Flat Plate Solar Collectors

Sunlight passes through the glazing and strikes the absorber plate, which heats up, changing solar energy into heat energy. The heat is transferred to liquid passing through pipes attached to the absorber plate. Absorber plates are commonly painted with "selective coatings," these coatings absorb UV and visible radiation, but are poor emitters of longer wave infrared so that they retain heat much better than ordinary black paint. Absorber plates themselves are made from copper, aluminium or stainless steel ultra-sonically welded to a copper pipe.

Occasionally non-selective coatings may be deliberately employed to increase heat losses at high temperatures and to prevent a solar collector from boiling. Non-selective collectors were more common in the past because of the increased cost of selective coatings. They are relatively uncommon in the marketplace today. However, deliberately decreasing the efficiency of the collector can be compensated for by increasing the collecting area.