Solar Panel Yields by UK Region

Where the regional figures come from

UK solar irradiance runs on a clear south-to-north gradient, modified by coastal cloud patterns. The south coast of England receives roughly 30% more annual solar energy than northern Scotland. The calculator's five figures are rounded planning values for a well-oriented UK commercial rooftop, not measured output from named arrays; the PVGIS tables above check them against modelled output for twenty UK cities, and your own site should be checked with PVGIS or an installer's survey. Within each region, local variation of ±5–8% is normal — a coastal site in Norfolk can out-yield an inland site in Surrey despite being further north.

What moves yield more than geography

Orientation. Due south is the benchmark. East-west arrays — the standard layout on flat commercial roofs — give up 10–15% of annual yield but spread generation across more of the working day, which usually raises on-site use enough to win on value. North-facing slopes lose 30%+ and are rarely worth panelling in the UK.

Pitch. The UK optimum is 30–40°, but most commercial roofs sit at 5–15° and lose only 5–9% against optimal. Ballasted flat-roof systems are typically mounted at 10–15° to balance yield, wind load and row spacing.

Shading. The factor that ruins more commercial yields than geography ever will. Roof plant, parapets, neighbouring buildings and even flue stacks can knock whole strings down. Modern panel-level optimisers contain the damage but do not eliminate it — a properly shaded site can lose 15–25% of modelled yield. This is a survey question, not a calculator question.

Temperature, dirt and degradation. Panels lose efficiency as they heat up, which is why the UK's cool, bright spring days out-perform heatwaves per unit of sun. Soiling costs 1–3% on most pitched commercial roofs (more near aggregate yards or under flight paths), and panels degrade about 0.4–0.5% a year — the calculator's 25-year figure already accounts for this.

Does region decide whether solar stacks up?

Less than most people assume. Moving the same 100kWp system from Scotland to South England adds about £5,300 a year at default rates — material, but smaller than the swing from on-site use percentage (35% vs 85% is worth about £6,700 a year on the same system) and comparable to the swing from your contract rate. A Scottish cold store running 24/7 refrigeration beats a Surrey office that is empty by 5pm, every time. Geography sets the ceiling; your load profile decides how close you get to it.

Pick your region in the calculator, then stress-test the on-site use figure against your operating hours. The worked examples show the full method at three sizes, and the methodology page documents every formula involved.