MV line ohmic loss

What this step does

The resistive loss of the medium-voltage line from the transformers to the substation or the injection point. It is computed once for the system, on the sum of the inverter outputs or, with the Cascade reference, on the power leaving the MV transformers, and grows with the square of that power.

The math

1. Running total
2. Loss at a timestep

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000\,P_{DC}}\sum_i L_i \tag{1}$$ $$L_i = \frac{f_{MVL}}{N_{inv}\,P_{ref}\,\text{PF}^2}\,P_{c,i}^2 \tag{2}$$

where

Symbol	Meaning	Unit
$E_{before}$	the running total of the loss diagram before this row	kWh/kWp
$E_{after}$	the running total after this row	kWh/kWp
$E_{row}$	the row taken as a loss	kWh/kWp
$\Delta t$	the length of one timestep	hours
$P_{DC}$	the DC nameplate of the system	kWp
$L_i$	the power lost at timestep $i$ over the whole system	W
$f_{MVL}$	the MV line loss at the reference power and unit power factor, as a fraction of the reference power	—
$N_{inv}$	the number of inverters	—
$P_{ref}$	the AC power reference of one inverter: its AC nameplate, or its share of the array's STC reference power, the DC nameplate reduced by the module and string mismatch derates (the Model tab's AC power reference step sets which)	W
$\text{PF}$	the power factor	—
$P_{c,i}$	the power the loss is computed on: the sum of the inverter outputs; when the Model tab's AC resistive reference step is set to Cascade, the power leaving the MV transformers	W

Reading the number

A loss, negative. A few tenths of a percent for a long line on a large system; zero on a rooftop system. The line length and conductor cross-section set it.

API

loss.mv_line

Symbols follow the symbol registry.