Solar water heating with solar thermal panels

Solar water heating systems – also known as solar thermal systems –  use energy from the sun to heat water for your showers, baths and hot taps.

You'll need panels on the roof, similar to solar PV, and a hot water cylinder to store the hot water.

In summer, solar thermal panels can provide most of your hot water. In winter, depending on your usage, you may find they only meet around a quarter of your needs, so you'll still need a boiler or immersion heater.

Fitting this type of water heating system isn’t cheap, so before you invest, you need to be sure that solar thermal panels are right for your home and your needs.

If you want to generate your own electricity with solar panels, head to our guide to solar PV panels instead.

How do solar thermal panels work?

Solar thermal panels use fluid-filled solar collectors (filled with a mixture of glycol and water) to collect infra-red energy from the sun. 

The solar energy is converted into heat, and the heated fluid is pumped via a circuit through the hot water cylinder to heat the water.

Depending on the amount of sunshine, additional heating – such as a boiler or immersion heater – may be needed to raise the water temperature further.

Types of solar thermal panels

There are two main types of solar water heating panels – flat plate and evacuated tubes. This refers to the way the water interacts with the panel. 

Evacuated tubes look like a bank of glass tubes fitted to your roof (the ones in the main image at the top of this page).

Flat plate systems can either be fitted onto the roof or integrated into it.

Evacuated tube systems are more efficient than flat-plate versions, so are often smaller but still generate the same amount of hot water.

How much do solar thermal panels cost?

Solar thermal panels typically cost between £3,000 and £5,000 to install.

For comparison, a conventional gas combi boiler costs between £1,350 and £6,300 to install. 

This will vary depending on which type you choose (evacuated tube or flat panel), the size of the system, the installer you choose and other factors.

Find out more about how much a new boiler costs.

Once installed, additional costs are minimal. Most systems use a small amount of electricity to run the pump but, in most cases, the pumping costs only cancel out about 8% of savings, and newer technology can typically reduce this to 3% or even zero.

You’ll need to bear in mind the cost of maintenance, although it's generally very low for solar water heating systems. For example, a replacement pump costs around £90, while new anti-freeze costs around £100. 

They only need servicing every three to seven years.

Most systems come with a five or 10-year warranty.

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Can I save money with solar water heating?

Savings with a solar water heating system are fairly modest. How much you can save depends on the type of water heating system you are replacing and the size of system you install. 

Bear in mind that the system should be able to provide most of your hot water in summer, but much less in winter, so you'll still need to supplement it with hot water from somewhere else in the coldest months.

As a general guide, you could save around £105 to £200 per year on your energy bills based on current fuel prices to reflect Ofgem's Price Cap from April 2024.

You’ll save the most if you are currently using electricity to heat your water – around £200 per year. If you are replacing gas-fired water heating (ie. water heated by a gas boiler) savings are likely to be closer to £105 per year.

Annual bill savings with solar water heating

• Oil – £130
• Coal – £145
• Gas – £105
• LPG – £145
• Electricity – £200

Data from Energy Saving Trust, showing how much you might save in a year depending on what you're currently using to heat your water, based on installing a 4m² panel system.

Rather than consider solar water heating solely as a way to save on your energy bills, it's useful to think of an installation as part of a broader project to decarbonise your home's energy use and make it more efficient. 

We recommend that you first make sure your home is as energy efficient as possible, then think about which types of renewable energy technology, including solar panels, might work together to suit your home's set up.  

Are solar thermal panels right for your home?

For maximum efficiency, you need to put your solar thermal panels on a south-facing roof at a 30-degree angle to the horizontal (up to 65 degrees will still work in the UK). 

Panels should be kept away from any shading (trees, buildings, chimneys, etc).

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 heavy tiles.

Not all heating systems are compatible with solar water heating. If you don’t currently have a hot water tank, you'll need to install one in order to benefit from solar water heating.

So check what extra equipment you’ll need – and how much it will cost – if you are considering solar thermal panels.

Some panels require regular checks of the unit and connections, or a wipe of the panel glass with mild detergent. Your installer should leave written details of any maintenance checks you should carry out from time to time. Bear in mind how difficult this might be when panels are up on your roof. 

Pros and cons of solar water heating

Pros

• Solar water heating can provide you with about 90% of your hot water needs in summer and 25% in winter.
• You could save between £145 and £275 per year on your fuel bills.
• Systems need little maintenance and the on-going costs are very low.
• Most solar water heating systems come with a five to 10-year warranty.
• Lowers your carbon footprint.

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.
• Not all boilers are compatible with solar water heating.
• Solar thermal panels can cost more to install than conventional electric and gas heating systems.

How to choose 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 to two square metres of panel 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 panel (such as flat-plate solar thermal panels), you'll need to cover a larger area than if you use a more efficient one, 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.

Finding a good trader – things to look out for

You'll need to hire a professional to install your solar water heating system. There are plenty of solar panel installers out there, so we recommend that you always collect a range of quotes to compare.  

Watch out for dodgy sales tactics, salespeople putting you under pressure to buy on the spot and exaggerated financial savings. We recommend you do your own research before inviting a company into your home.

You should only use installers and products that are certified by the Microgeneration Certification Scheme (MCS), then compare the estimates of costs and savings you're given by salespeople against other sources of advice.

You can search for a certified installer on the Microgeneration Certification Scheme website.

Solar thermal panel installation

As well as your panels, a solar water heating system involves pipe work, a thermostat and a hot water cylinder.  

Some also have a drainback system to drain water from inside the solar panel when the pump is switched off. This prevents water from freezing or boiling inside the panel.

You can add solar thermal panels to many existing hot water systems. However, you'll usually need to add an additional cylinder for pre-heated water or change your existing cylinder for one with a twin coil.

It's difficult to use a solar water heating system with a combi boiler. This is because combi boilers heat water directly from the mains water supply and don't have a tank; solar water heating systems supply warm, low-pressure water. Some new combi boilers do accept pre-heated water, so check with the manufacturer.  

To find out which boilers are the most reliable, take a look at our guide to the most reliable gas and oil boiler brands.

How to get the most from your solar thermal panels

Make the most from your solar hot water system by following these tips:

• Use as much hot water as possible from the solar-heated supply, rather than heating it up with an appliance using electricity. For example, fit a mixer shower (rather than electric).
• Change your habits to use more hot water – showers, baths and washing up – in the evenings. This is when water will be hottest, as it's had time to heat up through the day.
• Ensure your back-up system is set up to switch on at the right time. Before you installed solar water heating, it was probably set to give you a full tank of hot water in the morning. But if you don’t change it, your panels will have nothing to heat during the day.
• Insulate your pipes and water tank to make your system more efficient.
• Make sure your water tank is heated to more than 60 degrees at least once a week to avoid bacteria building up.
• Follow your installer’s advice on how to set the hot water controls to get the most from your system.

You should also make sure that you carry out any maintenance checks from time to time to make sure the system is working efficiently. Your installer should leave written details of these.

The most important thing to check for is leaks. If your system leaks antifreeze, you will probably be able to smell it – contact your installer.

During the lifespan of your panels, the anti-freeze may need replacing or topping up. This costs around £100.

Your installer may specify that your system needs to be checked by an accredited professional every few years. They will also check the pump. These last for around 10 years and cost around £90 to replace.

Do you need planning permission for solar thermal panels?

You don't need planning permission for most domestic solar water heating systems in the UK, as long as they aren’t too big.

But exceptions apply for listed buildings, buildings in conservation areas and World Heritage Sites.  

If this applies to you, contact your council to see whether you need to apply for planning permission for your solar panels.