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jeanphi500 avatar image
jeanphi500 asked

ESS with Multiplus II GX / what's the best solution: serial with everything on AC out or parallel with some parts on AC out

Hi everyone

I have ordered a Multiplus II GX 5000 and Pylontech batteries.
I'm hesitating on what configuration is best for me.I live in Belgium, have solar panels/inverters already in place and the goal is to improve my self consumption.

So far I have 2 options in mind:
- the serial one: the Multiplus sits between the grid connection and the rest of my installation, including the PV inverters
- the parallel one: the multiplus is parallel to the rest of the installation. AC in is bidirectional and is used to charge or feed based on the measurement from an external energy meter (ET112)

My grid connection allows a maximum of 50A single phase, and my panels have about 10kVA of maximal output power. Everything is excess of my own consumption is fed back to the grid and meter is counter rotating.

On paper the serial connection is really matching my needs and actually comes with free features like backup if the grid would fail. So far so good.
But when I ordered the material the technician advised me against that configuration. He seems to have a lot of experience and know what he's talking about. He told me the safest solution was to use it in a parallel fashion and connect only critical loads to the AC out.

So I'm now in front of a dilemma :-)

The 50A maximum current of the 5000 version is ok but it is exactly matching the grid connection.According to my consumption logs, last year I never exceeded 8000W of consumption. But I happened several times to feed in more than 9500W to the net. Is that ok for the Multiplus?

And what to think about the serial solution, is it safe? I mean sitting in the middle like that if the device fails chances are that I'm in the dark...

Opinions? Thanks!

ESS
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zl2fae avatar image zl2fae commented ·
Use the Victron as the "Gateway" device. Unless you can "cap" the output to 8kw on your existing Inverter you will need either three "5" Kw (really 4.5KW) Multiplus (the highest powered stackable Multiplus) or a "15" kw Quattro to maintain the 1:1 (or better) ratio. I recommend the Quattro as it allows easy future expansion when you expand your setup to allow rapid charging an EV. (Use an external GX mounted somewhere handy like the Kitchen).


My 2c worth based on the mistakes I made buying the 5Kw Multiplus.

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ponzoa answered ·

If your string inverter is equal too or less trhan 5kW, then connect the Multiplus to the grid and everything else off that. This would be an AC Coupled installation.

If your string inverter is larger than 5kW, then your can't do this. There is a 1.0 rule which states that in an ESS set up, the AC Coupled inverters must be the same (at most) or smaller than (power) that the Multiplus or Quattro.

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jeanphi500 avatar image jeanphi500 commented ·

My string inverters (I have several) rate to about 10 kVA output power. So yes it's well above 5kW.
I have to asdmit I never read about that 1.0 rule anywhere.. Why is it like that actually?
And does it then mean I can only use it in the "parallel way" I was describing. And then there I could still connect some critical loads plus string inverters that are less than 5kW then?

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Kevin Windrem answered ·
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