24 September 2013 UV aging and outdoor exposure correlation for EVA PV encapsulants
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Abstract
A widely cited approximation in the solar industry is that “one week of xenon arc weather-o-meter exposure is equivalent to one year of field exposure.” This statement is a generalization of test data generated in the mid-1990s as part of the NREL managed PVMaT-3 project. This approximation was based entirely upon yellowing of first generation EVA-based encapsulants in two different accelerated test conditions, xenon arc and mirror accelerated outdoor aging. First generation EVA encapsulants were developed by STR under the JPL solar project (1975-1986) and exhibit yellowing (or browning) with exposure to UV and heat. This yellowing mechanism was understood and resolved with newer generation EVA encapsulation products introduced in late 1990s. Modules were manufactured at the end of the PVMaT-3 project that included both older and newer generation encapsulants. Those modules were on a two-axis tracker in Arizona from 1996 to 2012 and are now undergoing diagnostic tests. Older generation standard-cure encapsulant used in these modules exhibited severe browning over cells and the modules exhibit approximate power loss of about two percent per year. This same standard cure encapsulant material has been tested with updated xenon arc exposure methods and optical transmission tests to estimate the loss in power due only to browning and reduction in light transmission.
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Charles G. Reid, Jayesh G. Bokria, Joseph T. Woods, "UV aging and outdoor exposure correlation for EVA PV encapsulants", Proc. SPIE 8825, Reliability of Photovoltaic Cells, Modules, Components, and Systems VI, 882508 (24 September 2013); doi: 10.1117/12.2028916; https://doi.org/10.1117/12.2028916
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