To make the math more complicated, you could theoretically have an unfoldable solar roof. Say you have cute, tiny one-person car with trunkspace for two bags of groceries, call that 1/9 the footprint of a "normal" car, and give it an expanding roof that can fill up a typical parking space. So you get to multiply the numbers by 9, which would mean a 10-minute drive to the neighborhood grocery store would require 60/9 roughly 7 minute charging? That's getting really close to useable, so we must have cheated a little too much with some of the "simple" math. Also probably the unfoldable solar panel ideal really just doesn't work for some reason that's extremely obvious to engineers.
I doubt that it will go mainstream, since you can only unfold it when the car is at rest. And it's permanently like having a loaded roof-rack for aerodynamics and weight. You'd always be asking - why not get put the panels on the roof of a house or other fixed structure? Easier and you can add even more of them.
