Performance
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.
UK cloudy weather is fully baked into solar yield modelling — not an afterthought, not a problem to overcome. The long-run average yield across the UK is 850-1,050 kWh per kW installed per year, depending on latitude. Year-to-year variation is typically ±5-8%: a sunny year might deliver 5% above average, a cloudy year 5% below. Across the 25-year asset life, the variations average out and the long-run figures hold reliably. UK silicon PV achieves 80-85% of Mediterranean yields per kW because cooler UK panel temperatures (which boost efficiency) partly offset higher cloud cover (which reduces irradiance). The economic case for UK commercial solar — 5-8 year payback in 2026 — already accounts for UK weather conditions.
Where the UK weather data comes from
Reliable yield modelling uses one of two open data sources:
- PVGIS (Photovoltaic Geographical Information System): EU Joint Research Centre database. Combines satellite irradiance data with geographic terrain. Free to query at re.jrc.ec.europa.eu/pvg_tools/en/.
- Solcast: commercial weather + irradiance API. Used by larger installers for higher-resolution daily forecasts. Free tier available; paid tier for full granularity.
Both ingest 15+ years of UK weather satellite data. Output is hourly irradiance for any UK postcode and panel orientation/pitch. PVSyst, the standard solar design software, imports from both.
Year-to-year UK solar yield variation
| Year | UK average yield (% of long-run) |
|---|---|
| 2018 (record sunny summer) | +9% |
| 2022 (warm but cloudy autumn) | +1% |
| 2023 (cooler, mixed) | -2% |
| 2024 (wet spring, mixed summer) | -4% |
| 2025 (close to average) | -1% |
| 2026 (typical) | 0% (long-run mean) |
Variation is comparable to other UK weather-dependent activities (agriculture, hydropower, gas heating demand). Solar economics are robust to ±5-8% variation because long-run averages dominate the 25-year cashflow.
Seasonal variation — UK winter vs summer
UK solar generates roughly 6x more in summer (May-Aug) than winter (Nov-Feb). For a 100 kW Midlands system:
- May-August: 13,000-14,000 kWh/month
- Nov-February: 1,900-2,800 kWh/month
The winter trough matters for businesses with high winter electricity use (heating, lighting). Solar covers maybe 5-10% of winter electricity consumption. In summer, solar can exceed daytime consumption.
This seasonality drives the case for:
- Battery storage (shifts summer surplus to evening) — less impact on winter
- Heat pump pairing (use solar surplus to displace gas heating) — significant impact
- Renewable contract for winter grid imports (ensures clean energy year-round)
Regional UK weather variation
Solar irradiance varies by region — but less than you’d think:
- South coast: ~1,030 kWh/kW/year
- Midlands: ~960 kWh/kW/year
- Glasgow: ~880 kWh/kW/year
- Inverness: ~840 kWh/kW/year
That’s about 22% range from south coast to far north. Compared to the difference between siting decisions (south-facing vs east-facing roof, 5-10% range) or panel quality (10-15% range over 25 years), regional variation is moderate.
Microclimate effects
Even within a single UK region, microclimate variation can be 10-15%:
- Coastal sites: clearer skies, more diffuse, fewer days with heavy fog
- Urban canyons: lower irradiance from horizon obstructions; some additional reflection from buildings
- Hill stations / valleys: morning fog reduces winter output; clearer summer skies
- Industrial areas with air pollution: 2-5% reduction in irradiance from particulates
- Coastal industrial (e.g. Teesside, Humber): salt + particulates require more frequent cleaning
PVGIS uses regional averages. For high-value projects (above £200k capex), commission a Solcast 15-year hourly dataset for the specific postcode — adds £400-£800 to design cost but improves yield prediction accuracy.
What UK weather doesn’t materially affect
Despite assumption, several UK weather concerns don’t materially harm solar:
- Rain washing panels: actually beneficial. Rainfall in the UK averages 800-1,400 mm/year, washing dust and pollen from panels. Self-cleaning is significant.
- Snow loading: most UK snow events drop from panels within 24-48 hours due to panel angle and warmth. Modern panels rated to 5,400 Pa snow load (well above UK requirements).
- Wind: UK wind speeds are within the design envelope of all Tier 1 panels and mounting systems. Panel datasheets quote 2,400 Pa wind load minimum.
- Lightning: standard surge protection devices (SPDs) on DC and AC lines protect against indirect strikes. Direct strikes are rare in low-rise commercial buildings.
- Hail: UK hailstones rarely exceed 25mm (the IEC 61215 standard test). Tier 1 panels survive larger hail in tests.
Common misconceptions about UK weather and solar
“UK is too northern for solar to work” — wrong by 2 million UK PV installations and 25 GW national solar capacity. Solar economics work down to Inverness.
“Solar only generates in summer in the UK” — wrong. Generates 365 days/year, just less in winter.
“Panels need cleaning constantly in UK weather” — wrong. UK rain handles most cleaning. Annual professional clean is optional, not essential.
“Heat tolerance is the priority for UK panels” — partially. Modern n-type panels with low temperature coefficient (-0.30%/°C) are slightly better in UK summer heatwaves but the gain over PERC (-0.40%/°C) is 2-3% across the year.
Next steps
For a yield model based on Solcast or PVGIS data for your specific postcode, request a feasibility study. Related: cloudy day generation, panel output, efficiency, cost guide, grants and funding.
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 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.