The basic principle common to all solar thermal systems is simple: solar radiation is collected and the heat is transferred to a heat transfer medium, usually a fluid or - in case of air collectors - air. The heated medium is used either directly - for instance to heat swimming pools - or indirectly, by means of a heat exchanger which transfers the heat to its final destination - for instance: space heating.

Solar thermal can be successfully applied to a broad range of heat demand including domestic water heating, space heating, and drying. New exciting areas of applications are being developed in particular solar assisted cooling. System design, costs and solar yield are being constantly improved.