A Solar thermal controller can be seen as the brains of a solar water heating system. It controlles and regulates the transport of heat between the storage vessel (geyser) and the solar collector.

With the use of temperature sensors the controller knows what the temperatures are at different places within the flow of the solar heating system. This enables the controller to allow or stop the circulation between the solar collector and the storage vessel, giving you complete controll over how the system will react.