How to buy solar panels Solar water heating explained

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Solar water heating can meet about a third of your hot water needs

A solar water heating system (also known as solar thermal system) uses panels fitted to your roof to heat water for use around the home. 

A typical solar hot water system is able to meet around a third of a household's hot water needs – a saving of £55 to £80 on your annual water-heating bills, based on a three-bedroom semi-detached house. 

Householders installing solar water heating systems can get £300 through the government's Renewable Heat Incentive Premium Payment scheme. 

Choosing a solar water heating system

When choosing a solar water heating system, you'll need to consider four major factors:

  • your average hot water use
  • the area of south-facing roof available
  • your existing water heating system
  • your budget. 

You'll need roughly one square metre of collector area per person in the household. Each metre of panel area will need between 30 and 60 litres of water tank volume.

If you use a less efficient collector (such as flat-plate solar water heating panels), you'll need to cover a larger area than if you use a more efficient collector (such as evacuated tubes). 

You'll also need to select system components (such as a hot water cylinder, controls and pipe work) and choose the location for your solar panels, considering shade, pipe runs, roof pitch and future access.

Solar water heating installation

There are plenty of solar panel installers out there, so we recommend that you always collect a range of quotes to compare – visit Which? Local to find recommended solar panel installers or search for an installer on the Microgeneration Certification Scheme (MCS) website.

We also have a guide on installing solar water heating systems, but beware of solar panel sales tactics. Our solar panel investigations found some salesmen using dodgy sales tactics and exaggerating the financial savings that could be made.

We strongly recommend that you do your own research first and only use MCS-certified installers and products. Then compare the estimates of costs and savings you are given by salesmen against other sources of advice.

Pros and cons of solar water heating systems

Pros

  • Solar water heating can provide you with about a third of your hot water needs.
  • Solar water heating can save you between £55 (if you have gas central heating) and £80 (if you have electric central heating) a year on your water heating costs.
  • The corresponding carbon savings are between 230kg and 510kg of CO2 a year.
  • Maintenance costs are very low – most solar water heating systems come with a 5-10 year warranty and require little maintenance.
  • It uses the sun’s heat – so there are no further costs once you've had the equipment installed, except, in most cases, a small amount of electricity needed to run the pump. In most systems the pumping cancels out only about 8% of the energy savings, and newer technology can reduce this to 3% or even zero.
  • In England, planning permission for most solar water installations is no longer needed – and governments in Wales, Scotland and Northern Ireland are currently discussing introducing similar initiatives.
  • A £600 grant is available through the Renewable Heat Incentive Premium Payment.

Cons

  • You'll still need a boiler or immersion heater to make the water hotter, or provide hot water when solar energy isn't available (on overcast days, for example).
  • An unshaded, mainly south-facing location is necessary for positioning the solar panels.
  • Initial costs are higher than for conventional electric and gas-heater systems.
  • Solar panels can be heavy, so your roof must be strong enough to take their weight, especially if the panel is to be installed on top of existing tiles.
  • The cost of a typical solar water heating system is around £3,000-£5,000 – a fairly expensive solution until the Renewable Heat Incentive comes into place.
  • In 2010 Which? went undercover to investigate solar water heating companies and posed as householders wanting to buy a system. In our probe, 10 out of 14 companies exaggerated the potential savings. You can watch a solar panel salesman in action in our undercover video.

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