The truth is it’s a marketing gimmick when you do see it. The roof area of a car is not nearly enough to do any meaningful amount of charging, and without being able to aim the panels, you’re getting oblique sun at best which is very poor efficiency to boot. The whole idea is frankly not worth the weight penalty and complexity of doing it.
Electric car batteries are huge capacity-wise, and car roof solar panels are tiny charging-wise. You need a house-roof-sized area to do the job.
