Solmetric PVA-1000S User Manual Download Page 9

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..................................................................................................................................... 7-1

I-V

URVE

ERMINOLOGY

.................................................................................................................................... 7-2

Performance Factor ........................................................................................................................................... 7-2

Fill Factor .......................................................................................................................................................... 7-2

................................................................................................................... 7-3

NTERPRETING

I-V

URVES

................................................................................................................................... 7-4

OTCHES OR STEPS

............................................................................................................................................ 7-7

Array Is Partially Shaded, or non-uniform soiling or debris is present ............................................................. 7-9

PV Cells Are Damaged ................................................................................................................................... 7-10

Cell String Conductor Is Short Circuited ........................................................................................................ 7-10

URRENT

................................................................................................................................................. 7-10

Uniform soiling ............................................................................................................................................... 7-11

Strip shade ...................................................................................................................................................... 7-11

Dirt dam .......................................................................................................................................................... 7-11

Module Degradation ....................................................................................................................................... 7-12

Incorrect PV Module Is Selected for the PV Model ....................................................................................... 7-12

Number of PV Strings in Parallel Is Not Entered Correctly in the Model ...................................................... 7-12

Irradiance Changed Between Irradiance and I-V Measurements .................................................................... 7-12

Irradiance Sensor Is Not Oriented in the Plane of Array ................................................................................ 7-12

Albedo Effects (reflection) Contribute Additional Irradiance ........................................................................ 7-12

Irradiance Is Too Low, or the Sun Is Too Close to the Horizon ..................................................................... 7-13

Manual Irradiance Sensor Is Not Accurate ..................................................................................................... 7-13

OW VOLTAGE

................................................................................................................................................. 7-13

PV Cell Temperature Is Hotter than the Measured Temperature .................................................................... 7-14

One or More Cells or Modules Are Completely Shaded ................................................................................ 7-14

One or More Bypass Diodes Are Conducting or Shorted ............................................................................... 7-14

OUNDER KNEE

................................................................................................................................................ 7-15

TEEPER SLOPE IN HORIZONTAL LEG

................................................................................................................ 7-16

Shunt Paths Exist in PV Cells or Modules ...................................................................................................... 7-16

Module I

Mismatch ....................................................................................................................................... 7-17

Tapered shade or dirt dam ............................................................................................................................... 7-17

ESS STEEP SLOPE IN VERTICAL LEG

................................................................................................................. 7-18

PV Wiring Has Excess Resistance or Is Insufficiently Sized ......................................................................... 7-18

Electrical Interconnections in the Array Are Resistive ................................................................................... 7-19

Series Resistance of PV Modules Has Increased ............................................................................................ 7-19

TRANSLATION OF I-V DATA TO STANDARD TEST CONDITIONS ..................................................... 8-1

ARAMETER DEFINITIONS

...................................................................................................................................... 8-1

RANSLATION EQUATIONS

..................................................................................................................................... 8-2

Figures

IGURE

EST LEADS AND CLIPS RATED FOR USE WITH THE

PVA-1500S ............................................................... 1-18

IGURE

ELCOME SCREEN

................................................................................................................................... 1-27

IGURE

REREQUISITES DIALOG

........................................................................................................................... 1-28

IGURE

NSTALLATION DEFAULT LOCATION DIALOG

............................................................................................ 1-28

................................................................................................ 1-29

Summary of Contents for PVA-1000S

Page 1: ...i Solmetric PV Analyzer I V Curve Tracer User s Guide PVA 1500V2 V3 with SolSensor 300V2 PVA 1500S with SolSensor 300 PVA 1000S with SolSensor 200 PVA 600 with SolSensor ...

Page 2: ...of a computer for example a hard disk CD ROM or other storage device If the PC Software is permanently installed on the hard disk or other storage device of a computer other than a network server and one person uses that computer more than 80 of the time then that person may also use the PC Software on a portable or home computer We hereby grant you a nonexclusive license to use one copy of the Em...

Page 3: ...ge that occurs as a result of the Buyer s system product or the Buyer s use of Solmetric products To the extent permitted by applicable law THE FOREGOING LIMITED WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES OR CONDITIONS EXPRESS OR IMPLIED AND WE DISCLAIM ANY AND ALL IMPLIED WARRANTIES OR CONDITIONS INCLUDING ANY IMPLIED WARRANTY OF TITLE NONINFRINGEMENT MERCHANTABILITY OR FITNESS FOR A PARTICULAR ...

Page 4: ...Software Embedded Software Hardware and Documentation and supersedes any and all prior oral or written agreements negotiations or other dealings between us concerning the PC Software Embedded Software Hardware or Documentation 2 This license agreement may be modified only in writing and written documentation must be signed by Buyer and Solmetric 3 In the event of litigation between Buyer and Solme...

Page 5: ...Markings 1 12 PVA 1000S Safety and Regulatory 1 12 Warnings Cautions and Notes 1 12 Declaration of Conformity 1 13 Cleaning 1 13 Instrument Markings 1 13 PVA 600 Safety and Regulatory 1 13 Warnings Cautions and Notes 1 13 Declaration of Conformity 1 14 Cleaning 1 14 Instrument Markings 1 14 SolSensor 300 and SolSensor 300V2 Safety and Regulatory 1 15 Warnings Cautions and Notes 1 15 Declaration of...

Page 6: ...attery on the PVA 1000S and PVA 600 I V Measurement Unit 1 33 Charging the SolSensor Battery of the Original SolSensor 1 34 YOUR WIRELESS NETWORK 1 35 Your PVA 1500xx SolSensor 300xx Wireless Network 1 35 Your PVA 1000S 600 SolSensor Wireless Network 1 36 2 SETTING UP AND USING THE I V MEASUREMENT UNIT AND SOLSENSOR 2 38 SYSTEM CONTROLS AND SETTINGS 2 38 Operational States of the PVA 1500xx I V Me...

Page 7: ... Help Menu 3 15 USING THE TAB SCREENS 3 16 Traces Tab 3 16 Table Tab 3 21 History Tab 3 22 Meg Test Tab 3 23 DESCRIPTION OF THE EXPORTED I V DATA FILE 3 24 BASIS OF PV PERFORMANCE PREDICTIONS 3 29 SolSensor Irradiance Calibration 3 29 Irradiance Measurement 3 30 Prediction of PV Performance 3 30 Translation of Measured Values to STC 3 30 Measurement of Isc 3 31 PVA PC SOFTWARE UPDATES 3 31 PVA 150...

