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5 Interpreting Measured I-V Curves

5-9

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. Reduced
shunt resistance (increased shunt conductance) results in a steeper slope in the I-V curve
near Isc and a reduced fill factor. A decrease in shunt resistance may be due to changes
within the PV cells or modules.

Potential causes of this deviation are summarized below, and then discussed in more
detail.

Potential causes located in the array include:



Shunt paths exist in PV cells



Shunt paths exist in the PV cell interconnects



Module Isc mismatch

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Содержание PVA-600

Страница 1: ...Solmetric PVA 600 PV Analyzer User s Guide ...

Страница 2: ...ter 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 Embedded Sof...

Страница 3: ...t 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 PURPOS...

Страница 4: ...oftware 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 Solmet...

Страница 5: ...l Safety Precautions 2 1 Battery Precautions 2 3 Measuring High Efficiency PV Modules 2 3 UNDERSTANDING THE PVA 600 2 3 Application Overview 2 3 I V Measurements 2 4 Logging Mode 2 4 PV Models 2 4 INSTALLATION PROCEDURE 2 5 Hardware Installation 2 5 Software Installation 2 5 SPECIAL XP OPERATING SYSTEM INSTRUCTIONS 2 6 INSTALLING DRIVERS FOR THE OPTIONAL PVA SENSOR KIT 2 7 CHARGING THE BATTERY 2 7...

Страница 6: ... the Modules and Enter String Information 4 18 Select an Inverter 4 20 Select Wire Gauge and Enter Wire Length 4 21 Select the Sensor Methods 4 22 Enter Array Slope and Azimuth 4 23 COPYING AN EXISTING MODEL FILE 4 24 MAKING MEASUREMENTS 4 25 SAVING DATA TO A DIRECTORY TREE 4 29 SAVING TRACE DATA 4 30 USING SNAPSHOT 4 31 SAVING A SCREEN IMAGE 4 31 VIEWING AND ANALYZING YOUR DATA 4 32 SETTING UP DA...

Страница 7: ...aded 5 15 PV Cells Are Damaged 5 15 Cell String Conductor Is Short Circuited 5 15 5 THE I V CURVE HAS A HIGHER OR LOWER VOC VALUE THAN PREDICTED 5 16 PV Cell Temperature Is Different than the Modeled Temperature 5 16 One or More Cells or Modules Are Completely Shaded 5 17 One or More Bypass Diodes Are Conducting or Shorted 5 17 Figures FIGURE 1 WELCOME SCREEN 2 5 FIGURE 2 DIRECTORY STRUCTURE OF PV...

Страница 8: ...AXIMUM POWER POINTS 4 33 FIGURE 42 LOGGING SCREEN 4 34 FIGURE 43 START LOGGING SCREEN 4 35 FIGURE 44 LOGGING DATA 4 36 FIGURE 45 THE FILL FACTOR IS DEFINED AS IMP X VMP THE GRAY AREA DIVIDED BY ISC X VOC THE CROSS HATCHED AREA 5 2 FIGURE 46 EFFECT OF SERIES AND SHUNT LOSSES ON THE SHAPE OF THE I V CURVE 5 3 FIGURE 47 A NORMAL I V CURVE FOR THE PARALLEL COMBINATION OF TWO STRINGS OF EIGHT 175 WATT ...

Страница 9: ...ECIFICATIONS 1 5 TABLE 5 PVA 600 STATES 3 2 TABLE 6 FILE MENU DESCRIPTION 4 2 TABLE 7 MODEL MENU DESCRIPTION 4 2 TABLE 8 UTILITY MENU DESCRIPTION 4 6 TABLE 9 HELP MENU DESCRIPTION 4 7 TABLE 10 TABLE TAB DESCRIPTION 4 8 TABLE 11 TRACES TAB DESCRIPTION 4 11 TABLE 12 VERIFY TAB DESCRIPTION 4 12 TABLE 13 LOGGING TAB DESCRIPTION 4 14 TABLE 14 SENSORS TAB DESCRIPTION 4 15 TABLE 15 TIME ZONES 4 17 ...

Страница 10: ...x The page left blank intentionally ...

