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Solar substrate

Solar substrate (backsheet): application and purpose

  A solar backsheet is the last layer at the solar PV panel and is typically made of a polymer or a combination of polymers  

Solar substrate (backsheet)

The purpose of photovoltaic (PV) backsheet is to protect the backside of the solar module from the effects of weather conditions and to mitigate any electric shock hazards. The backsheet consists of multiple layers of barrier films and adhesives. The construction of the backsheet is instrumental in protecting the solar cells from different environmental conditions like moisture, UV exposure and other performance threats while also improving solar module efficiency by aiding the reduction of partial discharge. To accomplish this, the solar panel material should be of a robust construction, typically a three layer laminate, and possess high dielectric properties.    

Backsheet composition

Backsheets are typically based on polymer materials and have  multi-layer construction, with a weather resistant outer layer, a core layer which is electrically insulating, and an adhesive inner layer. The outer layer is most commonly based on a fluoropolymer, such as PVF (polyvinyl fluoride). Yet, the growing need  to reduce cost while maintain or extend backsheet service lifetime has led to the development of new PV backsheets, like those based on non-fluoropolymer outer layers. Some of these newer backsheet materials are based on polyamides (PA) or polyesters (for example PET (polyethylene terephthalate) or PEN (polyethylene naphthalate) among others.    

Backsheet options

The mainstream encapsulant used in the PV industry is based on a random copolymer consisting of about 2/3 polyethylene and 1/3 poly vinyl acetate. It is usually used on the backside of PV modules in spite of the fact that good transmission of light is not necessary. Different layers are used to complement each other, for example EVA has some drawbacks include non ideal mechanical and thermal properties, a high diffusivity for water and poor electrical insulation, so another layer of polyethylene terepthalate (PET) can be typically placed behind the EVA to slow down moisture ingress and provide electrical insulation. Yet, PET is not very UV stable. Because of this, a layer of PVF is then used to help protect the PET. Other options like EPDM encapsulant films have good electrical insulation properties and good UV stability which enables expensive composite film laminates to be replaced by a single layer which also has a low cost. This allows the replacement of expensive laminate structure by a single layer.  
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