Page 8: ...UBLESHOOTING USING STATUS MESSAGES 5 1 TROUBLESHOOTING BY SYMPTOM 5 4 6 MEASURING IRRADIANCE TEMPERATURE AND TILT 6 1 INTRODUCTION 6 1 MEASURING IRRADIANCE WITH SOLSENSOR 6 3 SolSensor irradiance sensor 6 3 Preliminary Irradiance 6 3 SolSensor Precautions 6 3 Protecting the Irradiance Sensor Element 6 3 Cleaning the Irradiance Sensor 6 3 Orienting and mounting the irradiance sensor 6 4 Albedo effe...

Page 9: ... to the Horizon 7 13 Manual Irradiance Sensor Is Not Accurate 7 13 3 LOW VOLTAGE 7 13 PV Cell Temperature Is Hotter than the Measured Temperature 7 14 One or More Cells or Modules Are Completely Shaded 7 14 One or More Bypass Diodes Are Conducting or Shorted 7 14 4 ROUNDER KNEE 7 15 5 STEEPER SLOPE IN HORIZONTAL LEG 7 16 Shunt Paths Exist in PV Cells or Modules 7 16 Module Isc Mismatch 7 17 Tapere...

Page 10: ...ELESS NETWORK IS ESTABLISHED AFTER WHICH IT REMAINS ON 2 46 FIGURE 27 TRIPOD MOUNTING SETUP 2 48 FIGURE 28 EXAMPLE OF I V MEASUREMENT UNIT TEST LEADS CLIPPED TO THE BUSS BARS OF A PV COMBINER BOX 2 50 FIGURE 29 POWERING UP THE I V MEASUREMENT UNIT 2 51 FIGURE 30 PVA SOFTWARE MAIN SCREEN 3 2 FIGURE 31 FILE MENU 3 3 FIGURE 32 THE SITE INFO SCREEN OF THE NEW PROJECT WIZARD 3 4 FIGURE 33 CONTROLS IN T...

Page 11: ...STEEP THAN PREDICTED SLOPE IN THE VERTICAL LEG OF THE I V CURVE 7 13 FIGURE 64 I V CURVE MEASUREMENT SHOWING ROUNDER KNEE THAN PREDICTED BY THE PV MODEL 7 15 FIGURE 65 AN I V CURVE SHOWING STEEPER SLOPE IN THE HORIZONTAL LEG OF THE I V CURVE 7 16 FIGURE 66 MEASUREMENT WITH LESS STEEP SLOPE IN THE VERTICAL LEG OF THE I V CURVE 7 18 Tables TABLE 1 PVA 1500S ELECTRICAL AND MECHANICAL SPECIFICATIONS 1...

Page 12: ...xii This page is intentionally left blank ...

Page 13: ...to your PC Sensor measurements are also triggered simultaneously with the I V curve measurement and saved with the I V curve data The I V curve of a PV module string harness or array provides a detailed description of its energy conversion ability The curve nominally ranges from the short circuit current Isc at zero volts to the open circuit voltage Voc at zero current At the knee of a normal I V ...

Page 14: ...lecting Help About If you want to update just download the newer version and run the installer It is free and takes only a few minutes Version 4 x PVA software supports all the curve tracers that use SolSensor The PVA 600 which uses the earlier Wireless Sensor Kit requires version 2 2 6851 Computer Minimum System Requirements Test and Supported Operating System Windows 10 Windows 8 Windows 7 32 an...

Page 15: ... plug with plug on alligator clips for PVA 1500xx rated to 1500V DC 1 set MC 4 connector tool User s Guide available in the HELP menu of the PVA software and from http www solmetric com downloads pva html Quick Reference Card SolSensor Equipment SolSensor unit The PVA 1500S operates with the SolSensor 300 and the PVA 1500V2 V3 operates with the SolSensor 300V2 K type thermocouple temperature senso...

Page 16: ...ution 25 mV Current resolution 2 mA Measurement cycle time 6 23s typical measurement to measurement depending on voltage 2 I V sweep duration 3 0 05 2s Typically 0 2s for PV strings Number of I V trace points 100 or 500 user controlled Wireless range direct to PC open line of sight 100m US only Range for Europe pending evaluation at European mandated maximum radiated power level Operating temperat...

Page 17: ...Automatically selected Measurement sweep time depends upon the characteristics of the test device PV module string or array electrical characteristics 4 The measurement is controlled via wireless link from the user s tablet or notebook PC PVA 1500xx Test Lead and Clip Specifications Table 2 Electrical and mechanical specifications for the test leads and clips provided with the PVA 1500xx Parameter...

Page 18: ...strings Minimum recommended repetition rate 15s Number of I V trace points 100 or 500 user controlled Wireless range direct to PC open line of sight 100m US only Range for Europe pending evaluation at European mandated maximum radiated power level Operating temperature range 10 to 65ºC Storage temperature range 20 to 65ºC Operating humidity 90 RH non condensing Avoid exposing a cold instrument to ...

Page 19: ...stics of the test device PV module string or array electrical characteristics 4 The measurement is controlled via wireless link from the user s tablet or notebook PC PVA 600 Specifications Safety Rating Measuring Category CATIII 600V Table 4 PVA 600 electrical and mechanical specifications Parameter Specification Current Measurement Range1 0 to 20 A dc Voltage Measurement Range Voc 20 to 600 V dc ...

Page 20: ...ds upon the characteristics of the test device PV module string or array electrical characteristics 3 At ends of the primary test leads permanently attached to the I V Measurement Unit SolSensor 300 and SolSensor 300V2 Specifications Table 5 SolSensor 300 and SolSensor 300V2 specifications Parameter Specification Irradiance Sensor type Silicon photodiode with corrections for temperature spectral a...

Page 21: ...ly less than 1s Wireless range open line of sight 10m US only Range for Europe pending evaluation at European mandated maximum radiated power level Operating temperature range 10 to 45ºC Storage temperature range 20 to 65ºC Operating humidity 90 RH non condensing Avoid exposing a cold instrument to warm and humid air as condensation will result Store the instrument in the same conditions in which ...

Page 22: ...formation on accurate irradiance measurements Resolution 1 W m2 Measurement interval 0 1 s Measurement bandwidth approximately 10 Hz Temperature Sensor type Type K thermocouple Two inputs Measurement range 0 100ºC Accuracy Typically less than 2C including inherent thermocouple limitations Resolution 0 1ºC Measurement interval 1 s Tilt Sensor type Electronic Measurement range 0 90 deg from horizont...

Page 23: ...1 cm Depth 7 cm Ingress protection IP65 Safety and Regulatory PVA 1500xx Safety and Regulatory Warnings Cautions and Notes Before operating the PVA 1500xx familiarize yourself with the following notations WARNING A Warning calls attention to a procedure which if not performed correctly could result in personal injury or loss of life Do not proceed beyond a warning note until the indicated conditio...

Page 24: ...tion manual symbol The product is marked with this symbol when it is necessary for you to refer to instructions in the manual This symbol indicates separate collection for electrical and electronic equipment mandated under EU law as of August 13 2005 All electrical and electronic equipment are required to be separated from normal waste for disposal Reference WEEE Directive 2002 96 EC The IEC HV sy...

