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Solar Water Heating (FAQs)
- How effective is solar water heating in the UK?
Solar water heating is now very efficient. About 4m² of good quality panels on a roof should provide the average family with around 50-60% of their hot water needs spread throughout the year (100% on good sunny days, 10% on gloomy days).
- Is there a difference in the effectiveness of solar panels for different parts of the UK?
The solar radiation received on a collector facing due south at an incline of 30° varies from approximately 900 kWh/m³ per year in Scotland and the North of England, to approximately 1,300 kWh/m³ per year in the South West.
- What use are solar heating systems when the sun is not shining?
Over half the energy falling in the UK is in the form of diffuse sunlight. On a cloudy day when there is little or no direct sunlight there may be 300W/m² of diffuse light falling on a flat horizontal surface. This is sufficiently intense to be usefully collected by specially-designed solar collectors.
Whilst the highest amounts of monthly solar radiation are obviously experienced in the summer months, there is enough radiation coming from the sun in spring, autumn and winter to make a very useful contribution to a household’s energy needs. A properly sized system can be expected to provide the following:
- 80 – 90% of all summer hot water needs.
- 40 – 50% of spring and autumn hot water needs.
- 10 – 15% of winter hot water needs.
- Why do I need to have a back-up system in place to support my solar heating system?
The times of highest demand do not necessarily match the times of maximum solar gain – or sunshine. For example, the peak demands for space heating occur when it is cold and dark, when there is little or no sunlight, Some form of storage or back-up supply must therefore be incorporated into most systems.
- How much would a typical system cost?
Cost depends on the number of panels required, the size of the cylinder and on installation details such as accessibility for the scaffold and the complexity of the wiring. A typical system will cost around £2,000-£3,000 and a government grant of £400 is available to assist you.
- How should solar panels be fitted for maximum efficiency?
For maximum efficiency, solar panels should be mounted on a south facing roof at a 30° angle with the horizontal and away from trees, surrounding buildings and chimneys. Fortunately, the average tilt of a UK house roof is about the optimum for receiving solar energy in the UK.
- Why are solar collectors not designed to collect as much light as possible to convert to heat?
Collectors are designed not to collect as much light as possible as this would only overheat the system. Hot water usage and storage capacity is finite and the way in which people use hot water, and the times at which they use it will vary from day to day and have to be taken into account.
- What about the aesthetics of solar collectors?
The effect that solar collectors will have on the aesthetics of a building is really a matter of personal taste. Some people like an array of futuristic looking tubes on the roof whereas others prefer the flexibility that panels bring. Panels can be integrated into roof tiles which makes them look more pleasing and fits in better with architectural designs. By integrating panels into new buildings, significant savings can be made on roofing materials that would otherwise be incurred.
- Which system is most popular, evacuated tubes or flat plate collectors?
In Germany, where both types of solar systems have been used for over twenty years, the market originally favoured evacuated tubes and flat plate panels were considered as second best. Today vacuum tubes comprise only 18% of the market, with flat plate panels taking a massive 82%. The end users find panels just as efficient, more aesthetically pleasing but also longer lasting with fewer faults and service calls required.
- I have only limited south facing roof space – which panels are best?
Evacuated tubes perform slightly better than flat plate collectors in relation to their size. Generally a vacuum installation needs around 10-12% less roof space than an equivalent flat plate system.
- What if my roof faces south-west or south-east – will solar collectors still be effective?
Ideally the solar panels should be oriented to face south. However, they will work with only a slight loss of efficiency sited between 30 degrees east and 40 degrees west of south.
- How long do solar water heating systems take to install?
Time needed for installation will depend on the size and complexity of the job. However, most systems usually take 2-3 days to install.
- What servicing and maintenance do solar collectors require?
Installations with vacuum tubes usually require more service calls than installations with panels owing to the more fragile construction of tubes. Tubes can experience stress fractures caused by the expansion and contraction of the glass in tube systems which means that the vacuum fails. The whole of the heat systems in flat plate panels is made of metal; glass covers the absorber plate but rests on a washer which allows differentials in expansion and contraction. Well engineered flat plate panels are much more robust than tube systems.
- What financial incentives are there for me to install a solar heating system?
The Low Carbon Building Programme funded by the Government offers homeowners up to £400 to assist with installing a solar energy system. What’s more, a system that is installed by a heating professional attracts VAT at 5%.
- Is planning permission required?
Planning permission is not generally required for the installation of solar panels. However, it is always worth checking with your local planning authority, especially in conservation areas and other architecturally sensitive locations.
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