The electric version of the Fiat 500 is already pretty heavy. 2900lbs vs 2300lbs in the gas version,
and its got a pretty big frontal area, which makes the mileage go way down at high speeds..
I don't think adding solar panels on the roof would be a good idea.
Now if they were built into the roof. That's a different story, but then they wouldn't be dirt cheap.
Have you ever seen "who killed the electric car"? Pretty interesting how decent of a car the EV-1 was but it was still scrapped. GM has had some real blunders over the years and this was one of them.