UK solar calculator
Size a home solar system from your electricity bill — kW, panel count, roof area, cost with 0% VAT, and payback with SEG export payments.
Quick answer: At £0.24/kWh and 2.9 peak sun hours, a £150/month bill needs about 9.2 kW — 22 × 420 W panels covering ~44 m². A 4 kW system typically costs £5,000–£6,000 installed with 0% VAT, and the 9.2 kW system pays back in ~6.9 years.
Your details
Ballpark, not gospel. Sized at 78% real-world output with the UK sun-hour average — confirm shading, roof orientation and your supplier's SEG tariff with a local installer before buying.
Typical UK system sizes by monthly bill
| Monthly bill | System size | Panels (420 W) | Net cost (0% VAT) | Payback |
|---|---|---|---|---|
| £100 | 6.30 kW | 15 | £8,505 | 7.1 years |
| £150 | 9.24 kW | 22 | £12,474 | 6.9 years |
| £250 | 15.54 kW | 37 | £20,979 | 7.0 years |
Computed at £0.24/kWh, 2.9 peak sun hours and £1.35/W installed with 0% VAT. Run your exact bill above.
Questions people actually ask
Straight answers, no fluff. Then run your own numbers above.
How many solar panels do I need in the UK?
At £0.24/kWh and 2.9 peak sun hours, a £150/month bill needs about a 9.2 kW system — roughly 22 × 420 W panels covering ~44 m² of roof.
How much does solar cost in the UK in 2026?
Residential installs run about £1.35 per watt. A typical 4 kW system costs £5,000–£6,000 installed, and all residential installs currently carry 0% VAT — the discount is already in installer quotes.
What is the Smart Export Guarantee (SEG)?
Licensed suppliers must pay you for surplus electricity you export. Rates vary by supplier and tariff — shop SEG rates alongside your system quote, since strong export payments shorten payback on oversized systems.
What is the payback period for UK solar?
Around 7 years at current rates. A £150/month bill offsets £1,800 a year against a £12,474 net cost, paying back in about 6.9 years — with 25-year savings near £65,600 at 3% annual price growth.
Does the UK have enough sun for solar panels?
Yes — panels run on daylight, not heat. Southern England averages about 2.9 peak sun hours; a 9.2 kW array still generates roughly 7,600 kWh a year there.
How much roof space does UK solar need?
About 2 m² per panel including spacing. A 22-panel system needs roughly 44 m² of unshaded roof — south-facing is ideal, east/west splits work well too.
How much CO₂ does UK home solar avoid?
About 0.7 kg per kWh. A 9.2 kW system generating ~7,600 kWh a year offsets roughly 5.3 tons of CO₂ annually.
Should I add a battery in the UK?
It depends on your SEG rate. If export payments are low, a battery that stores daytime surplus for evening use can beat selling cheap and buying dear — size the bank on the solar system calculator.
Want batteries to keep your SEG exports? The solar system calculator sizes your inverter and battery bank. Comparing quotes? The solar cost calculator breaks down cost per watt, and the solar ROI calculator maps your payback year by year.