By Choe Sang-Hun
ANSAN, South Korea
In a tidal flat where crabs used to crawl and herons used to feed on clams, hard-hatted men and their trucks toil on the gray rock bottom of a rectangular hole the size of a dozen football fields and going 26 meters below the sea level.
When their work here is done by 2009, South Korea will have a new monument: the worlds largest tidal power plant.
With a capacity of 254 megawatts, enough to power the nearby city of Ansan, which has half a million people, the Sihwa Lake Tidal Power Plant would serve as a major emblem for a clean-energy movement in South Korea, the worlds 10th-largest emitter of global warming gases.
But energy experts say that the building under way on the embankment of this lake, 40 kilometers, or 25 miles, southwest of Seoul, also represents a larger trend: coastal nations around the world are looking more seriously at tidal waves off their shores as a source of renewable energy.
The worlds current largest tidal power plant, known as the Rance barrage, has a capacity of 240 megawatts. Situated in northwestern France, it was built 40 years ago. Since then, no major tidal power project had been undertaken until South Korean engineers began digging here in 2005.
But already, engineers here think that their new plant will not hold the No.1 title for long. From Canada and Britain to India and Russia policy makers are contemplating gigantic projects to harness tidal power, which they see as clean, inexhaustible and as reliable as the rotation of the Earth.
About 50 kilometers north of here, South Korean engineers plan to connect four islets by 2014. And about 50 kilometers south of Sihwa Lake, the authorities are conducting a feasibility study for one twice as big as Sihwa, although fishermen there complain that it would ruin their rich clam fields. Yu Yeong Sun, an engineer with the Korea Water Resources Corp. said This plant will generate electricity twice, for a total 10 hours, a day as long as the sea doesnt forget to rise and fall.
Along the coast here, the sea rises up to nine meters, or 30 feet, from low to high tide. The Sihwa plant would generate the electricity by using the movement of water between the sea and the lake, which was created when engineers built a 12.7-kilometer embankment to close a bay.
When the sea is on the rise, the water level on the sea side of the barrier gets meters higher than the water level on the lake side. Then suddenly the plants 10 turbines, to be installed in the middle of the seawall, will open. The water will rush into the lake with such tremendous force that it will spin the turbines, which drive generators.
When the sea retreats, the plants eight sluice gates will open to empty out the lake. This process will occur twice a day, as the sea rises and falls twice a day. The plant is 500 meters long.
Sihwas turbines, made by the Austrian company VA Tech Hydro, would together generate one-fourth of the electricity produced by a typical nuclear power plant, and would save South Korea 862,000 barrels of oil and 315,000 tons of carbon dioxide a year.
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When engineers completed their barrier in 1994, the idea was to turn tidal flats inside the bay into vast tracts of farm fields and create a freshwater reservoir covering 56 square kilometers, or 21 square miles.
With sea water cut off, the lake turned black with waste discharged from two nearby industrial complexes. It began to stink. The surface became covered with the floating corpses of birds and fish.
By 2000, the government admitted its mistake. It spent the equivalent of hundreds of millions of dollars to reduce industrial sewage and bring back wildlife. It punched holes into the dam to let seawater in and out. Installing a tidal power plant would solve the problem, the authorities say. Each day, it would circulate 150 million tons of water, or half the lakes content. South Korea, one of the top four oil importers in the world, depends on oil for 44 percent of its energy needs. The government wants to reduce that ratio to 35 percent by 2030 by diversifying energy sources. An immediate goal increasing the share of renewable energy in the total energy mix to cent by 2011, from 2.3 percent now 1.
Across the country, hundred wind farms, solar power plants mini-hydroelectric plants are operating or under construction. Electricity is up to seven times more expensive than electricity produced fossil-fuel or nuclear power plants.
Korea Water, which will spend about $382 million, to build the Sihwa plant, says the project 11 make profit. But its capital cost does not include the 600 billion won at the government spent to build the seawall a decade ago or the money used clean up the lake.
The Korea Rural Community and Agriculture Corp., a government- owned entity and veteran seawall builder, has recently joined an international bid to build a 64-kilometer breakwater in India, across the Gulf of Khambhat, also known as the Bay of Cambay. Indias plan calls for adding a 7,400-megawatt tidal power plant.
After testing a couple of small experimental plants, China has hired the British company Tidal Electric to carry a feasibility study for a 300-megawatt plant at the mouth of the Yalu river, near the coastal border with North Korea.
In London, some government ministers are championing the idea of a seawall on the Severn estuary, in south- western England, to build an 8,600- megawatt plant. Even bigger potential exists in northern France, on the Cotentin Peninsula, and in the Russian Far East, at Penzhinskaya Bay, according to experts.
But residents here welcomed a tidal power plant as a new tourist attraction. Their economy depends on tourists who come to see the regions famed sunsets and to eat roasted clams, a local delicacy. To increase the lure, the authorities plan to build a wind farm and solar power plant and turn Sihwa into a clean energy park.
