and longitude, the proper 10 km grid cell can be determinedusing the translate function listed below. The details of this translation will not be covered here, and arespecific to how NREL stores the weather files on the server.

Using the grid code and directory information returned from translate, we can create a URL for the weatherdata file that we wish to download. Using the built-in SamUL function ht t pdownl oad, we download thecompressed weather file to a local folder on our computer. Then, it is decompressed and the .gz extension

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removed using the decompress function. If the decompression succeeds, the compressed file is deleted,and we are left with the proper .tm2 weather data file that can be processed by SAM.

f unct i on get weat her ( addr , t ar get di r , weat her f i l e, l at , l on )

l at = - 1. 0

l on = - 1. 0

gr i d = " "

di r = " "

addr 2l at l on( addr , l at , l on)

t r ans l at e( l at , l on, gr i d, di r )

l ocal = t ar get di r + " / weat her _" + gr i d + " . t m2. gz"

ur l = " ht t p: / / mer cat or . nr el . gov/ per ez_t dy / " + di r + " / r adwx_" + gr i d +" _9805. t m2. gz"

i f ( not ht t pdownl oad( ur l , l ocal ) )

out l n( " f ai l ed t o downl oad\ n\ t " + ur l + " \ n\ t " + l ocal )

r et ur n f al se

end

weat her f i l e = s t r l ef t ( l ocal , s t r l en( l ocal ) - 3)

i f ( not decompr ess( l ocal , weat her f i l e ) )

out l n( " f ai l ed t o decompr ess f i l e. " )

r et ur n f al se

end

del et ef i l e( l ocal )

r et ur n t r ue

end

f unct i on t r ans l at e( l at , l on, gr i dcode, di r )

shor t _l at = i nt eger ( abs( l at ) )

shor t _l on = i nt eger ( abs( l on ) )

i f ( mod( shor t _l at , 2) > 0 ) shor t _l at = shor t _l at - 1

i f ( mod( shor t _l on, 2) > 0 ) shor t _l on = shor t _l on- 1

shor t _l on = shor t _l on + 2

di r = shor t _l on + " " + shor t _l at

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gl at = s t r i ng( i nt eger ( abs( l at ) * 10 ) ) + " 5"

gl on = s t r i ng( i nt eger ( abs( l on) * 10 ) ) + " 5"

i f ( s t r l en( gl on) <5) gl on = " 0" + gl on

gr i dcode = gl on + gl at

end

Processing the Input File

Now that we have access to weather data for each of the locations in the spreadsheet, the next task is toread it in and perform each simulation. After the simulation for each location is finished, we will immediatelywrite the results to another file. SamUL conveniently allows multiple files to be open at the same time.

The code below opens the input and output files, and scans each line of the input for the various inputparameters, runs a simulation, and writes the results to an output file.

set ac t i vecase( " Basel i ne PV Syst em" )

wor kdi r = " / User s / adobos/ Deskt op"

i nput = open( wor kdi r + " / i nput . csv" , " r " )

i f ( not i nput )

out l n( " coul d not open i nput f i l e" )

ex i t

end

out put = open( wor kdi r + " / out put . csv" , " w" )

i f ( not out put )

out l n( " coul d not open out put f i l e" )

ex i t

end

wr i t e( out put , " l at , l on, l coe nomi nal , l coe r eal , enet , payback\ n" )

dec l ar e buf f er

r eadl n( i nput , buf f er )

whi l e( r eadl n( i nput , buf f er ) )

col s = spl i t ( buf f er , " , " )

addr ess = col s [ 0]

s i ze = col s [ 1]

cos t = col s [ 2]

r at e = col s [ 3]

dec l ar e l at = - 1. 0, l on = - 1. 0, weat her f i l e=" "

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i f ( not get weat her ( addr ess, wor kdi r , weat her f i l e, l at , l on ) )

out l n( " f ai l ed t o get weat her dat a f or : " + addr ess)

ex i t

end

modul e_cost = cost / ( s i ze * 1000 )

set i nput ( " c l i mat e. l ocat i on" , weat her f i l e )

set i nput ( " pvwat t s . dcr at e" , s i ze )

set i nput ( " pvwat t s . t i l t " , abs( l at ) )

set i nput ( " pv . cost . per _modul e" , modul e_cost )

set i nput ( " ur . f l at . buy_r at e" , r at e/ 100. 0 )

out l n( " Si mul at i ng l ocat i on: " + addr ess)

s i mul at e( )

dec l ar e l coe_nom=0, l coe_r eal =0, enet =0, payback=0

l coe_nom = get out put ( " sv . l coe_nom" )

l coe_r eal = get out put ( " sv . l coe_r eal " )

enet = get out put ( " sv . annual _out put " )

payback = get out put ( " sv . payback" )

wr i t e( out put , l at +" , " +l on+" , " +l coe_nom+" , " +l coe_r eal +" , " +enet +" , " +payback)

end

c l ose( i nput )

c l ose( out put )

In this example, the cost data for each location represented the total installed system cost. However, SAMdoes not have a direct input for the total cost, as it is calculated from many different cost components. Totrick SAM into using the total cost that we have, however, we simply set all the costs to zero, and calculatean effective DC module cost given the nameplate size of the system and the total cost. Then, setting themodule cost variable to this value will naturally result in the desired total system cost as well.

This examples shows the power SamUL to automate an otherwise tedious and error prone task. While thedata set presented here is relatively small, one could imagine such a task for thousands of locations,system sizes, and costs. The ability to exercise SAM's capabilities via scripting is a tool of core importancein an advanced SAM user's toolbox.

The case study example and several others are included as part of the standard SAM installation. Pleasebrowse the examples for additional information, or contact Solar Advisor Support at

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7.9.8 Library Reference

Type/Data Manipulation

TypeOf

( ):STRING

Returns a description of the argument type.

Integer

( VARIANT ):INTEGER

Converts the variable to an integer number.

Double

( VARIANT ):DOUBLE

Converts the variable to a double-precision floating point number.

Boolean

( VARIANT ):BOOLEAN

Converts the variable to a boolean.

String

( ... ):STRING

Converts the given variables to a string.

IntegerArray

( STRING ):ARRAY

Converts a string delimited by {;, tn} to an integer array.

