How to measure different types of irradiation
The following table indicates which measurement instruments are necessary to measure the different types of irradiation.
GHI: Global Horizontal Irradiation
The total amount of radiation received from above by a horizontal surface. This value includes both Direct Normal Irradiation (DNI) and Diffuse Horizontal Irradiation (DHI).
Application:
- Fixed PV installations
- Comparisons with solar data bases to perform MCP (Measure Correlate Predict) evaluations
Measurement instrument:
- Pyranometer (horizontal)
- Reference cell
GTI: Global Tilted Irradiation
The total amount of direct and diffuse radiation received from above by a tilted surface. GTI is an approximate value for the energy yield calculation of fixed installed tilted PV panels.
Application:
- Fixed PV installations
Measurement instrument:
- Pyranometer tilted in the same angle as the solar module
- Reference cell
DNI: Direct Normal Irradiation
Direct Normal Irradiation is the amount of solar radiation received per unit area by a surface that is always held perpendicular (or normal) to the rays that come in a straight line form the direction of the sun at its current position in the sky.
Application:
- Concentrated Solar Power (CSP)
- Concentrated PV (CPV)
- Fixed PV installations
Measurement instrument:
- Pyrheliometer installed on a sun tracker
- Rotating Shadowband Irradiometer
DHI: Diffuse Horizontal Irradiation
Diffuse Horizontal Irradiation is the amount of radiation received per unit area by a surface (no subject to any shade or shadow) that does not arrive on a direct path from the sun, but has been scattered by molecules and particles in the atmosphere and comes equally from all directions.
Application:
- Fixed PV installations
- Redundancy calculations of GHI → GHI = DHI + DNI · cos(θ)
Measurement instrument:
- Pyranometer with shadow ball or shadow ring, installed in a sun tracker
- Rotating Shadowband Irradiometer
