PV Module Troubleshooting and Measurement
Contents
1. 5 2 z E Figure 22 Power degradation with time change 42 Table 11 Degradation rate for four different modules Time yrs 0 11 33 2 2 58 6 33 11 58 Degradation Rated power W Power output at STC W BP 275 75 81 6 78 7 77 74 77 38 75 81 66 98 1 40 SX 75 75 76 4 75 3 74 22 74 09 72 54 70 26 0 66 Time yrs 0 11 08 2 25 2 33 6 08 11 5 Power output at STC W BP285 85 86 7 86 1 83 74 83 1 83 82 76 29 0 94 Time yrs 0 11 58 2 67 2 75 6 5 11 92 Power output at STC W PW750 75 70 68 4 65 9 61 68 61 41 52 86 47 06 2 67 6 Limitations and further research As discussed above the actual electrical performance of four target modules has been successfully measured and the degradation rate was estimated by comparison with previous data However the measured results were not verified by the simulation process because the simulator was out of service It 15 suggested that a specific simulation process be conducted in future work so that it can determine if the measured results are coincident with the simulated results Equation 3 illustrates the residual between measured results and simulated results It is found that the less the deviation between the measured results and the simulated results the higher the accuracy of the estimated degrada2. E E 3 e 10 15 Voltage BP585 Module at 920 W m 40 C 2 30 PM Current 10 15 Voltage BP585 Module at 700 W m 33 C 1 30 PM 67 Current 10 15 Voltage Current Voltage SX 75 Module at 1043 W m 30 C 11 30 AM 68 E SX 75 Module at 1060 W m 35 C 12 30 PM 10 15 Voltage SX 75 Module at 1050 W m 35 C 1 30 PM 69 Current Current Voltage SX 75 Module at 700 W m 27 C 3 30 PM 70 Current 10 Voltage PW750 70 Module at 1043 W m 32 C 11 30 AM 71 E E 3 e 10 15 Voltage PW750 70 Module at 1060 W m 32 C 12 30 PM Current 10 15 Voltage PW750 70 Module at 1050 W m 32 C 1 30 PM 72 Current 10 15 Voltage PW750 70 Module at 920 W m 32 2 30 PM Current 10 15 Voltage PW750 70 Module at 700 W m 32 3 30 PM 73
3. Normalized Category al 1 Unfiled Brazier BP3160 U 2 El 2 Brazier BP3160 U 05 12 2011 11 11 00 Jol Unfiled Brazier BP3160U 05 12 2011 11 12 00 F i Unfiled Brazier BP3160U 05 12 2011 11 13 00 F 5 Unfiled Brazier BP3160U 05 12 2011 11 14 00 F 5 Unfiled Brazier BP3160U 05 12 2011 11 15 00 E 7 Unfiled Brazier BP 3160U 05 12 2011 11 16 00 H Unfiled Brazier BP 3160U 05 12 2011 11 17 00 EH Unfiled Brazier BP 3160U 05 12 2011 11 18 00 10 Unfiled Brazier BP 3160U 05 12 2011 11 19 00 E 1 Unfiled Brazier BP 3160U 05 12 2011 11 20 00 F 12 Unfiled Brazier BP 31600 05 12 2011 11 36 17 E 1 Unfiled Brazier BP 3160U 05 12 2011 11 37 00 F 4 Unfiled Brazier BP 3160U 05 12 2011 11 38 01 O 15 Unfiled Brazier BP 3160U 05 12 2011 11 39 00 O 15 Unfiled Brazier BP 31600 05 12 2011 11 40 00 E Unfiled Brazier BP3160U 05 12 2011 11 41 00 D 18 Unfiled Brazier BP3150U 05 12 2011 11 42 03 E 19 Unfiled Brazier BP 3160U 05 12 2011 11 43 00 F 2 Unfiled Brazier BP 3160U 05 12 2011 11 44 00 E a Unfiled Brazier BP 3160 U 05 12 2011 11 45 00 F 2 Unfiled Forrest Road 1680 BP 480H 05 12 2011 134347 E 23 Unfiled Forrest Road BP 480H 05 12 2011 13 45 00 a Unfiled Forest Road BP 480H 05 12 2011 13 46 00 E 5 Unfiled Forrest Road BP 480H 05 12 2011 13 47 00 F 5 Unfiled Forrest Road BP 480H 05 12 2011 13 48 00 pni 27 Unfiled Forest Road BP 480H 05 12 2011 13 49 00 Step 4 Double click on the curve which needs to be m
4. adio beet vetta mice A a 2 1 4 Thesis OUUIBE doe te c Sequin Ra Ka Ba Ra ka 3 2 Module degradation aaasnaaccssntassnnnnnnnnnnnsnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnsnnnnannnntannnans 4 2 1 Overview of module deeradatron o nee te treo epus ue denies 4 2 2 Cellfal re 5 2 ZN Hot SpOtUzs i etant e ettet e Weeds 5 20 1 1 BOISSON ei seid ied iaces ie a ana agi 6 2 22 Cracks aaa Saeed a ieee oe 7 2 3 Packaging material degradation dut pb cos 8 2 4 Powerlossesan solar cells m n Yg cease tsi Moe a Hadi e eise E eene e 9 24 1 Fundamental 198868 accio Seal a slaka SSS la AV t an V ata lala ds 9 DAD Recoimbifidbiolk sicut avec 10 2 4 3 Series Resistance and Shunt Resistance 12 2 4 4 Power loss exceeding the guaranteed 15 2 4 5 Power loss in different strings 16 2 5 Module Tallut6 awe eese De ate Rs d ul alana 18 2 5 Dustand Soling rarest cites nat nubi os broma lia ams dan s k 18 2 5 2 Shaditig aside de aleae Pa it Dey pando 19 3 Troubleshooting techniques aaaasnaaccssostcnnnnnannnnnnnnnnnncnsnnnnannnnnnnnnnannnnnnnnannnnnnnnaar 22 mSpeetiOD o o oreet Fon d eta qu eno aa 22 3 2 Intrared imaging c Deo ei ces m Ng d aad 27 3 3 Lock in
5. ReleUence c ee SENS ES ANN SE 47 APDPEONdICeSizsissssilsshhiuaansbaunbunba aluani anunnan s u ananinusnnnnna ee aH eH 50 Appendix A Procedure for converting the IV Curve measured in the field to STC using STC Mapping Spreadsheet roe Pere 50 Appendix B Procedures of Prova 210 Solar I V 58 Appendix C Pyranometers v Reference Cells for PV Installations 59 Appendix D Prova 210 Solar Module Analyzer Accuracy and Reliability 61 Appendix E Comparison of I V curves for different modules under different times OPUS day rop dotes e dai ket adeo E 62 1 Introduction 1 1 Background The Photovoltaic PV industry has developed very rapidly over the last decade in Australia Today more and more PV systems have been installed for both residential and commercial use due to the decreasing price and massive financial support In 2010 the total installed capacity of PV systems was about 383 MW which 15 an increase of 480 over 2009 Watt et al 2011 As a result of technological innovation the efficiency and reliability of PV modules have been greatly improved However it is known that some PV modules degrade rapidly and their actual outputs are much lower than normal ones In addition to power losses some of modules reveal a num
6. Short circuit current l 5 0A Open circuit voltage Voc 22 1V 22 0V Temperature coefficient of ls 0 065 0 015 C Temperature coefficient of voltage 80 10 mV C Temperature coefficient of power 0 5 0 05 C NOCT 47 2 C Maximum system voltage 600V U S NEC rating 1000V TUV Rheinland rating Maximum series fuse rating 20A U H versions 15A S L versions Source http www oksolar com pdfiles Solar 20Panels 20bp_585 pdf 4 2 2 Polycrystalline silicon p Si SX 75 amp PW750 70 To reduce the costs and increase the rate of production polycrystalline silicon technology has been developed The manufacturing process of polycrystalline silicon is simpler than that of monocrystalline silicon One of the easiest methods to produce polycrystalline silicon is to melt the starting material silicon scrap and pour it into a crucible and carefully control the cooling rate Markvart 2000 By this technology the typical crystallization rate is 3 5kg h which is much faster than the CZ method Markvart 2000 29 In this project two types of polycrystalline modules were chosen One 15 a 5 75 module which 15 produced by the Solarex Company It consists of 36 series connected polysilicon solar cells and it can charge batteries in virtually any climate BP Solar 2002 In addition the rated output of the SX 75 module is 75W The electrical characteristics of SX 75 module are shown in Table 3 Table 3 SX 75 modul
7. Time mm yy Figure 21 Power output for four different modules in different time 38 5 1 STC Test Results Table 10 shows the rated W the initial guaranteed minimum W IGM or tolerance the initial W values measured prior to outdoor exposure and the W value measured at the end of the test period Table 10 shows the number of months of outdoor exposure experienced by each module and the percentage differences between the initial and final W values In addition Table 10 gives us the warranty periods for each module Due to the rapid improvement of PV technology module warranty periods have steadily increased Mostly modules are guaranteed to perform to a percentage of the W IGM or a percentage of the rated power In this project PW750 70 module is guaranteed to perform 80 of the original W IGM after 25 years The other three modules are guaranteed to perform at 80 of the initial W IGM after 20 years 5 2 Initial STC Test Results The initial STC test results include the initial W value prior to outdoor exposure and the guaranteed minimum W IGM given by the manufacturers In most cases the initial W value is higher than the W IGM and rated value even if the module has experienced one year of outdoor exposure In this project we find that the initial W values for the SX 75 and BP585 modules are greater than their rated power 1 9 and 2 0 respectively The initial W value for BP275 module is 8 8 over its rate
8. 10 1109 WCPEC 2006 279952 Tobias I Carlos del Canizo and Jesus Alonso 2011 Crystalline Silicon Solar Cells and Modules In Handbook of Photovoltaic Science and Engineering 2 ed edited by Antonio Luque and Steven Hegedus 265 308 A John Wiley and Sons Ltd Thomas M G Durand S J and Rosenthal A L 1993 A Ten Year Review of Performance of Photovoltaic Systems In Proceedings of the 23 Photovoltaic specialists Conference Louisville KY May 10 14 1993 IEEE Whitaker C M Townsend T U Anat Razon Hudson R M and Xavier Vallve 2011 PV Systems In Handbook of Photovoltaic Science and Engineering 2 ed edited by Antonio Luque and Steven Hegedus 797 834 A John Wiley and Sons Ltd Yanli Liu Bingfeng Li and Dan Zhong 2010 Research on Domestic PV Module Structure Based on Fault Detection In Proceedings of the 8 World Congress on Intelligent Control and Automation Jinan China July 6 9 2010 171 175 IEEE 49 Appendices Appendix A Procedure for converting the IV Curve measured in the field to STC using STC Mapping Spreadsheet Definitions AOI Angle of incidence between beam from sun and normal to array plane almp Module Imp temperature coefficient normalized 1 C alsc Module Isc temperature coefficient normalized 1 C BV mpo Module Voc temperature coefficient at 1000 W m V C BV Module Voc temperature coefficient at 1000 W m V C Impo Imp at
