Why can’t we use separate batteries for each Multiplus in a 3-phase system ? Tying them all together into one giant battery sounds to me technically not so elegant. You could argue otherwise for Software reasons maybe, but then it could just be solved. Discharging and charging -partly- in sync would not be so difficult maybe ?
Or is this possible now ?
It’s the way Victron has chosen to architect their system. Other companies can offer a single inverter that will handle three phase with a single battery bank, or multiple inverters in parallel that each have their own battery bank.
Why? If you use batteries that can communicate with each other then you can distribute the batteries across the DC buss so that you can localize currents between sources, loads, and storage without requiring huge buss bars.
Advantages of seperate batteries in my opinion:
- Less components
- Lower Amps
- Simpler installation
- Safety (because of those)
Disadvantages I see are only at islanding:
- At islanding you don’t have all batteries available for any phase, so when only 1 phase is used then, you’ll have only 1 battery. But if you only use 1 phase at islanding, you could exchange batteries between the phases when needed.
- If you want to use 3-phases at islanding load distribution must then also be carefully done.
- Software complexity maybe.
Quick question, you mention other companies that offer parallel ( also 3-phase?) with different battery banks. Can you name 1 or more ?
Less components, perhaps, in the sense you don’t need a central DC buss. I disagree with your other reasons. The one possible benefit you didn’t mention is flexibility on the AC side so all inverters don’t need to be in close proximity to each other. However, it’s just opinion. Hoymiles is one such inverter manufacturer that uses individual battery banks per inverter. Pointguard Energy (USA) or Sigenergy (rest of world) is another. Neither are better or preferred (by me) over Victron except that in the USA Victron does not provide any products that allow for grid interactivity (ESS). It’s a huge bummer!
The simple answer if there is a high load on one ohase that bank will be depleted first. Then the inverter switches off. Then the system goes down. Possibly three phase devices have problems.
With a shared bank one phase can have a high load and not charge (various reason such as peak shaving -if the loads are lower on other phases they can charge) three phase ac ov with excess can charge if it above loads.
You can have two big mppts or even one, the bank is still charged.with separate phases each bank needs components.
The idea of a shared bank has many more operational disadvantages than the one time install disadvantage.
You’re right that Victron inverters require multiple inverters in a group for multi-phase systems and require a single battery bank. Other systems have multi-phase inverters in one unit and that’s not an issue if one of the inverters in parallel fail. Neither approach is “better” than the other except for maybe the Victron ecosystem doesn’t (currently) have inverter redundancy where multi-phase inverters in parallel sometimes do. Except for the most mission-critical applications this isn’t a concern if the overall system is designed well.
The 1 phase with high load doesn’t need to be discharged only. In 3 phase systems you can discharge 3 phases in sync, for the total load on the 1 phase. Only when you have a power fail like i mentioned there can be issues. The batteries are then equally charged when that happens.
Of course , on boats or other places where you need independent power a single battery bank is needed. But where I come from, domestic, 3-phase, dynamic prices, in the NL, backup power is almost totally useless.