Страница 11: ...rmal I V curve are the maximum power current and voltage Imp Vmp the point at which the array generates maximum electrical power All of these important voltages and currents are captured when the I V curve is measured The detailed shape of the curve between these points gives additional information about the health of the PV module string or array under test The value of a measured I V curve is gr...

Страница 12: ...ot be used Display Resolution 1024 X 600 minimum Processor Speed 700 MHz RAM 500 Mbytes Available Disc Space 100 Mbytes or more 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 User s Guide on I...

Страница 13: ...ter 1760 modules Simple Datasheet Model user enters datasheet values Battery Life 20 hours normal use Charging Time 6 hours Operating Temperature 0º C to 50º C Storage Temperature 20º C to 60º C Operating Humidity The normal humidity range is 80 relative humidity for temperatures up to 31ºC decreasing linearly to 50 at 40ºC Higher humidity levels should not affect the performance or safety of the ...

Страница 14: ...of the soft case Height 15 in Width 8 in Depth 5 in 1 At ends of the primary test leads permanently attached to the I V Measurement Unit PVA Sensor Kit Equipment Optional Irradiance Sensor Temperature Sensor 5 Pack of Replacement Temperature Sensors Wireless USB Adapter Transmitter irradiance Transmitter temperature Case Rechargeable AAA batteries and battery charger ...

Страница 15: ...of rdg or 1 0º C 1 8 º F Table 4 PVA Sensor Kit irradiance specifications Parameter Specification Sensor Type Silicon Solar Cell Angle of Incidence Effect Typically 1 if AOI is less than 60 degrees from normal Temperature Effect Typically 2 7 variation over 20º C to 70º C Uncertainty Contributed by Wireless Link 0 5 or reading Uncertainty from Time Lead or Lag in Reading Irradiance Sensor 0 5 to 5...

Страница 16: ...n damage to or 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 external case and or hard enclosure of the PVA 600 use a dry or slightly dampened c...

Страница 17: ...61010 1 2nd edition including Amendment 1 This product has been tested to the requirements of CAN CSA C22 2 No 61010 1 second edition including Amendment 1 or a later version of the same standard incorporating the same level of testing requirements This symbol indicates separate collection for electrical and electronic equipment mandated under EU law as of August 13 2005 All electrical and electro...

Страница 18: ...1 Introduction 1 8 The page left blank intentionally ...

Страница 19: ...A 600 should be extended to 5 000 to 10 000 connections PV Electrical Safety Precautions Installed PV systems are not consistent in design or construction Therefore the guidance provided in this section is general in nature and it is critical that the user apply techniques and precautions appropriate to the circumstances following best PV electrical safety precautions WARNING The information below...

Страница 20: ...ce the connector saver jumpers when they have reached 100 connections Make sure that user provided cables or clip leads used to extend the test leads of the PVA 600 are rated to safely handle the PVA 600 s specified maximum current and voltage When using probes or clip leads they should be of the insulated type with minimal exposed metal Keep your fingers behind the insulating finger guards WARNIN...

Страница 21: ...asure only one module or string at a time Understanding the PVA 600 Application Overview The PVA 600 is used during PV system installation and commissioning to ensure proper performance of PV modules strings and arrays The PVA 600 is also used for maintenance and troubleshooting to assist in locating the cause of performance problems in the system The PVA 600 consists of the following I V Measurem...

Страница 22: ...is intermittent and it is necessary to wait for a period of clear sky or when troubleshooting intermittent or temperature related performance problems When operating in the logging mode the I V Measurement Unit transmits the data continuously to the wirelessly connected notebook or tablet computer running the PVA 600 software The computer must be present during the logging period PV Models Three P...

Страница 23: ... does not automatically open as shown in Figure 1 either double click on the setup exe file on the DVD or run setup exe from the Run dialog Alternatively the installation file is available at www solmetric com Figure 1 Welcome screen 3 Follow the instructions in the welcome screen to install the PVA 600 software The drivers for the wireless USB adapter will also be installed 4 The directory struct...

