Solar thermal energy

Solar thermal energy is the use of sunlight to generate heat: collectors mounted on the roof capture solar radiation and convert it into heat, which is used for domestic hot water and to support the heating system. Unlike photovoltaics, it does not produce electricity but heat that can be used directly.

Updated 2026-10-11

Solar thermal energy: Handwerk & Bau – CityHero glossary graphic

What is Solar thermal energy?

Solar thermal energy refers to systems that convert solar radiation into usable heat. The core components are the solar collectors on the roof – usually flat-plate collectors or higher-performing evacuated tube collectors. Inside them, a frost-resistant carrier fluid circulates and heats up in the sun. This heat is transferred via a heat exchanger to a storage tank, from which you draw hot water for showering, the kitchen and heating.

An installation starts with a site assessment: specialists evaluate roof orientation, pitch, shading as well as the existing tank and heating system. The collectors, storage tank, pump and control unit are then sized and mounted, often combined with an existing heat pump, oil or gas heating. After the hydraulic integration and commissioning, the system runs largely automatically.

Solar thermal makes particular sense for single- and multi-family homes with steady hot-water demand and when a heating renovation is due. Costs depend heavily on collector area, tank size, the roof situation and the effort of integration.

Look for sound advice with a yield estimate, a correctly sized tank (too small wastes yield), clean hydraulic integration and specialist firms with references. Clarify cantonal and municipal subsidy options as well as warranty and maintenance services in advance.

Example: Solar thermal energy in practice

A family of four in a single-family home in the canton of Aargau replaces its old oil heating with a heat pump and, at the same time, has flat-plate collectors mounted on the south-facing gable roof. From spring to autumn, solar thermal covers a large part of the hot-water demand for showering and the kitchen, so the heat pump barely needs to run in summer. Before proceeding, the family compared several quotes from local plumbing and heating firms and clarified the cantonal subsidies.

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Frequently asked

What is the difference between solar thermal and photovoltaics?

Solar thermal converts sunlight directly into heat and provides hot water and heating support. Photovoltaics, on the other hand, generates electricity. Both systems can be combined on the roof but require different collectors or modules. Which system suits you depends on your demand for heat or electricity and the available roof area.

Is solar thermal worthwhile in Switzerland despite winter?

Yes, because the collectors also use diffuse light and deliver a meaningful heat contribution over the year – most of it from spring to autumn. In winter, the yield is usually not enough on its own, which is why the system supplements the existing heating rather than fully replacing it. A yield estimate from a specialist shows what is realistic at your location.

How much maintenance does a solar thermal system need?

The maintenance effort is low, as the system runs largely automatically. A periodic check by a specialist is recommended, covering aspects such as pressure, the pump, the control unit and the antifreeze fluid. This keeps yield and service life intact for many years.

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