Commercial Solar PV Yield by UK Region: kWh per kWp for Flat and Pitched Roofs
Updated 20 October 2026 · SEO Dons Editorial
Why one yield figure is not enough
A common rule of thumb says a UK solar array makes 900 to 1,000 kWh per kWp per year. That is a reasonable figure for a south-facing roof pitched at about 35° in the south and Midlands, and a poor one for a flat commercial roof carrying low-tilt east-west rows in the north. The gap matters because the number feeds directly into the generation line of the payback model, and into the guarantee a supplier may give. This table puts three common commercial layouts side by side for 13 locations, so the figure in a proposal can be checked against an independent source.
kWh per kWp per year by location and layout
Values are annual energy per 1 kWp installed, from the European Commission's PVGIS tool (version 5.3, SARAH3 radiation data), with system losses set to 14%. The east-west column is the average of an east-facing and a west-facing plane at 10° tilt, which is what an east-west rack delivers when both sides carry equal capacity.
| Location | South, 35° tilt | South, 10° tilt | East-west, 10° tilt | East-west as % of south 35° |
|---|---|---|---|---|
| Plymouth | 1,122 | 1,019 | 932 | 83% |
| Cardiff | 1,042 | 946 | 865 | 83% |
| Bristol | 1,023 | 928 | 849 | 83% |
| Norwich | 1,032 | 926 | 843 | 82% |
| London | 1,019 | 920 | 840 | 82% |
| Birmingham | 968 | 875 | 800 | 83% |
| Leeds | 947 | 851 | 775 | 82% |
| Newcastle | 948 | 844 | 764 | 81% |
| Belfast | 919 | 828 | 756 | 82% |
| Manchester | 886 | 807 | 741 | 84% |
| Edinburgh | 903 | 805 | 731 | 81% |
| Aberdeen | 893 | 791 | 715 | 80% |
| Glasgow | 853 | 772 | 707 | 83% |
Figures are rounded to the nearest kWh. They are modelled values for a plain site with no shading, not a measurement of any installed system, and they will differ from a site-specific PVSyst model that uses the actual horizon, module and inverter.
What the table shows
- Latitude and weather dominate. The best south-35° figure (1,122 kWh/kWp at Plymouth) is about 32% above the lowest (853 at Glasgow). The same array in Plymouth and Glasgow would not be priced on the same payback.
- Low tilt costs energy. A south-facing 10° tilt gives up roughly 9 to 10% against 35°, in return for a much lower profile on a flat roof, which matters for the planning height limit and wind loading (see planning permission for commercial rooftop solar PV).
- East-west rows yield less per kWp but fit more kWp on the roof. The east-west column sits at 80 to 84% of south 35°, so a supplier quoting 950 kWh per kWp for an east-west flat roof in the north is outside what PVGIS supports. In exchange, east-west rows need less spacing for row shading, so the roof area carries more capacity, and the daily output curve is flatter, which suits a building that uses power across the whole working day.
Using it to check a quote
Take the quoted annual generation, divide by the kWp, and compare with the row for your nearest location and the layout in the drawing. A figure more than about 5% above the PVGIS value needs an explanation: a different loss assumption, a different radiation database, a bifacial gain or an optimistic orientation. A figure well below it is usually a conservative loss allowance or heavy shading. Neither is automatically wrong, but the proposal should say which assumption it rests on.
The kWp number is itself an input to sizing a commercial solar PV system, where the 900 to 1,000 kWh rule of thumb is used for first-pass sizing. For a flat-roof east-west array, use the east-west column instead.
Method and limits
- Tool: PVGIS 5.3 PVcalc, radiation database PVGIS-SARAH3, 1 kWp, system losses 14%, fixed mounting. Run on 20 October 2026.
- Planes modelled: azimuth 0° (south) at 35° and 10°; azimuth -90° (east) and +90° (west) at 10°, averaged.
- Locations are city-centre coordinates. A site 30 miles away on a hill or in a valley can differ by several per cent, and PVGIS does not model local obstructions unless the horizon is supplied.
- It does not include inverter clipping, degradation over time, soiling beyond the stated loss figure or snow. Treat it as a first-year check, not a lifetime forecast.
To compare these yields against a specific roof, send the building details and we reply by email, or try the savings calculator for a quick projection.
Sources
- European Commission Joint Research Centre, PVGIS photovoltaic geographical information system, version 5.3 PVcalc, accessed 20 October 2026.