Water Wind to Harness Tidal Energy

A research group at Brown is working on a solution to gather tidal energy in shallow water, where the ebb and flow move fastest and the energy potential is highest.

Led by Shreyas Mandre, assistant professor of engineering, the group is developing a hydrofoil — a water wing — as a means to harvest tidal energy. And unlike other tidal energy technologies, the wing is a shallow water specialist.

With support from the Advanced Research Projects Agency-Energy (ARPA-E), the group has designed a small prototype which has been testing in the lab to prove the concept. Late last month, they presented their preliminary results at the ARPA-E Energy Innovation Summit in Washington, D.C., and at The Bicameral Task Force on Climate Change, organized by Sen. Sheldon Whitehouse (D-R.I.) and Rep. Henry Waxman (D-Calif.).

“We were very encouraged by the response we received,” Mandre said. “We’re looking forward to getting to work on the next phase of the project.”

A hydrofoil device catches the energy of tidal flows in much the same way that an airplane wing catches air. In the design Mandre and his team are developing, a wing is attached to a central pole on which it moves up and down. At the bottom of the stroke, the wing is oriented in a way that causes the water to push it upward. At the top of the stroke, the orientation pushes the wing back down. The up and down motion is used to power a generator.

Mandre and his colleagues have been testing their design using a small prototype about 16 inches wide. In a water flow created in the lab, they have shown that their device gathers power as much as two to four times more efficiently than existing hydrokinetic systems. And those data come from the relatively slow flow speeds achievable in the lab. The team expects their efficiency to increase in faster flows outside the lab.

And that’s the next step in the project — taking it outside the lab.

“We’re confident about how our lab results will scale with size,” Mandre said. “The next step is to demonstrate that with a larger device in a tidal test site.”

The group has arranged a partnership with a testing facility near Little Bay in New Hampshire. They’re now seeking federal funding and industry partnerships to build their new prototype and push the project forward.

“For a project like this to succeed, people with many different skills have to come together and cooperate,” Mandre said. “Attracting such a talent is our goal in the immediate future.”

Ultimately, the group hopes the device can play a role in harvesting the estimated 440 terawatt-hours per year of tidal power there for the taking in the United States. One terawatt-hour per year of electricity is enough to power 85,000 homes, so tidal power could make a substantial contribution to the U.S. power supply.

Press release, March 20, 2014; Image: brown