The "all electric" coach is probably a misnomer

What you might want to know, roof AC takes equivalent of 1 - 1.5 HP, so even with 3 of them, the 400HP + engine will never notice the load.
I am intrigued with 4 alternators though. My vintage conversion has single alternator, what I figure out is about 8,000W (it is in size of good bucket) and that alternator was build with passenger bus in mind, with lot of (incadescent) lights and gadgets.
What would make one putting 4 alternators?