Auxiliaries (fans, other)

What this step does

The row measures the energy the system consumes for itself, taken from the grid energy: a constant day draw while the inverters deliver more than a threshold, a draw proportional to their output, and a night draw while the sun is down.

The math

1. Running total
2. Loss at a timestep

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000\,P_{DC}}\sum_i L_i \tag{1}$$ $$L_i = A_{day}\,[P_{inv,sum,i} > P_{thr,aux}] + \frac{a_{aux}}{1000}\,\max(P_{inv,sum,i},\ 0) + A_{night}\,[\text{night}] \tag{2}$$

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
$A_{day}$	the constant day draw	W
$P_{inv,sum,i}$	the sum of the inverter outputs at timestep $i$	W
$P_{thr,aux}$	the output threshold of the day draw	W
$a_{aux}$	the draw proportional to the output	W/kW
$A_{night}$	the night draw	W
$[\,\cdot\,]$	1 when the condition holds and 0 otherwise; night is a timestep with the sun below the horizon throughout	—

Reading the number

A loss, negative. A few tenths of a percent on a utility system, more with trackers; close to zero on a rooftop system. The size of the draws relative to the system sets it.

API

loss.aux

Symbols follow the symbol registry.