Lifecycle degradation testing of photovoltaic (PV) modules in accelerated-degradation chambers can enable the prediction both of PV performance lifetimes and of return-on-investment for installations of PV systems. With degradation results strongly dependent on chamber test parameters, the validity of such studies relative to fielded, installed PV systems must be determined. In the present work, accelerated aging of a 250 W polycrystalline silicon module is compared to real-time performance degradation in a similar polycrystalline-silicon, fielded, PV technology that has been operating since October 2013. Investigation of environmental aging effects are performed in a full-scale, industrial-standard environmental chamber equipped with single-sun irradiance capability providing illumination uniformity of 98% over a 2 x 1.6 m area. Time-dependent, photovoltaic performance (J-V) is evaluated over a recurring, compressed night-day cycle providing representative local daily solar insolation for the southwestern United States, followed by dark (night) cycling. This cycle is synchronized with thermal and humidity environmental variations that are designed to mimic, as closely as possible, test-yard conditions specific to a 12 month weather profile for a fielded system in Tucson, AZ. Results confirm the impact of environmental conditions on the module long-term performance. While the effects of temperature de-rating can be clearly seen in the data, removal of these effects enables the clear interpretation of module efficiency degradation with time and environmental exposure. With the temperature-dependent effect removed, the normalized efficiency is computed and compared to performance results from another panel of similar technology that has previously experienced identical climate changes in the test yard. Analysis of relative PV module efficiency degradation for the chamber-tested system shows good comparison to the field-tested system with ~2.5% degradation following an equivalent year of testing.
KEYWORDS: Solar cells, Humidity, Silicon, Solar energy, Photovoltaics, Lamps, Temperature metrology, Environmental sensing, Manufacturing, Energy conversion efficiency
Lifecycle testing of full-scale photovoltaic (PV) modules was conducted in a large-sized, accelerated-degradation chamber in our labs that enables full-solar-spectrum irradiance, temperature, and humidity control. In-situ measurement of both polycrystalline and monocrystalline silicon PV module energy conversion characteristics were examined under environmental lifecycle conditions representative of Tucson, AZ. Specifically, the performance degradation of a Hanwha 295 W polycrystalline PV module and of a SunPower 320 W monocrystalline PV module were evaluated and compared. Results indicate that the initial efficiency of the polycrystalline module and the subsequent annual degradation occurred within expected ranges for that system. In contrast, the single-crystal module exhibited both a significant decrease in PV module efficiency during the test cycle, and early evidence of environmentally-induced materials degradation across the module. The temperature and time-dependence of PV module behavior were extracted to provide insight into early-stage performance degradation under conditions approximating field-relevant environments.
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