The real reason you don’t see parking lot solar a lot is that it’s far more expensive than just slapping some panels up in an empty field. For parking covering, the structures supporting the panels are taller, so they need to be more robust. You also have to worry about increased maintenance. Someone is going to ram a support pillar a truck once in awhile. There are far fewer people driving through empty fields. And whether to repair damage or simply to clean the panels off, there are advantages to open fields. Instead of having your panels scattered across a hundred small parking lots, they’re all in one spot. Much easier to arrange maintenance and cleaning. Not only do you save the drive, but bigger facilities can invest in cheaper solutions like panel cleaning robots.

The parking lot structures have the advantage of not taking up any additional land. But the construction and operation costs are sufficiently magnified that just building panels in an empty field is more cost competitive. Hell, if nothing else, panels in remote farm fields are maintained by rural labor, which tends to be cheaper than labor in expensive cities.