Quick answer
Yes. Modern solar panels generate electricity from diffuse (cloudy-day) light as well as direct (clear-day) light. Output on overcast UK days is typically 10-25% of clear-day output for the same hour. Annual UK generation is roughly 60% from clear/partly clear and 40% from overcast conditions.
Full answer
Solar panels work with photons regardless of whether they arrive directly from the sun or via cloud scattering. Cloudy days produce diffuse light — the same wavelengths the panel converts, just at lower intensity. A typical overcast UK day produces 100-300 W/m² of irradiance at the panel surface (compared to 800-1,000 W/m² for clear summer day).
Annual UK generation is roughly 60% from clear or partly-clear conditions, 40% from overcast or rainy conditions. The 40% is real and meaningful — it's not 'wasted' generation. UK national average yield of 900-1,000 kWh/kWp includes the cloudy-day contribution.
Newer panel technologies (monocrystalline N-type, HJT, bifacial) have improved low-light performance compared to older polycrystalline panels. They generate more output per unit of diffuse light, which matters in UK climate where overcast conditions are common.
What does NOT generate: very dense overcast with heavy rain, fog, or thick winter cloud at low solar elevation. These conditions produce near-zero output for 1-3 hours but rarely zero generation across a full day. UK winter days produce 5-30 kWh per kWp on average, dropping briefly to near-zero only during the worst overcast hours.
For modelling purposes, we use Met Office historical irradiance data for your specific location — accounting for UK regional climate variation. The model includes overcast-day contribution; the annual yield figure you receive is realistic for UK conditions, not an idealised clear-sky figure.
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