Washington Post: In the house that Tim Dowd is building in Howard County, he wants to keep the monthly electricity bill as low as possible. He has done everything he can think of, installing thicker walls with more insulation and buying higher-grade windows. Early in the process, he studied wind and solar power and geothermal heating. The solar system he settled on cost $35,000. “There’s no doubt about it: It takes a lot of green to be green,” said Dowd, 31, of Woodbine, a D.C. …