Abstract
Long-term photovoltaic (PV) module reliability is highly determined by the durability of the polymeric components (backsheet and encapsulation materials). This paper presents the result of experiments on encapsulant degradation influenced by the backsheet permeation properties. Towards this goal, one type of ethylene/vinyl acetate copolymer (EVA) was aged in glass/EVA/backsheet laminates in accelerated aging tests (up to 4000 h for Damp-Heat (DH) and up to 480 kWh/m2 for UV and UV-DH combined). The samples contained three backsheets with different permeation properties to examine their impact on EVA degradation. Thermal and chemical characterization shows that the EVA degradation is stronger with the glass–EVA–polyamide (PA)-based backsheet than with the polyethylene terephthalate (PET)-based backsheets. The higher oxygen transmission rate (OTR) of the PA-based backsheet may increase photo-oxidation and aggravating the degradation of EVA in the laminates. Furthermore, FTIR results were used to demonstrate the effect of damp heat exposure on the EVA interfaces, showing an accelerated degradation at the glass–EVA interface. The comparison of accelerated aging stress factors reveals that EVA suffers the strongest chemical and optical degradation when high UV, high temperature and high relative humidity are combined simultaneously.
Highlights
Photovoltaic (PV) modules are multi-layer structured devices in which the solar cells and circuitry are embedded in transparent polymeric encapsulants materials
One approach of this study was to analyze the chemical changes of the ethylene/vinyl acetate copolymer (EVA) due to the influence of different backsheet properties
Based on the previous results of EVA chemical changes through damp-heat aging, we further studied the influence of Vinyl Acetate (VAc) content on the combined UV/DH aging behavior of EVA, comparing with other standard tests, DH and dry-UV separately
Summary
Photovoltaic (PV) modules are multi-layer structured devices in which the solar cells and circuitry are embedded in transparent polymeric encapsulants materials. It has previously been found that small molecules, such as water vapor and oxygen, permeate through the backsheet and initiate degradation processes inside the PV modules [9,10,11,12,13] The ingress of such gases is governed by the permeation properties of the polymeric backsheets and/or encapsulation materials used. A correlation between the aging behavior of the backsheets and the electrical performances of PV modules has been reported [14] These results raise the question of how the backsheet permeation properties affect other PV module components, such as the commonly used encapsulant ethylene vinyl acetate (EVA). One main objective of this article is to describe the effect of the backsheet’s permeation properties on the encapsulant degradation To this end, different backsheets were used to understand their influence on different encapsulant degradation processes. Chemical, thermal and optical characterization methods were used to detect and understand the degradation of the encapsulant caused by applying both dry-UV and DH aging tests separately and simultaneously
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