Solar for Indoor vs Outdoor Swimming Pools

The outdoor pool: design for the season

Outdoor pool demand is a bell curve sitting almost perfectly under the solar production curve: heat-up in late April, maintenance heating through the summer, shutdown by October. This overlap means modest arrays achieve enormous demand coverage — the 1kWp-per-10m²-of-pool rule supplies a covered pool's heat pump for effectively the whole campaign, and seasonal solar fractions of 80–90% are routine without any storage — Solent Solar, who cover the south coast, see the strongest figures of all, since southern England's summer irradiance runs well above the UK average. The design priorities are afternoon-weighted orientation, a properly sized heat pump pairing, and ruthless attention to evaporation, since an uncovered outdoor pool loses heat to wind and sky faster than any sensible array can replace it. Where outdoor pools disappoint, the autopsy is almost always a missing cover or a heat pump scheduled to run at dawn.

What outdoor pools cannot expect from solar: shoulder-season miracles. Holding 28°C through a grey November requires buying most of the heat from the grid regardless of roof size — the honest options are accepting the season, or heating the human (a small heated splash of the budget goes a long way in wetsuit form for determined families).

The indoor pool: design for the year

An indoor pool hall is the most energy-intensive room in any UK building that has one: 28–30°C water, air held a degree or two warmer to manage condensation, and — the load owners underestimate — dehumidification running constantly, because every kilogram of evaporated water must be removed mechanically before it rots the building. Annual energy demand for a domestic indoor pool commonly runs 20,000–40,000kWh across heat and air handling. No domestic roof covers that with panels. The design goal flips from "cover the demand" to "buy down the baseload": the largest array the roof carries, feeding pool plant that never stops wanting power, achieves self-consumption fractions other solar owners dream about — every generated kilowatt-hour displaces a bought one, year-round, no export compromise.

Indoor specifics worth engineering properly: heat-recovery dehumidification units return evaporation heat to the water and slash the biggest line item; pool-hall covers still matter indoors (evaporation is humidity, and humidity is the dehumidifier's electricity); and because demand persists in winter, indoor pools are the one pool case where a battery and a time-of-use tariff genuinely earn their keep alongside the array.

Same hardware, opposite priorities

Both pools want PV feeding efficient electric plant — the technologies do not change, as the PV vs thermal comparison explains. What changes is the optimisation target. Outdoor: small-to-medium array, maximum seasonal overlap, zero storage, cover non-negotiable. Indoor: maximum array, baseload displacement, storage worth modelling, heat-recovery plant before panels. Budgets and payback bands for both appear on the costs page, the worked example runs an outdoor case end to end, and commercial-scale indoor pools — hotels, swim schools, leisure centres — continue on the commercial page. Unsure which physics problem you own? A pool with a roof you can see from the kitchen is a marathon; tell us about it via the contact form.