A solar thermal collector collects heat by absorbing sunlight. The term “solar collector” commonly refers to solar hot water panels, but may refer to installations such as solar parabolic troughs and solar towers; or basic installations such as solar air heaters. Concentrated solar power plants usually use the more complex collectors to generate electricity by heating a fluid to drive a turbine connected to an electrical generator. Simple collectors are typically used in residential and commercial buildings for space heating.
Flat-plate collectors are the most common solar thermal technology. They consist of an (1) enclosure containing (2) a dark coloured absorber plate with fluid circulation passageways, and (3) a transparent cover to allow transmission of solar energy into the enclosure. The sides and back of the enclosure are typically insulated to reduce heat loss to the outside air. A fluid is circulated through the absorber’s fluid passageways to remove heat from the solar collector. The circulation fluid in tropical and sub-tropical climates is typically water. In climates where freezing is likely, a heat-transfer fluid similar to an automotive antifreeze solution may be used instead of water, or in a mixture with water. If a heat transfer fluid is used, a heat exchanger is typically employed to transfer heat from the solar collector fluid to a hot water storage tank. The most common absorber design consists of copper tubing attached to thermally conductive copper or aluminum fins. A dark coating is applied to the sun-facing side of the absorber assembly to increase it absorption of solar energy. A common absorber coating is flat black enamel paint.
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