Страница 24: ...ace Special XP Operating System Instructions This section applies to computers running the XP operating system only Older computers running the XP operating system require special steps during the installation of the wireless USB driver Please pay close attention to onscreen prompts In addition please be aware that XP will require the re installation of the driver if you insert the wireless USB ad...

Страница 25: ...recharged by attaching the battery charger to the connector on the PVA 600 shown in Figure 5 and plugging the charger into an AC wall plug Figure 5 Battery charger connector on the PVA 600 Charging the battery can take up to 6 hours Once the battery has been charged the PVA 600 will operate for approximately 20 hours of normal operation There is no visible indication of charging on the PVA 600 fro...

Страница 26: ...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 ...

Страница 27: ...able or disable the I V Measurement Unit and to reset the unit When the I V Measurement Unit is turned on it searches for its wireless partner the 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 Sweep ena...

Страница 28: ... receives a sweep trigger from the PC application and a measurement is taken LED blinks momentarily at start of each sweep Sweep Disabled pause While the I V Measurement Unit is on press the power button once The sweep is disabled Disable the sweep before connecting or disconnecting the I V Measurement Unit to from PV modules or strings If left in Sweep Disabled mode for more than 15 minutes the I...

Страница 29: ...600 on an asphalt driveway or on a roof in direct sunlight 2 Ensure that the connector saver jumpers are installed on the primary test leads 3 If necessary connect alligator clip leads or extension cables to the connector saver jumpers Use only clip leads or cables that are rated for at least the maximum current and voltage of the I V Measurement Unit 4 If long extension cables are connected to th...

Страница 30: ...e polarity markings 4 Position the irradiance sensor in the same plane as the modules under test For example on the surface of a neighboring module that is not in the string of modules being tested 5 Ensure that the irradiance transmitter is not resting on the ground or on the roof and is not placed against a metal surface Elevating the irradiance transmitter improves the transmission range 6 Secu...

Страница 31: ...ical battery life of the temperature transmitter battery is 1500 hours 9 If the LOW BATT LED on either the irradiance or temperature transmitter is on replace the battery as follows a Remove the two screws securing the cover on the rear side of the transmitter b Remove the cover c Replace the battery with a Lithium AAA battery NOTE In emergencies you can substitute AAA Alkaline batteries However b...

Страница 32: ... PVA 600 to the test string The connection may be made at PV connectors at the ends of the test string or by clipping to the de energized buss bars in a DC combiner box as shown in Figure 8 using suitable test leads with MC 4 connectors at one end and insulated alligator clips at the other end Figure 8 Example of PVA 600 test leads clipped to the buss bars of a PV combiner box 4 If one or both of ...

Страница 33: ...th the wireless USB adapter connected to the PC If the wireless USB adapter is inserted into an operating PC a network will be established and the LED will become continuously lit no blinking If a network is not established within 15 minutes the I V Measurement Unit will turn off to conserve the battery I V Measurements The I V Measurement Unit will measure I V curves each time the user clicks on ...

Страница 34: ...ry s high temperature specification the measurement unit automatically shuts down disables itself and the Disabled message is displayed below the Measure Now button In thermal shutdown PV power is no longer dissipated in the measurement unit This removes one of the major internal heat sources To recover from thermal shutdown wait for the measurement unit to cool Placing it in the shade or a cool p...

Страница 35: ...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 Over Current Protection If greater than 20 A dc is applied to the I V Measurement Unit the PVA 600 detects the over current condition and switches into disabled mode automatically and an I ...

Страница 36: ...e 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 ...

Страница 37: ...e 10 Figure 10 PVA 600 main screen The Title Bar is located at the top of the main screen and displays the name of the product Also two of the most common Windows software buttons Minimize and Close are displayed in the upper right corner The Menu Bar is located just below the Title Bar and is a drop down menu system for setting up measurements The Tabs are located along the left side of the main ...

Страница 38: ...software application Model Menu Table 7 Model menu description Name Description New Creates a new model file used to set up new PV modules sensors and related site information The file will be saved in the Models folder Name name of model file Notes pertinent notes about the PV modules Latitude numeric entry in degrees Range is 90 to 90 Default is 38 25 Longitude numeric entry in degrees Range is ...

