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Solmetric PVA-600 User Manual

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Solmetric PVA-600
PV Analyzer
User's Guide

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  • Page 1 Solmetric PVA-600 PV Analyzer User‘s Guide...
  • Page 2 Software Title Part No. 600-90001 Solmetric remains the owner of all right, title and interest in Version 1.0.2985.0 the PC Software, Embedded Software, and Documentation. December 2010...
  • Page 3 You agree on termination of this license to either return to us or destroy all copies of the PC Software, Solmetric does not warrant any damage that occurs as a result of the Buyer‘s system, product, or the Buyer‘s use of...
  • Page 4 This license agreement may be modified only in writing and written documentation must be signed by Buyer and Solmetric. In the event of litigation between Buyer and Solmetric concerning the PC Software, Embedded Software, Hardware, or Documentation, the prevailing party in the litigation will be entitled to recover attorney fees and expenses from the other party.

  • Page 5: Table Of Contents

    NSTRUCTIONS PVA S ................. 2-7 NSTALLING RIVERS FOR THE PTIONAL ENSOR ............................2-7 HARGING THE ATTERY USING THE PVA-600 ............................ 3-1 ........................3-1 YSTEM ONTROLS AND ETTINGS PVA-600 States ..............................3-1 PVA-600............................. 3-3 ETTING P THE PVA S ...................... 3-4...
  • Page 6 ..........................3-9 OLTAGE ROTECTION ..........................3-9 URRENT ROTECTION ........................3-10 EVERSE OLARITY ROTECTION USING THE PVA-600 SOFTWARE ......................4-1 ............................4-1 CREEN VERVIEW ................................4-2 ITLE ................................4-2 File Menu ................................4-2 Model Menu ..............................4-2 Utility Menu ..............................4-6 Help Menu ................................
  • Page 7 PVA-600 ...................... 2-6 IGURE AUNCHING THE SOFTWARE 4. PVA-600 ...................... 2-6 IGURE SOFTWARE USER INTERFACE 5. B PVA-600 ................... 2-7 IGURE ATTERY CHARGER CONNECTOR ON THE 6. LED- ......................3-1 IGURE ILLUMINATED BUTTON SWITCH 7. PVA S ............................3-4 IGURE ENSOR 8.
  • Page 8 22. S ......................4-19 IGURE IMPLE PERFORMANCE MODEL 23. I ..........................4-20 IGURE NVERTER SCREEN … 24. C ....................... 4-20 IGURE HANGE INVERTER SCREEN 25. I ..................4-21 IGURE NVERTER ESCRIPTION AND ALUE COLUMNS 26. W ............................. 4-21 IGURE IRING SCREEN 27.
  • Page 9 Tables 1. PVA-600 ...................... 1-3 ABLE ELECTRICAL SPECIFICATIONS 2. PVA-600 ....................1-4 ABLE MECHANICAL SPECIFICATIONS 3. PVA S ..................1-5 ABLE ENSOR IT TEMPERATURE SPECIFICATIONS 4. PVA S ..................1-5 ABLE ENSOR IT IRRADIANCE SPECIFICATIONS 5. PVA-600 ............................3-2 ABLE STATES 6.
  • Page 10 The page left blank intentionally.

  • Page 11: Introduction

    1 Introduction Overview The PVA-600 PV Analyzer is a portable test instrument designed to measure the current- voltage (I-V) curves of PV modules and strings and immediately compare the results to on-board PV model predictions. Measurement results are easily saved for future reference and analysis.

  • Page 12: Computer Minimum System Requirements

    Systems that do not meet these requirements may not operate correctly. PVA-600 Equipment  I-V Measurement Unit  Soft Case  Wireless USB Adapter and PVA-600 Software Application  Battery Charger  MC-4 to MC-4 Connector-Saver Cable (2)  MC-4 to MC-3 Adapter Cable (2) ...

