A Flat Plate Collector is a heat exchanger that converts the radiant solar power from the sun into heat energy using the well-known greenhouse effect. It collects, or captures, solar power and use that energy to heat water in the home for bathing, washing, and heating; and it also can even be used to heat air-open swimming pools and hot tubs.

For most residential and small commercial hot water applications, the solar flat plate collector tends to be more cost-effective thanks to its simple design, low cost, and relatively easier installation compared to different types of hot water heating systems. Plus, solar flat plate collectors are more than capable of delivering the necessary amount of hot water at the required temperature.

A solar flat plate collector usually consists of an oversized heat absorbing plate, usually, a big sheet of copper or aluminum as they're both good conductors of heat, which is painted or chemically etched black to absorb as much solar radiation as possible for maximum efficiency. This blackened energy-absorbing surface has a lot of parallel copper pipes or tubes known as risers, running lengthways across the plate that contains the heat transfer fluid, typically water.

These copper pipes are fastened, soldered or brazed on to the absorbent plate to make sure maximum surface contact and heat transfer. Sunlight heats the absorbing surface which will increase in temperature. Because the plate gets hotter this heat is conducted through the risers and absorbed by the fluid flowing within the copper pipes which is then utilized by the household.

The pipes and absorbent plates are attached in an insulated metal or wooden box with a sheet of glazing material, either glass or plastic on the front to shield the attached absorbent plate and build an insulating air space. This glazing material doesn't absorb the sun's thermal energy to any important extent and thus most of the incoming radiation is received by the blackened absorber.

The air gap between the plate and glazing material traps this heat preventing it from escaping back into the atmosphere. Since the absorber plate warms up, it transfers heat to the fluid inside the collector, however, it additionally loses heat to its surroundings. To diminish this loss of heat, the base and sides of a flat plate collector are insulated with high-temperature rigid foam or aluminum foil insulation as shown.