Understanding grid power limitation

[alich90]

Hello!

I am having difficulties understanding how the grid limitation at injection point option works, and in which way it affects the inverter output. I have two models that are exactly the same except for the grid limitation.

Scenario 1: No grid limitation

Scenario 2: grid limitation that is higher than the sum of the rated power of the inverters. Hence it should technically not affect the output of the inverters. The grid limitation is applied at the injection point.

In the losses diagram however, the "Inverter Loss over nominal inv. power" in scenario 2 is 0.5% lower than in scenario 1. The "Unused energy (grid limitation)" is 0.0%.

How is having a grid limitation that should cause no effect making the inverters have a better output?

Thank you!

[Lazare Fesnien]

Hi,

The limitation itself will always be managed by the inverter as a clipping. By default, it will be accounted for in the simulation results as an inverter overload loss.

You can change this behavior by checking the box "Account as separate loss". In this case, the part of the inverter clipping that comes from the injection limitation, will appear as a separate loss, right before the grid injection.

The inverter overload losses will not contain this contribution any more, and the power at the inverter output will be increased by this amount.

This does not correspond exactly to the physical behavior of the system, which will always clip at the inverter, but it is meant to show explicitly the part of the clipping losses due to the injection limitation.

Please read : https://www.pvsyst.com/help/grid_power_limitation.htm?zoom_highlightsub=grid+limitation

[MNWild]

Let's say I wanted obtain a more accurate value for actual inverter setpoints in 8760(closer to reality):

1st: Would I have to run PVsyst once with default(non-separated) grid limitation setting to get cleaner* 8760 of inverter output set points.

2nd: Then run PVsyst 2nd time: selecting the grid limit setting to "account as separate loss". Then Pull this separated clipping "loss" from 8760.

3rd step: Would I subtract the 2nd step's "separated clipping loss" in 8760 from the 1st step's Inverter Output 8760? Is there a method to avoid two models?

*I deduced above because you stated the default grid limit settings(non-separated) 8760 will contain clipping "losses" inside "overload loss" 8760 field...But that 8760 field "overload loss" contains other losses. So a user can't simply subtract "Overload Loss" 8760 from the inverter output 8760 field to obtain inverter set-point closer to real world?

Note: I forget the sign convention off top of my head for these 8760 fields, but let's assume everything is positive: clipping losses and inverter output. Example so when I say subtracting I mean: 121MWinverter output - 20mw Clip will get us to 101MW inverter set point.

[Bruno Wittmer]

If you choose "account as separate loss" for the grid limitation clipping, the simulation itself will not change.

Apart from some possible small rounding errors, you should get exactly the same results for the generated energy.

The only difference is that the inverter power clipping losses, which were found in the simulation variable IL_Pmax, are now split in two variables: IL_Pmax and EGrdLim.

IL_Pmax is the amount of clipping due to the power limitation of the inverter, while EGrdLim is the additional clipping imposed by the grid injection power limitation.