The generator could be…
The generator could be powered by renewable fuel, such as renewable natural gas or propane. Both fuels currently have a carbon intensity lower than hydrogen, and are available today.
With a noise attenuated enclosure such a generator would be quiet too.
At the Advanced Clean Transportation show later this year, all the EV trucks in the demo area will be charged by level 3 propane fueled generator sets. With grid capacity at breaking point, this approach is essential and established.