here is a scaleable microgrid isolation device that fundamentally is a directional contactor to install at the service entrance. the idea is to have some battery and be able to defeat utility curtailment of your solar production, yet you can suck as much grid power as you want.
Yes, that's how most battery backup capable inverters work, they need a seperate box.
The Fronius one is nice in that for partial backup it doesn't need any external box, it's all built in.
If I have this correct, the Fronius Primo GEN24 will:
a) Give me battery backup for regular use during the night, scaleable as needed with the modular BYD battery solution.
b) If the power fails it will give me an automtic backup on an isolated power point, up to 3kW of power.
c) Will continue to operate independently during power failure to provide grid isolated solar+battery->power point during the day, and Battery-Powerpoint during the night. It will even work without a battery system during the day.
d) Optional full house backup if I install extra boxes on the grid side.
This means that durign power failure my 5kW enphase system is useless, and only my old 3kW+new install will work, but that's more enough for emergencies. With 3kW max it can even charge my EV.