PV vs Solar Thermal for Swimming Pool Heating
For forty years, "solar pool heating" meant black mats on the garage roof. PV's price collapse and the pool heat pump rewrote that default — but thermal still wins specific cases, and knowing which case is yours is worth four figures. Here is the comparison run properly.
How each one actually works
Solar thermal for pools is gloriously simple: the filtration pump diverts water through black polypropylene mats or tubes on a roof, the sun warms the water directly, and it returns to the pool a degree or two warmer. Collectors are simple and efficient in the right conditions, but measured UK performance is more modest: a monitored EEC project on eight English pools (1982–84) recorded seasonal collector efficiencies of 20–50%. There is no inverter, no certification trail, and not much to break beyond UV-aged plastic and the odd fitting.
The PV route is indirect: panels make electricity, and electricity becomes pool heat through an air-source heat pump whose coefficient of performance at pool temperatures — a flattering 26–30°C target — runs roughly 3.5 to 4.5 across a UK outdoor season (SPATA), with manufacturer datasheets rating 4.5–7.8 at 15°C air. Panel efficiency is only around 22%, but multiply by a COP of about 4 and the system lands a comparable share of roof sunlight into the water — from hardware that does something useful in the eight months the pool does not want it.
Where the 2026 maths separates them
Per square metre of roof in July, good thermal mats still edge PV-plus-heat-pump for raw pool heat. But pools do not buy July heat; they buy systems, and three asymmetries decide the purchase. Flexibility: a 4kWp PV array delivers roughly 3,800–3,900kWh a year (PVGIS: 947 to 981kWh per kWp from Leeds to Leicester), of which a May–September pool campaign uses perhaps half — the rest offsets the house at around 26p/kWh (Ofgem cap, October to December 2026) or exports under the SEG, while thermal mats produce nothing of any value from October to April. Tax: panels professionally installed in residential accommodation are zero-rated until 31 March 2027 (HMRC Notice 708/6, which does not mention pools, so confirm in writing); the notice lists solar collectors such as flat-plate and evacuated-tube systems, but polypropylene pool mats are not named, and a kit supplied without installation is standard-rated. Lifespan and degradation: panels typically carry 25-year output warranties, while polypropylene mats live their whole life in direct UV, so compare the warranty period you are actually offered.
Run cost-per-delivered-kWh-of-pool-heat over twenty years — including the heat pump (about £4,500–£8,200 installed for 9–13kW, Renewable Energy Hub, April 2026) and a mid-life thermal replacement — and PV-plus-heat-pump wins for any pool that also has a house attached. The margin widens if a heat pump was being purchased anyway (increasingly the UK norm for new pool builds), because then PV's marginal cost is just panels against the mats' full system.
The cases thermal still wins
Three honest ones. The summer-only outdoor pool with no heating ambition beyond extending June — mats plumbed into the existing pump loop, £2,500–£4,000 fitted, no electrical work and no new plant. The roof with space for one system only and a household whose electricity is already fully offset by an existing array — adding mats may beat extending an export-saturated array. And the off-grid or restricted-supply property, where a heat pump's 3–7kW electrical draw is unwelcome and thermal's pump-only demand fits the constraint. If you recognise your pool in those, mats remain a perfectly rational 2026 purchase; the costs page prices both routes side by side. A DIY kit is the cheapest version of the thermal route; what a kit can and cannot do is worked through separately.
The verdict, and the asterisk
Default verdict for UK pools in 2026: PV plus heat pump — the details of making that pairing sing are on the heat pump page. The asterisk applies to everyone: neither technology should be sized before a cover halves the demand, and the worked example shows the full sequence on a real pool. Still genuinely torn? Send the pool's details through the contact form — thermal-vs-PV is the question we most enjoy settling with arithmetic.
PV + heat pump vs solar thermal, scored
| PV + heat pump Indirect, electric | Solar thermal Direct, plumbed | |
|---|---|---|
| July heat per m² of roof | Strong | Strongest |
| Value October–April | House offset + export | None |
| Season extension (Apr/Oct) | Marginal | |
| VAT (domestic, installed) | 0% to Mar 2027 | Generally 20% |
| Warranted life | 25 yrs (panels) | Check offered warranty (mats) |
| SEG export eligibility | ||
| Installed cost (8×4m pool) | £9,500–£16,000 | £2,500–£5,000 |
| Best single use case | Pool + house, year-round value | Summer-only outdoor pool |
Sources and assumptions
Figures were checked on 20 October 2026. Where we found no UK source we say so, and where a number is our own assumption it is labelled.
- Ofgem, Changes to energy price cap between 1 October and 31 December 2026 (published 26 August 2026): electricity 26.32p/kWh (no VAT), gas 7.97p/kWh (5% VAT), GB average, Direct Debit.
- European Commission JRC, PVGIS v5.3 (SARAH3, 35° tilt, due south, 14% losses), queried 20 October 2026: Leicester 981, Leeds 947, Exeter 1,052 kWh/kWp/year; Leicester December 34 against June 117 kWh/kWp; May–September is 56–58% of the year.
- SPATA, swimming pool heating factsheet: heat pump COP of 3.5–4.5 for outdoor pools in season, 2.5–3.5 for indoor pools in winter; solar thermal collector area usually exceeds 50% of the pool surface. Undated.
- Zodiac pool heat pump datasheets (PX25, January 2025; Z260iQ): COP 4.5–7.8 at 15°C air / 26°C water / 70% RH, the low end at full power. Manufacturer ratings, not UK seasonal averages.
- European Commission (CORDIS), EEC solar pool heating project, eight English pools monitored 1982–84: about 0.5m² of collector per m² of water, collector efficiency 20–50%.
- HMRC, VAT Notice 708/6 (updated 31 January 2024): zero rate on installing energy-saving materials in residential accommodation, 1 May 2023 to 31 March 2027; the notice does not mention swimming pools; a supply without installation is standard-rated.
- Smart Export Guarantee rates, October 2026: MoneySavingExpert (updated 6 October 2026) lists standalone tariffs at 2–6p/kWh and 5.6–16p/kWh where you also take your electricity from the supplier; Ofgem's Year 5 report gives a 10.8p average for 2024/25. MCS certification or equivalent is required for installations up to 50kW (Ofgem generator guidance).
- Renewable Energy Hub, Heat pumps for swimming pools, estimated-cost table dated 20 April 2026 (equipment plus installation): 9kW £4,500–£7,000; 12kW £4,800–£7,700; 13kW £5,700–£8,200; 17kW £6,200–£9,300. The guide says real-world COP is typically 3 to 5.
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