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Performance and Aging of a 20-Year-Old Silicon PV System

This paper examines the long-term performance of a 20-year-old crystalline silicon system. The degradation was found to be about 0.8%/year and is consistent with historical averages. In contrast with the majority of historical degradation, the decline for this particular system is more attributable to fill factor (FF) than to short-circuit current (Isc). The underlying cause was determined to be an increase in series resistance. We found no evidence that this system degrades significantly differently from its worst performing strings and modules. Maintenance events during the 20 years were dominated by inverter issues with a total of four replacements.