Verifying PV Array Performance Webinar, 3Dec2010

8/8/2019 Verifying PV Array Performance Webinar, 3Dec2010

1/61

Verifying PV Array Performance

Paul HerndayApplications Engineer

[email protected]

Peter HobergVP Sales and Marketing Bryan BassSales Engineer


2/61

Solmetric Solutions


3/61

Topics

PV Array Performance Verification

I-V Curve Measurement

The Solmetric PV Analyzer: PVA-600

Test Process

Live Demo

Example Measurement Results

Effect of Shade on array performance

Access to PV Strings for Testing


4/61

What is Performance Verification?

a reference PV string

a performance spec

a performance model

Showing that measured performance meets a

performance standard, to within a specified margin.

Depending on the objective, the standard may be:


5/61

Performance Verification Methods

Inverter readoutcompared withsystem model

I-V curve measurementscompared with

PV model

DC measurementscompared with

PV model

Basic Comprehensive

I

V


6/61

When Do You Do Performance Testing?

Construction (in-process QA) Commissioning

Verify correct installation & design

Assure client that contract has been met

Create a performance baseline Regular audits/checkups

Service Calls

Troubleshoot poor performance


7/61

Additional Objectives

Expose problems earlier

Troubleshoot more efficiently

Get better commissioning data in less time

Close out projects earlier ($$$ flows earlier)

More rapidly localize problems to PV modules or inverter

Provide data for PV module warranty claims


8/61

Topics




Test Process

Live Demo





9/61

Benefits of I-V Curve MeasurementCompared with DMM & Clampmeter Testing

Curren

t

Voltage

Isc(Clamp meter)

Voc(Multi-meter)

Powe

r

Full I-V curve Much more diagnostic value Automated Fast, & less chance of record-keeping mistakes

String-level maxpower value andmax power point


10/61

Fill FactorReduced square-ness can indicate aging, defects

Curre

nt

Voltage

Imp

Vmp

Max Power Point

Area A = Imp x Vmp Area B = Isc x Voc

Isc

Voc

Fill Factor =Area A

Area B


11/61

Series and Shunt LossesContributors to reduced fill factor

Current

Voltage

Imp

Vmp

Isc Max Power PointImp, Vmp

Voc

Shuntloss

Seriesloss

Shunt losses reduce the current ratio Imp / Isc

Series losses reduce the voltage ratio Vmp / Voc


12/61

I-V Measurement Methods

Load can be:ElectronicResistive

Capacitive

I sense

V sense

Current

Voltage

Load considerations:

Voltage & current range

Power dissipation

Sweep dynamics, esp sweep

rate, which must be slower to

accurately test high-efficiency

modules

PV module, string,

or sub-array


13/61

Topics




Test Process

Live Demo





14/61

Solmetric PV Analyzer: PVA-600

Measurement of I-V curve Comparison to model results

QuickVerify readout

Wireless interface

Low-cost

CONFIDENTIAL


15/61

Optional wireless sensor kitIrradiance & temperature sensors


16/61

PVA-600 Block Diagram (simplified)

CPU &wirelessmodule

I sense

V senseC

Control button w LED(isolated)

Battery chargingconnector(isolated)

(1 of 3)

Capacitive I-V method, 3 auto-selected capacitor values

Capacitors over-sized to accurately test high-efficiency PV modules

Electrically isolated circuitry means a system ground is not required

Protection for over-voltage, -current, -temperature, & reverse polarity


17/61

PV Models in the PVA-600For predicting PV array performance

Sandia National Labs PV Array Model Most comprehensive (30+ parameters)

~400 modules modeled, more available mid-2011

5-Parameter Model

Developed at U. Wisconsin, used by CEC for NSHP program

~1,700 PV modules modeled at this time

Simple Datasheet Model

Translates Pmax (STC) to actual irradiance & temperature User enters data sheet parameters

These 3 methods are available in the Solar Advisor Model (SAM) from NREL and areembedded in the Solmetric PV Analyzer.


18/61

PVA-600 Specifications

Max DC input voltage: 600V

Max DC input current: 20A*

Maximum DC power: 12 KW (instantaneous)

Min Voc: 20V

Min Isc: 1A

I-V measurement time: 80-240mS typical

Points per I-V trace: Up to 100, depends on test device

Storage capacity: 1,000+ (PC running PVA SW)

*Strings of high-efficiency modules should be measured singly,not in parallel


19/61

Topics




The Test Process

Live Demo





20/61

Steps to test a PV arrayat a combiner box

Hardware setup (onsite):

1. Place the irradiance & temperature sensors

2. Isolate the combiner box (open DC disco)

3. De-energize the buss bars (lift the fuses)

4. Clip test leads to the buss bars

1. Insert a fuse

2. Press Measure

3. View and save results

String measurement (per string):

