You're not going to use glass panels in your roads. You're far more likely to use printed spools of flexible cells and cover them with a translucent, pourable protective layer. Some form of epoxy, or a concrete impregnated with optical fibers, perhaps? The efficiency per unit area will be horribly low, but when multiplied by the area of the whole road, you still end up with a lot of power.

You will lose some area to potholes. That's just another reason not to use the expensive, glass-covered cells.