Hey all, I work for a non-profit that handles energy efficiency and solar projects. I'd recommend to always keep in mind 'Reduce, then Produce'. I get into the attics of many multifamily buildings and see tons of issues, with insulation being the obvious need for improvement. Many, if not all, states have Weatherization Assistant Programs (WAP) that can help for free if you rent to low-income or seniors.
We haven't really dealt with too many multifamily properties going solar, as Virginia is not a very solar-friendly state, but we have had many approach us with the idea of going solar. As @Angel Dejesus has mentioned, the easiest way for a multifamily property to begin going solar is to install an array that will power the common electric usage, or if the entire property is master metered. It gets too complicated when it is sub-metered, as a solar system typically can only be attached to one meter in order to gain the advantages of Net Metering.
As solar prices have plummeted over that past 5 years, payback periods have become much shorter - especially as a business since you can depreciate the system (+30% Federal Tax Credit which reduces after 2019). A great resource for incentives is DSIRE.org.
Also, there are some low-income solar state programs out there as well (again nothing in Virginia - yet) that may be able to install solar for free on low-income properties.
Anyone else have solar on their rentals? I'd love to hear how you have the deal.