Infrastructure

Ocean Turbines Could Turn the Tide for Energy Generation

A tidal turbine has survived the infamous tides of Nova Scotia, but is the energy generated worth the trouble?

by Andrew Maykuth, Philly.com / September 5, 2017

(TNS) -- SAINT JOHN, New Brunswick — The next great hope for renewable energy is moored to a dock in this Canadian port city. It resembles a beached Ferris wheel.

Designed to capture the power of the legendary tides of the Bay of Fundy, the 52-foot-diameter Cape Sharp Tidal turbine endured the winter and spring on the seabed in Nova Scotia, generating electricity. Now in port for upgrades, the 1,100-ton machine looks as if it has survived a couple rounds with a powerful adversary.

Its paint is slightly worn. Fierce Fundy currents ripped away the metal anodes attached to the machine’s rotating rim. But the turbine survived, which is an improvement over an earlier model’s performance.

“This was the first machine that was able to generate power for that amount of time in that environment, so it was a resounding success,” said Christian Richard, director of Cape Sharp Tidal, a joint venture between Nova Scotia energy company Emera Inc. and the Irish turbine manufacturer OpenHydro.

Cape Sharp recovered the prototype from 190 feet of water in June and towed it to Saint John’s West Side Docks for modifications. It plans to redeploy the turbine this year for a new trial, along with an identical twin — taking, it hopes, another step toward the long-term goal of generating power from offshore underwater tidal farms.

Cape Sharp’s device, which can generate two megawatts of electricity, similar to a large wind turbine, is the first of several designs chosen for field tests by the Fundy Ocean Research Center for Energy (FORCE), a nonprofit supported by the Canadian government that aims to advance tidal-power generation and explore its impact on marine life. The lessons learned here could be applied around the world at places with potential for producing tidal energy, such as the mouth of Delaware Bay, off Cape May Point.

While renewable wind and solar power have become commercially competitive in recent years, the technology to unlock the vast clean-energy potential of the world’s oceans has been elusive.

Cape Sharp Tidal company has successfully deployed an experimental underwater turbine that generates electricity from the extreme tidal flows of the Bay of Fundy in Nova Scotia.

Designing a power plant that can withstand the harsh marine environment and capture in-stream tidal energy at a competitive price has proved to be a challenge.

Few places rival the Bay of Fundy’s potent tides, where the water level can rise and fall twice a day by as much as 50 feet. The tide here is a striking display of lunar and solar gravitational pull: It exposes the sea bottom, forces tributaries to flow upstream, and leaves docked vessels resting on the ground at low tide, like fish out of water.

In November, Cape Sharp Tidal lowered its turbine, cradled in an immense steel frame, into the Minas Passage, a three-mile-wide strait that magnifies Fundy’s tidal forces like a thumb over a hose.

“The Minas Passage has extremely high flow conditions, so it’s a proving ground for whether this is a commercially viable source of electricity elsewhere,” said Matthew Lumley, the FORCE spokesman.

The research center calls the conditions here the “Fundy Standard” for tidal technology, inadvertently invoking a Frank Sinatra standard: “If you can make it here, you can make it anywhere,” said Lumley.

Turbine designer OpenHydro, which is owned by the French industrial company Naval Group, deployed an earlier version into the Minas Passage in 2009, working with Emera’s Nova Scotia Power utility.

That test was a humbling demonstration of Fundy’s power. The 10-knot tidal forces in the passage exceeded estimates, as well as the turbine’s design. When OpenHydro retrieved its turbine a year later, its engineers said the fiberglass-reinforced plastic blades had survived only about three weeks in the fierce current.

“From an engineering perspective, it was a very good learning experience,” Richard said on a recent dockside tour of the new turbine, getting a laugh from other Cape Sharp employees. “We just took what we learned from that experience and embedded it in this design.”

The new turbine is larger, sturdier and can produce twice as much power as the first machine.

The 2009 failure only energized tidal energy’s proponents. Based on new data, researchers revised their estimates of the amount of power in the Minas Passage to 7,500 megawatts, of which about 2,500 MW could be realistically extracted. In 2005, the Electric Power Research Institute had estimated the location could yield about 300 MW.

Like other forms of renewable power, tidal energy is intermittent — electricity output ramps up every six hours and 25 minutes with each incoming or outgoing tide. But unlike unpredictable wind and solar energy, the size and time of tidal flows can be reliably forecast for years in advance.

Tidal power represents an attractive long-term option for Nova Scotia, which has set a target to produce 40 percent of its electricity from renewable sources by 2020. A switch from coal and fossil-fuel generation to clean energy is well underway. The province hosts about 300 wind turbines, and plans to import hydroelectric power in an undersea cable from Labrador.

“We’re uniquely motivated and uniquely positioned to look at this technology seriously,” said Lumley.

This isn’t the region’s first attempt at tidal generation. In 1984, Nova Scotia Power opened the 20-megawatt Annapolis Tidal Generating Station on the Bay of Fundy, still North America’s only such facility.

The Annapolis station is a tidal barrage, which captures the incoming tide behind a dam built across an inlet. The barrage generates power by releasing the impounded water through conventional hydroelectric turbines during the outgoing tide.

Large tidal barrages now operate in France and South Korea, but they have environmental drawbacks — sedimentation, shoreline erosion, and fish mortality. Developers of ocean energy have shifted their focus to capturing tide and wave movements in the open seas without having to build dams.

Commercial wave energy — producing power from the ocean’s wind-induced vertical motions — has also encountered challenges. Ocean Power Technologies Inc. of Pennington, N.J., formed in 1984 to build power-generating buoys, has moved away from its strategy of creating large devices that could be connected to the grid in groups.

“The immaturity of the technology, as well as the economics behind it, are just very difficult to overcome,” said George H. Kirby, the company’s chief executive. In recent years, the company focused on selling its smaller 3-kilowatt PowerBuoys for remote offshore applications in oil production, research, defense, and cellular communications.

Under the Obama administration, the U.S. Department of Energy’s water program spent $136 million from fiscal years 2008 to 2015 on 92 projects focused on ocean energy. The National Renewable Energy Laboratory deployed buoys this year off the Oregon and Maine coasts to record wave and tide movements.

Before tidal energy can achieve widespread adoption, it needs to overcome economic and technical obstacles. “It’s still a very nascent technology,” said Lumley, the FORCE spokesman.

Tidal technology has not yet converged on an optimal design. Cape Sharp Tidal’s turbine is an open-center machine, with the blades attached to the outer rim. Other firms are building propeller-like turbines, similar to wind turbines. The operators also need to retrieve and redeploy the machines every few years for maintenance, which may be more costly than the turbine itself.

In addition, the industry needs to convince regulators the underwater turbines are not harming the environment. Commercial fishermen in Nova Scotia attempted to block the deployment of Cape Sharp’s machine, claimed the turbine’s rotating blades would “chop whales into sushi.”

Cape Sharp Tidal says previous studies show that sea animals avoid the turbines when they are in motion. And they say the blades turn slowly, at about eight revolutions per minute. Preliminary sonar data from the recent deployment showed no evidence of harm. But national and provincial environmental authorities are watching the project closely.

The impact on marine life may be not be immediately obvious until hundreds of turbines are deployed. Some environmentalists and fishermen say they’re concerned that an industrial-scale operation could impair migratory patterns of fish or reproduction of lobster.

“It’s a new industry,” said Richard. “We’re introducing new technology into the environment, and the onus is on us to prove we’re not creating harm.”

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