It appears they didn't cover cargo transportation in the analysis. Curious if it may be worth for large trucks, over 20m long, as there is a large area available to install panels, and cargo transport is a hard to decarbonize sector. In long routes that extend east-west, I also imagine one coud try to adjust timing so the truck travels along the sun while it's day, and against it while it's night, so days in the local frame are slightly lenghtened, and nights are slightly shorter, improving light availability.
20m by 3m is 60m^2, with 300W/m^2 solar panels, it's less than 20kW.
A truck departs NY at the crack of dawn on the longest day of the year and cannonball-runs west at 100mph without hitting a single red light. The sun covers 15 degrees per hr. Denver is 30 degrees west of NY. The truck doesn't quite make it to Denver though, the sun sets on it somewhere in the middle of Nebraska. By chasing the sun, instead of 1700 miles, it gained a whole 1hr40mins of extra sunlight. That 20kW array turns that into 36kWh of extra power. By doing this chasing the sun instead of west-to-east, our truck turned a 1700 mile trip into something like 1718 miles.
On any 'typical' daily long-haul of 600 miles, we're looking at something more like an extra 3000-4000 feet. On something not as perfectly east-to-west like 900 miles NY to Atlanta, we're in the extra 100-200 feet, as long as it's not overcast.