Sono Motors [1] have plastered solar cells on the car body and claim that they could be able to cover 30 km of travel per day with them. Though even 10 km would be pretty helpful in a city, which is what your calculation implies (~4-5 m^2 usable surface area -> 10-15 km of additional distance).
Once you get past the various brand names they've applied to their technology (just go to the FAQ page), this is essentially a self-charging car, which is really cool.
Looks really interesting, specially for european cities I think.
But It's a pretty expensive deal, €16k for a car without the batteries (+€4k for them).
[1] https://sonomotors.com/