The amount of charge you would get from a solar panel on the roof would be negligable. It would take days or weeks with good weather to get enough charge to get to the next charging station. And the weight of the solar panels and charger would reduce your overall milage.

Some years ago before electric vehicles became as common Nissan was pushed into this on their Leaf. They did the math and had worked out that it would not work but eventually gave in to public pressure. However they mounted a smaller solar panel and would only charge the 12V service battery, not the main battery. This did make some sense as it allowed them to stay parked for weeks and months without running out of charge on the service battery.