Peak Sun Hours
Monthly peak sun hours for a US ZIP code, the worst month to design for, and a break-even check for your array.
Break-even check optional
System losses, 0.77 is typical
Results
Enter a ZIP code to see monthly sun hours.
Sun hours ·
Design value
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Worst month
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Annual average
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| Month | PSH |
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Break-even
Break-even PSH
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Days of autonomy
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Break-even PSH = daily Wh ÷ (array W × derate). Days of autonomy = usable battery Wh ÷ daily Wh.
Questions
What is a peak sun hour?
One hour of sunlight at 1,000 W/m². A site that gets 5 kWh/m² on the panel in a day has 5 peak sun hours.
Why design to the worst month?
An off-grid system has to keep up on the shortest days. Sizing to the worst month keeps the batteries from running down in winter.
Where do the numbers come from?
NREL PVWatts v8 using NSRDB typical-year weather, for a panel at the tilt and azimuth you enter.