among 10 module samples from the 2 sites, and analyses the electrical performance. .... Generally, PV module manufacturer is sure of maximum power loss ...
21st European Photovoltaic Solar Energy Conference, 4-8 September 2006, Dresden, Germany
CURRENT-VOLTAGE CHARACTERISTICS WITH DEGRADATION OF FIELD-AGED SILICON PHOTOVOLTAIC MODULES Gi-Hwan Kang1a, Kyung-Soo Kim1, Chi-Hong Parka, L.Waithirua, Gwon-Jong Yu1, HyungKeun Ahna, Deuk-Young Hana 1 Photovoltaic research group, Korea Institute of Energy Research(KIER) / a Department of Electrical Engineering, Konkuk University 1 71-2, Jang-Dong, Yuseong-Gu, Daejeon, 305-343, South Korea/ a 1 Hwayang-Dong, Gwangjin-Gu, Seoul 143-701, South Korea
ABSTRACT: This paper analyses the causes of maximum output power drop due to photovoltaic modules degradation characteristics on 10 samples used over a duration of 15 years. Each sample’s aging phenomenon and cause are analyzed through the I-V curves and hot spot test. The efficiency of the samples when compared to earlier maximum output power results shows a 13~25% drop. Electrode oxidation, and EVA sheet and back sheet delamination were found to be the main cause of aging. Of the 10 samples, 2 suffered from electrode oxidation, while another 2 from EVA sheet and back sheet de-lamination. 2 samples had no visible defects but the maximum power output showed a decrease of 20~25%, while the fill factor reduced suddenly by 6~10% from the standard level with the application of an irradiance of 1,000W/m2. The solar modules degradation was also evident with the increase in series resistance and subsequent deterioration of the modules electrical capacity. This research paper focuses on Korea’s photovoltaic systems distribution project investigating the aging precedent among modules currently in use, with the objective of evaluating photovoltaic modules durability. Keywords: Photovoltaic, PV Module, Degradation
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INTRODUCTION
Korea is in the process of pushing forward renewable energy projects, among them being photovoltaic systems, and is drawing up contingency plans in compliance with the climatic change convention. The Government is pushing forward a project to install 100,000 solar houses and a 1,3GW photovoltaic systems distribution project by 2012 through an yearly load map, and revaluating the reliability of PV systems currently in operation. Table 1 shows government budget estimates for installing PV systems in 100,000 households by 2012. However, the aging effect of photovoltaic modules in 2 base sites revealing that electrode erosion, EVA sheet and back sheet de-lamination in addition to other ageing processes, are proving many problem to the photovoltaic modules reliability. Therefore, this paper investigates aging effects among 10 module samples from the 2 sites, and analyses the electrical performance. Table 1: Solar house Plan in Korea (unit : x 1,000$) YearG PlanG BudgetG 2004G 200 G 6,300 1st 2005G 800G 22,400 StepG 2006G 2,500G 61,300 2007G 4,000G 70,000 2008G 2nd 5,500G 82,500 2009G StepG 7,000G 87,500 2010G 10,000G 125,000 2011G 3rd 30,000G 180,000 2012G StepG 40,000G 240,000 TotalG 100,000G 875,000
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EXPERIMENT METHOD
The research uses 48W 1991 Kyocera Co. (Japan) sample modules, which are poly crystalline photovoltaic 2146
model LA361K48, which were installed on a Korean island 15 years ago. Analysis was done on the samples to investigate the modules aging phenomenon and causes by use of electrical capacity efficiency test and thermal characteristic test. A Video Scope System was used for the naked eye examination. The Video Scope System (Sometech) has 410,000 pixels and resolution of 2,400, a high magnification to observe the final product surface and analyses equipment A Solar Simulator (Pasan ฌb) analyses the electrical characteristics drop phenomenon on the photovoltaic modules. With an irradiance regulatable between 400~1,200W/m2, and light uniformity and light stability below 1%, proves to be a very precise equipment. An Infrared Thermal Imaging System measures the aging samples thermal characteristics. Additionally, a FLIR system (ThermaCAM S60) measures the thermal phenomenon among the aging module samples using the infrared thermal imaging system, with a measurement range of between -40 ଇ ~1500ଇ and temperature accuracy of 2%. With the smallest focus of 0.3 meter, thermal characteristics of the photovoltaic array and the unit solar cell are observable, also proving to a useful device for analysis.
