Theory of Operation
Solar DHW systems collect heat from the sun by circulating a non-toxic anti-freeze solution through an array of solar collectors. The hot anti-freeze travels from the collectors to a solar storage tank. The tank water is heated by the anti-freeze through a heat exchanger. The exchanger is immersed in the solar water tank or mounted to the side of the tank, depending on application. 

 The heat stored can be used in a variety of manners. In a strictly DHW system, the solar-heated water is plumbed into a backup (fossil-fueled) water tank. Solar energy is thus preheating household water, and the backup tank will not have to fire-up if the incoming solar water is hot enough for household use. Larger DHW / Radiant Floor / Pool systems employ multiple heat exchangers in a non-pressurized tank to provide heating assist for domestic water, space heat, and perhaps summertime pool heating as well.