Solar Thermal

Why choose solar hot water?

In the context of ever-rising energy costs, climate change and changing legislation, the need for a heating and hot water technology that is future proof, cost effective and able to use an unlimited, sustainable source of energy is essential.

How solar works

It's time to harness the sun's energy

Every year the sun provides over 8,000 times as much energy as we consume worldwide and in the UK alone we receive between 900 and 1200kWh of energy per m2 of land per year.

On average, every home spends 20-25% of its combined annual energy bills on water heating. In the UK a well designed water heating system can provide almost all the hot water for a home during the summer months and on average around 50 -60% year round.

This is why solar water heating systems are one of the most cost effective and environmentally-friendly renewable energy solutions available, reducing fuel bills and carbon dioxide emissions.

Future proof energy costs

Using renewable solar energy means that running costs compared with traditional fossil fuelled water heating systems can be reduced. More importantly, using free energy from the environment future-proofs the system against fossil fuels as they become ever more scarce and their price inevitably continues to rise.


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/m2per year in the South West.

UK map outlining solar effectiveness
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 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 of the scaffold and the complexity of the wiring. A typical system will cost around £4000.

Do I need to change any equipment in my house?

As part of the installation, the hot water cylinder will be changed for a special one with an additional solar heating coil. A pump set will also be fitted to circulate the heating solution through the panels. A digital controller runs the system.

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° from 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.

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

Diagram showing change in performance due to panel orientation
I've heard 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, 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 2-3 days to install.

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.