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ALTHOUGH most modern attempts to harness tide wave power have failed, there is new optimism in the air. Scientists could soon start power generation with the help of underwater version!; of wind turbines. Efforts are on to set up "tidal farms" in coastal waters from the southwest of England to Southeast Asia (New Scientist, Vol 158, No 2139).
Canadian researchers plan to build the world's first multi-megawatt power station in a narrow channel between islands in the Philippines, to tap tidal power. Blue Energy of Vancouver, Canada, and the Philippines government signed an agreement last December to build the us $100 million power project. The first "underwater windmill" is also expected to supply Britain's national grid with power. The European Union (EU) will provide funds to a British-led consortium for setting up a single turbine off the coast of southwest England. Peter Fraenkel of the Hampshire-based company IT Power, who is leading the project, says the turbine will start supplying power by mid-2000.
In the past, large investments were required to place a turbine underwater. But the recent technological break-throughs have brought costs down. Today, jt is feasible to mount turbines on pipes that are easily placed in holes drilled in the seafloor.
Tidal prospects today are as good as any other projects, says Fraenkel. Researchers have identified several areas that offer potential for extracting more than 10 megawatts. But it would be important to know why only some sites are better for harnessing tidal power. According to Fraenkel, an ideal site should have water deep enough to cover a turbine. It means that a depth of between 20 and 30 metres as near as possible to the shore. The tidal currents should have a peak velocity of between two and three metres per second. It is also important that a grid connection is close to the site and the area is not a shipping zone. Now engineers are not only looking at estuaries, but also at the more common coastal currents generated by the tides.
Fraenkel played an important role in the compilation of a study for the F,U of potential sites for tidal current power generation which identified 106 potential sites, 42 of them around Britain. These included the islands and lochs of western Scotland and the Orkney and Shetland Isles, the Welsh island of Anglesey, the Scilly Isles, and Channel islands such as Alderney, which has one of the strongest tidal currents off Britain. In Europe, the researchers found potential sites in the Straits of Messina between Sicily and the toe of Italy, and the seas bordering the Greek islands.
It has been found that the best sites around the world are clustered on the edges of large oceans. In Asia, the myriad channels between the islands of the Philippines and Indonesia offer great potential, together with currents that run along the Chinese and Japanese coasts. Other sites such as the Atlantic waters off New Foundland and sites in the Pacific off British Columbia also offer great potential for generating tidal power.
Besides offering good power potential, islands are often in need of cheap electricity. Many islands are located far from large power plants. These islands rely on small, expensive and polluting power plants of their own. Stephen Salter of the University of Edinburgh, UK, is investigating the potential for replacing coal-fired power with tidal power on islands off the coast of China near Shanghai. Salter is known for his "nodding duck" machine for generating electricity from waves.
Lack of good data on the strength of currents is one of the biggest problems why tidal wave power has not been exploited extensively. Last year, Norwegian engineers planned to generate power for the town of Hammerfest on the Arctic coasl from turbines in Kval Sound. However, Torkild Carstens from the University of Trondheim's Foundation for Scientific and Industrial Research, says that the project could not be undertaken as the current was only half as strong as earlier suggested. After that, the EU provided funds to a research learn for developing instruments and computer models for making rapid estimates of tidal power potential.
Another problem is whether tidal power can be exploited economically. A recent feasibility study of tidal power in the Orkney and Shetland islands shows that it would respectively cost around two and four times the cheapest commercial rate from gas-powered power
stations. Fraenkel believes that turbines set in clusters would be as cheap as wind power. It would be enough to make it attractive for island communities. And he expects further technical advances and mass production to bring down the cost of setting up the plant.
These developments notwithstanding, it is still a long way before tidal power becomes a reality. Fraenkel fears that over enthusiastic claims for tidal power could wreck its future once again. So the world will have to wait and watch how scientists work out a feasible method to tap tidal power in future.