  • Page 13: Electrical Specifications

    50% at 40ºC. Higher humidity levels should not affect the performance or safety of the PVA-600. Conventional PV modules and strings may be measured in parallel, up to the current limit specified here. High-efficiency modules should NOT be measured in parallel.

  • Page 14: Mechanical Specifications

    1 Introduction Mechanical Specifications Table 2. PVA-600 mechanical specifications Parameter Specification PV Connectors MC-4 Weight 9.2 lbs (not including weight of the soft case) Height 15 in Width 8 in Depth 5 in At ends of the primary test leads permanently attached to the I-V Measurement Unit.

  • Page 15: Pva Sensor Kit Specifications (Optional)

    1 Introduction PVA Sensor Kit Specifications (Optional) Table 3. PVA Sensor Kit temperature specifications Parameter Specification Thermocouple Type Range -100º C to 1260º C (-148º F to 2300º F) Resolution 1º C Accuracy (greater of) ±0.5% of rdg or ±1.0º C (1.8 º F) Table 4.

  • Page 16: Safety And Regulatory

    Declaration of Conformity A declaration of conformity is available upon request. Cleaning To remove dirt or dust from the external case and/or hard enclosure of the PVA-600, use a dry or slightly dampened cloth only. WARNING To prevent electrical shock, disconnect the PVA-600 from the PV system and/or battery charger before cleaning.

  • Page 17: Instrument Markings

    1 Introduction Instrument Markings The PVA-600 has 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.
  • Page 18 1 Introduction The page left blank intentionally.

  • Page 19: Getting Started

    When the lifetime of the connector-saver jumper has been reached, it should be replaced, cut in half to prevent re-use, and recycled. With the use of connector-saver jumpers, the life of the primary test leads of the PVA-600 should be extended to 5,000 to 10,000 connections.
  • Page 20 I-V unit before connecting or disconnecting the test leads of the PVA- 600.  Do not use the PVA-600 to test devices that produce more than the instrument‘s specified maximum current and voltage.  Connect the test leads to the test device (PV module, string, or array) with the correct polarity.

  • Page 21: Battery Precautions

    Battery Precautions CAUTION The PVA-600 contains a 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.

  • Page 22: I-V Measurements

    Isc, Voc, and so on, are displayed in a table. Logging Mode The PVA-600 also provides a logging mode that captures I-V curves over a period of time. I-V curves are measured at time intervals, and summary data (not entire I-V data sets) is saved.

  • Page 23: Installation Procedure

    Alternatively, the installation file is available at www.solmetric.com. Figure 1. Welcome screen Follow the instructions in the welcome screen to install the PVA-600 software. The drivers for the wireless USB adapter will also be installed. The directory structure shown in Figure 2 is created in the Documents directory.

  • Page 24: Special Xp Operating System Instructions

    2 Getting Started When the installation process is finished, start the PVA-600 software by double- clicking on the shortcut icon on your desktop as shown in Figure 3. Or, select the list of programs in the Start menu, then select Solmetric>PV Analyzer>Solmetric PV Analyzer.

  • Page 25: Installing Drivers For The Optional Pva Sensor Kit

    Installing Drivers for the Optional PVA Sensor Kit The PVA Sensor Kit uses the same drivers as the PVA-600. Therefore, once the PVA- 600 Software has been installed, no additional installation is required for using the PVA Sensor Kit.
  • Page 26 The software 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 PVA-600 should not be operated while the battery is charging.

  • Page 27: Using The Pva-600

    Wireless USB Adapter that is plugged into your notebook or tablet computer, to establish a network for control and data transfer. Figure 6. LED-illuminated button switch PVA-600 States The PVA-600 has the following states:  Power off  Network search ...

  • Page 28: Table 5. Pva-600 States

    3 Using the PVA-600 Table 5. PVA-600 states PVA-600 State Description Power Button State Power Off PVA-600 is turned off. LED Off. Network Search Press the power button once. LED Blinking. Communication between the I-V Measurement Unit and the Wireless USB Adapter is attempted.

