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How do solar thermal systems work?

Solar thermal systems are a great option for those looking to reduce the cost of their hot water and limit their overall CO2 emissions. We look at how they work and how you could have one installed for free.

What are solar thermal systems?

Solar thermal systems, also known as solar water heating systems, use the heat from the sun to warm domestic hot water. They are most often used to compliment conventional gas boilers so that hot water can be provided when solar energy is unavailable.

The panels use the sun’s rays to heat up a mixture of water and glycol which is sent to a heat exchanger inside a water cylinder. The exchanger will then heat the water further inside the cylinder. Once the liquid releases its heat, the water goes back to the collectors in the panels to be reheated.

What are solar thermal panels?

Solar thermal panels are made of a dark absorbing surface, a transparent cover, a heat-insulating backing and a fluid that transports heat to the supporting water tank. The absorbing material can be made of a number of materials, including polymers, copper, aluminium and steel.

The sunlight which passes through the panel is refracted by its glass, which changes its wavelength and produces heat.

What are the benefits of a solar thermal system?

As well as lowering your carbon footprint, installing a solar thermal system will help to reduce your energy bills. The amount you will save depends on the system you’re replacing, but generally falls between £60 - £100.

However, the Government’s Renewable Heat Incentive (RHI) scheme may make fitting solar thermal worth it, with an estimated payment of £205 per year for a two-person household.

As well as providing you with around a third of your hot water requirement, other benefits include low maintenance and a 5 to 10-year warranty.

How much does a solar thermal system cost?

The cost of fitting a typical solar thermal heating system is usually between £4,000 - £5,000, which includes the solar panels and tank.

Are there any grants for solar thermal systems?

There are a number of grants to help fund a solar thermal system. The main ones are the Energy Company Obligation (ECO) grant, and the Green Homes Grant voucher scheme.

What are ECO Grants?

The Government’s Energy Company Obligation (ECO) is a government-backed energy efficiency scheme that obligates the UK’s big energy companies to help customers on certain benefits afford energy saving home improvements. As well as providing funding for a free boiler, it also covers a long list of other energy saving measures, including solar thermal systems.


What is the Green Homes Grant Voucher Scheme?

The Green Homes Grant voucher scheme (GHGVS) provides vouchers for energy efficiency measures, including funding for solar thermal systems. It is split between those on low incomes and certain benefits, who can apply for vouchers that cover the total cost up to £10,000, and a general scheme that is open to everybody and provides grants that cover two-thirds of the cost, up to £5,000.

By using the general scheme, homeowners looking to finance a £4,500 solar thermal installation can receive vouchers worth £3,000, leaving them with £1,500 to contribute. With the savings made through cheaper bills and take-up of the RHI, this contribution will pay for itself after 5 years.