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Josep morancho avatar image
Josep morancho asked

1 to 1 rule integrating Victron and Fronius

I have an off-grid system with a 5kw multiplus II, 3kw connected to a smsrtsolar 250/70 and 2 x pylontech US5000C.

I want to add to my house a 3kw aerotermia system for HSW and cooling during the day. I want to preserve the smartsolar PV power for critical loads of the house and add a 5kw Fronius PV inverter connected to a PV string of 3kw in the AC-out line of the multiplus

I know that in off-grid systems you have to follow the 1 to 1 rule but i want to understand that this does not apply to the nominal power of the fronius inverter as this refers to the real PV power connected to the Fronius inverter.

I mean. Fronius PV power can never be higher than Multiplus nominal power but Fronius PV power can be lower than Multiplus nominal power. For instance, you can have a 5kw multiplus and a 6kw Fronius but PV power of Fronius can not be higher than 5kw. Or for instance, you can have a 5kw multiplus and a 3kw Fronius as Fronius power will always be lower than max multiplud power.

Am I correct?

Thanks


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2 Answers
lifeingalicia avatar image
lifeingalicia answered ·

Hi be aware Kw and VA are different.

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

May answer your question

Power produced has to be consumed otherwise voltage goes sky high...

It takes a moment to adjust settings (ramp up/down) to changing power demands e.g. aircon cooking etc.

During these moments power has to go somewhere or is supplied and this is the battery. Thus rule 1:1 max handling of a multi.

It is advantageous to oversize the PV power e.g. 4Kw/peak on a 3Kw inverter as one rarely hits peak performance and the inverter simply ignores anything above rated power. (simplified).

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Josep morancho avatar image Josep morancho commented ·

Thanks but it raisea another doubt to me. You say that if AC load stops, power injected by the PV inverter goes to the multiplus and the multiplus will charge the battery.

What if the battery is full and battery BMS stops charging?

I understood that if PV inverter power is not required or it is required less power, the Multiplus will use the frequency shifting feature to inform Fronius PV Inverter that power has to be reduced.

Am I correct?

I mean, with the frequency shifting feature, both inverters adapts power required based in load changes. In the worst case, if battery is full and high AC load drops suddenly, frequency shifting will act quickly to manage the situation and stop power injection to avoid high voltage increase. Right?

Thanks


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Alexandra avatar image
Alexandra answered ·

@Josep morancho

Other reasons for the 1:1

The PV inverter injects power into the load. If it were to go down (various reason for this scenario); what takes the load? The inverter of course. If the inverter cant run it it should not be on the output of the inverter.

The other is if there is grid rejection and load drop off something has to handle the power overshoot. If AC PV is overpowered you can imagine things not going well.


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Josep morancho avatar image Josep morancho commented ·

Apologies but I do not understand you when you say "If the inverter cant run it it should not be on the output of the inverter."

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