Spectroscopic investigation of long-term outdoor-exposed crystalline silicon photovoltaic modules

Degradations of an encapsulant of a random copolymer of ethylene and vinyl acetate (EVA), in long-term outdoor-exposed (OE) crystalline silicon (c-Si) photovoltaic (PV) modules were investigated by Raman and Fourier transform-infrared (FT-IR) spectroscopy measurements. Two predominant chemical and photochemical degradations, discoloration (yellow-browning) and formation of acetic acid (AcOH), were observed in EVA encapsulants in c-Si PV modules exposed outdoors for approximately 27 years in Japan (Kirishima module). The yellow-browning of the encapsulants was suggested to be due to reaction of additives, such as UV absorbers that were incorporated in the encapsulants, because no marked degradation of EVA itself was observed in the FTIR absorption spectrum. Contrastingly, the absorption intensity of C = O of the colorless EVA in the Kirishima module decreased to 70 %, which was similar to that for the encapsulant in a damp-heat-tested (DHT) module at 85 degrees C with 85 % relative humidity for 4000 h (68 %), suggesting that AcOH was formed from EVA. The degradation mechanisms of the EVA encapsulants in long-term OE and DHT c-Si PV modules were explored by spectroscopy and other analyses.