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Solar Thermal

Solar thermal collectors provide hot water from the sun. They are unlikely to meet all of a building’s hot water demand all year round, so a supplementary heat source such as a boiler or an immersion heater may be needed to meet demand when the collector’s output is low, e.g. in the winter.

Solar thermal collectors are often well suited to tourism businesses, which have high hot water demand in the summer when the collectors are producing their greatest output. Solar thermal systems can also be used to heat swimming pools.

Are there any local heat loads which could be serviced by solar hot water?

The Technology

There are two main types of solar thermal collectors: flat plate and evacuated tubes.Evacuated tubes are more efficient, but also more expensive. Some evacuated tube collectors allow greater flexibility in their positioning because the individual tubes can be placed at an angle so the solar absorber inside the tube is facing south.

Solar thermal collectors can be built into the fabric of a building or bolted on afterwards. Some systems use a small pump to distribute the hot water, which requires electricity; these systems sometimes come with a small PV panel to provide this electricity.


Solar thermal collectors must be correctly angled and orientated for the best performance, and can face between southeast and southwest at an angle of between 30 to 50 degrees. Shading reduces performance and should be avoided.

The building’s roof must be able to take the weight of the collectors, which is a particularly important consideration when adding panels to an existing building. The heating system, particularly the hot water tank, needs to be compatible with solar thermal panels.

Operation and Maintenance

Solar water heating systems should last for around 25 years. They generally come with a ten-year warranty and require very little maintenance. A yearly check by the owner, preferably with a cleaning of the collector surface, and a more detailed check by a professional installer every three to five years should be sufficient maintenance.