How effective is solar water heating in the UK?

If correctly specified and installed, solar water heating can be 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 sunny summer days and even around 10% on a cloudy, winter’s day).

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/m2 per year in Scotland and the North of England, to approximately 1,200 kWh/m2 per year in the South West. This is illustrated on page 5 of this brochure.

Do solar heating systems continue to provide heat even when the sun is not shining?

On a cloudy day when there is little or no direct sunlight, there may still be 200W/m² of solar radiation light falling on the solar collector. This is sufficiently intense to be usefully collected by solar collectors. While 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.
  

Can i increase the number of collectors on the roof for better performance?

The greater the surface area of collector on the roof, the greater the heating capacity of the solar system. However, during the summer months the solar radiation levels can be much higher and the sun shines for longer, compared with the winter months and during these periods of hot weather a solar system can heat the stored water very quickly, spending the rest of the day trying to dissipate heat from the system to prevent overheating.

Oversizing the solar collectors will improve the spring/autumn/winter performance when expected output is quite low, but the system can quickly stagnate in summer conditions. To improve spring / autumn / winter performance the inclination angle can be increased. The Dimplex packages are selected to provide the correct balance of performance versus cost and reduce periods of overheating.

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.

What direction does my roof need to face in order for solar panels to provide maximum efficiency?

For maximum efficiency, solar panels should be mounted on a south facing roof at an angle of 30° – 50° 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.

If your roof faces east or west solar panels can still be installed, although this will have some effect on the efficiency. The same applies to the angle of the roof which, provided it is pitched between 30º and 50ºC, should still be suitable.

I’ve heard evacuated tube collectors are more efficient. Why would i consider a flat plate system?

It is true that evacuated tubes tend to provide a higher energy yield than flat plate systems in the spring/autumn time, however in the summer a correctly sized flat plate system will provide up to 100% of the hot water demand. Tubes generally also require slightly less roof space to yield the same amount of energy.

Benefits of flat plate systems however include lower initial cost, higher levels of robustness and lower maintenance. Flat plate systems also have the benefit of being able to be fully integrated into the roof line, which has a better appearance and also saves money on other roofing materials.

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 1-2 days to install. In Scotland and Northern Ireland planning permission is required for installations that protrude more than 150mm.

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?

From April 2008 new Government rules state that providing the solar installation does not protrude more than 200mm from the roof slope and is not in a conservation area or on a listed building, installation of solar panels are considered a permitted development, meaning that no planning permission is required.