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Solar Thermal Installation: What You Need to Know

Nick Geary
By: Nick Geary
Updated: 6th July 2022

Solar thermal panels turn free energy from the sun into hot water for your home.

They don’t cost any money to run, but can reduce your heating costs by as much as 70%.

Here we outline what's involved in solar thermal installation. As well as the pros, cons, costs, and potential savings.

What are solar thermal panels?

Solar thermal panels are a low-carbon renewable heating system.

They absorb heat from the sun (even on cloudy days) to warm the water in a cylinder. This hot water can then be used in a wet central heating system and to supply your taps and showers.

The panels are fitted to the roof of the property and are made of tubes of fluid (water and antifreeze). This fluid absorbs energy from the sun and transfers it to a heat exchanger. It then passes the heat to a hot water cylinder in your home.

Solar thermal panels can’t produce enough hot water to supply a home by themselves. But they can produce as much as 70% of a home's hot water. This reduces your heating bills, reduces carbon emissions, and eases the strain on your boiler.

What solar thermal installation involves

The average solar thermal installation involves fitting panels to the roof, plumbing it into your central heating with some electrical connections. Here we outline the key steps involved in solar thermal installation.

1. Getting quotes for solar thermal installation

The first stage of solar thermal installation is to get multiple quotes from different MCS registered installers.

Each one will assess your home and tell you what type and size of system would be best. This will include measuring the roof's orientation and inclination and how shaded it is by trees/other properties.

The installer should also estimate how much heat it should generate and how this will compare to your hot water consumption.

When you’ve compared at least 3 quotes you can be sure you’re getting the best deal. It’s also worth taking time to look into their credentials and customer satisfaction ratings,

It is important to ensure that your installer is MCS registered. This will ensure that the solar thermal installation has been installed correctly.

Planning permission is usually not required unless your property is listed or in a conservation area.

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2. Fitting solar thermal panels on the roof

Scaffolding may be needed for the safety of the installers.

The panels are attached to stainless steel brackets which are fitted to the roof rafters. The exact mounting method will vary depending on the installers. Roof tiles/slates will often need to be removed for this to happen, but they will be replaced.

Waterproof flashing will be applied to the roof in order to avoid any leakages. If you have a flat roof, the frame will be set at the appropriate angle to prevent leaks. The panels will also be angled to ensure they are exposed to as much sunlight as possible.

3. Installing the hot water cylinder

If you have a combi boiler, this will probably need to be removed and replaced with a system boiler. This is because a dual coil water cylinder (one which is heated by the boiler and one by the solar thermal system) is needed. And combi boilers don’t have a cylinder.

The new hot water cylinder will store the heat provided by the solar thermal panels. And they’re much larger than a standard cylinder with an immersion heater, so where it is installed will depend on the available space in your home.

4. Plumbing

The system pump and the expansion tank will be installed on the solar thermal loop. This helps to prevent pressure changes from causing damage to the system.

Insulated pipes will be installed to connect the pumping station to the solar thermal panel on the roof. This 'flow and return piping' contains the heat transfer fluid. The closer the hot water cylinder, pump, and the solar thermal panel are, the more efficient the system will be.

5. Fitting the generation meter and controls

A generation meter (MCS certified) will be installed to measure how much heat is being generated by the system. If you apply for the Renewable Heat Incentive, you will be paid for every kWh it generates. This meter and the controls will need to be installed by an electrician.

6. Pressurising the system

The system then needs to be pressurised to about 2 bar. This is because the heat transfer fluid is added to the closed loop system. This heat fluid operates in temperatures up to 200°C, protects metals in the system and acts as antifreeze when temperatures reach -25°C.

7. MCS registration

When the solar thermal installation is complete, the installer will register your system with the Microgeneration Certification Scheme (MCS). You will need the paperwork to apply for the RHI scheme.

How long does solar thermal installation take?

The average solar thermal installation takes 1-2 days to complete. Some may take longer.

You should be prepared to be without water at certain points during the installation.

Are solar thermal panels right for you?

We get a lot of cloudy days here in the UK. And this often puts homeowners off installing them. But the truth is that they still work when it’s overcast.

Having said that, solar thermal installation is not the right choice for every property. So we’ve outlined some of the pros and cons.

Pros of solar thermal installation

Cheaper heating bills

Solar thermal panels can produce 40-70% of the hot water needed by a family of 4 in a year.

This means you won’t be using your boiler so much. And that means buying less fuel from your supplier.

Earn money with the RHI

The government's RHI scheme was set up to encourage homeowners to install low carbon heating and reduce the country's reliance on fossil fuels.

As part of the scheme you’ll earn payments for the energy generated by your solar panels. The system must meet the scheme's criteria to be accepted onto the scheme.

Reduced carbon emissions

Using your boiler less often means less fuel consumption. And that means reduced carbon emissions, which is better for the environment.

Zero running costs

When the solar thermal panels have been installed, they run on free solar energy. So you won’t have to worry about any running costs.

Low maintenance

Solar thermal systems only need servicing every 3-5 years. They also typically come with a manufacturer warranty between 5-10 years.

Cons of solar thermal installation

Not a complete heating solution

Solar thermal panels cannot produce enough hot water to meet the demand in most homes. So a backup heating system, such as a gas boiler or immersion heater, will still be needed.

Solar thermal will not supply electric showers or cold-fill washing machines/dishwashers.

Property restrictions

Solar thermal panels need to be installed on a roof facing due south at a 20-50 degree angle for maximum efficiency.

However, they can work effectively when positioned between south east and south west. In some cases, it's possible to install them on the ground or a wall but any shade will reduce their effectiveness. You will also need space for a solar compatible water cylinder (large enough to hold around 2 days of hot water).

Not compatible with combi boilers

Solar thermal systems are often not compatible with combi boilers. This is because they’rere fed water directly from the mains and heat water demand.

Solar thermal installation costs

Solar thermal installation usually costs £3,000 - £5,000 for an average-sized family home. This cost is, of course, an estimate and larger homes with a higher demand for hot water may cost up to £7,000. You will need around 1m² of solar thermal panels per person living in the home.

People in the Home Size of System Required Average Cost of Installation
2 2m² £2,500 – £3,000
3 3m² £3,500 – £4,000
4 4m² £4,500 – £5,000
5 5m² £5,500 – £6,000
6 6m² £6,500 – £7,000

The installation cost will also be impacted by the complexity of the installation. If you do not have a hot water cylinder or your existing hot water cylinder isn’t solar compatible, you will need to buy one. This could come to an additional £600 to £1,000.

While the initial investment is quite high, solar thermal panels have no running costs. And you could be saving on your heating bills once they’ve been fitted.

The Energy Saving Trust estimates that solar thermal panels could save you:

  • £50 a year if you have a gas boiler
  • £55 a year if you have an oil boiler
  • £65 a year if you use coal
  • £80 a year if you have an electric boiler
  • £95 a year if you use LPG

Get quotes for solar thermal panels

We've made finding and comparing quotes easy and quick. All you have to do is complete a simple online form on our sister website, Solar Guide, and we'll connect you with up to 3 fully-qualified solar installers based in your area who will each provide a free quote.

Interested in Solar Thermal Heating


for Your Home? Get FREE QUOTES now


Nick Geary

About the author

Nick Geary

Nick has a wide range of experience writing about conventional and renewable heating solutions, and is always increasing his knowledge by researching any new heating technologies on the horizon.

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