DoubleArray

( STRING ):ARRAY

Converts a string delimited by {;, tn} to a double-precision floating point array.

Length

( ARRAY ):INTEGER

Return the length of an array.

Array

( ... ):ARRAY

Creates an array out of the argument list.

Allocate

( INTEGER:PRIMARY, [INTEGER:SECONDARY] ):ARRAY

Creates an empty array with the specified dimensions.

Resize

( , INTEGER:PRIMARY, [INTEGER:SECONDARY] ):NONE

Resizes an array or 2D matrix.

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Append

( , ... ):NONE

Appends one or more items to an array.

Prepend

( , ... ):NONE

Prepends one or more items to an array.

Input/Output

Out

( ... ):NONE

Print data to the output device.

OutLn

( ... ):NONE

Print data to the output device followed by a newline.

Print

( STRING:Format, ... ):NONE

Print formatted data to the output device using an extended 'printf' syntax.

In

( ... ):STRING

Request input from the input device, showing an optional prompt.

Notice

( ... ):NONE

Show a message dialog.

YesNo

( ... ):BOOLEAN)

Show a Yes/No dialog. Returns true if yes was clicked

ChooseFile

( [STRING:Initial dir], [STRING:Filter], [STRING:Caption] ):STRING

Show a file selection dialog, with optional parameters.

StartTimer

( NONE ):NONE

Starts a stop watch timer.

ElapsedTime

( NONE ):INTEGER

Returns elapsed milliseconds since last call to 'StartTimer'

MilliSleep

( INTEGER:Milliseconds ):NONE

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Sleep for the specified amount of time.

DateTime

( NONE ):STRING

Returns the current date and time.

Open

( STRING:File, STRING:Mode ):INTEGER

Opens a file for reading 'r', writing 'w', or appending 'a'.

Close

( INTEGER:FileNum ):NONE

Closes a file.

Seek

( INTEGER:FileNum, INTEGER:Offset, INTEGER:Origin ):INTEGER

Sets the position in an open file.

Tell

( INTEGER:FileNum ):INTEGER

Returns the current file position.

Eof

( INTEGER:FileNum ):BOOLEAN

Determines whether a file is at the end.

Flush

( INTEGER:FileNum ):INTEGER

Flushes the current file object to disk.

Write

( INTEGER:FileNum, ... ):BOOLEAN

Writes data as text to a file.

WriteN

( INTEGER:FileNum, VARIANT data, INTEGER: NumChars ):BOOLEAN

Writes character data to a file.

WriteLn

( INTEGER:FileNum, VARIANT data ):BOOLEAN

Writes a line to a file as a string.

ReadN

( INTEGER:FileNum, :Data, INTEGER:NumChars ):BOOLEAN

Reads characters from a file.

ReadLn

( INTEGER:FileNum, :Line ):BOOLEAN

Reads a line from a file, returning false if no more lines exist.

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ReadFmt

( INTEGER:filenum, STRING:format=[idgefxsb]*, STRING:delimiters, ... VALUE ARGUMENT LIST ):BOOLEAN

Reads a data line from a file with the given sequence of types and delimiters. Number of valuearguments must equal number of characters in format string

OpenWF

( STRING:file, [ARRAY:header info] ):INTEGER

Opens a weather (TM2, TM3, EPW) file for reading.

ReadWF

( INTEGER:filenum, ARRAY:y - m - d - h - gh - dn - df - wind - tdry - twet - relhum - pres *or* [INTEGER:y, INTEGER:m, INTEGER:d, INTEGER:h, DOUBLE:gh, DOUBLE:dn, DOUBLE:df, DOUBLE:wind,DOUBLE:tdry, DOUBLE:twet, DOUBLE:relhum, DOUBLE:pres]):BOOLEAN

Reads a line of data from a weather file.

CustomizeTMY3

( STRING:Source tmy3 file, STRING:Target tmy3 file, [ STRING:Column name=gh - dn - df - tdry - twet -wind - pressure - relhum, ARRAY:Values(8760) ]* ):BOOLEAN

Overwrites columns of 8760 data in a TMY3 file and writes a new file.

WFStatistics

( STRING:File, :DN, :GH, :AMBT, :WSPD ):BOOLEAN

Extracts annual averages of DN, GH, AmbT, and WSpd

WriteTextFile

( STRING:Filename, VARIANT data ):BOOLEAN

Writes a file of text data to disk. Returns true on success.

ReadTextFile

( STRING:Filename, :Data ):BOOLEAN

Reads a text file from disk, returning true on success.

GetHomeDir

( NONE ):STRING

Returns the current user's home directory.

Cwd

( NONE ):STRING

Returns the current working directory.

ChDir

( STRING: Path ):BOOLEAN

Change the current working directory.

DirectoryList

( STRING:Path, STRING:Comma-separated extensions, [BOOLEAN:Include folders]):ARRAY

Enumerates all the files in a directory that match a comma separated string of extensions.

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System

( STRING ):INTEGER

Run a system command, returning the process exit code.

Shell

( STRING ):BOOLEAN

Run a system command in a new console window. Returns true on success.

FileNameOnly

( STRING:Path ):STRING

Returns only the file name portion of a full path.

DirNameOnly

( STRING:Path ):STRING

Returns only the directory portion of a full path.

Extension

( STRING:File ):STRING

Returns the extension of a file.

DirExists

( STRING:Path ):BOOLEAN

Returns true if the specified directory exists.

FileExists


Returns true if the specified file exists.

CopyFile

( STRING:File1, STRING:File2 ):BOOLEAN

Copies file 1 to file 2.

RenameFile

( STRING:File1, STRING:File2 ):BOOLEAN

Renames file 1 to file 2.

DeleteFile

( STRING:File ):BOOLEAN

Deletes the specified file.

MkDir


Creates a directory including the full path to it.

RmDir


Deletes a directory and everything it contains.

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Decompress

( STRING:Archive, STRING:Target ):BOOLEAN

Decompresses an archive file (ZIP, TAR, TAR.GZ, GZ).

HttpGet

( STRING:Url ):STRING

Performs an HTTP web query and returns the result as plain text.

HttpDownload

( STRING:Url, STRING:LocalFile ):BOOLEAN

Downloads a file form the web, showing a progress dialog.

