Going with the flow
Offshore wind's biggest disadvantages are arguably its variability and the fact that the turbines are large and very visible. Some hydrokinetic technologies (wave and tidal) are designed to operate beneath surface of the ocean, and while they are also intermittent, their variability is more predictable. However, unlike these technologies actually operate in the water which raises concerns about harming marine life and affecting the physical characteristics of the oceans. (GW)
WHEN Christopher R. Sauer stands before the swirling waters of the Western Passage and describes his company’s alternative energy vision, he doesn’t see an army of wind turbines or banks of solar cells.
In fact, Mr. Sauer sees nothing at all that could block his view of Canada, just across the channel. For if his plans come to fruition, an array of turbines will be operating out of sight, deep under the water, cranking out power to a substation on shore.
His company, Ocean Renewable Power, is one of a number of start-ups trying to develop tidal energy — water-powered turbines that spin in the current as the tides come and go, turning generators to make electricity that is clean and, they hope, reasonably priced.
“We’re not going to beat out the old coal plants in the Ohio Valley,” said Mr. Sauer, who has decades of experience developing co-generation plants and other power projects. “But we will be competitive with any new power source, including fossil fuels.”
That’s an ambitious goal, but Mr. Sauer, the company’s president and chief executive, has at least gravity and the earth’s rotational energy on his side.
Tides come and go twice a day everywhere around the globe. In places like Eastport — a former sardine capital at the mouth of the Bay of Fundy that is surrounded by deep channels like the Western Passage — tidal power makes the most sense, at least for the moment.
Here the tides are very high and the current strong, reaching about 6 knots, or 7 miles per hour, at peak flows four times a day. “We’ve got the best tidal current on the East Coast,” Mr. Sauer said.
Tidal power is not a new idea. A few tidal generating stations are already operating around the world, including one in France that is more than four decades old. But they represent an older approach, one that employs barrages, or dams, to hold back the high tide. The water is then released through turbines, like a conventional hydroelectric plant, when the tide goes out.
Eastport itself was the site of an elaborate and enormous barrage project, proposed in the 1930s during the administration of Franklin D. Roosevelt, who knew of the great tides here, having spent many summers on Campobello Island nearby. The project, the East Coast’s answer to Hoover Dam, was abandoned after a year.
Dam-building is extremely costly and can create widespread environmental problems — the Eastport project, for example, would have bottled up two bays, forever altering the region’s ecosystem. Mr. Sauer and others say that placing turbines directly in the current is potentially much cheaper and more environmentally sound.
But no one knows for sure, because the underwater approach is in its infancy. While there are a few tidal current projects overseas, including one in Northern Ireland, there are only small development projects in the United States, including one undertaken by Verdant Power in New York’s East River, which also has a strong tidal current. Technologies are still being tested, and environmental questions are as yet unanswered. A tidal plant in Manhattan, Maine or elsewhere in the United States that would feed significant power to the grid is at least a few years away.
In many ways, tidal power is at a stage similar to wind power’s two or three decades ago. “That’s exactly the way wind started out, with fairly small projects,” said Robert Thresher, a research fellow with the National Renewable Energy Laboratory in Colorado, who, after years of wind-power research, now studies what is called marine hydrokinetics, a catch-all term for tidal, wave and ocean thermal energy. “They learned how to operate and maintain their machines. It was somewhat trial and error.”
Now large, efficient wind turbines are arrayed in vast farms. With tidal power, Mr. Thresher said, “I think you’ll see exactly the same kind of evolution” of the technology.
But it might not take as long, said Tim Ramsey, a project officer with the Energy Department, which began putting resources into tidal projects only two years ago.
“I don’t think we’re 20 or 30 years from being where wind is today,” Mr. Ramsey said. “It may only take us or 10 years to catch up.” Computers and other research tools are far better than they used to be, he said, and more accurate software models simulate turbine performance and efficiency.
“Our expectation is there is enough potential there to make it not only feasible but economical,” he said.
Tidal researchers have learned a lot from work on wind power. Flowing water behaves much like flowing air, but because water is denser, it contains far more energy for a given volume. That gives it an advantage over wind, said Paul Jacobson, a project manager with the Electric Power Research Institute, because the turbines can be much smaller.
Over all, however, far more power is potentially available from the wind (and the sun) than from tides. The Electric Power Research Institute estimates that at the sites it has studied — in areas with powerful tides like northern Maine, the Pacific Northwest and, above all, Alaska — a total of about 13 gigawatts is potentially available. By contrast, current estimates of potential wind power in the United States are at least several hundred times higher, and there are already about 35 gigawatts of installed capacity.
