introducing the solmetricpv analyzer

Introducing the Solmetric PV Analyzer and the New Features of v2.0 PVA Software

Paul HerndaySenior Applications [email protected] 707-217-3094

November 8, 2012

Next PVA WebinarNovember 29, 10am PST

http://www.solmetric.com/webinar.html

Upcoming Webinars

Tools for Solar Site Assessment and DesignNovember 20, 2012 10am PST

Introducing the Solmetric PV Analyzer and the New Features of Version 2.0 PVA Software

November 29, 2012 10am PST

To register:http://www.solmetric.com/webinar.html

Topics

• Brief introduction to I-V curves and the PV Analyzer

• Introducing free Version 2.0 PVA Software Upgrade

• Commissioning PV arrays

• Troubleshooting PV arrays

• Meg testing with the Megger® MIT430

I-V and P-V* CurvesExpect this general shape for healthy cells, modules, strings, or arrays

Cu

rren

t

Voltage

Isc

Voc

I-V curve

Vmp

Imp

Pow

er

P-V curve

Pmax

*P-V curve is calculated from the measured I-V curve

Max power point

I-V Curve Abnormalities

Any reduction of the knee of the curve

means reduced output power.

Cu

rren

t (A

)

Voltage (V)

Isc

Voc

Increasedslope

Reduced slope

Mismatch losses (incl. shading)

Normal I-V curve

Reducedcurrent

Reducedvoltage

Conventional Isc and Voc measurements do not reveal many of these effects

Solmetric PV Analyzer Users

EPC organizations

System Integrators

Consulting Engineers

Training OrganizationsTechnical colleges

IBEW

Training Centers

O&M Companies

Electrical contractors

Module Manufacturers

Inverter Manufacturers

Array

Irradiance sensor

Module backside

temperature sensor

Your PCWUSB2

WUSB1

I-V Measurement

Unit

Built-in PV models

Irradiance & temperature

Module, tilt, orientation…

5 dots predict the shape of the curve

Wireless

How it works

Data analysis and reporting are automated

Screen

shot

Wireless Measurement Network Built-in Analysis

• The five dots indicate the expected curve shape

• The dots appear whenever an advanced performance model (Sandia or 5-Parameter) is selected

• The middle red dot is the predicted max power point

• The yellow dot on the P-V curve marks the peak of that curve, and is not a prediction of the PV model.

Expected I-V Curve Shapedetermined by the advanced PV models

Dot 1 (Isc, 0)

Dot 2 (I, Voc/2)

Dot 3 (Imp, Vmp)

Dot 4 (I, [Vmp + Voc]/2)

Dot 5 (0, Voc)

1

5

32

4

I-V Measurement SetupExample: Measuring strings at a combiner box

Attach the thermocouple well away from module edges, using polyimide (Kapton) tape for best mechanical properties at high temperatures.

Courtesy of:Integrated Energy SystemsPittsburg Unified School DistrictSage RenewablesStellar Energy Solutions

Example Measurement Setup

Wireless Sensor KitIrradiance & temperature sensors

Irradiance

transmitter

Receiver (USB)

Temperature

transmitter

K-type

thermocouple

Omega Part #

5SRTC-GG-K-

30-72

.

Deploying irradiance & temperature sensors

Guarantee that the irradiance sensoris in the plane of the array by placing iton a module (that’s not in the stringyou are measuring) or mounting it to acorner of a module.

Mount the thermocouple 2/3 of the waybetween the corner and center of amodule. Use high-temperature tape (eg1-3/4 inch Kapton dots**). Press TC intocontact with backside.

** MOCAP MCD-PE 1.75 poly dot~$80/roll of 1000 [email protected]

Topics






Faster setup

-Project Wizard

-Web tool for azimuth, latitude, longitude

Large displays of Irradiance & temperature on every measurement screen

Array Navigator™ for touch-based data save and recall

Translates I-V curves to STC

5000 more module models, and automatic update of equipment databases

History tab shows tabular values for the last 20 measurements

Archiving of Meg Test data

-Saves manually entered meg test data to the new database(Solmetric now offers the Megger MIT-430 Insulation Tester)

Report generation capability via the updated I-V Data Analysis Tool (optional accessory for analyzing large quantities of test data)

