hen the steel shell called Osprey confronted the sea, it was W David facing Goliath. This

time, Goliath won. Osprey was an experiment in renew-

able energy production that challenged the power of the sea in 1995. A 750-metric ton structure the size of a small apart- ment house, it was designed to squat on the seabed, half submerged in 14 meters of water. Placed 100 m from shore at Dounreay, Scotland, it was to convert the energy in the waves striking it into elec- tricity. This David was supposed to shrug off the worst that the oceanic Goliath could throw at it and keep powering the lights of Dounreay with a steady stream of environmentally “green” electricity.

Instead, Goliath caught David off guard before the challenger could even take a stand. One day in early August, before the construction crew had finished in- stalling Osprey, huge waves rolled in and smashed open the structure’s gi- ant ballast tanks. Although Osprey’s builders had time to rescue valuable equipment, the sea eventually tore the device apart.

“It was not the best day I’ve had,” re- calls Allan Thomson, head of the com- pany that built Osprey. “But we learned a lot from it,” he maintains.

For instance, they learned that they had better go ashore to build their next wave-power plant-which they did. Now Thomson and his colleagues at Wavegen, a company in Inverness, Scotland, are celebrating. In Novem- ber, they commissioned as the world’s first commercial wave-power station a device they built into the rocky west coast of the Scottish island Islay. It generates a peak power of 500 kilowatts (kw), enough to run about 400 island homes.

The opening of the plant, named Limpet, stems from a dream that dates back at least 2 centuries. That’s when two French inventors filed the first known patent for a scheme to harness ocean waves to run a machine. Even Thomson and others at Wavegen admit, however, that the small power plant they’ve built is far from the ultimate real- ization of that dream.

Indeed, wave-power developers world- wide are devising many potentially more

234

effective technologies that they antici- pate could compete with other power sources and contribute to more electric grids within the next few years. Ironically, these innovations in renewable energy build upon the achievements of a decid- edly nonrenewable branch of the energy business: offshore oil and gas drilling.

If the spin-offs from that industry had been available to wavepower researchers in the 1970s, ocean power plants might al- ready be common. Without such a head start, however, Stephen Salter of the Uni- versity of Edinburgh and other re- searchers, mainly in the United Kingdom, devoted about a decade to the goal of building large-scale, 2,000-megawatt wave- energy plants. The collapse of that pro- gram-whether because of inadequate

winds continually pump energy into them. By the time the waves hit the coast, they’re brimming with power.

Waveenergy specialists have estimated the power content of waves off coasts all over the world. They rank the areas in terms of their waves’ average rate of ener- gy production, or power, in kilowatts per meter (kW/m) of shoreline. The ratings of the most power-rich areas, such as the west coasts of Scotland, northern Canada, the US. northwest and northeast seaboards, southern Africa, and Australia, range from about 40 to 70 kW/m. A typical American home, without electric heat, draws around 1 kilowatt on average and 3 to 4 kW during peak summertime use, says Steve Rosenstock of the Edison Elec- tric Institute in Washington, D.C.

Wave-power-poor areas include the coasts of the southeastern United States.

support or overly ambitious goals-left wave energy with a credibility problem and scared off investors. Now, wave ener- gy is riding a new surge.

aves are ultimately a form of solar energy. The sun heats up W Earth’s surface, causing winds

that, in turn, drive waves. The best wave- energy regions tend to be on seacoasts at the receiving end of waves driven by the wind across long fetches of water. As the waves travel-say across the North Atlantic to the west coasts of Europe-the

SCIENCE NEWS, VOL. 159

serve. Renewable-energy-markets ana- lyst Thomas W. Thorpe of AElA Technolo- gy in Harwell, England, has calculated wave power’s potential worldwide con- tribution. If the technologies being devel- oped today become widely used, wave energy could amount to nearly 16 per- cent of the world’s current total electrici- ty output, says Thorpe.

