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Power from Moving Water

Hopes abound that a new generation of technologies can make clean, affordable electricity from power of tides, waves, or any water in motion

October 4, 2004 | A version of this story appeared in Volume 82, Issue 40

A 300-kW turbine prototype, developed by Marine Current Turbines Ltd., was installed over a year ago in Britain's Bristol Channel to take advantage of the 5-knot tidal flow.
A 300-kW turbine prototype, developed by Marine Current Turbines Ltd., was installed over a year ago in Britain's Bristol Channel to take advantage of the 5-knot tidal flow.

Capturing and using the ocean's power to generate electricity is exploiting nature at its most basic. Covering 70% of Earth, the oceans hold immense energy through moon-driven tides and wind-powered waves, and they contain thermal energy from the heat of the sun.

For decades, scientists and engineers have tried to channel this potential into electricity with small success. They've found that containing and converting this potent power to electricity is far from simple or cost-effective.

But over the past few years, ocean energy advocates around the world have been claiming that technology is improving and that they are onto something big. Like renewable energy entrepreneurs in wind and solar power, those in ocean energy hope that global warming, high fossil fuel prices, growing worldwide electricity demand, and public opposition to environmentally invasive, big-scale energy projects will give them the push they need to get ocean energy to the marketplace.

These ocean technologists face a difficult task, however. First and foremost, the ocean is a wild partner. More than a few technologies have been torn apart when actually placed in the sea. And there is the money problem.

"They can't get government or private R&D funding without showing their device is feasible, and they can't prove it is feasible without R&D money to develop the technology," says Roger Bedard, manager for wave and tidal flow energy business development for the Electric Power Research Institute (EPRI), a utility-funded nonprofit center.

This dilemma is most obvious in the U.S., where there is no federal ocean energy program. Andrew R. Trenka, a project officer for Department of Energy biomass programs, was DOE's technical lead on ocean energy when it had a program 15 years ago. He says DOE did an assessment of ocean energy potential in the early 1990s after investing around $250 million, nearly all in ocean thermal energy technologies. DOE decided that the oceans' electricity contribution would be small and geographically localized and the return on investment would be marginal compared with wind, photovoltaic, or biomass. The program was soon shut down.

Trenka's favorite project, ocean thermal energy, which uses differences in temperature between near-surface and deep-ocean waters to generate power, required huge investments and a long payback, he says. Tidal and wave energy are the only technologies in play today, he adds.

Most action has been outside the U.S. However, into the federal void have stepped states and even a few cities and local utility districts that are ponying up small R&D grants or have made agreements to buy electricity generated by ocean energy demonstration programs.

EPRI is also involved and is nearing completion of an assessment of potential U.S. wave energy sites and starting to examine tidal flow areas. EPRI's program is partially funded by states, Bedard says, to serve as an "honest broker," putting technology developers together with funders and locations.

PART OF THE PROBLEM, he says, is that there are only five states with good tidal flows and maybe eight states with good waves. "The question is: Will Congress support something with so few states? We know we must diversify the nation's energy, but as the saying goes, 'Electrons flow according to the laws of physics; electricity flows according to the laws of politics.' "

State organizations are also trying to combine and focus their small resources. The Vermont-based Clean Energy States Alliance is made up of organizations in 12 states that have set up trusts to fund renewable energy projects. The states have put most of the money into wind, solar, and biomass, according to Lewis Milford, the alliance's director, but the states, too, are assessing ocean energy projects, which are starting to be funded.

In fact, small ocean energy projects are beginning in Massachusetts, New York City, off the coasts of Rhode Island, Hawaii, and Washington, and in San Francisco. Only two have produced electricity.

Money in the trust funds has come from bond initiatives or ratepayer assessments to support renewable energy. In San Francisco, for instance, voter-passed initiatives are providing $100 million for renewable energy projects.

Six Verdant Power 36-kW tidal turbines are being installed in New York City's East River in a pilot program the company hopes will grow to 300 units.
Six Verdant Power 36-kW tidal turbines are being installed in New York City's East River in a pilot program the company hopes will grow to 300 units.

"San Francisco has a rather visionary electorate," says Peter O'Donnell, senior energy analyst with the city. "The citizens are committed to eventually having 100% renewable power for the city. Some may say it's crazy, but it is a collective craziness."

The board of supervisors called for 1 MW of tidal power on the grid by January 2006, he says, but later scaled back to 150 kW.

The city is exploring placing a tidal-driven power source under the Golden Gate Bridge in the near term and, later on, placing wave units two or three miles off the coast in an area where it already has right-of-way for a sewage outfall.

