Technologies and Applications

Solar Thermal Energy

Technologie: Solarthermie
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Solar thermal energy can be used to heat non-potable water, for room heating and also for cooling.
Operating principle and different types of solar collectors
Unglazed absorbers are the simplest type of solar collector, consisting of a black plastic matting that is often used to heat water in swimming pools in order to reduce their operating costs. They are cheaper than a fossil-fuel boiler and achieve temperatures of 30–40 °C. Almost 90 % of the solar collectors in Germany are flat plate collectors. The metal solar absorber is fitted in a casing that reduces the rate of heat loss thanks to thermal insulation and a glass pane. Flat plate collectors generally operate in the temperature range of 60 – 90 °C.
Air heater solar collectors are a special kind of flat plate collector. Air is heated and normally used immediately to heat buildings, without having to be stored. Other applications are the drying of agricultural products and the heating of water (e.g. tap water) through an air-water heat exchanger. With evacuated tube collectors – in which the level of heat loss is significantly reduced thanks to high negative pressure in the glass tubes – even higher temperatures and degrees of efficiency are achieved. A collector is made up of several evacuated tubes.
Thanks to the rotatable mounting for the individual tubes, the flat absorber plate in the glass tubes can be turned to the optimum position for sunlight. For this reason, evacuated tube collectors can also be deployed almost horizontally on flat roofs. The individual tubes form a closed system that transfers the heat through a frost-proof cycle to the water to be heated.

Solar thermal systems
Pump-driven circulation system

  • The thermal energy obtained is fed to the energy storage system by means of a heat transfer medium.
  • The heat transfer medium is circulated by a pump. This means that the energy storage system can be lo-cated in the basement, which makes it easier to combine the solar thermal energy system and the con-ventional heating system.
  • The control unit monitors and regulates the system, to always ensure sufficient availability of heat energy.
    Thermal syphon system (convection)
  • These systems are ideally installed in frost-free areas and their design is undemanding and works without using electrical energy for pumps and regulators.
  • Heated liquids have a lower density than cold liquids. Therefore, gravity and the difference in buoyancy cause the heat transfer medium to circulate between the collector and the tank located above it.