Wind Power for Pennies
Windmills may finally be ready to compete with fossil-fuel generators. The technology trick: turn them backwards and put hinges on their blades.
The newest wind turbine standing at Rocky Flats in Colorado, the U.S. Department of Energy’s proving ground for wind power technologies, looks much like any other apparatus for capturing energy from wind: a boxy turbine sits atop a steel tower that sprouts two propeller blades stretching a combined 40 meters-almost half the length of a football field. Wind rushes by, blades rotate, and electricity flows. But there’s a key difference. This prototype has flexible, hinged blades; in strong winds, they bend back slightly while spinning. The bending is barely perceptible to a casual observer, but it’s a radical departure from how existing wind turbines work-and it just may change the fate of wind power.
Indeed, the success of the prototype at Rocky Flats comes at a crucial moment in the evolution of wind power. Wind-driven generators are still a niche technology-producing less than one percent of U.S. electricity. But last year, 1,700 megawatts’ worth of new wind capacity was installed in the United States-enough to power 500,000 houses-nearly doubling the nation’s wind power capacity. And more is on the way. Manufacturers have reduced the cost of heavy-duty wind turbines fourfold since 1980, and these gargantuan machines are now reliable and efficient enough to be built offshore. An 80-turbine, $245 million wind farm under construction off the Danish coast will be the world’s largest, and developers are beginning to colonize German, Dutch and British waters, too. In North America, speculators envision massive offshore wind farms near British Columbia and Nantucket, MA.
But there is still a black cloud hovering over this seemingly sunny scenario. Wind turbines remain expensive to build-often prohibitively so. On average, it costs about $1 million per megawatt to construct a wind turbine farm, compared to about $600,000 per megawatt for a conventional gas-fired power plant; in the economic calculations of power companies, the fact that wind is free doesn’t close this gap. In short, the price of building wind power must come down if it’s ever to be more than a niche technology.
And that’s where the prototype at Rocky Flats comes in. The flexibility in its blades will enable the turbine to be 40 percent lighter than today’s industry standard but just as capable of surviving destructive storms. And that lighter weight could mean machines that are 20 to 25 percent cheaper than today’s large turbines.
Earlier efforts at lighter designs were universal failures-disabled or destroyed, some within weeks, by the wind itself. Given these failures, wind experts are understandably cautious about the latest shot at a lightweight design. But most agree that lightweight wind turbines, if they work, will change the economic equation. “The question would become, How do you get the transmission capacity built fast enough to keep up with growth,’” says Ward Marshall, a wind power developer at Columbus, OH-based American Electric Power who is on the board of directors of the American Wind Energy Association, a trade group. “You’d have plenty of folks willing to sign up.”
And, say experts, the Rocky Flats prototype-designed by Wind Turbine of Bellevue, WA-is the best hope in years for a lightweight design that will finally succeed. “I can say pretty unequivocally that this is a dramatic step in lightweight [wind turbine] technology,” says Bob Thresher, director of the National Wind Technology Center at Rocky Flats. “Nobody else has built a machine that flexible and made it work.”
Steady as She Blows
Wind turbines are like giant fans run in reverse. Instead of motor-driven blades that push the air, they use airfoils that catch the wind and crank a generator that pumps out electricity. Many of today’s turbines are mammoth machines with three-bladed rotors that span 80 meters-20 meters longer than the wingspan of a Boeing 747. And therein lies the technology challenge. The enormous size is needed if commercial wind turbines are to compete economically because power production rises exponentially with blade length. But these vast structures must be rugged enough to endure gales and extreme turbulence.
In the 1970s and ’80s, U.S. wind energy pioneers made the first serious efforts at fighting these forces with lightweight, flexible machines. Several startups installed thousands of such wind turbines; most were literally torn apart or disabled by gusts. Taking lightweight experimentation to the extreme, General Electric and Boeing built much larger prototypes-behemoths with 80-, 90- and even 100-meter-long blades. These also proved prone to breakdown; in some cases their blades bent back and actually struck the towers.
All told, U.S. companies and the Department of Energy spent hundreds of millions of dollars on these failed experiments in the 1980s and early 1990s. “The American model has always gravitated toward the light and the sophisticated and things that didn’t work,” says James Manwell, a mechanical engineer who leads the University of Massachusetts’s renewable-energy research laboratory in Amherst, MA.
Into these technology doldrums sailed researchers from Denmark’s Ris National Laboratory and Danish companies like Vestas Wind Systems. During the past two decades they perfected a heavy-duty version of the wind turbine-and it has become the Microsoft Windows of the wind power industry. Today, this Danish design accounts for virtually all of the electricity generated by wind worldwide. Perhaps reflecting national inclinations, these sturdy Danish designs had little of the aerodynamic flash of the earlier U.S. wind turbines; they were simply braced against the wind with heavier, thicker steel and composite materials. They were tough, rugged-and they worked.
What’s more, in recent years, power electronics-digital silicon switches that massage the flow of electricity from the machine-further improved the basic design. Previously, the turbine’s rotor was held to a constant rate of rotation so its alternating-current output would be in sync with the power grid; the new devices maintain the synchronization while allowing the rotor to freely speed up and slow down with the wind. “If you get a gust, the rotor can accelerate instead of just sitting there and receiving the brute force of the wind,” says Manwell.
Mastering such strains enabled the Danish design to grow larger and larger. Whereas in the early 1980s a typical commercial machine had a blade span of 12.5 meters and could produce 50 kilowatts-enough for about a dozen homes-today’s biggest blades stretch 80 meters and crank out two megawatts; a single machine can power more than 500 homes.
