Actually there are some aspects that are admittedly simpler when you lay them on the ground, like for instance cleaning them with vehicles. Vertical panels next

Actually there are some aspects that are admittedly simpler when you lay them on the ground, like for instance cleaning them with vehicles. Vertical panels next to the roads would still be equally bad idea as there is a lot of chemicals and sand and air movement that would create you all kinds of problems, and plus you would have a lot more issues with vandals (or just people throwing half-empty bottles and other heavy garbage from cars), they'd obstruct the view, could be potential safety issue because of lights reflection in the night, etc.