Solar Panels for Pool Heating UK: PV + Heat Pump vs Solar Thermal

An outdoor pool sitting cold and unused for most of the year is a frustrating waste. In the UK, the unheated season runs roughly June to August — just ten weeks. With the right solar setup, you can push that window from April to October, nearly tripling useful swimming time. There are two main solar routes: solar thermal collectors (which heat water directly) and solar PV paired with an air source pool heat pump (which uses solar electricity to drive a heat pump that warms the pool). The right choice depends on your priorities, budget, and whether you already have solar panels on the roof.

How each system works

Solar thermal for pools

Solar thermal collectors circulate pool water through roof-mounted panels that absorb the sun's warmth. Unglazed rubber or polypropylene collectors are common for outdoor pools — they are cheaper, weigh less, and work well during the UK summer months when ambient temperatures are mild. Glazed flat-plate collectors perform better in spring and autumn when it is cooler, extending the season further, but they cost more. A typical system for an 8 m × 4 m pool (32 m²) requires around 20–25 m² of collector area. Installed costs range from roughly £3,000 to £8,000 depending on collector type, pool size, and roof space available.

Solar PV + air source pool heat pump

An air source pool heat pump extracts heat from the outside air and transfers it to the pool water — it does not generate heat directly, it moves it. Running this heat pump on surplus solar electricity is where the efficiency magic happens. Pool heat pumps designed for UK conditions typically achieve a Coefficient of Performance (COP) of 5 to 6 during the summer months, meaning every 1 kW of electrical input delivers 5–6 kW of heat to the water. A 4 kWp solar PV system generating around 3,400 kWh per year can therefore deliver the equivalent of 17,000–20,000 kWh of pool heat — more than enough for a medium domestic pool through the UK swimming season. A solar diverter device such as the myenergi Eddi redirects surplus PV generation (electricity you would otherwise export at a low Smart Export Guarantee rate) directly to the heat pump, maximising free energy use. The combined installed cost for an additional 1–2 kWp of solar PV plus a pool heat pump typically runs £8,000–£14,000.

Season extension: what each approach delivers

Without any heating, a typical UK outdoor pool is comfortable (around 20°C) only in July and August. With solar heating:

• Unglazed solar thermal: extends the season to roughly May–September — a gain of two to three months.
• Glazed solar thermal: can push to April–October in a good year, but output is weather-dependent and drops sharply in cloudy spells.
• Air source pool heat pump (solar or grid-powered): modern units operate efficiently down to outdoor temperatures of around 5–10°C, making an April–October season reliably achievable with a pool cover in place. On particularly warm days the heat pump can top the pool up quickly — something passive solar thermal cannot do. A floating pool cover is essential regardless of heating method; without one, heat loss overnight can outpace any system's output.

Cost comparison

If you already have solar panels on the roof, the calculus shifts significantly. Adding a pool heat pump and a diverter may cost £3,500–£6,000 for the hardware, making it highly cost-effective compared to installing a whole new solar thermal circuit. See our guide on solar panel costs in the UK for full system price breakdowns.

Which system is more flexible?

Solar thermal serves one purpose: heating water. It cannot power lights, run the pump, or charge an EV. If your household electricity needs grow — an electric car, a battery, a heat pump for the house — solar thermal contributes nothing to those demands. PV, by contrast, is a general-purpose electricity generator. Surplus PV can be diverted to the pool heat pump in summer, to a home battery in winter, or exported via the Smart Export Guarantee when nothing else needs it. For most households, the flexibility of PV justifies the higher upfront cost — especially if you are considering a battery or EV charger in the future.

Planning permission and regulations

Solar PV panels on a pitched roof typically fall within permitted development rights and require no planning permission, subject to standard size and listed-building rules.

Air source heat pumps benefit from revised permitted development rules introduced in May 2025, which removed previous restrictions on setback distance from the boundary and allowed larger outdoor units. To qualify as permitted development, the installation must not produce more than 42 dB(A) measured at 1 metre from a neighbour's nearest habitable room window. A competent installer will carry out a noise assessment as part of the design process. If planning permission is required (for example, in a conservation area or on a listed building), you will need to apply to your local planning authority.

MCS certification is required for the heat pump installation if you wish to claim the government's Boiler Upgrade Scheme (BUS) grant. The BUS currently offers £7,500 off the cost of an air-to-water heat pump, applied directly to your installer's invoice. Note that the BUS is primarily designed for space and domestic hot water heating; pool-only heat pump systems may not qualify — confirm eligibility with your installer and check the current Ofgem guidance before proceeding.

Solar thermal collectors for pools are generally not covered by MCS standards (MCS focuses on domestic hot water and space heating), so no accreditation is needed, but it also means no grant eligibility.

Indoor vs outdoor pools

Indoor pools lose far less heat through evaporation and convection, so they require less raw energy input to maintain temperature. That said, indoor pool buildings still benefit from solar PV + heat pump setups — the heat pump can recover heat from the humid air above the pool (an air-handling heat pump), while PV cuts the electricity bill. Solar thermal is less practical indoors because the collector area and pipework usually need to route through the building fabric, adding complexity and cost.

How to size solar PV for pool heating

A rule of thumb: plan for an extra 1–2 kWp of solar capacity on top of what your household needs for electricity. For a typical 8 m × 4 m pool, a pool heat pump will draw 2–4 kW of electricity at peak load. On a sunny summer day, a 1.5 kWp south-facing array generates enough surplus electricity to run the heat pump for several hours, keeping the pool warm throughout the season with minimal grid draw. A diverter relay (such as the myenergi Eddi) ensures that surplus generation is routed to the heat pump before it is exported, maximising free pool heating and reducing payback time. See our full guide on how many solar panels you need for household-sizing methodology.

Which approach should you choose?

Choose solar thermal if your sole goal is pool heating on a tight budget, you have no existing solar PV, and you do not foresee adding batteries, EVs, or a house heat pump in the coming years. Choose solar PV + pool heat pump if you already have solar panels, want the flexibility to use electricity across multiple home loads, or want a more reliably extended swimming season. For most UK households investing in renewables for the first time, the versatility of a well-sized PV system with a pool heat pump offers better long-term value.