How many solar panels do you need to run a heat pump?

By the SmartSolarSizer team · Published 20 October 2026

How much electricity does a heat pump use per year?

Your own figure beats any average. If the heat pump is already in, read a year's total from its app or your meter. If you're still on gas, the gas bill gets you most of the way there.

Take Ofgem's typical UK household, which burns 12,000 kWh of gas a year (Ofgem). The Energy Saving Trust says an A-rated boiler should turn about 90% of its fuel into heat (Energy Saving Trust); assuming yours does, that home actually uses around 10,800 kWh of heat. A heat pump doesn't make that heat from electricity one-for-one; it moves it in from outside air, giving three to four units of heat per unit of electricity on paper (Energy Saving Trust). Real homes do a bit worse. Which? says UK seasonal performance (SCOP) is generally around 3.0 (Which?), and the Energy Systems Catapult's field trial measured a median of 2.80 over the year, falling to 2.44 on the coldest days (Energy Systems Catapult). Divide the heat by 2.8 and the heat pump needs about 3,857 kWh of electricity a year, or 10.6 kWh on an average day.

US homes are bigger and the climate varies far more. EnergySage, working from NREL's ResStock model of US housing, puts the median heat pump at about 5,475 kWh a year (EnergySage), or 15.0 kWh a day. The US Department of Energy describes the same trick as delivering up to three times more heat than the electricity used (DOE).

Sizing solar to cover a heat pump's year

In London, 1 kW of panels makes about 1,022 kWh a year, so one 430 W panel gives 439 kWh. The UK heat pump needs 3,857 ÷ 439, which rounds up to 9 panels, a 3.9 kW array.

But the same roof also has to cover everything else. Ofgem's typical home uses 2,900 kWh of electricity before any heat pump, which alone would take 7 panels. Together that's 6,757 kWh and 16 panels (6.9 kW), well above the 4.5 kW the Energy Saving Trust gives as a typical UK home system (Energy Saving Trust). Don't size the array for the old bills and add a heat pump a year later, by which point the roof is half used. Sunnier places need far fewer panels, as the table shows.

Can a 4 kW solar system run a heat pump?

Over a year, just about. A 4 kW system in London makes roughly 4,088 kWh, slightly more than the 3,857 kWh a typical UK heat pump uses, and in New York it makes about 5,621 kWh against the US median of 5,475. What 4 kW can't do is cover the heat pump and the rest of the house: against the 6,757 kWh total it supplies about 60% of the year. On a December day in London it makes about 5.0 kWh, compared with the heat pump's average of 10.6 kWh, and a cold snap pushes that average up.

How do solar panels work with an air source heat pump?

They aren't wired to each other. The panels feed your home's supply through the solar inverter, and anything running at that moment, heat pump included, uses solar first. The grid makes up any shortfall, and any surplus goes out to the grid for export credit, through net metering in much of the US or export payments in the UK (how net metering works).

So the share of your solar that the heat pump actually uses depends on timing. The Energy Saving Trust says every heat pump needs space for a hot water cylinder (Energy Saving Trust), and that's the easiest load to move: schedule the cylinder to reheat in the early afternoon and it soaks up midday output all year round. In spring and autumn, letting the house warm a little during the sunny hours does the same for space heating. Sizing the array from the heat pump's rated kW, rather than its yearly kWh, gets you nowhere useful; the number that matters is energy over time.

Why winter is the hard part

A heat pump does most of its year's work from November to February, exactly when panels are weakest. These are the monthly totals for the 3.9 kW London system sized above:

June brings about 463 kWh; December about 149, less than a third. Matching even an average day's heat pump use with December sunshine would take about 20 panels, and December days aren't average: they're the coldest, and the field trial's performance factor drops to 2.44 on those days. Manufacturer data shows the same slide. One mini-split heat pump's coefficient of performance falls from about 4.2 at 47 °F (8 °C) to 2.7 at 17 °F (−8 °C) (Mitsubishi submittal). Many US systems also switch to electric resistance backup in deep cold, and resistance heat gives only one unit of heat per unit of electricity (DOE). Cold-climate heat pumps are designed to keep working in much colder weather (DOE), but they still use more power when it's cold.

