Real regional generation yields — a Scottish roof produces meaningfully less than a South England one — plus SEG export income, for an honest payback period.
Most online solar calculators use a single UK-wide generation figure — usually a South England number that doesn't reflect what a Glasgow or Aberdeen roof will actually produce. Annual generation per kWp of panel:
| Region | kWh per kWp per year |
|---|---|
| South England | ~1,050 |
| Midlands / North England | ~975 |
| Scotland | ~875 |
Based on a south-facing roof at roughly 35° pitch — east/west-facing or flatter roofs generate less regardless of region.
Power you generate and use yourself saves you the full retail electricity price (26.11p/kWh at the current price cap). Power you generate but don't use gets exported to the grid under the Smart Export Guarantee (SEG), paid at a rate your supplier sets — typically 4-15p/kWh, with premium tariffs (like Octopus's Outgoing) at the top end. Self-use is worth roughly 5x more per kWh than export, which is exactly why battery storage (to shift more generation into self-use) is often pitched alongside solar.
A 4kWp system in Scotland (£6,000 installed) generates about 3,500 kWh/year. At 45% self-use and a 5p/kWh export rate, that's roughly £507/year in combined savings and export income — an 11.8-year payback. The same system in South England, generating ~4,200 kWh/year, would pay back meaningfully faster.