Photovoltaic module degradation

DNV GL has reviewed literature reports on observed rates of degradation of photovoltaic (PV) modules and systems, and the reported data were filtered for applicability and relevance to current PV systems. The data were also reviewed for the quality of the measurement method to better account for uncertainty and to attempt to narrow the large range of reported degradation rates for crystalline silicon PV technologies. The results were statistically aggregated to calculate the module and system level degradation rates. This analysis yielded a mean module level degradation rate of -0.57%/year with a P80 confidence interval of -0.10 to -1.06%/year and a median system-level degradation rate of 0.77%/year (P80 confidence interval of -0.05 to -1.45%/year). This paper describes relevant concerns in evaluating degradation estimates and shows how results from over 2000 published instances of degradation results were reviewed to reach this finding.