Solar + Heat Pump (UK): How to Size Solar for Electrified Heating
Heat pumps transform your electricity demand profile. Here's how to size solar to match — and what to realistically expect.
The Energy Mismatch Problem
Heat Pump Demand
A typical UK air-source heat pump uses 3,000–5,000 kWh/year of electricity. ~70% of this falls in October–March — exactly when solar output is lowest.
Solar Supply
~80% of solar generation falls in April–September. Direct solar-to-heat-pump overlap is only 20–30% without smart controls or storage.
What This Means in Practice
Solar doesn't directly power your heating in winter. Instead, solar offsets your total annual electricity bill. In summer, surplus solar covers hot water (via the heat pump) and exports to grid. In winter, you draw from the grid but at a lower net annual cost.
Sizing Solar for a Heat Pump Home
| Home Type | HP Electricity | Household Electricity | Recommended Solar |
|---|---|---|---|
| 2-bed flat/terrace | 2,500–3,500 kWh | 2,000–2,500 kWh | 4–5 kWp |
| 3-bed semi | 3,500–4,500 kWh | 2,500–3,500 kWh | 5–7 kWp |
| 4-bed detached | 4,500–6,000 kWh | 3,500–4,500 kWh | 7–10 kWp |
| 5-bed + EV | 5,000–7,000 kWh | 5,000–6,000 kWh | 10–12 kWp |
Heat pump electricity assumes COP of 3.0–3.5 (typical UK ASHP). Solar sizes aim to offset 40–60% of total annual electricity.
Making It Work Better
Battery Storage
A battery stores summer solar surplus for evening use. Doesn't solve the winter gap, but maximises self-consumption in shoulder months (March–April, September–October).
Smart Tariffs
Time-of-use tariffs (e.g., Octopus Agile, Cosy) let you run the heat pump on cheap overnight electricity. Combined with solar for daytime, this dramatically cuts annual costs.
Hot Water Pre-Heating
Schedule hot water heating for midday to use solar directly. Most heat pump controllers allow this. Uses 2–3 kWh daily — perfectly matched to midday solar surplus.
Insulation First
Reducing heat demand (better insulation, draught-proofing) means a smaller heat pump and less electricity needed. This is the most cost-effective step before solar.
Related Guides
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