Device, inspired by bats' wings, could one day be deployed to remote areas like Alaska and the Amazon

ABOARD THE ORCA — On a converted pleasure cruiser in the middle of the Taunton River, engineers at Brown University are testing a device that they are betting on to transform how the flow of water can be harnessed to produce electricity. 

Suspended below the hull of a vessel that students found on Craigslist and christened the “Orca” — an homage to the trawler in “Jaws,” quips doctoral student Michael Miller — are posts fitted with sleek wings that move up and down as the boat cruises through the choppy waters, generating a constant stream of power.

Tongue-in-cheek movie references aside, what professor Shreyas Mandre, Miller and other members of Brown’s engineering department have been working on in the waters off Somerset for the past month is very serious.

They say they believe their 1-kilowatt prototype could represent the future of tidal energy. Its flawless performance so far has them dreaming of building full-scale systems that could harvest the power of much bigger rivers in remote locations far from other energy sources, such as in Alaska or on the upper reaches of the Amazon.

“That’s where we want to take this,” says Mandre.

The design of the device has its roots in a conversation that Mandre had five years ago with Kenny Breuer, another Brown engineering professor who was researching the unique way that bats fly. Both experts in fluid mechanics, they theorized that electricity could be generated using wings that would be pushed by moving water in a reversal of how a bat uses its wings to push through the air.

Their idea won a $750,000 grant from the Advanced Research Projects Agency-Energy, a federal program that supports the development of cutting-edge energy technologies, and they used the money to design and build a carbon-fiber model that they tested exhaustively and tweaked in a water tank at Brown.

The project has moved quickly from there aided by another $3 million in funding from ARPA-E — and by a startup community in Rhode Island that is small yet tight-knit. When the researchers were ready to move out of the lab, Thorne Sparkman, managing director of the state-backed Slater Technology Fund, introduced them to BluSource Energy, a Portsmouth engineering and fabrication business run by Tom Derecktor who comes from a family of well-known boat-builders.

BluSource built the aluminum-and-steel prototype, mounted it to the Orca and cut out a section at the front of the boat to allow the device to be deployed easily into and out of the water.

The beauty of the system is in its simplicity. Building it required specialized machining, but the electric generator at its core came off the shelf.

“That’s key when we’re trying to build something for commercial production,” Miller says.

He and the other researchers took what they learned in the lab — checking everything from the best angles for the hydrofoil wings to their performance in different turbulence levels — to design a working device.

“Since we proved the concept, we’ve moved onto the second stage,” Mandre says. “What we really want to learn is if our understanding of the hydrodynamics really plays out in the field.”

On a recent afternoon, Miller steers the Orca out of the Bristol Marine shipyard on the Somerset shore and heads into the 26-foot deep channel and up the Taunton. He presses a button to lower the prototype into the river. It rotates down and under the water, extending about 10 feet below the boat like a keel.

But unlike a keel, it’s far from stationary. The two posts pivot from their base and the wings oscillate when force is applied, mimicking the movement of a two-stroke engine to create power. Viewed side-on out of the water, the posts look like legs and the wings like feet as the device dances in a sort of herky-jerky jig.

In the water, it’s much more fluid, smoothly moving along and churning out greater amounts of electricity as the boat picks up speed. When Miller accelerates to 3.3 knots, the device generates 500 watts of power.

Sitting before a laptop in the back of the boat, research engineer Jennifer Cardona records the boat’s speed, the system’s power output and other data. Everything is working as planned, Mandre says.

“It has performed exactly as we expected,” he says. “It has had no hiccups.”

Although the prototype is being tested on a moving boat, the full-scale version would stay in one place. It would hang underwater from a floating pontoon, be towed into a river, bay or other waterway and then secured to the bottom. Once in place, the wings would undulate in the tides or currents and feed power where it’s needed.

Because of the low cost of building the device, it’s suitable for waterways with slower currents, where bigger, more costly tidal power systems are not economical, says Mandre. Typical tidal systems have rotating blades like wind turbines and, in some cases, require depths of more than 100 feet.

That restriction is one reason why tidal power has yet to progress beyond the testing stage in the United States despite estimates based on a Georgia Institute of Technology study that it could supply as much as 6 percent of the nation’s electricity. Other obstacles include the corrosive effects of water and possible negative impacts on marine life.

Still, as a potential clean, renewable source of power, the tides are particularly attractive. Their ebb and flow is predictable, unlike wind and sunlight. And because water is so dense, even at slow speeds it carries a tremendous amount of energy.

The Brown team believes the optimal size for their design is a 50-kilowatt system that would measure 40 feet long by 20 feet wide. It could be placed in waters of 30 or so feet of depth and in dense configurations to optimize production in the smallest area possible.

The researchers have targeted Alaska and Brazil because many communities in those places are beyond the supply of large power plants that burn coal, natural gas or other cheap fuels. Instead, they rely on diesel generators that are dirty, expensive to operate and difficult to refuel because of the distances involved and the often harsh terrain.

“We feel that we will be able to compete with diesel in that market,” Mandre says.

Building anything overseas is still far off. The more immediate concern is funding. The federal money runs out next year and the team is hoping to find a partner in the private sector that can help it get a full-size generator off the ground.

But even getting this far has been an achievement. As he stood on a dock after finishing up the day’s tests, Mandre said he was always confident in the original idea that was sparked by bat flight.

“We had this at the back of our minds all the time,” he says.


(401) 277-7457

On Twitter: @KuffnerAlex