If you’ve ever glanced at your energy bills and wondered if there’s a way to cut costs while helping the planet, solar thermal energy might sound like a smart option. Unlike solar panels, which generate electricity, solar thermal systems capture the sun’s heat to warm water for your home.
For UK households, this can mean a significant portion of hot water is covered by free solar energy—especially in summer—reducing reliance on gas or electric immersion heating.
However, while solar thermal once played a clearer role in low-carbon homes, installations in the UK are now in steep decline, and most current home-energy strategies focus instead on solar PV and heat pumps. That makes it worth understanding not just how solar thermal works—but whether it still makes sense today.
At its core, solar thermal (also known as solar water heating) is a relatively simple technology:
Roof‑mounted collectors absorb sunlight
Flat‑plate collectors: rectangular panels mounted flush to the roof
Evacuated‑tube collectors: rows of cylindrical tubes, typically more efficient in cooler or cloudier conditions
Heat transfer
The collected heat warms water (or a heat‑transfer fluid), which then transfers that heat to a hot‑water cylinder.
Support system
A small pump circulates the fluid, while a controller ensures the system only runs when it’s effective to do so.
Backup heating
Your boiler or immersion heater tops up hot water when solar heat isn’t sufficient.
In practice, solar thermal systems usually pre‑heat water rather than supply it all. Historic UK trials suggested that well‑installed systems could meet around 40–60% of annual hot‑water demand, with much higher contributions in summer than winter.
Important context: Much of the commonly quoted performance data comes from studies carried out more than a decade ago. Since then, household energy use, tariffs, and alternative technologies have changed significantly.
While these performance levels are still technically achievable, they don’t always translate into strong financial returns in today’s energy system—particularly for gas‑heated homes.
Even when solar thermal was more widely installed, it was never suitable for every property. Key factors include:
Roof suitability: Typically 2–5 m² of unshaded roof space is needed. South‑facing roofs perform best, though east–west roofs can work at reduced efficiency.
Hot‑water system: Homes with a traditional hot‑water cylinder are easiest. Combi‑boiler homes often need a new or additional cylinder, adding cost and complexity.
Household habits: Homes with high and consistent hot‑water use—such as families or home‑workers—benefit most, as they can use more of the solar heat generated.
The Centre for Sustainable Energy recommends high daily hot water demand to get the most out of solar thermal.
In practice, these requirements already limited the number of suitable homes. Today, many experts would add a fourth and increasingly important question:
Would the same roof space and investment deliver greater value if used for solar PV instead?
Installations in Decline: What the Data Shows
Solar thermal installation rates in UK homes have continued to fall sharply.
MCS‑certified domestic solar thermal installations (UK):
Year Installations 2022 571 2023 300 2024 173 2025 65 2026 4 This represents a collapse of over 99% in domestic installations since 2022.
For comparison:
Only around 0.2% of UK homes have solar thermal
Roughly 5% now have solar PV, with adoption continuing to rise
The trend is clear: households, installers, and policy have overwhelmingly shifted toward solar PV and heat pumps as the main tools for home decarbonisation.
Based on MCS domestic installation data, the cost of installing solar thermal has remained relatively high and variable.
Average domestic solar thermal installation costs (UK, MCS data):
| Year | Avg. cost per kW (£) | Avg. total installation cost (£) |
| 2022 | 2,283 | 5,694 |
| 2023 | 3,217 | 5,526 |
| 2024 | 3,316 | 5,877 |
| 2025 | 2,493 | 5,419 |
| 2026 | 3,465 | 6,064 |
This puts the typical upfront cost at around £5,000–£6,000, broadly unchanged over time, even as the cost of alternatives such as solar PV has fallen.
Running costs are low—pumps use minimal electricity and maintenance is infrequent—but the high capital cost relative to achievable savings remains the main barrier for most households.
Real‑world field trials by the Energy Saving Trust found that well‑installed systems supplied around 39% of annual hot‑water demand on average, with top‑performing homes reaching 60%.
Typical annual bill savings remain modest:
Gas‑heated water: ~£55–£110 per year
Electric immersion: ~£80–£210 per year
Savings vary with hot‑water use, tariffs, and system design. Given current installation costs, this results in long payback periods, particularly for gas‑heated homes, and helps explain the sharp decline in installations.
Larger, integrated “solar heat” packages—combining PV, heat pumps, and smart controls—can deliver higher lifetime savings, but these gains usually come from the wider system rather than solar thermal alone.
Even as energy prices fluctuate, the underlying limitations of solar thermal remain:
It offsets hot‑water energy only, not household electricity
Upfront costs are high relative to savings in gas‑heated homes
Compatible hot‑water storage is required; combi‑boiler homes often need extra work
Government grants and incentives are now focused mainly on heat pumps and solar PV
At the upper end of performance, solar thermal payback often approaches—or exceeds—system lifetime, especially when compared with PV systems that reduce both electricity bills and grid imports.
By contrast, solar PV generates electricity you can:
Use directly in the home
Export for payment
Use to power heat pumps, appliances, or EVs
Installing a solar thermal system is a relatively complex process, even for experienced installers. A typical setup includes roof‑mounted collectors, a hot‑water cylinder (often with a dedicated solar coil), and insulated pipework connected via a circulating pump and control system.
Key steps include:
Roof preparation and collector mounting
Collectors are mounted on a structurally sound roof, usually south‑facing, with careful attention to tilt and shading. Roof penetrations must be fully weatherproof.
Hydraulic connection
A closed‑loop system carries a water–glycol mixture between the collectors and the cylinder, with pumps, expansion vessels, and safety valves preventing freezing or overheating.
Cylinder and controls integration
Heat is transferred to a cylinder fitted with a solar coil, while differential controllers ensure the system runs only when collectors are warmer than the tank.
Commissioning and monitoring
Installers test pressures, antifreeze concentration, and control settings. Poor commissioning or incorrect sizing can significantly reduce performance and payback.
Both technologies use the sun, but they serve different purposes:
Solar thermal heats water for a hot‑water cylinder. It can reduce hot‑water energy use but does not generate electricity.
Solar PV generates electricity for appliances, heat pumps, or EVs, with surplus power exported to the grid.
For most households:
Consider solar PV if you want lower electricity bills, future flexibility, and long‑term decarbonisation.
Consider solar thermal only if you have very high hot‑water demand or are integrating it into a wider, carefully designed low‑carbon system.
In practice, PV is usually the first step, with solar thermal—if used at all—acting as a niche add‑on rather than a core upgrade.
| Technology | Main use | Strengths | Limitations |
| Heat pump | Space + water heating | Major carbon and energy reductions | May require radiator or insulation upgrades |
| Solar thermal | Hot water only | Free solar heat, low running cost | Limited scope, roof and usage dependent |
| Solar PV | Electricity generation | Flexible, scalable, exportable | Does not directly heat water |
While solar thermal can still play a role in integrated systems, PV and heat pumps now deliver broader and more flexible benefits for most homes.
Solar thermal still works technically, but our experts generally do not recommend it as a standalone upgrade for most UK homes today.
That’s because:
The same investment usually delivers greater savings and flexibility with solar PV
Heat pumps already provide efficient hot water
Roof space is often better used for electricity generation
Policy support and grants are focused elsewhere
Solar thermal now makes sense only in very specific situations, such as homes with exceptionally high hot-water demand, limited electrical capacity, or niche whole-system designs where it is already integrated.