Hydrogen vs. Battery Electric Cars

Simple solution for the charging-4000-trucks-at-once problem: have backup swappable batteries. Charge the batteries with the surplus midday solar energy, and swap the batteries out when the truck gets back to base. That would also have the potential to beat the 5-minute refill time of hydrogen. 

Quick 20-30 minute supercharge stops en route can keep trucks topped up for longer routes (drivers need breaks anyway, so longer charge times there aren't an issue).