One model of solar roofed electric car on the market recharges ~20 miles per day with the roof.
I wish they’d share the specs, but some back of the envelope math suggests you could get about the equivalent of a Level 1 charger from panels on the roof of a normal sized car. That lines up pretty well with your ~20 miles per day number with a typical EV.
This experiment is able to get about 500 miles of range from a single day of sunlight.
Obviously they made some serious usability (and aesthetic) compromises to get that - but most likely the biggest difference is just the weight of the batteries. This car has small batteries which means it doesn’t need massively power motors to accelerate up to speed.
For what it’s worth, my electric bicycle gets about 50 miles from a tiny battery. The solar panels on this car could theoretically charge my bike battery in ten minutes. Electric cars really are inefficient - you’re paying a massive price to be able to comfortably transport a family around, though obviously that’s worth it if you can afford to.
I’m not sure that it does. All the articles I can find word it as something like “has a range of 710 kilometers (441 miles) on a sunny day.”, without actually explaining it. I’m assuming that’s going from 100% charge to 0% charge, plus all the range gained by charging during the day.
They don’t actually say anywhere I can find how quickly it charges.
Also, looking up some other articles about it, apparently there’s a bunch of extra fold-out solar panels in the trunk
If you wanted maximum range, you’d start before dawn, drive most of your battery away, park somewhere all day to use that solar awning for all its worth, then continue driving at dusk.
