Cold water is moved via a pump from a water tank and travels through solar collectors in a solar panel. In the process, it is heated up by the power of the sun hitting the solar collectors. This heat is then carried away from the solar collectors by the water returning to a heated storage tank. Some solar water heaters have a shut-off valve that automatically closes when the sun goes down in order to save heated water. An auxiliary system will kick in when more hot water is needed. Auxiliary systems run on conventional energy, such as gas or electricity. A controller component regulates the pumping action of the water. The controller will close the check valve that sits between the solar panel and the hot water storage tank. It also turns the auxiliary power on when the solar cycle is not available (when the sun goes down).
Size and Heat Retention
Size is important. Solar water heater store hot water in a storage tank. A valve closes over the pipe on the storage tank to prevent the loss of heat from the hot water. The larger the storage tank, the longer you can go without recharging the water with heat from the sun. This is especially important for areas where there is frequent rain and overcast skies.
Automated Solar Water Heaters
Automated solar water heaters work by monitoring the water pump in relation to the availability of solar power from the sun. When the sun goes down, the automated solar water heater will stop the pump. In sequence, the valves over the water storage tank will close to prevent the loss of heated water. By preserving the heat in the water storage tank, hot water can be used for bathing or washing dishes even when there is no sunlight to power the solar water heater.
Auxiliary and Passive Solar Water Heaters
Most solar water heaters are not entirely independent of conventional power. When sunlight is not available as a power source, the solar power water heater will switch to auxiliary power (gas or electricity). A solar power water heater can provide on average about 90 percent of hot water from the sun alone. However, a passive solar water heater only provides about 40 percent of the home's hot water supply. This is due to the auxiliary heating processing in a second storage tank. The tank is preheated, thus more conventional power is necessary to get the water heated up before solar power can kick in.