There’s a lot of surface area on top of a trailer, just saying.
You can't effectively power any vehicle with 15% efficient solar panels.
It's fairly likely one could get well below that mass using some of the more experimental solar panel designs (such as those in use for solar aircraft), but it would probably not be cost-efficient .
[1] https://en.wikipedia.org/wiki/Solar_Impulse#Solar_Impulse_2_...
Trains might be closer but when single locomotives are measured in megawatts I'm not very confident.