How Many Solar Panels Do I Need? UK Output, Savings and Payback
Most UK homes fit 8 to 12 solar panels of 400 W, a system of 3.2 to 4.8 kW. Ten panels (4 kW) on a south roof in the Midlands make about 3,800 kWh a year, which saves and earns about £669 a year and pays back in about 10 years. The solar panel calculator works it out for your roof, location, prices and cost.
Output by system size
With 400 W panels on a south roof in the Midlands (950 kWh per kW), with 40% of the power used at home, and the cost at £1,600 per kW. The last columns show how much of a typical home's 2,700 kWh a year the panels make, and what they cost:
| Panels | System | Roof area | kWh a year | Share of 2,700 kWh | Installed cost |
|---|---|---|---|---|---|
| 4 | 1.6 kW | 8 m² | 1,520 kWh | 56% | £2,560 |
| 6 | 2.4 kW | 11 m² | 2,280 kWh | 84% | £3,840 |
| 8 | 3.2 kW | 15 m² | 3,040 kWh | 113% | £5,120 |
| 10 | 4.0 kW | 19 m² | 3,800 kWh | 141% | £6,400 |
| 12 | 4.8 kW | 23 m² | 4,560 kWh | 169% | £7,680 |
| 16 | 6.4 kW | 30 m² | 6,080 kWh | 225% | £10,240 |
Output by roof direction and region
For a 4 kW system (ten 400 W panels):
| Region | South | South-east or south-west | East or west | North |
|---|---|---|---|---|
| South of England | 4,000 kWh | 3,800 kWh | 3,400 kWh | 2,400 kWh |
| Midlands and Wales | 3,800 kWh | 3,610 kWh | 3,230 kWh | 2,280 kWh |
| North of England and Scotland | 3,600 kWh | 3,420 kWh | 3,060 kWh | 2,160 kWh |
A south-facing roof at a pitch of 30 to 40 degrees is the best. East and west roofs make about 85% as much, and spread the output across the morning or the afternoon. A flat roof can take panels on frames.
How long do they take to pay back?
For the 4 kW system at £1,600 per kW, with electricity at 26p. The payback depends on how much of the power you use at home (which saves 26p a kWh) and the export rate (which pays far less):
| Share used at home | Export 5p | Export 12p | Export 15p |
|---|---|---|---|
| 30% used at home | 14.9 years | 10.4 years | 9.2 years |
| 40% used at home | 12.6 years | 9.6 years | 8.7 years |
| 50% used at home | 10.9 years | 8.9 years | 8.2 years |
| 70% used at home | 8.5 years | 7.7 years | 7.4 years |
The more you use yourself, the shorter the payback. Run the dishwasher, the washing machine and the immersion heater in the day, charge an electric car at home, and think about a battery.
Cost and benefit
| Installed price | Cost of the system | Benefit a year | Payback |
|---|---|---|---|
| £1,300 per kW | £5,200 | £669 | 7.8 years |
| £1,600 per kW | £6,400 | £669 | 9.6 years |
| £1,800 per kW | £7,200 | £669 | 10.8 years |
Before you decide
- Shade. Trees, chimneys and neighbouring buildings can cut the output a lot. A survey checks it.
- The roof. It must be sound and have the strength for the panels, and fit the number of panels you want. Re-roofing later means taking them off.
- MCS and quotes. Use an MCS-certified installer, which is needed to be paid for the power you export. Get at least three quotes and compare the panels, the inverter, the warranty and the monitoring.
- Export payments. Under the Smart Export Guarantee, suppliers pay for the power you send to the grid, at rates from a few pence to about 15p per kWh. Compare tariffs.
- Planning. Most roofs do not need planning permission, but listed buildings and some conservation areas have rules.
- Tax. The installation of solar panels in a home has been zero-rated for VAT. Check the current rules.
These are estimates from typical yields and the prices stated. Real output varies with the weather, the shade and the equipment. For the cost of running an electric car, see the EV charging cost calculator, and see the electricity cost calculator for your own appliances.
Frequently asked questions
How many solar panels do I need for a typical UK home?
Most homes fit 8 to 12 panels of 400 W, which is 3.2 to 4.8 kW. A typical home uses about 2,700 kWh of electricity a year, which six panels (2.4 kW) can nearly match on a south roof: 2,280 kWh.
How much electricity do solar panels make in the UK?
About 850 to 1,050 kWh a year for each kW of panels on a south roof, so 3,800 kWh from ten 400 W panels in the Midlands. An east or west roof makes about 3,230 kWh and a north roof about 2,280 kWh.
How long do solar panels take to pay back?
Roughly 10 years for a 4 kW system at £1,600 per kW if 40% of the power is used at home and the rest is exported at 12p. Using more of it yourself shortens the payback.
How much roof space do I need for solar panels?
About 1.9 m² per panel: ten panels need about 19 m² of unshaded roof, which is a patch of about 5 m by 4 m.
Is it worth getting solar panels with a battery?
A battery stores the daytime surplus for the evening, so you use more of your own power and export less. It adds a few thousand pounds, so check the extra savings against the cost.
More guides
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.