> About 80% of this commercial space is parking lots. It's wasted space. Why not use it to produce power?

You didn't get my point obviously. Parking spaces are to park on. When a car is on a parking space, it's blocking the light from tiles under it and also casting a shadow.

> Why use additional fertile or constructible terrain to add solar tiles?

Because they won't have cars park on them. They will also be at an optimal angle and cleaner.