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SESK: Stuff Everyone Should Know · sesk.info/solar-peak-sun-hours

A location has 3.5 peak sun hours. What does that mean?

Sunlight reaches 1,000 W/m2 for the equivalent of 3.5 hours per day.

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  1. Sunlight equals 1,000 W/m2 for about 3.5 hours a day ✔
  2. The sun is above the horizon only 3.5 hours a day
  3. Panels shut off after 3.5 hours of sun

Why: Peak sun hours count the hours at full-sun intensity, 1,000 watts per square meter. Sizing a system divides daily energy needs by this number. It is not the same as hours of daylight.

Huh, didn't know that: In a University of Arizona example, a home using 6,000 kWh a year with 6.5 peak sun hours needs about a 4.5 kW array.

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What fills up a room but takes up no space? Light.
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References

Answer: Sunlight equals 1,000 W/m2 for about 3.5 hours a day. Peak sun hours count the hours at full-sun intensity, 1,000 watts per square meter. Sizing a system divides daily energy needs by this number. It is not the same as hours of daylight.

  1. University of Arizona Extension: Calculations for a Grid-Connected Solar Energy System (az1782) www.extension.arizona.edu/sites/default/files/2024-08/az1782-2019.pdf
    Peak sun-hours is equal to the number of hours the insolation value is at 1,000W/m2.
    Checked 2026-10-10.

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