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Quick Reference

Solar Position Algorithm Connected Components Accelerator Toolkit

About This Publication This quick reference provides instructions for using the Solar Positioning Algorithm with Connected Components Workbench software in a solar tracking application. The algorithm is provided as part of the Connected Components Accelerator Toolkit (CCAT).

The CCAT is available on the Connected Components Accelerator Toolkit DVD, publication CC-QR002, or through the Rockwell Automation Software Download and Registration System (SDRD) at http://www.rockwellautomation.com/rockwellautomation/products-technologies/connected-components/tools/accelerator-toolkit.page.

Before You Begin

Parameters related to geographical and environmental conditions of the observer were taken from the National Renewable Energy Laboratory (NREL) Solar Positioning Algorithm Calculator website at http://www.nrel.gov/midc/solpos/spa.html and used for validation of the

user-defined function block (UDFB).

Investigate parameters for other geographical locations because they are likely to change.

Topic Page

About This Publication 1

Overview of Solar Positioning 3

Solar Position Algorithm Description 4

Validation and Test Results 14

Additional Resources 16

http://www.nrel.gov/midc/solpos/spa.html

http://www.rockwellautomation.com/rockwellautomation/products-technologies/connected-components/tools/accelerator-toolkit.page

http://www.rockwellautomation.com/rockwellautomation/products-technologies/connected-components/tools/accelerator-toolkit.page

2 Solar Position Algorithm Connected Components Accelerator Toolkit

What You Need

Because the RA_SOLAR_POSITION_ALGRTHM instruction requires more than the standard amount of data memory to store temporary variables and constants, we recommend that you use one of the specified range of controllers:

• Micro830™ programmable controllers, 24-point base catalog numbers 2080-LC30-24xxx and 48-point base catalog numbers 2080-LC30-48xxx

• Micro850™ programmable controllers, 24-point base catalog numbers 2080-LC50-24xxx and 48-point base catalog numbers 2080-LC50-48xxx

You also need the following:• Personal computer• Connected Components Workbench™ software, version 2.0 and later• Standard USB for Micro830 controller• Ethernet network connection for Micro850 controller only

CCAT Solar Tracking Folder Contents

The CCAT Solar Tracking Folder in the Sample Code Modules, contains the following information:

• This Quick Reference document• The National Renewable Energy Laboratory (NREL) Technical Report

NREL/TP-560-343-2• RA_SOLAR_POSITION_ALGRTHM UDFB Connected

Components Workbench (CCW) exchange file in 7z format• An application example showing the possible uses of the

RA_SOLAR_POSITION_ALGRTHM user-defined function block (in a zipped CCW project folder)

IMPORTANT This specified range of controllers is a guideline that is dependent on the extensiveness of your controller code.

Rockwell Automation Publication CC-QR005A-EN-P - May 2013

Solar Position Algorithm Connected Components Accelerator Toolkit 3

Follow These Steps

Follow these steps to implement the Solar Position Algorithm.

Overview of Solar Positioning Solar trackers orient photovoltaic panels, reflectors, lenses, or other optical devices toward the sun. Since the sun’s position in the sky changes with the seasons and the time of day, trackers align the collection system to maximize energy production.

Tracker control algorithms typically incorporate a control strategy that is a hybrid between open-loop and closed-loop control. The open-loop components prevent the elimination of distortion of feedback signals from clouds that block the sun. The closed-loop components eliminate errors from variability in installation, assembly, calibration, and encoder mounting.

Closed-loop systems track the sun with a set of lenses or sensors with a limited field of view, directed at the sun, and are fully illuminated by sunlight at all times.

As the sun moves, it begins to shade one or more sensors. The system detects this movement and activates motors or actuators to move the device back into a position where all sensors are once again equally illuminated.

