Drop at the MPP current

Method

The voltage lost in the DC cables is computed once per timestep, at the array's maximum-power current, and kept for every operating point of that timestep. At a voltage $U$ at the inverter terminals, the array delivers the current its curve gives at $U + R_w I_{mpp}$. When the inverter stops and no current flows, the reported terminal voltage is the open-circuit voltage less the same drop.

The math

1. Voltage at the modules
2. Current at the operating point

$$U_{mod} = U + R_w\,I_{mpp} \tag{1}$$ $$I = I_{curve}(U_{mod}) \tag{2}$$

where

Symbol	Meaning	Unit
$U_{mod}$	the voltage at the modules	V
$U$	the voltage at the inverter terminals	V
$R_w$	the resistance of the DC cables between the modules and the inverter	Ω
$I_{mpp}$	the array's maximum-power current of the timestep	A
$I$	the array current at the operating point	A
$I_{curve}(V)$	the current the array delivers at voltage $V$ at the modules, from its current-voltage curve	A

References

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

API

inverter.dc_drop_reference = mpp_current

Symbols follow the symbol registry.