But as with offshore wind power, tidal energy would be produced near the coasts, and the coasts are where the people are.
“Cities are all built at the mouth of some estuary because in the good old pioneering days that’s where you could get transportation,” Dr. Thresher said. And estuaries make promising locations for tidal power, particularly if the technology improves and more power could be generated in slower currents.
“The appeal is not how large it is, but that it’s carbon-free and it’s there,” Dr. Thresher said. “You don’t have to build transmission lines.”
Like wind power — and solar power as well — tides are an intermittent resource. Even in areas with strong tides there are times, near low and high tide, when currents are too slow to turn a turbine.
Mr. Sauer estimated that in Eastport, his company’s machines would generate power about 75 percent of the time. “It’s variable,” he said. “It’s not a sole-source solution.”
Neither, he said, is wind or solar. But tides are highly predictable. “We can tell you for the next 100 years what we’re going to produce,” Mr. Sauer said. “With wind you can’t. With solar you can’t.”
That kind of dependability appeals to grid operators, said Mr. Jacobson of the Electric Power Research Institute. “They can ramp up other sources of generation and plan for that.”
In principle, some tidal turbines are very similar to wind turbines. Verdant Power’s East River project, for example, uses axial-flow turbines, in which the axis of rotation is aligned with the direction of water flow. Like wind turbines, they resemble large propellers, although they are stubbier and smaller than their wind counterparts.
Verdant Power in New York operated test turbines in the river, between Roosevelt Island and Queens, for several years. Recently it removed the turbines and is working on a next-generation model. It has applied for a license from the Federal Energy Regulatory Commission for a project to put an array of up to 30 turbines in the river that would generate up to 1 megawatt at peak times.
Trey Taylor, Verdant’s co-founder and president, said environmental studies should be finished by summer, “and we expect to get that license by the end of this year.” But the project cannot proceed until more financing is obtained.
For its projects — the company is also working in Alaska — Ocean Renewable Power decided to use a different kind of turbine, a cross-flow design in which the axis of rotation is perpendicular to the flow of water. It looks something like the working end of a reel-type lawnmower, only supersize.
A complete unit would have four 20-foot turbine sections, two on each side of a generator capable of producing, at peak, about 250 kilowatts. The units could be mounted on the bottom or moored under water and in some cases could be stacked as many as four high.
The company’s plan is to put one unit in the Western Passage next year, to be followed by more units there and in Cobscook Bay, on the other side of Eastport.
Now, though, the company is testing its turbine and generator system on a barge moored in Cobscook Bay. The turbine — two sections with the generator in the middle — can be raised and lowered into the water using hydraulic booms. With the turbine out of the water, the gray barge, topped by a shack full of power-regulating equipment, looks like a home-built high-tech paddlewheeler.
The company has had some problems — a coupling linking one side of the turbine to the generator broke, for instance — but over all, Mr. Sauer said, the tests are going well. At the same time, researchers from the University of Maine are studying the impact of the turbine on fish.
One concern about tidal turbines is that they could kill or injure fish that swim through them. While the study results are not yet in, Mr. Sauer said his company’s turbine was designed to rotate relatively slowly — about once a second — to minimize the danger.
Mr. Jacobson said that environmental reviews could be a “significant hurdle” for deployment of tidal energy systems. “These devices are going in new places, places where there hasn’t been industrial development,” he said. “So there are lots of questions.”
Cost is another big concern. “At the end of the day, we’re selling electricity, and electricity is a commodity,” Mr. Sauer said. Even with renewable energy credits and other incentives, he said, “clearly our first units in the water are not going to be competitive with coal. Our challenge is to get enough of them in the water and refine the manufacturing processes and other things we have to do to get them cost competitive.”
That will be difficult without financing, and for Mr. Sauer’s company, as for other alternative energy start-ups, raising capital is difficult. The company will soon be looking for $10 million to $12 million to continue development of the system and begin installing it in the Western Passage.
But Mr. Sauer is optimistic that once power starts being produced the company will attract a different kind of investor. “They aren’t going to be technology investors, they’ll be project investors,” he said.
Mr. Sauer’s vision extends far beyond Eastport and the Western Passage, all the way to Florida’s Atlantic Coast. There, the Gulf Stream, known locally as the Florida Current, flows at a constant 3 knots.
There are huge technological and practical hurdles to putting turbines in that current, one being that the water is 1,200 feet deep; another is that it is 20 miles off shore. But Mr. Sauer has his sights on that prize. “That’s the mother lode,” he said.