I have a 3 phase ESS based on Multiplus II units. On the AC out (critical loads) there are two Growatt PV inverters connected (both on a different phase). They are a bit older models that dont support the sunspec protocol. Their output is measured via two ET112 energy meter. The grid usage is metered via a 3P75CT meter. This is connected before the ESS however, so in case of a power failure this meter also stops working.
Normally all works fine, but this morning when we lost the grid connection for 2 hours, i noticed the PV inverters also stop working.
I guess this is because of the anti-islanding feature? But shouldnt they just keep working since the ESS supplies them with power?
Is there any way to have them work also when the grid connection is lost?
Yes, in general the Multiplus II will form a 50 Hz Grid that allows PV-Inverters to run. It utilizes Frequency-Shifting to raise it’s output frequency when it needs to have ACPV beeing throttled or completly shutdown. (Make sure your Growatt Inverters properly react to frequency shifting with reducing their Output Power, else you would risk overcharging your batteries and system shutdown)
The Multiplus / Battery needs to be able to absorb 100% of available ACPV at any time with no grid - thus, when the battery reaches 100% they will raise the output frequency to reduce the ACPV Production.
It’ll be restored dynamically as the need is detected, you can even configure a custom battery voltage level on which AC PV should resume Operation in the ESS-Assistant.
Also make sure to read the Factor-1 Rule for ACPV in Offgrid Systems:
I have several Hoymiles ACPV inverters at AC_out1.
One of them (HM-600) has faulty fixed grid settings. The recovery frequency is missing the decimal separator. Though after raising to 53 Hz and shutdown of Hoymiles, it does not restart. It needs to be power cycle, e.g. next night.
All other models (HMS-2000/1000) restart and adopt as soon as the frequency lowers.
Though it can be an issue with ACPV setting in VeConfigure or at the ACPV inverter.
The battery was at 70% charge at that time, so i dont think overcharging was the issue. My system respects the factor 1 rule, my PV inverters are only approx 2500w each.
Also if i look at the VRM history I dont see the frequency shifting happening. Only just before the grid came back the frequency was increased a bit. The error on the screen of the inverter seems to confirm this. It said something like no AC connection available, and started to retry after 60 secons. According to the manual there are different error messages in case of a too high frequency.
I’m running the DESS assistant, could it be that was preventing the charging? Or will it always charge on excess solar power?
DESS requires your solar-power to be visible to the GX. It will not use Grid-Values as grid turns from a “measured value” to a “controlled value” when using DESS.
So, it may happen under certain circumstances that DESS is choosing to low charge-settings.
But during a grid loss, DESS goes inactive anyway, so mostly not an issue for your observed case.
That is intendet. The Multis need to drive any ac coupled pv into a fault state before synchronizing with the grid. Else on a full battery to much acpv may cause overvoltage issues during the synchronizing process.
Are you sure you have connected the Growatts to ACOUT and not ACOUT2? ACOUT2 will be disconnected during Grid-Loss.
Sometimes people think it’s just a convenience-second-pair of terminals, but it isn’t.