ADVERTISEMENT
This article is from the In-Depth Report Today's Alternative Energy

Turning the Tide on Harnessing the Ocean's Abundant Energy

Several companies are in the midst of tests to determine whether their technology for harvesting renewable energy will sink or swim
wave, Pelamis, renewable energy



Courtesy of Pelamis Wave Power Ltd.

More In This Article

Three red snakelike devices bobbing in the waves three miles (4.8 kilometers) off the coast of Agucadoura, Portugal, represent the first swell of what developers hope will be a rising tide of wave power projects. Edinburgh-based Pelamis Wave Power, Ltd., (PWP) has since September been working with asset management firm Babcock & Brown, energy provider Energias de Portugal, and Efacec (a Portugese maker of electromechanical devices) on the Agucadoura project. This first phase will cost about $13 million and generate up to 2.25 megawatts. The company hopes to by early next year begin building installing another 25 wave-energy converters to increase the output to 21 megawatts, which is expected to serve the electricity needs of more than 15,000 Portuguese households.

Earth's oceans and rivers, pushed by wind and tugged by the moon and sun, ebb and flow over more than 70 percent of the planet, but only recently have researchers and scientists developed the materials and methods to finally harness some of that kinetic energy. There may not yet be a market for underwater turbines or wave-riding electrical generators designed to use ocean turbulence as a source of renewable energy, but that has not stopped a handful of entrepreneurs from trying to create one.

Although all renewable energy sources—sun, water and wind—suffer from peaks and troughs in productivity, "we consider wave energy to be more predictable than wind," says PWP CEO Phil Metcalf. "You look at the ocean 1,000 miles [1,600 kilometers] out, you'll get a good idea of what to expect over the next 24 to 48 hours. We think it's actually going to be easier to dispatch to the grid."

Pelamis's devices are big red cylindrical tubes, each 426.5 feet (130 meters) long, 13 feet (four meters) in diameter, weighing around 750 tons (635 metric tons), and with a life expectancy of up to 20 years. The tubes are connected by hinges so that they float like a snake in the water. As the tubes' sections rise up and down on the passing waves they tug on the hinges, which are resisted by hydraulic rams that pump high-pressure fluid through hydraulic motors and turn electrical generators to produce electricity. Power derived from the joints on each wave-energy conversion is fed down via a cable to a central undersea export cable, which carries the collective power generated from site to shore.

"Our machine works by reacting against itself," says Max Carcas, Pelamis's business development director. Most other technology developed for harvesting wave power—including Finavera Renewables's AquaBuOY, WaveBob Ltd.'s wave-absorbing buoy and another buoy-mounted generator made by SRI International—absorbs energy from riding the waves as they bob up and down.

Pelamis's tubes work best at a depth of more than 165 feet (50 meters) and roughly 3.7 miles (six kilometers) from the shore, where the waves are strong but a crew can still connect a cable from the tubes to the shore. "Waves lose energy once you get to get to less than half a wavelength depth—typically deep swell waves are 100 to 140 meters (330 to 460 feet) in wavelength—hence why we focus on being out above 50 to 70 meters (165 to 230 feet) of water," Carcas says. The distance off the coastline to get to this depth contour will vary from place to place but typically is two to 15 kilometers (1.2 to 9.3 miles), he adds.

Another approach operates at the bottom of New York City's East River, where in 2006 Verdant Power, Inc., planted six windmill-like turbines—each 16 feet (five meters) in diameter—30 feet (nine meters) below the surface and churning at a peak rate of 32 revolutions per minute to transform strong tidal forces into electricity. Despite a few setbacks—the river's powerful flow damaged the rotors and broke off some of the original fiberglass and steel blades—the company has managed to keep two of the turbines operational, supply electricity to a nearby supermarket and, more recently, attract $8.5 million in funding from sources including the U.S. Department of Energy and the Canadian government to further develop and test its technology.


