Solar Pool Pump Calculator (UK)

Size a solar-powered pool pump and PV array for a UK swimming pool. Calculates required flow rate, pump wattage, panel size and savings vs your existing mains pump.

Solar Pool Pump Calculator

Pool volume (m³) Total dynamic head (m) Turnovers per day Solar pump run hours/day Peak sun hours/day Existing mains pump power (W) Existing pump run hours/day Electricity rate (£/kWh) Solar pump + array cost (£)

Required flow rate

138.9 L/min

Recommended pump power

248 W

Solar array size

291 W

Daily solar energy

0.69 kWh

Annual savings

£68

Payback period

27.8 years

How to use this calculator

Enter nine values and the tool returns required flow, recommended pump wattage, matched PV array size, daily and annual solar yield, annual electricity savings versus your existing mains pump, and simple payback in years.

Pool volume (m³) — length × width × average depth in metres. A typical UK domestic pool is 40–60 m³.
Total dynamic head (m) — total resistance the pump overcomes. For a standard residential setup with a cartridge filter, 5–8 m TDH is normal. Add 1–2 m for sand filters and another 1 m per 15 m of horizontal pipe run.
Turnovers per day — SPATA recommends 1.0 turnover per day for domestic pools, 2.0 for heavily used or warm-water pools.
Solar pump run hours/day — six hours is the UK standard, aligned with summer peak-sun availability.
Peak sun hours/day — annual UK average is 2.6, summer (May–Aug) is 4.0–4.5, winter (Nov–Feb) is 0.8. Energy Saving Trust publishes regional figures: London 2.7, Edinburgh 2.4, Cardiff 2.6.
Existing mains pump power (W) — your current pump’s nameplate watts. A 0.5 HP single-speed is typically 500–700 W; a 1 HP is 750–1,100 W.
Existing pump run hours/day — what your current pump runs daily during swim season.
Electricity rate (£/kWh) — your current unit rate. The 2026 Ofgem default cap is around 27p/kWh; Economy 7 day-rate sits at 30–33p.
Solar pump + array installed cost (£) — typical UK DC pool pump kits cost £1,500–£2,200 supplied; MCS-certified installation adds £400–£800.

How solar pool pumps work in the UK climate

Three approaches are common in UK pool installations:

Dedicated DC variable-speed pump on a small PV array (off-grid). A 24 V or 48 V brushless DC pump runs directly from a 300–600 W PV array via an MPPT pump controller. No batteries. Brands sold in the UK: Lorentz PS2 (German), Sunray Solflo, Davey Eco-Salt with solar input.
AC variable-speed pump on the home’s existing domestic PV. The pump runs on grid power and the home’s solar offsets that consumption via self-consumption or SEG export displacement. Most efficient for pools at residences with existing 4 kW+ PV systems.
Hybrid changeover system. The pump runs on solar when available and falls back to mains automatically. Costs more (£400–£600 for the changeover controller) but gives year-round reliability.

For most UK pool owners, option 2 is the simplest because the typical domestic PV system already has spare capacity during pool-season midday. The calculator sizes for option 1 to give a conservative DC-only result; if you’re using option 2, treat the annual savings figure as a lower bound.

The math, derived from first principles

Step 1 — Required flow. For pool volume V (m³ × 1000 = litres), T turnovers per day, H hours run:

Q (L/s) = V × 1000 × T / (H × 3600)

For 50 m³, 1 turnover, 6 h: Q = 50,000 / 21,600 = 2.31 L/s, equivalent to 139 L/min.

Step 2 — Hydraulic power.

P_hyd (W) = Q (L/s) × H (m) × 9.81

For 2.31 L/s against 6 m head: P_hyd = 2.31 × 6 × 9.81 = 136 W.

Step 3 — Required pump shaft power. Combined pump + motor efficiency for residential variable-speed DC pumps is around 0.55:

P_pump (W) = P_hyd / 0.55

So P_pump = 136 / 0.55 = 247 W.

Step 4 — Required PV array. Allow 0.85 system derate for cabling, controller losses, soiling, and off-pointing:

P_array (W) = P_pump / 0.85

So P_array = 247 / 0.85 = 291 W — one 300 W standard residential panel is enough.

Step 5 — Annual savings. Daily kWh = P_pump × PSH / 1000. Compare to grid energy, displaced kWh × tariff rate gives annual £ savings.

Why payback is short in the UK

UK electricity prices are among the highest in Europe — 27p/kWh under the Ofgem cap in 2026 compares to 16p in France, 18p in Spain and 12p in the US. A 700 W mains pool pump running 6 h/day across a 180-day swim season uses 756 kWh costing £204. A 300 W solar array on the same duty cycle generates roughly 300 × 2.8 × 180 / 1000 = 151 kWh — displacing about £41 of grid use. The headline annual saving is modest in pounds because UK pool seasons are short, but DIY kit prices have come down so much that payback under 6 years is realistic.

