A flat-plate solar collector is one of the three main types of solar collectors, which are key components of active solar heating systems. Flat-plate collectors are the most common solar collectors for use in solar water-heating systems in homes and in solar space heating.

Construction:

A typical flat-plate collector is a metal box with a glass or plastic cover (called glazing) on top.  Small tubes run through the box, carrying the water or other fluid, such as antifreeze, to be heated. The tubes are mounted on a dark-colored metal absorber plate. Absorber plates are commonly painted with "selective coatings," which absorb and retain heat better than ordinary black paint. Absorber plates are usually made of metal—typically copper or aluminum—because the metal is a good heat conductor. The sides and bottom of the collector are usually insulated to minimize heat loss.

Working:

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.

Flat-plate collectors heat the circulating fluid to a temperature considerably less than that of the boiling point of water and are best suited to applications where the demand temperature is 30-70°C (86-158°F) and/or for applications that require heat during the winter months.