String Manipulation

StrPos

( STRING, STRING:Search ):INTEGER

Returns the first position of the search string, or -1 if not found.

StrRPos

( STRING, STRING:Search ):INTEGER

Returns the first position of the search string from the right, or -1 if not found.

StrLeft

( STRING, INTEGER:N ):STRING

Returns the left 'N' character string.

StrRight

( STRING, INTEGER:N ):STRING

Returns the right 'N' character string.

StrLower

( STRING ):STRING

Returns a lower case version of the string.

StrUpper

( STRING ):STRING

Returns an upper case version of the string.

StrMid

( STRING, INTEGER:Start, [INTEGER:Count] ):STRING

Returns the substring from the specified start position, of length 'count'. If 'count' is not supplied, theremainder of the string is returned.

StrLen

( STRING ):INTEGER

Returns the length of a string.

SamUL 457


StrReplace

( STRING, STRING:s0, STRING:s1 ):STRING

Returns a string with all instances of 's0' replaced with 's1'.

StrCmp

( STRING:s0, STRING:s1 ):INTEGER

Case-sensitive comparison. Returns 0 if equal, positive if s0 comes before s1, and negative if s1 comesbefore s0.

StrICmp

( STRING:s0, STRING:s1 ):INTEGER

Case-insensitive comparison. Returns 0 if equal, positive if s0 comes before s1, and negative if s1comes before s0.

StrGCh

( STRING, INTEGER:position ):STRING

Gets the character at the specified position.

StrSCh

( STRING, INTEGER:position, STRING:char):NONE

Sets the character at the specified position.

Split

( STRING, STRING:delimiters ):ARRAY

Splits the string into an array.

Unsplit

( ARRAY, STRING:delimiters ):STRING

Unsplits an array into a string.

Format

( STRING:Format, ... ):STRING

Formats data into a string using an extended 'printf' syntax.

Math

Mod

( INTEGER, INTEGER ):INTEGER

Returns the remainder after X is divided by Y

Abs

( NUMBER ):NUMBER

Absolute value of the number.

Min

( NUMBER, NUMBER *or* ARRAY ):NUMBER

Returns the smaller of two values, or the smallest in an array.

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Max

( NUMBER, NUMBER *or* ARRAY ):NUMBER

Returns the larger of two values, or the largest in an array

Ceil

( NUMBER ):DOUBLE

Returns the number rounded up to the nearest integer.

Floor

( NUMBER ):DOUBLE

Returns the number rounded down to the nearest integer.

Sqrt

( NUMBER ):DOUBLE

Returns the square root of a number.

Pow

( NUMBER:X, NUMBER:Y ):DOUBLE

Returns 'X' raised to the 'Y' power.

Exp

( NUMBER ):DOUBLE

Returns the exponential value, base 'e'.

Log

( NUMBER ):DOUBLE

Returns the logarithm of a number, base 'e'.

Log10

( NUMBER ):DOUBLE

Returns the logarithm of a number, base 10.

Sin

( NUMBER ):DOUBLE

Returns the sine of a radian value.

Cos

( NUMBER ):DOUBLE

Returns the cosine of a radian value.

Tan

( NUMBER ):DOUBLE

Returns the tangent of a radian value.

ASin

( NUMBER ):DOUBLE

Returns the arcsine of a number in radians.

SamUL 459


ACos

( NUMBER ):DOUBLE

Returns the arccosine of a number in radians.

ATan

( NUMBER ):DOUBLE

Returns the arctangent of a number in radians.

ATan2

( NUMBER:Y, NUMBER:X ):DOUBLE

Returns the arctangent of 'Y'/'X' in radians.

IsNan

( DOUBLE ):BOOLEAN

Returns true if the number is NAN.

NanVal

( NONE ):DOUBLE

Returns NAN.

UnifRand

( NONE ):DOUBLE

Returns a random number with uniform distribution (0..1).

NormRand

( NONE ):DOUBLE

Returns a random number with normal distribution around 0.

SAM Functions

SetInput

( STRING:Variable name, VARIANT value):NONE

Sets an input in the active case.

GetInput

( STRING:Variable name ):VARIANT

Returns an input value from the active case.

GetOutput

( STRING:Variable name ):ARRAY

Returns a base case output from the active case's results as a double-precision array.

ResetOutputSource

( NONE or STRING:Simulation name, INTEGER:Run number ):NONE

Resets the output data source to default BASE case, or changes it to a different simulation and runnumber.

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ClearSimResults

( STRING:Simulation name ):NONE

Clears all results for the specific simulation name.

SetActiveCase

( STRING:Case name ):NONE

Sets the active case.

GetActiveCase

( NONE ):STRING

Returns the active case name.

SwitchToCase

( NONE ):NONE

Switches to the active case tab in the interface.

ChangeConfig

( STRING:Technology, STRING:Financing ):BOOLEAN

Changes the current case's configuration. Application must be '*'.

ListCases

( NONE ):ARRAY

Lists all the cases in the project.

ProjectFile

( NONE ):STRING

Returns the current project file name.

AppYield

( NONE ):NONE

Yields the interface to respond to user input.

SaveProject

( NONE ): BOOLEAN

Saves the project.

SaveProjectAs

( STRING ):BOOLEAN

Saves the project to the specified file.

Simulate

( BOOLEAN:Save hourly data ):NONE

Runs a base case simulation with the current inputs, with the option of saving hourly results.

MPSimulate

( STRING:Simulation name, ARRAY[ARRAY]:Variable name/value table NRUNS+1 x NVARS with toprow having var names ):BOOLEAN

Runs many simulations using multiple processors.

SamUL 461


WriteResults

( STRING:File name, STRING:Comma-separated output variable names):BOOLEAN

Write a comma-separated-value file, with each column specified by a string of comma-separated outputnames.

ClearResults

( NONE ):NONE

Clear the active case's results from memory.

ClearCache

( NONE ):NONE

Clear the memory cache of previously run simulations.

DeleteTempFiles

( NONE ):NONE

Delete any lingering simulation temporary files.

SetTimestep

( STRING:Timestep with units ):NONE

Sets the TRNSYS timestep for the active case.

ReloadDefaults

( NONE ):NONE

Reloads all default values for the active case.