Страница 39: ... model predicts the maximum power voltage and current at the existing irradiance and temperature Based on data sheet values this model can be used with almost any PV module with basic specifications NOTE While default values are included in the Simple Performance Model screen you will have to replace these values with those from your desired module of Modules in String enter number of modules in s...

Страница 40: ...0002485 Ω foot 6 AWG 0 1620 in 4 115 mm 0 0003951 Ω foot 8 AWG 0 1285 in 3 264 mm 0 0006282 Ω foot 10 AWG 0 1019 in 2 588 mm 0 0009989 Ω foot 12 AWG 0 0808 in 2 053 mm 0 001588 Ω foot 14 AWG 0 0641 in 1 628 mm 0 002525 Ω foot 16 AWG 0 0508 in 1 291 mm 0 004016 Ω foot Wire Gauge AWG selects the wire gauge of conductors between the PV string and the point at which the I V curve is being measured Wir...

Страница 41: ...s the sensor Assumes functional PV module s Use wireless temperature sensor temperature is transmitted wirelessly when using the PVA Sensor Kit Offset enter the temperature offset to be added to the module backside temperature to determine cell temperature NOTE The offset will vary typically from 0º C to 8 º C during a day depending on mounting and wind conditions The default value of 3º C is only...

Страница 42: ...he currently loaded Model file including Name Location Modules String Inverter Wiring Sensor Methods and Array Plane parameters Properties can be changed in this view The changes are saved Utility Menu Table 8 Utility menu description Name Description Settings Used to select the I V Measurement Unit and PVA Sensor Kit communication ports manually NOTE If the Wireless USB Adapters are installed int...

Страница 43: ...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 Figure 11 is an example of the Table tab screen Figure 11 Table tab ...

Страница 44: ... is selected predicted temperature is left blank The temperature value in the Measured column is either the manually entered value or the wireless sensor value depending on which option is in effect If neither of these methods is selected no value is displayed Epoa W m 2 Displays the predicted and measured irradiance in the plane of the array The irradiance value in the Predicted column is derived...

Страница 45: ... I V measurement process is paused by pressing the button on the I V Measurement Unit In this state PV source connections may be changed without interrupting a measurement WARNING PV circuits continue to present danger of electrical shock while system is paused FAILURE TO TAKE APPROPRIATE SAFETY PRECAUTIONS COULD LEAD TO PERSONAL INJURY OR LOSS OF LIFE Disabled indicator Displayed when a problem e...

Страница 46: ...rom the test string calculated from the I V curve simply by multiplying I x V for each I V point The yellow point simply indicates the maximum value of the measured P V curve It is not the predicted maximum power value 3 Model prediction points The five purple I V points are the predicted I V values for the five key points as defined by the Sandia or 5 Parameter performance model If the actual I V...

Страница 47: ...ower actually measured for the system This value corresponds to the single yellow point on the P V curve The black target line is the maximum power predicted by the performance model The numeric Performance Factor value is the ratio of actual to predicted maximum power as a percentage NOTE Typically if a string is operating correctly the Performance Factor will be between 95 and 105 when using the...

Страница 48: ...wer 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 Target Displays the maximum power predicted by the performance model and the selected sensor method STC Displays the predicted maximum power under Standard Test Conditions ...

Страница 49: ... clearly see when the modules entered a late afternoon shade condition Figure 14 Logging tab There are three values displayed on the graph 1 The small black dots are measured maximum power 2 The orange steps represent the maximum value measured during each 15 minute interval 3 The yellow line is the target predicted maximum power in each 15 minute interval The time axis autoscales to display all t...

Страница 50: ...The date and time are taken from the PC s internal clock when the first measurement is started Start Logging button Sample Rate minutes sets time interval between actual measurements Log File sets name for csv data file The log file is stored in the Log Files folder Change File button allows you to change to a different file name Load File button Allows you to select and load an existing csv file ...

Страница 51: ...er the distance between the PVA 600 and the sensors the lower the signal level Wireless Interface Displays whether the sensor s wireless sensor USB interface adapter was found or not The Help button accesses information to aid in troubleshooting the problem Setting Up a New Model The following procedure shows how to set up the PVA 600 for particular PV modules strings inverters sensor methods and ...

