Solar water heating (SWH) is the conversion of sunlight into energy to heat water by using a solar thermal collector. Solar water heating systems are available in various configurations.
In a thermosiphon SWH system the storage tank is horizontally mounted above the solar collectors on the roof. No circulating pump is required as the hot water naturally rises into the tank through thermosiphon flow. In a pump-circulated system the storage tank is mounted in the roof or on the ground and is below the level of the collectors, a circulating pump moves water or heat transfer fluid between the tank and the collectors.