Start

Overview of Solar Positioning, page 3

Solar Position Algorithm Description, page 4

Solar Position Algorithm UDFB, page 6

Use the Solar Position Algorithm, page 8

Validation and Test Results, page 14



Open-loop systems typically employ electronic logic, which is based on a mathematical formula, to control device motors or actuators to follow the sun.

Solar Position Algorithm Description

The National Renewable Energy Laboratory (NREL) Technical Report NREL/TP-560-34302, revised January 2008, is included with the Solar Positioning Algorithm and sample program. It provides information and code examples for a Solar Position Algorithm for Solar Radiation Applications. The accuracy that can be achieved by using this algorithm is equal to ±0.0003° in the period from year -2000…6000. This report is a step-by-step procedure for implementing an algorithm to calculate the solar zenith and azimuth angles.

Rockwell Automation used this report to build a standard logic template that can be implemented by OEMs to develop tracker equipment.

Based on the Micro800™ controller platform, the implementation of the algorithm provides reduced execution time and more precision due to native support of 64-bit floating-point trigonometric math instructions.

Data specific to the geographical location must be entered to perform the mathematical calculations accurately. The values include the time zone (TZ), longitude, latitude, pressure, elevation, temperature, surface slope, surface azimuth rotation, and Delta T (difference between earth rotation time and terrestrial time). Once the local parameters are entered, the program calculates the azimuth and zenith angles and the time of sunrise, transit, and sunset for the day of calculation.



Figure 1 - Position of the Sun Relative to the Observer

The zenith angle is the angle between the direction of the sun (direction of interest) and the zenith (straight up or directly overhead). The user-defined function block (UDFB) calculates the zenith angle in degrees and provides the value by means of the Out_Zenith output. The sun’s elevation, or altitude, is the angle from the horizontal plane and the sun’s central ray or just the compliment of the zenith angle (90° - zenith angle).

The azimuth angle is measured clockwise from true north to the point on the horizon directly below the object. The program calculates the local (from observer) azimuth angle and displays it according to two notations:

• Out_AzimuthAstro output provides the astronomer’s azimuth angle, measured westward from south (-180…180°)

• Out_AzimuthNavi output (0…360°) denotes the navigator’s azimuth angle, measured eastward from north, which is most often used in solar tracking applications

SunZenith

(Straight Up

North

East

South

West

θ = Zenith Angleφ= Azimuth Anglee= Elevation Angle



Solar Position Algorithm UDFB The Solar Positioning Algorithm is a user-defined function block (UDFB), named RA_SOLAR_POSITION_ALGRTHM, which can be imported and used in Connected Components Workbench software, version 2.0 or later.

The RA_SOLAR_POSITION_ALGRTHM UDFB is capable of calculating the position of the sun, relative to the observer, based on a number of geographical and environmental parameters at a specific moment in time. It also calculates the times of sunrise, transit, and sunset for the day.



Input and Output Parameters

Table 1 - Input Parameters

Name Data Type Description

Cmd_Calc BOOL Run calculation

Cmd_SunRTS BOOL Calculate the sunrise, transit, and sunset times

In_Year DINT Year of event

In_Month DINT Month of event

In_Day DINT Day of event

In_Hours DINT Hour of event

In_Minutes DINT Minute of event

In_Seconds DINT Second of event

Par_TimeZone LREAL Observer time zone (negative west of Greenwich) [hours]

Par_DeltaT LREAL Terrestrial Time (TT) - Universal Time (UT) difference [seconds]

Par_Longitude LREAL Observer longitude (negative west of Greenwich) [degrees]

Par_Latitude LREAL Observer latitude (negative south of equator) [degrees]

Par_Elevation LREAL Observer elevation [meters]

Par_AtmRefract LREAL Atmospheric refraction at sunrise and sunset [degrees]

Par_PressureAvg LREAL Annual average local pressure [millibars]

Par_TempAvg LREAL Annual average local temperature [degrees Celsius]

Par_Slope(1)

(1) Optional - this parameter is needed to calculate the Out_Incidence output angle.

