> Even if I assumed maximum malice, how are these inverters going to perform a coordinated attack on the grid?

They’re network-connected and remotely controllable. The concern is compromise of the vendor/cloud infrastructure allowing large numbers of inverters to be manipulated simultaneously.

Or even Trojan horse style malware is a possibility I suppose (Stuxnet).

That’s basically the threat model that they are using. If people want to argue with that, then that’s something to poke at