Page 25: ...he manufacturer s declaration that the product meets the requirements of the applicable EC directives The C tick mark is the manufacturer s declaration that the product complies with the EMC regulations of Australia and New Zealand The instruction manual symbol The product is marked with this symbol when it is necessary for you to refer to instructions in the manual This symbol indicates separate ...

Page 26: ...ot attempt to clean internally Instrument Markings The PVA 600 have the following markings on the front and or rear panel Familiarize yourself with these markings before operating the PVA 600 The instruction manual symbol The product is marked with this symbol when it is necessary for you to refer to instructions in the manual The cTUVus mark signifies that the product has been thoroughly tested a...

Page 27: ...or white disc is cleaned using a more carefully controlled process to avoid damaging the irradiance sensor See the SolSensor 300 Precautions Cleaning section for details WARNING To prevent electrical shock disconnect SolSensor from the battery charger before cleaning Use only a dry cloth or cloth slightly dampened with water to clean the external enclosure parts Do not attempt to clean internally ...

Page 28: ...destruction of the instrument Do not proceed beyond a caution note until the indicated conditions are fully understood and met NOTE A Note provides important or special information Declaration of Conformity A declaration of conformity is available upon request Cleaning To remove dirt or dust from the SolSensor enclosure use a dry or slightly dampened cloth only The irradiance sensor white disc is ...

Page 29: ...lectrical and fire safety regulations of Canada and the United States The instruction manual symbol The product is marked with this symbol when it is necessary for you to refer to instructions in the manual This symbol indicates separate collection for electrical and electronic equipment mandated under EU law as of August 13 2005 All electrical and electronic equipment are required to be separated...

Page 30: ...ame as the leads pictured in Figure 1 so it is ok to continue using them WARNING Operating temperature and humidity of the test leads and clips are more narrowly specified than the PVA 1500xx I V Measurement Units For details see PVA 1500xx Test Lead and Clip Specifications in this Guide WARNING Do not use the PVA 1500xx series test leads and clips to measure mains circuits circuits energized by e...

Page 31: ...ve the connector saver jumpers connected to the PVA 1500xx s primary PV leads at all times Make all your PV circuit connections disconnections to the connector saver jumpers not to the PVA 1500xx connectors CAUTION When the lifetime of the connector save jumpers has been reached typically 100 connection disconnection cycles remove them cut them in half to prevent further use and recycle them Repla...

Page 32: ... to the test device PV module string or array with the correct polarity Protect the primary test lead connectors of the PVA 1500xx by installing connector saver jumpers Replace the connector saver jumpers when they have reached 100 connections Special 1500v test leads and alligator clips are provided with the PVA 1500xx Do not substitute other test leads Also do not use the test leads from a PVA 1...

Page 33: ...PVA 1000S Precautions Using PV Connector Saver Jumpers PV connectors regardless of manufacturer are not designed for large numbers of connection disconnection cycles For this reason the PVA 1000S is shipped with connector saver jumpers attached to its own PV connectors The connector saver jumpers are intended to take wear and tear greatly extending the life of the PV connectors on the test leads a...

Page 34: ... eye protection Wear fall protection where required Assume that metal surfaces are energized unless proven otherwise Isolate the PV source circuit under test from the inverter and from other PV source circuits before making any connections to the test device PV module string or array Always pause the measurement sequence using the LED illuminated pushbutton switch on the I V Unit before connecting...

Page 35: ...he battery charger supplied by Solmetric Measuring High Efficiency PV Modules High efficiency PV modules produce a short but intense inrush current at the start of the I V measurement In extreme cases this inrush current can trigger the I V Measurement Unit s over current protection circuit causing the I V Unit to internally disconnect from the PV source circuit and temporarily enter the over curr...

Page 36: ...tial dangers of each PV system and take appropriate precautions FAILURE TO TAKE APPROPRIATE SAFETY PRECAUTIONS COULD LEAD TO PERSONAL INJURY OR LOSS OF LIFE Never work alone Do not use the PVA 600 in wet environments Do not operate or subject the PVA 600 to temperatures beyond the published operating and storage temperature specifications Wear electrical safety gloves Wear eye protection Wear fall...

Page 37: ... contains a small lithium battery and should not be disposed of with general refuse Dispose of the battery in accordance with all local codes and regulations for products containing lithium batteries Contact your local environmental control or disposal agency for further details WARNING Only use the battery charger supplied by Solmetric Measuring High Efficiency PV Modules High efficiency PV modul...

Page 38: ...lled water Let the excess water runoff carrying dust and dirt with it Dry the white acrylic disc with a soft clean dry cloth Never use soap or chemical solutions or abrasive cloths WARNING To clean the irradiance sensor use only distilled water and a clean soft dry cloth Soap or chemical cleaners and coarse cloth can cause permanent damage to the acrylic material and degrade irradiance measurement...

Page 39: ...software USB flash drive into the slot on your Windows computer 2 If the welcome screen does not automatically open as shown in Figure 2 either double click on the setup exe file on the USB flash drive or run setup exe from the Run dialog Alternately the installation file is available at http www solmetric com downloads pva html Figure 2 Welcome screen 3 Follow the instructions in the welcome scre...

Page 40: ...n location A default location is provided Figure 4 Installation default location dialog 6 Partway through the installation of the PVA 1000S or PVA 600 the following screen will appear asking you to insert the wireless USB adapter that will communicate with the I V Unit NOTE The wireless USB installation is not required for PVA 1500xx Go to step 9 ...

Page 41: ...the software will operate normally but will not be able to communicate with the I V Measurement Unit or SolSensor When you later insert the Wireless USB Adapter while the PVA software is running driver software will be loaded from the Wireless USB Adapter This completes the software installation Figure 6 Insert wireless USB adapter PVA 600 and PVA 1000S only 8 When the Wireless USB Adapter driver ...

Page 42: ...e shortcut icon on your desktop as shown in Figure 8 Or select the list of programs in the Start menu then select Solmetric PV analyzer Solmetric PV Analyzer The icons differ by the version number of the PVA software v3 for the PVA 1000S and PVA 600 and v4 for the PVA 1500xx Figure 8 Launching the PVA software 11 The screen shown in Figure 9 will appear while the software is accessing the PV model...

Page 43: ...1 x software you will see the Models and Traces folders in the list If v1 x software was never installed on this computer those two folders will not appear Figure 11 Directory structure of PVA software Updating the PV Equipment Databases If your PC is connected to the internet when you start the PVA software the software will check whether updated PV module or inverter equipment databases are avai...

