What it is and how it works

Collectors on the roof absorb sunlight as heat. A fluid runs through them, picks that heat up and carries it down to a coil inside your hot water cylinder. A small pump and a controller move the fluid whenever the collectors are warmer than the water in the cylinder, and stop when they are not.

There are two kinds of collector. Flat plate is an absorber sheet behind glass, robust and usually cheaper. Evacuated tube is a row of glass tubes with the air drawn out of them, which cuts heat loss and helps on cold bright days. Which suits your roof comes out of the survey.

Because it skips the step of making electricity, solar thermal harvests more energy from a square metre of roof than photovoltaic panels do. The catch is that all of that energy is hot water, and once the cylinder is hot the system has nowhere to put any more.

The cylinder question, first

This decides most solar thermal enquiries before anything else does.

Solar thermal needs a hot water cylinder with a spare coil for the solar circuit to heat. If you have a system or regular boiler with a cylinder in the airing cupboard, you are most of the way there, and often the cylinder is simply swapped for a twin-coil one.

If you have a combi boiler, you have no cylinder at all. Adding one means finding the space, running new pipework and rethinking the whole hot water arrangement. That is a large job for a modest saving, and we will usually tell you not to do it.

Solar thermal or solar panels?

An honest comparison, because they want the same roof.

Solar panels make electricity. That offsets the full price you pay per unit, runs everything in the house, charges a battery or a car, and anything spare can be sold under the Smart Export Guarantee. A smart diverter, such as the myenergi eddi we fitted to this London home, sends surplus generation to the immersion heater in the cylinder. So panels can heat your water too, as one job among several.

Solar thermal does one job, and does it well. It is worth the roof when three things are true together. Hot water demand is high and stays high through the year. A suitable cylinder exists, or is going in anyway. And there is roof left after a sensibly sized array of panels.

For a large family on oil, with a cylinder and a big roof, that adds up. For a three-bedroom semi with a combi, it does not, and we would rather say so at the survey than sell it to you.

Cost, VAT and grants

We give a fixed price after the survey, itemised across the collectors, the cylinder, the pipework, the pump station and the controls.

0% VAT. Solar panels are an energy-saving material for VAT, and HMRC’s definition includes solar collectors such as evacuated tube or flat plate systems along with the pipework, circulation system, pump, storage cylinder, control panel and heat exchanger. That means the whole installation, cylinder included, is zero-rated in Great Britain until 31 March 2027. The rate is due to return to 5% from 1 April 2027.
No grant. The Boiler Upgrade Scheme covers heat pumps and biomass boilers, not solar thermal. The Domestic Renewable Heat Incentive closed to new applicants at midnight on 31 March 2022 and nothing replaced it for this technology.

Figures reviewed 20 September 2026.

Planning

Solar thermal equipment on a house is covered by the same permitted development right as solar panels, under rules that changed on 27 August 2026. On a pitched roof the collectors must not project more than 0.2 m beyond the slope, and must not sit above the ridge. On a flat roof they must not sit more than 0.6 m above the highest part. Listed buildings need listed building consent, and conservation areas restrict anything on a wall or roof slope facing a highway.

We set out the position for your house in writing at the survey. There is more detail in our guide to solar panel planning permission after the August 2026 rule change.

Solar thermal with the rest of the house

Solar thermal sits most naturally alongside an air source heat pump, because a heat pump installation brings in a twin-coil cylinder anyway and the collectors can take the summer hot water load off it entirely. Where you are choosing between technologies rather than adding one, our design and consultation work compares them on your own usage before you spend anything.

Pros and cons

Pros

Makes hot water directly, without converting sunlight into electricity first
The whole system is zero-rated for VAT until 31 March 2027, including the cylinder, pump and controls
Takes a big share of the summer hot water load off your boiler or heat pump
Harvests more energy per square metre of roof than photovoltaic panels do
Quiet, with very little to go wrong once it is commissioned
Solar thermal on a house is usually permitted development

Cons

It needs a hot water cylinder with a spare coil, so a house with a combi boiler usually cannot have it without a much bigger job
There is no grant. The Boiler Upgrade Scheme covers heat pumps and biomass, and the Domestic Renewable Heat Incentive closed to new applicants on 31 March 2022
It only makes hot water, so it earns nothing once the cylinder is up to temperature
It competes with solar panels for the same roof, and for most homes the panels are worth more
The contribution in December and January is small, so you still need the boiler or heat pump behind it
The cylinder it needs is usually larger than the one it replaces, which has to go somewhere

Who it suits

Larger households that use a lot of hot water all year round
Homes that already have a hot water cylinder and a system or regular boiler
Homes on oil or LPG, where the fuel being displaced is expensive
Houses with roof space to spare once a sensible solar panel array has been placed
Homes already fitting a heat pump, where a twin-coil cylinder is going in anyway

What is included in a Bespoke installation

A survey of the roof, the loft, the airing cupboard and the existing hot water system
An honest comparison against solar panels with a diverter, on your own usage
Supply and installation of the collectors, pipework, pump station and controls
A twin-coil cylinder where the existing one cannot take a second coil
Commissioning, including the heat transfer fluid and the control settings
A handover showing you the controls and what the system is doing

Frequently asked questions

Can I have solar thermal with a combi boiler?

Usually not, at least not simply. A combi heats water on demand and the house has no cylinder, so there is nothing for the collectors to heat. Fitting solar thermal then means adding a cylinder, finding room for it and reworking the plumbing, which turns a modest job into a large one. If you have a combi and want solar hot water, solar panels with a diverter are almost always the better answer.

Is there VAT on solar thermal?

Not at the moment. Solar panels are an energy-saving material for VAT, and HMRC's definition covers solar collectors such as evacuated tube or flat plate systems together with the pipework, circulation system, pump, storage cylinder, control panel and heat exchanger. The whole installation is zero-rated in Great Britain until 31 March 2027, after which the rate is due to return to 5%.

Is there a grant for it?

No. The Boiler Upgrade Scheme pays towards heat pumps and biomass boilers, and solar thermal is not on the list. The Domestic Renewable Heat Incentive, which did pay for solar thermal, closed to new applicants at midnight on 31 March 2022 and has no successor. The case for solar thermal rests on the fuel it saves.

Should I have solar thermal or solar panels?

For most homes, panels. They offset electricity at the price you pay for it, they run everything in the house rather than only the hot water, spare output can be sold under the Smart Export Guarantee, and a smart diverter can send the surplus to your immersion heater anyway. Solar thermal wins where hot water demand is high and steady all year, where a suitable cylinder already exists, and where there is roof left over. We compare both on your own figures at the survey.

Do I need planning permission?

Usually not. Solar thermal on a house is permitted development in England under the same rules as solar panels, which changed on 27 August 2026. Panels on a pitched roof must not stand more than 0.2 m out from the slope or above the ridge, and on a flat roof not more than 0.6 m above the highest part. Listed buildings need consent, and conservation areas have tighter rules on anything facing a road.