A novice. Planning first 3phase ESS with a future addition of PV.

3 x Multiplus-II 48/15000 one per phase. Between 4~8 battery banks of 48V.

Currently struggling to understand if I need an external transfer switch (ETS) if I only use one Multiplus-II per phase. Not parallel.

Any advice highly welcome?

I would hire a professional to make a complete design! please DM.