  • Page 29: Setting Up The Pva-600

    PVA-600 is placed, and exposure to direct sunlight. CAUTION Place the PVA-600 in the shade to reduce the likelihood of thermal shutdown. Never place the PVA-600 on an asphalt driveway or on a roof in direct sunlight.

  • Page 30: Setting Up The Optional Pva Sensor Kit

    3 Using the PVA-600 Setting Up the Optional PVA Sensor Kit Figure 7 shows the PVA Sensor Kit components that will be set up. Figure 7. PVA Sensor Kit Connect the Sensor Wireless USB Adapter to a USB port in your computer.

  • Page 31: Connecting To The Solar Pv Equipment

    3 Using the PVA-600 Ensure that the temperature transmitter is not resting on the ground or on the roof, and is not placed against a metal surface. Elevating the temperature transmitter improves the transmission range. To turn on the irradiance and temperature transmitters, press the I/0 button on each transmitter.

  • Page 32: Figure 8. Example Of Pva-600 Test Leads Clipped To The Buss Bars Of Apv Combiner Box

    Figure 8. Example of PVA-600 test leads clipped to the buss bars of a PV combiner If one or both of the terminals of the test device must be some distance from the I-V Measurement Unit, use extension cables made of UL (or equivalent) listed PV wire, with correctly installed connectors.

  • Page 33: Powering-Up The I-V Measurement Unit

    3 Using the PVA-600 Powering-Up the I-V Measurement Unit Press the power button once on the I-V Measurement Unit. Refer to Figure 9. Figure 9. Powering-up the I-V Measurement Unit The LED will begin to blink indicating that the I-V Measurement Unit is attempting to establish communication with the wireless USB adapter connected to the PC.

  • Page 34: Sweep Disabled

    Unit to disable the measurement sequence. Pressing the red button again restarts the measurement sequence. WARNING If the LED on the PVA-600 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.

  • Page 35: Operating Under High-Temperature Conditions

    I-V sweeps. Over-Voltage Protection If greater than 600 V dc is applied to the I-V Measurement Unit, the PVA-600 detects the over-voltage condition and switches into disabled mode automatically and an I-V measurement does not take place.

  • Page 36: Reverse Polarity Protection

    3 Using the PVA-600 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 PVA-600 switches into disabled mode, and an I-V measurement does not take place. 3-10...

  • Page 37: Using The Pva-600 Software

    4 Using the PVA-600 Software Main Screen Overview The PVA-600 software runs on a PC and is the main user interface for making measurements, storing data, and viewing data. The main screen is divided into three main areas as shown in Figure 10.

  • Page 38: Title Bar

    4 Using the PVA-600 Software Title Bar The product name is displayed in the Title Bar. In addition, the Minimize and Close buttons are displayed and function in the same way as they do in other Windows® applications. Menu Bar File Menu Table 6.
  • Page 39 CAUTION – Conventional PV modules and strings can be measured in parallel up to the specified current limit of the PVA-600. However, high-efficiency modules and strings should NOT be measured in parallel. The large current transient produced by these modules can electrically stress the instrument.
  • Page 40 4 Using the PVA-600 Software Name Description This is the resistance of the external wiring calculated from user entries of wire length and wire gauge: Rseries = [Resistance per Foot] * Wire Length Resistance Per Foot is calculated from the table below: The first column is Wire Gauge (AWG);...
  • Page 41 PV modules. Horizontal plane measurements are not supported. Determine irradiance from IV curve: PVA-600 extracts irradiance mathematically from measured I-V data. This method is used when the main objective is to demonstrate consistency among PV strings and to observe subtle deviations from predicted I-V curve shape.

  • Page 42: Utility Menu

    Wireless I-V Measurement Unit USB Interface: select communications port to use for communication between the PVA-600 and the PC. Select the port with the ―+‖ symbol. Wireless Sensor USB Interface: select communications port to use for communication between the PVA Sensor Kit and the PC.

