A 3-bedroom house is the most common property type quoted for solar in the UK, so this is the best-documented sizing question there is. Here is what the numbers actually look like.
The short answer
Most UK 3-bed homes are quoted a 3.5 kWp to 5 kWp system: roughly 8 to 12 panels at 430-450 W each, needing about 18-27 m² of unshaded roof.
| System size | Panels (approx) | Typical installed cost | Annual output (south-facing) |
|---|---|---|---|
| 3.5 kWp | 8 | £5,500 - £7,000 | 2,900 - 3,300 kWh |
| 4.4 kWp | 10 | £6,500 - £8,000 | 3,600 - 4,100 kWh |
| 5.3 kWp | 12 | £7,500 - £9,500 | 4,400 - 4,900 kWh |
Prices include panels, inverter, mounting, scaffolding, DNO notification and certification. Solar for domestic properties is currently zero-rated for VAT.
Size to your consumption, not to your roof
A typical 3-bed household uses 2,700-3,500 kWh of electricity a year. A 4 kWp system generates roughly 3,700 kWh — but generation and consumption do not line up in time. Without a battery you will typically self-consume only 35-50% of what you produce; the rest is exported.
That matters because a unit you use yourself is worth your full import rate, while an exported unit is worth your Smart Export Guarantee rate, which is usually much less.
So:
- Home empty all day, no EV, no battery — a smaller system sized nearer your daytime baseline often pays back faster per pound spent.
- Someone home during the day, or an EV, heat pump or battery — go bigger. Self-consumption climbs and every extra panel earns its keep.
Roof orientation and pitch
- South facing is the benchmark: 100% of the figures above.
- East or west facing delivers roughly 80-85%, spread more evenly across morning and evening — which often suits working households better because it matches usage.
- East-west split across both roof faces is common and perfectly sensible.
- North facing is not worth it.
Shading is a bigger deal than orientation. A single chimney or tree shading one panel can drag down a whole string unless the installer specifies optimisers or micro-inverters. Ask specifically how shading is being handled.
What payback looks like
For a 4 kWp system at £7,000 on a typical 3-bed:
- Self-consumed electricity saves your import rate on roughly 1,600-1,900 kWh a year
- Exported electricity earns your SEG rate on the remainder
- Combined benefit typically lands around £600-£900 a year
That is a payback in the region of 8-11 years, with panels warrantied for 25 years and inverters typically 10-12. Add a battery and the annual benefit rises while the payback period usually stays similar or lengthens slightly — batteries buy resilience and self-sufficiency more than they buy speed.
Questions to ask every installer
- What is the estimated annual generation, and is it from an MCS-compliant calculation?
- What self-consumption percentage have you assumed in the savings figure?
- How is shading handled — string inverter, optimisers, or micro-inverters?
- Is scaffolding included, and is the price fixed?
- What are the separate warranties on panels, inverter and workmanship?
Compare at least three quotes on the same system size. On a 3-bed, the spread between the cheapest and dearest quote for identical hardware is routinely £1,500 or more.
Read next: how much solar panels cost in the UK and are solar panels worth it.