National Geographic: Deep in the dark of the Minnesota night, some appliance was kicking on to rob Ed Kohler of hard-earned cash. He’d look later and see nighttime energy spikes reported by PowerMeter, Google software that monitors home electrical use. “All the lights were out, but something’s cycling,” said the 36-year-old Kohler, marketing manager at a Minneapolis web-development firm. “So I think about it and, aha, figure out it’s the refrigerator.” A 19-year-old refrigerator, a real energy hog …