Advanced EVA-Based Encapsulants: Final Report, January 1993--June 1997

This report describes work performed by STR, Inc., under this Photovoltaic Manufacturing Technology (PVMaT) subcontract. The purpose of the three-phase PVMaT program was to further define the problem of EVA-based PV encapsulant yellowing in fielded modules, research possible chemical mechanisms, and then combat the yellowing phenomenon by developing advanced PV encapsulants. Phases I comprised aliterature search on EVA-based encapsulant browning, survey of and site visits to installations reporting discolored encapsulant in fielded modules, and analysis of browned EVA-based encapsulant. During Phase II, development work, including reformulation, resulted in four experimental encapsulants with greatly reduced browning. After 40 weeks in the Weather-O-Meter, glass/glass laminatesprepared with new formulations (standard and fast cure) showed no visible yellowing. During Phase III, these four experimental EVA-based encapsulants from Phase II were successfully prepared on a pilot scale using production equipment, and the resulting sheet was used, without significant problems, by six different module producers to fabricate full-size modules. With only a couple ofexceptions, curing of these modules was at a consistently high level, with average gel content greater than 83%, versus a typical 80% for current EVA-based materials. STR will continue to keep these modules on outdoor test after the subcontract is completed.