The newest challenge facing the Danish design is finding ways for it to weather the corrosive and punishing offshore environment, where months can pass before a mechanic can safely board and fix a turbine. Vestas, for one, is equipping its turbines with sensors on each of their components to detect wear and tear, and backup systems to take over in the case of, say, a failure in the power electronics.
Vestas’s approach goes to the test this summer, as Denmark’s power supplier begins installing 80 Vestas machines in shallow water 14 to 20 kilometers off the Danish coastline. It will be the world’s biggest offshore wind farm, powering as many as 150,000 Danish households.
These upgrades will make big, heavy turbines more reliable, but they don’t add up to a fundamental shift in the economics of wind power. Nations like Denmark and Germany are prepared to pay for wind power partly because fossil fuels are so much more costly in Europe, where higher taxes cover environmental and health costs associated with burning them. (About 20 percent of Denmark’s power comes from wind.) But for wind power to be truly cost competitive with fossil fuels in the United States, the technology must change.
What makes Wind Turbine’s Rocky Flats design such a departure is not only its hinged blades, but also their downwind orientation. The Danish design faces the blades into the wind and makes the blades heavy so they won’t bend back and slam into the tower. The Wind Turbine design can’t face the wind-the hinged blades would hit the tower-so the rotor is positioned downwind. Finally, it uses two blades, rather than the three in the traditional design, to further reduce weight.
Advances in the computer modeling of such dangerous forces as vibration helped the design’s development. Flexible blades add an extra dimension to the machine’s motion; so does the fact that the whole machine can freely swivel with the wind. (Traditional designs are driven to face the wind, then locked in place.) Predicting, detecting and preventing disasters-like rapidly shifting winds that swing a rotor upwind and send its flexible blades into the tower-are control challenges even with the best design. “If you don’t get that right, the machine can literally beat itself to death,” says Ken Deering, Wind Turbine’s vice president of engineering.
Two years ago, when Wind Turbine’s prototype was erected at Rocky Flats, there were worries that this machine, too, would beat itself to death. Thresher says some of his staff feared that the machine, like its 1980s predecessors, would not long escape the scrap heap. Today, despite some minor setbacks, those doubts are fading.
Emboldened by its early success, Wind Turbine has installed, near Lancaster, CA, a second prototype, with a larger, 48-meter blade span. By the end of this year, the company expects to boost blade length on this machine to 60 meters-full commercial size. What’s more, this new prototype has a thinner tower, aimed at reducing the noisy thump-known as a “wind shadow”-that can occur each time a blade whips through the area of turbulent air behind the tower. And with its lighter weight, the turbine could be mounted atop higher towers, reaching up to faster winds.
Whatever the advances in technology, however, the wind power industry still faces significant hurdles, starting with uncertain political support in the United States. In Europe, wind power is already a relatively easy sell. But in the United States, wind developers rely on federal tax credits to make a profit. These vital credits face chronic opposition from powerful oil and coal lobbies and often lapse. The wind power industry raced to plug in its turbines before these credits expired at the end of last year, then went dormant for the three months it took the U.S. Congress to renew them. Congress extended the credits through the end of next year, initiating what is likely to be yet another start-and-stop development cycle.
A second obstacle to broad adoption is the wind itself. It may be free and widely accessible, but it is also frustratingly inconsistent. Just ask any sailor. And this fickleness translates into intermittent power production. The more turbines get built, the more their intermittency will complicate the planning and management of large flows of power across regional and national power grids. Indeed, in west Texas, a recent boom in wind turbine construction is straining the region’s transmission lines-and also producing power out of sync with local needs: wind blows during cool nights and stalls on hot days when people most need electricity.
Texas utilities are patching the problem by expanding transmission lines. But to really capture the value of wind power on a large scale, new approaches are needed to storing wind power when it’s produced and releasing it when needed. The Electric Power Research Institute, a utility-funded R&D consortium in Palo Alto, CA, is conducting research on how to make better one-day-ahead wind predictions. More important, it is exploring ways to store energy when the wind is blowing. “We need to think about operating an electrical system rather than just focusing on the wind turbines,” says Chuck McGowin, manager for wind power technology at the institute. Storage facilities “would allow us to use what we have more efficiently, improve the value of it.”
In the northwest United States, one storage option being developed by the Portland, OR-based Bonneville Power Administration balances wind power with hydroelectric power. The idea is simple: when the wind is blowing, don’t let the water pass through the hydroelectric turbines; on calm days, open up the gates. And the Tennessee Valley Authority is even experimenting with storing energy in giant fuel cells; a pilot plant is under construction in Mississippi.
Wind power faces plenty of obstacles, but there’s more reason than ever to believe these obstacles will be overcome. Worries over the environmental effects of burning fossil fuels and political concerns about an overdependence on petroleum are spurring a boom in wind turbine construction. But it is advances in the technology itself, created by continued strong research efforts, that could provide the most critical impetus for increased use of wind power.
At Rocky Flats, four rows of research turbines-a total of a dozen machines ranging from 400-watt battery chargers to grid-ready 600-kilowatt machines-share a boulder-strewn 115-hectare plain. With the Rocky Mountains as a backdrop, their blades whup against the breezes blowing in from El Dorado Canyon to the west. At least, they do much of the time. “We have a lot of calm days, in the summer in particular, and for a testing site it’s good to have a mix,” Thresher says.
Calm days may be good for wind turbine research, but they’re still among the biggest concerns haunting wind turbine commercialization. While no technology can make the wind blow, lower-cost, reliable technologies appear ready to take on its fickleness. And that could mean a wind turbine will soon sprout atop a breezy hill near you.