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Winding Up PUBLIC ACCESS

Two Companies-One Big, One Small-Aim to Put Wind Turbines on the U.S. Electrical Map.

[+] Author Notes

Associate Editor

Mechanical Engineering 125(01), 36-39 (Jan 01, 2003) (4 pages) doi:10.1115/1.2003-JAN-1

This article reviews today’s wind turbines that are a far cry from the windmills that once reached into the rural sky to pump water for irrigation. A single utility-scale turbine, built from European designs, can provide enough electricity to power more than a thousand homes when the wind is blowing. Wind power is increasingly viewed as an ecologically friendly energy source, without the carbon emissions of fossil fuels or the watershed wrecking force of hydropower. Wind power enthusiasts point out that wind is the fastest-growing source of electricity in the world. In the United States alone, the amount of installed wind power grew by 66 percent in 2001, according to the American Wind Energy Association in Washington. WTC’s two-bladed design makes the most of the lightness the downwind configuration can offer. Each blade is reinforced by a hydraulic piston running from the hub, and the root itself is attached to the rotor shaft by a hinged coupling. The pistons can reposition each blade independently over the course of a single rotor sweep.

Jacob Stone Drove up a gravel lane on his family's farm in Madison, N.Y., with one buck already in the bed of his pickup. But on that chilly November afternoon, the snow-covered corn stubble of the Stone farm wasn't just a hunting ground; it was also a power plant. Looming 220 feet overhead, seven wind turbines were spinning a dozen times a minute, making a gentle whir every time a blade passed by.

Times have been hard for farmers in up state New York, and royalties from the electricity harvested by the turbines "weren't making us millionaires," Stone said. "But the money helps keep the farm going."

The turbines in Madison, owned by PG&E National Energy Group of Bethesda, Md., and rated at 1.65 megawatts each, began operating in the fall of 2000.

Twenty-five miles to the west in Fenner, the largest wind farm east of the Mississippi, a 20-turbine, 30-MW facility spread over 14 farms, began service in late 2001. More and more, farms and ranches across the country are also harvesting the wind.

The wind turbines of today are a far cry from the windmills that once reached into the rural sky to pump water for irrigation. A single utility-scale turbine, built from European designs, can provide enough electricity to power more than a thousand homes when the wind is blowing.

Wind power is increasingly viewed as an ecologically friendly energy source, without the carbon emissions of fossil fuels or the watershed wrecking force of hydropower. And last month, the former senator from Nebraska, Bob Kerrey, called for national energy independence by relying more on renewable power sources, including wind.

Now two American manufacturers are attempting to move wind power into the mainstream through radically different approaches. Industrial giant General Electric and a scrappy start-up, The Wind Turbine Co., are working to develop a new generation of wind turbines that will produce electricity more cheaply than any other source. If one-or both-succeed, wind turbines like ones on the Stone farm will sprout up everywhere the wind blows.

Wind power enthusiasts like to point out that wind is the fastest-growing source of electricity in the world. In the United States alone, the amount of installed wind power grew by 66 percent in 2001, according to the American Wind Energy Association in Washington. Globally, capacity grew some 37 percent.

Impressive, but that growth is off a very small base. The worldwide wind power capacity is 27,000 MW, and in the United States, wind accounts for 4,265 MW of generating capacity, producing 11.2 billion kilowatt-hours of electricity annually. That's less than 1 percent of the national total, or only enough electricity to light up Delaware.

Even in California, which has the largest wind power infrastructure, with 1,713.5 MW of generating capacity, wind produces less electricity than just one of that state's nuclear power plants. Wind may account for 18 percent of the electricity consumed in small, windy Denmark, but in the U.S., it has made scarcely a ripple.

Even so, some experts are confident that wind can make a leap from a so-called alternative energy source to a mainstream power solution. Some of this relates to the sheer size of the resource: The Great Plains have been called "the Saudi Arabia of wind power," and harnessing the wind potential of North Dakota alone could light up a third of the United States. Wind turbines are also becoming a more mature technology, better understood mechanically and increasingly dependable.

"The industry average for the turbines installed in the early 1980s was an availability of only 25 percent; 75 percent of the time they were down," said John Dunlop, A WEA's northern plains regional manager. "Now, projects have a guaranteed availability of 95 percent, and there are projects running at 99 percent on a yearly basis."

Most importantly, wind power is dropping in price. Current wind farms can produce electricity for as little as 5 cents per kilowatt hour. That's a bit above the wholesale price for electricity in most parts of the country, although a federal production tax credit makes it competitive with traditional sources.

However, the price keeps falling, and Bob Thresher, director of the National Wind Technology Center in Boulder, Colo., says that as the technology improves, wind is approaching a critical threshold, 3 cents per kilowatt-hour, the rough cost of a gas-fired combined-cycle plant. "If wind is the cheapest electricity on the grid, utilities will dispatch it first and use it first ," Thresher said. "They'll bring in the fuels only when they have to. Wind would have that place at 3 cents per kilowatt-hour.

