Hourly Irradiance: GHI vs POA

🔹GHI – Global Horizontal Irradiance

The total solar irradiance received on a flat, horizontal surface. Includes:

• Direct beam radiation (projected onto the horizontal plane)

• Diffuse sky radiation

• Ground-reflected radiation (albedo)
  → Used as a reference for comparing site conditions.

🔹 POA – Plane of Array 

The total solar irradiance received on the tilted surface of a photovoltaic (PV) module.

It includes:

• Direct irradiance projected at the actual angle of incidence

• Diffuse sky irradiance, adjusted for the tilt and orientation

• Ground-reflected irradiance (albedo), depending on ground reflectivity and panel height

POA irradiance is directly affected by:

• Panel tilt and azimuth

• Solar geometry (sun position throughout the day/year)

• Local shading from surrounding objects or terrain

→ It is the most relevant input for assessing actual system performance and is used in PR (Performance Ratio) calculations.

🔹 In Dashboard

Depending on the site configuration:

• The site reference orientation may differ from the actual POA. In such cases, GHI (horizontal irradiance) is typically used as a standard reference across all sites to enable consistent performance comparisons. It is also used in site-level PR calculations.

• The inverter orientation corresponds to the actual POA. This irradiance is used for inverter-level PR calculations, as it reflects the real exposure of the modules.