Global Irradiance
Total solar radiation hitting a horizontal surface -- the sum of direct and diffuse radiation.
Also known as: Total Radiation, Solar Irradiation
What Is Global Irradiance?
Global irradiance is the total solar radiation that hits a horizontal surface on the Earth’s surface. It consists of two components:
- Direct radiation: Radiation coming directly from the sun
- Diffuse radiation: Radiation scattered by clouds, atmosphere, and reflections
Values for Germany
| Region | Global Irradiance (per year) |
|---|---|
| Northern Germany | approx. 950—1,050 kWh/m² |
| Central Germany | approx. 1,050—1,150 kWh/m² |
| Southern Germany | approx. 1,150—1,300 kWh/m² |
| Germany (average) | approx. 1,100 kWh/m² |
For comparison: in southern Spain, global irradiance is approximately 1,800 kWh/m²; in the Sahara, it exceeds 2,500 kWh/m².
Significance for Photovoltaics
Global irradiance is the decisive factor for the yield of a PV system. It varies depending on:
- Location (latitude)
- Season (summer vs. winter)
- Weather (cloud cover)
- Orientation and tilt of the modules
Practical Tip
For yield calculations of a PV system, site-specific radiation data is used. The EU’s free tool PVGIS provides precise global irradiance data for any location in Europe.
Related Terms
Solar Constant
Radiant power of the sun per square metre at the top of Earth's atmosphere -- approximately 1,361 W/m².
kWh (Kilowatt-Hour)
Unit of electrical energy -- one kWh equals the energy converted at a power of 1 kW over one hour.
PVGIS
Free EU online tool for calculating solar yields based on location, orientation, and tilt angle.
kWp (Kilowatt Peak)
Unit for the maximum power output of a solar module or PV system under Standard Test Conditions (STC).