  • Page 43: Help Menu

    4 Using the PVA-600 Software Help Menu Table 9. Help menu description Name Description User’s Guide Accesses the PVA-600 User‘s Guide. About Accesses the software version number and software build date. Tabs Table Tab The Table tab presents a summary of the I-V measurement results displayed in the Traces tab, as well as predicted values from the selected performance model.

  • Page 44: Table 10. Table Tab Description

    4 Using the PVA-600 Software Table 10. Table tab description Name Description Active Indicates the table containing the latest measurement data. Predicted Displays the predicted values from the selected performance model. Measured Displays actual measured values most recently measured. Pmax (W) Displays the predicted and measured maximum power values in Watts.
  • Page 45 4 Using the PVA-600 Software Name Description No USB Wireless Displayed when the USB Wireless Adapter is not found. When displayed, clicking on this indicator accesses information to aid in (indicator) troubleshooting the problem. No I-V Unit (indicator) Displayed when communication between the I-V Measurement Unit and PC is not established.

  • Page 46: Traces Tab

    4 Using the PVA-600 Software Traces Tab The Traces tab displays the most recent measurement results along with the predicted shape of the I-V curve (if an advanced PV model is selected). Figure 12 is an example of the Traces tab screen.

  • Page 47: Verify Tab

    4 Using the PVA-600 Software Table 11. Traces tab description Name Description Current (A) Displays the current scale along the vertical axis on the left side of the graph. Voltage (V) Displays the voltage scale along the horizontal axis of the graph.

  • Page 48: Figure 13. Verify Tab

    4 Using the PVA-600 Software Figure 13. Verify tab Table 12. Verify tab description Name Description Power Displays the power scale along the vertical axis on the left side of the graph. Performance Factor Displays the ratio of actual to predicted maximum power as a percentage.

  • Page 49: Logging Tab

    4 Using the PVA-600 Software Logging Tab The Logging tab displays maximum power values (equivalent to those shown in the Verify tab) which have been accumulated (or logged) over a time period. Figure 14 is an example of the Logging tab screen. You can clearly see when the modules entered a late afternoon shade condition.

  • Page 50: Sensors Tab

    4 Using the PVA-600 Software As each value is acquired by the PVA-600 it is stored in a csv file in the Log Files folder. The intent is to show the performance of the array over a time period. This time period may be from a few minutes to an entire day.

  • Page 51: Setting Up A New Model

    Start the PVA-600 Software On the PC, double-click on the Solmetric PV Analyzer icon to start the PVA-600 application. The Table screen appears as shown in Figure 16. Figure 16. Table screen...

  • Page 52: Enter The Name And Notes

    4 Using the PVA-600 Software Enter the Name and Notes In the Model menu, select New… to access the screen used to set up a new model as shown in Figure 17. Figure 17. Model screen Click in the Name text box and enter the desired name for this model. The model file will be saved in the Models folder.

  • Page 53: Table 15. Time Zones

    4 Using the PVA-600 Software Click in the Time Zone text box and enter the time zone for this model. The numeric entry is in hours relative to GMT as shown in Table 15. Table 15. Time zones Time Zone GMT –...

  • Page 54: Select The Modules And Enter String Information

    4 Using the PVA-600 Software Select the Modules and Enter String Information Click on the Modules/String button to access the screen used to set up new module and string information as shown in Figure 19. Figure 19. Modules/String screen If you will be using a Sandia or 5 Parameter performance model, select Detailed Performance Model and perform the following steps: Click on the Change…...

  • Page 55: Figure 21. Module Property And Value Columns

    4 Using the PVA-600 Software Figure 21. Module Property and Value columns Click on the OK button. If you will be entering performance model parameters from the manufacturer‘s published specifications, select Simple Performance Model and perform the following steps: Click on the Edit… button to access the screen used to enter the manufacturer‘s published specifications as shown in Figure 22.