Page 44: ...g indicator feature is not available for the PVA 1000S or PVA 600 Figure 12 Battery charger connector on the I V Measurement Unit Charging the battery can take up to 6 hours Charge the battery every night before use in the field The PVA software interface will warn you when the battery level is low and close to shutting down the I V Measurement Unit Also you can check the battery voltage level by ...

Page 45: ... glows steadily A SolSensor 300 can be upgraded to a SolSensor 300V2 Return to factory is required Contact Solmetric www Solmetric com for assistance You can check the battery voltage level by clicking on the Ready button in the PVA software following an I V measurement or by selecting Battery Level in the Utility menu There is no charging indicator on SolSensor 300 SolSensor 200 or the original S...

Page 46: ...oftware user interface displays the Disabled alert below the Measure Now button when the battery is nearing the end of its charge In this state no measurements can be taken CAUTION The I V Measurement Unit cannot be operated while the battery is charging Charging the SolSensor Battery of the Original SolSensor The SolSensor battery is not removable It may be recharged by attaching the battery char...

Page 47: ...he SolSensor are relayed through the I V Unit To see a diagram of your wireless network select the network icon at the lower left corner of any screen in the PVA software Figure 16 The WiFi network of the PVA 1500xx SolSensor 300xx and your PC Your I V Unit and SolSensor 300xx come from the factory paired to one another A SolSensor can only be paired to one unique I V Unit at a time A SolSensor ca...

Page 48: ...The wireless network that interconnects your PC to the I V Measurement Unit and SolSensor uses a Zigbee protocol and operates in the 2 4 GHz frequency band NOTE Your I V Measurement Unit SolSensor and Wireless USB Adapter come from the factory paired to one another They are labeled with matched Network ID numbers that look like this example Network ID 0F96E4A7 This protects their communication net...

Page 49: ...combiner box which happens to be farther away from SolSensor The mesh network may then switch to indirect communication to SolSensor using the I V Measurement Unit as the relay station Table 7 Direct and indirect wireless links between PC PVA and SolSensor Communication route Interface to I V Measurement Unit Interface to SolSensor PC to I V Measurement Unit Direct PC to SolSensor Direct PC to I V...

Page 50: ...ates a Wi Fi hotspot to which you will connect via your PC s network list When the PVA 1000S or PVA 600 is turned on it searches for the matched Wireless USB Adapter For the network to be established the Wireless USB Adapter must be plugged into your PC the PV Analyzer software must be launched and the COM port into which the USB Adapter is plugged must be selected in the Utility menu Figure 19 LE...

Page 51: ...rements cannot be taken while charging Re pairing with SolSensor Five flashes and a longer pause repeated Press 5x in rapid succession to initiate the re pairing This functionality is available in the PVA 1500V2 V3 only After you see groups of five flashes on the I V Unit press SolSensor s LED button 5x in rapid succession to initiate re pairing To reset IV Unit or SolSensor Hold the pushbutton do...

Page 52: ...l flash in groups of five until re pairing is achieved If it is necessary to reset either the PVA 1500xx I V Unit or the SolSensor 300xx just hold the LED pushbutton down for 5 seconds and release Operational States of the PVA 1000S 600 I V Measurement Unit Table 9 describes the operational states of this instrument Table 9 Pushbutton LED table for the PVA 1000S 600 I V Units I V Unit State LED Be...

Page 53: ...ar the PV circuits to be measured 2 Ensure that the connector saver jumpers are installed on the primary test leads The connector saver jumpers protect the PVA s main lead connectors from the wear and tear of repeated interconnections They should not be removed except for replacement 3 If necessary connect alligator clip leads or extension cables to the connector saver jumpers Use only clip leads ...

Page 54: ...o be compromised by soiling Cover the irradiance sensor with the protective cap whenever it is not actually mounted and in use CAUTION To clean the irradiance sensor use only distilled water and a soft cloth A soft microfiber cloth and a spray bottle of distilled water are supplied as standard accessories to SolSensor Spray the white sensor element and gently wipe it with the microfiber cloth Do n...

Page 55: ...er and later in the day Figure 21 SolSensor tool lanyard secured to a racking member To mount SolSensor follow these steps 1 Remove SolSensor the Module Frame Clamp and the tool lanyard from the soft case 2 Attach the tool lanyard to an eyelet on SolSensor Then loop the lanyard around a racking member and clip it back on itself as shown in Figure 21 3 Place SolSensor against the top horizontal leg...

Page 56: ...ich it could slip allowing SolSensor to come loose 5 Squeeze the clamp mechanism until SolSensor is firmly held against the side of the module frame Figure 23 Tip of frame clamp properly seated on inside surface of module frame 6 Inspect the mounting and assure that the posts and blue ears are in contact with the upper edge of the module frame If there is space under one or both of the blue ears t...

Page 57: ...side far enough under the module to avoid the cooler outer edges When testing single free standing modules attach the thermocouple tip as shown in Figure 25 For most accurate temperature measurements use a wide piece of high temperature polyester tape Other types of tape will sag at high temperature allowing the tip of the thermocouple to pull away from the backsheet of the module Use firm pressur...

Page 58: ... blink on and off as it attempts a wireless connection and will glow steadily when the connection is made The SolSensor 300xx links to the PVA 1500xx I V Unit which relays its communications with the PC Make sure the I V Unit is turned on The original SolSensor links to the wireless USB adapter plugged into your PC Figure 26 SolSensor pushbutton with LED lit LED blinks until wireless network is es...

Page 59: ...x which reduces wireless range As described above you can use a bar to mount SolSensor to the torque tube of a single axis tracker Transmission range can also sometimes be increased by locating SolSensor on the top frame edge of a top row module or near the end of an array where there is better line of sight to where the I V Measurement Unit is set up If it is not possible to achieve the necessary...

Page 60: ...llowing you to set the tilt independent of the azimuth Typically you will mount the tilt unit on the panning unit which is in turn mounted on the leveling indicator and the leveling unit and the tripod itself 6 Adapter plate Firmly attach this plate to the bottom of SolSensor and to the top of the tilt unit To properly deploy SolSensor on a tripod setup follow these steps The instructions assume t...

Page 61: ...hermocouple 6 Adjust the leveling unit to center the bubble and then lock the leveling unit 7 Rotate the panning unit to orient SolSensor to the desired true azimuth then lock panning unit Be sure your compass has been adjusted for the local magnetic declination A magnetic declination calculator is available at http www ngdc noaa gov geomag web id declinationFormId To avoid distortion of the earth...

Page 62: ...ngs run directly to the inverter isolate the strings from one another by pulling their series fuses 2 Press the button on the I V Measurement Unit to disable the I V sweep WARNING PV circuits continue to present danger of electrical shock while the system is paused FAILURE TO TAKE APPROPRIATE SAFETY PRECAUTIONS COULD LEAD TO PERSONAL INJURY OR LOSS OF LIFE 3 Following safe operating procedures con...

