Modeling of Rates of Moisture Ingress into Photovoltaic Modules

Encapsulant materials are used in photovoltaic devices for mechanical support, electrical isolation, and protection against corrosion. During long-term exposure of photovoltaic modules to environmental stress, the ingress of water into the module is correlated with decreased performance. By using diffusivity measurements for water through ethylene vinyl acetate (EVA), we have modeled moisture ingress using finite-element analysis with atmospheric data from various locations such as Miami, Florida. This analysis shows that because of the high diffusivity of EVA, even an impermeable glass back-sheet is incapable of preventing significant moisture ingress from the edges for a 20-30-year lifetime. Once moisture penetrates a module, it can condense and increase corrosion rates. Significantly reducing moisture ingress requires a true hermetic seal, the use of an encapsulant loaded with a desiccant, or the use of an encapsulant with a very low diffusivity.