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Andy avatar image
Andy asked

2-phase Multiplus with AC coupled solar and high feed-in tariff. Will this work?

Hello everyone. I need your help with a tricky set up. I contacted the Victron Dealer in Brisbane but wasn't convinced he actually understood the requirements of my setup. His reply was, it can't be done...

So here are the questions to the professionals out there:

Here is my situation at the moment. 3-phase supply plus PEN are coming in to the meter box at the garage. There was a 3-phase pump installed from the meter box (not any more) and the meter box has also a couple of fuses and M.E.N. link for the pump and the garage load itself. An earth rod is installed.

From this meter box at the garage, only 2 phases plus the PEN are going to the house which is ca. 50m away. Inside the house, there is another sub panel installed with RCD, breakers and 2nd M.E.N. link just for the house. Also a 2nd earth rod is next to the house.

grid-connection-house.jpg

Q1: Can I install 2 Multiplus II 48/5000 in the garage (one on each phase) and run the house from it with the existing cables (L2, L3, PEN)? See graphic below.
32kWh LiFePO4 batteries will be charged from DC through MPPTs only from the garage.

Q2: The AC-coupled solar on the house should not charge the batteries at all and only feed back into the grid (very high feed-in tariff of 54.2c/kWh). I would run the house from the grid during the day with the AC coupled solar providing power to the house and feed its excess energy back to the grid through the Multi. Due to the feed-in contract, I cannot try and maximise the feed-in power during the day (and therefore achieve a higher payout). Both Multis would be turned off or on bypass during the day, so connect L2 and L3 directly to the grid. Energy can then flow both ways without having the Multis doing anything. Again, I'm not allowed to change that. If the sun goes down, I would disconnect the grid and run the house solely from the battery as the AC coupled solar form the house would not produce any power any more.

grid-connection-2x-multiplus.jpgBest scenario would be to stay connected to the grid even after sunset and the Multis powering the house and keeping the meter at 0W import. If more power is needed than they will produce (unlikely), the grid provides the remaining power.

So, is this achievable at all in any way? I'm not sure because of the PEN connection from the meter box to the house. It's not a Neutral as such.

Thanks for all your input and ideas in advance...

Cheers,
Andy

Multiplus-II
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2 Answers
wkirby avatar image
wkirby answered ·

Hi Andy.

Two MultiPlus' can be configured 120° / 240° apart, but all MultiPlus' forming a group need to be the same. With your house PV on only one phase, this MultiPlus needs to be able to accommodate the 1:1 rule even if you don't intend to convert the house PV to DC. So then the second MultiPlus needs to be the same model even if it does not have any AC PV on its phase.

Taken from the ESS manual: https://www.victronenergy.com/media/pg/Energy_Storage_System/en/configuration.html
My initial thoughts are along these lines, set charge power to zero:

1629116377629.png

Those are my thoughts. I have not tried this, but hopefully someone else would chime in with their ideas.
How does this affect your contract from the sense that it is a "software" setting that is not allowing house PV to charge the battery for example?


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Andy avatar image
Andy answered ·

Thanks @WKirby, that's great feedback. I have planned to have both Multis as 48/5000, so they will be the same and also follow the 1.0 rule (or 1:1).

The limited charging settings is a good tip and should solve this problem too until the contract runs out in 2028.

The contract only says, I cannot run any loads from alternative power sources (gen, battery) as long as the solar receiving the high feed in tariff is running. People have tried that and used generators to run their house during the day to maximize the feed-in power and payment of their solar. However this is allowed after sunset, blackouts or if I turn of the house PV. Technically, I can charge the batteries from the house PV but financially it does not make sense as long as the contract is in place.

Do you see any problems with the PEN been the only connection from the Multis to the house? We don't have a separate PE running...

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