Страница 52: ...or this model The model file will be saved in the Models folder 3 Click in the Notes text box to enter notes for this model Enter Latitude Longitude and Time Zone 1 Click on the Location button to access the screen used to set up location information as shown in Figure 18 Figure 18 Location screen 2 Click in the Latitude text box and enter the latitude for this model 3 Click in the Longitude text ...

Страница 53: ...ime Zone GMT 1 WAT West Africa GMT 2 AT Azores GMT 3 Brasilia Brazil Buenos Aires Argentina Georgetown Guyana GMT 4 AST Atlantic Standard GMT 5 EST Eastern Standard GMT 6 CST Central Standard GMT 7 MST Mountain Standard GMT 8 PST Pacific Standard GMT 9 YST Yukon Standard GMT 10 AHST Alaska Hawaii Standard CAT Central Alaska HST Hawaii Standard GMT 11 NT Nome GMT 12 IDLW International Date Line Wes...

Страница 54: ...l select Detailed Performance Model and perform the following steps a Click on the Change button to access the screen used to select the PV module manufacturer and module number as shown in Figure 20 Figure 20 Change module screen b Click on the Manufacturer dropdown menu and select the manufacturer c Click on the Module dropdown menu and select the module number Data for the specific module appea...

Страница 55: ... parameters from the manufacturer s published specifications NOTE There are multiple formats in which manufacturers supply their module s temperature coefficients Be careful to enter values in the temperature coefficient text box in units of C for accurate results If the manufacturer for instance supplies coefficients for Voc STC in V C this value can be converted to C by dividing the supplied num...

Страница 56: ... on the Change button to access the screen used to select the inverter manufacturer and model number as shown in Figure 24 Figure 24 Change inverter screen 3 Click on the Manufacturer dropdown menu and select the inverter manufacturer 4 Click on the Inverter dropdown menu and select the model number Data for the specific inverter appears in the Description and Value columns Figure 25 is an example...

Страница 57: ...n Figure 26 The gauge and length are used to calculate the series resistance per foot Figure 26 Wiring screen 2 Click on the Wire Gauge AWG dropdown menu and select the external wiring gauge 3 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 ...

Страница 58: ...ods 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 Controls for entering irradiance and or temperature manually ...

Страница 59: ... Use wireless temperature sensor The Offset number is a temperature offset added to the module backside temperature to get an approximation of the PV cell temperature 5 If you want the PVA 600 to extract the irradiance mathematically from the measured I V data select Determine irradiance from I V curve 6 If you are using a manual sensor to measure irradiance select Enter solar irradiance manually ...

Страница 60: ...enter the azimuth of the array in degrees from true North 4 Click on the OK button Copying an Existing Model File Making a copy of an existing model file can save time by allowing you to quickly edit only those parameters that require change then saving these changes to a new file name 1 Select Copy in the Model menu The Model screen appears as shown in Figure 31 Figure 31 Copying a model file ...

Страница 61: ... the software the USB port will be found automatically If you install the Wireless USB Adapter s after starting the software you must select the proper USB ports on your PC manually using the Utility Settings menu 4 If you are using the PVA Sensor Kit perform the following a Insert the Wireless Sensor USB Adapter into a second USB port on your PC NOTE On some PCs the USB adapters may not fit side ...

Страница 62: ...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 NOTE If communication is not established within one minute a Move the PC closer to the I V Measurement Unit b Reset the I V Measurement Unit c Remove and replace the Wireless USB Adapter Figure 33 Turn on the I V Measurement Unit 10 If you ...

Страница 63: ...nal level increases Refer to Setting Up the Optional PVA Sensor Kit for setup information d Ensure that the Temperature box blinks green every ten seconds If the box is not blinking you may need to move the PC closer to the sensor transmitter location or reposition the sensor transmitter Ensure that the signal level increases Refer to Setting Up the Optional PVA Sensor Kit for setup information 11...

