Why Solar and Heat Pumps Work Well Together in the UK
Air source heat pumps (ASHPs) are most efficient in mild conditions — exactly the weather the UK has for much of the year. Combined with solar panels, the pairing works because:
- Seasonal alignment in spring and autumn: These months offer the best solar yield (20–40% more than winter) while remaining mild enough for the heat pump to achieve a Coefficient of Performance (COP) of 3.0–4.0. You get cheap solar electricity powering a highly efficient heating device.
- Summer hot water production: UK summers rarely need space heating, but hot water demand is constant. Directing surplus solar generation to immersion heating or to the heat pump's hot water function is highly effective.
- Reduced overnight import: A battery added to the combination can store solar energy for evening and overnight heat pump operation, cutting peak-rate electricity imports.
Sizing the System Correctly
How much solar do you need for a heat pump?
A typical UK semi-detached home with an ASHP uses 3,000–5,000 kWh of electricity per year for heating and hot water. At UK average irradiance of approximately 900 kWh/kWp/year, the rough sizing guide is:
| Annual heat pump electricity use | Recommended solar array size |
|---|---|
| 3,000 kWh | 5–6 kWp |
| 4,000 kWh | 6–8 kWp |
| 5,000 kWh | 8–10 kWp |
These figures assume a south-facing roof with minimal shading. East-west split arrays achieve around 85% of south-facing output and spread generation across more of the day, which better matches heat pump operating hours.
Battery storage sizing
For a heat pump household, a 5–10kWh battery is typically sufficient. A larger battery is only beneficial if you also have a hot water cylinder and can use it as a thermal battery. GivEnergy's 9.5kWh unit and the Sungrow SBR series are widely installed alongside ASHPs in 2026.
→ Before you read on — see what payback looks like for your roof in under a minute.
Controls: Making Solar Power the Heat Pump Automatically
Without smart controls, your heat pump and solar panels operate independently. The heat pump runs on its own schedule; the solar panels export to the grid whenever generation exceeds household loads. This is wasteful.
Smart controls to consider
- Eddi power diverter (myenergi): The Eddi detects surplus solar generation and diverts it to your immersion heater or wet underfloor heating. Simple to install, cost-effective, and widely compatible.
- Heat pump smart scheduling: Most modern heat pumps from brands like Vaillant, Mitsubishi, and Samsung allow time-based scheduling. Set the primary heating run to coincide with your peak solar window (typically 10:00–15:00 in UK conditions).
- Home energy management system (HEMS): More sophisticated options like Solis EMS or Givenergy's AIO platform can simultaneously manage solar, battery, and heat pump operation, prioritising self-consumption.
Seasonal Performance in the UK
Spring (March–May)
The optimal season. Solar yields climb from 50 kWh/kWp in March to 100+ kWh/kWp in May. Outdoor temperatures of 8–15°C give ASHPs a COP of 3.5–4.5. This is when the combination delivers its maximum value.
Summer (June–August)
Space heating demand drops to near zero. Solar generation peaks. The primary benefit is free hot water. If your heat pump includes a domestic hot water (DHW) function, scheduling it to run during midday solar generation is straightforward.
Autumn (September–November)
Similar to spring but in reverse. October is often the inflection point where import electricity use begins to rise meaningfully.
Winter (December–February)
The challenging season. UK solar yields drop to 25–40 kWh/kWp per month. The heat pump runs longest when solar generation is lowest. Battery arbitrage (charging overnight on cheap rates, running the heat pump from stored energy) becomes the primary strategy. Octopus Cosy or Economy 7 tariffs are useful here.
Economics in 2026
A typical scenario for a 3-bed semi-detached home in the Midlands:
- Solar system cost: 8kWp system with 9.5kWh battery — approximately £14,000–£17,000 installed
- Heat pump cost: Air source heat pump — approximately £8,000–£12,000 (after any available grant)
- Annual electricity savings: £1,400–£1,900 from self-consumption
- SEG income: £150–£250 per year
- Combined payback: 8–12 years depending on energy prices
The economics improve significantly if electricity prices rise, which most forecasters expect through the late 2020s.
→ Numbers speak louder: calculate your annual solar return and take the guesswork out.
