PV vs Solar Thermal for Swimming Pool Heating

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. Collector efficiency is high — 60–70% of incident solar energy lands in the water when the sun shines and the pool is cooler than the roof. 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 4 to 6. Panel efficiency is only around 22%, but multiply by COP 5 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 3,400kWh a year, of which a May–September pool campaign uses perhaps half — the rest offsets the house at 24–28p/kWh or exports under the SEG, while thermal mats produce nothing of any value from October to April. Tax: professionally installed domestic PV is zero-rated until 31 March 2027; thermal pool mats are generally a standard-rated leisure purchase. Lifespan and degradation: panels carry 25-year output warranties, where polypropylene mats fade, harden, and leak on a 10–15 year horizon, usually losing their pump-pressure tightness before their absorbency.

Run cost-per-delivered-kWh-of-pool-heat over twenty years — including the heat pump's £2,500–£4,500 and one mid-life thermal re-roof — 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.

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.