Looking back, Swarthmore's leaders are a tad foggy on how the borough came to far outpace other communities in the use of alternative energy.
Maybe it stemmed from the borough's long history of environmental activism. Or the nature of a town founded by Quakers that is host to a celebrated liberal-arts college.
In any event, Swarthmore has achieved a level of green that most towns would envy. In the last year, more than a quarter of the energy needed to power its homes, buildings, and schools - 27.9 percent - came from renewable sources.
That was enough to rank the borough third in the nation in an Environmental Protection Agency competition among communities vying to buy the largest percentage of green power.
"Wow. That's an incredible number," said Jonathan Edwards, vice president of SmartPower, a national nonprofit marketing firm that promotes renewable energy.
"There is no question that Swarthmore is a poster child for that region in terms of all they do with clean energy."
Blaine Collison, director of the EPA's Green Power Partnership, which sponsored the challenge, said, "Every time I look at Swarthmore, I think, 'We want more of that.' "
Those involved acknowledge that Swarthmore's well-educated and relatively wealthy residents might be an easy sell on clean power. Census data show that 77.2 percent of Swarthmore adults have a bachelor's degree or higher. More than half the households have incomes that exceed $100,000.
Then again, Phil Coleman, an energy analyst at the Department of Energy's Lawrence Berkeley National Research Lab in California (he telecommutes), recalls that in an early organizing meeting, one person challenged, "If we can't do it, who the hell can?"
The race was on.
Swarthmore has a history of environmental actions, its leaders note. It adopted recycling and banned leaf-burning long before most.
In the late 1990s, wind power wasn't on many people's radars. But it was for Thurm Brendlinger, a longtime borough resident who was a wind-power advocate with the Clean Air Council. He started making suggestions.
In 2002, Swarthmore laid claim to being the first municipality in the state to make a pure Pennsylvania-generated wind purchase.
It wasn't a lot of power - only enough to power the traffic lights - but it was a statement, Borough Manager Jane Billings said.
Somewhere along the way, Swarthmore College engineering professor Carr Everbach began calculating. Using air-pollution data, actuarial tables, and more, he concluded that the college's annual power use - in this region, coal predominates - caused one premature death every two years.
For a college with Quaker roots and a highly active student environmental group, Earthlust, that didn't sit well.
Not long after, the college began buying wind power.
"It really is a social experiment, deciding you want to do something with your energy profile," said Ralph Thayer, the college's director of maintenance.
In 2006, SmartPower came calling with a challenge. The goal was for local governments to buy 20 percent of their power from renewable sources, and for at least 200 households to do likewise.
The first 20 communities to do so would win a one-kilowatt solar array. The deadline was 2010. Swarthmore hit its mark in 2007.
Things took off when Peco Energy Co. began stuffing its monthly bills with promotional materials for its wind-power program. At one point, advocates in Swarthmore were handing out fliers that read, "It Takes a Borough . . . to Lead Our Country to Clean Energy."
The EPA launched its challenge in September 2010. For one year, it monitored participating communities' energy use and charted their green-power progress.
In addition to Swarthmore, 32 communities took the challenge - 11 from Oregon, and no others from Pennsylvania or New Jersey.
Advocates began talking to neighbors about renewable power. They held workshops. They staffed a table at the farmers' market. Quarter by quarter, they watched the numbers come in.
At one point, Swarthmore was in second place, and Billings, the borough manager, hoped to surge ahead.
But far in the lead was Brookeville, Md. Not far from Washington, it has just 90 households.
Billings jokingly cried foul. She realized it was unlikely Swarthmore would ever catch Brookeville. "But it really pumped me up to call the college and see if they would commit to more," she said.
The college did. By now, it is at 100 percent, as are the borough's offices.
Truth to tell, it was the college that really tipped the scales for the borough. But in the end, 13 percent of the green power was bought by households and businesses.
"It was not that much more expensive," said Andrew Bunting, owner of Fine Garden Creations and curator of the college's Scott Arboretum.
"We felt that this was something very little we could do," said Joshua Bush, vice president of Park Avenue Travel.
For Dave Welsh, president of the real estate firm his father founded, it was simply "a slam dunk."
The year ended weeks ago.
Swarthmore placed third.
Hillsboro - one of the Oregon towns - came in second with 35.7 percent of its power coming from green sources.
Brookeville had bought 45.7 percent green power.
The EPA's Collison acknowledges that Brookeville may be a bit of an outlier. "But they're an interesting example of what's possible. Somebody did it."
Swarthmore isn't finished.
About two years ago, advocates launched aFewSteps.org, a broader initiative to take the area's sustainability farther. The group incorporates three neighboring municipalities - Rutledge, Nether Providence, and Rose Valley.
But as far as power goes, the group is pushing for more people to switch from Peco to a provider with more renewable options, especially now that doing so doesn't have to cost any more than the status quo.
Beth Murray, who a few years ago led an informal group of Swarthmore mothers on a quest to green up their lives and homes, is starting to establish "affinity groups" of residents who can help one another reduce their power use and make other changes.
What gratified Coleman about the way the town came together in all this was "not the competitive aspect, but the unity."
Yeah, but what about Brookeville?
"I want to take on that community," Murray said with a grin. "I think we can do it."
Contact staff writer Sandy Bauers at 215-854-5147, email@example.com, or @sbauers on Twitter. Visit her blog at philly.com/greenspace.