Failure modes of polyolefin encapsulated double glass modules and corresponding degradation modeling — Part 1 optical durability

This research focuses on the reliability and durability of polyolefin in double glass photovoltaic (PV) modules, which is popular among PV maunfactures. We investigate three predominant failure modes, discoloration, delamination, and PID, of polyolefin under various stresses close to outdoor environment conditions and propose service lifetime prediction based on data-driven degradation models. In this paper, the transmittance of 6 types of laminated commercial polyolefin with exposure to UV and moisture at elevated temperatures are measured. Polyolefin demonstrates good optical durability, some even better compared to EVA. We show that measured decrease in transmittance translates into a two-step decay for short-circuit current of PV (Isc) module. The Isc degradation can be well fitted by models of exponential decay and piecewise linear decrease. The latter has fit parameters with physical meanings and is thus preferred. To correlate Isc results of different aging tests with field performance, modified Arrhenius equation considering the impact of UVB irradiance and temperature is used. The Isc decreases of PV modules caused by discoloration of 2 types of polyolefin in Miami are estimated, ~3.6% and ~1.3% respectively for 30 years.