In a tall building, you have more floors that house energy consumers, for the same amount of the roof space. This means that the energy captured offsets a small

In a tall building, you have more floors that house energy consumers, for the same amount of the roof space. This means that the energy captured offsets a smaller share of the electricity consumed by the building, and the complexity may not be worth it. Usually roofs of tall buildings are already crowded with radiators of HVAC systems.