But the average American drives less than 40 miles per day (33 is the current estimate). The relative charge doesn't matter, because what this suggests is that most Americans would be able to go most days without spending any effort or money at all on charging.

You're forgetting america loves its covered parking

America also loves reserving vast swathes of the road for on-street parking, as well as endless fields of parking lots, not to mention that an enormous number of homeowners would rather park in their driveway and use their garage for storage.

I'm not trying to say solar roofs on cars make sense as a default option, but focusing on "percentage of battery charged" is the wrong metric. Most Americans would get by just fine on a relatively modest amount of charge per day, especially if we got over our range anxiety of insisting on massively oversized batteries for the average EV, which drastically increases weight and decreases efficiency.

It's interesting how much people expect an EV battery to be at 100% charged at all times but have you met the sort of person that tries to keep an ICE vehicle 100% fueled at all times? (It's costly and wasteful and a logistics nightmare, before also getting into questions of how dangerous it can be.)

Double an ioniq 5's miles per kw/h to 8m/kWh, use the maximum possible insolation (1kw/m^2) and theoretical PV efficiency (70%, reality is 30% btw) and you get... 8kw/h@12hrs a day generated and 3.75kwh needed. about double what this impossibly optimistic calculation gives. Half all the inputs and double the consumption and you get a quarter of the power needed.

10% of the battery per day, which would cover all of my driving other than the rare long road trip. I have plenty of weekends where I drive 200 miles, but then the battery would recharge over the week when I drive less than 40 miles a day