UK regional pool-pump sizing

Region	Annual PSH	Swim season	Recommended array size for 50 m³ pool
South-East England	2.9	180 days	300 W
South-West / Wales	2.6	165 days	350 W
Midlands	2.5	150 days	350 W
North England	2.4	140 days	400 W
Scotland	2.2	120 days	450 W
Northern Ireland	2.3	130 days	400 W

Northern regions need slightly larger arrays to make up for the lower PSH.

Sizing rules of thumb (UK domestic pools)

Pool size	Typical mains pump	TDH range	DC solar pump size
20 m³ (small fibreglass)	350 W	4–6 m	100–150 W
30 m³	500 W	5–7 m	150–250 W
40 m³	600 W	6–8 m	200–300 W
50 m³	750 W	6–8 m	250–400 W
80 m³ (large overflow)	1,100 W	7–10 m	500–750 W

Regulations and certification

MCS certification — required if you want 0% VAT under the energy-saving materials relief. Both the panels and the installer need to be MCS-listed.
BS 7671 (IEE Wiring Regs 18th Edition) — DC pumping systems must comply with the same earthing, protection, and isolation rules as any DC PV installation. SELV-band (below 50 V) avoids notifiable Part P work.
Pool equipment electrical zones (BS EN 60364-7-702) — the pump itself must be installed outside Zone 0/1/2 of the pool, with IP44 enclosure minimum.
Planning permission — domestic PV up to 50 m² is permitted development under the Town and Country Planning (General Permitted Development) Order 2015 as long as it’s not on a listed building or in a conservation area.

Common UK installation mistakes

Sizing for the year-round average PSH instead of summer PSH — pool pumps only need to run during swim season, so use summer numbers (April–September).
Mounting the array flat on a south-facing patio — works in summer but UK installs almost always perform 5–10% better on a 30–35° pitched south-facing roof.
Skipping the changeover relay on a hybrid system — without it, both sources can fight each other and trip the consumer unit RCD.
Using a domestic mains pump on solar via an inverter — pump start surge often exceeds the inverter’s short-term rating and trips the array. DC-direct pumps don’t have this issue.
Buying an off-brand controller — Lorentz, Sunray, and Pentair branded controllers all have current limits and surge protection. Cheap ebay/AliExpress units burn out within a season.

Sources

Energy Saving Trust — Solar PV — UK PV system guidance and regional output figures.
MCS — Microgeneration Certification Scheme — certified installer and product lists.
Ofgem — Default tariff cap — current UK domestic electricity rate cap.
SPATA — Swimming Pool & Allied Trades Association — pool design standards and turnover guidance.
Solar Energy UK — Industry data — UK solar market and pricing trends.
GOV.UK — Energy-saving materials VAT relief — 0% VAT scheme details for PV installations through March 2027.

Frequently asked questions

Are solar pool pumps worth it in the UK?

Yes for any pool used April to October — UK domestic electricity prices have settled around 27p/kWh in 2026 under the Ofgem price cap, which makes even a 700 W single-speed pool pump cost £400–£500 per year to run for the swim season. A 400 W solar PV array dedicated to a DC pool pump can cut that to near zero on sunny days and roughly half overall, paying back in 4–6 years. The bigger win is usually swapping a single-speed pump for a variable-speed one at the same time.

How big should my pump be for a UK domestic pool?

Most UK residential pools are 30–60 m³ and need one full turnover per day per the SPATA Pool Design Standard. For a 50 m³ pool with 6 m total dynamic head and 6-hour run time, the required hydraulic power is about 140 W, which maps to a 250 W shaft pump and a 300 W solar array. The calculator above does this from your actual pool volume and head — UK pools rarely exceed 50 m³ except hotel and gym installations.

What's the difference between mains and solar pool pumps?

Mains pumps are typically 230 V AC induction motors at 750–1,500 W, designed to run at full speed whenever switched on. DC solar pumps are 24 V or 48 V brushless motors that match their speed to available solar power — they ramp up at midday and slow down on cloudy mornings. The result is gentler filtration, longer pump life, and electricity independence during daylight hours. Mains-powered variable-speed pumps (Pentair IntelliFlo, Hayward EcoStar) sit between the two and pair well with grid-tied domestic PV.

Will my solar pool pump work in winter?

DC solar pumps work whenever the array produces enough power — typically December solar production in the UK is 10–20% of June output, so a pump sized for summer filtration will run only a couple of hours mid-day in winter. Most UK pool owners winterise the pool (drain, cover, shock-treat) from October to April anyway, so off-season pump operation isn't required. If you operate year-round (indoor pool or heated pool), keep a mains backup.

Does VAT or any government scheme cover solar pool equipment?

Domestic solar PV installations attract 0% VAT until 31 March 2027 under the energy-saving materials VAT relief — this applies to a PV array dedicated to a pool pump if it's installed on the dwelling. The DC pump itself, mounted in pool equipment housing, may or may not qualify depending on the installer's interpretation; most include it as part of the PV system invoice. The Smart Export Guarantee (SEG) isn't usually relevant because the pump consumes the power rather than exporting it. MCS certification of the installer is required for VAT relief.

Solar Pool Pump Calculator (UK)