Features of v2 PVA PC software

Array Navigator™

•Represents the PV system architecture

•Created by the Project Wizard

•Touch a string location to save or recall data

•Also contains information needed by the PV model (eg wire gauge and lengths)

•Currently limited to sequential labeling schemes (numbers or letters)

Array Navigator™

The Project File

• Contains array details, performance model, and measurement data

• Easy to share between offices

• Foundation for future advanced analysis and reporting capabilities

Version 1.X Software Version 2.X Software

(legacy)

(legacy)

Project file

.csv

Saving a measurement result with V1.2

Windows file save interface

Saving a measurement result with V2.0

v1.2.4440 v2.0.5644

5param: 4,991 8,722

Sandia: 517 554

Simple: 0 11,454

Unique modules: 11,821

Additions to the Module Database

Roughly 2,178 module models exist with only the simple model

(11,454 - 8,722 - 554).

Live Software Demo

• Demo uses saved data

• Screens are also captured on the following slides

Traces tab

Project Wizard, Step 1Notes & Info

Project Wizard, Step 2Performance Model

Project Wizard, Step 3Site Info

Roof Measurement Tool

Autofill icon

Project Wizard, Step 4Array Navigator™

Autofill Tool

System Tree

Saving a test result

Traces screen

Environmental Inputs controls

Table screen

Verify screen

History screen

Meg Test tab

Topics






• Clear sky

– For high irradiance and normal curve shape

– For stable irradiance and more meaningful statistics

• 4 hour window centered on solar noon*

– For representative irradiance, spectral and reflective effects

• Low wind

– For stable temperature and more meaningful statistics

Recommended environmental conditionsfor performance testing with any type of instrument

http://www.esrl.noaa.gov/gmd/grad/solcalc/

*Solar Noon Calculator:

In practice, it is sometimes necessary to measure under less than

optimum conditions.

Why do we want stable conditions?

• Meaningful comparison of measured and modeled performance requires knowledge of

the irradiance and temperature at the time of the performance measurement

• Under changing conditions, any time delay between the performance and

irradiance/temperature measurements translates into irradiance/temperature

measurement errors

• The greater the time delay & change of conditions, the greater the error. (The Wireless

Sensor Kit keeps this delay minimal).

• The performance models translate these errors into apparent string-to-string variations

in Isc, Pmax, Performance Factor, etc.

• Translating data to STC suffers from the same type of error.

• Accuracy & precision cannot be regained by translation (to STC or other conditions)

• This limitation applies to all forms of performance measurement, not just curve tracing

Unstable sky conditions

I-V Measurement SetupExample: Measuring strings at a combiner box

Attach the thermocouple well away from module edges, using polyimide (Kapton) tape for best mechanical properties at high temperatures.

Measurement Process860kW 7-inverter system

Courtesy of Portland Habilitation Center and Dynalectric Oregon

1. Open the DC disconnect for the

sub-array you want to test.

Measurement Process


2. Locate the

combiner box

Measurement Process


3. Lift all of the fuses

Measurement Process


5. Push down one fuse

at a time, take the I-V

trace, view and save

results. Takes ~ 10-15

seconds per string.

4. Clip the PV Analyzer

to the buss bars

Displays Generated by theI-V Data Analysis Tool*

1950

2000

2050

2100

7

6

5

4

3

2

1

0

Fre

qu

en

cy

Pmax (Watts)

7

6

5

4

3

2

1

0

Cu

rren

t (A

mp

s)

0 100 200 300 400 500

Voltage (Volts)

7

6

5

4

3

2

1

0

Cu

rren

t (A

mp

s)

0 100 200 300 400 500

Voltage (Volts)

*Optional accessory $95

• A histogram worksheet is created for each performance parameter, revealing patterns in the data

• Each histogram represents the frequency of different values of a measured parameter, across a group of string measurements

• In this example, the spread of Pmaxvalues (upper graph) is largely explained by variation of irradiance (lower graph)

Histograms

• Fill Factor is a very useful diagnostic tool (details in the next slides)

• Compared with Pmax or Isc, Fill Factor has a weak dependency on irradiance, making it a useful metric even under conditions of rapidly changing irradiance

• In this example, notice the clean, bell-shape of the fill factor (lower graph), compared with the Pmaxdistribution (upper graph)

Fill Factor Histogram

Topics






Max power point

I-V Curve Signatures of PV Problems

Any reduction of the knee of the curve

means reduced output power.

