UK commercial solar generates between roughly 845 and 1,025 kWh per kWp per year, depending on location, with a UK average of 905. A 500 kWp system therefore produces around 452,500 kWh a year at average sunshine. These are net figures from SAP 10.3 Appendix U, already adjusted for losses.
Generation by region
UK solar generates between roughly 845 and 1,025 kWh per kWp per year, depending on where the site is. These are the net specific yields our calculator uses, already adjusted for real-world losses:
| Region | Annual yield | 500 kWp generates |
|---|---|---|
| South West | 1,025 kWh/kWp | 512,500 kWh |
| South East | 1,010 kWh/kWp | 505,000 kWh |
| Midlands and Wales | 950 kWh/kWp | 475,000 kWh |
| UK average | 905 kWh/kWp | 452,500 kWh |
| North of England | 900 kWh/kWp | 450,000 kWh |
| Scotland | 845 kWh/kWp | 422,500 kWh |
The spread from Scotland to the South West is about 21%. That is real, but it is smaller than most people assume: a Scottish warehouse is not a bad solar site, it is a site with a fifth less sunshine than Cornwall.
Where these figures come from
The yields come from the Standard Assessment Procedure, SAP 10.3, Appendix U, which is the UK government's published solar radiation dataset. Table U6 in that appendix maps postcode districts to 21 sunshine regions, so entering a postcode gives a more precise figure than picking a region from a list.
We convert the SAP radiation data using the Appendix U equations for an east-west layout at 10 degrees tilt, which is the standard arrangement on commercial flat and shallow-pitched roofs, and anchor the result to a modelled reference of 905 kWh/kWp for the East Pennines. The figures in the table above are already net of losses, so they are what you would expect to meter, not a theoretical maximum.
A south-facing array at optimal tilt will beat these numbers. A shaded or north-facing roof will fall short of them. The full method is set out in how the calculator works.
From roof area to kilowatt hours
Three steps take you from a roof to an annual figure:
- Usable area. Take about 80% of the gross roof area for a pitched or flat roof. The rest goes to edges, rooflights, plant and walkways.
- System size. Each 510 W panel occupies roughly 2.57 m². Usable area divided by about 6.3 gives kWp.
- Generation. Multiply kWp by the regional yield above.
Worked through for a 3,200 m² pitched warehouse roof at UK average sunshine: 998 panels, 508.98 kWp, and 456,021 kWh in year one. Over 25 years, allowing for degradation, the same roof produces about 10.9 million kWh.
What reduces output
- Degradation. Panels lose about 1% in the first year and roughly 0.4% a year after that. A 25-year-old array still produces around 90% of its original output.
- Shading. Plant, flues, parapets and neighbouring buildings. Even partial shading on one panel affects its string.
- Orientation and tilt. East-west layouts produce slightly less in total than south-facing ones, but spread output more evenly across the day, which often suits a working site better.
- Soiling. Dust, moss and bird mess. Rain handles most of it in the UK; sites near quarries or food processing may need occasional cleaning.
- Inverter and cable losses. Already included in the figures above.
Winter and cloudy days
Solar panels work on daylight, not heat or direct sun, so they generate in overcast conditions, just less. A UK commercial array typically produces about ten times as much in June as in December. Roughly three quarters of annual output arrives between March and September.
This matters for sizing. A system matched to your summer midday demand will export heavily in June and cover only part of your load in December. If winter demand is what you are trying to cover, you are usually looking at a larger array, a battery, or accepting that solar handles part of the year rather than all of it.
Common questions
How much electricity does 1 kWp of solar generate in the UK?
Between about 845 and 1,025 kWh a year, depending on location. The UK average used by our calculator is 905 kWh per kWp per year. Scotland is at the lower end at around 845, and the South West at the upper end at around 1,025. These are net figures, already adjusted for real-world losses.
How much does a 500 kWp commercial system generate?
Around 452,500 kWh a year at UK average sunshine, rising to about 512,500 kWh in the South West and falling to about 422,500 kWh in Scotland. Over 25 years, allowing for panel degradation, a 500 kWp system produces roughly 10.7 million kWh.
Does solar work in winter and on cloudy days?
Yes, but at much lower output. Panels respond to daylight rather than heat or direct sun, so they generate under cloud. A UK array typically produces around ten times as much in June as in December, with roughly three quarters of annual output falling between March and September.