Exelon's John Rowe has been planning for expensive carbon for a decade. Now it's time to push for the payoff. On a cold December Chicago afternoon John Rowe stands at a window in his office, a dim, quiet, three-room suite lined with history books and sprinkled with objets d'art, including a stone horse from the Tang Dynasty and an Egyptian sarcophagus. From his 54th floor perch he is looking north to the high-rises of the Gold Coast below and the frigid waters of Lake Michigan shimmering with weak, fading winter light beyond. "You can't sit up here in the afternoon...