  • Page 56: Select An Inverter

    4 Using the PVA-600 Software Select an Inverter Click on the Inverter button to access the screen used to select the manufacturer and model number of the inverter as shown in Figure 23 and perform the following steps: Figure 23. Inverter screen Click on the Change…...

  • Page 57: Select Wire Gauge And Enter Wire Length

    Click in the Wire Length (Feet) text box and enter the one-way length of the PV output conductors from the ends of the strings/module under test to the point where the PVA-600 is connected. For instance, if you have two 10 foot leads running between the I-V unit and the string, enter ―10‖ (not ―20‖).

  • Page 58: Select The Sensor Methods

    4 Using the PVA-600 Software Select the Sensor Methods Click on the Sensor Methods button to access the screen used to set up irradiance and temperature methods as shown in Figure 27. Figure 27. Controls for deriving the irradiance and/or temperature from measured I-V curve (array-as-sensor method) Figure 28.

  • Page 59: Enter Array Slope And Azimuth

    PV cell temperature. If you want the PVA-600 to extract the irradiance mathematically from the measured I-V data, select Determine irradiance from I-V curve. If you are using a manual sensor to measure irradiance, select Enter solar irradiance manually and enter the irradiance in the Irradiance (POA) text box.

  • Page 60: Copying An Existing Model File

    4 Using the PVA-600 Software Figure 30. Array Plane screen Click in the Slope (degrees) text box and enter the slope of the array. Click in the Azimuth (degrees from true North) text box and enter the azimuth of the array in degrees from true North.

  • Page 61: Making Measurements

    Ensure that the PVA Sensor Kit components are connected properly. Refer to Setting Up the Optional PVA Sensor Kit. On the PC, double-click on the Solmetric PV Analyzer icon to start the PVA-600 application. Turn on the irradiance and temperature transmitters by pressing the I/0 button once.

  • Page 62: Figure 32. Open A Model File

    Turn on the I-V Measurement Unit by pressing the red power button shown in Figure 33. The LED will begin to blink indicating that the PVA-600 is attempting to establish communication with the wireless USB adapter connected to the PC. Once communication is established, typically in less than 20 seconds, the Measure Now button will become active.

  • Page 63: Figure 34. Irradiance And Temperature Communication Status

    4 Using the PVA-600 Software Figure 34. Irradiance and temperature communication status If the Wireless Interface: Not Found message appears, select Settings from the Utility menu and set up the wireless sensor USB interface manually. Select the communications ports with the ―+‖ sign.

  • Page 64: Figure 35. Predicted /M

    4 Using the PVA-600 Software Figure 35. Predicted/Measured columns in Table tab 13. Click on the Traces tab to view the I-V and P-V graphs as shown in Figure 36. NOTE The first time a measurement is made, the data may not scale properly because the PVA- 600 uses the first measurement to check the voltage and current details of the circuit under test before choosing the most appropriate internal settings.

  • Page 65: Saving Data To A Directory Tree

    Figure 37. The Performance Factor is the ratio of actual to predicted maximum power as a percentage. Figure 37. Performance Factor value 16. Pause the measurement sequence of the PVA-600 by pressing the power button shown in Figure 33. WARNING Do not disconnect from the tested string unless the red power button is turned off.

  • Page 66: Saving Trace Data

    4 Using the PVA-600 Software Figure 38. Creating a directory tree In Figure 38 measurement result files are shown in one of the combiner folders. Saving Trace Data The Traces tab is the main screen for graphically analyzing I-V measurement results.

  • Page 67: Using Snapshot

    4 Using the PVA-600 Software Using Snapshot The Snapshot feature places the most recent measurement results in a column in the right hand table for comparison with previous or subsequent measurements. You can store up to 25 columns of data.

  • Page 68: Viewing And Analyzing Your Data

    Figure 40. Trace data The first 12 lines of the csv file contain information used for debugging, servicing, or troubleshooting of the system by Solmetric engineers. If the Sandia or 5 Parameter Performance Model is used, Lines 13 through 18 display the...