9. 14 08 2012 Martin J 2003 Training Report at MUERI Murdoch University Energy Research Institute Munoz M A Alonso Garc a M C Nieves Vela and Chenlo F 2011 Early degradation of silicon PV modules and guaranty conditions Solar Energy 85 2 2264 2274 Mathew J K Joseph Kuitche and Govindasamy TamizhMani 2010 Test to failure of PV modules Hotspot testing In proceeding of the 35 IEEE Photovoltaic Specialists Conference Florida Tampa Convention Center in beautiful Tampa Bay June 20 25 2010 2839 2843 IEEE McMahon T J 2008 Solar cell module degradation and failure diagnostics Reliability Physics Symposium IEEE 172 177 doi 10 1 109 RELPHY 2008 4558880 48 Quintana M A King D L McMahon T J and Osterwald C R 2002 Commonly observed degradation in field aged photovoltaic modules In proceeding of the 29 IEEE Photovoltaic Specialists Conference New Orleans Louisiana May 19 24 2002 1436 1439 IEEE Roman E Alonso R Ibanez P Elorduizapatarietxe S and Goitia D 2006 Intelligent PV Module for Grid Connected PV Systems Industrial Electronics IEEE Transactions 53 4 1066 1073 June 2006 doi 10 1109 TIE 2006 878327 Takashima T Yamaguchi J Otani K Kato K and Ishida M 2006 Experimental Studies of Failure Detection Methods in PV Module Strings In proceeding of the 4 World Photovoltaic Energy Conversion Conference May 7 12 2006 2227 2230 doi
10. In Photovoltaics System Design and Practice edited by Herbert Eppel 127 221 A John Wiley amp Sons Ltd Herrmann W Wiesner W and Vaassen W 1997 Hot spot investigations on PV modules new concepts for a test standard and consequences for module design with respect to bypass diodes In proceeding of the 26 IEEE Photovoltaic Specialists Conference Anaheim CA September 29 October 3 1997 1129 1132 doi 10 1109 PVSC 1997 654287 King D L Quintana M A Kratochvil J A Ellibee D E and Hansen B R 2000 Photovoltaic module performance and durability following long term field exposure Progress In Photovoltaics Research and Application 8 2 241 256 doi 10 1002 SICI 1099 159X 200003 04 8 2 241 AID PIP290 3 0 CO 2 D Kurnik J Marko Jankovec Kristijan Brecl and Marko Topic 2011 Outdoor testing of PV module temperature and performance under different mounting and operational conditions Solar Energy Materials amp Solar Cells 95 373 376 Markvart T 2000 Solar Cells In Solar Electricity 2 led edited by Tomas Markvart 23 79 UK University of Southampton Markvart T 2000 Solar Cells In Solar Electricity 2 eg edited by Tomas Markvart 23 79 UK University of Southampton Matrix Solar Technologies 2012 Photovoltaic Module PW750 70 PW750 80 and PW750 85 Specification Sheet http www altestore com mmsolar others Matrix Photowatt 750 Data Sheet pdf Accessed
11. Voltage Measurement i 1160g 40 90z Batteries included Dimension 257 L x 155 W x 57 H mm 10 1 L x 6 1 W x 2 2 H Accessories User Manual x 1 AC adaptor x 1 Software CD x 1 Software Manual x 1 RS232C to USB Bridge Cable x 1 Kelvin Clips 2 clips x 1 set 210 Lithium battery 11 1V Rechargeable x 1 200 Battery 1 2V AA Rechargeable x 8 Resolution Accurac x 1 96 1 of Ishort 90pA x 1 96 1 of Ishort 0 9mA 1 96 1 96 of Ishort 0 9 saus TRIO FAX 1300 853 409 ne SERVICE Smartcal m 61 Appendix E Comparison of I V curves for different modules under different times of the day Current Current Voltage BP275 Module at 1043 W m 32 C 11 30 AM 62 Current 10 15 Voltage E E 3 e Voltage BP275 Module at 1050 W m 32 1 30 PM 63 Current 10 15 Voltage BP275 Module at 920 W m 37 C 2 30 PM Current 10 15 Voltage BP275 Module at 700 W m 30 3 30 PM 64 E 3 e 10 15 Voltage BP585 Module at 970 W m 31 10 30 AM Current 10 15 Voltage BP585 Module at 1043 W m 30 C 11 30 AM 65 Current 10 15 Voltage Current Voltage BP585 Module at 1050 W m 33 C 1 30 PM 66
12. curves in the spreadsheet Rounded degradation figures typically varied by 1 in the RRPGP Occasional outliers beyond this were removed Sometimes variability exceeded this value and outliers could not be identified Such data was deemed bad data and could not be used This was found to occur when we were attempting to take curves in a short break 10mins in the clouds Variability in the fill factor figures occurred to a much lower extent than in the power degradation figures 27 Appendix B 1 2 3 4 5 6 7 8 9 Procedures of Prova 210 Solar Z V Tracer Attach the temperature sensing element of the temperature probe to the back of the solar module using the aluminium tape to get the most approximate temperature at the back of the module For achieving the best results we can use a 15 mmx100 mm piece of Al tape to attach the temperature probe to the back of the module Calibrate the voltage and current and press the ZERO CAL button It can improve the accuracy of the instrument before operation Connect the PV module to the solar module analyzer using the leads Plug the red and black leads into the mating connectors of Prova 210 then connect the negative lead to the PV module followed by the positive red lead Press the power button of the Prova 210 to switch the unit on Setup menu to 0 minutes and input the measured module area solar radiation Press the AUTO SCAN button and all the measured data will be
13. the V curves of the three strings of 24 cells in a module The V curves not only show the current and voltage changes but also indicate the maximum power point the blue dot The current in the central string of cells is much lower than the other strings this indicates a defect in this area The right side string is not normal and has defects while the left side string looks good whole module 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 0 5 0 0 Current A 0 10 20 30 40 50 Voltage V Figure 10 Electrical curve of a defective module Source Munoz et al 2011 Early degradation of silicon PV modules and guaranty conditions 16 central string 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 0 5 0 0 Current A 10 15 20 Voltage V eo Figure 11 curve of the central string of cells of the module Source Munoz et al 2011 Early degradation of silicon PV modules and guaranty conditions string 6 0 5 0 4 0 3 0 Current A 2 0 1 0 0 0 10 15 20 Voltage V o O1 Figure 12 I V curve of the right side string of cells of the module Source Munoz et al 2011 Early degradation of silicon PV modules and guaranty conditions string 5 0 4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 0 5 0 0 0 5 10 15 20 Voltage V Current A Figure 13 curve of the left side string of cells of the module Source Munoz et al 2011 Early degradation of silicon PV m
14. thermography tti eique v ce eee sns et 23 3 4 Electroluminescence EL and Photoluminescence PL imaging techniques 24 3 5 Resonance ultrasonic vibrations RUV technique esses 25 4 PV module performance measurements and degradation rate estimation 26 AA Backeround ss ea aee e et ac pese da cL a UN eee 26 4 2 Description of different PV modules used in the 26 4 2 1 Monocrystalline silicon mc Si BP275 amp BP585 27 4 2 2 Polycrystalline silicon p Si SX 75 amp PW750 70 29 4 3 Major proeed tess iouis eth aret ein D b E 31 4 3 1 Temperature eoe e Oei inc 31 4 3 2 Solar Radiation Measurement 31 4 3 2 don DM aal da ub Nac Rudi Dale a ded a a 32 4 3 3 I V curve measurement and mapping to STC sss 32 5 Results 15 5 1 0 34 5 1 STC Test Results sas oe dE du ag 39 5 2 mitial STC Test ReSUlt cis etait abd opu 39 5 3 STC power after outdoor exposure ala epa vi aede 40 5 4 The rate of module degradation nana eds 41 6 Limitations and further research aanssssstvrttcnniinnnnnnnnnnsnnnnnannnnindnnnnnaannnnnnum 43 7 Conclusions and Recommendations e eere eee eee eee eee een tentata a 44
15. 2 PM 3 30 29 700 3 06 20 27 44 84 4 3 23 94 73 03 PM AVG 76 29 36 Table 10 STC results and variation in Wp over a 12 year period for four different modules Anna Carr s Results Jennifer Martin s Results A Zendegani s Results My Results Cell Wp Wp Wp Wp Exp Wp Diff Ex Wp Wp Diff Ex Wp Diff Exp Wp Diff dule Rated Warranty Initial Final initial po May Final initialto po Mar initial to o Aug 1 initial to e W W Period W Sure Mar 02 to sur 03 Jun 03 Jun 03 sur 07 Mar 07 sure 2 W Aug 12 W W Mar 0 W W W 2 BP2 mc 75 70 20yrs 56 81 6 16 78 7 3 55 2 6 77 7 77 38 5 17 6 4 75 81 7 1 11 8 17 9 75 Si 10yrs 63 mths yrs 4 yrs yrs 66 98 BP5 mc 85 80 20yrs 64 86 7 13 86 1 0 69 2 3 83 7 83 1 4 15 6 1 83 82 3 32 11 5 76 29 12 85 S 10yrs 72 mths yrs 4 yrs yrs SX p Si 75 70 20yrs 56 76 4 16 75 3 1 44 2 7 74 2 74 09 3 02 6 5 72 54 5 05 11 9 70 26 8 04 75 10yrs 52 mths yrs 2 yrs yrs PW p Si 70 65 25yrs 52 68 6 19 65 9 3 94 3yr 61 6 61 41 10 48 6 7 52 86 22 94 12 1 47 06 31 4 750 mths S 8 yrs yrs 70 37 Wp in different periods 9 BP275 H SX 75 ABP585 750 70 o E 2 3 9 E E Mar 03 Dec 05 Sep 08
16. 6 0 7 Cell Voltage V Figure 7 Effect of shunt resistance on the curve of solar cells Source Emery 2011 Handbook of Photovoltaic Science and Engineering 13 Normally Rs increase results from delamination of contacts or corrosion induced by water vapor while decrease is mainly due to hot spot partial shading thermal stress and localized ohmic shorts Alers et al 2011 Figure 8 shows the simulation results for a given module with one cell shaded 50 and a range of shunt resistances for the cell It can be found that a shaded cell leads to Rsy decrease and MPP reduction while an unshaded cell has no impact The thermal stress results from the module temperature increase can cause decrease Figure 9 illustrates a log normal distribution of the shunt resistance in an unstressed module and a stressed module It is seen that the distribution of of the stressed module becomes broader and shifts to a smaller value Alers et al 2011 4 Shunt resistance of shaded cell 9 40 ohms e 16 ohms Current A N x 8 ohms 1 4 ohms No Shading 0 0 10 20 30 40 50 Voltage A Figure 8 Simulation results for the module with one cell shaded 50 and a range of shunt resistances for the cell Source Alers et al 2010 Degradation of individual cells in a module measured with differential IV analysis 14 Stress Tested In Normal Probability 1 10 100 1000 Shunt R
