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How many solar panels do I need?
Enter your yearly electricity use and where you live to estimate the system size, number of panels and roof space needed to cover your usage.
Defaults from our sources, last updated 2026-10-23.
Estimates only, not financial advice. Results use average UK figures and the assumptions shown. Your real costs depend on your home, tariff, region and installer quotes. Always get several quotes from certified installers and check current tariff rates before deciding. Don't rely on these results alone: see our disclaimer.
How the calculator works
It divides the electricity you want to generate by the yearly output of 1 kWp of panels in your region and roof direction. That gives the system size in kWp. Dividing by the panel wattage gives the number of panels, rounded up. Roof area assumes about 1.9 m² per panel, typical for 430–460 W panels, and doesn't include edge gaps.
Typical answers
Ofgem's typical medium household uses 2,500 kWh of electricity a year. In south-west England a south-facing roof produces around 1,000 kWh per kWp, so matching that use needs about 2.5 kWp, or 6 panels of 450 W. In northern Scotland, where yields are nearer 760 kWh per kWp, you'd need about 8 panels. The Energy Saving Trust says the average home system is about 4.5 kWp, typically around 12 panels covering 20 to 30 m² of roof.
| Yearly use | System (south-west England) | 450 W panels | System (north-west England) | 450 W panels |
|---|---|---|---|---|
| 1,800 kWh | 1.8 kWp | 4 | 2.1 kWp | 5 |
| 2,700 kWh | 2.7 kWp | 6 | 3.1 kWp | 7 |
| 3,500 kWh | 3.5 kWp | 8 | 4.1 kWp | 10 |
| 4,500 kWh | 4.5 kWp | 10 | 5.2 kWp | 12 |
| 6,000 kWh | 6.0 kWp | 14 | 7.0 kWp | 16 |
South-facing roof, 100% of yearly use, using our regional yields of 1,000 and 860 kWh per kWp.
Should you cover 100% of your use?
Generating as much as you use over a year doesn't mean you'll stop buying electricity. Most solar comes in summer and in the middle of the day, while most homes use more in the evenings and in winter. Without a battery, households typically use only 30–50% of their solar directly and export the rest, usually for less than they pay to import. So sizing is a balance:
- Bigger systems cost less per kWp because scaffolding and labour are shared, and they produce more in winter. They make more sense with a good export tariff, an EV, a heat pump or a planned battery.
- Smaller systems are cheaper and more of their output is used at home, but you'll still buy most of your winter electricity.
Planning to get an electric car or heat pump? Add their use. An EV doing 7,500 miles a year needs roughly 2,400 kWh (try our EV charging calculator), and a heat pump often adds 2,500–4,000 kWh (see our heat pump running cost calculator).
Roof space and limits
Installers leave gaps around the edges of the roof, and chimneys, vents and windows reduce usable space. Larger systems may also need your network operator's approval before connection: systems with inverters above 3.68 kW per phase normally need approval in advance, which your installer handles. Shading matters a lot, since a small shaded area can cut a string's output unless optimisers are fitted.
Next steps
Once you know the size, check the likely price in our solar panel cost guide and the payback in our solar payback calculator.
FAQs
How many solar panels do I need for a 3-bedroom house?
A typical 3-bedroom home using about 2,700–3,500 kWh a year usually fits 8–12 panels (around 3.5–5 kWp). Your roof size, direction and budget matter as much as your usage.
How many kWh does one solar panel produce in the UK?
A 450 W panel on a south-facing roof produces roughly 342–450 kWh a year, depending on region, tilt and shading.
Can I have too many solar panels?
You can install more than you use and export the surplus, but each extra exported unit earns your export rate rather than saving your full import price. Large systems also need network operator approval.
How much roof space do I need?
Allow about 1.9 m² per panel plus edge gaps. A 4.5 kWp system typically needs 20–30 m² of roof.
Related calculators
Sources
- Energy Saving Trust – Solar panels: costs, savings and benefits
- European Commission JRC – PVGIS solar irradiance tool
- Ofgem – Energy price cap unit rates and standing charges (1 Oct–31 Dec 2026)
- Ofgem – Typical domestic consumption values (2026)
- MCS – Find a certified installer
Estimates only, not financial advice. Results use average UK figures and the assumptions shown. Your real costs depend on your home, tariff, region and installer quotes. Always get several quotes from certified installers and check current tariff rates before deciding. Don't rely on these results alone: see our disclaimer.