Hidden Vortex is key to new Green Energy Source

A bane of Big Oil's offshore rigs could become a boon for renewable energy.

By tapping the natural motion of slow-moving water, a new hydrokinetic generator could open vast new swaths of the ocean for energy production.

When ocean currents flow over any kind of cylinder, like the long cables that hold drilling platforms in place, small vortices are created. They eventually spin away, or shed, causing vibrations that over time can destroy an oil rig's moorings.

Now, a University of Michigan engineer who long worked on suppressing this phenomenon, has developed a prototype energy-harvester that can capture the mechanical energy it creates.

"About four years ago, it dawned on me that we should enhance the vibrations and try to harness the energy," said ocean engineer Michael Bernitsas, who has founded Vortex Hydro Energy to commercialize his idea. "No one has ever thought of patenting this idea, even though vortex induced vibrations were first observed in 1504 by Leonardo da Vinci."

Energy experts consider the movement of water in oceans a vast untapped source of clean energy that could provide up to 10 percent of U.S. demand (pdf). A variety of schemes have been proposed to capture this mechanical energy, usually involving turbines to capture fast-moving water generated by tides or a strong current. But few projects have progressed beyond the science project stage. The most advanced is a Pelamis Wave Power project off the coast of Portugal, which provides a mere 2 megawatts of power.

One major problem is that most underwater turbines require the water to be moving very fast. One study suggested that hydrokinetic projects only made economic sense in currents moving at over six knots, which are highly rare. It's all the ocean's other currents, which are generally under 3 knots, that Bernitsas sees as his technology's main advantage.

"There is a huge amount of hydrokinetic energy in currents but a lot of that we cannot harness with the present technology and that's where my device comes in, to extract energy at speeds down to 1 knot," said Michael Bernitsas, who has founded Vortex Hydro Energy to commercialize his idea. "It taps into a new energy source."

That idea has attracted some name-brand backers. The National Science Foundation, the U.S. Navy, and the Department of Energy have together contributed about $2 million to Vortex to further develop the concept.

Prototypes of the device — known as Vortex Induced Vibrations Aquatic Clean Energy — are essentially round cylinders a few inches across suspended in water on a spring. The vortices generated by water flow move the cylinder up and down. The VIVACE system converts that mechanical energy into electricity via rotary or linear generators.

In the future, Bernitsas wants to create modular 50 kilowatt units, like the artist's rendering seen above. They could be strung together for larger applications into power plants producing as much as a gigawatt of power.

The engineers are working on making the basic system components more efficient, too. The cylinders of the early designs have sprouted tails, which allow them to use more of the energy in the vortices. It's an idea that the engineer has borrowed from whales, fish, tadpoles and other creatures that move in liquid, which he says all have a bluff, or not slender, body followed by a tail.

"The muscle power the fish have is not enough to support the speed at which they are going," he said. "So, if you study more carefully, there are lots of things going on. A fish will curve its body, collect a vortex, shed it, and collect one on the other side and shed that, alternating on the two sides of its body."

The design of the system allows it to take much more energy out of the water than turbine-based systems. In technical terms, the energy density of the system is higher. For example, in a three-knot current, the VIVACE gets 50 watts per cubic meter of water, while the Pelamis system, considered the world leader in ocean energy, gets 21.

The innovative nature of the idea, however, is no guarantee of commercial success.

"I think that it's at a very, very early stage of development," said Roger Bedard, an analyst at the Electric Power Research Institute in Palo Alto, California, and world expert on ocean energy.

And Bernitsas' system would be subject to the United States' regulatory process, which was designed with large hydroelectric dam projects in mind, and that has hampered all hydrokinetic energy technology development.

"You have to go through 20 to 25 different regulatory agencies in this country," Bedard said.

Governmental risk frightens potential investors. Erik Straser of the Silicon Valley-based venture capital firm Mohr Davidow Ventures, sees potential regulatory and technical issues, too.

"This seems like it would be have some issues with permitting," Straser wrote in an e-mail to Wired.com. "I think that and reliability will be the key issues to deployment and efficacy."

Bernitsas believes that his technology is much more environmentally friendly than other marine projects, so he's looking forward to working with regulators.

Still, the tide could be turning, no pun intended, for marine and hydrokinetic projects. The recent Wall Street bailout bill included tax credits for these projects, which could stir investor interest.

For now, Bernitsas isn't focused on large-scale production just yet. The first ready-to-use prototype, slated for splash down in the Detroit River, will be ready in about a year.

"We're where cars were 100 years ago," Bernitsas said. "Hopefully it won't take us 100 years to get where we need to be."

Images: 1. An artist's rendering of a future VIVACE power plant. 2. A schematic of the early VIVACE prototype. Courtesy the University of Michigan.

Video: Early proof-of-concept device generating electricity, which in turn powers the lightbulbs. Courtesy Vortex Hydro Power.

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