Pairing a Pool Heat Pump with Solar PV

Why pool heat pumps flatter solar

Heat pumps moving heat into 28°C water work against a far kinder gradient than space-heating units chasing 50°C radiators, so pool models rate at coefficients of performance of 4.5–7.8 at 15°C air on manufacturer datasheets (SPATA gives 3.5–4.5 as a typical outdoor-season average) — and they post them in the afternoon, when air is warmest and your array is producing. The synchronicity is the whole design: solar electricity is worth most consumed on site, and a pool heat pump is a large, shiftable, afternoon-hungry load. A kilowatt-hour that would have exported for around 5p becomes about four kilowatt-hours of pool heat, which a gas boiler would charge about 38p to make (7.97p per kWh at 85% efficiency; cost per kWh of heat compared). That multiplication is why using the generation on site beats exporting it.

Sizing the heat pump to the pool

Pool heat pumps are rated in thermal kilowatts, and the season decides the size: for a covered 8×4m outdoor pool swum May to September, 9–13kW thermal is the standard band, drawing roughly 2–3kW electrical at typical COPs. Size for the spring pull-up — getting the pool from 12°C to 28°C in late April is the hardest job of the year, heating 38m³ by 16°C takes about 700kWh of heat before any losses (1.163kWh per m³ per degree), so a week to ten days of daytime running is realistic for a unit in this band. Oversizing by one model step is cheap insurance that also enables quieter, lower-speed running all summer; inverter-driven (variable speed) models do this automatically and are worth their premium in both noise and COP. Indoor pools change the duty entirely — year-round heating plus the air-handling interactions covered on the indoor vs outdoor page.

Sizing the array to the heat pump

The working rule from the homepage — about 1kWp of PV per 10m² of pool surface for a covered outdoor pool — exists to keep the heat pump fed through the season without grotesque export surplus. For the 8×4m example: 3–4kWp, generating 12–18kWh on decent swimming-season days against a heat-pump demand of 10–20kWh. Match a little generously if the house will absorb surplus; match tightly if export is your fallback. Two design notes that earn their keep: panel orientation slightly west of south shifts production into the warm afternoon hours when the heat pump's COP peaks, and leaving inverter headroom makes the inevitable "add two panels" conversation cheap later. MCS installation keeps the Smart Export Guarantee available and the install zero-rated for VAT until March 2027.

The controls are the secret

An unconfigured system runs the heat pump on its own thermostat schedule — often at 7am, on grid electricity, hours before the panels wake. The fix costs little: at minimum, a timer confining heating to 10am–5pm; better, the heat pump's own solar-priority mode or a relay driven by the inverter's surplus-export signal, so the unit ramps when self-generated power is actually flowing. Timing the heat pump to the array's output is what lifts self-consumption of pool-season generation; our worked example assumes a cautious 60%, and an unconfigured system will do worse. While you are in the plant room: if the circulation pump is a single-speed relic, replace it with a variable-speed unit before adding any panel (how many panels the pump itself needs is worked through separately) — the 900–1,000kWh a season it wastes (about 1,350kWh for a 1.1kW single-speed pump against about 400kWh for a variable-speed one) is the cheapest energy you will ever recover, as the worked example demonstrates.

Cost picture for the full pairing on the costs page; short version — a heat pump about £4,500–£8,200 installed for a 9–13kW unit (Renewable Energy Hub installer guide, April 2026), 3–4kWp PV about £4,800–£7,800 (DESNZ 2025/26: £1,595 per kW median, £1,955 domestic mean), controls and electrics £300–£600. Against a gas boiler on a covered pool the heat pump alone saves roughly £185 a season, so payback is long unless it replaces direct electric heating or a boiler already due for replacement, and the panels also serve the house. If a heat pump already cools your plant-room budget, PV's marginal payback is faster still. Tell us what is currently bolted to your pool via the contact form and we will sequence the upgrade sensibly.