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RESULT AND INVESTIGATION
The solar cell is a semiconductor that produces electricity from sunlight with current flow on the cells surface, a thin electrode is molded with a silver paste which may suffer serious corrosion when exposed to humidity. This paper illustrates that electrode oxidation in 2 of the 10 samples, as shown in Fig. 2. The cause of the electrode oxidation is weathering of the EVA sheet and back sheet when humidity penetrates microscopic cracks on the back sheet.
21st European Photovoltaic Solar Energy Conference, 4-8 September 2006, Dresden, Germany
Electrode oxidation is hence the photovoltaic modules greatest problem in its useful life, and care should be taken at the initial stages of the manufacturing process to prevent moisture infiltrating through the back sheet. Fig. 3 shows the effect of gradual magnification of photovoltaic modules electrode oxidized with passage of time, resulting in thermal aging in the oxidized vicinity and ultimately, the gradual shortening the useful life of the photovoltaic modules. Fig. 4 presents EVA sheet and back sheet delamination that was found 1 one of the 2 sites. Presently, the samples analyzed are in use and sampling is therefore impossible. Even though the samples have of low electrical performance efficiency, more than 60% of photovoltaic modules in the site have been found to exhibit serious degradation.
Additionally, the 2 samples with the lowest power due to electrode oxidation or other aging phenomenon undetectable by naked eye tests, had big drops in maximum output power caused centrally by degradation of the cell itself. From the I-V results of the oxidized samples, maximum output was higher for cells with degradation than for those that showed aging. This result is not influenced greatly by the light from the source which gives out light instantaneously at 25ଇ and 1,000kW/m2.
Figure 5: Properties of field aged PV modules used in experiment
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G Figure 2: Photograph of Electrode oxidized PV modules
Figure 3: Photograph of solar cell grid
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Figure 6: I-V curve of field aged PV modules To find the effect of series resistance of PV module, the resistance ranging between 0.27 and 1.61 : was connected to PV module. Then I-V curve was measured. The higher resistance results in the lower fill factor. So the maximum output power was reduced. From fig.7 result series resistance reduces Pmax and degradation of PV module’s performance. 0015+0015 Reg Module Sun Simulator Data 3
Figure 4: De-lamination of EVA and Back sheet
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Fig. 5 and Fig. 6 depict the photovoltaic modules maximum output power and I-V characteristic curves. Among the 10 samples modules, 2 with electrode oxidation and 8 others maximum output power ranged from 36.0W~38.3W, a drop of approximately 8~13% from their initial production value. 2 samples interestingly showed no signs of aging with the naked eye experiment, but had reduced maximum output power by 20~25% to 36.0W and 38.3W. The I-V characteristic curves of the oxidized sample modules had the lowest power as opposed to the other 8 which showed similar characteristics.
1.5 N Reg. 0.270 0.469 0.660 0.972 1.142 1.610
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Figure 7: Series resistance characteristics of PV module Fig. 8 shows a PV arrays with aging photovoltaic modules. It is evident that when a load is connected and 2147
21st European Photovoltaic Solar Energy Conference, 4-8 September 2006, Dresden, Germany
generation is in action, the solar cell thermal aging is accelerated shortening the photovoltaic module useful life. It can be inferred that inclusion of similar aging modules in the systems results in acceleration of the total system aging rate.
Fig. 11 shows reference photovoltaic module and electrode oxidized photovoltaic Fill Factor value verses varying irradiance condition for the comparative analysis of the curves rate of change. From the Fig. 11, when the oxidized photovoltaic module’s fill factor is 1000W/m2, a -6%~+10% change is visible, with a -2%~+3% change for the reference PV module. 115.0 degraded non degraded
F.F value (%)
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G Figure 8: Thermal property of field aged PV modules Fig. 9 delineates I-V curves where the irradiance condition is allowed varies between 1200~500W/m2 using the sample modules with oxidized electrodes and the series resistance is observed. The test result reference photovoltaic module’s fill factor changes microscopically, but for the sample modules with oxidized electrodes, it is evident that the more the irradiance is increased, the faster the reduction in aging. If this phenomenon in the module is allowed to proceed, the solar cells internal series resistance and electrode contact resistance can be analyzed. 4
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Figure 11: Properties of fill factor with different irradiance conditions
In Fig. 12 analyzes the irradiance condition variation with maximum output voltage and maximum output current. In reference to photovoltaic module, as the irradiance condition increases, both the maximum output voltage and current increase. However for the oxidized sample, as the irradiance increases the power output reduces, and this phenomenon is the causes of the reduction in the fill factor. From this results, since series resistance on the modules surface increasing due to oxidation as the fill factor reduces, and also we analyzed the cause of the reduction in the fill factor due to reduction in maximum output power. Therefore the more the temperature increases the faster the degraded modules series resistance increases.