Страница 64: ...tage and current details of the circuit under test before choosing the most appropriate internal settings After the second measurement the data will scale properly and should be similar to the graph shown in Figure 36 Figure 36 I V and P V graphs 14 To save the data to a csv file click on the Save Trace button then enter a filename in the Save As dialog box The trace data file will be saved in the...

Страница 65: ...he next string to be measured 18 Repeat the process for each string to be measured Saving Data to a Directory Tree To streamline the process of saving I V data to your PC create a directory tree before going to the job site The directory tree is a nested set of folders that has the same structure as the PV array to be tested Then when saving an I V trace on site just direct the Save File dialog bo...

Страница 66: ...ve trace data can be saved as a csv file for future analysis 1 While viewing measured data in the Traces tab click on the Save Trace button 2 In the Save As dialog box enter a filename and select the storage location The default storage location is the Traces folder Data will be saved in the csv file format NOTE To save time in the field set up a Windows directory tree with the same architecture a...

Страница 67: ... 25 columns of data 1 Click on the Table tab 2 Click on the Snapshot button The data column is displayed in the Snapshots table as shown in Figure 39 Figure 39 Snapshot table 3 To clear the last Snapshot column click on the Clear Last button 4 To clear all Snapshot columns click on the Clear All button Saving a Screen Image To save an image of the current screen click the camera icon in the lower ...

Страница 68: ...rmation 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 five predicted current and voltage points of the selected model the Simple Performance Model has no predicted points SC First point at short circuit current Isc X Second point at one half of the open circuit voltage MP T...

Страница 69: ...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 When using the wireless PVA Sensor Kit the end points may not match the predicted points when using the Sandia or 5 Parameter Performance Models The remainder of the csv file contains the actual measured voltage current an...

Страница 70: ...an be reloaded at a later time and displayed on the PC using the Load File button in the Logging tab NOTE While in logging mode all measurement data is stored in the PC Therefore be sure the PC is always within communication range of the I V Measurement Unit If communication is temporarily lost logging will continue but data values of 0 will be displayed and stored 1 On the PC double click on the ...

Страница 71: ...ilename and select a storage location for the log file You can also enter the path and filename by typing it into the Log File text box The default location is the Log Files folder Data will be saved in the csv file format 6 Click on the OK button The current graph is cleared the date and time is updated from the PC and logging begins immediately The graph shows measured array power in Watts over ...

Страница 72: ...Tpv Predicted Tpv Voc Isc Vmpp Impp 8 18 2010 15 18 40 230 39 230 11 N A 747 41 53 33 50 01 79 7 4 07 63 24 3 64 8 18 2010 15 19 40 230 12 229 82 N A 746 8 53 33 50 06 79 68 4 07 62 97 3 65 8 18 2010 15 20 40 229 77 229 05 N A 744 5 5536 67 49 77 79 76 4 06 63 17 3 63 8 18 2010 15 21 39 228 37 228 31 N A 740 88 5536 67 49 99 79 66 4 04 63 12 3 62 8 18 2010 15 22 40 227 25 227 27 N A 736 75 5536 67...

Страница 73: ...ptor used to communicate with the I V Measurement Unit Plug the USB adaptor into an open USB port You may need to go to the Utilities menu select Settings and follow the instructions to locate the USB adaptor 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 No I V Unit message In this case the PC has foun...

Страница 74: ...ts internal settings for the measurements to follow Simply press Measure Now again to begin collecting valid data Subsequent traces are noisy If each trace is noisy check for low light conditions This may be caused by cloud cover by low sun angles or when testing un mounted PV modules by having the modules pointed away from the sun For best results perform PV measurements of fixed arrays within a ...

Страница 75: ...eviations 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 module characteristics available for over 2000 model numbers Number of PV modules in series Number of PV modu...

Страница 76: ...t Vxx FF Fill Factor Imp Vmp Isc Voc The fill factor FF of a PV module or string is a measure of the square ness of the curve as shown in Figure 45 PV modules of a given manufacturer and model will have similar fill factors if performing normally Figure 45 The Fill Factor is defined as Imp x Vmp the gray area divided by Isc x Voc the cross hatched area Series and shunt losses have a pronounced eff...

