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Photo of a wind turbine nacelle bolted to a coupling device that, in turn, is connected to a large electric motor via a shaft.

NREL's newest dynamometer is capable of testing wind turbines up to 5 megawatts in-capacity. The device exposes the wind turbine's drivetrain and generator—housed in the white nacelle on the left—to the loads and torques that they may experience in the field.
Photo by Dennis Schroeder, NREL

From the Start: NREL Nurtures a Growing Wind Industry

The National Wind Technology Center grew from a site for testing small turbines into the nation's premier research facility for wind energy technologies, helping the wind industry grow with it.

On the plains south of Boulder, Colorado, nestled against the foothills, is the 305-acre National Wind Technology Center (NWTC), the nation's premier research facility for wind energy technologies. The NWTC is a satellite campus of NREL and is located about 25 miles north of NREL's main campus. It hosts four megawatt-scale wind turbines, two 600-kilowatt research turbines, and an assortment of small wind turbines. Its world-class structural testing laboratory and dynamometer test facilities draw wind turbine manufacturers from around the world.

But this impressive site grew from much humbler beginnings, in the days before a true utility-scale wind turbine market existed. NREL's efforts grew alongside the wind power industry, first with testing capabilities and then with engineering solutions to many of the fledgling industry's biggest technical problems. In some ways, NREL is the Johnny Appleseed of wind turbine technology: the lab planted the seeds of engineering and testing, and years later, wind turbines began sprouting up all over the country. Yet today's blossoming industry was a distant vision in the late 1970s.

The Early Days

Shortly after NREL began operating as the Solar Energy Research Institute (SERI) in 1977, the current location of the NWTC became the site of a test facility for small wind turbines—the kind a homeowner, small business, ranch, or farm might use. Rockwell International originally operated the site, but SERI took over in 1984, testing the performance of new small wind turbines to assure potential buyers that the turbines function well.

"That role is still going on," said NREL Wind Energy Research Fellow Robert Thresher. "There are two small turbines under test right now, and we've tested eight to 10 turbines over the past three to five years."

Back when SERI started operating the wind test site in 1984, the utility-scale wind industry was in its very early years. Strong incentives in California were driving the installation of wind power facilities there—some 10,000 wind turbines were installed between 1981 and 1985—but the turbine designs of that era were prone to failure. To address that issue, the U.S. Department of Energy (DOE) funded the Cooperative Field Test Program, under which SERI researchers headed into the field to work with industry to improve the performance and reliability of their turbines.

"We worked with industry, and we ran tests on raising the turbines higher off the ground, looked at wind wakes, and did all kinds of research in the field," said Thresher. "That was really our first big cooperative program with the industry."

Developing World-Class Testing Facilities

NREL's involvement with the wind power industry grew by leaps and bounds in the late 1980s and throughout the 1990s, and the laboratory developed unique testing capabilities along the way. With blade failures common in the field, the wind industry developed a standard practice for all wind turbine blades to be full-scale tested before they were deployed commercially. As a result, one of NREL's top priorities was to build a mechanical testing facility for wind turbine blades. Blade testing began in 1989 and the facility—now called the Structural Testing Laboratory—has tested more than 100 wind turbine blades to the breaking point in the past quarter century. Watch the video to learn more about the Structural Testing Laboratory.

Wind blade testing also led to a research agreement with Kenetech Windpower, Inc., then the U.S. leader in the wind power industry. Industry needs also led NREL to build a dynamometer to test turbine drivetrains. The dynamometer is essentially a big motor that simulates the loads that the spinning rotor places on the drivetrain, including "off-axis" loads that come from gusty winds.

"The industry was saying they needed a way to test their drivetrains to put forces on the machinery before they deployed them in the field," said NREL Principal Engineer Walt Musial. "Based on this input from industry, the 2.5-megawatt dynamometer was built and commissioned in 1999. It was the first of its kind: there were lots of dynamometers out there, but they couldn't test a wind turbine at the same power levels and torque levels that we needed. So we built one that was unique, and it's been busy ever since.

"A lot of the gearbox manufacturers had ways to test their gearboxes, but we were testing not just the gearbox but the whole drivetrain, and running it through conditions that resembled what it would actually see in the field. We could make sure that all the systems were operating exactly as they were designed before they got deployed in the field, so we cut down on the number of field failures that happened at the early parts of installations.

"We didn't really know how valuable it would be as a shakeout of the full design until we got it going, and then we realized that we couldn't test a gearbox until we got all the other stuff to work."

Getting Involved on the Design Side

Aerial photo of three large and two small wind turbines on the plains with foothills in the background.

Four large utility-scale wind turbines and two smaller research turbines are the visual centerpiece of today’s National Wind Technology Center near Boulder, Colorado.
Photo by Dennis Schroeder, NREL

While NREL got heavily involved in the testing of wind turbines and blades, it also started working on the design end. Early wind turbine blades were adapted from helicopters, but NREL researchers decided to apply their aerodynamics expertise, designing a more aerodynamic blade that would better handle the roughness caused by dirt and bugs accumulating on the blades. The result was three families of turbine blade airfoils—cross-sections of the blades from the root of the blade to the tip—that licensees could use to design and build their own turbine blades. Not only did these airfoils solve the roughness problem, but once mounted on a hub to form a complete rotor—the spinning, external part of the wind turbine—they also captured about 40% more energy. The blades also changed the way the wind industry thought about airfoils.

