Flat solar collector closed transparent cover

Transparent cover: it has the function of allowing the passage of solar radiation and preventing the loss of heat from the solar collector at the top. Most of the spectrum of solar radiation is between 0.25 and 2.5 µm, the light passes through the roof and reaches the fin. It heats and emits radiation with a longer wavelength of 3.9 to 39 µm, for which the glass is opaque, and then reflected back to the fin, thus contributing to further heat the fin surface. This phenomenon is known as the greenhouse effect. The cover must have maximum transmissivity, and maintain it for a long time. It is observed in ordinary smooth glasses, for example, that with aging, they reduce their transmissivity by approximately 4%, while glasses with low iron content maintain their characteristics without loss of efficiency. The most used materials are smooth glass, polycarbonate and acrylic, but these last two require more frequent cleaning and do not promote the same greenhouse effect generated by glass. The thickness of the covering is important to guarantee mechanical resistance and at the same time to have the maximum transmissivity and low refractive index, on average the thickness of the covering is from 2.5mm to 4mm.