How men would cage the power of the sea
Edinburgh — From a gangway above the 30-meter-long pool, Dr. Martin Greenhow steadies the toy fishing trawler with a long pole. "Push the green button," he says, pointing to a bank of electronic devices.
I push it and 89 paddles along one edge of the tank begin their slow, computer-orchestrated movement. Nineteen seconds later a miniature mountain of water -- the kind that happens once every 50 years -- crests over the ship and sends it scuttling to the bottom.
Even on a small scale, it is a graphic illustration of the power of waves -- power that an energy-hungry world is striving to tap. The waves that batter Britain along the Hebrides and the Cornish coast are among the most powerful in the world, packing an average of 45 kilowatts of power for each meter of wavefront.
Further, they provide maximum energy during the winter months when mankind's demand is highest.
Not surprisingly, this island nation is the world leader in research into wave-power devices -- with seabound Japan a close second. and the $:100,000 ($ 225,000) wave-testing tank at Edinburgh University, which was the first facility of its kind in the world, is providing insights into the relative merits of a host of different devices.
Dr. F. J. P. Clarke of the government-run Energy Technology Support Unit of Harwell, Oxfordshire, feels that "renewable energy sources" -- solar, wind, wave , tidal, geothermal, and biomass (vegetable products) systems -- might provide energy worth up to 60 million tons of coal equivalent (mtce) of the 330 mtce which Britain uses each year.
There is, he feels, no energy shortage. The real problem is to discover ways to extract energy cheaply. That is the challenge which Stephen Salter of Edinburgh University set himself seven years ago, when, he says, "My wife asked me to look into energy." His invention, the Salter duck, will ultimately take shape as a 30-meter-long, wing-shaped device that bobs up and down on the surface. That motion is converted into hydraulic pressure which powers a 2 -megawatt generator inside the duck.
Strung together into miles-long rows of at least 68 ducks, the whole necklace will be anchored out of sight several miles offshore and feed currently by cable into Britain's electricity grid.
His is only one of many models now being tested. Some, like the massive concrete doughnuts developed by Vickers Ltd., sit on the sea floor in shallow water. Others, like the oscillating air column, are the size of a seven-story building lying on its side and floating far out to sea. Still others are long spines with rubber bags attached.
One, designed by Sir Christopher Cockerell (inventor of the Hovercraft), uses rafts the size of helicopter pads buckled together into pairs.
All depend on a relationship between something moving -- air, water, or hydraulic fluid -- and something relatively stable, such as an anchor, pylon, or large floating wall. It is this relationship that Mr. Salter, who combines expertise in mechanical and electrical engineering, has had to rethink.
Rejecting air and sea water as too dirty and subject to marine fouling, he settled on what he calls the "nicest fluid" -- clean oil -- as the moving element.
Inside each duck, which is sealed into the almost complete vacuum of 10 -meter-diameter cylinder, will be four gyroscopes -- each with a 22-ton flywheel spinning constantly for stability. The movement of the duck is controlled by internal computers, which let energy pour into the flywheels during rough periods and come out into the generator as needed.
To the layman, that sounds expensive. But, Mr. Salter argues, a ton of stell costs more than a computer. "What I'm trying to do is find places to shove computers in to save steel," he says.
He is, without doubt, a perfectionist. His aim: To produce a machine that will run for 25 years in some of the severest conditions known to man with no servicing at all. If he can succeed, the $:1.6 million ($3.6 million) per duck will be well worth the investment.
Mr. Salter is up against some entrenched thinking."All the pressures of our present accounting system," he says, "make you make garbage that you throw away in five years." But he is helped by North SEa of technology and encouraged by the success of long-lasting satellite structures.
Has mankind ever developed anything that has lasted 25 years without servicing, I ask him. His surprising answer: Britain's sewer system, some of which has survived for 150 service-free years -- so long that nobody knows exactly where some of it is located.
Will wave energy prove efficient? Britain's electricity now costs about 2 pence (4.5 cents) per kilowatt-hour. Recent research has brought down the wave-power costs to an estimated 5 to 15 pence (12 to 34 cents) per kilowatt-hour. Mr. Salter looks forward to producing energy from the waves in the early 1990s, he says, although many feel wavepower technology belongs to the 21st century.
Meanwhile, in the laboratory his colleague, Dr. Greenhow, redesigns the polystyrene models, seeking ways to improve on the record of 92 percent energy extraction which he already has achieved.
Dr. Salter has a strong incentive: A 10 percent loss of efficiency translates into $:10 million ($22.5 million) a year for a string of ducks.
"That's 10 times my salary for every duck," he smiles, tinkering with another bolt.