Solar water heating or SWH is the process of converting sunlight into energy that can then be used for domestic water heating. This heated water can be used for washing in the home, radiant floor heating, or to heat swimming pools.
Solar water heating systems use a large number of different technologies and these technologies can be used almost anywhere in the world. Each of these systems include two main components – storage tanks and solar collectors.
Generally speaking, solar water heating systems are composed of two main pieces: storage tanks and solar collectors. The collectors serve the purpose of collecting and retaining heat from the Sun. Once the collectors capture the energy from the Sun, this heat is transferred to a liquid known as the heat transfer fluid. If this fluid is water it takes the heat from the collector and moves the warm water for use or storage. However if this fluid is not water, heat exchangers are used to transfer the heat from the heat exchange fluid to a home’s water supply. Pumps are sometimes used in active heating systems to control what temperature the water gets to and how quickly it moves.
STORAGE TANKS AND SOLAR COLLECTORS
Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.
Three types of solar collectors are used for residential applications:
Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors — typically used for solar pool heating — have a dark absorber plate, made of metal or polymer, without a cover or enclosure.
Integral collector-storage systems
Also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.
Evacuated-tube solar collectors
They feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy but inhibits radiative heat loss.