Definition
A thermosiphon system is a solar water heater in which the storage tank is mounted above the collector so that heated water rises naturally into the tank and cooler water sinks back, without any pump or controller. Typical residential units combine 1.5–4 m² of flat-plate collector with a 150–300 L tank, in direct or indirect (heat-exchanger jacket) versions. They dominate residential solar water heating in the Mediterranean, Middle East and Africa.