Flat-Plate Collectors
Typical flat-plate collectors have a metal container with a glass or plastic cover (called glazing) and a dark-colored absorber plate on the bottom. The sides and bottom of the collector are usually insulated to minimize heat loss.
Sunlight passes through the glazing and strikes the absorber plates, changing solar energy into heat energy and heating the plates. The heat is transferred to liquid passing through pipes attached to the absorber plate. Absorber plates are commonly painted with "selective coatings," which absorb and retain heat better than ordinary black paint. Absorber plates are usually made of metal—typically copper or aluminum—because the metal is a good heat conductor. Copper is more expensive, but is a better conductor and less prone to corrosion than aluminum. In locations with average available solar energy, flat plate collectors are sized approximately one-square meter per 12.5 litres of one-day's hot water use.
Applications: The main use of this technology is in residential buildings where the demand for hot water has a large impact on energy bills. This generally means a situation with a large family, or a situation in which the hot water demand is excessive due to frequent laundry washing.
Commercial applications include laundromats, car washes, military laundry facilities and eating establishments. The technology can also be used for space heating if the building is located off-grid or if utility power is subject to frequent outages. Solar water heating systems are most likely to be cost effective for facilities with water heating systems that are expensive to operate, or with operations such as laundries or kitchens that require large quantities of hot water.
Unglazed liquid collectors are commonly used to heat water for swimming pools. Because these collectors need not withstand high temperatures, they can use less expensive materials such as plastic or rubber. They also rarely require freeze-proofing because swimming pools are generally used only in warm weather or can be drained easily during cold weather.
While solar collectors are most cost-effective in sunny, temperate areas, they can also be cost effective virtually anywhere in the country so should be considered.
