How Many Solar Panels Do I Need?
The short answer: most UK homes need between 8 and 14 solar panels. But the right number depends on your energy usage, your roof space, and how much of your electricity bill you want to offset. This guide walks you through the calculation.
How Much Electricity Does a UK Home Use?
The average UK household uses around 2,900 kWh of electricity per year, but this varies significantly:
| Home Size | Occupants | Annual Usage |
|---|---|---|
| 1–2 bed flat | 1–2 people | 1,800 – 2,400 kWh |
| 3 bed semi-detached | 2–4 people | 2,800 – 3,500 kWh |
| 4 bed detached | 3–5 people | 3,500 – 5,000 kWh |
| Large home / EV owner | 4+ people | 5,000 – 8,000+ kWh |
If you have an electric vehicle, heat pump, or electric heating, your usage will be significantly higher — and solar becomes even more valuable.
How Much Does One Solar Panel Generate?
A modern 400W solar panel installed in East Sussex generates around 340–380 kWh per year (assuming good south-facing orientation and minimal shading). East Sussex receives approximately 1,750–1,850 hours of sunshine per year — above the UK average — which improves output compared to northern England or Scotland.
How Many Panels Do I Need? (By Home Size)
| Home Size | System Size | Panels (400W) | Annual Output |
|---|---|---|---|
| 1–2 bed | 3kW | 7–8 panels | ~2,700 kWh |
| 3 bed semi | 4kW | 9–10 panels | ~3,400 kWh |
| 4 bed detached | 5–6kW | 12–15 panels | ~4,250–5,100 kWh |
| Large home / EV | 8–10kW | 20–25 panels | ~6,800–8,500 kWh |
How Much Roof Space Do I Need?
A typical 400W solar panel is roughly 1.7m × 1.1m (about 1.87 m²). For a 4kW system (10 panels), you need around 18–20 m² of usable roof space — equivalent to a rectangle roughly 4m × 5m.
If your south-facing roof is smaller, east/west splits or high-efficiency panels (450W+) can make better use of the available space.
Should I Install More Panels Than I Need?
Yes — within reason. Oversizing by 20–30% is common practice because:
- You earn more from the Smart Export Guarantee on exported excess
- Your energy usage is likely to increase (EVs, heat pumps)
- Adding panels later is more expensive than installing them now
- Battery storage becomes more valuable with a larger array
There are limits — your DNO (Distribution Network Operator) must approve systems over 3.68kW. We handle all DNO applications as part of every installation.
What About Adding a Battery?
Without battery storage, you typically use around 30–40% of the electricity your panels generate. The rest is exported. A battery raises self-consumption to 70–80%, making each kWh generated more valuable. For a 4kW system, this difference can be worth an extra £300–£600/year.
We recommend considering battery storage alongside your solar installation for the best long-term return.
Getting the Right Size System
The most accurate way to size a system is a free professional survey, where we assess:
- Your roof orientation, pitch, and available area
- Shading analysis (from trees, chimneys, neighbouring buildings)
- Your energy bills and usage patterns
- Your future plans (EV, heat pump, extension)
Request a free survey and system recommendation →
Lee Standell
Solar Energy Specialist at Eastbourne Energy