While it hasn’t made it to an episode of Portlandia (yet), the City of Roses can add another specialty item it’s known for championing: the group purchasing home-solar discount program.

A program that started in Portland in 2009 with a group of motivated neighbors has been steadily spreading across the United States. In the years since its debut, similar Solarize programs have sprouted in other communities, and spinoffs, named after the original program in Portland, have set up shop across the country: In the upper corners of the U.S., you can find Solarize Washington, Massachusetts, Vermont, Connecticut and New York, with sub-Solarizes galore for cities and towns in each of those states.

The way it works is fairly simple: Solarize launches a campaign in a predefined geographic area (whether it be a neighborhood or city) encouraging homeowners to get as many of their neighbors to install solar as possible. The incentive? Contractors offer the community five different tiers of volume discount pricing, meaning that as the number of installations goes up, the price for a solar installation goes down.

How did this program expand so quickly and spawn a slew of sister campaigns both in the same state and around the nation? What has fueled its success? Where has it fallen short of expectations? In a series of posts over the next three weeks, we will take a longer look at Solarize and its history.

The first effort to obtain discounts on solar through group purchasing was spearheaded by a Portland neighborhood that had the idea to collectively purchase home solar PV systems for volume discounts. According to Linda Irvine, Alexandra Sawyer and Jennifer Grove, staff at nonprofit organization Northwest Sustainable Energy for Economic Development (SEED) and authors of the second edition of the Solarize guidebook [PDF], the Energy Trust of Oregon had developed a similar model and wanted to test it.

Aided by a wide range of community support and technical assistance from the Energy Trust, the 2009 campaign managed to install solar on 130 homes and get 300 residents on board after six months, according to the guidebook funded by the U.S. Department of Energy (DOE) and the National Renewable Energy Laboratory. Buoyed by its success, the DOE donated funds so Portland could replicate it across the city the very next year through its planning and sustainability bureau. As a result, 400 more PV systems in Portland were installed in 2010, estimated to be a 400 percent increase in PV installation compared to the year before.

Overall, from 2009 to 2011, the city’s Solarize campaigns achieved 560 home PV installations and a total installed capacity of 1.7 MW, the report said. Homeowners participating in the program received a 30 percent discount.