A solar water heater is a device that uses the energy of the sun to heat water that is generally for home or building use. This type of alternative, renewable energy is one of the most common uses for solar energy. Depending on the type of water heater, there are several different ways in which it may work. Generally, all solar water heaters do three basic things: energy collection, energy transfer, and energy storage.
Collectors begin the process of heating water in a solar water heater by capturing energy from the sun. Three basic types of collectors may be used: batch collectors, flat-plate collectors, or evacuated tube collectors. Batch collectors heat the water in dark tanks, and store it there until ready for use. Flat-plate collectors use a series of parallel tubes to heat water, covered by a plate of glass. The evacuated tube collectors use an insulated bottle approach to heat the water, and are generally considered to be the most efficient way, but the startup costs are greater.
The circulation is another portion of solar water heaters that may be different, depending upon the model. Circulation can be done via a direct system, or an indirect system, which heats another liquid, and then transfers that heat to the water. Water can be transferred to the storage area either via a pump or by natural convection. Most installation companies will put an indirect circulation system in if there is a danger of liquid water freezing, as is the case in colder climates.
The main benefit of a solar water heater is its ability to save on energy costs. Depending on the time of the year, weather conditions, and type of collector being used, it may not be possible to supply water for an entire household using a solar water heater. If that is the case, then a backup water heater of some type, usually run by traditional electricity, can help make up the difference.
Drawbacks to the solar water heater system are generally the startup costs and the reliability of the hot water. Installation costs can run as high as five times that of a high-efficiency water heater running on traditional sources of energy. Further, to always ensure that hot water is available, some other type of water heater may also be required. If there is a power outage, and the owner is using a pump to transfer water to the storage area, that may be impossible.