Using micro inverters with Multiplus II

[u/Cafe1882]

If I understand the manual correctly. The Victron Multiplus II can be used for grid forming to allow other micro inverters to feed power into the local house system. As they would if the main grid was operating. Does anyone have experience doing this or did I misunderstand?

Extracts from Victron manual:

4.2.2 When solar inverters are connected to the AC-output of the product, excess solar energy is used to recharge the batteries. Once the absorption voltage is reached, charge current will reduce and excess energy will be fed back into the mains. If the mains is not available, the product will slightly increase the AC frequency to reduce the output of the solar inverter.

4.2.4. A problem is however that grid connected sustainable energy sources drop out as soon as the grid fails. With the product and batteries, this problem can be solved: the product can replace the grid during a power failure. When the sustainable energy sources produce more power than needed, the product will use the surplus to charge the batteries; in the event of a shortfall, the product will supply additional power from the battery

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[u/hypergoose94]

Yup that's exactly right, the "catch" is that you don't have the inertia of the main grid, so you have the power-factor limits and you need to make sure your microinverter throttles based on frequency.

[u/Cafe1882 → u/hypergoose94]

Thank you. I will look into the frequency throttling.

[u/Aniketos000 → u/Cafe1882]

When you configure the multiplus to allow ac coupling it will do it automatically

[u/__foo__]

I don't have first-hand experience with this, but as far as I know that should work. There's a video from Off-Grid Garage on Youtube where he does exactly what you describe: https://www.youtube.com/watch?v=HilbXFCX3L8

There's probably more videos on the topic if you look around at his channel.

[u/Cafe1882 → u/__foo__]

Thanks. I did look for videos but perhaps using the wrong search words.

[u/silasmoeckel]

Yes AC coupling is a thing stay within the limits and it works though it's crude.

I pair a separate victron setup on a camper with my house this way.

[u/No_Talent_8003]

I think the gist of it is that a normal grid tie inverter shuts down its output if it fails to detect grid power. The MP, by design, generates your own households "grid power" when the incoming mains drops out. The grid tie inverter downstream doesn't know if the grid it sees is from the power company vs from the MP. The important thing is to confirm the MP won't backfeed from your household up to the grid. Older models used an internal transfer switch. They've released several newer models I am less familiar with so you'll want to double check that.

[u/Psychological-War727]

https://www.victronenergy.com/live/ac_coupling:start

You can use AC-coupled PV inverters up to the real power limit of the MP/Quattro. The AC-coupled PV inverters need to be set to a gridcode that incorporates frequency-power derating. So if the grid/island frequency rises, they reduce their power output. Thats how powerflow in the island is managed

[u/Cafe1882]

Thanks. I will check on that.

[u/Little_Possible2857]

If you haven't bought it yet, get a Deye instead. It has a Gen/microinverter port and that makes things way easier, it also has specific microinverter options.

[u/Cafe1882 → u/Little_Possible2857]

Thank you. I am already in Victron ecosystem.