Ebb and Flow Energy

High-Tech Plans to Generate Undersea Electricity

Say anything, but don’t accuse Jared Blumenfeld of thinking small. The director of San Francisco’s Department of the Environment has been staring at the Golden Gate Bridge a lot lately, wondering how the picture-postcard scene would look if he tucked a huge electric power plant beneath it.

If done right, the Golden Gate vista wouldn’t change—the generator would be hidden hundreds of feet underwater at the mouth of San Francisco Bay. Blumenfeld is working furiously to install a prototype that taps power from the twice-daily tide currents. His hope is that in a decade the city will produce more energy than it consumes, all of it pollution-free.

Though not quite ready for prime time, tide energy technologies have advanced rapidly in the last five years. Entrepreneurs say recent wind-turbine innovations translate easily to undersea arrays. The most promising work comes from Canada, Australia, Norway and Britain, where governments want to incubate the relatively obscure new field.

"If you had asked about ocean energy two years ago, everyone would have said it was a dead horse," says Ann Marie Harmony, president of Practical Ocean Energy Management Systems, a nonprofit in San Diego. "Now it is seen as an immature industry."

The U.S. Department of Energy has taken a wait-and-see approach. It has funded just one ocean-energy project, which is stalled over money issues. A Maryland-based mom-and-pop company called Underwater Electric Kite has built a 40-foot-wide twin-turbine generator that floats under the surface, anchored to the seabed. It will be deployed in the Gulf Stream, 11 miles off the Florida coast, but the 120-kilowatt system also works in tidal basins and rivers.

The largest tide generator, built in La Rance, France in 1966, produces 240 megawatts. But engineers had to build a big dam, inundating wetlands. New systems are more environmentally friendly, relying on natural tidal current in bays and inlets.

Most literally look like underwater windmills. One resembles a revolving door. Another uses complex hydraulics and flapping fins that suggests a stingray.

Though few have produced any hard numbers, some companies claim they can be cost-competitive with natural-gas-fired plants. "These technologies are further along than most people realize," Blumenfeld says.

San Francisco is eyeing a technology that uses the force of water moving through fins to suck air down through tubes, which drives turbines on land. The company, HydroVenturi, says its system is cheaper to maintain, with no moving blades underwater. That also means less blunt trauma for marine life.

Garold Sommers, a Bechtel employee and senior advisor to the federal Department of Energy’s hydropower program in Idaho, said several new tide-energy ideas have come across his desk in the last month. "The technology works," Sommers says. "Whether it’s viable or not as an alternate energy source, it’s worth looking at." The federal government killed its ocean-energy office in 1994, but is now contemplating bringing it back.