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Solar Water Heating Systems

sunset_heating_400Solar water heating systems offer efficient and clean energy for heating your domestic water (e.g. for your shower, bath, kitchen).

Solar water heating system are a proven technology and have been around for decades. Installing a system can be a first (and relatively low-cost) step towards reducing carbon emission that can be taken by individuals, companies and public institutions.

Environmentally, the savings in terms of carbon emissions are impressive, with the average household saving close to half a tonne of CO2 emissions per annum.

Unlike common perception that solar water heating requires a lot of direct sun light, in reality a solar water heating system concentrates diffused solar radiation from the sun and uses it to help heat water. The heated water can be used for domestic (showers, baths, sinks) and industrial purposes. There are two main types of solar collectors, which can be used in solar heating systems: evacuated tubes and flat plate collectors. Both technologies are proven and work on similar principle, with some differences and respective advantages and disadvantages.

Introduction to Domestic Solar Thermal Systems

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Solar panels normally fall within “Permitted Development Rights” therefore not requiring planning permission. Typically domestic installations can be completed within 2 days, and will potentially require scaffolding to comply with Health and Safety requirements. The existing cylinder will likely be changed to a dual coil cylinder.

Domestic Solar Thermal Systems in the UK

Despite common belief that the UK is constantly overcast and sees no sun, actually solar energy in the UK is far greater than most people imagine. Effectively the UK gets around 65% of the sun radiation of Spain. Not only in the summer, but also in the spring and autumn (and on clear winter days) the UK receives very useful amounts of solar energy.

By tilting a surface to an angle (of 30-60 degrees) the amount of solar radiation falling on it will be greater than that falling on a flat surface in this country. Fortunately, the average tilt of a UK house roof is about the optimum for receiving solar energy in the UK.

UK solar irradiation - Annual Total kWh/m2uk_irradiation_levels_map_400

The above figure shows the total average solar radiation falling on one square metre surface inclined at 30 degrees to the horizontal, measured in kilowatt hours.

Taking into account that the average property requires approximately 3,000-4,000 kWh per year for domestic water heating, these figures bring out a remarkable fact.

The amount of solar energy falling on the total roof area of an average house is many times that required to provide all its heating and hot water.

An independent survey of domestic hot water solar systems installed in the UK between 1970 and 1994 was recently undertaken on behalf of the Department of Trade and Industry.

The key points arising from this survey are:

  • Solar heating systems can meet around half the users' annual household hot water needs
  • On average, solar heating systems provide 20 years or more of useful service
  • The systems are generally considered to be very reliable
  • The majority of users say they are "very satisfied" with their systems

Domestic Systems Pricing and Economics

There are widely accepted views that the decades of cheap oil and gas have come to an end. The UK heating sector will become increasingly vulnerable to supply risks as these become largely based on imported oil and gas. It makes little sense to burn valuable (and increasingly expensive) fossil fuels to bring water to temperatures that can easily be obtained by solar water heating technologies.

Typically, solar heating systems installed into existing households are priced around 4,000 (depending on the size of house, type of collector, etc.), with an expected payback period of around 8 years (in many cases this can go down to 6 years). In a new property development, the costs and the payback period are significantly more attractive.

In March 2006 British Gas announced a dramatic hike in bills of 22% - more than ten times the rate of inflation and the biggest single increase in British history (British Gas has a 55% share of the gas market and 23% of electricity. It has eleven million gas accounts and six million electric). The latest increase is following a 14% price hike in September 2005. According to British Gas, soaring crude oil prices - which surged close to $100 close to the end of 2007 - and dwindling North Sea reserves have made wholesale prices more expensive.

A well designed solar heating system, using good quality collectors, should contribute between 1,500kWh and 2,000kWh for a family of four, which is equivalent to around 50% of the household's water heating energy needs on an annual average.

Installation and Maintenance

The installation is carried out by capable heating engineers with special training for installing solar water heating systems. Typical installation for an existing house can be completed within 2 days, however the disturbance is kept to a minimum with a large chunk of the work done on the roof and inside the loft. Hot water is normally resumed within a few hours.

The system as a whole requires virtually no maintenance. Visual inspection to ensure pressure is stable and that there are no leaks is all that is required. The only active maintenance required is to change the anti-freeze liquid every 5 years, as it is loosing its property over such period.

Leading Manufacturers of Solar Thermal Systems

The UK solar thermal market is well developed and has attracted some of the leading names in the solar thermal sector. Some players, such as Chromagen, are fairly new to the UK, having built a strong presence in many other countries (notably Germany, Spain, Greece). However, there are other players that leverage their strong position in the domestic boiler market to offer solar systems as well. This group includes Worcester Bosch, Vaillant, Viessmann, Baxi, Ideal Boilers, Grant and others.


This page has been written with contributions from experienced plumbers from Merseyside and Gas Safe engineers from Fulham. Several of the company's heating engineers from Kent have worked on similar issues as well as some of our experienced heating engineers from Camden and our Ilford plumbing and heating engineers.