PC setup (can be done in advance):

Set up the PV model (type & number of PV modules, etc)

Choose an array tree for saving test results


21/61

I-V measurement setupExample: measuring strings at a combiner box


22/61

Portland Habilitation Center PV System860kW 7-inverter system by Dynalectric Oregon


23/61

Testing at combiner boxes860kW System at Portland Habilitation Center, by Dynalectric Oregon


24/61

Combiner Boxes (two per inverter)860kW System at Portland Habilitation Center, by Dynalectric Oregon


25/61

Combiner Box860kW System at Portland Habilitation Center, by Dynalectric Oregon


26/61

Testing individual PV strings860kW System at Portland Habilitation Center, by Dynalectric Oregon


27/61

Array tree for saving I-V data

Measurement datafrom individual PVstring tests

Same hierarchyas the PV system


28/61

Overlay plots of I-V curves,raw and normalized

User-defined metrics

Performance analysisEvaluation of the array tree data

Histograms

Pmax, Fill factor,Imp/Isc, Vmp/VocIsc, Voc, etc

Reports


29/61

Topics




The Test Process

Live Demo





30/61

PVA-600 PV Model

Built-in models predict shapeof IV curve

Sandia, 5-Parameter, Simple

CONFIDENTIAL


31/61

PVA-600 Model

Built-in models predict shape of IV curve Sandia, 5-Parameter, Simple

CONFIDENTIAL

M d I V & P V


32/61

Measured I-V & P-V curvesRed dots are the model predictions

Shaded area is the inverters MPPT voltage range

Model set to array as sensor mode


33/61

Table View

CONFIDENTIAL


34/61

Verify View

CONFIDENTIAL


35/61

Irradiance and Temperature

CONFIDENTIAL


36/61

Topics




The Test Process

Live Demo





37/61

Setup for Static LoadI-V Measurement

Comparison


38/61


39/61

PV module with 100 ohm shunt resistance

Demonstration: Single PV module with external resistor


40/61

PV module with 2.5 ohm added series resistance

T bl h ti l


41/61

0

1

2

3

4

5

6

7

8

0 50 100 150 200 250 300 350 400

Voltage - V

Curren

t-A

String 4B14

String 4B15

Troubleshooting exampleComparison of typical (blue) and atypical (red) I-V curves

Troubleshooting example


42/61

Troubleshooting exampleProblem isolated to failed module

Irradiance changed between measurements


43/61

Field-aged thin film string

Array-as-sensor mode


44/61

Topics




The Test Process

Live Demo




PV Module with Bypass Diodes


45/61

+

PV Module with Bypass DiodesExample: 72-cell module

Partial shading


46/61

Partial shadingInverter must identify and track the right peak

Current

Voltage

Isc

Voc

Power

Max Power(until the shade pattern changes!)

Partially shaded residential array


47/61

Partially shaded residential arraySingle string, along lower edge of roof

Partially shaded residential array


48/61

Partially shaded residential arraySingle string, along lower edge of roof


49/61

Shading Pattern Effects

Sub-cell shading


50/61

Sub cell shadingBusiness card on 1 cell in a string of 15, 48-cell modules

Shade 2 cells in the same cell string


51/61

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

Shade 2 cells in adjacent cell strings


52/61

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

Shade taper along a cell-string


53/61

Shade taper along a cell-stringSingle module with 72 cells and 3 bypass diodes

Shade taper across a cell-string


54/61

Shade taper across a cell-stringSingle module with 72 cells and 3 bypass diodes

Shadow of leafless tree branch


55/61

Shadow of leafless tree branchSingle module with 72 cells and 3 bypass diodes

T i


56/61

Topics




The Test Process

Live Demo




String Access Points


57/61

DC

Disco

DCDisco

String Access PointsBest choice depends on system layout

InverterServicePanel

DC

Combiner

4

2 5DC

Disco

3

1

The challenges of string access


58/61

The challenges of string access

#1: Electrical isolation

#2: Electrical connection

Easy when strings are individually fused

Difficult in small, non-fused (2-string) residential systems

Commercial combiners typically provide enough space, but safetyshields may make block alligator clip access to the buss bars

Difficult in un-fused residential systems if the source conductors run

directly to inverter-integrated DC disconnect

Recommendation:Every PV system should have means for isolating and connecting to

string conductors for testing purposes, typically at the combiner

box or the inverter.

Lifti C d t f St i A


59/61

Lifting Conductors for String Access

Recommendation


60/61

Recommendation

Every PV system should have means to access PV strings at

combiner box (or residential inverter) for testing purposes.

Access means safely and quickly isolating and connecting to

individual strings.


61/61

Verifying PV Array Performance

Verifying PV Array Performance Webinar, 3Dec2010

Documents

Transcript of Verifying PV Array Performance Webinar, 3Dec2010