Ultraviolet light test and evaluation methods for encapsulants of photovoltaic modules

Photovoltaic (PV) modules are exposed to harsh conditions of heat, humidity, high voltage, mechanical stress, thermal cycling, and ultraviolet (UV) radiation. The current qualification tests (e.g. IEC 61215) do not require UV exposure sufficient to evaluate a lifespan of 20 years or more. Methods to quickly evaluate the UV durability of photovoltaic materials are needed. The initial performance and cost of encapsulant materials must be taken into account, but equally important is their ability to maintain adhesion and transmissivity under UV exposure. This can be evaluated under highly accelerated conditions with light from a xenon arc lamp using glass that transmits more UV radiation than a module would normally see. The use of highly UV transmissive glass (no Ce to block UV-B radiation) results in a UV dose that is about 3.8 times greater with regard to adhesion than a Ce-containing glass. With this configuration, the effect of 20 years of exposure, as compared with the use of UV-B blocking glass, can be simulated in just over 6 months using standard commercial accelerated stress chambers. This also indicates that the use of non-UV blocking glass may significantly reduce the long-term adhesive stability of PV materials.