He mentions that the mega chargers will all be solar powered. I don't know how this will be possible as the user base grows. The amount of energy needed for even a small fleet will be huge.
Tesla semi consumption: < 2 kWh/mi
One charge: 500 miles => < 1 MWh
There are about 2 million semi trucks in the US (tractor trailers). Assume that each semi fully charges once a day, 300 days a year.
The conversion of all of the country's semis to Tesla vehicles powered with solar generation requires under 600 TWh a year, eight times current US solar level; still only 15% of current total US electricity generation. Likely within 10 years, or sooner.
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.