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Solar Thermal Installation: What You Need to Know

Solar thermal panels are a low carbon heating system which use the free energy generated from the sun to produce hot water for your home. They do not cost any money to run, but can reduce your heating costs by as much as 60%. 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?

This hot water can then be used in a wet central heating system and to supply your taps and showers. Solar thermal panels are installed on the roof of your property. Tubes of fluid (water and antifreeze) inside the panels absorb energy from the sun and transfer it to a heat exchanger. This passes the heat to a hot water cylinder in your home.

Solar thermal panels do not 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.

Solar thermal installation: what’s involved?

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 several different MCS registered installers. They will assess your home and tell you what type and size of system would be best for your home. 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 have compared at least three quotes, looked into their credentials and customer satisfaction ratings, you can be sure you are getting the best deal from a reputable company.

It is important to ensure that your installer is MCS registered, as this will ensure that the solar thermal installation has been installed correctly and you will be eligible for the Renewable Heat Incentive payment (more information below).

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

To fit the solar thermal panels, scaffolding may need to be installed for the safety of the installers. The panels are attached to stainless steel brackets which are fitted to the roof rafters, although 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 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 and a dual coil water cylinder (one which is heated by the boiler and one by the solar thermal system), plus the pump and system control panel. This can be done in the loft or an upper floor of the property.

The new hot water cylinder will store the heat provided by the solar thermal panels and is 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 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 (which is MCS certified) will be installed which will measure how much heat is being generated by the system in kWh. 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 averal solar thermal installation will take 1 or 2 days to complete although some may take longer. You should be prepared to be without water at certain points during the installation.

Are solar thermal panels the right choice for you?

There is a misconception that solar thermal technology is not effective in the UK because of the number of overcast days we have. However, while solar thermal panels will not produce as much hot water during the winter, they will work all year round.

Having said that, solar thermal installation is not the right choice for every property, so we have outlined some of the main pros and cons here.

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 will need to use your boiler less and will buy less fuel from your supplier.

Earn Money with RHI

Eligible solar thermal systems could bring extra money into your bank account through the Renewable Heat Incentive (RHI) scheme, as the government will pay you for every unit of energy your solar thermal panels generate.

Reduced carbon emissions

Using your boiler less often will mean less fuel consumption and therefore 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.

Low maintenance

Solar thermal systems only require professional servicing every 3-5 years and are typically covered by manufacturer warranties between 5-10 years. In addition, the solar thermal system will reduce the strain on your boiler as it won’t be working as hard so this should lengthen its life.

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

Property restrictions

To work at optimum efficiency solar thermal panels need to be installed on a roof facing due south at a 20-50 degree angle from horizontal, although 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 on a wall but any shade will reduce their effectiveness. You will also need to have space for a solar compatible water cylinder which is 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 as they are fed water directly from the mains and heat water demand.

How much does a solar thermal installation cost?

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 because you have a combi boiler, or your existing hot water cylinder is not solar compatible, you will need to buy one which could cost between £600 – £1,000.

However, when considering the cost of solar thermal installation, you need to take into consideration the fact that your heating bills will be cheaper going forward as you will be able to reduce how often you use your boiler. Using a solar thermal system, you could save up to 60% on your domestic hot water energy costs. The Energy Saving Trust estimates that solar thermal panels could save you £50 a year if you have a gas boiler, £55 if you have an oil boiler, £65 if you use coal, £80 if you have an electric boiler and £95 if you use LPG (liquid petroleum gas).

Grants and incentives for solar thermal installation

If your solar thermal installation is completed by 31st March 2020, you could be eligible for a grant to reduce the cost of installation and could receive payments under the Renewable Heat Incentive scheme for 7 years.

Green Homes Grants

Until 31st March 2021, the government is offering grants to help homeowners in England to improve the energy efficiency of their homes. Green Homes Grants are vouchers which will cover two-thirds of the cost of installing solar thermal panels (or an air/ground source heat pump or biomass boiler). The vouchers are capped at £5,000 in most cases although low income households may be entitled to up to £10,000. Find out more about Green Homes Grants.

Visit Solar Guide for more information on Green Homes Grants for solar thermal, or click here if you are interested in a heat pump.

Renewable Heat Incentive (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 like oil, gas, coal and LPG, all of which emit carbon. If your solar thermal system is installed correctly and meets the scheme’s criteria you’ll receive payments for every unit of energy generated by your solar thermal panels.

As of September 2020, the tariff for solar thermal is 21.36p per kWh of renewable heat. The RHI scheme will close to new applications on 31st March 2021, so don’t delay if you hope to benefit from payments for the next 7 years. Find out more about the RHI.

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.


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