Multiplus II ac out 1:1 rule

Q&A and troubleshooting
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1

Hello everyone!

I have a medium sized multiplus setup, for a smaller farm. Consisting of 3xMultiplus 15000, and 8x17kwh LiFePo4 batteries. As far as solar goes, we are talking about a huawei sun2000 50ktl, so a 50kw solar inverter. Currently the huawei is connected straight to grid, but i want to connect it to the ac out side. Huawei is prepared for frequency derating.

My question is, how strict is the 1:1 rule, and what could go wrong by crossing this limit? The huawei can be limited to 45kw max production, but is this going to be necessary? Is the 1:1rule that strict? I do have a 22kw smart controlled boiler heater and 10 000L boiler set up for export, that comes on as soon as i start exporting, and its a modulated setup, not just an on/off switch.

The multi 15k is supposed to be 15 000va, but the charger is 200A max. At 51.2v that would mean 30720W. I presume, the excess over 30kw, is going to be exported. Now since i have my siemens boiler setup, on the ac out of the multi, as soon as i start exporting(go over 30kw solar) my boiler heaters kick on.

I was thinking that i should limit the huaweis solar production to 45kwp thus, not exceeding the 45kva of the three multiplus. Then i remembered, this inverter is rated at 100A max transfer capacity. So i started thinking, and realised, maybe 10% overcurrent is not going to be a problem, because of my siemens boiler system instantly catching any exported power, before it gets exported. Currently the system is running with the huawei on the grid side, and i have never seen more than 30kw of “export”, since some power is always consumed.

If in case my batteries go full, and my 10k liters boiler also gets up to temp(which i doubt, its been installed for years, and i have never seen the siemens reach max tmp) what do you think could go wrong? Some say i will get dc ripple alarm, others say nothing, will happen, others say the multiplus’s gonna go up in flames(x doubt).

What would you guys do? Limit the huawei or not?

Thank you all for your response!

2

The 1:1 rule is there for stability reasons. It is mentioned and in more than one place so it definitely an important detail.
(And you can damaged the inverters.)

Is your power room also climate/temperature controlled?
I can tell you from experience charging from ac pv on the output (when offgird) makes the system hot, it will derate.

Limit the pv inverter if you must use it.

You are talking of export which means you are grid connected there for the frequency shifting will not work.

3

What do you mean, frequency shifting will not work if i am grid connected? If my multis AC in, is grid connected, why wouldnt the frequency shift work on its AC OUT? I might be missing something, but as far as i understand, this is the whole point of AC coupled microgrid. Otherwise as soon as grid is disconnected, solar charging stops, as grid connected inverters have to shut off, ass soon as the grid goes down. My power room is perfectly climate controlled yes:)
thanks for your reply!

Gergo

4

I do understand now, since it is grid tied it is synced to the grid, so it will not frequency shift, because its grid tied. Can the excess solar pass through my multi, from ACout to ACin? So in case i lose the grid, then it would work in freq derating mode? So that my grid tied inverter actually has a microgrid in case the Grid fails?

5

Yes. That is why it synchronises to the grid.

Correct. If programmed correctly.

6

Thank you for your replies. After the system is set up, and everything works, i will report back the results. I will try and set up the huawei so that it responds quick to freq derating, so that hopefully, my 50kw solar, and 45kva multiplus will not cause a stability issue. Ive seen this done before on a much smaller scale. Otherwise im gonna have to limit the Sun2000 to 45kw max continuous…I was thinking about a NodeRed solution. As soon as grid fails, cerbo gx, can send a command through modbus, so that the huawei limits its maximum output power to 44-45kw(on top of freq derating). I will have to try and set this up.