LREAL Surface slope (measured from the horizontal plane) [degrees]

Par_AzmRotation(1) LREAL Surface azimuth rotation (measured from south to projection of surface normal on horizontal plane, negative west) [degrees]

Table 2 - Output Parameters

Name Data Type Description

Sts_ER BOOL Error occured during execution

Err_Value DINT Execution error,• 00001 – One or more input parameters out of range• 00002 – Sun is always above or below the horizon for the day of

calculation

Out_Zenith LREAL Topocentric zenith angle [degrees]

Out_AzimuthNavi LREAL Topocentric navigator's azimuth angle (measured eastward from north) [0…360°]

Out_AzimuthAstro LREAL Topocentric astronomer's azimuth angle (measured westward from south) [-180…180°]

Out_Incidence LREAL Incidence angle for a surface oriented in any direction [degrees]

Out_SunRiseTime TIME Time of sunrise

Out_SunTransitTime TIME Time of sun transit

Out_SunSetTime TIME Time of sunset



Execution Time

These are the execution times:• Approximately 125 ms for calculation of sunrise, transit, and sunset times• Approximately 35 ms for calculation of sun’s position

The StsER output parameter, when set high, indicates that the instruction encountered an error.

Use the Solar Position Algorithm The RA_SOLAR_POSITION_ALGRTHM user-defined function block (UDFB) is provided as a Connected Components Workbench export file in the 7z format (RA_SOLAR_POSITION_ALGRTHM.7z). The file is in the Solar Tracking folder within the Sample Code Modules. This folder also contains an application example (SPA_M830_24QBB_ExampleApplication) that demonstrates the use of the UDFBs.



Import the User-defined Function Block

You must have a least one UDFB or program already defined in your project before importing a UDFB or program. To import the UDFB, right-click Import and choose Import Exchange File.

The algorithm requires several complex mathematical expressions to be calculated at the same time. Standard Micro800 controller memory settings restrict extensive memory allocation for temporary variables required by the calculations. Building a project with the newly imported UDFB results in an insufficient memory error.

TIP The instruction uses several other internal UDFBs. These are imported automatically and do not require any action.



To eliminate the error, follow these steps to change the settings of the controller.

1. In the Project Organizer, select the controller and press F4.

The Property window appears.

2. Increase the Memory Size parameter to at least 11,000 KB.

The value can change, dependent on the rest of the controller logic.

Execute the UDFB

The instruction requires one scan to execute. Because the position of the sun does not change quickly, you should execute the instruction only when needed.

The instruction is programmed to perform initialization of constants on the first scan of the controller. For proper operation, place the instruction in a program or rung to be executed unconditionally (that is, with no jumps, IF THEN ELSE statements, and so forth).

For proper initialization, do not condition the EN input when EN/ENO bits are used. See Figure 2. Disabling EN/ENO bits and conditioning the first input of the instruction does not prevent proper initialization unless the rung is not be executed at all (for example, the Jump instruction was used). See Figure 3.

The Cmd_Calc input starts the execution of the instruction and calculation of sun’s position.

The combination of Cmd_Calc and Cmd_SunRTS inputs implies that only the times of sunrise, transit, and sunset (RTS) are calculated while the position is not.

Because the time needed to calculate the RTS is approximately 200 ms and is needed only once per day, execute this calculation before the regular operation of the solar tracker.



The RA_SOLAR_POSITION_ALGRTHM instruction can also be used in programming languages other than Ladder Logic. Examples of the UDFB called in Function Block Diagram and Structured Text are shown in Figure 4 and Figure 5, respectively.

Figure 2 - Ladder Logic: without Conditioning

Figure 3 - Ladder Logic: with Conditioning



Figure 4 - Function Block Diagram

Figure 5 - Structured Text



Use RTC in Combination with UDFB

One of the possible sources of date and time data for the instruction can be the real-time clock (RTC). This functionality in Micro830 and Micro850 controllers is achieved via a plug-in module (catalog number 2080-MEMBAK-RTC).

