System Sizing & Physics

Peak Sun Hours (PSH) vs Daylight Hours Distinction

Core Question: Why is 8 hours of daylight NOT the same as 8 Peak Sun Hours (PSH) in solar engineering calculations?

Governing Physics Formula / Design Rule
1 PSH = 1 kWh/m² of Total Daily Solar Irradiance = Cumulative Solar Energy Equivalent at 1,000 W/m²

Executive Technical Summary

Daylight hours count any time the sun is visible in the sky. Peak Sun Hours (PSH) integrate the entire day variable solar irradiance curve into an equivalent number of hours at standard 1,000 W/m² peak intensity.

Detailed First-Principles Explanation

A sunny day in Germany might have 14 hours of summer daylight, but due to low sun angles in the morning and evening, the integrated daily solar radiation totals only 4.2 kWh/m² — which equals 4.2 PSH. In Arizona, 12 daylight hours can deliver 6.5 PSH.

Critical Field Pitfall & Safety Warning

Sizing solar systems using "hours of sunshine" from weather apps instead of NASA/NREL satellite PSH irradiation data will result in 40%~60% under-sized solar systems.

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