Night consumption

What this step does

The inverter draws a small standby power on every timestep in which it does not produce. The row takes it from the inverter output. It is zero when the transformer night disconnect is on (Losses tab).

The math

1. Running total
2. Loss at a timestep

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000\,P_{DC}}\sum_i L_i \tag{1}$$ $$L_i = N_{inv}\,P_{nt} \quad (\text{the inverter does not produce}) \tag{2}$$

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
$N_{inv}$	the number of inverters	—
$P_{nt}$	the night consumption of one inverter	W

Reading the number

A loss, negative: a few hundredths of a percent on utility and rooftop systems alike. A higher standby draw and longer nights make it larger.

References

1. King, Gonzalez, Galbraith & Boyson 2007, Performance Model for Grid-Connected Photovoltaic Inverters, Sandia report SAND2007-5036

API

loss.inv_night

Symbols follow the symbol registry.