Solar thermal systems convert solar irradiation into heat so that it can be used to heat domestic hot water or for back-up heating.

The solar irradiation is converted into heat in the collector whose main component is a selectively-coated absorber. The heat is pumped via a closed piping system, the solar circuit, from the collector to the storage tank. The solar energy system not only provides hot water in the summer and in transitional periods, but can even provide some in winter. A frost-resistant mixture of water and glycol is used to prevent the heat-transfer fluid from freezing in the solar circuit.

Key:
A    Solar collector
B    Solar station
C    Storage tank
D    Boiler
E    Water withdrawal

Solar controllers as temperature difference controllers and solar stations

The transport of heat from the collector to the storage tank is controlled according to the temperature difference. The controller starts the circulation pump of the solar circuit as soon as the temperature in the collector is several degrees warmer than the temperature at the bottom of the storage tank. This transports the solar fluid from the collector to the lower heat exchanger, where the heat is transferred to the drinking water in the storage tank via the solar circuit heat exchanger. The cooled solar fluid then flows back to the collector in the return pipe.

The heated drinking water rises in the storage tank. The water is stratified in the storage tank according to its density or temperature: the hottest water is at the top (where it is tapped), the coldest water is at the bottom (where cold water is fed in).

With the current standard system size for one to two family houses (approx. 1.0 to 1.5 m² collector surface per person and approx. 80-100 l storage tank volume), in summer, the drinking water is primarily heated by the solar energy system. This results in an annual solar coverage (percentage of the total energy requirement for heating drinking water provided by solar energy) of approx. 60%. The remaining 40% must be covered by back-up heating. This is generally provided by a boiler and by the upper heat exchanger for back-up heating, which is located in the storage tank.

You can select a tailor-made controller from the Steca solar thermal controller product family based entirely on the requirements of your solar energy system. A range of monitoring and control functions guarantee that your solar energy system runs safely and maximise its service life.

Key:
A      Solar collector
B      Storage tank
C      Pool
D      External heat exchanger
E      Pumps
F      Temperature sensor