Day and night draw

Method

The auxiliary draw of a timestep has up to three parts. The constant day draw applies while the inverters together deliver more than the threshold. A draw proportional to their output is added whenever they deliver power. The night draw applies on a timestep with the sun below the horizon throughout. The draw is subtracted from the system's power after the transmission and other losses, so on a night timestep the grid energy is negative. During a shutdown period the day and proportional parts are zero.

The math

$$A_{aux} = A_{day}\,[P_{inv,sum} > P_{thr,aux}] + \frac{a_{aux}}{1000}\,\max(P_{inv,sum},\ 0) + A_{night}\,[\text{night}] \tag{1}$$

where

Symbol	Meaning	Unit
$A_{aux}$	the auxiliary draw of the timestep	W
$A_{day}$	the constant day draw	W
$[P_{inv,sum} > P_{thr,aux}]$	1 when the inverters deliver more than the threshold, else 0	—
$P_{inv,sum}$	the sum of the inverter outputs	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
$[\text{night}]$	1 when the sun stays below the horizon for the whole timestep, else 0	—

References

1. PVsyst 8 help, Auxiliaries consumption

API

ac_losses.use_auxiliaries = true

Symbols follow the symbol registry.