Catching the Currents
Tidal power isn't for the faint-hearted, as Verdant Power CEO William Taylor knows from experience. The first time Taylor's company sank an experimental turbine into New York City's East River, in late 2006, the powerful tidal currents — they can run up to 6 m.p.h. (almost 10 km/h) on a good day — smashed the device's fiberglass blades. Next they tried a turbine with rotors made of aluminum and magnesium, but after a couple of months the river won again. Finally, in the summer of 2008, Verdant sank a third design, with blades of tough aluminum alloy. These proved strong enough, and were soon generating sufficient electricity to power the lights at a nearby supermarket. That might seem like a small return for an operation that has cost millions of dollars, but Taylor isn't discouraged. "It's all part of the mantra — learning by doing," says the 61-year-old. "The potential of tidal can be just enormous."
Tidal power doesn't get the attention — or the venture capital — that higher-profile renewable energy sources such as solar or biofuels do, but there's a lot of energy waiting to be tapped in the motion of the ocean. Unlike the breeze or the sun, tidal currents are utterly predictable — sailors have charted them for centuries — which means engineers know exactly how much energy they'll get, and when they'll get it. The mechanics are physics 101 — at their most basic, tidal turbines act as underwater windmills, transforming sea currents into electrical current. And there is no shortage of potential sites around the world — a study by the Electric Power Research Institute estimated that as much as 10% of U.S. electricity could eventually be supplied by tidal, a potential equaled in Britain and surpassed in powerful coastal sites like Canada's Bay of Fundy.
But tidal power's takeoff has been held up by red tape, environmental concerns and the difficulties of building and maintaining infrastructure under the water. In the 42 years since the 240-MW Rance tidal plant was completed on the northern coast of France, not a single utility-scale commercial project has been built. "It will be viable, but I still think it will stay last on the list for a while," says Miriam Horn, a writer at the green group Environmental Defense Fund. "It will take a lot of [government] support."
That support has been largely missing in the U.S., where state aid for alternative energy that isn't grown by corn farmers is all but nonexistent. But that hasn't deterred start-ups like Verdant or Washington-based Oceana Power from investing in the technology. Verdant, launched in 2000, is expanding beyond its test in New York City and plans projects off the coast of Texas and in Canada, which has an estimated 15,000 MW of potential tidal energy. Oceana — which boasts environmental luminaries like Climate Institute president John Topping among its founders — has proceeded more slowly on actual projects, but through a network of regional subsidiaries it has staked out claims in tidal waters throughout the U.S., including beneath the Golden Gate Bridge in San Francisco. Competition has sometimes caused friction between the two companies, but they both agree that government red tape is hampering development of the nascent industry. More than a dozen federal, state and local-government agencies share control over the nation's tidal waters, which can make obtaining a permit a bureaucratic nightmare. "It will be one way in California and another way in Massachusetts," says Daniel Power, Ocean's CEO. "There's a lack of precedents here so everyone is getting their sea legs."
Things are slightly more advanced in Europe. The Rance plant in northwestern France is the only utility-scale tidal power system in the world — but it's a tidal barrage plant that involves damming water, a method that has more serious environmental impacts than the new generation of tidal turbines. The far northern town of Hammerfest, Norway, has hosted a 300 kW experimental tidal project for several years. The U.K., while hardly free from red tape, is also ahead of the U.S. That's partially a reflection of the British government's stronger stance on cutting carbon emissions, but also because tidal power has obvious appeal to an island nation. Bristol-based firm Marine Current Turbines (MCT), whose directors have been working in the field since the early 1990s, established a successful 300-kW turbine off Lynmouth, Devon, in 2003. Now MCT is developing a $20 million commercial-scale tidal-energy project in Northern Ireland's turbulent Strangford Narrows. Called SeaGen, the project has already broken records: last month it became the first tidal turbine to hit a capacity of 1.2 MW. The company next plans a 10.5-MW project off the Welsh island of Anglesey in partnership with npower renewables, part of utility giant RWE.
The chief obstacle these days is finance, not science, says Wright. Tidal projects have high initial construction costs — turbines are practically handmade — and that won't change until the market grows and developers can harness economies of scale. That requires subsidies. "This technology needs to be scaled up quickly," says Wright. "The government needs to believe this can happen." It might also require a streamlining of environmental regulations, according to Verdant's Taylor. Rules have already slowed several projects. Verdant had to spend $2 million on its New York operation just to ensure its turbines weren't making sashimi out of the local sea life. (They weren't.) Advocates argue that tidal power has enough potential advantages — unlike wind turbines, tidal generators are invisible, for instance — to be worth promoting. "It's going to happen," says Oceana's Power. "It's just a question of when and how quickly."
Go with the Flow
THEORY Like an undersea windmill, tidal-power plants use rotors to drive turbines. The density of water means a seamill can generate more power than a windmill of the same size
PRACTICE The SeaGen power plant, which began generating electricity off Northern Ireland last year, uses twin 600-kW turbines to develop 1.2 MW in a flow of 5 knots (2.4 m/sec.)
PROS AND CONS Tidal power is more predictable than solar or wind, and undersea machinery is less obtrusive than huge windmills. But start-up costs are still high and the ocean can be tough on equipment Source: Marine Current Turbines