The reason solar on your car doesn't make sense is because the extra weight will end up costing you more energy than it brings. You simply don't get enough area

The reason solar on your car doesn't make sense is because the extra weight will end up costing you more energy than it brings. You simply don't get enough area on a car for the charge generated to be in any way significant. The extra couple of kgs won't use much extra energy to lug around either, but unless you drive very very little, it's likely to be a net loss in the end. Even ignoring any risk of theft, it's not worth it.