Effect of EVA discoloration in 25-year-old single crystalline silicon photovoltaic modules operated under moderate climate

Abstract

In this study, the effect or absence thereof of discoloured ethylene vinyl acetate (EVA) on the electrical characteristics of photovoltaic (PV) modules was investigated. The field samples for discoloured EVA were PV modules that had been in operation for 25 years since 1986 in a modulated climate in South Korea. The I-V characteristics of 25-year-old, discoloured single crystalline silicon (sc-Si) PV modules were measured, and the results showed that the maximum power (Pmp) had degraded by approximately 25.5 %. The sc-Si single-cell PV module had a discoloured EVA, which was separated from it to determine the correlation between the discoloration of EVA and power degradation. The yellowness index (YI) of the EVA was in the range of 36–44. The relationship between the YI and transmission of 25-year-old discoloured EVA was also determined through measurements. The short-circuit current (Isc) and Pmp of the PV modules were measured, which were found to be degraded by 22.2 % and 21.3 %, respectively, owing to the discoloured EVA. The output characteristics of the solar cell in the discoloured region of the EVA were analysed. The results showed that the Isc degradation rate varied linearly with the EVA discoloration area. The discoloration of the EVA was the main effect (83.5 %) among the failure modes of the 25-year-old sc-Si PV module. It accounted for 0.85 % of the 1.02 % annual degradation of the PV module. Isc and Pmp exhibited linear degradation corresponding to areas of 25 %, 50 %, 75 %, and 100 % discoloration in single-cell PV modules.