Page 63: ...nt Unit can be turned on before or after starting the PC software When using the PVA 1000S or PVA 600 the wireless USB adapter should be plugged into your PC prior to launching the PVA software Press the power button once on the I V Measurement Unit Refer to Figure 29 below Figure 29 Powering up the I V Measurement Unit The LED will blink on and off until the I V Unit connects to your PC at which ...

Page 64: ... take another measurement just press the LED pushbutton again WARNING If the LED on the PVA is illuminated either solid on or flashing do not connect or disconnect the PV leads Over Temperature Protection Built in safeguards prevent the I V Measurement Unit from operating at potentially damaging internal temperatures The I V Measurement Unit absorbs energy with each measurement and across a series...

Page 65: ...measurements e g while moving to the next combiner box then the thermal capacity is more than 800 measurements at 25 deg C ambient temperature and 250 measurements at 45 deg C ambient After reaching the thermal capacity every minute of cooling i e no measurements increases the number of subsequent measurements that will be allowed before thermal capacity will be reached again CAUTION The rigid gre...

Page 66: ...in excess of 1100 V is detected the I V Measurement Unit switches into disabled mode and the status indicator displays Disabled Reduce the voltage below 1000V to resume normal operation If a voltage more than 1500 V is detected the I V Measurement Unit is internally disabled to prevent continued use of a damaged unit Resetting or restarting the I V Measurement Unit will not re enable it Please con...

Page 67: ...is designed to tolerate that intense pulse from a single high efficiency module or string but measuring two or more in parallel will damage the instrument CAUTION Do not measure high efficiency PV modules or strings in parallel Reverse Polarity Protection If the I V Measurement Unit is connected with the wrong polarity across a string an internal protection diode opens the circuit the I V Measurem...

Page 68: ...1 Getting Started 2 56 Over Voltage Warnings ...

Page 69: ...or example in a 50 MW project create a separate Project for each pad or each inverter This will also improve the speed of the Data Analysis Tool that you will use to analyze your data NOTE Be sure that your PC is set to the correct date and time and that the time zone and daylight savings setting are correct These parameters are used to calculate the position of the sun at the exact moment of the ...

Page 70: ...ll the software where you took your measurement in the array This allows the PV model to retrieve wiring characteristics and other details that are unique to that location and also tells the software where to save the measurement result The predictive model points Isc max power point and Voc are displayed on the I V curve graph only after you have identified the location of the measurement Main Sc...

Page 71: ...nu Browse Project Used to access previously saved Projects for retrieval Recent Projects Provides convenient access to recent Projects Export Trace for Active Measurement Exports the measurement results for the measurement currently displayed in the Traces screen as a csv file Export Traces for Entire System Exports the measurement results for the currently loaded Project as a Windows folder tree ...

Page 72: ...ture for horizontal single axis tracking systems which allows the I V curves to be taken while the tracker is working This has the advantage of taking all of your measurements at the greatest possible irradiance level The user enters the morning azimuth of the array and at solar noon the software adds 180 degrees for the afternoon azimuth Figure 33 shows example settings for a fixed non tracking a...

Page 73: ...ne These values must be correct for the irradiance sensor to correctly interpret the irradiance and for the PVA software to correctly calculate the Performance Factor The time date and time zone cannot be corrected after the measurements have been taken This caution applies to the PC that is controlling the I V curve measurement process not the PC on which the PVA project file was originally creat...

Page 74: ...ping the name of the manufacturer When your manufacturer appears in the short list click on it to select it Then repeat that process for the model number of the PV module If you wish to add that module to your Favorites list click the star icon After you have selected the model number the performance parameters for that module appear in the scrolling table as shown in Figure 37 Figure 37 Selection...

Page 75: ... the final step in creating a Project This screen is used to describe your PV system hardware The information you enter here is used for two purposes 1 Create a visual tree representation of your array that you can touch to save and recall your measurement data 2 Create the PV model that the software uses to predict expected performance An example of a finished array tree is shown in Figure 39 For...

Page 76: ... default system tree shown in Figure 40 Figure 40 The default system tree in the Symmetrical Tree Builder Edit the tree so that it matches the design of your PV field You can change any of the following Number of layers in the tree Names of the layers The quantity in each layer Represent items by number or alphabetically Number of modules in each string To add a layer to the tree highlight the nex...

Page 77: ...s Strings PV modules Which elements can nest under a Combiner Groups Combiners Strings PV modules Which elements can nest under a String PV modules TIP Rename the layers to agree with the naming conventions used in your engineering drawings so that there will be no confusion about where measurements were made Try not to use more non electrical layers than necessary block field parking lot etc Also...

Page 78: ...energy is always lost in the wiring and the purpose of this feature is to enable the software to calculate those losses of voltage and power so that they do not make the PV modules look like they are underperforming To use the wiring properties controls first select a level of the tree to which you want the changes to apply The changes you make will be applied to all strings at or below the level ...

Page 79: ...Highlight the Project file you want to recycle and copy and paste it 5 Rename the copy with the name of your new project 6 From the PVA software File menu select Browse Project and navigate to the new Project file 7 Use the screens in the Properties menu to edit the Project as needed You will need to delete all of the data to avoid confusion with the new data The easiest way to do this is to delet...

Page 80: ...V curve Inverter Green shading indicating the max power voltage tracking range for the selected inverter To show this legend at the bottom of the Traces screen check Show legend under chart Show Meg Test Tab Click the check box to display the Meg Test tab at the left side of the measurement screen Utility Menu The Utility Menu provides access to housekeeping functions and miscellaneous tools The U...

Page 81: ...ng Irradiance Temperature and Tilt for guidance on sensor choices Global Sensor Configuration The controls shown in the figure below allow you to change the sensor choices for all of the measurements currently saved in the project Select the desired sensors from the dropdown lists CAUTION This action cannot be undone Create a backup file before taking this action See Chapter 6 Measuring Irradiance...

Page 82: ...es that accompany status and disable messages The battery voltage at which the unit will shut down is also reported Wait 30 seconds to check the battery voltage if you just removed the I V unit from the charger or just turned on the I V Unit This allows internal functions to complete for a more accurate battery reading In the PVA 1500xx software the battery levels of both the I V Measurement Unit ...

Page 83: ...0 communications between the instruments and the PC can be direct or indirect relayed by either of the instruments and their SolSensor Refer to this screen to find out what firmware version is running in the I V Unit and SolSensor User s Guide Accesses the PVA User s Guide The guide can be downloaded and printed if desired a hard copy of the guide is not provided with the products In addition the ...

Page 84: ... expected locations of Isc maximum power point and Voc The graph area can display four types of information selectable by the user from the View menu I V curve This solid red curve displays the measured I V points transmitted from the I V Measurement Unit Points below 0 V are not displayed I V curve prediction markers The three red dots are the predicted I V points for the short circuit current Is...

