Degradation of Backsheets for Crystalline Photovoltaic Modules under Damp Heat

Abstract

The reliability of crystalline silicon photovoltaic (PV) modules is determined not only by the efficiency loss of the silicon cells but also by the degradation of other components (ethyl vinyl acetate, ribbon, glass, and backsheet). Among these components, the backsheet provides electrical insulation and physical support, and acts as a barrier against moisture and weathering of the PV module. We investigated the degradation of different types of backsheets under damp heat conditions [95°C/85% relative humidity (R.H), 85°C/85% R.H]. During the damp heat treatment, tensile tests were carried out to investigate the mechanical degradation of the backsheets. The molecular weight of the polyethylene terephthalate (PET) in the backsheets was measured by gel permeation chromatography (GPC) to understand the intrinsic mechanism of degradation. After damp heat test, mechanical degradation of backsheet occurred significantly beyond passing the specified molecular weight region of PET film in backsheet materials. By finding the correlation between tensile strength and the molecular weight of the backsheets, our results make it possible to improve the reliability of backsheets.