I’d like to extend my current setup (primary setup) with a second battery storage system and additional PV system (secondary setup). Both would be located in/on a garage and coupled by 3phase AC only. Is this setup basically possible and how to adjust the Multiplus so the power gets distributed accordingly? Since the PV system on the garage faces more to the south/east, production between primary/secondary varies during the day.
I simplified the drawing and ignored all fuses and GX devices for now. If this is not possible at all, is there any Victron DC/DC converter so I can connect both batteries in parallel. Due to the different chemistries (NCA / LiFePO) the OCV differs and the benefit of the NCA battery is negligible when they are hard wired in parallel.
Main question is why do you want to do it this way, instead of either just extending the battery connected to the main system, and if needed expanding the inverter power by paralleling another set of inverters? (I see that the batteries are of different voltages - so that is one reason)
However, yes it is technically possible to do what you want, BUT the main inverters must be of greater power than the secondary inverters, plus any Ac sources on the load bus (not shown in your drawing), to obey the 1:1 power rule.
Using 3 x 5kW inverters for the main pack and 3x3kW inverters for the secondary system does obey this rule, BUT is likely to have some stability issues, as the inverter powers are not that different. Separate control systems will also be needed. It would be better to have the main inverter pack at least twice the capacity of the secondary inverter system. Controlling the systems will also take careful (control) planing to avoid shunting power between the 2 battery packs.
Thanks for your advice. The primary battery is roughly 27 kWh, while the secondary would be about 21 kWh depending on the usable voltage window. There are no further sources, dispite the grid.
The 1:1 rule is valid for all PV systems but it is not necessary for the AC right? The passthrough current is up to 35 Amps for the MP-II 3000 as far as I know. This is more than enough as my main fuses are 35 Amps only. Normally, our consumption is higher since we have EV and heatpump. Does it make any difference to use AC IN or AC OUT1 on the secondary system?
Do you know any useful DC/DC converter to combine both battery systems directly?
I would extend the primary battery or replace by a new stack of 3-4 15kWh batteries. One 15kWh battery costs around 1,600 EUR.
For the additional al PV I would use a Fronius PV-inverter.
Pro:
It saves you a lot of headaches combining the two system.
No need to get approval from grid provider as only DC is changed.
If needed, you can expand your 3p MP2 5K to an 3p 2x MP2.
Higher system efficiency as AC PV can be used directly without conversion loss by manageable loads, e.g. EV, heat pump, water heating element, air condition.