Always install the module in the first plug-in slot. Configure the module in the Controller Properties dialog box.

When the module is properly configured and enabled, you can use the RTC_READ instruction to read data from the RTC. Because of the format of particular elements of RTC data, the data type is UINT. Convert it to DINT to match the RA_SOLAR_POSITION_ALGRTHM input data type.

Figure 6 - Using Real-time Clock Functionality



Validation and Test Results The user-defined function block (UDFB) was implemented based on the Solar Positioning Algorithm (SPA) published in the National Renewable Energy Laboratory (NREL) Technical Report NREL/TP-560-34302, revised January 2008. NREL refers to the precision of the algorithm as ±0.0003°.

To verify the correctness of the implementation of the SPA, a simulation was performed for a period of 1 year with a sampling period of 30 minutes. Based on 17,521 samples gathered, the error of calculation versus results obtained by the NREL Solar Positioning Algorithm Calculator was calculated as follows.

These are the simulation parameters.

These results justify the statement that the accuracy of the SPA implementation for Micro800 controllers is much greater than the mechanical accuracy that standard mechanical systems could provide.

Angle Average AbsoluteError Value

Zenith 3.41872E-05

Azimuth 7.2167E-05

Incidence 5.26098E-05

Parameters Values

Start date and time 1/January/2009 00:00:00

End date and time 31/December/2009 23:30:00

Sampling period 30 minutes

Number of samples 17,521

Time zone -7.0 [hours]

ΔT 67.0 [seconds]

Latitude 39.742476 [degrees]

Longitude -105.1786 [degrees]

Elevation 1830.14 [meters]

Average annual pressure 820.0 [millibars]

Average annual temperature 11.0 [degrees Celsius]

Atmospheric refraction 0.5667 [degrees]

Surface slope 30.0 [degrees]

Surface azimuth rotation -10.0 [degrees]



Notes:


Additional Resources These documents contain additional information concerning related products from Rockwell Automation.

You can view or download publications at http://www.rockwellautomation.com/literature/. To order paper copies of technical documentation, contact your local Allen-Bradley distributor or Rockwell Automation sales representative.

Resource Description

Industrial Automation Wiring and Grounding Guidelines, publication 1770-4.1

Provides general guidelines for installing a Rockwell Automation™ industrial system.

Micro830 and Micro850 Programmable Controllers User Manual, publication 2080-UM002

Provides a reference guide for Micro800 controller systems, plug-in modules, and accessories. It also contains procedures on how to install, wire, and troubleshoot your controller.

Connected Components Accelerator Toolkit Building Block Project Descriptions Quick Reference, publication CC-QR003

Provides descriptions of the available Connected Component Accelerator Toolkit projects.

Product Certifications website, http://rockwellautomation.com/rockwellautomation/certification/

Provides declarations of conformity, certificates, and other certification details.

Allen-Bradley, Rockwell Software, Connected Components Workbench, Micro800, Micro830, Micro850, and Rockwell

Automation are trademarks of Rockwell Automation, Inc.

Trademarks not belonging to Rockwell Automation are property of their respective companies.

Publication CC-QR005A-EN-P - May 2013Copyright © 2013 Rockwell Automation, Inc. All rights reserved. Printed in the U.S.A.

Rockwell Otomasyon Ticaret A.Ş., Kar Plaza İş Merkezi E Blok Kat:6 34752 İçerenköy, İstanbul, Tel: +90 (216) 5698400

http://literature.rockwellautomation.com/idc/groups/literature/documents/qr/cc-qr003_-en-p.pdf

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1770-in041_-en-p.pdf



http://www.ab.com

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/2080-um002_-en-e.pdf

http://www.rockwellautomation.com/literature/


http://www.ab.com

http://www.rockwellautomation.com/rockwellautomation/certification/overview.page

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