It seems inefficient to not put solar panels over a parking lot. I'm not sure how shade is a major consideration here or how light weight solar panels are a large expense compared to the cost of space in a city. Parking garages are often net negatives to cities and parking lots are generally major negatives to cities since they drive density down and reduce foot traffic (which reduces economic churn). At least this way the city gets another small use out of that area in the form of some local electricity generation. Density and variety of use are major factors in urban health.