Plane orientation irradiance POA

Many users measure irradiance with a solarimeter in the plane of array (POA). In PVsyst simulations, this corresponds to the GlobInc value (or GIPMeas, "Global in Plane Measured" when importing a custom weather file).

When importing measured data, if you lack horizontal irradiance measurements, you can use POA measurements. In this case, you must define the solarimeter's orientation.

Note: in tracking systems, the solarimeter can also be fixed to the tracker's axis. PVsyst can use this data as long as the tracking strategy matches PVsyst's tracking mode. However, be aware that if the solarimeter is within the tracker array, it will be shaded by neighboring trackers, particularly affecting the diffuse and albedo components.

For simulations, PVsyst recalculates horizontal global and diffuse irradiation values that would produce the measured tilted-plane irradiation (reverse transposition). The Hay model is recommended for the retro-transposition (and imposed since PVsyst 8.1.0).

During data analysis and simulation comparisons, PVsyst uses only global horizontal irradiance as the starting point. This is necessary because optical processing (shadings, IAM, etc.) requires beam, diffuse, and albedo components.

The calculated GlobHor values can potentially be used for other plane orientations, provided the orientations are not too different. However, these values cannot be entirely accurate for other orientations, as some information about irradiance is lost when transposing to different planes.

Important: because the transposition process depends on solar geometry, the time reference for data registration must be well-defined during the meteorological data import stage.