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Identifying early-stage discoloration in EVA encapsulants

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The packed mini-PV module laminate samples after testing. Image: Indian Institute of Technology

A new, non-destructive method has been proposed by researchers in India who claim identifying early-stage discoloration in EVA encapsulants can help detect degradation in solar panels before power output is affected. The scientists used an ultraviolet accelerated aging test during 34 days on three encapsulant samples.

Identifying early-stage discoloration in the ethylene-vinyl acetate (EVA) copolymer encapsulants used for crystalline solar module lamination can spot panel degradation before power output is affected.

Discoloration reduces direct short circuit current, making it a prime source of reduced panel performance, alongside premature delamination.

Researchers led by academics from the Indian Institute of Technology (IIT) Bombay have proposed a new, non-destructive method of detecting early-stage photobleaching and discoloration in EVA encapsulants. Both phenomena were described as ‘opposite reaction mechanisms’ in encapsulants by the researchers. Discoloration, caused by the presence of conjugated compounds, volatiles and other gaseous elements, leads to the appearance of fluorophores – fluorescent chemical compounds which intercept UV light and reduce light transmittance and reflectance within PV panels. Photobleaching occurs when fluorophores are converted to non-fluorescent form and is usually localized at the edges of solar cells and does not hamper performance.

To spot early-stage discoloration and photobleaching, the IIT Bombay group used fluorescence imaging, which is typically used to detect EVA encapsulant degradation, and Raman spectroscopy, a technique used to observe vibrational, rotational and other states in molecular systems. The researchers analyzed UV-cut (C), UV-transparent (T) and combined – TC – EVA encapsulant, single-cell solar module samples in a UV accelerated-aging test. The samples were placed over 12cm thick glass wool insulation and tightly packed with aluminum tape. The results showed the order in which the two opposite reaction mechanisms occurred differed depending upon the nature of the cell which underwent the accelerated aging process.

“It is found that the oxygen diffusion coefficient of the T sample is four and nine times slower than the TC and C samples, respectively, in the photobleached region,” the scientists said. “Fluorescence imaging and spectra and Raman spectra were taken before and after the accelerated test and indicated that discoloration causing fluorophore generation was higher after [photobleaching] for transparent and combined EVAs, whereas [it was] higher at the center for UV-cut EVA laminates.”

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The three encapsulant samples analyzed in the study before testing. Image: Indian Institute of Technology