A New Twist on Hydropower

Continued from page 1

Harnessing the current: An artist's rendition of how a commercial VIVACE system might look. Passive bars, positioned horizontally, are boxed together in a single unit that could be placed at the bottom of a river or in the path of an ocean current. Dozens of 500-kilowatt units could be grouped together in different configurations to create multimegawatt systems. Credit: Vortex Hydro Energy

"It fits into the environment: if it's a canal, we can adjust to the canal, and if it's open water, we can make it bigger," he explains, adding that the slow movement of the cylinders makes the system safer for fish.

Peter Fiske, vice president of research and development at PAX Scientific, an engineering firm that specializes in fluid dynamics, says that conventional water turbine technologies suffer from the "Cuisinart effect": they chop up fish. "The good thing about the VIVACE design is that it's just rocking back and forth, and doesn't involve chopping through the water," says Fiske.

He commends Bernitsas for tackling the study of nonsteady state fluids, an area of engineering that's often avoided, but he questions whether VIVACE can be meaningfully scaled up outside the lab. "Getting many, many megawatts of electricity out of it is another thing altogether," Fiske says.

Some aren't so sure that the system can tap enough energy to make it worthwhile. "Will it work? Probably. Is it the most effective means? I don't think so," says professor Frank Fish, an expert in hydrodynamics at West Chester University of Pennsylvania. "Most of the energy of the flow is moving from the front of the cylinder to the back, rather than in this fluid-induced vibration."

But Bernitsas, who founded a company called Vortex Hydro Energy to commercialize his invention, is convinced that VIVACE can be refined to a point at which it can generate electricity at 5.5 cents per kilowatt-hour for projects 10 megawatts or larger in size. This would make VIVACE competitive with fossil fuel and nuclear generation. Modules would be manufactured in 500-kilowatt units.

Bernitsas says that there's plenty of room to improve the efficiency of the system, and he plans to do this by learning from fish and from the way their tails and scales can affect hydrodynamics. Scales, depending on how rough they are and where they're located, can amplify oscillation. "And based on the properties of the tail," he says, "we can change both the amplitude and frequency of the cylinder oscillation to make it more benign to the surrounding environment."

The first two prototypes are being built with help from the Naval Facilities Engineering Command, in Washington, DC, and with funding from the U.S. Department of Energy and the Office of Naval Research.