Evacuated tube collector is made of double layer borosilicate glass tubes evacuated for providing insulation. The outer wall of the inner tube is coated with selective absorbing material. This helps absorption of solar radiation and transfers the heat to the water which flows through the inner tube.
The solar radiation is absorbed by flat plate collectors which consists of an insulated outer metallic box covered on the top with glass sheet. Inside there are blackened metallic absorber (selectively coated) sheets with built in channels or riser tubes to carry water. The absorber absorbs the solar radiation and transfers the heat to the flowing water.
Flat plate collector’s work on copper pipes running through a glass covered collector, often connected to a water storage tank on the roof. The sun heats the copper pipes and the resulting hot water is thermo-siphoned out of storage tank.