Solar Water Heating
Active Solar Heating technology means uses the solar radiation for heating water. Thus, the abundant free energy from the sun can be harnessed to meet part of the domestic hot water demand and reduce the consumption of conventional fuel, which causes climate change and pollution.
The UK receives vast amounts of solar energy which on average equals 60% of the annual received on the equator. The available range of high quality products enables householders to make efficient use of the Sun. Thus, even in the spring and autumn and on clear winter days the solar system can be useful.
The systems consist of solar collectors, a preheat tank (optional), a pump, a control unit, connecting pipes, the normal hot water tank, and a conventional heat source (a standard solar system in the UK cannot provide enough heat to supply hot water at the desired temperature, throughout the year). Active Solar Heating systems will typically convert 40 to 50% of the solar energy falling on the solar collectors into useful heated water.
Solar Water Heating technology is ideally suited to use on residential buildings, providing hot water. The use of active solar heating in households has grown substantially in the UK over the last few years, with many examples already in operation. SWH systems can be incorporated into buildings in various ways. Sloping rooftops are an ideal site, where collectors can simply be mounted using frames. Systems can also be incorporated into the actual building/roof fabric. In most SWH systems, only the collectors are visible. They look similar to dark roof lights. The overall area of the collector array may be typically 3-4 square metres. It is ideal if the roof is South facing, but anywhere between East and West will work, though not as effectively.
When the sun is shining, water is pumped through the solar panel and is heated by solar energy. This heated water then flows through a heat exchanger, warming the water stored in the hot water cylinder. If necessary, a boiler provides top-up heating.
An electronic controller constantly compares the temperature of the solar collectors with the temperature of the water in the cylinder. Whenever the collectors are hotter than the cylinder, the controller switches on the system's circulating pump. A mixture of antifreeze and water is then circulated through the collectors and the cylinder's heat exchanger, heating the cylinder in just the same way as a central heating boiler.
In the summer the water in the cylinder can reach a temperature of 80°C within half a day, and the insulation on the cylinder will keep the water warm for the next day. Typically the solar hot water system will reduce your domestic hot water bill by 50%.
A house roof is ideal for installing an Solar Water Heating system – there is plenty of ‘unused’ space, the visual intrusion is minimal and direct exposure to sun light is the greatest. Roof conditions of course vary and several key factors should be taken into consideration when assessing the solar potential of your home:
- Orientation - Solar Water Heating systems are most effective on roofs facing south, south-east and south-west (up to 95% efficiency). In the UK, a north-facing Solar Water Heating roof will operate at about 60% efficiency.
- Tilt – Solar Water Heating systems can be installed on any flat-surface roof. Ideally the roof should be sloped to maximise exposure to solar radiation and to allow rain to wash dust off the collectors.
- Available area: Solar Water Heating systems can take from 1 m2 to more typically 2-4 m2
- Shadowing – preferably the roof should not be shaded by tall trees or neighbouring buildings.
Solar Water Heating roofs do not usually require planning permission and typically fall within what is known as ‘permitted development rights’. However, if you live in a house divided into flats or the building is listed or in a conservation area you should call your council to check on local policy.
For a family of four, a well designed Solar Water Heating system should contribute between 1,500kWh and 2,000kWh, which will be equivalent to 40 to 50% of the household's water heating energy needs. The value of this saving will depend on the type of energy displaced. Typically installation of these systems onto existing houses are priced in the range of £2,500 to £4,500 (depending on the size of house, type of collector, etc.).
