Case Study: Turning the Tides into Electricity

New York City hopes to generate enough power for 8,000 homes with underwater turbines

Traditionally, New Yorkers have considered the East River—alongside pigeons and trash—an indelible part of the landscape, better off overlooked. But the city and state have partnered with Verdant Power to install a fleet of submerged turbines near Roosevelt Island, a few hundred feet east of Manhattan, that will transform the river into a valuable power source.

New York is already one of the world’s most energy-efficient cities—an average New Yorker uses about half the electricity an average San Franciscan does. Yet an anticipated influx of new residents will further strain existing energy sources, so city and state officials gave Verdant about $3 million to harness power from the river’s strong tidal currents.

Verdant’s turbines resemble their wind-farm cousins, with triple-bladed rotors that generate electricity from kinetic energy. The East River’s tides turn the rotors only about once every two seconds. But since water currents are about 1,000 times as dense as wind currents, each turbine sends up to 36 kilowatts into the Roosevelt Island grid. When all 300 planned turbines are installed—in the next decade, if all goes as planned—the underwater field will produce 10 megawatts of power, enough electricity for 8,000 homes.

But hydropower is tricky. During initial tests last summer, tides were 20 percent more powerful than anticipated, and the currents simply snapped the blades off the turbines. Verdant says it can solve the problem with reinforced turbines; the replacements should be ready for East River testing this year. The company is also in talks to install similar systems in the St. Lawrence River in Ontario and in Seattle’s Puget Sound.