Solar swimming pool water heaters rank as the most successful yet least heralded commercial solar application. The storage unit for the solar heated water already exists which is the swimming pool. The pump needed to push water through the solar collector also must be bought irrespective of the technology used to heat the water. The pool owner merely has to purchase the solar collectors and some connectors and fittings. Of course, the outdoor swimming season harmoniously coincides with the maximum output of the solar collectors. Even when other forms of energy are selling very cheaply, the pool owner buying a solar unit starts to save money very quickly.
In the United States alone, solar swimming pool heaters have produced the energy output equivalent to ten nuclear power plants. With the rapid price decline in solar collectors, pool owners can afford smaller collectors that have a much higher output per unit foot print. Pool systems can be operated in two different ways. The 1st method uses a digital control switch with temperature sensors. This can be programmed to open or close a diverter flow valve. If the pool is too hot the digital controller will sense this and bypass the solar system allowing the tub to cool off. It will also open the valve only during periods where there is solar gain during the day and shut off the system at night when there is no solar radiation. The 2nd method uses a manual flow valve to adjust the bypass flow. This method is less expensive but it means you must shut off the bypass valve every evening to avoid heat losses.