How much roof does a solar array need?
A modern panel is about 1.9 m² and produces around 420 W in full sun. Everything else follows from those two numbers.
1.1 × 4 kW array
20 m² is bigger than 4 of the 7 references on this page.
Reference figures are measurements and are rounded; the unit conversion behind them is exact.
| Reference | Size | Yours ÷ theirs | Note |
|---|---|---|---|
| one panel | 1.9 m² | 10.5× | About 420 W |
| 1 kW array | 4.5 m² | 4.44× | |
| 3 kW array | 13.6 m² | 1.47× | A small UK home system |
| 4 kW array | 18.1 m² | 1.1× | The most common UK domestic size |
| typical UK roof face | 30 m² | 0.667× | |
| 10 kW array | 45.2 m² | 0.442× | |
| EV-charging array | 90.4 m² | 0.221× | About 20 kW |
Worth knowing
- A 4 kW array needs about 18 m² of unshaded roof and generates roughly 3 400 kWh a year in southern England — most of an average household’s electricity.
- Panel efficiency has risen from about 15% to 22% in fifteen years, so the same roof now carries nearly half as much again.
Frequently asked
How many solar panels fit on a roof?
Divide the unshaded roof area by about 1.9 m² per panel, then subtract 10–15% for edge clearance and access. A typical 30 m² roof face takes 13 to 14 panels.
Does orientation matter more than area?
Both matter, but orientation is cheaper to get right. In the UK, an east or west roof yields about 85% of a south-facing one; a north roof yields about 60%.