If you're making your diesel from CO2 pulled from the air, pollution aspects don't really apply (at least, CO2 emission issues don't, there's still NOx, but that's what cat piss is for).

Problem is, converting atmospheric CO2 back into fuel makes the efficiency issue drastically worse. Maybe with enough solar panels and windmills, and use the Fischer–Tropsch process with the excess energy that the grid isn't consuming.

Of course, that would be for mobile fuel, if solar plants were going to do anything like that for later use generating electricity during peaks, making diesel is dumb; you'd want to use hydrogen or ammonia for in-place energy storage.