That would be nearly 2,000 terawatt- hours (TWh) annually, or as much as the world’s large-scale hydroelectric plants produce, Thorpe reported last December at the Fourth European Wave Energy Conference in Aalborg, Denmark.

APRIL 14, 2001

Helping spur the technology tc- ward those goals, Europe’s central government, the European Union, is aiming to double to 12 percent by 2010 the contribution of renewable sources, including waves, to the re- gion’s energy supply. Meanwhile, the United Kingdom recently passed leg- islation covering the same time peri- od. It will require power companies to boost the renewable portion of their total power output to 10 percent.

On this side of the Atlantic, how- ever, the U S . government has made little effort to develor, wave enerm,

totypes built in Scotland, Australia, India, China, and elsewhere during the past 15 years, use what’s known as an oscillating water column to turn wave energy into electricity. En- gineers are preparing to power up soon, another 400-kW oscillating-wa- ter-column plant sponsored mainly by the European Union on Pic0 Is- land in Portugal’s Azores. It is ex- pected to supply some 10 percent of the electricity for the island’s 15,000 inhabitants.

These onshore systems trap waves in a Dartiallv submerged, arti-

despite what some researchers say Many researchers first test their wave-power ficial cavern with hole in one wall is great potential for the technology designs, such as this pinched cylinder (arrow) called above the water line. The hole leads along some U S . coasts. For in- a duck, in waves created in a lab. to an airdriven turbine. As the crest stance, the Department of Energy of a wave enters the cavern, it raises sponsors no wave-power research, ac- sieur Girard and his son to use direct me- the water level quickly, pushing the air cording to spokesman Christopher Pow- chanical action to drive pumps, saws, above the wave through the hole and ers of the agency’s National Renewable mills, or other heavy machinery. These spinning the turbine’s blades. The tur- Energy Laboratory in Golden, Colo. French inventors envisioned attaching bines are designed to turn the same way

heavy wooden beams to docked battle no matter which way the air flows ships and taking advantage of their ves- through them, so the machine also runs sels’ bobbing to operate the beams as as the retreating wave sucks air back in- levers against fulcrums on shore. However, to the chamber. When the waves be- there is no evidence that the men ever car- come too rough, a valve closes to pro-

tect the turbine. ried out their plan. Nowadays, a wave harnesser’s objective Although Limpet now supplies power

is typically electricity from a generator. to the local electric grid, it can’t yet beat Within such a device, the converted wave the prices of other renewable or conven- momentum spins coils of wire inside ring- tional energy sources. Wavegen expects shaped magnets to produce a current. to generate a kilowatt-hour of electricity

Wavegen’s Limpet plant, as well as pro- for 7 to 8 cents, whereas fossil fuel and

o convert wave action into useful energy, a power plant must provide a way for the waves to drive some-

thing-such as turbine blades or pistons. The apparatus might briefly store the waves’ energy, or it might apply the waves’ momentum immediately to some mechanism.

The first wave-power patent was for a 1799 proposal by a Parisian named Mon-

T

Power of waves inspires ingenuity Oscillating Water Column

turbine ’ -generator

Wwefl Y Waves push air through turbine, then suck it back, as they advance and recede. Devices operate onshore (above) or offshore.

Archimedes Wave S w i na

Pelamis McCabe Wave Pump

Serpentine device flexes in oncoming waves. Pivoting of segments drives pistons that pressurize oil, which runs generators.

Nodding Duck

Bobbing of outer barges, hinged to central barge stabilized by underwater plate, runs pumps.

IPS Buoy

Air tank in fixed, submerged tower rises and falls with passing waves. The oscillations turn a generator shaft.

Waves tip beak of floating device (seen on end). Beak‘s rotation relative to central shaft pumps oil, which drives generator.

Seawater inside open-ended tube stabilizes piston. Motion of bobbing buoy relative to piston shaft drives generator.

