1) What are peak sun hours?
A peak sun hour (PSH) is one hour of sunlight at an intensity of 1,000 W/m² (the standard test condition for solar panels). Daily PSH is the total solar energy received in kWh/m² divided by 1 kW/m².
Example: 5.5 kWh/m²/day ≈ 5.5 peak sun hours.
2) Solar irradiance explained
Irradiance is the power of sunlight hitting a surface (W/m²). Over time, it accumulates into insolation (kWh/m²/day). PSH is simply a way to express insolation in hours of “full sun.”
3) Sun path basics (diagram)
This simplified diagram shows how the sun travels across the sky. The **higher** the arc at your location and date, the **more** irradiance you receive (all else equal). The animated sun slides along a representative daytime path.
4) Regional differences
PSH varies worldwide:
- Northern Europe: 2.5–3.5 PSH
- U.S. Midwest: 4–5 PSH
- U.S. Southwest: 6–7 PSH
- Tropics/deserts: 5–8 PSH
5) How to use PSH in sizing
Production estimate formula:
Energy (kWh/day) = System size (kW) × PSH × Performance ratio (PR)PR accounts for inverter, wiring, shading, and temperature losses (usually 0.7–0.8).
6) Factors that reduce PSH
- Shading: trees, chimneys, nearby buildings.
- Tilt & azimuth: panels not facing equator or off optimal angle.
- Weather: frequent clouds reduce insolation.
- Seasons: winter days shorter, summer longer.
Always use local monthly PSH data when sizing batteries or backup systems. A 25-year ROI assumes annual averages, but storage needs depend on winter lows.
7) Worked example
A 6 kW system in a location with 5.5 PSH/day and PR=0.75:
6 × 5.5 × 0.75 = 24.75 kWh/dayThis offsets a household using ~25 kWh/day.