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How does thermal solar energy work?

Solar systems for generating thermal energy save money and CO2

The sun provides the earth’s finite resources with an almost inexhaustible source of energy. It sends its energy to the earth’s surface free of charge and constantly – it only has to be captured and used.

Solar systems are one of the keys to a more environmentally friendly and climate-friendly future – in addition, thermal solar energy saves costs. The principle and technical implementation of heating and hot water production using solar energy are conceivably simple and efficient.

How thermal solar energy works

When a garden hose lies in the sun, the water inside heats up. The same principle is used by solar systems to generate thermal energy. Solar radiation is converted into thermal energy in solar collectors and transferred to a heat transfer medium. This heat transfer medium, which has a temperature of up to 90 °C, circulates between the collector and the accumulator tank, where it transfers the thermal energy to the drinking or service water via a heat exchanger.

This can then be used as conventional hot water. Solar thermal energy can also be used to support the heating system.

Elements of a thermal solar system

Solar panels

The solar panel captures the solar energy and transfers it in the form of heat to a heat transfer medium circulating in it. This is usually a mixture of water and antifreeze.

The efficiency of a solar panel doesn’t only depend on external influences such as weather and solar radiation, but also on its size and position. Accordingly, the collector area, roof orientation and roof pitch are essential factors. Ideally, solar panels are oriented towards the south and are at right angles to the sun’s rays.

Solar control unit

The solar control unit is the operating centre of a thermal  solar system. It monitors the storage level of the accumulator tank and controls the solar pump accordingly in order to transport thermal energy from the collectors to the heat exchanger or the accumulator tank.

Heat exchanger

The heat exchanger is the interface between energy generation and energy use. Here, the collected heat energy is transferred from the heat transfer medium to the drinking and service water by means of spiral-shaped smooth or finned pipes. The thus cooled carrier medium is pumped back into the solar collector, where it heats up again. In this way, the solar circuit keeps turning.

Accumulator tank

Heat exchangers are usually integrated into the accumulator tank, where the hot water is stored until it is needed. The storage tank should not only be large enough to cover nightly consumption, but also to be able to bridge sunless days when little solar energy is generated.

However, since in most cases not all of the demand can be covered by thermal  solar energy, and in order to ensure safety in winter and during prolonged bad weather, an auxiliary heating system is connected to the accumulator tank.

Using thermal solar energy in the household

Once the solar system has brought the thermal energy from the collectors on the roof to the accumulator tank, it can be used in different ways: On the one hand, as hot water in the bathroom, kitchen, etc. This use of thermal solar energy can cover about 60 % of the energy demand for hot water preparation.

On the other hand, the hot water from the storage tank can be fed into the heating circuit to support the main heating system. For example, a cost-effective and ecological combination of a pellet boiler and thermal solar energy is possible. Such a heating system is not only considered 100 % CO₂-neutral, but can also save up to 30 % of heating costs.
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