APRIL 14,2001 SCIENCE NEWS, VOL. 159 235

nuclear plants yield the same energy for about 5 cents. Nonetheless, waveenergy developers take heart that their project- ed generation cost has already dropped to about half of what it was for wind ener- gy at an equivalent developmental stage.

For now, being onshore is an advan- tage for wave-power generators. The rela- tive simplicity of onshore plants, com- pared with devices meant for deep water, is helping researchers and builders get the Limpet and the Azores plants up and running. However, such shoreline plants also face an insurmountable obstacle that will soon end their dominance with- in the field, wavepower developers say.

No matter how potent the waves off a particular stretch of coast may be, “in shallower water, the wave energy is ab- sorbed by the seabed,” notes George W. Taylor of Ocean Power Technologies in Pennington, N.J. “By the time a wave is breaking on a reef or sand bar, it has lost most of its energy.”

Taylor is cofounder of a company that is creating buoys that generate 20 kW of electricity each for recharging US. Navy robot submarines. The devices, devel- oped with funding from the Office of Naval Research, could also supply elec- tricity to offshore desalination plants or, in arrays, produce municipal power-the company’s main goal, he says. The buoys generate additional power from stream- ers of an innovative piezoelectric plastic (SN: 11/18/89, p. 328). A piezoelectric substance creates electricity when de- formed by an outside force. The stream- ers hang below the waves, and their flex- ing captures energy from the passing tidal currents, says Taylor.

The optimal location for harvesting wave energy is in water about 50 to 100 m deep, says wave-power developer Richard Yemm of Ocean Power Delivery Systems in Edinburgh. There, waves retain nearly all the power they’ve gathered while crossing the ocean, but the sea bottom is near enough that anchoring wavepower equipment is easier and cheaper than in deeper waters.

Yemm’s company is developing a sinu- ous device made up of interconnected floating tanks meant to wriggle along the wave tops. Named Pelamis after a genus of sea snakes, the 120-m-long sea serpent pushes pistons with its flexing motion. That action pressurizes oil, which then runs electric generators.

As a former wind-power developer, Yemm argues that placing a wave-power plant onshore is akin to “building a wind turbine behind a tall building.”

he names of many of the offshore devices now being developed sound T as jolly as carnival rides. There are

the Mighty Whale, Wave Dragon, Archimedes Wave Swing, WavePlane, Pen- dulor, and Salter’s Nodding Duck, to name just a few.

are operating in “a ver; hos- Four huge tubes jut from the base of a new type of tile environment,” says Anto- oscillating-wave-column device installed in February nio F. de 0. Falcao of the Lis- off Plymouth, England. The tubes make this device, bon Institute of Technology which floats with tubes down, able to harvest in Portugal. simultaneously waves of differing frequencies.

Althoigh offshore is the way to go, he says, “you have problems of getting electricity to land and also of an- choring. In stormy weather, you have very large forces, and you have the problem of maintenance if you are very far from the coast, especially in winter.” There’s also the tendency of seawater to short-circuit and corrode equipment. Falcao is the leader of the Pic0 Island project.

Offshore-wave-power developers are moving ahead with some trepidation. Yemm, for instance, is concerned that one of the new offshore devices might pull loose of its moorings and drift into a ship’s path or wash up on a beach. The demise of the Osprey didn’t help wave- power public relations. “We can’t afford a

screw-up,” says Salter. Fortunately, wave-power developers

say, many solutions to the problems Fal- cao notes already exist, thanks to the offshore oil and gas industry. The fossil- fuel industry has developed better ways to anchor equipment, more durable and corrosion-resistant materials, and irn- proved cables for carrying electric cur- rent underwater. For instance, electrical connectors that are easily mated and unmated underwater are proving vital to modular wave-energy designs. Be- cause of the know-how and technology of oil-rig builders, says Yemm, “wave en- ergy is now [becoming] not only practi- cal but inevitable.” u

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236 SCIENCE NEWS, VOL. 159 APRIL 14, 2001