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Solar water heating

solar thermal panelSolar water heating systems can now be divided into two different categories. One type, traditionally called solar thermal, captures the sun's rays to heat a fluid, which then flows through a circuit to transfer its heat to a hot water tank. The other type of system uses electricity generated by solar panels to power an immersion heater in a hot water cylinder. See Optimiser makes the most of solar PV. This article focuses on solar thermal.

The technology of solar thermal heating is simple and relatively cheap, making solar hot water generally the most cost-effective renewable measure to fit to your home. They are very efficient and work well even in Staffordshire. Solar panels are fitted to your roof, facing south west to south east. These collect heat from the sun's radiation. A heat transfer system uses the collected heat to heat water, which is then stored in a hot water cylinder.

A more recent introduction to the UK are thermodynamic solar panels. These work on a different principle, rather like a fridge in reverse, and are a cross between a conventional solar thermal system and an air source heat pump. Like solar thermal, the technology uses flat panels to extract heat from the surrounding air, but they rely much less on direct sunlight, and can be mounted on vertical wall or flat roofs, as well as on pitched roofs. In fact they work in all weathers and at night. A refrigerant fluid runs in veins through the panel at a very low temperature, so heat will be absorbed even down to sub-zero ambient temperatures. solar PVT

Solar photovoltaic-thermal (PVT) panels are hybrids that combine the functions of solar water heating and solar electricity production. They are useful in maximizing the yield of renewable energy when space is at a premium.

What are the costs and savings?

Conventional solar thermal systems can provide almost all of your hot water during the summer months and at least a third of your total hot water needs. The average system reduces C02 by around 350kg per year and cuts about £50-80 a year from your hot water bills, depending on the fuel replaced. It will also be eligible for the domestic Renewable Heat Incentive (RHI; see below), which will provide incentive payments for the heat produced. The typical installation cost for a domestic system is £3000 - £5000. The Energy Saving Trust has more information about solar water heating.

Important points

  • Solar water heaters work best if your existing central heating system already  includes hot water stored in a cylinder (as opposed to instantaneous hot water provided by a combi boiler)
  • Preferably you will need between 2 and 5 square metres of south-east to south-west facing roof space that receives minimal shading during the day (about 1 square metre per person).
  • You may also need space for an additional water cylinder, although some systems use the existing cylinder.
  • There are a range of systems and technologies. Consult two or three companies for advice on your particular circumstances and a quotation.
  • Look for installers who are members of the Solar Trade Association.
  • Beware of some national companies who use hard-sell techniques and make exaggerated claims. Their products may be good, but their prices may be high and customer services low.
  • Solar water heating systems generally come with a 5-10 year warranty and tend to require little maintenance

Renewable Heat Incentive scheme

Solar hot-water systems are eligible for incentive payments under the Renewable Heat Incentive scheme. Systems must have been installed after 15 July 2009, and both the product and the installer must be accredited under the Microgeneration Certification Scheme to qualify. The current tariff is around 20 pence per kilowatt hour of heat produced, calculated according to the technical specification of the product. Expected annual payments typically range from £200 to £500, depending on the size of the system. This makes solar thermal a much more attractive proposition.