Investigation into the causes of browning in EVA encapsulated flat plate PV modules

The problem of browning in a number of EVA (ethylene vinyl acetate) encapsulated flat plate photovoltaic modules has led to the questioning of EVA as a suitable material for such applications. By isolating the variables that could possibly lead to EVA browning, such as module construction, types of glass superstrate, additives, and processing conditions, we have been able to determine those significant specific variables that seem to have the most influence on discoloration. When "standard-cure" EVA-based laminates were exposed to accelerated UV aging, measurable yellowing of those laminates was evident after only one to two weeks exposure, and visual discoloration was observed after four to six weeks. Some samples yellowed quickly and some not at all, and there were significant differences in the rates of discoloration between "standard-cure" and "fast-cure" EVA. This paper looks at the results of these studies, especially focusing on the effect of additives in the EVA on the rate of yellowing, and discusses how preliminary results can be used to reformulate EVA encapsulants.