Just been reading your issues, are you running Mulitplus or Mulitplus-II, hopefully II’s as if you are could you not swap over to the s99 external transfer switch firmware and fit a 4 pole contactor. Technically you haven’t changed the topology for the solar and it’s all on AC Out of the inverters. Just an idea if you have the right inverters!
Hello @Oldrich Oldrich77. I have experienced the trouble you are having. I resorted to using Node-RED. I found that I could not utilise the available PV power (to feed back to the grid) when the battery was too close to fully charged. A combination of CCL and CVL would throttle the MPPT.
Starting with Feed-In disabled and DVCC Voltage off (zero), I charge the battery to 100%. After a few minutes of 100%, I set the DVCC Voltage to a VERY SPECIFIC VALUE, in my case 53.7 V, and enable Feed-In. That Voltage value has the battery SOC sitting beween 97 and 98%. You will have to find your own. Above 98% SOC the PV throttling starts. Also, when Grid Feed-In is ON, I set SolarVoltageOffset (effectively /Control/EffectiveChargeVoltage) to 0.6 Volts in order to maximise Feed-In power. Grid Feed-In usually raises SolarVoltageOffset by 0.4 Volts as part of ESS functionality, so now it is a full 1.0 Volts.
That last adjustment, of setting SolarVoltageOffset to 0.6 V, is the first thing you should try, it might just be enough on its own. But its unlikely. I reckon your battery BMS is calling the shots aggressively, like my case. So sit at 97-98% SOC and you’ll be cruising.
I suppose the problem with starting with SolarVoltageOffset is that you need something like Node-RED to implement it. So before starting down this path, first slide your DVCC Voltage down very slowly (0.1V steps) to see if your PV power increases to a stable value. Give it a few minutes because the initial response is a tiny battery discharge.
Thank you Nick, Matt and Biff for your suggestions and for sharing your experiences.
Unfortunately, moving the Fronius from AC-IN to AC-OUT is not an option in my case because the system is registered under a government-approved feed-in scheme and receives a Green Bonus subsidy. The AC-coupled topology therefore cannot be changed.
I also prefer to keep the system operating according to the battery manufacturer’s recommended settings and would rather not use custom Node-RED logic to hold the battery at a lower SOC or modify charging voltage behaviour.
What I find interesting is that several users seem to have observed similar behaviour with ESS, AC-IN coupled Fronius PV and DC-coupled Victron MPPT when the battery is near full charge.
Thank you again for your time and help. I will continue monitoring the system and collecting data when the issue occurs.