LSA feld test annual report, August 1979-August 1980

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Abstract
After almost four years of endurance testing of photovoltaic modules, no fundamental life-limiting mechanisms have been identified that could prevent the twenty-year life goal from being met. The endurance data show a continual decline in the failure rate with each new large-scale procurement. Cracked cells and broken interconnects continue to be the principal causes of failure. Although the modules are more adversely affected physically by hot, humid environments than by cool or dry environments, there are insufficient data to correlate failures with environment. There is little connection between the outward physical condition of a module and changes in its electrical performance. Electrical degradation is a transient condition that is generally intermittent and is present before a module destined to fail finally fails. Analysis of year-long electrical performance data indicates that the fill factor is insensitive to most measurement problems and remains the best diagnostic tool for determining module degradation. Investigations at the JPL site reveal that shadowing the indirect component of irradiance can reduce the electrical output of modules and result in anomalous performance data. Extrapolating this result to arrays suggests that a loss of power can result if indirect shadowing is not considered in the array layout. The introductionmore » of the Portable I-V Data Logger was a success. About 1200 high quality I-V curves were obtained during a tour of the 15 remote sites. Next year a major reorganization in the inventory of test modules is planned. A significant portion of the older modules will be removed and replaced with modules from the upcoming Block IV large-scale procurement. « less

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