Run 0.2 % above the ceiling, cut back (PVsyst application)

Method

On a timestep where the array could deliver more, each inverter brings its output down to the ceiling of the Grid power limitation step raised by the overload tolerance of 0.2 % (1). The array's operating point and the inverter's efficiency loss follow that output. The AC losses after the inverters are taken on it (2). The power above the limit is then cut: at the injection point from the energy injected (3), at the inverter output from the inverter output (4). Without the separate loss the inverter output reports the output less the cut, and the cut is counted in the power-limit row, Inverter Loss over nominal inv. power. With the separate loss the inverter output reports the output without the limit, and the cut joins the Unused energy (grid limitation) row. Inside a shutdown period nothing is cut, and the inverter output is the output of (1).

The math

1. Output of each inverter
2. Losses after the inverters
3. Cut at the injection point
4. Cut at the inverter output

$$P_{inv} = (1 + k_{ol})\,P_{max} \tag{1}$$ $$L_{ac,aux} = L_{ac,aux}(N_{inv}\,P_{inv}) \tag{2}$$ $$P_{cut} = \max\!\big(0,\ N_{inv}\,P_{inv} - L_{ac,aux} - P_{grid,lim}\big) \tag{3}$$ $$P_{cut} = \max\!\big(0,\ N_{inv}\,P_{inv} - P_{grid,lim}\big) \tag{4}$$

where

Symbol	Meaning	Unit
$P_{inv}$	the output of one inverter. On a timestep the limit binds	W
$k_{ol}$	the overload tolerance on the AC limit, 0.2 %	—
$P_{max}$	the AC ceiling of one inverter. Set by the Grid power limitation step	W
$L_{ac,aux}$	the AC losses and auxiliaries after the inverters. When the inverters deliver the power in brackets together	W
$L_{ac,aux}(P)$	the AC losses and auxiliaries after the inverters. When the inverters deliver the power in brackets together	W
$N_{inv}$	the number of inverters	—
$P_{cut}$	the power cut by the limit	W
$P_{grid,lim}$	the grid power limitation as active power	W

References

1. PVsyst 8 help, Grid power limitation
2. Analysis of PVsyst 8.1.5 outputs shows this convention in its results.

API

ac_losses.grid_limit_ceiling = pvsyst_8

Symbols follow the symbol registry.