[Retric]

People are actually doing this right now due to terrible power distribution networks.

If you work out power needs, you can do AC with rooftop solar up to ~5 story buildings. Building past that point need real infrastructure. But, getting water and sewage is much harder to get working in a city that size than power.

A larger issue is solar has a relatively large upfront cost which is prohibitive in poor areas and ripe for theft.

The low end for AC is probably a 1kW system which can keep ~1,000+sf reasonably cool and runs some lights for well under 3,000$* in materials and the solar should last around 15-25 years. Costs will go up if you have a lot of people or equipment in that space, excess humidity, or want large temperature changes but this is just a baseline. Wiring up for more apartments is fairly simple, but your going to run out of roof for tall buildings.

*Costs without battery storage or grid tie in are far lower.

PS: Most people would want more than just AC and very low power lights. But, costs actually drop per watt as you scale, and installation does not take much in the way of training.

[hx87]

You can also put panels on walls as long as they have adequate solar exposure.

[Retric]

Near the equator you’re going to get minimal power that way, but further north or south you can get a fair amount of power on one side of a building assuming you’re not shaded by other tall structures. Street level in Manhattan for example gets less sunlight than you might think. You also run into a tradeoff with windows.