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.
Common concerns, answered honestly
"What if we move premises?"
A common objection — and a fair one. If your remaining lease is under five years, a PPA (the funder owns the system, you buy the power) usually beats an outright purchase, or we build roof-rights portability into the deal. We model lease length explicitly and tell you if solar genuinely isn't the right fit.
"What if the roof needs work?"
We survey the roof structure before quoting. Older or asbestos-cement roofs are costed transparently up front — no surprises after contract. See roof suitability for the full checklist.
"What if payback takes too long?"
Typical UK commercial payback is 5–8 years against a 25-year asset — but we won't oversell it. If your load profile or tariff doesn't stack up, our savings calculator and free desk feasibility will show you honestly. See is it worth it?