I have two solar inverters connect to the "critical loads" output (AC-OUT1) of the MultiPlus-II in an off grid situation. This means the MultiPlus-II is disconnected from the grid, i.e. nothing connected on AC-IN1.
The inverter of the MultiPlus-II is providing a stable 50 Hz 230V grid on AC-OUT1 so the solar inverters are seeing a grid (provided by the MultiPlus-II) and are powering on. They "monitor" the grid for about 30 seconds like usual and then they should switch to producing energy and feeding it back into the grid. At this point however, both the solar inverters display a similar error message.
Zac-Bfr at <some value> Ohm
According to https://my.sma-service.com/s/article/Blink-code-3-dZac-Bfr-dZac-Srr-Zac-Bfr-Zac-Srr?language=en_US, this indicates that the impedance of the grid (provided by the MultiPlus-II) is too high.
The solar inverters then shut down (or re-initiate), monitor the grid for some time and end up display the same Zac-Bfr message with a slightly different impedance value in Ohm.
I have tried connecting only solar inverter 1 or only solar inverter 2 to the MultiPlus-II but the result remains the same Zac-Bfr message.
Why don't my solar inverters "like" (the impedance of) the MultiPlus-II grid and what can I possibly do about it?