The simplest solar collectors are flat-plate collectors. The plates are fixed, and the sun shines on them at various angles as it moves. The hot fluid flows to a heat exchanger, a device like an automobile radiator through which water circulates, and transfers its heat to the water. How solar energy heats a house Another kind of collector, designed specifically for heating air, is the transpired solar collector. Such collectors consist of flat or ridged plates pierced by an array of small holes.
Air is drawn through the holes and is heated by the sun-warmed plates.
As much as 80 percent of the solar energy collected by the plates is transferred to the air stream. A solar furnace is a type of solar collector that concentrates sunlight to produce temperatures high enough for use in industrial processes. One such furnace operates at the National Renewable Energy Laboratory in Golden, Colorado. In the Colorado installation, a single mirror tracks the sun and directs solar radiation into a series of concentrating mirrors. The mirrors reflect the beam of light through a system of attenuators and shutters, devices that control the intensity of the beam and turn it on and off.