I²R on the MPP current

Method

The design loss fraction at standard conditions is turned into a wiring resistance at the array's standard-condition operating point. At every timestep the loss is that resistance times the square of the array current at its maximum-power point, scaled by the current factor of the flat derates.

The math

$$L_i = R_w\,(i_f\,I_{mpp,i})^2,\qquad R_w = f_w\,\frac{V_{mp,array}}{I_{mp,array}}\Big|_{STC} \tag{1}$$

where

Symbol	Meaning	Unit
$L_i$	the wiring loss at timestep $i$	W
$R_w$	the DC wiring resistance	Ω
$i_f$	the current factor of the flat derates: the square root of the product of the quality, light-induced degradation, light-soaking and mismatch factors	—
$I_{mpp,i}$	the array current at maximum power at timestep $i$	A
$f_w$	the design loss fraction at standard conditions	—
$V_{mp,array}, I_{mp,array}$	the array voltage and current at maximum power under standard conditions	V and A

References

1. Analysis of PVsyst 8.1.5 outputs shows this convention in its results.

API

dc_losses.ohmic_model = ohmic_i2r

Symbols follow the symbol registry.