I have seen many establishments having a backup electric supply using a Diesel Generator Set (AC / 3 phase). e.g. Something like in the Photo Below. What happens if the connected load grows beyond the capacity of a single generator? e.g. The unit in the photo is rated for 200 kVA. Suppose the load requirement grows can a second similar unit be bought and connected in parallel? Or do they have to scrap the 200 kVA unit and buy a new (say) 400 kVA unit? If paralleling AC generators what kind of circuitry is needed?