O'Donnell says a $4 million tidal demonstration is planned for next year, and a British company, HydroVenturi Inc., has shown an interest in building and paying for the unit. But questions have been raised about the company's ability to secure funding. The company's London office did not respond to C&EN's interview requests.

"What we are trying to do in San Francisco is a natural reaction to the absence of leadership from Washington," O'Donnell continues. "We have talked to DOE, but they are interested in clean coal."

Europe, Australia, and other parts of the world are further along in developing alternative energy sources, mostly because of active support by their governments, which in turn spurs private funders to come to the table. Government encouragement has been in the form of R&D seed funds, engineering support, or mandated production goals or targets requiring utilities to buy renewable energy, which can sometimes include ocean energy.

As a result, several overseas projects are generating electricity from ocean power--although the quantities are small and not at commercial scale. More are planned, but where ocean energy is today is similar to where wind energy was a few decades ago, says George M. Hagerman Jr., senior research associate at Virginia Polytechnic Institute & State University's Center for Energy & the Global Environment.

"Most of the ocean technologies have undergone 'proof of concept' demonstrations, but they are in their infancy compared to wind energy," Hagerman says. "With wind there used to be many different technologies with all kinds of turbines out there. Now, most wind farms look pretty much the same. This is not true for ocean energy.

"The Energetech wave device looks nothing like the Pelamis wave energy converter or the Archimedes Wave Swing or the Wave Dragon, yet all use wave power as a source of energy," he explains. "They are completely different. It is a sign of immaturity in the industry.

A 125-kW Ocean Power Technologies energy buoy off the coast of Hawaii supplies electricity to a Navy installation.
A 125-kW Ocean Power Technologies energy buoy off the coast of Hawaii supplies electricity to a Navy installation.

"MOST IMPORTANT, you must remember, it is one thing to have a device in a wave tank or conduct a demonstration and show good efficiency and all that, but it is another thing altogether to build at full scale, put in it the ocean, and let the ocean hammer on it for a couple of decades."

Still, Hagerman is an ocean energy advocate, albeit a realistic one. He points to several technologies that, in his view, have commercial potential and are "in the water" or soon will be.

The technologies come in two broad forms--those that use waves and those that use tidal energy. Both waves and tides vary in intensity, but tides can be predicted decades in advance, Bedard notes, unlike wind or sunlight irradiance. Predictability is important when supplying electricity to the grid or to individual users.

Waves are powered by winds and uneven solar heating, he says, and wave energy works best in ocean depths of at least 50 meters, before waves lose energy to the friction of a shallow sea bottom.

Moon-driven tides are completely predictable and can be powerful forces, especially in areas with high tidal ranges where a turbine could be powered on incoming and outgoing tides. Natural constrictions can also help funnel the tidal flow to turbines, he notes, pointing, for example, to the mile span under the Golden Gate Bridge, which results in powerful currents as the huge bay fills and drains twice a day.

"Water is almost 1,000 times denser than air," Bedard adds, "so you can get the same ocean energy from a machine much smaller than a wind turbine and much cheaper."


The size advantage opens up new applications, Bedard believes, and energy developers are looking at small turbines that can be driven by rivers, streams, or sewage-treatment outfalls--essentially any concentrated moving water.


A sampling of technologies identified by Hagerman, Bedard, and others includes wave generators and free-floating power buoys that use waves for energy and turbines of various sizes to take advantage of the potential energy in tides, rivers, and other water in motion.

The only U.S. company to receive federal aid is a $12 million U.S. Navy appropriation for New Jersey's Ocean Power Technologies (OPT) for a series of pilot buoy projects offshore of Hawaii. CEO George W. Taylor says the company has now contracted to produce up to 1 MW of electricity for a Marine base in Hawaii. Taylor says OPT's systems approach is modular, based on small 125-kW buoys. However, he says, the company is developing a larger 500-kW buoy. It also has other small projects under development for Lockheed Martin Corp. and New Jersey, and OPT is discussing a large-scale project for Spain.

Another U.S. buoy company, AquaEnergy, is seeking permits to install four 250-kW buoys offshore Washington state. If its buoys are permitted and installed, AquaEnergy has a purchase agreement with a Clallam County Public Utility, which will buy the power for 4.5 cents per kW hour.

Ocean waves also power the 500-kW Limpet system, installed in 2000 on Scotland's west coast. Developed by Wavegen of Inverness, Scotland, Limpet is built onshore and generates electricity by using ocean waves to fill and empty a contained structure, pulling and pushing air through a turbine in what's called an "oscillating water column." Wavegen plans a second installation to be tunneled into a cliff face in the Faroes Islands, which are located midway between Iceland and Norway.

