History of silicone gel in photovoltaic industry

Earlier solar panels

Historically, the earlier and quite widespread technological and design solutions is to use as a encapsulant of silicone elastomers based on low molecular weight siloxane rubber cold cure. Along with the indisputable advantages, such as high optical transparency and resistance to the light aging, such encapsulants have several disadvantages, the main ones being the duration of the curing process and, consequently, low productivity, lack of adhesion and the need for special surface treatment of solar cells and protective coatings, and toxicity of used catalysts curing.

Much more tech thermoplastic adhesives have been based on polyvinylbutyral. However, under the influence of light, high temperature, humidity and atmospheric oxygen PVB gradually turn yellow, and this process is catalyzed by the migration of metal ions from the contacts of solar cells.

EVA solar panels

Since the mid-eighties of the last century, as a polymer filler have been widely applied films based on a copolymer of ethylene and vinyl acetate with vinyl acetate content of 28 - 33% (film EVA) with a thickness of 0,2 to 0,6 mm. This material was selected by employees Springborn Laboratories from a large number of investigated materials (copolymers of ethylene with methacrylic acid and its derivatives, butylacrylate copolymers, polyurethanes and others), based on favorable combination of mechanical and optical properties with low cost.

The main components that make up the industrial films in addition to ethylene and vinyl acetate, are:

  • UV - absorber
  • UV - absorber
  • antioxidant
  • peroxide coupling agent
  • silane adhesion promoter

Peroxide cross-linking to the content of low-melting copolymer gel - fraction (the main indicator of the degree of structuring of the material), about 85% is used to improve the heat resistance of the products and their mechanical strength. Depending on the properties of the peroxides used different film standard (slow), fast and ultra-fast lacing.

Reduction of power

To use a standard cross-linking of the films used in more complex schedule for lamination temperature and long holding time at finite temperature (from 20 to 40 minutes depending on the brand of the film). Application of rapid cross-linking of the films can reduce the lamination process and, therefore, significantly enhance performance. The relative accessibility and ease of use EVA film allowed several companies to establish mass production of photovoltaic modules. However, since the late eighties, there were work, compile and analyze long-term experience in the natural-climatic testing and operation of modules from EVA films, in which it was noted darkening of EVA, leads to different degree of reduction of power, especially in systems working with solar radiation concentrators.

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