  • Page 69: Figure 41. Predicted Current

    4 Using the PVA-600 Software Figure 41. Predicted current, voltage, and maximum power points NOTE If the Sandia Model is selected and the array itself is being used as the sensor, the end points of the measured I-V trace will match the predicted points. If the 5 Parameter Model is selected and the array itself is being used as the sensor, the end points may not match the predicted points.

  • Page 70: Setting Up Data Logging Mode

    0 will be displayed and stored. On the PC, double-click on the Solmetric PV Analyzer icon to start the PVA-600 application. Click on the Logging tab to access the screen shown in Figure 42.

  • Page 71: Figure 43. Start Logging Screen

    4 Using the PVA-600 Software Figure 43. Start Logging screen Click in the Sample Rate (minutes) text box and enter the sample rate (from 1 to 60 minutes). Click on the Change File… button to enter a filename and select a storage location for the log file.

  • Page 72: Viewing And Analyzing Logging Data

    4 Using the PVA-600 Software Viewing and Analyzing Logging Data In Logging mode, as each value is acquired by the PVA-600 it is stored in a csv file in the Log Files folder in the following format:  Date (mm/dd/yyyy) ...

  • Page 73: Troubleshooting Pva-600 Operation

    4 Using the PVA-600 Software Troubleshooting PVA-600 Operation This section describes steps to troubleshoot the operation of the PVA-600. Troubleshooting of actual PV systems is not included. “Disabled” message If the message ―Disabled‖ appears in the indicator panel directly below the Measure Now button, it means that the I-V Unit has turned itself off to protect against a condition of over-voltage, -current, or –temperature.
  • Page 74 4 Using the PVA-600 Software Wireless Interface Not Found When using the wireless sensor kit, this message may appear in the status indicator in the Sensors tab. Check that the sensor kit‘s wireless USB adaptor is plugged into the PC, and that the wireless transmitters attached to the sensor cables are turned on and within range.

  • Page 75: Interpreting Measured I-V Curves

    5 Interpreting Measured I-V Curves 5 Interpreting Measured I-V Curves Introduction A PV module, string, or array has a characteristic curve of current versus voltage; the ―I- V curve‖. The PV Analyzer‘s mathematical models predict the ideal shape for this curve for thousands of different PV modules and configurations.

  • Page 76: I-V Curve Terminology

    5 Interpreting Measured I-V Curves I-V Curve Terminology These abbreviations will be used in the following discussion:  Short circuit current  Max power current  Max power voltage  Open circuit voltage  Voltage at one half Voc  Current at Vx ...

  • Page 77: The Shape Of A Normal I-V Curve

    5 Interpreting Measured I-V Curves Figure 46. Effect of series and shunt losses on the shape of the I-V curve The fill factor is the ratio of two areas defined by the I-V curve. These areas represent electrical power (watts) because they are the product of a voltage and a current. Fill factor is the area represented by the max power point, divided by the area represented by Isc and Voc.

  • Page 78: Interpreting I-V Curves

    5 Interpreting Measured I-V Curves A normal I-V curve has a smooth shape with three distinct voltage regions as shown in Figure 47: A slightly sloped region above 0 V A steeply sloped region below Voc A bend or ‗knee‘ in the curve in the region of the maximum power point In a normal curve, the three regions are smooth and continuous.
  • Page 79 5 Interpreting Measured I-V Curves double check the measurement connection, and ensure the proper temperature and irradiance values are used. Potential causes of deviations between measured and predicted I-V curves are discussed below.

  • Page 80: The Measured I-V Curve Shows Higher Or Lower Current Than Predicted

    5 Interpreting Measured I-V Curves 1. The measured I-V Curve Shows Higher or Lower Current than Predicted An example of this type of deviation is shown in Figure 48. Figure 48. Example of a measured I-V curve that shows higher current than predicted Potential causes of this deviation are summarized below, and then discussed in more detail.