Verdant's turbines require tides that move at least six feet (1.8 meters) per second in order to generate enough energy for them to be cost-effective, and the East River is more than obliging. "The East River is a good tidal channel that links the Long Island Sound to the ocean," says Trey Taylor, the company's president and head of market development. "Plus, New York is an expensive place to buy power, so it would be easier here to prove that this could help."

Verdant plans to next year test a new type of turbine in Canada on the Saint Lawrence River, near Cornwall, Ontario, that is heavily weighted and sits on the riverbed rather than being moored to the bottom. These two turbines are expected to generate more than 120 kilowatts of energy and will be easier for the company to remove when repairs are needed. (They have to wait for slack tide to do any work on the turbines in the East River.)

The East River site produced nearly 50,000 kilowatt-hours of energy from December 2006 to May 2007, and the testing spot has the potential to support as many as 300 turbines and nearly 10 megawatts of installed capacity. By 2010, Verdant's hope is to increase its turbine farm in New York City to 30 devices producing more than a megawatt of energy (800 households use about one megawatt). The company is also looking at sites in China and India.

Verdant is the main player in a market trying to catch on. Another tidal power company, East Yorkshire, England–based Lunar Energy, in March began working with Korea Midland Power Company to create a giant 300-turbine field in the Wando Hoenggan Water Way off the South Korean coast. The plant is expected to provide 300 megawatts of renewable energy to Korea Midland Power by December 2015. Researchers at Florida Atlantic University's Center of Excellence in Ocean Energy Technology in Dania Beach are using a $5-million state research grant awarded in late 2006 to develop technologies that tap into the powerful Gulf Stream and take advantage of large water temperature differences off Florida's shores. The researchers envision thousands of underwater turbines producing as much energy as 10 nuclear power plants and supplying one third of the state's electricity.

The U.S. government has made it clear that advanced water-power projects are a priority. Including its plans to help Verdant, the Energy Department in September said it would dole out up to $7.3 million over the next five years to advance commercial viability, cost-competitiveness and market acceptance of new technologies that can harness renewable energy from oceans and rivers.

It is unclear just how much it will cost to tap into energy from large bodies of water. Verdant's Taylor says his company is at least two years away from being able to quote costs to potential customers. That said, a rough cost estimate for Verdant's marine renewable energy technology is up to $3,600 per kilowatt—a higher price tag than wind power, fossil fuels or hydroelectric dams today, he says. He also points out, however, that Verdant will be able to lower its costs over time through the mass production of its technology and the reduction of inefficiencies in the licensing and implementation processes.

Verdant, which operates its kinetic (non-dam) hydropower project in the East River under a preliminary permit from the Federal Energy Regulatory Commission (FERC), plans to by the end of the year apply for a FERC pilot commercial license that would allow the company to create a field of up to 40 underwater turbines with up to 1.5 megawatts of capacity. It took four years to secure the necessary permits from the New York State Department of Environmental Conservation and the U.S. Army Corps of Engineers to get the project to where it currently is. Verdant has spent at least $9 million thus far on its East River project; one third of funds were spent on studies to gauge the potential impact of the turbines on vessel navigation, aquatic life and fish migration.

Taylor hopes to eventually have two fields of underwater turbines in the East River with a total installed capacity of up to 10 megawatts. Other opportunities abound throughout New York State, he adds. "One estimate predicts as much as 1,000 (megawatts) of potential installed capacity for the state," whose State Energy Research and Development Authority (NYSERDA) chipped in $3 million toward the East River project. "With a commercial license issued, and with the field built, we will continue with operational tests, generating and delivering grid-connected power to paying customers."

Rights & Permissions
Share this Article:

Comments

You must sign in or register as a ScientificAmerican.com member to submit a comment.
Scientific American Back To School

Back to School Sale!

12 Digital Issues + 4 Years of Archive Access just $19.99

Order Now >

X

Email this Article

X