Residential solar energy systems are, in most cases, installed in a distributed fashion atop the roofs of single-family homes. But what happens if your roof is no good for solar? Or you live in a multi-tenant building, which often posses challenges relating to roof access and ownership.

An alternative has emerged in recent years that enables groups of residents to band together to purchase and install a solar power system in a single, communal location. Commonly referred to as a solar garden or a solar community, the approach enables individuals to reap the benefits of solar power — namely lower electricity bills — without hosting the system on site.

It can be a difficult feat to pull off, however. If you’re trying to start a solar movement within your community but are stuck at the starting line, caught between deciding who to talk to and which roofs are suitable for solar, there’s a new guide that can help you get your solar revolution off the ground.

Called “A Guide to Community Solar: Utility,Private and Non-profit Development,” it was developed by a group called Northwest Sustainable Energy for Economic Development (SEED) — a non-profit organization dedicated to building a framework for clean and affordable energy systems throughout the Northwest. The guide is meant to answer many questions about building a community solar operation, which means many members of a single community own or receive energy from a single energy system.

The newly released guide also includes a set of best practices developed by the Interstate Renewable Energy Council. Dubbed the Model Community Renewables Program Rules, IREC’s documentation offers: examples of community solar projects from around the United States; a template that states and utilities can use to encourage community solar; and guidelines as far as taxes and other financial issues that come along with such a system.

One state in which we’ve already seen a community solar project in is Colorado, where in June 2010 Governor Bill Ritter signed the Community Solar Gardens Act into law. The act allows residents of 10 or more to each own a share of a solar energy system and get refunds on their utility bill. And just a few weeks ago, the Eagle County Board of County Commissioners amended Colorado’s ECO-Build Rebate Program to allow community-owned solar projects to apply for the rebate.

In 2008, the National Renewable Energy Lab (NREL) found that only about a quarter of all roofs are good for solar. The rest are off limits because of structural, shading or ownership issues. So a community-based model may open up the possibility for many more people.

But it doesn’t come without drawbacks. One is that you have to find a proper location for the communally owned system, where as a rooftop typically has a single owner and offers existing infrastructure. Moreover, most solar rebate programs do not include a provision to community solar projects. So unless bands of community members are willing to fully pay for the system — which is unlikely — more amendments similar to the one made to Colorado’s ECO-Build program will have to be made around the country in order for the community model to really catch on.