Threshold on the plane global

Method

At every timestep the global irradiance on the module plane after transposition, the sum of its direct, circumsolar, diffuse and ground-reflected parts, is compared with the threshold. When it is below the threshold, each of those parts is set to zero, and the horizon, shading, soiling and reflection steps see a dark timestep. When it is at or above the threshold, the light passes unchanged. The irradiance removed over the year forms the loss-diagram row "Global incident below threshold". A threshold of 0 W/m² removes nothing.

Settings

Setting	Value
Threshold $G_{thr}$	7 W/m² (default; input options.glob_inc_threshold_wm2)

The math

$$G_{inc} = \begin{cases} G_{trp} & G_{trp} \ge G_{thr} \\ 0 & G_{trp} < G_{thr} \end{cases} \tag{1}$$

where

Symbol	Meaning	Unit
$G_{inc}$	the global irradiance on the module plane after the threshold	W/m²
$G_{trp}$	the global irradiance on the module plane after transposition	W/m²
$G_{thr}$	the low-light threshold	W/m²

Note

The default of 7 W/m² is PVsyst 8's value. PVsyst lists it among its advanced parameters (Settings > Edit advanced parameters) as the "Global incident threshold", read from the parameter file param.dat that ships with the program; its help gives no source for the number. pvlib and PVWatts apply no threshold on the plane irradiance. In SAM's detailed photovoltaic model, the CEC and Mermoud–Lejeune module models compute no power below 1 W/m² of effective irradiance, the irradiance that reaches the cells.

References

1. Analysis of PVsyst 8.1.5 outputs shows this convention in its results.
2. PVsyst 8 help, Hidden parameters (Settings > Edit advanced parameters)
3. Dobos 2014, PVWatts Version 5 Manual, NREL/TP-6A20-62641
4. pvlib python documentation, pvlib.modelchain.ModelChain (pvlib-python.readthedocs.io/en/stable/reference/generated/pvlib.modelchain.ModelChain.html)
5. NREL System Advisor Model, SAM Simulation Core source code, module models shared/lib_cec6par.cpp and shared/lib_mlmodel.cpp (github.com/NREL/ssc)

API

options.use_glob_inc_threshold = true, options.glob_inc_threshold_wm2 = 7

Symbols follow the symbol registry.