The world installed about 117 gigawatts (peak) of solar PV last year . If the average panel is 17% efficient that's more than 680 million square meters of panels being manufactured per year. World motor vehicle production in 2018 was 96 million . To put more solar panels on vehicles than we already put in fields and on rooftops, the average vehicle would need more than 7 square meters of surface covered with panels. That's neglecting that most vehicles are still internal combustion vehicles that couldn't do much with the electricity those panels would generate.
Yeah, it's the old square-cube law in action.