question

AC input types are basically static (Input 1 should either always be a generator or always be a grid). The best way to do this wouldbe to use a Quattro as it designed for two AC inputs and use with both grid and generator.

You can get away with this in a MP II but will probably end up having to do the changes manually every time you swictch from grid to gen (not ideal).

Good question Ross. Theoretically the MPII should see the gen output as grid (after the initial grid fail depending on ATS delay) and sync accordingly, then keep doing whatever ESS it’s setup to do. But in reality it depends on the generator. If it’s a high end full inverter 9kVA Full Sine Wave then all would be normal. But… if it’s a cheap Chinese Industrial grade genset, then it’s output would be a dirty square wave that swings between 48-52 hertz with voltage bouncing around. This output would rejected by the MPII as “week AC” and treated as a continued failed grid / LOM event and the MPII would just remain in anti-island mode. The only way around this is to disable "LOM" detection in the Grid Code VE_Config. Type "B" LOM Detection should still work fine with a decent stable generator. The perfect solution is to install a Quattro and therefore have a dedicated Generator AC Input AND a Grid AC Input.....

I have written an enhancement for adding an automatic transfer switch ahead of a Multi:

https://github.com/kwindrem/ExtTransferSwitch

This uses a digital input to tell the GX device if the incoming power is grid/shore or generator. The GX device then changes the input type from grid/shore to generator and sets the AC input current limit to appropriate values.

I can not speak to what happens with ESS feed-in when on generator. Does an input type of Generator disable feed-in? If not, additional work would be needed in ExtTtransferSwitch and I'd need help from someone who understands ESS to make sure power is not fed back to the generator.