11 September 2008 Low-cost single-layer replacement for the back-sheet and encapsulant layers
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Abstract
Ethylene propylene diene monomer (EPDM) based polymers have been formulated for specific use in photovoltaic modules to produce better performance and longer term stability at a lower cost than standard materials. EPDM formulations are advantageous over ethylene vinyl-acetate (EVA) because they can use the same lamination/cure cycle as EVA, they do not need a second back-sheet protective material (e.g. PET/Tedlar), they have a lower glass transition temperature, no melting transition, more constant mechanical moduli as a function of temperature, they are less polar than EVA (provides better corrosion protection), and they have excellent damp heat (85°C/85% relative humidity) resistance against delamination. Module designs typically use EVA on the back side of cells despite the fact that transparency is not advantageous. We have developed a single encapsulant layer that will replace standard module back-sheet constructions consisting of EVA/PET/Tedlar. Because a single low-cost material layer is used, it will provide a significant materials cost savings of about $6 to $8/m2 as compared to traditional back-sheets. Electrical insulation tests were conducted using 0.85 mm thick stainless steel sheets as a model for a cell. It was found that a polymer layer thickness of about 0.33mm provided better high voltage electrical insulation than a combined film of Tedla (0.038 mm) / PET (0.051 mm) / EVA (0.55 mm). When formulated with a white pigment, reflectivity was comparable to TedlarTM. Upon accelerated exposure to light at 60C and 60% RH it was found that an EVA layer in front of these materials would decompose before significant yellowing and delamination of the back EPDM layer occurs.
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Michael D. Kempe, Michael D. Kempe, Prem Thapa, Prem Thapa, } "Low-cost single-layer replacement for the back-sheet and encapsulant layers", Proc. SPIE 7048, Reliability of Photovoltaic Cells, Modules, Components, and Systems, 70480D (11 September 2008); doi: 10.1117/12.795413; https://doi.org/10.1117/12.795413
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