17. 75 module is the only one whose power output is still higher than its IGM of 70 W while the other three modules have degraded below to their minimum tolerance It was also discovered that the performance of the SX 75 module is quite good with the lowest degradation rate of 0 66 year while the 45 situation for the PW750 70 module 15 the worst and has resulted in considerable power losses of over 20 W equal to a degradation rate of 2 67 year after 12 years of exposure However it is inevitable that experimental errors induced by changed meteorological conditions and the inaccuracy of equipments can affect the accuracy of the measured results So it is recommend that a specific simulation be used in future research 46 Reference Alers G B Zhou J Deline C Hacke P and Kurtz S R 2011 Degradation of individual cells in a module measured with differential IV analysis Progress In Photovoltaics Research and Application 19 977 982 doi 10 1002 pip 1013 Boyle G 2004 Solar Photovoltaics In Renewable Energy Power For A Sustainable Future 2 ed edited by Godfrey Boyle 66 104 London Oxford University Press BP Solar 2012 Photovoltaic Module BP275 Specification Sheet http www troquedeenergia com Produtos LogosModulosSolares BP 275F pdf Accessed 14 08 2012 BP Solar 2012 Photovoltaic Module SX 75 SX 80 and SX 85 Specification Sheet http www solarpanelsaustralia com au downloads bps
18. 85 70 Time Module Temperature 9C 10 30 AM 29 31 31 31 11 30AM 30 30 32 40 12 30 PM 33 35 33 32 1 30 PM 32 35 32 33 2 30 PM 35 40 37 40 3 30 PM 30 27 30 29 4 3 2 Solar Radiation Measurement Solar radiation 15 a key parameter that can determine whether a PV module works properly Basically the solar radiation involves two components direct beam and diffuse radiation In this project a thermopile pyranometer is mounted flat on the solar module for measuring total solar irradiance Compared with other techniques for solar irradiance measurement the thermopile pyranometer has significant advantages of quick response and high accuracy However a thermopile pyranometer should be calibrated before starting measurement otherwise it may result in considerable errors 31 4 3 2 1 Pyranometer For maximizing the accuracy of solar irradiance readings a Kipp amp ZonenSP Lite 2 pyranometer was used to measure solar irradiance Compared with reference cells a Kipp amp ZonenSP Lite 2 pyranometer is much more accurate and simpler to use Appendix C Its sensitivity is 64 4 uV W m at normal incidence and airmass 1 5 solar irradiance and its response time is less than 500 ns The Kipp amp Zonen SP Lite 2 pyranometer can operate under all weather conditions and the working temperature ranges from 30 C to 70 C www kippzonen com The calibration procedure 15 based on a comparison with a reference SP Lite pyranometer under artific
19. P480H module It took great effort to extract the correct datasheet for BP480H from the PV manufacturer One module label only carried Vmpo amp Impo information not Voco amp Isco Because the module number was a reasonable match to the SMD and Vmpo and Impo were exact matches it is likely that the SMD entry chosen accurately reflected the module in question As an extra precaution the datasheet was requested from the manufacturer with the following reply after a long delay and a reminder Given author s experience with BP and Sharp the reluctance of manufacturers to maintain and supply data on PV modules of a reasonable age adds to difficulties in assessing degradation Open the STCMS STC mapping tool_master_220611 xls and save it with an appropriate filename for the curve or curves being mapped Open the SMD in excel and copy the row corresponding to the PV module being tested Paste this row into the STCMS at row 5 If the SMD entry is not an exact match to the module label as described above then the appropriate figures should be adjusted in the spreadsheet at this stage Step 2 Enter the system commissioning date in row 7 Step 3 The Daystar IV curve tracer produces a file with extension This file must be opened using the Daystar IV curve tracer software Resulting in a display like that below 51
20. PV Module Troubleshooting and Measurement Zihang Ding This dissertation is presented for Master of Science In Renewable Energy of Murdoch University Western Australia November 2012 Copyright 2012 Zihang Ding li I declare that this dissertation 15 my own account of my research and contains as its main content work which has not been previously submitted for a degree at any tertiary institution Zihang Ding iii Abstract Over the past few years the solar photovoltaic PV industry has taken the lead in the market growth of the Australian renewable energy industry Due to the steady manufacturing cost reduction and Australian government support a great number of PV modules have been installed for domestic and commercial use It is well known that the performance of PV modules is greatly influenced by many factors such as solar irradiance ambient temperature and the angle of incidence In addition the output of PV systems gradually degrades over time under exposure to the sun and other environmental conditions such as a high temperature and moisture Normally the limited warranty period of PV modules ranges from 20 to 25 years which means the rate of degradation should be less than 1 per year However we found that some PV modules performed much worse than the normal ones and their outputs dropped much faster than the expected Therefore in any PV module troubleshooting it is important to figure out the c
21. STC A Isc at STC RRPGP In this document refers to the project of 1 semester 2011 funded by RRPGP SMD Sandia Module Database STCMS STC mapping spreadsheet V impo Vmp at STC V Voco Voc at STC V Step 1 Check that PV module is in the SMD and copy and paste into STCMS The STCMS uses the model as outlined in King Boyson and Kratochvil 2004 As such it relies on the SMD for solar module characteristics Therefore the solar array being mapped must contain modules that are included in the SMD For the RRPGP a match was judged as exact if the model number was basically the same as that listed in the SMD and the Voco Isco Vmpo Impo figures given on the module label matched exactly those listed in the SMD Sometimes an exact match was not found Where an exact match was not found a module was selected from the same family with similar Voco Isco Vmpo amp Impo These figures where then adjusted to exactly reflect those given on the module label Further validation of this method could be conducted by sourcing the original datasheet for each module Figures for alsc BVoco and the power temperature coefficient are commonly supplied on datasheets These figures can be checked against the alsc and BVmpo given on the SMD This extra validation was conducted on one module type BP480H in the RRPGP because the nearest match on the SMD appeared such that it may not have 50 been sufficiently similar to the B
22. Tobias 2011 Basically there two types of shading near field shading and horizon shading For near field shading it just affects only a fraction of an array However horizon shading can influence either all or none of an array The typical examples of near field shading include local obstructions like trees and walls and rooftop facilities Electrically near field shading can be seen as a mismatch issue because 1f one string in a module 15 shaded the whole module will be shaded and the entire module can 19 only generate the same amount of current as its weakest string Tobias 2011 Figure 15 shows an example of near field shading P ars Figure 15 Near field shading induced by trees Source Emery 2011 Handbook of Photovoltaic Science and Engineering Horizon shading includes distant hills or some very large objects which are very close to the array such as adjacent rooftops or buildings Tobias 2011 Horizon shading can obstruct any beam radiation from falling on the array so a horizon shaded array can only receive diffuse radiation Figure 16 shows an example of horizon shading po NEL ut 2 y P rJ 274 55 Aa Figure 16 Horizon shading induced by adjacent array Source Emery 2011 Handbook of Photovoltaic Science and Engineering 20 Near field shading 15 complex to model but very easy to avoid By contrast horizon shading 15 simple to model but difficult or impossible to reduce As is s
23. ad decreased by 10 48 to a value of 3 6 W Well below the guaranteed minimum power IGM of 65 W After 6 to 7 years of sun exposure 2007 the measured maximum power of the PW750 70 polycrystalline module was very close to its 25 year warranted minimum value of 52 W 40 Compared with its initial W value the measured peak power had dropped by nearly 25 However the two BP mc Si modules and SX 75 51 module degraded much more slowly by less than 9 4 Compared with the two mono crystalline silicon modules the BP585 module has the lowest power loss which 15 less than 6 After about 12 years of outdoor exposure the module degradation in these four modules continues As is shown in the current results the measured W values of the BP275 and BP585 modules had dropped by 17 9 and 12 to the values of 3 1 and 3 8 W below their IGM of 70 and 80 W However the two BP mc Si modules were still in higher than their warranted values The SX 75 polycrystalline silicon module was the only module whose power degradation is the slowest lt 8 1 after 12 years outdoor exposure and its measured W value is still higher than its IGM value of 70 W 5 4 The rate of module degradation According to the four groups of measured results in four different periods one can determine the changes of module performance and determine the rate of module degradation As is shown in Figure 22 the relationship between power degradation and time fits a st
