Generator time is a negative entry on the balance book, always. There is also immensurable cost of noise of fumes - to me this is more important than the ability to run 120V devices.
If this is a mobile installation like a canopy on a scooter it will take longer than 10 years to return the investment, because of shading at some times. To maximize the output, he could make the panel removable with 15-20 ft extension so that it would stay in sun when the scooter is parked in shade. I wouldn't bother with solar at all, unless charging is needed outdoors, away from 120V sources.
