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The principle is relatively simple. A box made of galvanized sheet steel, made of stainless steel, glass fiber reinforced plastic (GRP) or aluminum gets a decent insulation. Therein lies the absorber and covers it with a well translucent material, which must produce a greenhouse effect. Short-wave radiation must
get into the box well and prevent as much radiation as possible. There is a special solar safety glass that is particularly low in iron. Common insulating materials are polyurethane foam and mineral wool.
flat-plate collectorscan be integrated in the roof (new building), placed on the roof by means of suitable support structures (retrofitting) or placed free.
A special variant is the vacuum flat collector. To reduce the convection losses, the air is pumped out of the housing (evacuated). This evacuation is only effective for a limited time and must be repeated in periods that are manufacturer-dependent.
by Peter Morgenroth