"NREL showed the industry the properties that were necessary for a wind turbine airfoil," said Musial. "We created the whole concept that wind turbines needed different airfoils, and rotor designs had to be different than for an airplane. So we developed the capability here—and this is before the current computer technology was available—to design, test, and build these new wind turbine rotors, which produced about 40% more energy than the ones built in the 1980s."

The airfoils were a definite success, and at some point most wind turbines on the market were employing the NREL design. However, the ultimate impact of the airfoil work is how it changed the industry approach to customized blade design.

While working on airfoils, NREL was also leading efforts to improve wind turbine design as a whole. In 1990, DOE initiated the Advanced Wind Turbine Program to assist industry in incorporating advanced technology into its wind turbine designs. The NREL-led program started by studying three existing wind turbines and examining ways to improve their performance, using such approaches as larger rotors, integrated drivetrains, better braking systems, and more aerodynamic blades that used NREL airfoils.

"NREL's involvement in these advanced turbine designs ensured that best engineering practices were being followed that would lead to certification," said NREL's Brian Smith.

The program's immediate goal was to make the turbines more resilient to the loads and buffeting caused by the wind, ultimately lowering the cost of wind energy. The program explored such concepts as variable-speed wind turbines, which could adjust their speed with the wind to capture more energy; rotors that could adjust the pitch of their blades to optimize wind energy capture; and turbines that actively pointed into the wind rather than passively turning downwind like a pinwheel. NREL worked directly with the wind turbine companies to review and analyze their design concepts and to test their prototypes.

One result of this program was the Zond Z40, developed by Zond Energy Systems, which had a 550-kilowatt generating capacity and was a three-bladed turbine that pointed into the wind. Although Zond is no longer in business, its technology was passed along through several companies, and the essential DNA of the Zond Z40 can now be found in General Electric's (GE) 1.5-megawatt wind turbine. This wind turbine has dominated the U.S. market for years and remains GE's top seller, with more than 16,500 units installed globally, making it the most widely deployed wind turbine in the world.

NREL also stepped up its Johnny Appleseed role for the wind industry, providing technical support to a project that literally scattered wind power plants across the country: the Utility Wind Turbine Verification Program. A collaboration between DOE and the Electric Power Research Institute—the utility industry's research organization—the program encouraged wind installations in locations other than California. It ultimately resulted in the first wind farms built in Iowa, Nebraska, Texas, and Vermont. Today, 39 states and Puerto Rico are home to utility-scale wind projects, and Texas now has more wind power capacity than California—more than twice as much!

Recent Years and Looking Ahead

With the wind power industry now booming, it is also maturing. NREL's involvement has changed in many ways, while remaining the same in others. NREL still carries out mechanical tests of wind turbine blades and drivetrains, as well as performance tests of small wind turbines. NREL also works directly with manufacturers of both small- and utility-scale wind turbines to improve their technologies. In fact, Siemens, Gamesa, and Alstom have installed megawatt-scale wind turbines at the NWTC under cooperative research and development agreements (CRADAs) with NREL. A GE 1.5-megawatt turbine is also installed at the NWTC for research and development.

But as the needs of the wind power industry have evolved, so has NREL's research focus. NREL is now examining advanced wind monitoring and control schemes for individual wind turbines and for entire wind farms. While wind turbines currently rely on anemometers to measure wind speed, new laser-based systems can "see" wind gusts coming and help the wind turbine control system to adjust operation in anticipation of the coming winds. The result is better energy capture with lower loads on the turbine.

Meanwhile, NREL is applying fluid dynamics and supercomputers to understand how the wind moves through an entire wind farm. This work may inform wind farm layouts and operations, as upwind turbines may need to point slightly away from the wind to avoid detrimental wakes hitting the downwind turbines.

The industry also continues to face some of the same challenges it has always dealt with, including gearbox failures. To help industry address this challenge, NREL initiated in 2007 the Gearbox Reliability Collaborative (GRC), which consists of wind turbine manufacturers, project owners, researchers, and consultants. In its first five years, the GRC produced a new and improved gearbox design that incorporates advanced technology that increases the reliability of wind turbine gearboxes.

As its Johnny Appleseed role continues, NREL is hoping to plant the seeds for wind turbines to sprout in an entirely new location: the ocean.

"To do so, over the past 10 years we've aggressively partnered with European research laboratories; the groups that are developing offshore wind projects, including all of the DOE-sponsored offshore wind demonstration projects; the regulators who are permitting those projects; and in the future, we hope to be partnering with the projects that are being developed with private money," said Musial.

Ultimately, NREL hopes to extend the wind industry into the deep ocean, where floating wind turbines are needed.

"For our vision, which would involve hundreds of offshore wind farms in the United States, we'll need to not only deploy wind turbines in shallow water, but also develop technology for deeper water as well," said Musial.

Partnering: An Engine for Innovation

FALL 2014 / Issue 7

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Editorial Team

  • Kim Adams | Managing Editor
  • Bill Gillies | Creative Director
  • Dennis Schroeder | Photographer
  • Jennifer Josey | Editor
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