ListTechnologies

( NONE ):ARRAY

Returns an array of all the technologies in SAM.

ListFinancing

( STRING:Technology ):ARRAY

Lists all financing options in SAM for a given technology.

TechnologyType

( NONE ):STRING

Returns the active case technology type.

FinancingType

( NONE ):STRING

Returns the active case financing type.

ActiveVariables

( [STRING:Technology, STRING:Financing] ):ARRAY

List all active variables for the current case or technology/market name.

FluidDensity

( INTEGER:Fluid number, DOUBLE:Temp 'C ):DOUBLE

Returns density at temperature Tc for a given fluid number (pressure assumed 1Pa).

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FluidSpecificHeat

( INTEGER:Fluid number, DOUBLE:Temp 'C ):DOUBLE

Returns specific heat at temperature Tc for a given fluid number (pressure assumed 1Pa).

FluidName

( INTEGER:Fluid number ):STRING

Returns fluid name for a given fluid number.

PtOptimize

( NONE ):NONE

Optimizes the power tower heliostat field, tower height, receiver height, and receiver diameter.

LHSCreate

( NONE ):INTEGER

Creates a new Latin Hypercube Sampling object.

LHSFree

( INTEGER:lhsref ):NONE

Frees an LHS object.

LHSReset

( INTEGER:lhsref ):NONE

Erases all distributions and correlations in an LHS object.

LHSSeed

( INTEGER:seed ):NONE

Sets the seed value for the LHS object.

LHSPoints

( INTEGER:lhsref, INTEGER:number of points ):NONE

Sets the number of samples desired.

LHSDist

( INTEGER:lhsref, STRING:distribution name, STRING: variable name, [DOUBLE:param1, DOUBLE:param2, DOUBLE:param3, DOUBLE:param4] ): NONE

Sets up a distribution for a variable.

LHSCorr

( INTEGER:lhsref, STRING:variable 1, STRING:variable 2, DOUBLE:corr val ):NONE

Sets up correlation between two variables.

LHSRun

( INTEGER:lhsref ):BOOLEAN

Runs the LHS sampling program.

LHSError

( INTEGER:lhsref ):STRING

Returns an error message if any.

SamUL 463


LHSVector

( INTEGER:lhsref, STRING:variable ):ARRAY

Returns the sampled values for a variable.

STEPCreate

( NONE ):INTEGER

Create a new STEPWISE regression analysis object.

STEPFree

( INTEGER:stpref ):NONE

Frees a STEPWISE object.

STEPInput

( INTEGER:stpref, STRING:name, ARRAY:values ):NONE

Sets a STEPWISE input vector.

STEPOutput

( INTEGER:stpref, ARRAY:values ):NONE

Sets a STEPWISE output vector.

STEPRun

( INTEGER:stpref ):NONE

Runs the STEPWISE analysis.

STEPError

( INTEGER:stpref ):STRING

Returns any error code from STEPWISE.

STEPResult

( INTEGER:stpref, STRING:name ):ARRAY

Returns R2 and SRC for a given input name.

OpenEIListUtilities

( NONE ):ARRAY

Returns a list of utility company names from OpenEI.org

OpenEIListRates

( STRING:Utility name, , ):INTEGER

Lists all rate schedules for a utility company.

OpenEIApplyRate

( STRING:Guid ):BOOLEAN

Downloads and applies the specified rate schedule from OpenEI.

URdbFileWrite

( STRING:file ):BOOLEAN

Writes a local URdb format file with the current case's utility rate information.

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URdbFileRead

( STRING:file ):BOOLEAN

Reads a local URdb format file and overwrites the current case's utility rate information.

7.10 Generating CodeSAM's code generation feature allows you to call SAM from the following scripting and programminglanguages:

Python

C

MATLAB

VBA programs

To use the feature, you should be familiar with one of the languages, and have the necessary software toedit, compile, and run code written in the language.

When you generate code for a SAM case in one of the languages, SAM creates a text file containing linesof code that:

1. Assign input values for all of the variables in the case.

2. Makes a call to SAM's simulation engine to run a simulation.

3. Generates output using some of SAM's basic metrics (total annual output, real and nominal LCOE).

To familiarize yourself with the feature, set up a simple case in SAM, and generate code for the languageyou would like to use. Explore the code that SAM generates and experiment with it to see how you canassign values to SAM input variables, control simulations, and access SAM results.

The following example shows how to use the code generation feature with Python. The procedure is similarfor the other languages.

To generate sample code in Python:

1. Start SAM and create a new case: Photovoltaics, Component-based Models, Residential.

2. Run the case to see the results.

3. Create the Python code: On the Case menu, click Advanced, Generate Python Code.

4. Save the file to a folder on your desktop: \python_example\my_pv_case.py.

5. Click No at the prompt to view the file.

6. Open the folder on your desktop to see the following two files: pysam.py and my_pv_case.py.

The file pysam.py is the Python/SAMSIM.dll interface code that is always generated. Themy_pv_case.py file is the file that contains all of the inputs.

To run run the Python script (in Windows):

1. In Windows, open a command prompt: From the Windows Start menu, type cmd.exe and pressthe Enter key.

2. Navigate to the desktop\python_example folder: Type cd Documents and Settings\[username]\Desktop\python_example.

3. Try to run the script by typing python my_pv_case.py.

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If the script fails because it cannot find samsim.dll, copy samsim.dll from the SAM installationfolder to the python_example folder.

4. When the script runs, you should see something like the following:

C: \ Document s and Set t i ngs\ adobos\ Deskt op\ py t hon_exampl e>pyt honmy_pv_case. pyTRNSYS16 ( I VF- SAM) 31OCT10TRNSTART10 %20 %30 %40 %50 %60 %70 %80 %90 %100 %TRNENDLcoe( r eal ) = 12. 7051132298Lcoe( nom) = 15. 4848167856E_net = 6987. 46656644

5. SAM does not need to be open to run the script. Close SAM and try running the script again toverify this.

Once you've run SAM from the Python script, you can try the next procedure to see how to use the script tochange the value of a SAM input variable, in this case the array tilt angle.

To change values of SAM inputs from the Python script:

1. At the command prompt type notepad my_pv_case.py to open the script in the Notepad texteditor.

Notepad should open with the Python code that SAM generated. This file sets up all of the inputsas they were originally set in the SAM file from which it was created.

