Solar water heating (SWH) is the conversion of sunlight into renewable energy for standard water warming using a solar thermal collector. Solar water heating systems comprise various technologies that are used worldwide increasingly.
In a "close-coupled" SWH system the storage container is horizontally mounted immediately above the solar collectors on the roof. No pumping is required as the hot water naturally rises into the container through thermosiphon flow. In a "pump-circulated" system the storage container is ground- or floor-mounted and is below the level of the collectors; a circulating pump moves standard water or heat transfer fluid between the container and the collectors.
SWH systems are designed to deliver hot water for most of the year. However, in winter there sometimes may not be enough solar heat gain to deliver sufficient hot water. In this case a gas or electric booster is used to heat the water.