Illegal as in a fine? going to jail?Most grid-tied hybrid inverters here are higher voltage DC, in the 400 V range. 48 V is uncommon.
You are far more restricted with battery choices as they need communications to operate, so often these systems are set to operate with only one, maybe two battery models. And what happens is those battery modules go out of production making expansion later problematic.
An example of grid-tied HV DC is a Fronius Gen24 Plus inverter + BYD batteries.
Even then you need to decide which type of battery module to go with, and you can't mix and match. It's very solid stuff, premium prices.
BYD Battery-Box Premium HVS/HVM
www.fronius.com
Examples of higher voltage battery systems sold here:
BYD
Tesla Powerwall
LG Chem Resu
Sungrow
Goodwe
Huawei
AlphaESS
Enphase
Sungrow
SolarEdge
and about a dozen others.
Here higher voltage DC batteries are the norm and none of it is DIY (not legal here).
I'm curious how illegal diy is down under