2. Replace the simulation calls at the bottom of the file with a loop that changes the tilt:

cxt = sam. cr eat e_cont ext ( ' dummy' )set up_case_i nput s( cx t )sam. set _s( cx t , ' s i m. hour l y_f i l e' , ' C: / Document s and Set t i ngs/ adobos/sam_pyt hon/ hour l y . dat ' )sam. set _s( cx t , ' t r nsys . wor kdi r ' , ' C: / Document s and Set t i ngs/ adobos/sam_pyt hon' )sam. set _s( cx t , ' pt f l ux . wor kdi r ' , ' C: / Document s and Set t i ngs/ adobos/sam_pyt hon' )sam. set _s( cx t , ' t r nsys . i ns t al l di r ' , ' C: / SAM/ 2010. 11. 9/ exel i b/ t r nsys ' )sam. set _d( cx t , ' t r nsys . t i mest ep' , 1. 0)sam. set _s( cx t , ' pt f l ux . exedi r ' , ' C: / SAM/ 2010. 11. 9/ exel i b/ t ool s ' )

f or t i l t i n [ 10, 15, 20, 25, 30] :sam. set _d( cx t , " pv . ar r ay . t i l t " , t i l t )cx t = s i mul at e_cont ext ( cx t , ' t r nsys . pv ' )cx t = s i mul at e_cont ext ( cx t , ' f i n. r es . l oan' )pr i nt ' Ti l t =' , t i l tpr i nt ' Lcoe( r eal ) =' , sam. get _d( cx t , ' sv . l coe_r eal ' )pr i nt ' Lcoe( nom) =' , sam. get _d( cx t , ' sv . l coe_nom' )pr i nt ' E_net =' , sam. get _d( cx t , ' sys t em. annual . e_net ' )

sam. f r ee_cont ext ( cx t )

3. Run the python my_pv_case.py script.

It should display energy production and LCOE values at array tilt values of 10, 15, 20, 25, and 30

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degrees.

7.11 Libraries

Contents

Overview describes SAM libraries.

Accessing Libraries from Input Pages explains how to use libraries to populateinput variables on input pages.

Library Descriptions describes the libraries in the current version of SAM and theinput pages that display values from each library.

Default and User Libraries explains the difference between libraries that come withthe software, and libraries that you add to your projects.

Managing Libraries with the Library Editor describes the buttons on the libraryeditor and explains how to use it to create and modify libraries.

OverviewA library is a collection of stored values for some sets of input variables on SAM input pages. A libraryallows you to populate a set of variables by choosing an entry from the library. For example, each entry inthe photovoltaic inverter library stores a set of values for the variables describing the characteristics of aninverter in the Sandia inverter database. When you choose an inverter from the library, SAM populates theinverter characteristic variables on the Inverter page with values from the library. See Accessing Librariesfrom Input Pages for details.

For advanced analyses, you may want to add your own entries to a library, or to modify entries in anexisting library. The library editor allows you to add and manage libraries. You should only add or modify alibrary entry when you have a complete set of data for the entry. Because values in the entry may beinterdependent in ways that are not obvious, you can easily introduce errors to simulation results bychanging values in a library entry. An obvious example would be changing one of the power values for anentry in the inverter library without changing the current and voltage values. In general, you should notmodify libraries unless you are familiar with both the characterization of the physical componentrepresented by library entries, and with SAM's mathematical representation of the component.

Note. If you decide to modify or create your own libraries, you should first read about the differencebetween default and user libraries, and refer to the instructions for working with the library editor.

Accessing Libraries from Input PagesDepending on the library, SAM either displays a "Choose from library" or "Library" button, or displays thelibrary entries as a list directly on the input page. For some components, to choose an item from a library,you click the Choose (or Library) button and then click the item's name in a list of library items. SAM

Libraries 467


automatically populates appropriate variables on the input page, which you can edit if necessary. Forexample, on the physical trough model's Collectors page, to choose an entry from the parabolic troughcollector library, click Choose collector from library. SAM displays a list of collectors from the library.When you click a collector name in the list, SAM copies collector geometry and optical parameter valuesfrom the library to the variables on the Collectors page.

If you change the value of one of those variables, SAM indicates that the parameters on the input page differfrom parameter values in the library by displaying "No library match" in the library name box:

For other libraries, such as the component-based photovoltaic model's Sandia module library, SAM displaysthe list of library items directly on the input page. When you choose an item from the list, SAM copiesvalues from the library to the project's case, and displays some of them as read-only values on the Modulepage. If you want to use change a value, you must create a new user library.

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Note. SAM often only displays a subset of the parameters from a library on input pages. If you want tosee the complete parameter set for a library item, you can view the values in the library editor.

Library DescriptionsSAM uses libraries to store parameter sets for the following performance model components and displaysthem as lists on the relevant input pages.

BIOBIB Fuels

Not used.

CEC Modules (CECModule)

List of photovoltaic modules from the California Energy Commission database of approved modulesdisplayed on the Module page.

CSP Empirical Trough TES Dispatch (EmpiricalTroughDispatch)

Storage dispatch schedules based on time-of-use rates of different electric utilities for the empiricaltrough model displayed on the Thermal Storage page.

CSP GSS TES Dispatch

Storage dispatch schedules based on time-of-use rates of different electric utilities for the empiricaltrough model displayed on the Thermal Storage page.

CSP Physical Trough Receiver (HCE) (PhysicalTroughHCE)

Receiver characteristics for the physical trough model displayed on the Receivers (HCEs) page.

CSP Physical Trough SCAs (PhysicalTroughSCA)

Collector characteristics for the physical trough model displayed on the Collectors (SCAs) page.

CSP Physical Trough TES Dispatch (PhysicalTroughDispatch)

Storage dispatch schedules based on time-of-use rates of different electric utilities for the physical

Libraries 469


trough model displayed on the Thermal Storage page.

CSP Tower TES Dispatch (TowerDispatch)

Storage dispatch schedules based on time-of-use rates of different electric utilities for the power towermodel displayed on the Thermal Storage page.

CSP Trough HCEs (TroughHCE)

Receiver characteristic for the empirical trough model displayed on the SCA/HCE page.

