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:  

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:       

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: