Quick guide
| Home | Typical electricity use | Panels | System size |
|---|---|---|---|
| 1 to 2 bedrooms | 1,800 kWh a year | 7 to 8 | about 3 kW |
| 3 bedrooms | 2,700 kWh a year | 10 to 11 | about 4.5 kW |
| 4+ bedrooms or electric car | 4,000+ kWh a year | 13 to 16 | 5.5 to 7 kW |
These assume modern panels of around 400 to 450 watts each. Each panel is roughly 1.7 by 1.1 metres.
Work it out yourself
- Find your yearly electricity use on your bill or supplier app.
- Divide by about 950 (what each kW makes a year in much of the UK). That's the system size in kW that would make roughly as much as you use over a year.
- Divide by 0.43 to get the number of panels.
Example: 2,700 kWh ÷ 950 = 2.8 kW, or about 7 panels. Many people go bigger, because exports earn money and electricity use often grows with a heat pump or electric car.
What limits it
- Roof space and shading.
- Your network operator: systems over about 3.68 kW per phase need approval, which your installer arranges.
- Budget: see what each size costs.
Sources: Reonic regional yield table, Energy Saving Trust figures via Which?.