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thanar avatar image
thanar asked

GX-less Multiplus II with support from the Grid doesn't work as expected.

I just completed a Multiplus-II 5000/48 installation.

The grid is on AC-in, while all loads are on AC1-out. The MPII is connected to a DC BUS, where two SmartSolars and a bunch of LFP batteries are also connected. There is no GX device on the installation, for now.

The goal is to be able to use all available solar production (4kWp installed) and have the grid as support, for when the solar production is slim. Since there is no GX device, smart shunt, nor can-connected batteries, I have adjusted "DC input" voltages accordingly in "Inverter Settings", so as to not run down the batteries excessively.

However, it seems like this setup doesn't work exactly the way I want it to: Starting up the MPII with no AC-in works fine, however as soon as AC-in is electrified, the MPII goes into "Passthrough" mode and inverting stops, hence not using any of the solar production.

Only way I was able to make it work (kind of) the way I want, is to fiddle with the "AC Input Control" settings, in which case my loads are being fed by either the inverter, or the grid. I was aiming for true parallel feed from inverter and the grid at the same time.

I suspect that I will be able to make more adjustments if I put a GX Cerbo into the mix, but I was hoping I could set it up as originally intended without one. Is there something I miss? Some secret setting, or a jumper cable I missed somehow during installation?

Multiplus-IIESSsolargrid parallel
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shaneyake avatar image
shaneyake answered ·

You need to be running ESS and this requires a GX Device. The whole victron system is built around a GX like the Cerbo so I don't know why you wouldn't have one.

Please have a look at the Manual.
https://www.victronenergy.com/media/pg/Energy_Storage_System/en/ess-introduction---features.html

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thanar avatar image thanar commented ·

So, with no GX device, there is no way to make the system work as expected? i.e. power the loads from both inverter and the grid?

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shaneyake avatar image shaneyake thanar commented ·
There are workarounds like using Power Assist and Input current limit as you described but that is all you can do without a GX. You need a GX for what you are trying to do.


What country are you in? As ESS my require permission from your utility.

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thanar avatar image thanar shaneyake commented ·

Unfortunately, "Power Assist" and "Input current limit" work in exactly the opposite way that I need; they prioritise the grid.

I am in Greece, and feed-in is prohibited for the time being. That's why for now I decided to go with no GX unit, since I really don't need all the additional calibration offered by the ESS environment.

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shaneyake avatar image shaneyake thanar commented ·

So the problem is that grid+inverter means the inverter and grid are connected and this is why you get into problems.

You can use ignore AC which will disconnect from grid under certain conditions and reconnect once the battery is low.
You can use the Generator Assistant to set a voltage to connect and voltage to disconnect and then use the General Flag Assistant to ignore AC.

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thanar avatar image thanar shaneyake commented ·

Sorry, I don't understand what you mean by the following statement of yours: "So the problem is that grid+inverter means the inverter and grid are connected and this is why you get into problems."

Could you please elaborate?

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shaneyake avatar image shaneyake thanar commented ·

Victron inverters are hybrid inverters so when grid is present, the inverter will synchronize to the grid and inject power. It will try to balance this with the power used on the AC_OUT but it is never perfect so some power does end up going out of AC_IN. The only way to never feed-back is to disconnect the inverter from the grid when it is running, this can be done by the inverter opening it's input contactors but when those contactors are closed the AC_IN and AC_OUT are joined.

You can still use ESS if your utility is okay with small amounts of export but if they want true zero export then you can't use ESS and have to use ignore AC approach.

But I would ask the installers in the area what they are doing.

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