A typical flat-plate collector is a metal box with a glass or plastic cover (called glazing) on top 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 plate, which heats up, changing solar energy into heat energy. 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-half- to one-square foot per gallon of one-day's hot water use.

Low Temperature Collectors
Low temperature solar collectors are typically unglazed flat plate collectors, intended to operate at temperatures only 5 to 30 degrees above ambient temperature. Low temperature liquid collectors are used for swimming pool heating. With light glazing and enclosure, they are used as air collectors for agricultural low-temperature applications such as crop drying.

Plastic low-temperature collectors have been used widely for swimming pool heating. However, because of the deteriorating effects of ultra violet radiation and stagnation temperatures on some plastic solar collectors, metal collectors are being more widely utilized. Unglazed collectors with aluminum absorber plates and copper water passages appear to be most cost effective over the typical metal collector lifetime of 20 years or more. All-copper collectors for swimming pool heating also work well, but are generally more expensive for the same performance characteristics. Copper is preferred over any other metal for water passages because of its high conductivity and compatibility with water. Almost all other metals must be separated from direct contact with the water being heated by a heat exchanger, which seriously reduces the collector efficiency.

Medium Temperature Collectors
Medium temperature collectors typically are flat-plate collectors, enclosed in an insulated case, with one or two glazings. The intended temperature range of operation is from about 15 to 200 degrees F above ambient temperature. For the lower end of this range, single-glazed collectors with non-selective absorber plates are most cost effective. In the middle and high end of the range, selective collectors with one or two glazings become more cost effective. Typical applications include water heating, space heating and some medium temperature industrial heating uses.

High Temperature Collectors
High temperature collectors include some overlap from flat plate collectors in the medium temperature range, with selective absorber plates and heavy insulation, and may have temperature capabilities enhanced in installation by being mounted in a sun-tracking system