Durability of polymeric encapsulation materials in a PMMA/glass concentrator photovoltaic system. (13th July 2016)

• Record Type: Journal Article
• Authors: Miller, David C.; Kempe, Michael D.; Muller, Matthew T.; Gray, Matthew H.; Araki, Kenji; Kurtz, Sarah R.
• Is Part Of: Progress in photovoltaics. Volume 24:Number 11(2016)
• Page Start: 1385
• Page End: 1409
• Publication Date: 2016-07-13
• Subjects: durability -- reliability -- polymer -- UV degradation -- weathering; Solar cells -- Periodicals; Photovoltaic cells -- Periodicals; Solar power plants -- Periodicals; 621.31245
• DOI: 10.1002/pip.2796
• Languages: English
• ISSNs: 1062-7995

Abstract

Abstract: The durability of polymeric encapsulation materials was examined using outdoor exposure at the nominal geometric concentration of 500 suns. The results for 36‐month cumulative field deployment are presented for materials including: poly(ethylene‐co‐vinyl acetate), (EVA); polyvinyl butyral (PVB); ionomer; polyethylene/polyoctene copolymer (PO); thermoplastic polyurethane (TPU); poly(dimethylsiloxane) (PDMS); poly(diphenyl dimethyl siloxane) (PDPDMS); and poly(phenyl‐methyl siloxane) (PPMS). Measurements of the field conditions including ambient temperature and ultraviolet (UV) dose were recorded at the test site during the experiment. Measurements for the experiment included optical transmittance (with subsequent analysis of solar‐weighted transmittance, UV cut‐off wavelength, and yellowness index), mass, visual photography, photoelastic imaging, and fluorescence spectroscopy. While the results to date for EVA are presented and discussed, examination here focuses more on the siloxane materials. A specimen recently observed to fail by thermal decomposition is discussed in terms of the implementation of the experiment as well as its fluorescence signature, which was observed to become more pronounced with age. Modulated thermogravimetry (allowing determination of the activation energy of thermal decomposition) was performed on a subset of the siloxanes to quantify the propensity for decomposition at elevated temperatures. Supplemental, Pt‐catalyst‐ and primer‐solutions as well as peroxide‐cured PDMS specimens were examined to assess the source of the luminescence. The results of the study including the change in optical transmittance, observed failure modes, and subsequent analyses of the failure modes are described in the conclusions. Copyright © 2016 John Wiley & Sons, Ltd. Abstract : Most specimens show minimal evidence of aging; only 4 of 29 specimens have "failed" to date. Failure modes including combustion, thermal decomposition, fracture, and haze formation have been observed. Effects of aging are suggested by peripheral appearance, photoelasticity, and fluorescence spectroscopy. Thermal degradation is unlikely to contribute to immediate or long‐term degradation of siloxanes unless aided by another mechanism, for example, discoloration.