Underwater wind turbines — it’s an idea so simple you wish you’d patented it. Actually, they’re called tidal turbines, and their rotors are propelled by tidal currents instead of wind. The largest test of this new type of power production is under way in New York City’s East River, with six 35-kilowatt turbines scheduled to be installed by mid-March in a channel that’s off-limits to large vessels. As the 16-ft.-dia. rotors spin, as close as 6 ft. to the water’s surface, they’ll provide power to a supermarket and a parking garage. Once the test wraps up in June 2008, Virginia-based Verdant Power hopes to add hundreds more turbines, potentially reaching a total capacity of as much as 10 megawatts — enough to power 4000 homes. The test should answer real-world questions, such as whether the rotors will become encumbered by barnacles. But with researchers estimating that our rivers and estuaries could provide up to 130,000 gigawatt-hours per year — about half the yearly production of the country’s dams — it’s only a matter of time before major energy utilities begin testing the waters.