24. and hail damage could result in micro cracks This study also introduces two major types of module failure caused by soiling and shading Both types of module failure can lead to considerable power losses 44 In general module troubleshooting 15 divided into four steps The first step 15 visual inspection in order to detect bubbles delamination encapsulant discoloration glass breakage and obvious cell cracks The next step 15 thermal analysis using an infrared camera to detect hot spots or an abnormal area of a module which has a much higher temperature A bypass diode 15 an effective way to eliminate hot spots but it can result in extra power losses In addition the LIT technique combined with IR imaging is used to detect shunt defects Further analysis consists of EL and PL imaging techniques which can detect invisible defects such as micro cracks Although the RUV technique has high accuracy in micro crack detection it is relatively expensive and complex The final step is outdoor PV module performance measurements In this study mapping measured results to STC 15 one of the most important steps in the outdoor PV module performance measurement because the results measured in different weather conditions are difficult to compare and need to be normalized to the same condition for comparison In terms of the normalized results it was found that the four measured modules have different rates of power degradation in a 12 year period The SX
25. apped to STC to open the curve window as seen below 52 f IVPC South West Test Day1 ivd CEK Peak Power W 75631 Vpeak V 29 781 Ipeak A 25624 Fil Factor PA 581 39 348 hc A 32 316 40 r 35 30 4 25 20 Amps A 15 10 50 Site Brazier Sub System 8 160 W Module BP3160 U Irad 1 W m2 Inad 2 w m2 Temp 1 C Temp 2 C Time Date Noer Start of Steve Benzie property Dirty slope 30 degrees z 793 999 456 44 11 08 22 Step 5 Press control D to display the curve data and select the required data as shown below selected section in blue 53 IVPC South West Test Day1 ivd Site Sub System Module ID Misc Category Voc Isc Fill Factor Peak Power Irrad 1 Irrad 2 Temp 1 Temp 2 Step 6 Press control to copy data Open STC mapping spreadsheet STC mapping tool master 220611 xls and save it under an appropriate name for the curve being mapped Paste data into area adjacent to yellow highlighted area as shown below The yellow area is the original reference calculation and formulas which must remain untouched 54 Ea 0 6 F STC mapping tool_master_220611 xls Compat
26. auses that result in dramatic power losses and measure the output of the proper PV modules under operating conditions over a long term A rated PV module refers to Standard Test Conditions STC of 1000 W m solar irradiance Air Mass AM1 5 and a cell or module temperature of 25 C measured prior to outdoor exposure However module performance in real conditions is iv variable Therefore it is necessary to provide more information a module in actual operating conditions over a long term This study 15 divided into two parts The first part is a theoretical analysis of module degradation and troubleshooting techniques The second part is mainly practical measurements for module degradation estimation PV module performance measurements are used to obtain highly accurate output data from four different PV modules representing three different technologies monocrystalline silicon mc Si polycrystalline silicon p Si and laser grooved buried contact crystalline silicon LGBC c Si Degradation rate estimation is based on comparisons of three groups of previous test results obtained in three different periods 2002 2003 and 2007 by three PhD Murdoch University students Finally a verification process by a simulator is briefly introduced Acknowledgements I really appreciate my major supervisors Sinisa Djordjevic and Trevor Pryor for their academic and practical support and encouragement throughout the project I also wou
27. ber of safety issues caused by cell damage and packaging material degradation All of the above problems that affect module performance are referred to as module degradation Normally the lifecycle of a PV module ranges from 20 to 30 years which means the rate of module degradation should be less than 1 per year Nevertheless it 18 reported that some modules initially exceed the guaranteed level Rapid module degradation can lead to short module lifecycle and high replacement cost Therefore it is necessary to provide effective troubleshooting techniques and proper module performance measurements for reducing module degradation 1 2 Objective of the Thesis The main objective of this project is to investigate the mechanisms of module degradation and compare different troubleshooting techniques This project also aims to specify the procedure for outdoor measurements of PV module performance and estimate the module degradation rate The objectives are achieved by both specific theoretical analysis and practical measurements The test samples include four different PV modules consisting of three different PV technologies monocrystalline silicon mc Si polycrystalline silicon p Si and laser grooved buried contact crystalline silicon LGBC c Si 1 3 Research Focus The study focuses on the exploration of the mechanisms of module degradation and module performance measurement and comparison The fundamental questions that the project wi
28. d value However PW750 70 module was about 2 below its rated value This exception could result from module damage during transportation 39 5 3 STC power after outdoor exposure Figure 21 presents four groups of outdoor results measured in different periods They include three previous outdoor results provided by A Carr J Martin and A Zendegani in 2001 2003 and 2007 respectively and the results measured in the current study in August 2012 In order to better compare the initial results and the outdoor results the percentage difference between the initial W value and the measured W after outdoor exposure are calculated It was found that W decrease in the four modules observed by Carr after the first 16 months of outdoor exposure agrees with those tested after 15 months of sun exposure at CH Testing Center for PV modules Cycle 8 project Chianese et al 2002 Chianese et al 2002 noted that similar maximum power losses in almost all crystalline silicon modules range from 0 7 to 3 5 after 15 months of outdoor exposure and the power degradation is caused by the decrease of carrier lifetime in the bulk material After 3 years of outdoor exposure it can be seen that the maximum power losses of the four modules were between 3 and 11 Although the four modules experienced a large degradation their W values were still within the tolerance range provided by the manufacturers The only exception was the PW750 70 module which h
29. e Test Voc Test Pmax Test Ise STC Voc STC Pmax STC ature radiation A V W A V W CO W m 10 30 31 970 3 862 20 4 54 07 3 91 23 35 65 65 AM 11 30 32 1043 4 078 20 36 56 04 3 83 23 32 64 61 AM 12 30 33 1060 4 424 20 58 42 4 09 23 22 67 93 1 30 32 1050 4 331 20 01 57 23 4 04 22 95 65 86 PM 2 30 37 920 3 686 19 68 49 24 3 92 24 77 70 57 PM 3 30 30 700 2 809 20 28 40 65 3 95 24 28 67 27 PM AVG 66 98 Table 8 Measured results and mapped results for SX 75 module Time Tempe Solar Ise Test Voc Test Pmax Test l STC V STC Pmax STC rature radiation A V W A V W CO W m 10 30 31 970 4 575 19 87 58 33 4 63 22 81 71 73 AM 11 30 30 1043 4 731 19 88 58 94 4 45 22 2 66 13 AM 12 30 35 1060 5 071 19 22 58 35 4 69 23 08 71 68 PM 1 30 35 1050 4 905 19 29 56 79 4 58 23 19 70 43 PM 2 30 40 920 4 253 18 94 49 57 4 52 24 99 76 35 3 30 27 700 3 233 19 78 41 37 4 55 22 8 65 25 PM AVG 70 26 35 Table 9 Measured results and mapped results for BP585 module Time Tempe Solar Voc Test Pmax Test Ll4 STC Voc STC Pmax STC rature radiation A V W A V W CO W m 10 30 31 970 4 645 20 33 62 98 4 7 23 27 76 86 AM 11 30 30 1043 4 557 20 24 62 84 4 29 22 56 69 97 AM 12 30 32 1060 4 88 19 8 63 66 4 52 22 7 73 26 PM 1 30 32 1050 4 692 19 83 61 72 4 36 25 32 82 2 PM 2 30 40 920 4 076 19 59 54 2 4 33 25 64 82 4
30. e electrical characteristics SX 75 SX 80 SX 85 Maximum power Pmax 75W 80W 85W Voltage at Pmax Vmp 16 5V 16 8V 17 1V Current at Pmax Imp 4 54A 4 75A 4 97A Guaranteed minimum Pmax ZOW 75W 80W Short circuit current Isc 4 97A 5 17A 5 30A Open circuit voltage Voc 20 7V 21 0V 21 3V Maximum system voltage Temperature coefficient of Isc Temperature coefficient of Voc Temperature coefficient of power ENSE AEE 0 5 0 05 mG 47429Q M maeman Source http www solarpanelsaustralia com au downloads bpsolar_sx80 pdf The other type of module is PW750 70 This module contains 4x9 high efficiency polycrystalline solar cells with an anti reflective material BP 2002 The rated power is 70W at STC The electrical characteristics are shown in Table 4 Table 4 PW750 70 module electrical characteristics Electrical Characteristics STC Power Rating W 70 Open Circuit Voltage Voc V 21 3 Short Circuit Current lsc A 4 50 Voltage at Maximim Power Vmp V 16 7 Current at Maximim Power Imp A 4 20 Panel Efficiency 10 2 Fill Factor 73 0 Source www posharp com 30 4 3 Major procedures 4 3 1 Temperature measurement A thermocouple probe was used to measure the back of module temperature Table 5 shows the different module temperatures measured at different times Table 5 Module temperature results Module Type PW750 SX 75 BP275F 5
