There are many reasons why individual homeowners cannot install solar systems on their homes including shade trees, poor orientation, rental occupancy, historic district restrictions and others.
Where these difficulties exist residents are now taking a relatively new approach of joining together to build and install a single larger solar installation on a building (host site) nearby and essentially leasing roof space for an extended period of time (often 15-20 years). The property owner of the host site in return for that roof space buys cheaper electricity from the community group that has organized as a for profit limited liability corporation (LLC).
The community group realizes a moderate profit over time and is responsible not only for the original financing but also for long term maintenance. Two Maryland examples are University Park Community Solar LLC and Greenbelt Community Solar LLC.