SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/solar-cloudy-day

On thick cloudy days, how much can the direct beam of sunlight be reduced?

By up to 100% on thick, cloudy days.

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  1. By about 1%
  2. By 100% ✔
  3. By about 10%

Why: Direct sunlight can be blocked completely by thick clouds. Panels still make some power from diffuse light, but much less.

Huh, didn't know that: Even on clear, dry days, the atmosphere can reduce direct beam sunlight by about 10%.

The dad joke
What kind of shorts do clouds wear? Thunderwear!
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References

Answer: By 100%. Direct sunlight can be blocked completely by thick clouds. Panels still make some power from diffuse light, but much less.

  1. DOE: Solar Radiation Basics www.energy.gov/eere/solar/solar-radiation-basics
    by 100% during thick, cloudy days
    Checked 2026-10-10.

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