Solar Thermal Technology Factsheet

The technology

Solar thermal heating systems (STHS) utilise thermal energy from the sun to supply heat to hot water systems – as opposed to generating electricity, which is a separate technology called PV. This is achieved by using a solar collector filled with liquid, which absorbs heat from the radiation coming from the sun (it does not have to be sunny to work) and transfers this heat, via a heat exchange system to a dual coil (or supplementary) hot water tank that is also attached to the main boiler or immersion for backup as and when required – see diagram, below left.

Solar Thermal Schematic Solar Thermal Mounting Angles

Choice of collector technology is split between flat plate collectors (below left) and evacuated tube systems (below right). The former are cheaper than the latter, but not as efficient per sqm (square metre). STHS can provide a minimum of 50% of hot water requirements for homes, offices and schools etc. over the course of a year, although the reality is often much higher. In a domestic situation, this will be virtually 100% of hot water requirements from mid-May through to mid-September, but even in the depths of winter can be as much as a 20% contribution.

Solar Thermal Garage Roof Solar Thermal School Roof

Systems are best located on unshaded roofs with a southerly aspect, although, as the diagram above right implies, they can work at other angles, with some drop-off in efficiency. In a standard domestic context around 2.5–4 square metres of roof space is required for the collectors, depending on hot water requirements, and the hot water tanks will be slightly larger than a conventional single coil model.

Solar Thermal Tiled RoofA recent addition to this technology has been solar thermal tile products which, although more expensive than the conventional tube or flat plate based collectors, will certainly find a place in the market on aesthetic grounds. This is most likely in conservation areas and on listed buildings.

Operation and maintenance

Collectors tend to be guaranteed for 10-20 years and should last significantly longer. Concerns are occasionally raised regarding the strength of evacuated tubes, but these are extremely robust and would require the force of a hammer to break. Individual tubes and coverings for flat plate collectors are easy and cheap to replace in the unfortunate case of an accident. Other parts such as pumps and the hot water tank have standard time guarantees associated with mainstream plumbing products.

Maintenance is minimal; it would be reasonable to check the system and circulating liquid on a 5 year cycle, although it could be included with annual boiler servicing.


To give an initial idea of costs, a conventional domestic system would feed into a 200 litre hot water storage cylinder and be a typical size for a three-bed semi-detached house. This would cost in the region of £3,500-4,500 plus VAT installed, depending on which type of collector system is specified.

The Government is expected to introduce the Renewable Heat Incentive (RHI) from June 2011. Energy users that generate heat from renewable technologies will be paid at a level set for each technology and range of size.


New guidance for this technology in domestic settings is expected soon. However, planning permission is usually required only when a building is listed and/or in a conservation zone. Some local planning authorities have stipulations as to the proportion of a roof area that can be covered with collectors without requiring a planning application, so guidance from local planning officers should be sought. If required, examples of installations, even on listed buildings, can be supplied by TV Energy.

Key links

  • Solar Trade Association – - members are bound by codes of conduct regarding sales techniques and workmanship.
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