How much a solar panel makes depends on where the roof is. We measured sunshine on real roofs in 15 counties across England, Wales, Scotland and Northern Ireland with Google's Solar API, and ran each through the calculator for a typical 4 kWp system.
| County | Yield (kWh/kWp) | 4 kWp makes | Payback |
|---|---|---|---|
| Cornwall England | 1,176 | 4,704 kWh | 7.2 yrs |
| Kent England | 1,126 | 4,504 kWh | 7.5 yrs |
| Norfolk England | 1,102 | 4,408 kWh | 7.6 yrs |
| Hampshire England | 1,091 | 4,364 kWh | 7.7 yrs |
| Devon England | 1,081 | 4,324 kWh | 7.7 yrs |
| Cardiff Wales | 1,019 | 4,076 kWh | 8.1 yrs |
| Leicestershire England | 999 | 3,996 kWh | 8.2 yrs |
| Northumberland England | 950 | 3,800 kWh | 8.5 yrs |
| West Yorkshire England | 929 | 3,716 kWh | 8.6 yrs |
| Gwynedd Wales | 924 | 3,696 kWh | 8.7 yrs |
| Greater Manchester England | 919 | 3,676 kWh | 8.7 yrs |
| Edinburgh Scotland | 872 | 3,488 kWh | 9.1 yrs |
| Cumbria England | 853 | 3,412 kWh | 9.2 yrs |
| County Antrim Northern Ireland | 840 | 3,360 kWh | 20.4 yrs* |
| Highland Scotland | 743 | 2,972 kWh | 10.2 yrs |
* Northern Ireland has no Smart Export Guarantee, so nothing is assumed for exported power. With Great Britain's export rate the payback would be about 9.3 years in County Antrim, in line with Great Britain counties that get similar sunshine.