Impact of moisture on PV module encapsulants

Water vapor is one of the major reasons for corrosion and aging within photovoltaic modules. We investigated different encapsulants for photovoltaic devices in respect of their water vapor transmission rate (WVTR), diffusion profile and saturation concentration for varied climatic conditions (temperature and relative air humidity). For measuring the WVTR a gravimetric testing procedure was used, the diffusion profile was detected by infrared-absorption-spectroscopy in the wavelength range of 1.7 μm to 2.9 μm. The tested materials are a fast-cure ethylene vinyl acetate (EVA fc), a poly vinyl butyral (PVB), a thermoplastic polyurethane (TPU), an ionomer (ION) and a thermoplastic silicone (TSI). It was ascertained that the thermoplastics foils (TPU and TSI) have the highest WVTR, the ionomer the lowest. The saturation concentration of PVB was the highest at all, followed by TPU and EVA. The silicone and the ionomer store practically no water.