31. endix A 33 5 Results and discussions Tables 6 9 illustrate the testing results and mapping results obtained from the four different modules Six hourly readings were taken between 10 30 AM and 3 30 PM for each module and all the measurements were taken at the same time and under a clear sky to ensure no apparent error occurs Compared with the rated output it is found that the actual results are much lower This demonstrates that PV modules exposed to outdoor conditions for 12 years can experience a gradual power decrease However it requires further analysis to calculate the exact degradation rate and examine if such a large power decrease is within the guaranteed level Table 6 Measured results and mapped results for PW750 70 module Time Temperature Solar Isc Test Voc Test Pmax Test I4 STC Voc STC Pmax STC C radiation A V W A V W W m 10 30 29 970 3 523 20 19 38 5 3 57 22 65 46 25 AM 11 30 30 1043 3 83 19 98 38 27 3 61 22 3 43 82 AM 12 30 33 1060 4 23 19 39 39 02 3 91 22 61 46 96 PM 1 30 32 1050 4 094 19 59 38 42 3 83 22 53 45 77 PM 2 30 35 920 3 481 19 26 34 2 3 71 23 71 49 35 PM 3 30 30 700 2 644 19 7 29 64 3 72 23 7 50 22 PM AVG 47 06 34 Table 7 Measured results and mapped results for BP275 module Time Temper Solar Is
32. erated electron hole pairs have energy in excess of the band gap however their states will decay to near the edges of their respective bands immediately Markvart 2000 Also the second law of thermodynamics proves that there is a conversion efficiency limit for a solar cell therefore the fundamental power losses cannot be avoided ME photon Figure 3 The generation of electron hole pairs by light Source Markvart 2000 Solar Electricity 2 4 2 Recombination Recombination is defined as an opposite process to carrier generation when an electron hole pair disappears Markvart 2000 Recombination occurs when the electrons fall back into the valence band and recombine with holes In this case both 10 the voltage and current will be reduced and therefore the power output decreases Markvart 2000 Surface recombination and recombination at contacts are two common types of recombination As shown in Figure 4 there are two ways for minimizing the recombination losses 15 to attach a layer of passivating oxide to reduce surface recombination the other 15 to surround the contacts by heavily doped regions acting as minority carrier mirrors which can prevent the minority carriers from getting into the contacts and recombining Markvart 2000 Silicon dioxide on front passivates the surface and Heavy doping under contacts reduces surface recombination keeps minority carriers away from high recombination f
33. esistance MQ cm Figure 9 Log normal distribution of the shunt resistance in an unstressed module and a stressed module Source Alers et al 2010 Degradation of individual cells in a module measured with differential IV analysis 2 4 4 Power loss exceeding the guaranteed level Every module has its own rated maximum power and the allowed tolerance and this information can be obtained under standard test conditions Also manufacturers regulate the guaranteed power that a module can deliver Normally the guaranteed power 15 90 of the rated maximum power for a period of 10 15 years Munoz 2011 If the time 15 increased up to 20 25 years the guaranteed power will decrease to 80 of the rated maximum power However some new modules have been found to have higher power losses than their guaranteed level after only a few weeks Munoz 2011 Measuring the representative samples periodically can detect significant power loss 15 higher than the guaranteed level but it is difficult because all the samples must be disconnected from the solar plant when they are under examination Munoz 2011 2 4 5 Power loss in different strings As shown in Figure 10 there is a problem occurring in one string of cells due to a jump in the curve The curve analysis can be used to measure module performance string by string By comparing different V curves from different strings the defective areas can be detected Figures 11 13 represent
34. hown in Figure 17 and Figure 18 we can see that partial shading leads to great power losses in a crystalline silicon module whose the output dropped from 24 W to 4 8 W I V and P V Characteristics 25 E S E E O Power W 10 Voltage V Figure 17 A crystalline module without shading I V and P V Characteristies 5 Current A Power W Voltage V Figure 18 A crystalline module with partial shading Source pec621 1lab dinz 31180265 xlsx 21 3 Troubleshooting techniques 3 1 Visual inspection Visual inspection which 15 the first step of fault detection allows some module degradations to be detected by sight The method 15 suitable for detecting some visible defects such as yellowing delamination bubbles cracks in cells misalignments and burnt cells Also visual inspection can determine whether a PV module should be tested with the following procedures The inspection must be performed under natural sunlight where PV modules can get good quality solar radiation Furthermore reflections should be avoided during the test because it can result in defective images In addition it is essential to inspect PV modules from different angles for differentiating the layer where the defects could be and avoiding the errors caused by defective images Tobias 2011 In order to reduce detection errors one should take a group of photos rather than a single one 3 2 Infra
35. hown in the Table 1 below Table 1 BP 275 module electrical characteristics Typical Electrical Characteristics BP 270F BP 275F Maximum Power Pax 70W 75W Voltage at Pmax Vmp 17 0V 17 0V Current at Imp 4 16A 4 45A Warranted minimum Pmax 65W 70W Short circuit current 4 48A 4 75 Open cicuit voltage 21 4V 21 4V Temperature coefficient of Isc 0 065 0 015 C Temperature coefficient of Voc 80 10 mV C Temperature coefficient of Power 0 5 0 05 C NOCT 47 2 C Maximum System Voltage 600V Source http www troquedeenergia com Produtos LogosModulosSolares BP 275F pdf The other type of monocrystalline module is BP585 This module is produced by the BP Solar Company as well However the BP585 module is different from the BP275 module because the BP Solar Company used a world leading commercial laser cell processing technology to produce the BP585 module By using this technology the 28 efficiency of the BP585 15 increased to 17 and the module surface can absorb more solar radiation and reduce reflection BP Solar 2002 The rated output of the BP585F 15 85W and it consists of 36 laser grooved buried contact monocrystalline silicon cells Table 2 lists its electrical characteristics Table 2 BP 585 module electrical characteristics BP 585 580 Maximum power P max 85W 80W Voltage at Pmax Vip 18 0V 18 0V Current at P max Imp 4 72A 4 44A Warranted minimum Pmax 80 8W 76W
36. ial sun generated by an AC voltage stabilizer This confirms that the instrument calibration factor is 1 of the stated calibration factor for an angle of incidence around 50 degrees www kippzonen com 4 3 3 I V curve measurement and mapping to STC A Prova 210 solar module analyzer was utilized for measuring the I V curve of the PV modules The accuracy and reliability of this device can be found in specification sheet Appendix D It can be seen that both the voltage and the current should be measured within 1 and this means that the power may be calculated with 2 accuracy In this project the accuracy of the I V curve testing is largely depended on the voltage and current measurements of this device so a proper calibration is necessary to ensure that no obvious error occurs The calibration method can be found in the measurement procedure Appendix B 22 After obtaining test results by using the Prova 210 solar module analyzer a STC mapping spreadsheet STC mapping tool master 220611 xls at MU was used to normalize the results to STC This is because the electrical characteristics of modules are greatly affected by local climate conditions temperature solar irradiance etc which means the test results are different and cannot be directly compared to previous results Mapping testing results to STC can make all the results comparable and help to calculate the degradation rate The specific mapping procedure is described in App
37. ibility Mode Microsoft Excel Home insert _ Pagelayout Formulas Data Review View Add Ins 7m d 5 B date Calibri gt v E Wrap ext General d f 157 Paste ar Merge amp Center m 99 Conditional Format Cell Insert J Format Painter B kaa PESENE IE al Formatting as Table Styles Clipboard 5 KR sj Number Tz Styles EF c e NEM 1 Notes 2 3 INPUTS 4 Model Vintage Area Vintage Area Material Series Cells Par 5 BP Solar BP380 2006 E 2006 E 0 649 2006 E 0 649 mc Si 36 6 4 7 System commissioning date mm dd year 30 01 2005 30 01 2005 8 13 q coulomb 1 602180E 19 1 602180E 19 1 602180E 19 1 602180E 19 1 60218 19 1 60218 19 1 14 k J K 1 380660E 23 1 380660E 23 1 380660E 23 1 380660E 23 1 38066 23 1 38066E 23 1 16 COPY amp PASTE FROM IVPC 10 37 Percent diffuse assumption Step 7 If more than one curve was taken with the same array then repeat from step 4 pasting into adjacent columns as shown below In the RRPGP usually ten curves had been taken 1 minute apart When first pasted the date format is mm dd yyyy and this must be manually changed to dd mm yyyy on each column 55 4 D x STC mapping tool_master_220611 xls Compatibility Mode Microsoft Excel ca Insert Layout Formulas Data Review View Add Ins P cut Calibri A a elle ER e
38. kage current and ground faults Quintana et al 2002 In addition package damage can produce safety hazards in high voltage systems due to the lack of protective insulation Such failures may induce electric shock and create a pathway for electrochemical corrosion Quintana et al 2002 The potential shock hazard can be worsened by moisture intrusion into the package 2 4 Power losses in solar cells 2 4 1 Fundamental losses Photovoltaic energy conversion relies on the quantum nature of light which it is seen as a flux of particles called photons which carry the energy Markvart 2000 Equation 1 demonstrates that each photon carries the energy However only a part of photons can be converted into electricity by solar cells On a clear day about 4 4 10 7 photons on average reach a square centimeter of the Earth s surface every second Markvart 2000 However not all the photovoltaic energy can be absorbed and transformed to electricity by the solar cells because only those photons whose energy in excess of the band gap are available Solar cells are made from semiconductors so when such a photon goes into solar cells the absorption process produces electron hole pairs D Where 7 15 the Planck constant c 15 the speed of light and 2 is the wavelength of light The nature of the absorption process also proves that there 15 a fraction of power from photons lost in the form of heat See Figure 3 It is because all the gen
