How we calculate your solar savings
Every figure on this site comes from one model with the assumptions below. We update the prices each time the Ofgem price cap changes.
Last updated October 2026
Current assumptions
| Electricity unit rate | 26.32p per kWh |
| Electricity standing charge | 54.83p per day |
| Export rate (Smart Export Guarantee) | 12p per kWh |
| Overnight smart tariff rate | 8.5p per kWh |
| Yearly electricity price rise | 3% |
| Yearly panel output loss | 0.5% |
| Panel size | 440 W |
| Installed cost | £2,400 + £1,050 per kWp |
| 5 kWh battery | £3,000 |
| 10 kWh battery | £5,000 |
| Grid carbon intensity | 0.207 kg CO₂e per kWh |
Unit rate and standing charge are the Ofgem price cap averages for 1 October to 31 December 2026, excluding VAT on electricity for that period.
Sunshine by region
Output per kWp is for a south-facing roof at 35°, based on typical UK solar irradiance by region. We group postcodes by their area letters.
| Region | kWh per kWp per year |
|---|---|
| South West England | 1040 |
| The South coast | 990 |
| London and the South East | 960 |
| The Midlands and South Wales | 920 |
| North Wales and Cheshire | 880 |
| Northern England | 860 |
| Scotland | 800 |
| Northern Ireland and the islands | 830 |
Adjustments
- Roof direction: south-east and south-west 95%, east and west 83%, flat roofs on tilted frames 90%, north 62%.
- Shade: a little shade 88%, heavy shade 72%.
- Self-use without a battery: 50% if someone is home most days, 40% some days, 30% rarely.
- Battery: a 5 kWh battery adds 25 percentage points of self-use and a 10 kWh battery 35, capped at 90%. Batteries also charge on an overnight tariff for about 140 winter days.
- Usage: taken from your bill after the standing charge. A planned EV adds 2,500 kWh a year and a planned heat pump 3,500 kWh.
Limits of the estimate
Your actual savings depend on your exact roof pitch, shading, usage pattern, tariff and installer price. A survey measures these properly. Treat our figures as a guide to whether solar is worth looking into, not as a quote.
Sources
- Ofgem: energy price cap unit rates and standing charges
- European Commission PVGIS: photovoltaic geographical information system
- Ofgem: typical domestic consumption values
- MCS: Microgeneration Certification Scheme