Factors that Affect the EVA Encapsulant Discoloration Rate upon Accelerated Exposure

Several factors that affect the discoloration rate of the ethylene-vinyl acetate (EVA) copolymer encapsulants used in crystalline-Si photovoltaic (PV) modules upon accelerated exposure have been investigated primarily by employing UV-visible spectrophotometry, spectrocoloimetry, and fluorescence analysis. A variety of film samples including the two typical (unprimed) EVA formulations, A9918 and15295, were studied. The films were laminated, cured, and exposed to either a concentrated 1-kW Xe or an enhanced-UV light source. The results indicate that the extent of EVA discoloration can be affected by factors of two general categories: chemical and physical. In the chemical category, the degradative factors include (1) EVA formulation, (2) presence and concentration of curing-generated,UV-excitable chromophores that depend on the type of curing agent used, (3) loss rate of the UV absorber, Cyasorb UV 531(TM), (4) curing agent and curing conditions, and (5) photobleaching reactions due to diffusion of air into the laminated films. In the physical category, the factors involve (6) UV light intensity, (7) UV-filtering effect of glass superstrates, (8) gas permeability ofpolymeric superstrates, (9) film thickness, and (10) lamination-delamination (maybe chemical and/or mechanical effect, too).