Maximum at the nominal power

Method

The ideality factor is the one at which the maximum power of the curve at standard test conditions equals the nameplate power (1). The array nominal energy is counted from the nameplate (2). The datasheet maximum-power point is not used.

The math

1. The third point
2. The array nominal energy

$$\max_{V}\ V\,I(V) = P_{nom} \quad \text{at } G_{ref},\ T_{ref} \tag{1}$$ $$P_{nom,arr} = N\,P_{nom}\,\frac{G}{G_{ref}} \tag{2}$$

where

Symbol	Meaning	Unit
$I(V)$	the module current at voltage $V$ on the fitted curve	A
$P_{nom}$	the module's nameplate power	W
$G_{ref}$	the irradiance of standard test conditions, 1000 W/m²	W/m²
$T_{ref}$	the cell temperature of standard test conditions, 25 °C	K
$P_{nom,arr}$	the array nominal power of the timestep	W
$N$	the number of modules	—
$G$	the effective irradiance	W/m²

References

1. Mermoud & Lejeune 2010, Performance assessment of a simulation model for PV modules of any available technology, 25th European Photovoltaic Solar Energy Conference

API

options.module_stc_point = pnom

Symbols follow the symbol registry.