39. lar cells have shunt defects there will be a temperature discrepancy It is possible to adjust the injection current to measure different types of shunt defects LIT test can be performed in dark condition DLIT as well as illumination condition ILIT In the case of ILIT solar cells often work under open circuit conditions By using this method small defects can be detected because the detector is locked with bias current and it is not necessary to use high current Munoz 2011 Normally for taking simple IR images the detector is a charge coupled detector CCD and the range of wavelengths is 3 5 um because the temperature is at midrange Munoz 2011 23 3 4 Electroluminescence EL and Photoluminescence PL imaging techniques As discussed above both IR imaging and LIT techniques are based on thermal effects However EL and PL imaging techniques depend on photons emitted by recombination of excited carriers in a solar cell The Electroluminescence EL effect makes use of the inherent property of some materials that can emit photons in a strong electric field when injecting a current Munoz 2011 In this case a current 15 injected into the solar cells and then initiates the EL effect In contrast the Photoluminescence PL effect occurs when those excited carriers which have absorbed photons become unstable and re emit photons Munoz 2011 In this case the excitation can be achieved by incident light over the module and light emis
40. ld like to thank Dr David Parlevliet for providing me with many experimental devices and useful guidance vi Glossary Abbreviation EL IGM Isc Imp I V curve LGBC MPP MPPT NREL MU mc Si p Si Pmax POA PL PV STC Definition Electroluminescence Initial Guaranteed Minimum Pmax of module Short Circuit Current Maximum Power Current Current Voltage Characteristic Curve Laser Grooved Buried Contact Maximum Power Point Maximum Power Point Tracker National Renewable Energy Laboratory USA Murdoch University Monocrystalline silicon Polycrystalline silicon Maximum Power Plant of Array Photoluminescence Photovoltaic Standard Test Conditions 1000W m AM Mass 1 5 and 25 C cell Temperature Temperature Coefficient Maximum Power Voltage Open Circuit Voltage Watt Watt hour Peak Watt Module efficiency Temperature Coefficient of Power Temperature Coefficient of Current Temperature Coefficient of Voltage vii Table of Contents PRPS ERAGE ede a a desta aan aan danas incu la T ERE Ua rd a iv ACknoWwledo0cMents snsus inmunsnitksvmssitss bsskinsi bssiandaninisasnainas kanriusninnndandaninah kanin vi CGHIOSSWEV edens E P IA AE NEN Un EUN e anana aana vii o oii RIO SURE T ENS D IIO SIUE 1 RAC KOT OUI ec ono eta ud ied a ecu ur 1 1 2 Objective OP the THESIS sci vs av o Oe OR e D Se 2 1 3 Research
41. ll address are e How module degradation occurs and how it impacts module performance e How to detect module degradation Why comparing results of STC is so important 1 4 Thesis Outline This project consists of five components Firstly the study discusses the mechanisms and impacts of some typical module degradations Secondly some advanced troubleshooting techniques such as infrared imaging IR and lock in thermography LIT and electroluminescence EL and photoluminescence RL imaging are introduced After that a series of PV module performance measurements temperature solar irradiance I V curve characteristics on four target modules are deployed The measured results are mapped to STC and compared to three groups of previous results for calculating degradation rate Anna Carr who was a Murdoch PhD student measured the first group of results of the four modules in 2001 2002 Jennifer Martin who was a MUERI trainee continued the study over 5 years 2002 2007 Zendegani another Murdoch MSc student did further research on the performance for the four modules and obtained the third set of data in 2007 Then a verification process is used to evaluate the accuracy of the estimated degradation rate Finally recommendations and conclusions are presented 2 Module degradation 2 1 Overview of module degradation It was not until the early 1970s that information on module degradation was collected Quintana et al 2002 Howe
42. m at ground level varies considerably Advantage 2 Pyranometers measure the total solar spectrum from 0 3 to 3 micrometers wavelength and give an integrated measurement of the total short wave solar energy available under all conditions Pyranometers have been the instruments used to measure solar radiation for over 80 years The worldwide solar radiation database is founded on pyranometer measurements Also the pyranometer calibration factor is very stable over time Performance classifications are defined by ISO 9060 and the calibration methods by ISO 9847 Advantage 3 The advantage here is that the pyranometer integrates over time typically between 5 and 20 seconds This means that sudden changes such as passing small clouds birds and planes will not give transient spikes or dips in the data A pyranometer will give a correct integrated values over a day when using sample intervals of 20 seconds or more Advantage 4 When different PV cell types are used in one plant a separate reference cell for each type should be used but only one pyranometer is required for monitoring all types 59 Advantage 5 The temperature dependency of pyranometers can be as low as 1 over 70 temperature range depending on type This 15 much lower than that of PV panels and reference cells Advantage 6 Most panels and reference cells have performance are specified under Standard Test Conditions These are conditions of 25 ambient tempera
43. n General d gi cm gt i Copy ce B ZI U amp EE Merge amp Center v 55505 Conditional Format Cell Insert Delete Format J Format Painter ora Mera JEN E Formatting as Table Styles Paste Clipboard E Font iE Alignment ic Number Ta Styles Cells F17 n EI I B JL c aaa 1 Notes 2 3 INPUTS 4 Model Vintage Area Vintage Area Material Series Cells Parallel C S Isco 5 BP Solar BP380 2006 E 2006 E 0 649 2006 E 0 649 mc Si 36 1 6 7 System commissioning date mm dd year 30 01 2005 30 01 2005 8 13 q coulomb 1 602180E 19 1 602180E 19 1 602180E 19 1 602180E 19 1 60218E 19 1 60218E 19 1 60218 19 1 6 14 J K 1 380660 23 1 380660 23 1 380660 23 1 380660E 23 1 38066E 23 1 38066E 23 1 38066E 23 1 3 1 2 5 12 2011 5 12 2011 11 08 22 11 11 00 Brazier Brazier 8 160 W BP3160 U BP3160 U Unfiled Unfiled 39 949 39 831 32 316 32 619 59 1 59 763 1 765 9 29 781 29 553 25 624 25 918 793 822 999 999 45 6 46 4 44 4 45 7 10 10 37 Percent diffuse assumption 22 Step 8 Once all the curves are entered into the STCMS Ensure a figure for percent diffuse is in each relevant column for row 37 Step 9 Enter latitude and longitude in rows 40 43 Step 10 AOI If the array is on a tracker then AOI is best measured directly before commencing taking of curves In this case the measured AOI must overwrite the fo
44. odules and guaranty conditions 2 5 Module failure 2 5 1 Dust and Soiling It has been proved that dust soiling leaves bird droppings soot snow and frost can reduce the amount of electrical current produced by PV modules Therefore the power output of PV modules will suffer considerable losses Basically all the above effects vary with local climate and tend to be seasonally dependent Tobias 2011 Dust accumulation 15 largely affected by local weather patterns local 5015 air and automobile traffic and agricultural activities It was identified that soiling could lead to monthly power losses up to 25 and yearly losses of 7 if no proper mitigation was carried out Tobias 2011 Therefore regular module array cleaning is necessary to minimize dust and soiling effects According to recent studies it was found that a single washing in the middle of the dry season could reduce annual dust losses by half 18 from 6 to 3 Tobias 2011 Figure 14 illustrates dust induced shading on PV modules ere du l d MS 4D 4 Piere 5 Figure 14 Dust induced shading PV modules Source Qasem et al 2012 Dust induced shading on photovoltaic modules 2 5 2 Shading Shading 15 another common module failure induced by external factors e g dust tree shadings It has been demonstrated that shade covering as little as 5 10 of an array can reduce power output by over 80
45. olar sx80 pdf Accessed 14 08 2012 BP Solar 2012 Photovoltaic Module BP585 Specification Sheet http www oksolar com pdfiles Solar o20Panels 620bp 585 pdf Accessed 14 08 2012 Carr A J 2005 A detailed performance comparison of PV modules of different technologies and the implications for PV system design methods PhD thesis Murdoch University Chianese D Cereghetti N Friesen G Bur E Realini A and Rezzonico S 2002 Power and Energy Production of PV Modules In Proceeding of the PV in Europe from PV Technology Energy Solutions Rome Italy October 2002 http www isaac supsi ch isaac pubblicazioni Fotovoltaico Conferences Roma 620 Italy 20 20PV 201n 20Europe 20 20October 202002 pb2 1 20power 20and 2 Oenergy 20production 200f 20pv 20modules pdf Accessed 12 10 2012 Emery K Burdick J Catyem Y Dunlavy D Field H Kroposki B Moriarty T Ottoson L Rummel S Strand T and Wanlass M W 1996 Temperature dependence of photovoltaic cells modules and systems In proceeding of the 25 IEEE Photovoltaic Specialists Conference Washington DC May 12 17 1996 1275 1278 IEEE Emery K 2011 Measurement and Characterization of Solar Cells and Modules In Handbook of Photovoltaic Science and Engineering 2 ed edited by Antonio Luque and Steven Hegedus 797 834 A John Wiley and Sons Ltd 47 Haberlin H 2010 Solar Modules and Solar Generators
