Inverter Loss due to voltage threshold

What this step does

The row measures the array energy lost when the array's maximum-power voltage falls below the bottom of the inverter's MPPT window, which happens with short strings in hot weather. The inverter holds the array at the bottom of the window, or stops when the array cannot reach it. The voltage at the inverter terminals is the module voltage less the drop in the DC cables, so long cables can push an array below the window. Three Model tab steps shape the row: MPPT minimum sets the operating point below the window, MPPT minimum loss row decides which of these timesteps count here rather than in Inverter Loss over nominal inv. power, and DC drop reference sets whether the cable drop uses the maximum-power current or the current at the operating point.

The math

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000\,P_{DC}}\sum_i L_i \tag{1}$$

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

Reading the number

A loss, negative. Zero for strings sized inside the window, on utility and rooftop systems alike; short strings on hot timesteps make it large.

API

loss.inv_vmppt_min

Symbols follow the symbol registry.