By solar thermal energy is meant the use for heating purposes of solar radiation energy. It differs from solar photo-voltaic, which refers to the production of solar electrical energy. A solar thermal system works in principle as a garden hose exposed to the sun: The sun heats via the solar collector a fluid that circulates there. This heat is then injected into the heating system. The sensors are usually on a roof, but can also be mounted on facades and balconies.
The solar system can be combined with the different types of heat production. With some heat producers and in some cantons, it is mandatory to install thermal panels to meet renewable energy rates.