A solar water heating system uses solar collectors, usually mounted on a roof, to capture energy from the sun. There are two types of collector: flat plate and vacuum tube.
With a direct system, the water flowing through the system also comes out of the taps. With an indirect system a heat transfer fluid is used instead.
An electronic controller compares the temperature of the solar collectors with the temperature of the water in the cylinder. If the collectors are hotter than the cylinder, the controller switches on the system, and circulates the heat transfer fluid through the cylinder’s heat exchanger. This heats the cylinder in just the same way as a central heating boiler. For information on solar for electricity, see the Solar PV page.