Hello,
We have 3x Multiplus II 48/15000 KVA 200-100, running 3 phase, OFF GRID.
We have 30 KWP solar array, with 3 DC VICTRON MPPT solar charge controllers.
We are going to ADD 24 KW solar on another connected building, with a FRONIUS 3 phase SYMO PV Grid Inverter, AC coupled to the victron.
Rrgarding the 1:1 rule, how does this apply to us?
The PV inverter must not have a PEAK output greater than 45 KW (15000x3) or no greater than 15kw?
thanks
45kW
But also note the restrictions of the 1:1 rule regarding battery capacity!
The 1:1 refers to inverter AC PV ratio. (DC mppts can be ignored the system will control them)
Basically if the inverter cant invert the same load as the AC PV (the inverter size not pv installed size) then you cant have it on the output.
Als as already commented make sure the battery can sink an overshoot or discharge to match load if the ac PV suddenly drops off suddenly.
according to victron documentation, its 1.5 KWP requires 4.8 KWH of battery of Lithium, which we have, we have more. thank you
Victron and Fronius recomend a PV array+inverter no mroe than 75-80% of the Victron inverter size. (per their advanced webinar). So in my system 3x Multiplus II 48/15000 , I should have a PV inverter with no more than peak 36 KW. So I’m thinking to go with a Fronius Symo 17.5-3-m which has peak 26kw I believe AC output. And will match up with my 22 KW of panels.
Do you have a link?
Webinar: Fronius & Victron Energy: Easy system set-up (youtube.com)
There is also a webinar from my African colleagues, that they are more experienced in off grid systems.
Advanced Webinar: AC Coupling with Fronius & Victron (AFR) (youtube.com)
No, for a 15kVa three phase (aka 45kVa) it is 940A nominal discharge on your battery bank minimum.
When we speak of battery sizing it is not storage size but the ability to provide the discharge and charge current.
No, I’m speaking about storage size as does vicrtron, which isn’t exclusive of what you’re saying (my bank has a 1040 amp nominal discharge current and higher peak)
1,5 kWp installed AC PV power requires 4.8 kWh of battery storage:
100 Ah at 48 Vdc
200 Ah at 24 Vdc
400 Ah at 12 Vdc
Each additional 1.5 kWp of AC PV will require an additional proportional 4.8 kWh increase in battery storage.
And I am speaking from experience.
Size the bank for the discharge current as per the inverter manual. If you have already fulfilled that 
Once the base is good. Size the AC PV that can be supported by the inverter system. The bank has to be able to sink overshoot production/sudden discharge without collapsing the system.
Some batteries have a 1.5 or 2C discharge so now storage size also comes into play - hence the Victron documentation - they wont have the capacity to since the kWatts