Page 85: ...saved it the ID will show the date time and the location in the system tree and indicate that the data has not been saved If you have assigned and saved the trace the ID will show the date time and location in the system tree Also shown in the measurement ID is a link showing the time offset from GMT Click on the link to check the time zone Current A Displays the current scale along the vertical a...

Page 86: ...you want the model points to appear but don t want to save the trace just click the Assign button After a measurement has been saved the Assign and Save button becomes the Reassign button Click the Reassign button if you accidentally saved a measurement to the wrong location in the system tree When the tree appears just click on the correct location and then click Assign and Save again The locatio...

Page 87: ... Utility menu No I V Unit in Status indicator PVA 1000S PVA 600 Displayed when communication between the I V Measurement Unit and the USB wireless adapter at the PC is not established Click on the question mark icon for information to aid in troubleshooting the problem The most common reasons for this state include wireless out of range or the I V Measurement Unit has turned itself off after 15 mi...

Page 88: ... 600 Displayed if SolSensor is turned off or out of wireless range of the PC However if the wireless USB adapter is not plugged in or that COM port is not selected in the Utility menu the message will be No USB Wireless Summary Bar Located directly below the displayed I V curve the Summary Bar displays the results of the currently displayed measurement The Performance Factor represents the measure...

Page 89: ... of the measured parameters to Standard Test Conditions 1000W m2 and 25 C Pmax W Measured maximum power values in Watts Vmp V Voltage at the maximum power point Imp A Current at the maximum power point Voc V Open circuit voltage The Voc measurement is performed by a high impedance voltmeter circuit immediately before the actual I V sweep This Voc value is accurate even if the measured I V curve do...

Page 90: ...lds up to 32 results Once that limit is reached the oldest measurement result is dropped from the table each time a new measurement is taken The parameters displayed in the History tab are identical to the results shown in the Table tab The History tab is especially useful for inspecting the agreement between measurements taken at a combiner box during commissioning tests and also for displaying s...

Page 91: ...used to record resistance measurement results obtained from a separate instrument such as the Megger MIT430 Insulation Resistance Tester Data is entered manually The Meg Test tab is hidden by default To enable this tab use the control in the View menu Figure 49 Meg Test tab ...

Page 92: ...Automatically assigned identification number The ID number increments by one count each time a measurement is added Resistance The measured value of insulation resistance in megohms Click in this field to enter the value manually Voltage The voltage at which the insulation resistance was measured Click in this field to enter the value manually Description Optional description of the device under t...

Page 93: ...rarchy It is also possible to view the individual I V trace data files using a program that can read csv files such as Microsoft Excel tm This section describes the organization and contents of the csv file Figure 50 shows the header information section of the csv file and the following table describes its contents Figure 50 Header Information section of the exported csv file Table 15 Description ...

Page 94: ...e fitted curve This value of Vmp is then used to interpolate Imp max power current from the I V curve This method reduces the amount of uncertainty contributed by electrical noise in the current and voltage measurements The Data Analysis Tool DAT re calculates Pmax for its purposes of charting and reporting data It fits a fourth order polynomial so there is often a very slight difference in Vmp Im...

Page 95: ...ugged into SolSensor TC1 socket Temperature Thermocouple 2 The temperature reading from the thermocouple plugged into SolSensor TC2 socket Pitch The angle of SolSensor long axis relative to horizontal Roll The angle of rotation of SolSensor about its long axis Tilt SolSensor tilt calculated from the pitch and roll Below Figure 53 shows the Model Details section of the exported csv file and Table 1...

Page 96: ...el Mfr Manufacturer of the PV module Module Model Model number of the PV module of Modules in String Number of modules connected measured in series of Strings in Parallel Number of strings measured in parallel Inverter Mfr Manufacturer of the inverter Inverter Model Model number of the inverter Wire AWG Wire gauge of the conductors between the point of measurement and the PV source Wire Length Len...

Page 97: ...ther factors The following discussion outlines the process by which SolSensor is calibrated and measures irradiance and the process by which the PVA software predicts the expected I V curve SolSensor Irradiance Calibration The SolSensor factory calibration process involves this sequence of steps Calibration of the electronic tilt sensor Calibration of the angular response of the irradiance sensor ...

Page 98: ...irradiance that the module can convert into electricity Prediction of PV Performance The PVA software compares the measured I V curve to the predictions of built in PV performance models The Performance Factor is calculated from this comparison The prediction process involves these steps User creates a Project and inputs all of the required parameters including selection of their PV module from th...

Page 99: ...al charge At the start of the sweep this reservoir of charge quickly flows into the pre charge capacitor stepping its voltage such that the first I V point is in positive voltage territory In some instances especially with 500 points the first few I V points may be slightly elevated due to the residual discharge of the PV module capacitance In such cases you may see a slight flat plateau in the I ...

Page 100: ...sly connected to the I V Unit If your instrument is a PVA 1500S with SolSensor 300 and your instrument s firmware is less than version 1 1 the first version that s capable of field firmware update the PC software recommends returning the instruments to Solmetric for installation of field update capable firmware You have the option to do so or not The following table summarizes your options PVA PC ...

Page 101: ...n the Help menu to make sure that you have selected the right version of software for the version of PVA hardware that you will be using The PVA 1500xx uses version 4 x software and the PVA 1000 and PVA 600 use version 3 x software To check the latest available version number visit http www solmetric com downloads pva html Create a Project in the PVA software See the earlier chapters in this User ...

Page 102: ...nce for your measurements Performance measurements are best performed in the range of 700 1000 watts per square meter If possible choose a day when the skies will be clear If there are clouds try to trigger your measurements at moments when there are no clouds near the sun Also try to do your measurements in a 6 hour window centered on solar noon If you are measuring a horizontal single axis track...

Page 103: ...by Solmetric d with your PVA Launch the PVA software Double click the PVA icon and the software will start Make sure that you are running the most recently available version of software To check your current software version click About in the Help menu Compare it with the most recently available version which you ll find at www Solmetric com under Support Downloads PV Analyzer Software and Docume...

Page 104: ...and straighten the lead Avoid kinking the lead Insert its yellow plug in the T1 socket at the end of SolSensor Straighten the last few inches of the thermocouple lead The tiny ball at the end is where temperature is measured Place the last few inches of the thermocouple wire against the back of the PV module Choose a location that is away from the cooler outer edges of the array Apply the green di...

Page 105: ...ent way to clip in the common lead you may be able to insert a short insulated wire pigtail in a spare terminal and connect the alligator clip to the pigtail Are you measuring strings in parallel If you are measuring multiple strings in parallel be sure that the maximum PV current you plan to measure is always less than the specified maximum current of the I V Measurement Unit To estimate the maxi...

