Solar water heating uses heat from the sun to warm up a liquid that is pumped through a panel on your roof. In the most common kind of system, this liquid then goes through a coil in a hot water cylinder where the heat is transferred to water.

A solar collector comprises the housing that contains piping through which the carrier fluid circulates and a glass panel to retain the radiation from the Sun. The temperature inside the collector increases and this heat is then transferred to a carrier fluid. In an open loop system, the hot water is heated directly. A heat transfer medium such as glycol is employed in a closed loop system. Solar thermal panels are generally black in appearance for maximising energy adsorption and the glass panels have special coating in order to retain as much heat as possible.

The heated carrier fluid circulates around the system, with a pump in an active system or by natural convection in a passive system, to the hot water cylinder. The cylinder should be a twin coil cylinder.

Two types of collectors exist: flat plate and evacuated tube. Flat plate collector can be mounted on or flush with the roof. The air in the collection tubes can be evacuated to reduce heat losses within the frame by convection. Evacuated tube collectors need to be re-evacuated every few years. They are more difficult to install but are more efficient and allow higher temperature heating.

Solar thermal collectors offer a good price-performance ratio. Solar hot water systems are ideal for any development with high hot water requirements, such as hotels, care homes and leisure centres. Many systems have been installed in the UK and they work well, even without direct sunlight. In a domestic situation, 50-70% of hot water needs can be met.

Solar thermal systems should be sized to the hot water requirements of the user: any excess heat that is generated cannot be exported elsewhere. The optimal angle for mounting depends on when the water demand is greatest. Ideally, the collectors should be mounted onto an unshaded, south-facing roof. Where possible, solar thermal systems should not be visible from the road or in the sight line of other buildings. When they are roof-integrated, the panels look similar to a roof light. Space for a preheat cylinder is required in the roof space if possible. In a residential block, a communal hot water system with a heat metering system can be implemented although additional room for a plant room would be required.

Solar thermal technology is a cost effective way to reduce carbon emissions, especially if it is replacing electrical water heating. A system to provide 50-70% of the hot water needs for a 4-bed house costs in the region of £2500. Reductions for bulk purchases and installations can be expected.

Please email or call CEN on 020 8683 6694 for further information or advice.