A row of houses in the countryside. Some of them have a solar energy system on the roof. The sky is partly cloudy.
© Getty Images / Westend61

Building and buying

Solar thermal systems: functioning, costs and subsidies

Thomas Bott

The sun provides not only light, but also energy. This can be used in many different ways. Electricity can be generated thanks to a photovoltaic system, for example. A lot is known about photovoltaic systems – but hardly anyone seems familiar with the equally useful solar thermal systems that use solar energy for heating. These systems are a very good addition to modern buildings. Find out here what is behind the technology, where you can use it and what costs are incurred.

Solar thermal systems: the concept and function explained

The term is made up of the words “solar” for solar energy and “thermal” relating to heat. A solar thermal system therefore uses the power of the sun to heat water. First and foremost, this requires collectors, which are responsible for absorbing the energy. A distinction can be made between two types:

  • Flat plate collectors
    A flat absorber is located under dark solar glass. This absorber is usually made of copper, aluminum or glass. A special coating ensures that it absorbs as much heat as possible and loses very little of this heat once it has been absorbed. Behind the absorber there is a pipe system containing a mixture of water and antifreeze.
  • Tube collectors
    This design incorporates several tubes with an absorber in the middle, surrounded by a vacuum. The advantage of this is that the absorbed heat is virtually unable to escape. Below the absorber there is also a pipe containing a mixture of water and antifreeze. This feeds the heat into the circuit. The heat pipe is where evaporation occurs. Consequently, the heat does not enter the heating circuit until it reaches a collection point.
A close-up of modern tube collectors. The multiple tubes that make up the solar thermal system can clearly be seen.

Tube collectors store the heat of the sun more efficiently but are also more expensive than flat plate collectors.

The water from the collector circuit flows through a heat storage tank. An exchange of heat takes place here with the water contained in the tank. The cooled water from the circuit flows back to the collector. The heat storage tank then supplies the heating system according to requirements. But watch out, there are different types:

  • Buffer tank for the heating system
  • Hot water tank for hot water
  • Hybrid storage tank that supplies both heating energy and hot water

When planning your future system, it is therefore crucial to consider which type of collectors and heat storage tank you wish to use. An expert will help you with the individual planning, taking into account your own specific needs. Of course, the surface area of the collectors and the capacity of the storage tank also play a major role. Here too, professional advice will help you to make your choice.

Heating via a solar energy system: only useful as supplementary heating

A solar thermal system is mainly responsible for producing hot water. It can cover up to 60 percent of the needs of a single-family house. The picture is not as rosy when it comes to supplying heating energy. Only about 30 to 40 percent of the energy required can be generated by a solar thermal system. This makes it unsuitable as a primary heating source.

In fact, this kind of system is a good supplement for your existing heating system. It can help you to save money you would otherwise spend operating an oil or gas heating system. The systems together heat a storage tank. You can produce less energy with your fossil heating thanks to the proportion of energy supplied by your solar thermal system.

Costs: what to expect for a solar thermal system

The cost of a solar thermal system depends on your personal needs. A greater surface area for the collectors in terms of square meters will result in more heat production, but also higher costs. The type of collectors you opt for – either the flat plate or tube variety – is also a key factor. Tube collectors are considerably more expensive. Last but not least, the cost also depends on the heat storage tank. A hybrid system with a large volume is expensive. On average, you should expect an initial investment of around 30,000 francs for a solar thermal system.

Six tube collectors forming a solar thermal system are mounted on a tiled roof; a chimney can be seen above them, and there is a skylight below.

A larger surface area means more solar energy that can be used for heating. However, having more square meters of collectors also implies higher acquisition costs.

Savings: economic efficiency of solar thermal energy

The high acquisition costs are offset by low operating costs. You don’t need to purchase any fuel because the sun provides the energy free of charge. The hardware will last up to 30 years and the annual maintenance is relatively inexpensive. Savings on your primary heating also contribute to the economic efficiency. By using solar thermal energy, you reduce the amount you would otherwise pay for more expensive heating oil or gas. The overall heating costs will therefore be noticeably lower thanks to your supplementary heating system. However, whether or not a solar energy system will pay for itself during its service life depends on your individual situation. You may well end up paying more for it in the long run.

Subsidies: financial support in Switzerland

In principle, subsidies are available through the cantons’ harmonized promotion model (HFM 2015). Point M-08 establishes a minimum subsidy rate of 1,200 francs plus 500 francs per kilowatt (kW). However, some cantons may offer considerably more money. For example, the canton of Basel-Landschaft pays out 3,000 francs plus 600 francs per kilowatt.

Environment: good carbon footprint for operating solar energy systems

A solar energy system does not involve any combustion. No emissions are produced by exhaust gases. There is also no waste, unlike with wood heating, which leaves ashes, for instance. A solar thermal system is a closed and locally clean system. However, the source of the necessary electricity is a different matter again. If you want to make the system as green as possible, you should also take advantage of the energy of the sun: with a photovoltaic system.

But even then, the solar thermal system is of course not completely CO₂ neutral. The usual industry emissions are produced when manufacturing the collectors, the tank and other parts. However, this is also the case with all other heating systems.

Solar thermal systems: advantages and disadvantages at a glance

  • Advantages
  • Disadvantages
  • No fuel necessary. Energy is obtained from the sun free of charge.
  • Only suitable as supplementary heating.
  • A solar thermal system does not cause any CO₂ or fine dust emissions during operation.
  • Relatively expensive to purchase.
  • Solar thermal energy can cover up to 60 percent of hot water consumption and 35 percent of heating requirements.
  • Profitability depends strongly on individual factors.
  • The system can be combined with other heating systems.
  • Low operating costs. Annual maintenance is very cost effective.

Conclusion: solar thermal energy can save you money

Heating and hot water thanks to the power of the sun – that’s what a solar thermal system promises you. Whether or not this is really worthwhile depends entirely on your demands and requirements. However, the environmental benefits of using solar thermal energy as a supplement to fossil fuel systems should not be underestimated. The energy production does not emit any CO₂ locally. In an ideal case scenario, the necessary electricity should also come from a photovoltaic system. Good advice and planning are always vital.

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