Solar roof calculator: how much solar can I fit on my roof?
Enter your roof and see how many solar panels fit, their peak power and how much electricity they would make in a year. It works for houses, flat roofs and business roofs, with real yields for 20 places: 13 across the UK, plus Serbia and Bosnia and Herzegovina.
Your roof
- Layout: 5 across and 2 up the slope, panels upright.
- 1,019 kWh per kWp a year here, about the best a roof can do in London.
- About as much electricity as 1.8 typical UK homes use in a year (2,500 kWh each, Ofgem).
Assumes 430 W panels, 1.72 m by 1.13 m, with 0.4 m clear at the edges. Before shading from trees, chimneys and neighbours, roof strength and wiring; an installer's survey sets the final number.
Yields: PVGIS 5.3 (European Commission Joint Research Centre), 14% system losses, queried 13 November 2026. Free to use; nothing you enter leaves your browser.
How many solar panels can I fit on my roof?
Measure the part of the roof that gets sun, leave a clear strip around the edges and count how many whole panels fit. A typical 430 W panel is about 1.72 m by 1.13 m (1.94 m²). On a 7 m by 4.9 m roof face with 0.4 m clear all round, 10 panels fit: 4.3 kWp, about 4,380 kWh a year facing south in London.
That is close to a typical home system: the Energy Saving Trust uses 4.5 kWp. When we screened 1,910 buildings in Great Baddow, Chelmsford, from 1 m LiDAR, the typical house had 22.7 m² of suitable roof, about 4.1 kWp. Chimneys, roof windows, vents and valleys all take space, so measure around them.
How much electricity will solar panels on my roof make?
Multiply the system size in kWp by your area's yearly yield. A south-facing 35° roof makes 1,019 kWh per kWp a year in London, 896 in Manchester and 853 in Glasgow, so a 4 kWp system makes roughly 4,080, 3,580 and 3,410 kWh a year there. A typical UK home uses 2,500 kWh a year (Ofgem).
| Place | South | East | West | North |
|---|---|---|---|---|
| London | 1,019 | 817 | 787 | 541 |
| Plymouth | 1,121 | 877 | 889 | 584 |
| Cardiff | 1,042 | 809 | 834 | 548 |
| Birmingham | 968 | 775 | 757 | 524 |
| Manchester | 896 | 724 | 708 | 497 |
| Newcastle upon Tyne | 950 | 738 | 731 | 490 |
| Belfast | 919 | 728 | 722 | 498 |
| Glasgow | 853 | 673 | 683 | 469 |
| Aberdeen | 892 | 685 | 683 | 454 |
| Belgrade, Serbia | 1,261 | 995 | 986 | 652 |
| Novi Sad, Serbia | 1,267 | 1,004 | 989 | 654 |
| Sarajevo, BiH | 1,202 | 981 | 936 | 654 |
Does the direction of my roof matter?
Yes, but less than most people expect. In London a 35° roof facing south-east or south-west makes 95% and 93% of what a south-facing one does, east 80% and west 77%. East and west roofs often carry panels on both sides, which can make up the difference.
Will solar panels work on a north-facing roof in the UK?
They work, but they make much less. A north-facing 35° roof in London makes 53% of a south-facing one. On a shallow 10° north slope it is 74%, so low-pitched north roofs are worth checking, steep ones rarely are.
Can I put solar panels on a flat roof?
Yes. Panels go on low frames, either in rows facing south or in east-west pairs back to back. On a 10 m by 6 m flat roof in London with 0.5 m clear at the edges, south rows at 10° fit 15 panels (about 5,930 kWh a year) and east-west pairs fit 12 (about 4,330 kWh a year).
South rows make more per panel but need gaps so one row does not shade the next; our calculator spaces them for the midday sun on the shortest day. East-west pairs pack tighter (with a 0.5 m walkway between pairs here) and spread generation across the morning and evening. In England, panels on a flat roof of a house can stand up to 0.6 m above the highest part of the roof without planning permission. For warehouses and other business roofs, see our commercial guide.
Is my roof suitable for solar panels?
Most roofs are. Check five things before you get quotes:
- Direction and pitch. South is best, east and west still work well, north only on shallow slopes (see above).
- Shade. Trees, chimneys and taller buildings that shade the roof cut output; the calculator does not include them.
- Space. Enough clear roof for the system you want, around windows, vents and valleys.
- Condition and strength. Panels last for decades, so replace a roof that is near the end of its life first, and ask the installer to confirm the roof can carry the weight.
- Planning. Listed buildings and conservation areas have extra rules (below).
Do I need planning permission for solar panels in England?
Usually not on a house. Under the rules in force since 27 August 2026, panels on a pitched roof must stick out no more than 0.2 m from the slope and sit no higher than the highest part of the roof, chimneys aside. On a flat roof they can stand up to 0.6 m above its highest part.
Listed buildings need consent. In a conservation area or World Heritage Site, panels on a wall, balcony or roof enclosure that fronts a highway need permission. Wales, Scotland and Northern Ireland have their own rules, and the rules for business roofs differ. Source: The Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2026. Your council can confirm for your address.
How this calculator works
It fits whole panels inside the clear part of the roof, both ways round, and keeps the layout with more panels. Yearly generation comes from PVGIS 5.3, the European Commission's solar model, for 20 places, every roof direction and pitches from 10° to 50° (in between, it interpolates), with 14% system losses. It leaves out shading, roof strength, inverter size and grid limits, so treat the answer as the most your roof could carry, not a quote.