Performance
How much energy does a commercial solar panel produce?
A typical 540 W commercial solar panel in the UK produces 480-580 kWh per year, with the variation driven by location (south coast vs Scottish highlands), orientation, pitch, and shading. South-facing 35-40 degree pitch in the Midlands is the benchmark — about 530 kWh/panel/year. The whole system produces 850-1,050 kWh per kW of nameplate annually.
A typical 540 W commercial solar panel in the UK produces 480-580 kWh per year. The variation comes down to location (south coast and East Anglia get more sun than Scotland), orientation (south-facing optimal, east-west splits acceptable), pitch (30-40 degrees ideal, flat roofs lose 5-10%), and shading. The benchmark figure for a south-facing 35-degree pitch in the English Midlands is about 530 kWh per 540 W panel per year, or roughly 980 kWh per kW of installed capacity annually. Across the full UK, expect 850-1,050 kWh/kW/year — the upper end on the south coast, the lower end in northern Scotland. Multiply by your system size to get total generation: a 100 kW system produces 85,000-105,000 kWh/year.
Generation by location across the UK
Solar irradiance varies by latitude and weather pattern. PVGIS-SARAH2 averaged 2005-2020 figures for a south-facing 35-degree pitched panel:
| Region | Annual generation per kW |
|---|---|
| South coast (Cornwall, Sussex, Kent) | 1,000-1,050 kWh/kW |
| South-west / Devon | 980-1,030 kWh/kW |
| London / South-east | 970-1,010 kWh/kW |
| East Anglia | 980-1,030 kWh/kW |
| Midlands | 940-980 kWh/kW |
| Wales | 920-970 kWh/kW |
| Yorkshire / Lincolnshire | 920-960 kWh/kW |
| North-west England | 880-930 kWh/kW |
| North-east England | 880-920 kWh/kW |
| Scottish lowlands | 850-900 kWh/kW |
| Scottish highlands | 800-850 kWh/kW |
| Northern Ireland | 880-930 kWh/kW |
Generation by month — UK solar isn’t year-round
UK solar generation follows a strong seasonal curve. For a 100 kW Midlands system generating ~95,000 kWh/year:
| Month | % of annual | kWh |
|---|---|---|
| December | 2% | 1,900 |
| January | 3% | 2,850 |
| February | 5% | 4,750 |
| March | 8% | 7,600 |
| April | 11% | 10,450 |
| May | 13% | 12,350 |
| June | 14% | 13,300 |
| July | 13% | 12,350 |
| August | 11% | 10,450 |
| September | 9% | 8,550 |
| October | 6% | 5,700 |
| November | 3% | 2,850 |
| December | 2% | 1,900 |
Summer (May-August) produces about 50% of the annual total. Winter (November-February) produces about 13%.
Daily generation profile
A typical UK summer day on a 100 kW south-facing system:
- 06:00: 2 kW (sunrise; rising)
- 09:00: 35 kW
- 12:00: 75 kW (peak)
- 15:00: 60 kW
- 18:00: 20 kW
- 21:00: 0 kW (sunset)
Total day: 380-420 kWh. Total month (June, ~30 days): 11,500-12,600 kWh.
A typical December day on the same system: 2-15 kW peak at midday, total day 8-25 kWh. Total month: 250-1,800 kWh depending on weather.
What reduces panel output
| Factor | Impact |
|---|---|
| Off-south orientation (45° east of south) | -5% |
| Off-south orientation (90° east, true east) | -15% |
| Pitch angle 0° (flat) | -5% |
| Pitch angle 60° (steep) | -8% |
| Soiling (1 year unwashed) | -3 to -5% |
| Soiling (5 years unwashed in dusty area) | -10% |
| Partial shading (chimney, dormer) | -5 to -25% depending on inverter type |
| Temperature derating (UK summer peak) | -3 to -5% (vs nominal STC at 25°C) |
| Tier 1 panel degradation (year 25) | -10 to -13% |
How modern panels compare to old
A 2026 540 W Tier 1 panel produces roughly 4x the annual energy of a 2010 145 W panel of the same physical footprint. Modern panels are bigger (M10/M12 cells vs 156mm), more efficient (22% vs 14%), and degrade slower (0.45%/year vs 0.7%/year).
If you have a system installed pre-2015, replacing 145 W panels with 540 W panels on the same roof can quadruple generation. Often economical as a “repower” project at year 12-15 of asset life.
Common misconceptions about panel output
“Panels need direct sun to generate” — wrong. Diffuse light from cloudy skies generates 10-25% of peak rated output. UK has 60-70% cloudy days per year and panels generate every day they have light.
“Panels overheat in summer and lose output” — partially true. Panels have a temperature coefficient of -0.3 to -0.4%/°C above 25°C. In a UK heatwave panel temperatures hit 50-60°C, losing 8-15% vs nominal. But total summer generation is still much higher than winter because day length and irradiance dominate.
“Output drops 1%/year forever” — wrong. Tier 1 panels degrade 0.4-0.5%/year. After 25 years, output is 87-90% of original. Then it stabilises and panels typically run another 15-20 years.
“South-east UK gets twice as much sun as Scotland” — exaggerated. South coast generates about 20-25% more annually than Scottish highlands. Solar economics work even in northern Scotland, just with longer payback.
Next steps
For a PVSyst yield model for your specific roof, request a feasibility study. See: panel efficiency, cloudy weather generation, UK weather impact, system sizing, cost guide.
Related questions
Do solar panels work on cloudy days?
Yes — solar panels generate electricity from diffuse light on cloudy days, typically producing 10-25% of their peak output. UK weather averages 60-70% cloudy days per year, but cloudy generation accumulates substantially: a 100 kW system in the UK generates 85,000-105,000 kWh/year despite cloud cover. Panels actually perform marginally better in cool cloudy conditions than in hot direct sun above 30°C.
How efficient are commercial solar panels?
Commercial solar panels in 2026 typically achieve 20-23% efficiency at Standard Test Conditions, with leading Tier 1 modules (Trina Vertex S+, JA Solar Deep Blue, Longi Hi-MO 7) reaching 22.5-23%. Higher efficiency means more kW from less roof area, useful where space is tight. The system as a whole loses 8-15% to inverter, cabling, soiling, shading, and temperature — real-world AC output is typically 85-92% of DC nameplate.
How does UK cloudy weather affect commercial solar performance?
UK cloudy weather is fully accounted for in commercial solar yield calculations — the long-run average is 850-1,050 kWh/kW/year across the UK, with year-to-year variation typically ±5-8%. Cloudy days reduce instantaneous output but accumulate over the year. UK silicon PV achieves 80-85% of Mediterranean yields per kW because cooler panel temperatures partly offset higher cloud cover.