A solar water heater is a combination of a solar collector, an energy transfer media and a thermally insulated hot water storage unit or geyser.
I. A flat plate solar collector is an energy conversion device that absorbs solar radiation and transfers the energy to the working fluid passing through the collector. The principal features of flat plate collector are:
a) A high solar transmission cover which is usually toughened glass.
b) An absorber plate, coated with a high absorption and low emmitance layer which is usually a mat black high temperature paint or special selective coating.
c) A high conductivity absorber plate which is usually a fin and tube construction. The absorber can be copper, aluminium, steel/galvanized steel, stainless steel or even a UV stabilized polymer
d) A heat removal fluid passage-way good thermal contact to the absorber plate. This passage is usually a tube made of the same material or similar as the absorber plate itself, and
e) A non corrosive and water proof casing, with insulation on the back and sides to reduce down the sideward heat loss. Insulation can be polystyrene, polyurethane or glass wool and each with variations in thickness.
2. The energy transfer medium is either water or a mix of water and propylene heat transfer glycol heat transfer fluid. This is an anti-freeze liquid and a corrosion inhibitor.
3. The solar geyser can be made of steel with a protection inner lining, copper, stainless steel or a polymer. Solar geysers come in standard sizes as per conventional geysers. Some makes are vented but most are pressurized from 100kPa to 600kPa depending on the material used. The difference compared to a conventional geyser is that there are extra connections for the solar circuit.
Solar water heaters can be plumbed in series to pre-feed or add volume to existing geysers, or can totally take the place of the existing geyser. Solar geysers can be mounted on top of the roof, if the structure can hold the mass, under the roof at high level or at ground level in a plant room/utility cupboard. Due to aesthetic mounted horizontally, but for better thermal stratification, it is preferable to mount them vertically.