Page 106: ...bined current is within the specified current range of the I V Measurement Unit Note that in some locations the irradiance can greatly exceed 1000 watts per square meter If that is the case and the modules are directly facing the sun the string currents can be significantly higher than the STC currents listed on the PV module label Select the first PV circuit to be measured If you are using the st...

Page 107: ...ement of the session or if the string under test has very different electrical behavior from the ones you measured before it It is a side effect of a feature in which the PV Analyzer keeps improving its performance by optimizing its internal configuration based on the previous measurements Inspect the sensor values that were saved with the measurement They appear directly below the I V curve graph...

Page 108: ...en helpful to clear the History table before moving on to the next combiner box From time to time back up your data The PVA software will remind you to back up your data Always do this It is possible for PVA Project files to become corrupted Also create a backup when you are finished measuring a PV installation Select Backup Project from the File menu This space is left blank intentionally ...

Page 109: ... TAKE APPROPRIATE SAFETY PRECAUTIONS COULD LEAD TO PERSONAL INJURY OR LOSS OF LIFE Ready message When Ready appears in the Status indicator the wireless link to the I V Measurement Unit is established and the equipment is ready to take a measurement Clicking on the Status indicator in this state pops up a message indicating the present battery voltage compared with the shutdown battery voltage If ...

Page 110: ... use Current in excess of xxA was detected In this case clicking on the Disabled message pops up text advising that the maximum input current specification has been exceeded If you are measuring strings in parallel reduce the number of parallel strings High efficiency PV modules and some thin film technologies cause a high current pulse to flow at the start of an I V measurement If you are measuri...

Page 111: ...ou may need to go to the Utilities menu select Settings and follow the instructions to locate the USB adapter Be aware that each I V Measurement Unit is matched with the USB adapter it was shipped with mixing them up will make communications impossible Matching USB adapters to I V Measurement Units allows multiple PV analyzers to be used on large projects without disturbing each other s wireless l...

Page 112: ...sor 300xx units are paired at the factory to the specific I V unit that shipped with your SolSensor If you have a new SolSensor that was never paired to your I V unit or it has lost its pairing it may be re paired to the I V unit by following the steps in Operational States of the PVA 1500xx I V Measurement Units Troubleshooting by Symptom No I V Measurement Unit message This message in the Status...

Page 113: ...ndirect one instrument relays the signal to the other Indirect links allow operation at greater distances from the PC but the network may be unavailable for 10 20 seconds during the switch between direct and indirect A brief dropout can also occur between the PVA 1500xx and your PC If the link does not restore in 2 minutes you may be out of wireless range Similarly communication with the SolSensor...

Page 114: ...uit current For best results perform measurements of fixed arrays during the hours of maximum irradiance Strings of low Isc modules can be tested in parallel to increase current and reduce noise I V curve drops to zero current at one or more points This can occur if there is an unstable electrical connection in the PV circuit being measured This is not a problem with the I V Measurement Unit In st...

Page 115: ...5 Troubleshooting PVA Operation 5 7 Solmetric Technical Support Phone 707 823 4600 X2 Toll Free 877 263 5026 Email support solmetric com ...

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Page 117: ...you ll need to make informed choices for your specific application Measuring irradiance presents a number of requirements and challenges Irradiance must be measured in the plane of the array POA Irradiance may not be uniform across the surface of the array due to shading and albedo effects as well as local cloud effects Irradiance can vary rapidly Irradiance sensors may have different spectral res...

Page 118: ...rrents and wind An air gap between a backside temperature sensor and the actual backside surface results in significant temperature error Massive temperature sensors particularly bulky RTD devices do not track rapid changes in module temperature Surface and material issues limit the accuracy of infrared temperature measurements These topics are all discussed in this chapter The PVA software provid...

Page 119: ...irradiance sensor white acrylic disc covered using the supplied black rubber cover Remove the cover after mounting SolSensor in the plane of the array and replace the cover again before moving SolSensor to another location WARNING The white acrylic eye of the irradiance sensor is a precision optical element which must be kept in like new condition to assure accurate measurements It is easily damag...

Page 120: ...s PV arrays and irradiance sensors can pick up significant amounts of irradiance reflected off of surrounding surfaces Examples of albedo effects include reflections from adjacent roof surfaces building walls and other PV arrays The strength of the albedo effect is not as much a function of the perceived color of the surface as one might think Even the surface of a blacktop parking lot reflects su...

Page 121: ...g cell technologies that have a poor spectral match to the SolSensor silicon irradiance sensor Since the predicted Isc value is forced to agree with the measured Isc value it is easy to notice any deviations between the shapes of the measured and predicted I V curves The From I V irradiance option also has certain limitations Uniform soiling is interpreted as reduced irradiance and thus does not c...

Page 122: ...ring PV Module Backside Temperature with a Thermocouple Measurement of backside temperature is one of the traditional methods used by I V curve tracers It has several benefits and limitations The Backside Thermocouple method provides these benefits It is a direct method with no dependence on a PV model It enables you to choose the location for temperature measurement it s best to choose an average...

Page 123: ... the tape to do its job 2 The second reason is that because heavier gauge thermocouple wires are more massive the thermocouple is not able to respond as quickly to temperature variations caused by wind or changes in irradiance Under changing conditions a measurement delay translates into a measurement error 3 The third reason for using a relatively fine wire gauge is that the thermocouple wires th...

Page 124: ...s firmly pressed against the surface If there is a wrinkle in the tape at the location of the thermocouple bead start over Choosing a location to mount the thermocouple on the module or array Even on a windless day with steady irradiance there will be a temperature gradient across the module or array with the edges typically run cooler than the middle Some guidelines apply When testing a single is...

Page 125: ...IR thermometers allow continuous adjustment for emissivity Some models provide only a high medium low setting which limits your accuracy Some use a factory preset emissivity and are not user adjustable PV module backsides do not all have the same emissivity so you much either adjust the emissivity control of the instrument to match the backside surface or change the emissivity of the backside surf...

Page 126: ...r Rapid temperature changes can result from variable cloudiness and also from gusty wind Since the predicted Voc value the right hand red dot superimposed on the displayed I V curve is forced to is forced to agree with the measured Voc value it is easier to notice any deviations between the shapes of the measured and predicted I V curves The From I V temperature option also has certain limitations...

Page 127: ...ed using the From I V method At irradiance values between 400 and 800W m2 the PVA software progressively shifts between the thermocouple and From I V methods This strategy employs the From I V method at high irradiance values where it is most accurate and relies on the backside thermocouple at low irradiance values where there is a relatively small temperature offset between module backside and ce...

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Page 129: ...e most common patterns of deviation and identifies possible causes for these deviations Inputs to the PV Model The modeling features of the PV analyzer predict the shape of the I V curve for comparison with measured results For the prediction to be valid the inputs to the model must be valid The model inputs are PV model parameters stored in the PVA PC software Number of PV modules in series Numbe...

