From the eastern edge of Roosevelt Island, the past and perhaps the future of New York power are on display. Just south of the Roosevelt Island Bridge to Queens rise the smokestacks of KeySpan’s giant Ravenswood electricity generating station, a behemoth that runs on natural gas and fuel oil. North of the bridge, black cables snake out of the churning surface of the East River. They connect a makeshift control room inside an old shipping container on the island to a battery of futuristic mechanisms that could shape an energy future that does not pollute or use foreign oil —...