Flat-plate collectors (FPCs) are by far the most used type of collector. When solar
radiation passes through a transparent cover and impinges on the blackened absor-ber surface of high absorptivity, a large portion of this energy is absorbed by the
plate and then transferred to the transport medium in the fluid tubes to be carried
away for storage or use. The underside of the absorber plate and the side of the
casing are well insulated to reduce conduction losses. The operation of the collector
depends to a great extent on the way the riser tubes are fixed to the absorbing plate.
They can be welded to the absorbing plate, or they can be an integral part of the
plate. Due to the introduction of highly-selective coatings, actual standard flat-plate
collectors can reach stagnation temperatures of more than 200
C. With these collectors, good efficiencies can be obtained up to temperatures of 100
C.