With the increasing use of thermal insulation in buildings and the resulting reduction in heating energy requirements, the share of energy required for heating water in a building’s total energy requirement is growing in significance.

Thermal solar systems can cover a considerable portion of this energy requirement. Current systems for solar water heating function highly reliably and enable annual energy yields of 350 to 500 kilowatt hours per m² of collector area. At the same time, they cut the emission of c. 100-150 kg of the greenhouse gas CO2. Solar thermal systems directly use the sun’s radiation and convert it into heat on an absorbing surface, which is particularly of use in the field of hot water supply.

A thermal solar system must carry out the following tasks:

• Conversion of the sun’s irradiated energy into heat with the use of collectors
• Heat transfer to the storage tank via the piping system
• Storage of heat in buffer tanks until required by the user.

In the process, energy is lost at the collector, in the piping system, and in the storage tank. Minimizing these energy losses is the job of practical adaptation and planning of the solar system for each specific scenario.

The system efficiency serves to evaluate these losses. It is defined as the ratio of available energy from the solar system to the irradiated energy onto the collector area. The percentage of total energy available covered by solar power is termed the solar fraction.