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taylortops avatar image
taylortops asked

AC connecting four independent off-grid systems

I was interested in @drmi 's questions about connecting two ESS systems: https://community.victronenergy.com/questions/10357/two-ess-systems-grid-parallel.html....

I'm looking at a property with 4 x independent off-grid systems, each using a Multiplus 2 and are about 500m apart from each other. I'm interested in connecting these so that the stronger systems can support the AC power delivery of the weaker ones. (One gets great morning sun, and another gets great afternoon sun.) This would classify as island grid I guess. DC Connect is not an option. It appears that the 4 x systems could be connected via their AC-In. I'm also wanting to account for one or more of the systems going offline occasionally. Each would just treat the AC input as unreliable grid. Daisy chaining AC Out to AC In of the next and so on would not really be workable.

Can this be done? If so, do I need the current sense on AC-In or do I need full metering? Do the systems need to be aware of each other via GX? I know I need to configure for ESS, but any special settings needed for feeding AC only once batts are full?

Multiplus-IIESS
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2 Answers
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Mike Dorsett answered ·

I've been living with two multiplus inverters running in parallel on a single system for a few years. I would think that with the 4 inverters you would also need to connect their VE bus ports as well as paralleling the AC side in order to maintain inverter synchronisation. However, to do this, the inverters need to be the same model and firmware state. The inverters would all try to produce equal power in this type of setup.

With trying to combine all these in an ESS format - only AC in connected, I suspect that this would not work as the inverters would be in 'grid following' mode, and you don't have a 'grid forming' system. Designating the strongest system as a master (Not in ESS mode) and then connecting the others to the AC out side of the master might work, but the grid would be weak. This would also have the advantage of allowing a generator to connect to the AC in of the master unit.


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taylortops answered ·

Some interesting ideas, thank you, especially the "grid forming". You can parallel up 6 units but this wouldn't work for this scenario as the battery banks are 500m apart from each other, too far to connect DC. It's AC coupled for sure, but how... I'm not certain. Also, there is no master since strongest depends on the time of day. But true, one system is tiny, two are middling, one is big, maybe one could operate as the lead. Helpful ideas, thank you.

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toin avatar image toin commented ·
I'm not shure if even ac is viable because verry heavy cable would be needed to keep the voltagedrop over those distances to an aceptable level


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