CSP Trough Parasitics (TroughParasitics)

Parasitic loss coefficients for different reference power cycle options of the empirical trough modeldisplayed on the Parasitics page.

CSP Trough Power Cycles (TroughPowerBlock)

Steam turbine characteristics for different reference power cycle options of the empirical trough modeldisplayed on the Power Block page.

CSP Trough SCAs (TroughSCA)

Collector characteristics for the empirical trough model displayed on the SCA/HCE page.

Dish Stirling Systems (DishStirlingSystem)

Complete system descriptions for the dish-Stirling model displayed on the System Library page.

Energy Payment Dispatch (EnergyPaymentDispatch)

Energy payment allocation factors and schedules displayed on the Energy Payment Dispatch page.

Large Scale Wind Turbine Library (LargeScaleWindTurbine)

List of turbines for the Utility Scale Wind model displayed on the Wind Farm Specifications page.

SHW Collectors (SHWCollectors)

Not used.

SHW Draw Profiles (SHWDrawProfile)

Not used.

SRCC (SRCCCollectors)

List of solar water heating collectors displayed on the SWH System page.

Sandia Inverters (SandiaInverter)

List of inverters from the Sandia inverter database for the photovoltaic model displayed on the Inverterpage.

Sandia Modules (SandiaModule)

List of modules from the Sandia module database for the photovoltaic model displayed on the Modulepage.

Small Scale Wind Library (SmallScaleWindTurbine)

List of wind turbines for the Small Scale Wind model displayed on the Small Scale Wind System page.

TOU Utility Rates (TOURateSchedule)

Retail time-of-use rates for projects with residential or commercial financing displayed on the UtilityRate page.

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Wind Turbine Library (WindTurbine)

Not used.

Default and User LibrariesSAM stores data for each library in library files. A library file is a text file with a the .samlib extension. Youcan find the library files in the library folder (/exelib/libraries in your SAM installation folder). SAM uses alibrary type definition file with the .samlibtype extension to map values from the library file to SAM inputvariables.

There are two types of libraries, default libraries indicated in lists by the prefix "SAM/" in lists, and userlibraries indicated by the prefix "USER/":

Default libraries are available to all project files on your computer and cannot be modified from the libraryeditor. SAM considers any library file stored in the library folder to be a default library, and indicatesdefault libraries in lists on input pages with the prefix "SAM/." Although you can use a text editor tomodify a default library, we recommend using the library editor to create a copy of the default library forediting so that you always have a copy of the original default library that came with SAM. Note that youcan add your own library to the default collection by creating a library file and putting it the librariesfolder.

User libraries are libraries stored in the project file. A user library must be added to a project file to beavailable in the file. User libraries are indicated in lists by the prefix "USER/." Unlike default libraries,user library parameters are stored in the project file and can increase the project file size. To make auser library available to more than one SAM project on your computer, you can either export it as alibrary file and then import it into other projects, or you can export to the default library folder so that it isavailable to all projects on your computer.

SAM displays user libraries at the end of the list. For example, the modules from the user library for theSandia PV module model appear at the end of the list of modules:

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Managing Libraries with the Library EditorThe library editor allows you to create and edit user libraries. You cannot edit default libraries from thelibrary editor. To edit a default library, you can either create a copy of the library as a user library (therecommended approach), or you can edit the file directly using a text editor. See Default and User Librariesfor details.

To open the library editor:

On the File menu, click Libraries.

Note. In order for the library editor to be fully functional, you must open a SAM file before opening thelibrary editor. If you open the library editor from SAM's welcome page, only the export function is active.

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Libraries

Shows the list of default libraries with the prefix "SAM/" and any user libraries in the project with theprefix "USER/". Click a library name to display the library's contents. Each library entry is a row in thetable.

New User Library

Click to add a new user library to the project. SAM stores user library data in the project file rather thanin external library files.

Remove User Library

Click to remove a user library. You cannot remove a default library indicated by the "SAM/" prefix.

Add Entries

Add rows of data to a user library. You must choose a user library indicated by the "USER/" prefixbefore adding entries. You cannot add entries to a default library with the "SAM/" prefix.

Export

Export the current library to a library file (.samlib). Export a library when you want to use it in a differentproject. You must import the library into the other project for it to be available in that project. You canexport a library to the default library folder (/exelib/libraries in your SAM installation folder) to make thelibrary available to all SAM projects on your computer.

Import

Create a new user library by importing entries from a library file (.samlib). When you import a library,SAM stores the library entries in the project file, which affects the file's size.

Help

Display the Libraries help topic.

Close

Close the library editor.

Libraries 473


To create a new user library:

1. Open the library editor.

2. Click New User Library.

3. Type a name for the library in the Import Library window. This is the name that will appear in librarylists.

4. Choose a library type in the New User Library window. See the table of library types for typedescriptions.

When you create a new user library, SAM adds an empty library with the name you specified and the prefix"USER/" to the list of libraries. To assign values to the entry, you must first add a copy of an existing entry,and then modify its values. This helps to ensure that no library entries have blank values.

To add entries to a new or existing user library:

1. Click the user library's name in the Libraries list. User libraries are indicated by the prefix "USER/".

2. Click Add Entries.

3. In the Copy Existing Entry window, check one or more items that have similar characteristics to theentry you want to add.

4. Click OK.

5. To rename a library entry, in the library table, right-click the entry's name, and choose Renamefrom the shortcut menu.

6. To add values to a library entry, you can either

change values manually by double-clicking each cell and typing a value, or

copy a row of values from a comma-separated text file or Excel worksheet file, and then rightclicking the library entry's name and choosing Paste Values in the shortcut menu.

Note. The library editor does no error checking, so be sure to use valid values in your library entries.

To modify values in a default library:

1. Create a new user library of the same type as the default library (see instructions above).

2. Add the entry that contains the values you want to modify from the default library and change thevalue (see instructions above).

Note. You can also use a text editor to change values directly in a default library. You should only usethis approach if you are very familiar with the parameters stored in the library, and are certain that youwant to discard the original values stored in the library. We recommend only modifying copies oflibraries. See Default and User Libraries for file location details.