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Figure 12: Properties of maximum output voltage and maximum output current with different irradiance conditions
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CASE STUDY (18 month Filed Aged Module)
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To find out the I-V characteristics of field-aged silicon PV module, we tested 18 month filed aged three PV modules installed at South Korea. Fig. 13 shows the appearance of 3 modules. There were cell, Al frame damage and frame corrosion, even though it has been passed only 18 months.
21st European Photovoltaic Solar Energy Conference, 4-8 September 2006, Dresden, Germany
model 21. But 0.7V Isc reduction happened in model 155 and 231. Because of Voc and Isc reduction in model 155 and 231 is more than model 21, the maximum output power reduction rate ranged from 2.9~3.5% compared to 1.6% in model 21. Table 2: 18 month filed aged PV module’s properties Figure 13: Appearance of field aged PV modules Figure. 14 delineates I-V curves for three modules. From this results, maximum output power’s reduction rate was diverse. It ranged from 1.6%~3.53%, a drop of approximately 2.1W~4.7W from their initial production value. It gives that maximum power reduction rate per year ranges from 1.4~2.35 %/year. Generally, PV module manufacturer is sure of maximum power loss reduction rate less than 1%/year. But, from above results, there could be abnormal failure of PV system because of environmental condition or initial manufacturing problem.
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CONCLUSION
This paper analyses the causes of maximum output power drop due to photovoltaic modules degradation characteristics on 10 samples used over a duration of 15 years. Each sample’s aging phenomenon and cause are analyzed through the I-V curves and hot spot test. The efficiency of the samples when compared to earlier maximum output power results shows a 13~25% drop. Electrode oxidation, and EVA sheet and back sheet de-lamination were found to be the main cause of aging. Of the 10 samples, 2 suffered from electrode oxidation, while another 2 from EVA sheet and back sheet de-lamination. 2 samples had no visible defects but the maximum power output showed a decrease of 20~25%, while the fill factor reduced suddenly by 6~10% from the standard level with the application of an irradiance of 1,000W/m2. The photovoltaic modules degradation was also evident with the increase in series resistance and subsequent deterioration of the modules electrical performance.
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Figure 14: I-V curve of field aged PV module A comparison of the 3 individual module’s parameters is described at Table 2. There was a change in Voc 0.5V in model 21. And Voc reduction of model 155 and 231 was 0.7V. About the Isc, there was no change in
REFERENCE
[1] M.A.Quintana, D.L.King, F.M.Hosjing, J.A.Kratochvil, R.W.Johnson, B.R.Hansen, N.G.Dhere and M.B.Pandit, "Diagnosic Analysis of Silicon Photovoltaic Module after 20-Year Field Exposure", 28th IEEE Photovoltaic Specialists Conference, Anchorage, P. 1420, 2000. [2] G.H.Kang, G.J.Yu, H.K.Ahn and D.Y.Han, "Conside- ration of Electrical Properties in Field-aged Photovoltaic Module", J. of KIEEME(in Korean), Vol. 17, No.12, p.1289, 2004. [3] Antonio Parretta, Mariano Bombace, Giorgio Graditi and Riccardo Schioppo, "Optical degradation of Long Term, field aged c-Si photovoltaic modules", Solar Energy Materials & Solar cells, Vol.,86, p.349, 2005. [4] 衴絥蒃衒赂箸蕍粽荓, “譭蓪衴覉诓竏絛菵蕍粽 筛脊ˉ , 诐茶 13 総繱 萿ံၛၹြ̔ 芈蔋絛菵誺 豗筛脊絣粱蚸譑蔋肏茶籂膊篶苗, p. 47, 诐茶 14 総 3 蚰. 2149
