Plugging in a car is enormously better for the planet than filling up at the pump. But how green is your power source when you plug in? That was a question UC Berkeley Ph.D. student and Sierra Club member Gavin McCormick wanted to explore when he developed WattTime, a real-time energy monitoring service that lets you know the best times to plug in a car, run the dishwasher, or do the laundry.

"This is a way to look at your carbon footprint in real time," said McCormick. "The focus isn’t peak versus off-peak hours. We’re focused on clean versus dirty energy. With utilities providing power from a variety of different sources, home and business owners have almost no way of knowing where those sources are coming from."

WattTime, which is still in beta, sends text message alerts that detail how green the electricity is at any given moment and location. In general, research shows that the cleanest energy in the Midwest and Mid-Atlantic happens during the day, "or right after you get home from work," said McCormick; the Southwest, the Rockies, and Texas  around bedtime; and the New England and West Coast states around five or six in the morning. McCormick likened WattTime to weather updates -- something that can change within an hour.