Naïvely, "more panels == more electricity". But since we haven't run out of efficient places to put panels, that means any put in ridiculous places (on top of cars; under sidewalks etc) are not a good use of panels.

Panels must be positioned to face the sun, must be unobscured, must be in daylight during prime hours to make it worthwhile. Car roofs are often none of those things.

You want car parks turned into solar stations? Then mount them in the car park over the cars, angled at the sun permanently. Its a simple change, cheaper, and works many many times better. And gets crap off your car making it lighter and reducing drag.