The math really isn't that different from "should I install solar on my house". Although I live (and own rental properties) in an area with lots of sunshine, we also have relatively inexpensive electricity, about 15% cheaper than the US national average. Every time I look into solar, the answer is the same: it will take longer for it to pay off for me than the lifetime of the components. The only places around here where solar pays off is where the grid isn't already available, in which case the cost of solar installation often dwarfs the cost of extending the grid.

Even once solar makes sense for the house I live in, its a tougher sell in a rental: If I were to do install solar on a rental, there's the added complexity of "how do I charge the tenant for electricity?". I could not charge them, but have higher rent. But it takes a pretty sophisticated tenant to properly account for the value there, so that would make the units appear less price competitive than they actually are. I could install a meter and charge them the same way as a power company does. But does that make me a power company? Are there a bunch of new rules I would have to follow? What do I do if someone doesn't pay the bill? I'm sure I could figure it all out, but it makes the investment less attractive, which means the price of solar relative to buying from the grid has to be even better before I would go down that route.

(edited for typos)