Now that the BYD battery is here, I finished the automatic switchover box. It physically disconnects the house from the grid and instructs the inverter to start in island mode. Upon grid availability again, the inverter monitors its stability and switches back to grid-tie mode.
First time building such a distribution box, I realize the wiring is far from perfect. Tested it under 14kW load while monitoring with an IR camera for heating/loose connections. Works perfectly 🙂