Reference values
| Solar constant (top of atmosphere) | 1 361 W/m² |
|---|---|
| AM1.5 global (STC) | 1 000 W/m² — standard test |
| AM1.5 direct + diffuse | 900 W/m² direct, 100 W/m² diffuse typical |
| Bright overcast | |
| Heavy overcast | |
| Full moon |
Annual insolation by region (kWh/m²/day)
| Region | Average |
|---|---|
| Northern Canada / Scandinavia | 2.5 – 3.5 |
| Northern US / UK / N. Europe | 3.0 – 4.0 |
| Central US / Central Europe | 3.5 – 4.5 |
| Southern US / Mediterranean | 4.5 – 5.5 |
| Desert Southwest US / Sahara | 5.5 – 7.0 |
| Equatorial Africa / SE Asia | 5.0 – 6.0 |
| Australia (inland) | 5.5 – 7.0 |
Peak sun hours (PSH)
| Definition | Daily energy equivalent of 1 kW/m² — 5 PSH means 5 kWh/m² per day |
|---|---|
| Use | Simpler than integrating hourly irradiance for PV sizing |
Notes
- Insolation varies by tilt and azimuth of the surface — fixed-tilt at latitude is a reasonable default.
- Tracking systems harvest 20–40% more, at added cost/maintenance.
- Clean panels matter: soiling can cost 5–20% output in dusty regions.
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