" I've been struggling for 30 years to get the cost of wind down so it can compete on the grid," Thresher added. "And we're still a penny and a half away."

Reaching that threshold won't be simple. Wind is a much more complicated resource to harness than is coal or even hydropower. The wind doesn't always blow, or it blows at the wrong speed or in disruptive gusts, so wind power is inherently unreliable, and backup power or costly storage systems are necessary. And the best wind sites are often far from population centers, which creates problems in delivering wind power once it's captured.

Even capturing the wind efficiently is fraught with challenges. Utility grade wind turbines have been getting progressively larger, with rotors upward of300 feet across from blade tip to blade tip. The greater the area encompassed by the rotating blades, the more wind the rotors can capture.

But this size comes with a cost: The mass of the rotor blades rises by the cube of their length, meaning that bigger wind turbines can cost more per watt than smaller ones. Add to that the challenge of building a tower 200 or even 300 feet tall to mount the turbine, or of keeping such a huge contraption oriented into a constantly shifting wind, and wind power quickly turns from a cheap source of energy to a logistical headache.

Recognizing the potential-and problems-in harnessing the wind, the U.S. Department of Energy has worked to assist the development of wind energy. It has the turbine testing facility in Boulder where Thresher works, for instance, and has funded research into advanced control systems and high-tech rotor blades. In the mid-1990s, the DOE gave $40 million in seed money to private companies to develop a new generation of lowcost, utility-scale wind turbines. The intent was for American companies to devise and build the machines that realize Bob Thresher's dream of making wind "the cheapest stuff on the grid."

There's more than corn to harvest on this farm in Fenner, N.V. The wind power that's collected by each of these GE Wind Energy l.5-MW turbines can light up nearly 1,000 homes.

Grahic Jump LocationThere's more than corn to harvest on this farm in Fenner, N.V. The wind power that's collected by each of these GE Wind Energy l.5-MW turbines can light up nearly 1,000 homes.

In spite of the DOE's interest, wind energy is still an industry dominated by European manufacturers. The top companies in the American market are Vestas Wind Systems and NEG Micon, both Danish firms.

The Europeans have the advantage of a consistent prowind business climate, said Steve Zwolinski, president of GE Wind Energy in Tehachapi, Calif. "You need four things to put wind together: wind, obviously; a transmission and distribution infrastructure; public support, and some sort of public subsidy," Zwolinski said. "They've had all four in Germany on a consistent basis during the last decade."

The United States, on the other hand, has not provided constant public or political support to wind, and this factor has created "a much more sporadic industry," Zwolinski said.

He may help to change this. In May 2002, General Electric bought the wind power division of Enron the bankrupt energy giant, and instantly became a major force in the industry. One of the product lines GE got in the deal is a 1.5-MW turbine, the largest now manufactured in the U.S. First shipped in the late 1990s, the 1.5- MW machine is the company's workhorse, with more than a thousand now in service throughout the world. "And we'll probably double that by the end of 2003," Zwolinski predicted.

Efficiencies of scale aside, wedding a windmill company to a diversified industrial giant ought to lead to a higher level of sophistication in wind power design. "The design of wind turbines is not as robust as other very advanced electromechanical devices," Zwolinski said. "Reliability still needs to be built into the design."

In its far-flung businesses, GE already has expertise in most of the individual parts of a wind turbine, from composite material for extruding rotor blades to generators to power system electronics. To take advantage of this edge, GE Wind has doubled the number of engineers since buying the business from Enron and h as upped the spending on technology sixfold.

One place to view a possible windfall from this investment is in Albacete, Spain, where GE Wind is testing an experimental 3.6-MW wind turbine. The machine is enormous, with a rotor some 330 feet in diameter mounted on a nearly 40-story tower. Although the giant machine is being tested on land, it is designed for offshore installations, where strong, sustained winds and the high cost of building a platform make very large wind turbines both advantageous and necessary.

The testing of the 3.6-MW turbine has been uneventful, and GE Wind hopes to begin building a wind farm in the waters of the Irish Sea this year.

A technician works to install a l6O-foot-long blade on a 3.6-MW turbine built by GE Wind Energy. Such mammoth machines are being developed for offshore wind farms.

Grahic Jump LocationA technician works to install a l6O-foot-long blade on a 3.6-MW turbine built by GE Wind Energy. Such mammoth machines are being developed for offshore wind farms.

If GE Wind plans to draw on the technological reservoir of its parent company to gradually improve its standard design, The Wind Turbine Co. of Bellevue, Wash., is taking the opposite strategy. WTC has designed and built a radically different kind of wind turbine, one that promises to be lighter and cheaper than competing makes. "When it comes to pushing the envelope," A WEA's Dunlop said, " nobody else even comes close."

There's just one problem: The people behind the company are pinning their hopes on a design that has failed again and again over the past three decades.

Virtually every commercial wind turbine operates with the rotor turned to face the wind and with the nacelle housing the generator trailing behind. That design has the inherent advantage of capturing an unobstructed cross-section of the wind, but at the cost of building strong, rigid components.