  • Page 81: Pv Array Is Soiled

    5 Interpreting Measured I-V Curves PV Array Is Soiled The effect of uniform soiling is like pulling a window screen over the entire array, or reducing the actual irradiance; the overall shape of the I-V curve is correct, but the current at each voltage is reduced.

  • Page 82: Irradiance Sensor Calibration Factor Is Entered Incorrectly

    5 Interpreting Measured I-V Curves Irradiance Sensor Calibration Factor Is Entered Incorrectly The irradiance sensor in the optional wireless sensor kit has a calibration sticker. For accurate measurements, the calibration factor value on the sticker must be entered into the PV Analyzer software. Reflections Contribute Additional Irradiance The energy production of PV modules can be increased by reflections from nearby buildings, automobiles, and other reflecting surfaces.

  • Page 83: The Slope Of The Curve Near Isc Does Not Match The Prediction

    5 Interpreting Measured I-V Curves 2. The Slope of the Curve near Isc Does Not Match the Prediction An example of this deviation is shown in Figure 49. Figure 49. An I-V curve showing more slope than expected in the region above Isc The slope of the I-V curve in this region is affected by the amount of shunt resistance (or shunt conductance - the inverse of shunt resistance) in the electrical circuit.

  • Page 84: Shunt Paths Exist In Pv Cells Or Modules

    5 Interpreting Measured I-V Curves Shunt Paths Exist In PV Cells or Modules Shunt current is current that bypasses the solar cell junction without producing 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.

  • Page 85: The Slope Of The Curve Near Voc Does Not Match The Prediction

    5 Interpreting Measured I-V Curves 3. The Slope of the Curve near Voc Does Not Match the Prediction An example of this type of deviation is shown in Figure 50. Figure 50. An I-V curve in which the slope of the measured I-V curve near Voc does not match the predicted slope The slope of the I-V curve between Vmp and Voc is affected by the amount of series resistance internal to the PV modules and in the array wiring.

  • Page 86: Pv Wiring Has Excess Resistance Or Is Insufficiently Sized

    5 Interpreting Measured I-V Curves 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. The resistance of additional wire between the PV modules and the PV Analyzer should be accounted for by entering the wire gauge and length in the Wiring section of the model.

  • Page 87: The I-V Curve Has Notches Or Steps

    5 Interpreting Measured I-V Curves 4. The I-V Curve Has Notches or Steps Examples of this type of deviation are shown in Figure 51, Figure 52, and Figure 53. Figure 51. The effect of partial shading on two paralleled strings of eight 175-watt modules Figure 52.
  • Page 88 Figure 53. The effect of intentionally shading entire modules in different combinations, in two parallel-connected strings NOTE The graphic shown in Figure 53 is not a screen generated by the PVA-600 Software interface. In general, these types of patterns in the I-V curve are indications of mismatch between different areas of the array or module under test.

  • Page 89: Array Is Partially Shaded

    5 Interpreting Measured I-V Curves Array Is Partially Shaded Partial shading of a PV cell reduces the current that can be generated by that cell, which in turn reduces the maximum current that can be produced by other series connected cells.

  • Page 90: The I-V Curve Has A Higher Or Lower Voc Value Than Predicted

    5 Interpreting Measured I-V Curves 5. The I-V Curve Has a Higher or Lower Voc Value than Predicted An example of this type of deviation is shown in Figure 54. Figure 54. Example of an I-V curve with lower Voc value than predicted Potential causes are summarized below, and then discussed in more detail.

  • Page 91: One Or More Cells Or Modules Are Completely Shaded

    5 Interpreting Measured I-V Curves One or More Cells or Modules Are Completely Shaded Shading a cell or module with very high opacity (hard shade) causes its bypass diode to begin conducting when any current passes through it. In this case, the notch in the I-V curve discussed in 4.

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