I've recently discovered that my country (Lithuania) offers solar park shares for residential customer (who mostly live in apartments). Coupled with some p2p lending that could easily convert millions of people to solar power with little of difference in monthly cost (well quick math says +50% for first 10 years, then -90% till panels decay).

Retrofitting roofs with panels seems wildly inefficient compared with using robots to plant thousands of panels few hundred miles away.

n.b. you do get slightly dicked by 'maintenance fees', but those probably gonna go down with time.