Washington Post: One March day in 2008, Ketch Ryan, a long-time environmentalist, sent a message to her neighborhood group e-mail list in the town of Chevy Chase, inviting neighbors to see the modest two-kilowatt solar-panel array she had just installed on her south-facing roof to convert sunlight into household electricity. “Loads of people came,” Ryan said. They asked questions about the process and how to do it themselves. The Common Cents Solar Co-op was born then and there, founded by Ryan and …