Cu

rren

t (A

)

Voltage (V)

Isc

Voc

Shunt losses*

Series losses**

Mismatch losses (incl. shading)

Normal I-V curve

Reducedcurrent

Reducedvoltage

Conventional measurements do not reveal many of these effects.

Isc

Voc

Useful diagnosticsFill Factor, Current Ratio, Voltage Ratio

Cu

rren

t

Voltage

Fill Factor =Imp x Vmp (watts)

Isc x Voc (watts)

aSi: 0.50 – 0.70

xSi: 0.75 – 0.85

GaAs: 0.85 – 0.9=

Current ratioImp/Isc

Voltage ratioVmp/Voc

Imp

Vmp

Max Power Point

String of Field-aged, Early TF ModulesDegraded fill factor, lower output power

Array-as-sensor mode for viewing relative changes in curve shape

0

1

2

3

4

5

6

7

8

0 50 100 150 200 250 300 350 400

Voltage - V

Cu

rren

t -

A

String 4B14

String 4B15

Troubleshooting exampleAnomalous slope in string I-V caused by single high-resistance module

Example of a series resistance failureinside a module J-box

Probably failure mode:

Heat cycling � bond degradation � resistive heating

Dropped Cell String

• Shorted bypass diode, or

• Mismatch causing diode to turn on

when current starts flowing

I-V Curve of a Partially Shaded String

• Multiple ‘knees’ � multiple power peaks

• Peaks evolve as conditions change

• Inverter tries to find and track the highest peak

Cu

rren

t

Voltage

Isc

Voc

Pow

er

Partially shaded residential arrayMeasure the single string mounted along lower edge of roof

I-V Curve of the partially shaded stringSingle string mounted along lower edge of roof

Approximately 40% reduction in string’s output power

Shade 2 cells in the same cell-stringSingle module with 72 cells and 3 bypass diodes

Shading one

cell string

drops 1/3 of

PV module

voltage and

power

Shade 2 cells in adjacent cell-stringsSingle module with 72 cells and 3 bypass diodes

The same

amount of

shade,

oriented

differently,

drops 2/3 of

PV module

voltage and

power.

Summary of PV Analyzer benefits

•Single connection at combiner box

•Single measurement for each string

•Most complete performance measurement possible

• Independent Pmax measurement for each string

•Built-in PV models give instant performance check

•Don’t need to bring inverter online

•Automated data analysis

•Teaches us to “think like a PV array”

I

V

Testing PV array performance faster and better

Next topic: Insulation resistance testing

Topics






Insulation Resistance Testing of PV ArraysWhere are we?

1. The industry is trending toward the best practice of meg testing all systems during commissioning and at maintenance intervals.

2. Meg testing is not yet being done on all commercial systems, and is rarely done on residential systems.

3. Source circuits are often tested in aggregate, with string-level testing if the aggregate resistance is low.

4. Methods for sub-array test are not standardized or widely understood. Best reference is Bill Brooks’ ‘re-wrenches’ post.

5. In general, string or sub-array resistance values are compared for consistency rather than held to a specific spec.

6. PV module leakage is usually the dominant effect.

7. Insulation problems will be much more common as PV systems age.

Preparation: Open the DC Disconnect � Lift string fuses � Lift negative feeder cable(s)

Lift

Meg Testing at the Subarray Level

Lift

Example assumes a

negative-grounded array

Lift

Combiner box

Preparation: Open the DC Disconnect � Lift string fuses � Lift negative source cable

Lift Lift

Meg Testing at the String Level

Example assumes a

negative-grounded array

Lift

Free I-V Curve Posterhttp://www.solmetric.com/specialoffers.html

SolarPro Magazine, Aug/Sep 2011

Introducing the Solmetric PV Analyzer and the New Features of Version 2.0 PVA Software

Paul HerndaySenior Applications [email protected] 707-217-3094

November 8, 2012

Next PVA WebinarNovember 29, 10am PSThttp://www.solmetric.com/

webinar.html

introducing the solmetricpv analyzer

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