But you have to consider that you're going to have vehicles driving on it, like all the time, as well as the fact that solar panels generate a lot less energy when laid flat on the ground, versus at a fixed angle or, better yet, one that changes throughout the day to maximize exposure.

Even if the rubber from the tires didn't scratch whatever is covering the solar panels, anything harder than the glass covering that gets caught in the treads will, not to mention skid marks and what-have-you. Every time it gets scratched or smudged, the efficiency decreases further.

Yes, the pylons are expensive, but the amount of efficiency measures you give up and maintenance costs you takeon make it not worth it.