Solar thermal (hybrid) water heating

The solar system – from the sky to your roof

Solar thermal water heating systems consist of solar thermal collectors and a hot water storage tank. The solar panels collect and convert the heat from the sun into useable hot water that can be used for tap water preparation and/or space heating.

Solar thermal water heating systems have both environmental and economic benefits. They use renewable energy to warm up water and they do not emit any pollution, contributing to a reduction in greenhouse gas emissions and the improvement of local air quality. Furthermore, solar water heaters can reduce fuel consumption substantially.

Solar water heating systems are a fully mature technology and have been used for many decades to provide heat in households, businesses and industry. In most cases solar water heaters will supply only a certain share of the required heat demand. A complementary heating system (usually a boiler) is therefore often installed to provide heat when the sun's heat is not sufficient.

Solar water heating is particularly applicable in rural homes and buildings, which often have more surface available for the installation of the solar collectors than those in urban areas. Larger systems are available that can heat large volumes of water for agricultural applications such as milk production.

The initial investment costs required for a heating system that combines solar with a complementary installation such as a boiler are higher than single technology solutions. However, the fuel savings can be substantial and installations are usually economically attractive without government incentives. The solar collectors have a long lifetime (> 25 years) and require almost no maintenance

General Info

What is it?

Solar thermal water heating systems are collecting the heat of the sun for space heating and hot tap water purposes. A solar water heater most often supplements an existing heating installation such as a boiler, and increases the overall efficiency of a heating system significantly.

What are the benefits?

Low carbon: A solar water heater does not emit any pollution, or greenhouse gases. Compared to conventional heating systems, solar water heaters contribute to a reduction of greenhouse gas emissions and improvements of local air quality.

Efficiency and fuel savings: Solar water heaters contribute to a substantial reduction in fuel consumption. Even in countries with low solar radiation e.g. United Kingdom and the Netherlands, installations can still provide 40-60% of the hot tap water requirements throughout the year, substituting the associated fuel costs that are saved. For southern EU-regions coverage of up to 90% of the energy demand for hot tap water is feasible. Coverage ratios of over 25% of the total heat demand of a building are common. Systems are able to recover heat of the sun even on cloudy and cold days.

How does it work?

Solar water heating systems consist of solar thermal collectors and a hot water storage cylinder or tank. The collectors collect the heat from the sun and use it to heat water that can be used for tap water preparation and/or space heating.


In most situations a solar water heating system is complemented by a boiler to heat the water when the sun radiation is not sufficient. Solar thermal systems are typically designed for integration (add on) in already existing heating installations.

Installations are available in different sizes and types and can be fitted on most roofs. Increasingly, they are integrated into the design of new or retrofitted buildings, including (sun-facing) facades.

Detailed Info

Costs, Savings, Earnings

Solar water heating systems operate without fuel. Costs of operation are therefore very low. Only the pump that circulates the water through the system consumes some electricity. The initial investment represents the largest share of the total costs of these systems.

Payback periods in countries with low radiation e.g. the United Kingdom are in the order of 7-15 years, depending on the type of system installed, the location and orientation, etc. In southern European countries, payback periods are shorter and very attractive.

Environmental Impacts

The environmental impact of solar water heating systems is limited. They produce virtually no greenhouse gas (GHG) emissions during use and save fuel.


The efficiency of solar water heating systems varies with the desired output water temperature. When using solar heating for heating floors or pools (output water temperature is usually below 30ºC) efficiencies can reach 70-80%. When using solar thermal panels to heat water (output water temperature above 45ºC) efficiencies drop to 50-60%.

Commercial Maturity

Solar heating systems are a fully mature technology and have been used for many decades. Experienced installers are widely available.


In the EU, the quality label Solar Keymark sets minimum requirements for solar thermal systems.

Level of Maintenance

LOW: Solar water heating systems require almost no maintenance apart from occasional cleaning of the collector surface. The rest of the (central) heating system, pumps, pipes, radiators, etc. have comparable maintenance requirements as those connected to a traditional boiler system. Systems have a long lifetime of up to 25 years.

Technical Details

There is a wide variety of solar thermal systems in terms of the type of collector (flat/evacuated tube), the type of circulation (open or closed) and the type of pumping system (active/thermo syphon).

Systems with flat panels, close circulation and active pumping are most commonly used. The typical size of a flat solar thermal panel is between 2m² and 2,5m². A typical solar thermal system for hot water preparation in the EU has 5 m² of solar collectors and a 300 liter hot water storage tank. This would be sufficient for a 3-4 member household (approximately 150 litres/day at 50ºC)

Regional variations

As rules of thumb, in northern European countries such as the UK or the Netherlands, installations can provide 60% of the hot water needs with reasonable payback times. In southern Europe this is up to 90% with short and attractive payback periods.

Trade associations

Association of the European Heating Industry (EHI)

European Solar Thermal Industry Federation (ESTIF)