46. osses recombination series resistance etc and module failure e g shading soiling 2 2 Cell failure 2 2 1 Hot spot A hot spot is a very common cell defect that results from cracked or shaded solar cells Hot spot is characterized by cell overheating induced by short circuit in series connection Herrmann et al 1997 Normally a PV module consists of several strings and each string contains more than two series connected cells If one of the series connected cells is shaded or cracked the operating current produced by the whole string will drop dramatically and approach the short circuit current of the bad cell Haberlin 2010 In this case the series connection is short circuited and the voltage on the bad cell becomes negative and is subjected to the cumulative voltage of all other cells Haberlin 2010 Such a high reverse biased voltage can result in huge power dissipation in the form of heat Overheated cells can induce a considerable temperature rise of up to 150 C Wiesener et al 1997 The accumulated heat can burn the cells and damage the packaging materials of PV modules Figure 1 shows some hot spots detected by an infrared camera In this infrared image the red colour areas indicate the bad cells which experience the hot spot with a high temperature while the light yellow and green areas illustrate the good cells with the normal operating temperature 17 07 2012111 26 137AM Figure 1 Some hot spot areas de
47. pes of crystalline silicon solar cells monocrystalline and polycrystalline 26 silicon In this project two monocrystalline silicon modules and two polycrystalline silicon modules were selected See Figure 20 Figure 20 Four test modules on test at ROTA 4 2 1 Monocrystalline silicon mc Si BP275 amp BP585 The monocrystalline silicon solar cell is one of the most common PV technologies Monocrystalline silicon has a pure structure without defects In the current PV industry the most common crystallization method is called the Czochralski CZ method Its basic principle 15 to use a small polysilicon crystal properly cooled as a seed to start the crystallization process Tobias 2011 On the one hand this process is very slow which increases the cost of the manufacture On the other hand monocrystalline silicon has a higher efficiency than polycrystalline silicon With the 27 improvement of monocrystalline silicon technology the production has become more and more cost effective Two different types of monocrystalline module were selected The first one is BP275 which 15 produced by the BP Solar Company It consists of 36 series connected solar cells laminated between sheets of ethylene vinyl acetate EVA and high transmissivity low iron 3 mm tempered glass BP Solar 2002 Its rated power output is 75W and it can charge 12 V batteries virtually in any climate The Electrical characteristics of the BP275 module are s
48. raight line By using Excel 2007 one can obtain four different linear equations The value of R is defined as the goodness of fit The four linear equations have a very high R value gt 0 86 which indicates a good correlation of maximum power with time change The slope represents the annual power degradation From the linear equations one can see that the two BP modules degrade 0 811 W year and 1 142 W year respectively BP585 and BP275 Also 4 it is shown that the PW750 70 module degrades most obviously at 1 83 W year while SX 75 module has the slowest power degradation with 0 5 W yr The annual degradation W year is divided by the initial power output and multiplied by 100 to give the module degradation rate Table 11 shows the estimated degradation rates for four different modules Finally it is determined that the performance of the SX 75 module is better than the other three modules which just has degraded 0 66 year The BP285 module degrades 0 94 year but is still within the 1 upper limit By contrast the PW750 70 module has the poorest performance with the highest degradation rate of 2 67 year Wp degradation in 12 year period y 0 8113x 86 434 R 0 8661 y 1 1423 80 999 R 0 9486 y 0 5009x 75 832 R 0 9684 y 1 8286 67 299 R 0 95827 BP275 SX 75 BP585 PW750 70 Linear BP275 Linear SX 75 6 8 Linear BP585 Time yrs Linear PW750 70 o E
49. red imaging IR IR imaging has been considered as a common and direct technique for detecting hot spots in PV cells This technique is based on the property that all the materials emit different electromagnetic radiation with the temperature variation of materials Munoz 2011 During operation of a PV module the temperature of the PV cells that have hot spot is much higher than that of normal cells So this temperature difference will result in two different infrared images However the energy that real materials 22 receive cannot be fully emitted and some parts of the energy will be absorbed or reflected by the air Munoz 2011 Therefore it is necessary to calibrate the infrared camera before taking photos Krenzinger and Andrade 2007 recommend an accurate way of calibration that takes sky temperature and the errors caused by reflection into account Munoz 2011 When starting to detect hot spots by using an infrared camera one should know the ambient temperature so that one can perform corrections Infrared cameras have advantages of high resolution and accuracy that can help us to locate the hot spot and make a comparative analysis with normal cells 3 3 Lock in thermography LIT LIT 15 a non destructive way to find module defects It mainly uses injection current to detect local shunt defects In this case a pulsed current 15 injected into a solar cell Then the temperature increases where local shunts are situated So if some so
50. rmula in row 73 and no data needs to be entered in row 44 amp 45 AOI was assumed constant for all curves taken within 20 minutes This was the method used for arrays mounted on trackers in RRPGP If the array is fixed then the STCMS calculates AOI from rows 44 to 47 which must be entered In RRPGP Solar elevation and solar azimuth row 46 amp 47 where calculated using the website http www srrb noaa gov highlights sunrise azel html with offset to UTC 8 and manually entering the latitude longitude date and time information 56 Anecdotal sensitivity analysis revealed that results were unaffected by assuming the sun position remained constant for up to 20 minutes Therefore a single value for sun position was entered in to row 46 amp 47 across all curves as long as the curves were all taken within 20 minutes Step 11 A figure for altitude must be entered in row 48 RRPGP used google earth data for this Step 12 Length of string row 51 and Number of strings row 52 must be entered If this is incorrect it results in obvious but not real degradation figures further down the spreadsheet Step 13 Below row 57 is the STCMS outputs so no more data is required to be entered below this row The formulas may need to be copied and dragged across from the reference column c so that each curve has its own calculations Degradation figures can be gleaned from rows 112 to 118 It is a good idea to check that degradation is similar across all
51. ront Front Contact contact Heavy doping at rear of cell keeps minority carriers in this case electrons away from high recombination rear contact Rear Contact Figure 4 Silicon dioxide layer and heavy doping at rear of cells for reducing surface recombination and recombination at contacts Source http pveducation org pvcdrom design surface recombination 11 2 4 3 Series Resistance and Shunt Resistance Both series resistance Rs and shunt resistance Rsu can impact PV module performance As the equivalent circuit of a solar cell Figure 5 shows increasing Rs can lead to drop in Zs while decreasing can result in Voc reduction Rs Figure 5 An equivalent circuit of solar cells Source Emery 2011 Handbook of Photovoltaic Science and Engineering The fill factor FF is defined as the ratio of the maximum power point MPP to 7 times open circuit voltage See Equation 2 Figure 6 and Figure 7 illustrate the effects of Rs and Rsu on the Z V characteristics of solar cells It can be seen that both FF and MPP reduce as Rs increases decreases FF ImpXVmp 2 IscXVoc 12 Rs 200 4 Cell Current A 0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 Cell Voltage V Figure 6 Effect of series resistance on the curves of solar cells Source Emery 2011 Handbook of Photovoltaic Science and Engineering 4 0 very large Cell Current A 060 0 1 0 2 0 3 0 4 0 5 0
52. sion from the excited carriers can be detected by an infrared camera Although EL and PL imaging techniques use an infrared camera to take the images the image is much better than those which use thermograph techniques EL and PL imaging techniques are suitable to detect much smaller module defects micro cracks without destroying the module As Figure 19 shows one string of cells reveals a darker area with the EL imaging technique which confirms that the string has some defects due to less luminescence 24 1 8 i 8 F 1 EI 4 e i 4 sp E ii H e A 4 E i Ee t s EEI x E n 3 x t gt E r 32 1 H 3 i m Figure 19 EL image of the previous PV module where a defect in some cells of one string of cells is confirmed Source Munoz et al 2011 Early degradation of silicon PV modules and guaranty conditions 3 5 Resonance ultrasonic vibrations RUV technique The RUV technique is another technique used to detect micro cracks It is based on the analysis of the ultrasonic vibrations that follow an excitation Munoz 2011 Its principle is to detect the deviation of characteristic frequency of the resonance after emitting a certain ultrasonic frequency Munoz 2011 This deviation is received by a piezoelectric transducer and transformed into electric signal and then the electric signal is processed by a computer equipped with a data acquisi
