question

nzmikec avatar image

ESS using Multiplus II and Fronius, 1-1 rule

Hi,

I currently have a Fronius primo 5kw inverter with 4kw of solar (2 arrays NW and NE) and am looking to add a victron Multiplus-II GX to provide some storage and redundancy for power outages.

I understand that with 4kw of solar and the inverter being only 3kw I will run into trouble with a grid outage if I have the solar inverter on the output of the multiplus due to the 1-1 rule.

Im wondering if there is any way to reduce the fronius down to 3kw as soon as the grid fails to make this work?

I guess any system would need to be very fast to avoid any inverter shutdown however if the solar inverter was to shut down for a short time then ramp back up slowly to a reduced output this might work?


Any thoughts are very much appreciated.

Thanks

Mike

ESSFronius
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3 Answers
Rob Duthie avatar image
Rob Duthie answered ·

Hi Mike

If the Fronius is on the input to the victron it does not matter much, as the Victron will only take what it needs to charge the battery and any surplus goes to the grid and loads etc. I have a very similar system, that has 6kw of PV and a 3kw mulitplus2 unit and 3kw Fronius and two other smaller inverters feeding in which exceeds this rule, and it quit happy and runs perfectly .

Having it on the output yes as it over powers the mulitplus2, so put it on the input to over comes the limitations. and it works just as well as a back system and grid tie.

You can power limit the Fronuis if required, why not use it full capacity to get the full benefit of a ESS system, that is what i have done, and it has put me in credit with the power retailer.

Because getting 8 cents per kWh is not much, but when you add in the battery backup and supply at night time the benefits are huge.

My Power bill sits a zero import of power and all export of power during the day, as the mulitplus2 takes care of the power flow in either direction.


Regards

Rob D

NZ

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sathr avatar image
sathr answered ·

Hi,

Before i open another question, i would install a multiplusII 5000kw with a Fronius 6.0-1 not matching the rule 1:1 exactly, will that be a big problem ??


Thanks for the help.

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nzmikec avatar image
nzmikec answered ·

Thanks Rob,

I guess Im interested in running the fronius on the output of the multiplus to allow charging while the grid is down. Powercuts are normally short in duration however it would be nice if the system could charge and remain off grid in an extended outage.

Just want to be ready for the zombie apocalypse scenario I guess :)

One thought I had was that I could move some of the solar from the fronius to an MPPT but that would require more hardware and it would feel that im limiting what I already have with the fronius.

It looks that having some MPPT DC solar is the way to go anyway so when off grid the system can recover from a low battery state.

Im also in NZ getting the 8c/kw, batteries seem like a no brainer especially when you get the benefit of a redundant power supply.

I have 7kw/h of nissan leaf cells and a Batrium BMS awaiting an inverter.

@Rob Duthie who did you use for an installer or suppler?


Cheers,

Mike

1 comment
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Hi

My self as i am a installer electrical engineer etc

Yes i have used Nissan leaf cells and standard BMS for a Chinese company i use there BMS

which to date run perfect with a Bluetooth app to monitor etc much cheaper and less clumsy than a batrium system , they are rated to 100 amps etc, and fully configurable etc.

You know you can power limit the Fronius inverter if required but waste full .

Just put the solar on the input to the Victron and, and have the correct sized battery bank to cope.

So you will need to separate you PV systems out for the MPPT an Fronius to use the full

PV and not overload the Victron from the Fronius.


Regards

Rob D