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sailing-pieter avatar image
sailing-pieter asked

AC coupling on a Boat with micro inverter

So I have an electric boat with a 48V LiFePo4 battery and a multiplus II 48/5000

Ideally I would place 3-4 flexible solar panel in series to create the required voltage and use a victron MPPT. However, shading of the panels will become a huge issue on my boat and also the placing&cabling is challanging.

Therefore, I dived into AC coupling and I want to use a single fixed solar panel with a micro inverter). The micro inverter I am looking at support Island mode: https://enphase.com/installers/microinverters/iq8 The article on the victron website about AC coupling states that it will not work on a boat https://www.victronenergy.com/live/drafts:off-grid_documents:choosing_dc_and_or_ac_solar

My question is, why wont it work on a boat? What is so different than a other offgrid situation?

Other questions I have are:
Does the multiplus sync to the micro inverter, or does the micro inverter syncs to the multiplus?
I have my multiplus set in AES mode to limit stand by power consumption, is that possible using Island mode?

Of course another solution is get a MPPT Boost module (which Victron does not sell). But I prefer not to, or do you think that is the way to go? I don't how that works when the multiplus charger is on and the MPPT is still delivering power.

Multiplus-IIAC PV Coupling
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rvicev avatar image rvicev commented ·

The Victron article is ¨under construction¨ and incomplete.

It doesn´t say that it won´t work on a boat, but rather ¨not suitable¨. I suppose the author(s) meant to say ¨less suitable¨ because a solar inverter = something like a Fronius - is assumed. You´re proposing to use a micro-inverter .....

When AC-(Out1)-coupled, the solar (micro-)inverter should synchronise to the MultiPlus, not the other way around .....

How well does this work with Enphase IQ8 ? Can you get away with just the IQ8 micro-inverter, or do you also need other Enphase components for configuration (IQ Gateway, etc). I haven´t got a clue because Enphase is not exactly promoting AC-coupling, but maybe sobody has tested this ?

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wkirby answered ·

When the MultiPlus is connected to shore power then the PV inverter will also be connected to shore power via the MultiPlus and feed-in would be possible. Feed-in is almost certainly not allowed at the marina.
Similarly, if the MultiPlus is charging from a generator, the the PV inverter may end up back feeding the generator, which may cause problems.
The PV Inverter synchronises to the MultiPlus.
A PV inverter would not start when the MultiPlus is in AES mode because the output would not be continuous or the modified sine wave would not be acceptable for the PV inverter.

Another MPPT (boost MPPT controller) and the MultiPlus could quite happily charge at the same time, why not? Two different charging sources would result in a quicker charge time. Just ensure that the charge profiles on each device are the same and that the maximum charge current of the two sources does not exceed the maximum charge current that the battery can accept.

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