53. t but can affect the module performance greatly Micro cracks can lead to a loss in cell consistency and trigger recombination problems Munoz 2011 Sometimes we can see there are different colour lines in the cells even 1 micro cracks are not visible When one uses the electroluminescence EL technique to test these coloured lines there is a good accordance between the lines and micro cracks Munoz 2011 By using EL testing one can see that micro cracks are darker because there is no light emission or their emission is much lower than other areas Figure 2 illustrates some micro cracks are detected by EL imaging technique Figure 2 Micro cracks shown in an EL image The black and white image 15 taken by the EL technique the colour image 15 taken by an infrared camera Source Munoz et al 2011 Early degradation of silicon PV modules and guarantee conditions 2 3 Packaging material degradation Module package degradation is a potential issue that can result in poor module performance and a safety hazard However it is often overlooked because package degradation is very slow and hard to detect Although module package material degrades with the aging of the module hot spot heating moisture intrusion and wear and tear can accelerate the degradation Quintana et al 2002 Some typical module package degradations include glass breakage encapsulant discoloration and delamination Package damage can result in excessive lea
54. tected by an infrared camera 2 2 1 1 Bypass diodes Bypass diodes are widely used to minimize hot spot and shading impacts on PV modules The main procedure is to connect bypass diodes to the shaded string or blocked cells which have a hot spot in parallel Due to the reverse electrical properties of bypass diodes the negative voltage induced by a hot spot or shaded cells can lead to a current in the bypass diodes and a short circuit in whole module which can protect the physical structure Yanli 2010 Although bypass diodes can extend the lifecycle of PV modules power losses associated with the current passing through bypass diodes cannot be avoided Yanli 2010 If bypass diodes are undersized or suffer failure they can produce adverse impacts like overheating cells 2 2 2 Cracks in cells A cell crack occurs when solar cells suffer external force or thermal stress Today many PV manufacturers try to minimize the thickness of solar cells to reduce the cost For example the thickness of a solar cell has decreased from 300 um to less than 200 um while the area can be up to 210 mm 210 mm Munoz 2011 This thinner and larger structure makes PV modules more fragile and susceptible to cracking Munoz 2011 Therefore cell cracks often occur in manipulation module lamination and storage Also extra thermal stress like hot spot heating can result in cell cracks Micro cracks consist of many tiny cracks that are not often visible by sigh
55. tion rate The basic simulation process is to use the computer to simulate module degradation trends under STC The four basic simulation parameters are Imp Voc and Vinp Pmp meas Pmpsimul x 100 3 pv Pmp meas 43 7 Conclusions and Recommendations PV technology has become competitive with fossil fuels in Australia due to the decreasing price and non polluting aspects Massive financial support and technological innovation are two big drivers that keep the PV market growing However it cannot be ignored that module degradation has become a potential issue that could constrain the PV industry s development This study summarized four basic categories of module degradation They are cell failure module failure packaging material degradation and power output decrease In addition each category of degradation includes several different cases It was found that hot spot is the most common cell failure issue mainly resulting from cracked and shaded cells which can cause the overheated spot It has been proved that solar cells that are in a long term overheated status could experience power decrease and damage the whole structure permanently In addition to hot spot this study demonstrated that micro cracks in cell could destroy the whole module structure and drastically shorten module lifecycle Micro cracks in cell often occur in the manufacturing process or transportation Also it has been seen that thermal stress
56. tion system Munoz 2011 It has been proved that the resonant frequency drops and the bandwidth of the resonant frequency increases when a crack exists 25 4 PV module performance measurements and degradation rate estimation 4 1 Background It is well known that PV module performance under outdoor exposure varies with meteorological conditions The actual output may differ from the rated output because of the wide range of temperature and solar radiation Also module degradation can greatly affect the actual output Therefore PV module performance measurement 15 necessary to evaluate if a module is operating properly Normally PV module performance is characterized by the current voltage V testing Under STC the V characteristics of a module are measured at 1000 W m of solar radiation 25 C and Airmass 1 5 However the actual V curves will vary under different weather conditions In this project four different types of PV modules a 75W BP275 monocrystalline module 75 W SX 75 polycrystalline module 85W BP565 monocrystalline module and a 70W PW750 70 polycrystalline module are measured 4 2 Description of different PV modules used in the project Crystalline silicon solar cells and modules have been the dominant PV technology since the beginning Today it is estimated that crystalline silicon occupies about 85 of the PV market Tobias 2011 Due to different manufacturing processes there are two major ty
57. transformed into a I V amp P V curve then store the data pressing the REC button and note the record number Connect the solar analyzer to the computer and start the Solar Module Analyzer 12A software Click the Communication button Select REC LOAD to download the recording 10 Click on Export to Excel to save all records in csv format 11 Click on Clear to delete the records from the unit for the next students 58 Appendix C Pyranometers v Reference Cells for PV Installations Advantages of a pyranometer over a reference cell 1 pyranometer gives an independent accurate reading of the total available solar radiation The pyranometer are classified and calibrated to ISO standards The response time of the pyranometer is longer than a PV cell The pyranometer is PV cell type independent A pyranometer can have a very small temperature coefficient PV cells are specified at STC Standard Test Conditions Reference cells and PV panels suffer more from pollution than pyranometers Performance Ratio or Performance Index calculations are more accurate using a OO ON oD pyranometer Explanations of the above advantages Advantage 1 Depending on the technology amorphous silicon thin film CdTe or triple junction cells etc and the cell panel window material PV cells have different spectral responses Due to the changing position of the sun Air Mass pollution humidity clouds etc the solar spectru
58. ture 1000W m2 global solar irradiance air mass 1 5 and no wind The global radiation when under test is measured with a pyranometer These conditions are far from realistic in the real world and an accurate measurement with a pyranometer shows the real performance Advantage 7 There is a conception that pyranometers need to be cleaned very frequently and this is advised for optimum performance However reference cells with a flat surface suffer more from deposits than the hemi spherical dome of a pyranometer Advantage 8 Performance Ratio PR or Performance Index PD calculations when based on accurate independent data from a pyranometer are more relevant than when based on a reference cell with lower accuracy and the same inherent flaws as the panel itself A pyranometer depending on the type can measure with 1 accuracy 60 Appendix D Prova 210 Solar Module Analyzer Accuracy and Reliability PROVA 200 Solar Module Analyzer 6A 60V PROVA PROVA 210 Solar Module Analyzer 12A 60V Electrical Specifications 23 C 5 C Four wire Measurement PROVA 200 PROVA 210 DC Voltage Measurement DC Voltage Measurement 1 1 of Vopen 0 09V 0 01 V Accuracy 0 10V 0 001 V 1 1 of Vopen 0 1 V 10 60V 0 01 V X 196 1 of Vopen 0 1 V DC Current Measurement Accurac x 1 1 of Ishort 0 9mA x 1 1 of Ishort 9mA 1 1 of Ishort 9mA PROVA 200 24 General Specifications DC
59. ver the work was not well coordinated because the data from various measurement techniques and analytical methods are different and it 15 difficult to prescribe a standard that makes it easy to compare module degradation For example a PV system test demonstrated that module performance lost 1 2 per year during a ten year period from the mid eighties to the mid nineties Thomas et al 1994 However the data from a poly crystalline module that was continuously exposed outdoors in an open circuit configuration for eight years at Sandia showed that the power loss 15 around 0 5 per year King et al 2000 According to recent research at the National Renewable Energy Laboratory NREL it was observed that the performance of both mono and poly crystalline field aged modules degraded about 0 7 per year primarily because of short circuit current losses caused by UV absorption at or near the top of the silicon surface Osterwald et al 2002 On the other hand data from the LEEE TISO CH Testing Centre for Photovoltaic Modules showed that power degradation rates of c Si modules was between 0 7 9 8 in the first year and 0 7 4 9 in the second year Quintana et al 2002 The causes of module degradation are various Basically they can be grouped into four categories cell failure e g cell crack hot spot package material degradation 4 e g delamination encapsulant degradation glass breakage power degradation e g fundamental power l
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