Basics of Solar Water Heating
The
most popular type of solar collector for water heating is the flat panel
design (other types include evacuated-tube, concentrating, and integral
collector storage). A flat panel collector is an insulated weatherproof
enclosure with an absorber plate, flow tubes, and a transparent cover. The
transparent cover allows solar energy to pass through and be absorbed by
the absorber and flow tubes. The heat generated is then transferred to the
fluid circulating through the flow tubes. Once the solar energy is collected,
it is commonly employed with the pumped indirect SWH system. Best suited
for colder climates, an indirect system pumps heat-transfer fluids (usually
a non-toxic propylene glycol-water antifreeze mixture) through collectors,
and then transfers the heated fluid from the collectors to a storage tank.
Heat exchangers transfer the heat from the fluid to the household water
stored in the tanks. Water stored within the tank is then heated when the
fluid passes through a heat exchanger located inside the storage tank. Antifreeze
fluid is used to prevent collector piping from freezing and allow for the
maximum transfer of heat from the solar collector to the storage tank. Many
indirect system designs also incorporate an external heat exchanger.