What technology generates the current has nothing to do with whether or the GPs concerns are valid. It's all about transportation, not just generation.
Do the math. It will not work. Sunlight in full sun with the sun at 90 degrees relative to the panels, in winter (cool panels) will give you about 200 watts / square meter of surface of electricity at the exit of the inverter.
You'll need a little bit less grid, definitely not a lot. Those buildings are typically multi-layer and don't have a roof over the top layer (though not always) so it's not a trivial modification either. You could design that in from day 1 of course and it will help a little bit but that's borderline making money rather than a significant reduction in infrastructure.
Say your carpark is 100 meters long and 30 meters wide, that will house 50x4x4 = 800 cars to charge but you're collecting (on a good day) no more than 100x30x200 = 600 KW. It's not nothing, but if you take into account that a single normal car charger is already 3 KW to charge a full park of such cars would require 2.4 MW. And that's the slowest rate of charge for those cars, go faster and the requirements shoot up. Best case with only 4 decks of cars you're looking at a 25% reduction. Worst case not more than 10%. Good but not great.
The grid is definitely going to see some structural modifications before we can push the equivalent of our current gasoline consumption through it.