That's why "how much solar offsets my heat pump over the year?" is the useful question. Building enough panels to run it directly in January would leave most of them idle from April to September.

Do you need a battery with solar and a heat pump?

No. A battery is optional, and it solves a different problem from the one above. It shifts energy by hours: store midday output for the evening, when heating demand climbs, or charge from the grid overnight on a cheap time-of-use tariff. Which? notes these tariffs can cut heat pump running costs, though you need a smart meter and should watch out for very high peak rates (Which?). What a battery can't do is store June for January.

Off grid, a heat pump is hard to justify on solar alone: you'd need a very large array and a generator for winter. If you try it anyway, the inverter needs at least 4,000 W continuous for a 3,000 W heat pump (running watts × 1.25). Variable-speed (inverter) heat pumps ramp up gently, so start-up surge is modest. Our main calculator is more cautious and sizes from the surge figure, so it may suggest a slightly larger unit. On a grid-tied home none of this applies, because the solar inverter is sized for the panels, not the heat pump.

Is a heat pump worth it with solar?

Solar makes a good heat pump install better; it won't rescue a poor one. The running-cost maths in the UK is tight. Which? says electricity costs around four times as much per unit as gas on the standard capped rate, and in its example a heat pump needs a SCOP of at least 2.9 before it saves money against a gas boiler on standard rates (Which?). That's right around the field-trial median.

Solar changes part of that sum. Every kWh you generate and use yourself avoids the import price, and inside a heat pump it becomes about 2.8 kWh of heat. The limit is timing again: most self-used solar arrives between April and September, when the heat pump is mostly making hot water. The bigger savings come from a well-designed system on a heat pump tariff, which is the condition attached to the "more than 50%" running-cost saving quoted by Which?.

Solar panels vs a heat pump: which first in the UK?

They do different jobs. Solar cuts the electricity you buy; a heat pump replaces gas heating and adds about 3,857 kWh to your electricity use. If your boiler is fairly new, the Energy Saving Trust warns a heat pump won't necessarily be cheaper to run (Energy Saving Trust), so solar first is usually the safer spend. If the boiler is near the end of its life, do the heat pump first while the Boiler Upgrade Scheme grant is available in England and Wales (Scotland runs its own grants through Home Energy Scotland). Your installer must be MCS-certified to apply for it (Which?). Check the current grant terms before you plan around them.

If solar comes first, size it, or at least leave roof space, for the 16-panel house you'll have once the heat pump arrives.

Ground source and pool heat pumps

A ground source (geothermal) heat pump tends to be more efficient than an air source one but is considerably more expensive to install (Energy Saving Trust). The panel maths is the same: use its yearly kWh, which will be lower. A pool heat pump is a different case. It runs mainly in the swimming season, when panels produce the most, so it lines up with solar far better than home heating does; size it from its own seasonal kWh. The pump that filters the pool is a separate load, covered on our pool pump page.

Common questions

Sources

Solar output for every location comes from the European Commission's PVGIS 5.3 (1 kW system, panels at the best fixed angle facing the equator, 14% system losses), retrieved 20 October 2026. Panel counts assume 430 W panels, the most common size in 2025 home solar quotes (EnergySage).

• Ofgem: average gas and electricity use explained
• Energy Saving Trust: in-depth guide to heat pumps
• Which?: air source heat pump costs and savings
• Energy Systems Catapult: Electrification of Heat trial, real-world heat pump performance
• EnergySage: how many solar panels for an air source heat pump
• US DOE Energy Saver: air-source heat pumps
• Energy Saving Trust: solar panels (typical 4.5 kWp system)
• Mitsubishi MSZ-FS12NA submittal (COP at 47 °F and 17 °F)
• US DOE Energy Saver: electric resistance heating
• US DOE Energy Saver: heat pump systems

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