Do Solar Panels Work on Cloudy UK Days?
Honest answer + the longer story behind the question.
60-second answer
Yes — solar panels generate on cloudy UK days, just at 10–30% of bright-sun output depending on cloud thickness. Diffuse light still drives photovoltaic conversion. UK PVSyst yield modelling already accounts for the country’s typical cloud cover — and even Manchester and Glasgow deliver 850–900 kWh/kWp/year, well within commercial-viability thresholds.
Why panels still work in diffuse light
Crystalline silicon solar cells respond to a wide spectrum of sunlight including diffuse and indirect light. Cloud cover scatters direct sunlight but doesn’t eliminate it — the panels see ~25% of clear-sky irradiance under thick overcast. Light cloud or hazy days deliver 60–80% of clear-sky output. Even fog allows measurable generation (5–15% of clear-sky).
UK regional irradiance differences
Annual irradiance varies across the UK but the differences are smaller than most people assume. South-east England (Kent, Essex) gets ~1,050 kWh/kWp/year. London ~1,000. The Midlands ~970. North-west England ~920. Glasgow ~870. Aberdeen ~830. Cornwall ~1,030. Even the lowest UK regions support commercially viable solar with 4–7 year payback.
Real UK cloudy-day generation example
From a real 250 kW system on a Manchester factory, cloudy-day generation in January 2025: average 87 kWh/day across 18 cloudy days (vs 240 kWh/day clear-sky maximum). Even that worst-case month contributed ~3% of annual generation, exactly matching PVSyst forecast.
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