Страница 77: ...c In an ideal but unrealizable PV module the two areas would be identical and a fill factor of 1 0 would result The Shape of a Normal I V Curve Figure 47 shows a normal I V curve red line as a starting point for the discussion The predicted I V curve shape is shown by the five dots The power versus voltage curve is also visible blue line Power is calculated as the product of measured current and v...

Страница 78: ... between Vmp and Voc OC Fifth point at open circuit voltage Voc Interpreting I V Curves Most array problems show deviations between measured and predicted I V curves that fall into one of these categories 1 The measured I V curve shows higher or lower current than predicted 2 The slope of the I V curve near Isc does not match the prediction 3 The slope of the I V curve near Voc does not match the ...

Страница 79: ...asured I V Curves 5 5 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 ...

Страница 80: ... soiled especially uniformly PV modules are degraded Potential causes associated with the model settings include Number of PV strings in parallel is not entered correctly in the model Potential causes associated with irradiance or temperature measurements include Irradiance changed during the short time between irradiance and I V measurements Irradiance sensor is oriented incorrectly Irradiance se...

Страница 81: ...bers may have different Isc specifications Check that the module you selected from the on board module list matches the nameplate on the back of the PV modules If the array is known to have a mix of PV modules of different types this can also contribute to changes in Isc Number of PV Strings in Parallel Is Not Entered Correctly in the Model The measured value of Isc scales directly with the number...

Страница 82: ...o Close to the Horizon Crystalline silicon PV modules behave somewhat differently in low light conditions Also early and late in the day sunlight hits the surface of the PV module at glancing angles and differences in the reflectivity of the surfaces become more important Finally the spectrum of sunlight changes in the course of a day For best results measure PV arrays during the central part of t...

Страница 83: ... shunt conductance the inverse of shunt resistance in the electrical circuit Reduced shunt resistance increased shunt conductance results in a steeper slope in the I V curve near Isc and a reduced fill factor A decrease in shunt resistance may be due to changes within the PV cells or modules Potential causes of this deviation are summarized below and then discussed in more detail Potential causes ...

Страница 84: ...ver time or can degrade until the module is damaged irreparably Smaller shunts can self heal if the high current through the shunt path causes the small amount of material shorting the cell to self immolate Larger shunts can result in localized temperature rises in the module that can reach the melting point of encapsulant material or the module backsheet Modules that have failed in this manner wi...

Страница 85: ... 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 Increased resistance reduces the steepness of the slope and decreases the fill factor Potential causes are summarized below and then discussed in more detail Potential causes located in the array include PV wiring has excess resistance or is insufficiently sized Electric...

Страница 86: ...sufficient to minimize DC power losses from series resistance in cabling Some sizing guidelines call for a maximum 1 voltage drop due to cabling which could result in larger sized cabling than would be required to meet code safety considerations Electrical Interconnections in the Array Are Resistive Electrical connections anywhere along the current path can add resistance to the circuit Assure tha...

Страница 87: ...ples 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 The shading impact of placing a business card on a single cell in a string of fifteen 180 watt modules ...

Страница 88: ...dications 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 in series connected modules are activating and passing current around the affected module s Potential causes are summarized below and then discussed in more detail Potentia...

Страница 89: ...impact of partial shading on the I V curve is to create a distortion or notch as shown in Figure 53 In a single PV string the vertical height or current at which the notch appears is equal to the reduced short circuit current of the partially shaded cells The horizontal or voltage distance from Voc to the notch is related to the number of cell strings within modules that have been bypassed PV Cell...

Страница 90: ...ting or shorted PV Cell Temperature Is Different than the Modeled Temperature The module Voc is dependent on the temperature of the solar cells with higher temperatures resulting in a lower Voc It is possible that a poor thermal connection exists between the temperature measurement device and the back of the module Also if the temperature measurement is taken on the front side of the module direct...

Страница 91: ... diode s to conduct even in the absence of shade or severe module to module mismatch The I V curve shape may look normal except that the Voc value is lower than predicted If the reduction in Voc is approximately equal to a multiple of the Voc of a module cell string in 72 cell modules typically Voc 3 look for a module s with conducting or shorted bypass diodes Start by inspecting module front and ...

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