To "convert" a user library to a default library:

1. Click user library's name in the Libraries list.

2. Click Export and save the file in the libraries folder (/exelib/libraries in your SAM installation folder).

3. SAM will display the library with the "SAM/" prefix, and make it available to all SAM projects onyour computer.

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8 References

Parabolic Trough Technology and ModelingBurkholder F et al, 2009. Heat Loss Testing of Schott's 2008 PTR70 Parabolic Trough Receiver. NationalRenewable Energy Laboratory NREL/TP-550-45633. http://www.nrel.gov/docs/fy09osti/45633.pdf

Forristall R, 2003. Heat Transfer Analysis and Modeling of a Parabolic Trough Solar ReceiverImplemented in Engineering Equation Solver. National Renewable Energy Laboratory NREL/TP-550-34169. http://www.nrel.gov/csp/troughnet/pdfs/34169.pdf

Kelly B and Kearney D, 2006. Parabolic Trough Solar System Piping Model. National Renewable EnergyLaboratory NREL/SR-550-40165. http://www.nrel.gov/csp/troughnet/pdfs/40165.pdf

McMahan A, 2006. Design & Optimization of Organic Rankine Cycle Solar-Thermal Power Plants. Master of Science Thesis. University of Wisconsin-Madison. http://sel.me.wisc.edu/publications/theses/mcmahan06.zip

Moens et al, 2005. Advanced Heat Transfer and Thermal Storage Fluids, National Renewable EnergyLaboratory. NREL/CP-510-37083. http://www.nrel.gov/docs/fy05osti/37083.pdf

Patnode A, 2006. Simulation and Performance Evaluation of Parabolic Trough Solar Power Plants. Masterof Science Thesis. University of Wisconsin-Madison. http://sel.me.wisc.edu/publications/theses/patnode06.zip

Pilkington Solar International GmbH, 2000. Survey of Thermal Storage for Parabolic Trough Power Plants.National Renewable Energy Laboratory. NREL/SR-550-27925. http://www.nrel.gov/csp/troughnet/pdfs/27925.pdf

Price H et al, 2006. Field Survey of Parabolic Trough Receiver Thermal Performance, National RenewableEnergy Laboratory NREL/CP-550-39459. http://www.nrel.gov/docs/fy06osti/39459.pdf

Stuetzle T, 2002. Automatic Control of the 30 MWe SEGS VI Parabolic Trough Plant. Master of ScienceThesis. University of Wisconsin-Madison. http://sel.me.wisc.edu/publications/theses/Stuetzle02.zip

Troughnet Parabolic Trough Solar Power Network, National Renewable Energy Laboratory, http://www.nrel.gov/csp/troughnet. References to SAM modeling on Troughnet, http://www.nrel.gov/csp/modeling_analysis.html#system

Wagner M, 2008. Simulation and Predictive Performance Modeling of Utility-Scale Central ReceiverSystem Power Plants. Master of Science Thesis. University of Wisconsin-Madison. http://sel.me.wisc.edu/publications/theses/wagner08.zip

Dish-Stirling Technology and ModelingFraser P, 2008. Stirling Dish System Performance Prediction Model. Master of Science Thesis.University of Wisconsin-Madison. https://www.nrel.gov/analysis/sam/pdfs/thesis_fraser08.pdf

International Energy Agency SolarPaces technology characterization Solar Dish Engine. http://www.solarpaces.org/CSP_Technology/docs/solar_dish.pdf




http://sel.me.wisc.edu/publications/theses/mcmahan06.zip

http://sel.me.wisc.edu/publications/theses/mcmahan06.zip


http://sel.me.wisc.edu/publications/theses/patnode06.zip

http://sel.me.wisc.edu/publications/theses/patnode06.zip




http://sel.me.wisc.edu/publications/theses/Stuetzle02.zip

http://www.nrel.gov/csp/troughnet

http://www.nrel.gov/csp/troughnet

http://www.nrel.gov/csp/modeling_analysis.html#system

http://www.nrel.gov/csp/modeling_analysis.html#system




http://www.solarpaces.org/CSP_Technology/docs/solar_dish.pdf

http://www.solarpaces.org/CSP_Technology/docs/solar_dish.pdf

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Power Tower Technology and ModelingInternational Energy Agency SolarPaces technology characterization Solar Power Tower. http://www.solarpaces.org/CSP_Technology/docs/solar_tower.pdf

Kistler B, 1986. A User's Manual for DELSOL3: A Computer Code for Calculating the OpticalPerformance and Optimal System Design for Solar Thermal Central Receiver Plants. SAND86-8018.http://prod.sandia.gov/techlib/access-control.cgi/1986/868018.pdf

NREL 2007 Solar Power Tower, Dish Stirling and Linear Fresnel Technologies Workshop presentations.http://www.nrel.gov/csp/troughnet/wkshp_power_2007.html

U.S. Department of Energy Energy Efficiency and Renewable Energy. Concentrating Solar PowerTechnologies: Power Tower Systems. http://www1.eere.energy.gov/solar/power_towers.html

Wagner M, 2008. Simulation and Predictive Performance Modeling of Utility-Scale Central ReceiverSystem Power Plants. Master of Science Thesis. University of Wisconsin-Madison. http://sel.me.wisc.edu/publications/theses/wagner08.zip

Photovoltaic ModelingArizona State Photovoltaic Testing Laboratory. http://www.poly.asu.edu/ptl

Bower W et al, 2004. Performance Test Protocol for Evaluating Inverters Used in Grid-ConnectedPhotovoltaic Systems. http://bewengineering.com/docs/index.htm

California Energy Commission, New Solar Homes Partnership Calculator: CECPV Calculator. The CECcalculator uses the same module performance model as SAM's CEC performance model; documentationincluded with the CECPV Calculator explains details of the model. http://www.gosolarcalifornia.ca.gov/nshpcalculator

De Soto W, 2004. Improvement and Validation of a Model for Photovoltaic Array Performance. Master ofScience Thesis. University of Wisconsin-Madison. http://minds.wisconsin.edu/handle/1793/7602

De Soto W et al, 2003. "Improvement and Validation of a Model for Photovoltaic Array Performance."Solar 2003 Conference Proceedings. American Solar Energy Society.