Page 130: ...ared Like most array performance measurements the comparison is more accurate if the irradiance levels are high Performance measurements taken at less than 400W m2 irradiance are not good predictors of how the string will perform at high irradiance If a PV string or module is operating correctly and is not shaded soiled or age degraded and is measured at high irradiance the measured Performance Fa...

Page 131: ...e red line as a starting point for the discussion The predicted I V curve shape determined by the PVA built in PV model is shown by the three dots The power versus voltage curve is also displayed blue line Like the I V curve itself the P V curve represents the entire family of points at which the PV circuit could be operated or loaded The P V curve is generated by multiplying I x V for at every po...

Page 132: ...ls have sharper knees thin film modules usually have more gradual knees The three PV model points are defined from left to right as follows SC First point at the predicted short circuit current Isc MP Second point the predicted maximum power point Imp Vmp OC Third point at the predicted open circuit voltage Voc Interpreting I V Curves PV module or string performance problems will cause deviations ...

Page 133: ...7 Interpreting Measured I V Curves 7 5 5 4 Rounder knee 6 ...

Page 134: ... values instrument settings or measurement connections Always select the correct PV module from the on board PV module list double check the measurement connection and ensure that irradiance measurements are taken in the plane of the array and are as simultaneous with the I V sweep as possible Small deviations between the measured and predicted I V curves are very common given the uncertainty asso...

Page 135: ...7 Interpreting Measured I V Curves 7 7 1 Notches or steps Examples of this type of deviation are shown in Figure 60 Figure 61 and Figure 62 Figure 60 The effect of partial shading on a string I V curve ...

Page 136: ...ications of mismatch between different areas of the array or module under test Although the figures shown above all involve shading mismatch can have other causes The notches in the I V curve are indications that bypass diodes are activating and passing current around module sub strings internal cell strings that are not able to pass the full current of the stronger modules Potential causes are su...

Page 137: ...le that has 3 bypass diodes will slightly reduce the current in 24 cells Bypass diodes prevent that cell from going into reverse bias If the PV module is supplying a load and the current demanded by the load is above the reduced current provided by the partially shaded cells the bypass diode will begin conducting and pass current around the shaded cell strings Without the bypass diode present the ...

Page 138: ...l a portion of the cell may be electrically isolated This has the same effect on the I V curve as shading of an equivalent area of a normal cell A notched I V curve can result depending on the severity of the PV cell damage Cell String Conductor Is Short Circuited A localized hot spot as discussed in X Steeper Slope in Horizontal Leg can also cause a bypass diode to turn on effectively removing a ...

Page 139: ...ly shaded by the top edge of a neighboring row of modules For modules with conventional bypass diode configurations the response to this shade is different between portrait and landscape orientations of the shaded module In portrait orientation uniform partial shading across the lower row of cells causes a reduction in Isc and Imp just as if there were less light If the shading is identical across...

Page 140: ...est when the sky conditions are not stable for example partially cloudy and a manual irradiance sensor is being used The process of orienting the manual sensor noting the value and entering the value into the PVA software takes much more time than the automated process used by SolSensor Irradiance Sensor Is Not Oriented in the Plane of Array The accuracy of the irradiance measurement is very sensi...

Page 141: ...thin a two hour interval either side of solar noon See this web site to determine solar noon for your location http www esrl noaa gov gmd grad solcalc Manual Irradiance Sensor Is Not Accurate Hand held irradiance sensors vary widely in their calibration accuracy response to off angle light and spectral match to the array being measured All of these variables affect accuracy 3 Low voltage An exampl...

Page 142: ...letely Shaded Hard shade on an entire cell causes its associated bypass diode to begin conducting a very low current making it look like Voc has shifted downward If you are uncertain check the value of Voc that the PVA software lists in the Table tab This value is measured under open circuit conditions just a moment before the I V measurement actually begins One or More Bypass Diodes Are Conductin...

Page 143: ...ment showing rounder knee than predicted by the PV model Rounding of the knee of the I V curve can be a manifestation of the aging process Before concluding that this is the case check the slopes of the horizontal and vertical legs of the I V curve If they have changed it can produce a visually similar effect in the shape of the knee ...

Page 144: ...g power short circuiting a part of a cell or module Some amount of shunt current within a solar cell is normal although higher quality cells will have a higher shunt resistance and hence lower shunt current Shunt current can lead to cell heating and hotspots appearing in the module encapsulant material Shunt current is typically associated with highly localized defects within the solar cell or at ...

Page 145: ...will have some mismatch due to slight manufacturing variations slightly different installation angles or special cases of shading and non uniform soiling Special cases of shading can also cause more slope in the upper leg of the I V curve The most common case takes place in multi row tip up arrays in which the upper edge of one row of modules casts a sliver of shadow across the lower edge of anoth...

Page 146: ... of PV modules has increased PV Wiring Has Excess Resistance or Is Insufficiently Sized The electrical resistance of the PV modules and their connecting cords are accounted for in the models stored in the PV analyzer module database If the PV output conductors for example from string to combiner box are very long or the wire gauge unusually small or both the PV model can be adjusted to account for...

Page 147: ...lls may increase series resistance Corrosion damage is more common in aged modules in humid or coastal environments Manufacturing defects within the module can also result in poorly interconnected solar cells If you see a burn mark along one of the module s internal ribbon conductors it may be an indication that an interconnection is becoming more resistive These burn marks tend to be located at t...

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Page 149: ...ormance parameters derived from the I V curves to STC conditions Fast changes in irradiance and temperature caused by rapidly moving clouds will be difficult to correct accurately so clear days are still required for quality end results Translation will introduce error in proportion to the span of the translation This should be taken into account when assessing the consistency of performance acros...

Page 150: ...from the sensor and adding the temperature differential typically 3 degrees Translation equations The basic translation model used here makes the following approximations 1 Pmp is proportional to E the irradiance 2 Imp does not depend on temperature 3 Vmp is independent of E 4 Pmp varies with temperature according to γmpp taken from the datasheet 5 Voc is independent of E In light of these approxi...

Page 151: ...ollows where the subscripts are defined as m measured and trans translated Isctrans Iscmeas Etrans Emeas 1 αIsc 100 Tmeas Ttrans Voctrans Vocmeas 1 βVoc 100 Tmeas Ttrans Imptrans Impmeas Etrans Emeas Vmptrans Vmpmeas 1 γmpp 100 Tmeas Ttrans Pmptrans Pmpmeas Etrans Emeas 1 γmpp 100 Tmeas Ttrans ...

Page 152: ...8 Translation of I V Data to Standard Test Conditions 8 4 This page is intentionally left blank ...

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