Tech Trends-The Light from the Sea30 Nov, 2005 By: Kenneth Wong Cadalyst
Ocean Waves Bring Renewable Energy to North Devon
LYNMOUTH IN NORTH DEVON, United Kingdom, is a fishing village and a seaside resort tucked between wooded hills and devilish cliffs. Its cobbled walkways face the breaking waves along the Devonshire coastline immortalized in "The Rime of the Ancient Mariner." The same seascape that once inspired Coleridge to pen his poetic masterpiece has also prompted another type of creativity: the quest for renewable energy.
A decade ago, Professor Peter Fraenkel, the man who would later become the technical director of MCT (Marine Current Turbines Ltd., www.marineturbines.com), tested his concept for a hydropower turbine by dragging a model behind a boat. In June 2003, the sunniest month of the year for Devon, a red-and-black structure appeared roughly a mile off Lynmouth harbor. It was the Seaflow 300kW, the first commercial marine turbine prototype based on Fraenkel's concept. His 30-kilowatt model that once sputtered in a lake has evolved into something much larger: a £3.5 million project, undertaken by a consortium of U.K. and German companies, supported by the U.K. Department of Trade and Industry.
The Landscape and the Wildlife
The marine turbine is a waterborne cousin of the controversial wind turbine. In January 2003, on the other side of the Atlantic, the Cape Wind project that was meant to put 130 wind turbines in Nantucket Sound drew objections from some local heavyweights, Senator Ted Kennedy and CBS newsman Walter Cronkite among them. Cronkite once wrote in his syndicated column, "Since I won't like the looks of that vast field of towers; and I won't like their interference with glorious sailing in the sound; and I will worry about the wildlife. . . I am opposed to the project." Later, after meeting with a Cape Wind representative, Cronkite decided to revise (though not necessarily reverse) his position; he conceded his reaction to the project had been premature and requested the Alliance to Protect Nantucket Sound to pull ads featuring statements from him ("Cronkite Withdraws Ad Against Turbines," Mark Lovewell, The Vineyard Gazette, August 29, 2003, www.mvgazette.com/news/2003/08/29/cronkite_withdraws_ad.php).
Joe Verdi, the commercial director of MCT, is well aware of the usual objections to wind turbines, but he's confident his marine turbine won't have similar obstacles because nearly three-quarters of it remains submerged until it requires maintenance. "What we've found," Verdi says, "is that the people who don't like the wind turbines have actually accepted our technology, because the visual impact is very minimal."
What about the underwater wildlife, the natural habitants of the Devonshire coast? Will they have a run-in with the marine turbine's 36' rotor blades? Verdi wants to assure everyone that the marine turbine's blades are nothing like an electric fan's. "They won't chop your fingers off," he says. "Whereas the wind turbine blades rotate at about 25rpm, the marine turbine blades operate at about 12–15rpm. The water is so dense that things get drawn through the helix rather than chopped up."
The Wisdom from the Sea
"The sea is extremely unforgiving," Verdi says, his tone taking on an old salt's reverence. "You make one mistake and she has you." On the other hand, punishing as she is, she also blesses the marine turbine with certain advantages. "Conditions under the sea are far more predictable and stable than at or above the surface; temperature conditions vary much less between summer and winter and so are easier to contend with." Verdi says, "You can predict as much as 20 years ahead, so you know when you can dispatch energy. And water is 800 times denser than air, so the energy (for a given rotor area) from the marine turbines is 4 times greater than what you get from the same area of a wind turbine rotor." Because the Seaflow 300kW is meant to stay underwater for long periods, MCT initially had some concerns about marine growth, such as barnacles. As it turns out, the machine's interaction with the tide has a self-cleaning effect, so the maintenance crew returned to find the rotor and the pile to be, in Verdi's words, "clean as a whistle."
The partially submerged design also offers protection from inclement weather. "The Bristol Channel is quite exposed," says Verdi. "The next landfall from here is the eastern coast of the United States, so the Lynmouth prototype has seen a fair share of Atlantic weather, but the weather is confined to sea level for the most part. Down below, the water is fairly benign. It really doesn't impact the turbine at all, because it sits a lot lower down in the water column. The current stays the same no matter what happens on the surface. The unit's loading can take the force of a storm."
Figure 1. Marine Current Turbines Ltd.'s sea-powered turbines operate on the same principle as wind turbines, using underwater currents instead of the wind to generate renewable energy. Eventually the existing prototype Seaflow, a single-rotor turbine capable of producing 300 kilowatts, will be replaced by Seagen (shown here), a double-rotor unit capable of producing 1 megawatt of power.
The Seaflow has been in operation for more than two years now. It's controlled remotely from MCT's Bristol office. MCT's engineering director Angela Robotham and her team have accumulated valuable information from hands-on experiences. The turbine was modeled in Autodesk Inventor (figure 1), allowing Robotham and her team to explore what-if scenarios using ANSYS and other FEA (finite element analysis) applications. The culmination of this data will result in a new unit three times more powerful than the existing one. The current prototype, the single-rotor Seaflow, generates about 300 kilowatts. Its successor, the double-rotor Seagen, will generate 1 megawatt and is expected to connect to the National Grid by 2006. The plan is to eventually install a farm of these units so they can make significant energy contribution to the area.
Following the tradition of maritime exploration, MCT is already eying neighboring France's northern coast for possible turbine sites. The requirements are fairly simple: water speed 4.5 to 5 knots and water depth 65' to 100'. Areas near Alaska, Oregon and parts of Japan and Canada are under consideration as well. The Seaflow 300kW has the capacity to churn out enough energy to keep the living rooms lit and the Christmas trees blinking in about 200 typical U.K. households.
Kenneth Wong is a former editor of Cadence magazine. As a freelance writer, he explores innovative use of technology and its implications. E-mail him at email@example.com.