King D et al, 2004. Photovoltaic Array Performance Model. Sandia National Laboratories. SAND2004-3535. http://photovoltaics.sandia.gov/docs/PDF/King%20SAND.pdf

King D et al, 2007. Performance Model for Grid-Connected Photovoltaic Inverters. Sandia NationalLaboratories. SAND2007-5036. http://infoserve.sandia.gov/sand_doc/2007/075036.pdf

Neises T, 2011. Development and Validation of a Model to Predict the Temperature of a Photovoltaic Cell.Master of Science Thesis. University of Wisconsin-Madison. http://sel.me.wisc.edu/publications/theses/neises11.zip

Marion B, 2010. Overview of the PV Module Model in PVWatts. Presented at PV Performance ModelingWorkshop, Albuquerque, New Mexico. National Renewable Energy Laboratory. NREL/PR-520-49607.

Marion B et al, 2005. Recent and Planned Enhancements for PVWATTS. National Renewable EnergyLaboratory. CP-520-37016. http://www.nrel.gov/docs/fy05osti/37016.pdf

Marion B et al, 2001. PVWatts Version 2: Enhanced Spatial Resolution for Calculated Grid-ConnectedPV Performance. National Renewable Energy Laboratory. CP-560-30941. http://www.nrel.gov/docs/fy02osti/30941.pdf

http://www.solarpaces.org/CSP_Technology/docs/solar_tower.pdf

http://www.solarpaces.org/CSP_Technology/docs/solar_tower.pdf

http://prod.sandia.gov/techlib/access-control.cgi/1986/868018.pdf

http://www.nrel.gov/csp/troughnet/wkshp_power_2007.html

http://www1.eere.energy.gov/solar/power_towers.html



http://www.poly.asu.edu/ptl


http://www.gosolarcalifornia.ca.gov/nshpcalculator

http://www.gosolarcalifornia.ca.gov/nshpcalculator









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May 2011

Project Economics and FinancingShort W et al, 1995. Manual for the Economic Evaluation of Energy Efficiency and Renewable EnergyTechnologies. National Renewable Energy Laboratory. NREL/TP-462-5173. http://www.nrel.gov/docs/legosti/old/5173.pdf

Wiser R, 1997. "Renewable energy finance and project ownership", Energy Policy Vol 25 No 1 pp 15-27.

Wiser R et al, 1997. Financing Investments in Renewable Energy: The Role of Policy Design andRestructuring. Ernest Orlando Lawrence Berkeley National Laboratory. http://eetd.lbl.gov/ea/EMS/reports/39826.pdf

Wiser et al, 1996. Alternative Windpower Ownership Structures: Financing Terms and Project Costs.Lawrence Berkeley National Laboratory. http://eetd.lbl.gov/ea/emp/reports/38921.pdf

TRNSYSKlein S et al, 2004. TRNSYS 16 A Transient Simulation Program. Solar Energy Laboratory, University ofWisconsin-Madison. http://sel.me.wisc.edu/trnsys/

Klein S et al, 2007. TRNSYS 16 A Transient Simulation Program, Volume 5 Mathematical Reference.Solar Energy Laboratory, University of Wisconsin-Madison.

Weather DataEnergyPlus Weather Data Format Description. http://apps1.eere.energy.gov/buildings/energyplus/pdfs/weatherdatainformation.pdf

Hay J and Davies J, 2980. Calculation of the Solar Radiation Incident on an Inclined Surface. Proceedingsof the First Canadian Solar Radiation Workshop.

Marion W et al, 2008. Users Manual for TMY3 Data Sets. National Renewable Energy Laboratory NREL/TP-581-43156. http://www.nrel.gov/docs/fy08osti/43156.pdf

Marion W et al, 1995. User's Manual for TMY2s Typical Meteorological Years. National RenewableEnergy Laboratory. http://rredc.nrel.gov/solar/pubs/tmy2/PDFs/tmy2man.pdf

Meteonorm. http://www.meteonorm.com/

Perez R et al, 1988. The Development and Verification of the Perez Diffuse Radiation Model. SandiaNational Laboratories SAND88-7030.

Reindl D et al, 1990. Diffuse Fraction Correlations. Solar Energy Vol 45 No 1.

Solar Prospector. http://mercator.nrel.gov/csp/

Weather Analytics TMY Anywhere. http://weatheranalytics.com/globaltmy.html

Useful Web SitesGo Solar California: http://www.gosolarcalifornia.ca.gov

SolarPACES, International Energy Agency: http://www.solarpaces.org

U.S. Department of Energy Solar Energy Technologies Program: http://www1.eere.energy.gov/solar

Database of State Incentives for Renewables and Efficiency at http://www.dsireusa.org

National Renewable Energy Laboratory



http://eetd.lbl.gov/ea/EMS/reports/39826.pdf

http://eetd.lbl.gov/ea/EMS/reports/39826.pdf

http://eetd.lbl.gov/ea/emp/reports/38921.pdf

http://sel.me.wisc.edu/trnsys/

http://apps1.eere.energy.gov/buildings/energyplus/pdfs/weatherdatainformation.pdf

http://apps1.eere.energy.gov/buildings/energyplus/pdfs/weatherdatainformation.pdf


http://rredc.nrel.gov/solar/pubs/tmy2/PDFs/tmy2man.pdf

http://www.meteonorm.com/

http://mercator.nrel.gov/csp/


http://www.gosolarcalifornia.ca.gov

http://www.solarpaces.org

http://www1.eere.energy.gov/solar

http://www.dsireusa.org

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Energy Analysis, http://www.nrel.gov/analysis

National Center for Photovoltaics, http://www.nrel.gov/pv

Concentrating Solar Power Research, http://www.nrel.gov/csp

Publications, http://www.nrel.gov/publications/

Sandia National Laboratories

Photovoltaic Systems Research & Development, http://photovoltaics.sandia.gov

Concentrating Solar Power, http://www.sandia.gov/csp/csp_r_d_sandia.html

Publications, http://www.sandia.gov/news/publications/index.html

http://www.nrel.gov/analysis

http://www.nrel.gov/pv

http://www.nrel.gov/csp

http://www.nrel.gov/publications/

http://photovoltaics.sandia.gov

http://www.sandia.gov/csp/csp_r_d_sandia.html

http://www.sandia.gov/news/publications/index.html