Solar Water Heaters

Solar water heaters channel the sun's thermal energy to heat water. They come in a variety of designs according to the circulation system and collector type.

Batch collectors, also known as integrated collector-storage (ICS) systems, heat water in dark tanks or tubes within an insulated box, storing water until drawn. Water can remain in the collector for long periods of time if household demand is low. A tempering valve serves as protection from scalding at the tap by mixing in cold water with the heated water. Batch collectors are incompatible with indirect or closed loop systems (these systems use a non-freezing liquid to transfer heat from the sun to water in a storage tank) and are generally not recommended for cold climates.

Flat-plate collectors typically consist of copper tubes fitted to flat absorber plates. The most common configuration is a series of parallel tubes connected at each end by two pipes, the inlet and outlet manifolds. The flat plate assembly is contained within an insulated box, and covered with tempered glass. Flat plate collectors generally contain 40 gallons of water. Two collectors can provide roughly half of the hot water needed to serve a household of four.

Evacuated tube collectors are the most efficient collectors available. Each evacuated tube made of either glass or metal contains the water or heat transfer fluid and is surrounded by a larger glass tube. The space between them is a vacuum, so very little heat is lost from the fluid.These collectors can even work well in overcast conditions and operate in temperatures as low as -40°F. Individual tubes are replaced as needed. However, these are also the most expensive.