Another Scottish company, Ocean Power Delivery Ltd., has developed Pelamis, a snakelike floating device, recently moored offshore of Scotland. Last month, Pelamis was tied into the U.K. electric grid and began generating a peak output of 750 kW. Pelamis comes in several articulated, hinged sections, each 40 meters long and 3.5 meters in diameter. As ocean waves jerk the sections to and fro, hydraulic rams within the joints pump oil through turbines, driving generators and producing electricity, which is fed to the grid onshore.

The Australian company Energetech is installing a pilot wave energy project off the Australian coast. The 485-ton structure is tethered above the sea bottom and uses wave energy to drive air through an enclosed, funneled chamber, increasing air speed and concentration, before reaching a turbine and generator. It has a top system output of 750 kW.

U.S. trials are planned for Pelamis and Energetech technologies. Connecticut, Rhode Island, and Massachusetts have committed to provide $1 million of the $3.5 million needed for an Energetech pilot project in Port Judith, R.I., for a three-year trial starting in 2006. Maine is exploring a Pelamis pilot project.

Looking at turbines, the world's largest tidal turbine--a turbine powered by incoming and outgoing tides--is La Rance station, which produces some 240 MW and straddles a French estuary. Built in the 1960s, La Rance is likely to be the last of its type due to costs, size, and environmental problems.

Instead, a second generation of individual freestanding turbines are being installed in Europe and the U.S.

Marine Current Turbines Ltd., for example, placed a pilot 300-kW single rotor turbine in the Bristol Channel in southwest England and Wales in May 2003. Technical Director Peter Fraenkel says the company has developed a new generation of twin rotor units with the potential to generate up to 1 MW, depending on tidal flow. A trial is expected late next year, Fraenkel says, and the units will be arrayed in "farms."

These units are similar to wind turbines, he says, but with much smaller and slower rotors--in the range of 30 feet in diameter, as compared to 300 feet for a wind turbine. Tidal turbines turn about 30 revolutions per minute, about half the speed of wind turbines.


In New York City's East River, a Virginia company, Verdant Power, is installing much smaller 15-foot-diameter turbines in a localized energy application for the borough of Queens and the community of Astoria next to the river.

Trey Taylor, Verdant cofounder and president, says his company's "free-flow" turbine systems would generate "village-scale" electrical power. The goal is distributed energy, generated in an environmentally benign way from a renewable source.

Verdant ran one of its small 36-kW turbines in a trial last year and is now installing six turbines on the bottom of the East River, generating 200 kW of peak power. If all goes well, over the next two years, Verdant will expand the system to 200 to 300 turbines, generating 10 MW of electricity, he says.

Taylor sees future applications ranging from remote villages to areas with limited transmission lines, like New York City.

"RIVERS, STREAMS, tides, ocean currents, aqueducts, irrigation canals, wastewater treatment outfalls--they all can be used for electrical power," Taylor says.

Verdant has received about $1 million from the New York State Energy Research & Development Authority, which supports renewable energy. A NYSERDA official emphasizes that the project is one of few potential new sources of electricity for New York City. Nothing will be visible from the river surface other than a power line, the official says, but notes that many tests are to come, particularly impact on aquatic life, ship traffic, and maintenance.

A NYSERDA study estimates there is the potential for 1,000-plus MW of stream-based electricity generation in New York state.

Verdant also recently won a $500,000 grant to install six turbines in the Merrimack River in northern Massachusetts through the Massachusetts Technology Collaborative program.

How far these small grants will go toward commercialization of ocean energy is questioned by Bedard, who stresses that no new energy source has been developed without strong government support.

Artist's conception of a wave farm of 750-kW Pelamis wave converters, one of which is being installed off the coast of Scotland by maker Ocean Power Delivery Ltd.
Artist's conception of a wave farm of 750-kW Pelamis wave converters, one of which is being installed off the coast of Scotland by maker Ocean Power Delivery Ltd.

Jimmy Ferguson, managing director of Wavegen, notes that the U.K. has a goal of generating 10% of its electricity from renewable energy sources by 2010 and 15% by 2015, and Scotland has set a target of 40% renewable energy by 2020.

The U.K. government, he says, has invested more than $100 million in marine power, and his company gets about 30% of its funding from the government, which greatly leverages the 70% in private equity.

"Renewables aren't cheap," he says. "To take off, they need something like a golf handicap to allow them to go head-to-head with fossil fuels. Otherwise, you will get these little groups to put in a small installation; an odd prototype will pop up here and there to prove the technology.

"It won't take off in a big way until the proper legislative framework is put in place and the business community can see a way that they can turn a buck and provide a greener planet and make a good business case at the same time.


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