It’s very easy to screw up distilation. If the temperture is not carefully controlled and you miss the points to discard the head and tails, you end up with lighter (like methanol) and heavier (like propanol or butanol) alcohols, all of them much more toxic than good old ethanol.
Even on ideal conditions (close to the Equator, no clouds) like in Northeast Brazil, you only get 5.5 to 6.0 kWh/m^2 of Solar energy, which means the roof of a small car, with 1 m^2 of solar panels, would only generate that amount of electricity if they were 100% efficient. That’s just 10% of the battery capacity of a small EV, like a BYD Dolphin.
My point is, even if solar panels doubled their efficiency, they would still only capture about half the energy of the Sun (currently, the best panels are at 24% efficiency), which means only about 2.5 to 3.0 kWh per day.