Solar Irradiance Calculator Formula
Understand the math behind the solar irradiance calculator. Each variable explained with a worked example.
Formulas Used
Daily Irradiance
daily_kwh_m2 = peak_sun_hours * orientation_factorDaily Energy on Panel
daily_kwh_total = peak_sun_hours * orientation_factor * panel_area_m2Annual Energy on Panel
annual_kwh_total = peak_sun_hours * orientation_factor * panel_area_m2 * 365Variables
| Variable | Description | Default |
|---|---|---|
peak_sun_hours | Peak Sun Hours per Day(hours) | 5 |
panel_area_m2 | Panel Area(m²) | 20 |
orientation_factor | Orientation Factor (0-1) | 0.9 |
How It Works
Solar Irradiance and Energy Collection
Solar irradiance is the power of sunlight per unit area. Peak sun hours convert variable sunlight into an equivalent number of hours at 1,000 W/m².
Formula
Daily Energy (kWh/m²) = Peak Sun Hours x Orientation Factor
Total Daily Energy = Daily Energy x Panel Area
Peak sun hours vary by location: 3-4 in northern climates, 5-6 in temperate zones, and 6-8 in sunny regions.
Worked Example
A 20 m² array in a location with 5 peak sun hours and 90% orientation factor.
- 01Effective irradiance = 5 x 0.9 = 4.5 kWh/m²/day
- 02Daily energy = 4.5 x 20 = 90 kWh/day
- 03Annual energy = 90 x 365 = 32,850 kWh/year
Frequently Asked Questions
What are peak sun hours?
Peak sun hours represent the equivalent hours per day of sunlight at 1,000 W/m² intensity. Five peak sun hours means the total daily energy equals five hours of full noon sun.
How does panel angle affect irradiance?
Tilting panels to match your latitude maximizes annual energy capture. The orientation factor accounts for sub-optimal tilt or azimuth angles.
Where can I find peak sun hours for my area?
The NREL PVWatts tool and Global Solar Atlas provide location-specific solar resource data including peak sun hours.
Ready to run the numbers?
Open Solar Irradiance Calculator