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abdallah-salamah avatar image

Combining AC coupling and DC coupling off grid system

Are there rules to combine Fronius inverter ( AC coupling ) with Solar charger ( DC coupling ) other than rule 1.1 in the ac coupling side ?

offgrid
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2 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @Abdallah Salamah,

The main rule is the one you have already mentioned, a 1:1 maximum to Fronius AC PV and Victron Inverter Charger Power rating.

There are not any hard additional limits with the inclusion of DC PV with a Victron MPPT. However good system design does still apply.

The system should have some consideration of balance for supplying sufficient current from the battery to the inverter to run the loads (without presuming there is any PV to assist).

The batteries should be reasonably sized to absorb the expected DC current that is generally available. Being aware in the total system design that the realistic yield from the PV will be diminished/limited if the batteries are unable to absorb all the charge current that is available.

With both of those considered, combining AC and DC PV in off grid is superior in almost every way, providing additional inverter capacity for daytime loads, reducing the heat load on the DC battery inverter to run AC loads. If used properly, gaining maximum efficiency from the system by the superior conversion efficiency of high string voltage DC PV to a 240V AC sinewave to run loads.

Combined with the greater efficiency of DC MPPT's to charge DC batteries for night time use.

Victron DC MPPTs will also wake the system up from a low battery voltage shut down condition that would otherwise prevent the inverter from starting up, and is normally required for the AC PV to synchronise to the waveform before it will begin production.

So in an off grid environment is CLEARLY superior to AC PV alone. Which would otherwise require a generator start to recover from a flat battery.

The relevant documentation is here:

https://www.victronenergy.com/live/ac_coupling:start https://www.victronenergy.com/live/ac_coupling:fronius https://www.victronenergy.com/live/assistants:pv-inverter-support

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Thank you sir
another question, what is the hub which will be used ?

Please follow the community guidelines about one question per post.

Hello @Guy Stewart (Victron Community Manager),

I would like to know how much DC coupling to apply in an AC off grid system for a well balanced system.

Does the amount of power to be installed on the DC side in an off-grid AC system depend on the capacity of the batteries? If so, what should be the power on the DC side, to avoid the batteries being flat? If there is a generator, is it necessary to add a DC coupling, or would it be interesting to start the generator automatically in case of low batteries?

Thank you

jmarc avatar image
jmarc answered ·

Q: In the case of an offgrid AC coupled system, Is the system smart enough to regognize when their is unused power coming from the AC connected panels and use this excess to charge the Quattro battery? Or is the Charger mode only available if there is power on the AC-IN.

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The system is smart enough and will take excess AC PV and charge the batteries. Once the batteries are full the system will frequency shift to ramp down the AC-PV inverter as once the batteries are full the power can't be used.