Powered by Tides

The hydrofoil team adjusts the position of the water wing and the generator in the water. Photograph courtesy Kenny Breuer

 

Renewable energy is a key component of today’s power supply. While renewable sources like wind, solar, biomass, geothermal and hydroelectricity continue to gain importance, the search is on for more reliable, secure, automated and powerful renewable energy technologies.

Enter the water wing. Designed by a team of researchers at Brown University, Rhode Island, the water wing, also known as a hydrofoil, catches the energy harnessed in shallow tidal waters. Here, water ebbs and flows the fastest and, therefore, has high energy-generating potential.

“Marine power is reliable, predictable and has a high energy density,” says Kenny Breuer, professor of engineering at the university. “It’s a perfect complement for other renewable energy sources, such as solar and wind power.”

The team’s approach to harnessing marine power involves attaching a wing to a central pole, on which it moves up and down. At the bottom, the position of the wing causes the water to push it upward, and at the top of the pole, the orientation pushes the wing downward. This motion fuels a generator. Additionally, the wing continuously optimizes its tidal power conversion efficiency by using an onboard control software, which responds to real-time measurements. The computer algorithm monitors and controls the fine motion of the wing for maximum efficiency. This helps to constantly search for the best movement, given that tidal currents change continuously.

The inspiration for hydrofoil came from both Breuer’s and his colleague, Assistant Professor Shreyas Mandre’s work on fluid mechanics of a pitching plate, funded by a grant from the U.S. Air Force Office of Scientific Research, and Breuer’s own work on animal flight, particularly of bats. Breuer says he “was inspired by the flapping motions that bats use during flight.” Breuer and Mandre received a pilot grant for one year from the U.S. Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E). This was ultimately expanded into a three-year grant, completed in 2017, to develop the technology and build the wing prototype.

“The original grant was successful in that it demonstrated the viability of the technology,” says Breuer. “The technology is very robust and relatively low-tech. That means, it can be ideally implemented in remote areas, where wind and solar might not reach or might be difficult to install or maintain.”

The hydrofoil’s design also allays concerns about interruptions from commercial and recreational shipping traffic and harm to wildlife. Although it operates in often-busy bays and inlets, it can lie flat on the sea floor when ships need to pass. Also, its flapping fin-like motion is not as violent as that of a spinning turbine, making it less dangerous for marine animals.

Breuer and his team had the opportunity to test the technology out, with satisfying results. “When we installed our second prototype (“Joule”) in the Cape Cod Canal, there was a very exciting moment when we released the brake, and the device started up, just as we predicted, and we were generating power! To see our plans in action was a very exciting moment for all of us—faculty, staff and, particularly, our students,” says Breuer.

Following the initial success of the project, the team is now looking for funding to embark on the necessary next steps.

“We have had some informal industrial interest in the technology, but we need to demonstrate some additional aspects related to reliability and large-scale operation before companies invest. We are currently looking for funding to do those demonstrations. In the meantime, there are some small-scale experiments and computations by Professor Jennifer Franck, who was at Brown but is now on the faculty of University of Wisconsin-Madison, aimed at pushing the technology and the underlying science forward.”

This ongoing effort, once it comes to fruition, will enhance the reach and impact of clean energy, Breuer hopes. “My goal is that this technology should form an important component in a mix of sustainable energy sources in the future.”

Carrie Loewenthal Massey is a New York City-based freelance writer.

---

---