Turning the turbine around, creating a so called downwind machine, has intrigued engineers for more than a generation. Downwind machines can employ lighter and more flexible rotor blades than those used by upwind turbines, since the wind will bend the blades away from the support tower. And the towers themselves can be allowed to flex. What's more, the downwind blades should orient themselves into the best position to capture the wind, in theory eliminating complicated control mechanisms, or at least reducing them.

Unfortunately, developing a design that can take advantage of this capacity to shed stresses, instead of absorbing them as the rigid upwind machines do, requires enormous computing power. "In the early days of the wind business, designs were improved by trial and error," said WTC president Larry Miles. "They couldn't do the kind of dynamic analysis that it takes to do what we're doing now."

Easier on the Birds

From half a mile away, the wind turbines in Madison, N.V., seemed as harmless as the afternoon breeze they were harnessing. But the noise-like the swinging of a half-dozen rusty gates-would take some getting used to.

Scratch that. The sound was actually the honking of a flock of migrating geese rooting around in a stubbly field.

But the association of birds with wind power is often not so benign. Some environmentalists oppose wind turbines because of their potential to smite birds in mid-flight. Wind farms have been derided as "Bassmatics for birds" or "condor Cuisinarts." That reputation was always a bit overblown, experts say, and newer designs have almost eliminated it. "In a year, we found four dead birds in Madison," said Paul Kerlinger, a biologist and environmental consultant in Cape May, N.J. "People hit more birds with their cars."

You get only one chance to make a first impression, and the first utility-scale wind project to gain notice was installed in Altamont Pass, east of San Francisco, in the 1980s. Even today, the wind farm is one of the nation's largest, with some 7,000 turbines on 80,000 acres generating some 640 million kilowatt-hours a year.

But the site also happens to be the breeding ground for a number of bird species, including golden eagles, and the combination proved deadly. By one count, approximately 40 eagles and nearly a hundred other birds are struck and killed by rotor blades each year.

Fortunately, Altamont seems to be the exception, not the rule. Much of that is due to the evolution of wind turbine design. Rather than filling a site with thousands of small turbines, modern wind farms feature fewer, larger units. And the large rotors turn more slowly than smaller ones, creating less of a danger for passing birds. Tower design has changed for the better as well: Lattice towers that provide multiple perching spots have given way to sleek tubular models.

The result, says Kerlinger, is that bird deaths from newer wind installations are not ecologically significant. "Wind is, all things considered, about as environmentally benign a power source as you can find," he said.

The National Audubon Society tends to agree. Bob Perciasepe, Audubon's senior vice president for public policy, warns against setting up wind farms too close to environmentally sensitive areas or migratory fly-ways. But he said that coal-burning power plants pose a greater threat to bird populations than do wind farms.

"In the Northeast, loons are accumulating mercury from power plant emissions," Perciasepe said, and acid rain creates calcium-deficient eggshells. "There are avian impacts from fossil fuel pollution, and those impacts are lessened by using renewable energy."

Guy wires help to support the slender. flexible tower of this 500-kW downwind turbine. which is being tested by The Wind Turbine Co.

Grahic Jump LocationGuy wires help to support the slender. flexible tower of this 500-kW downwind turbine. which is being tested by The Wind Turbine Co.

WTC's two-bladed design makes the most of the lightness the down-wind configuration can offer. Each blade is reinforced by a hydraulic piston running from the hub, and the root itself is attached to the rotor shaft by a hinged coupling. The pistons can reposition each blade independently over the course of a single rotor sweep. "The blade can flap with very little force put on the blade support," Miles said. "The fatigue loading on the root of the blade and throughout the length of the blade is significantly smaller on our machine than it is on an upwind style machine."

The payoff for all this is load reduction: The blades can be considerably thinner-and lighter-than those found on upwind machines. And the design also allows for other weight savings in the nacelle. "You can look at the weight of the machine on the top of the tower as a proxy for the cost," Miles said, "and the rotor diameter as a proxy for the power production." The weight relative to the area swept by the rotor for the WTC machine will be about 40 percent less than that of the industry leader, Miles said. It's a design that should, in theory, drive down the cost of wind energy.

In December 2001, WTC installed a 5OO-kW downwind turbine in rural Los Angeles County, California, for testing. Shortly after the beginning of the shakedown period, a signal processor failed in the pitch control system, and the control piston pulled the blade backward until it smacked into the tower. "It didn't do any damage to the tower. It barely scuffed the paint," Miles said. "But we learned one the hard way."

The accident was a setback for the program; a new blade won't be up and running until this month. But WTC expects to move quickly into development and testing of a more advanced blade, and the company expects to begin installing turbines for commercial use early next year.

Between WTC's gamble and GE Wind's refining, wind turbines could be ready to break into the mainstream of electrical generation before the end of the decade. In places like the Stone farm, windy November afternoons won't just make for good hunting. They'll keep the lights burning all over the land.

Copyright © 2003 by ASME
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