Jan. 21, 2000 ALBUQUERQUE, N.M. -- Three small wind turbines spinning in the Texas Panhandle as part of a series of experiments being conducted by the Department of Energy's Sandia National Laboratories promise to answer some big questions researchers have long asked about how to harness wind power to generate electricity.
Members of Sandia's wind energy technology department installed the turbines -- each 16 meters in diameter on 22-meter tall towers -- last fall at the Department of Agriculture's research station in Bushland, Tex. The turbines will be used to measure loads caused by unusual events in the inflow (turbulence) and to study ways of building better blades.
"This will be the first time Sandia will test propeller-blade turbines on a long-term basis," says Herb Sutherland, one of the engineers working on the project. "We hope to gather load and wind inflow information continuously for approximately one year."
Before this project, data was typically taken in short segments that covered only a few hours of operation. The long-term data will permit the researchers to develop design tools and components that will increase the efficiency of the turbine and its ability to produce reliable electrical power.
Sutherland says the decision to test the turbines in Bushland, 13 miles west of Amarillo near I-40, was not difficult to make.
"In one calendar year of testing, we get five times as much data in Bushland as we would get in Albuquerque," he says.
Sandia has been field-testing turbines at the Bushland site since the late 1970s and during that period successfully completed several joint programs. These multiyear programs, which focused on egg beater-shaped vertical axis turbines, culminated with development and testing of a 34-meter diameter turbine, expanding vertical axis technology to large machines. The vertical axis projects were concluded after the technology lost favor with the US wind industry. Sandia has now shifted its research to horizontal-axis turbines -- the turbines with propeller-type blades.
The three turbines being tested at Bushland were originally used to generate electricity for a commercial "wind farm" in Palm Springs, Calif. They are smaller than the newer utility-grade wind turbines -- many of which have rotors that are slightly smaller than a football field -- but are more suitable for conducting experiments.
"We wanted something smaller, namely a turbine that we could handle relatively easily and that was cost effective," Sutherland says. "It's often too expensive to do research and development with the large turbines. Once we come up with a design that works at that smaller size, we will scale it up for the larger turbines."
The Bushland turbines will be used for two experimental projects, including the Long Term Inflow Structural Testing (LIST) project headed by Sutherland and the Blade Manufacturing Initiative (BMI), led by Tom Ashwill.
As part of the LIST project, automated instruments will take measurements of wind speed, wind direction, and blade loads at regular intervals -- 30 per second -- over a year. The data will be gathered by a team of researchers, stored on CDs, and sent to Sandia for analysis.
"We are particularly interested in wind loads created by large wind gusts passing through the rotor," Sutherland says. "A gust induces extraordinary loads into the blades that can significantly reduce their ability to function reliably. A single large event can reduce the life of a turbine blade by half."
By studying data from the experiments, the researchers hope to draw a better understanding of the effects of wind inflow and turbulence on blades -- information that can be used in creating a better blade design.
A major technical challenge is the gathering, archiving, and analysis of the immense amount of data collected during the year-long test program. A new data acquisition system is being developed for the project.
The system will interface with a Sandia-developed software program that allows information to be acquired, archived, and analyzed. A major step is automation achieved by the software package, which will permit a week of data to be taken and archived without intervention of an operator.
Blade Manufacturing Initiative
The other project at Bushland, BMI, will spend the next several years determining how to build a better blade.
"We will be looking at advanced materials, better manufacturing processes, and more efficient blade designs all in an effort to develop blades that are lighter, more reliable from a structural standpoint, and less expensive," Ashwill, the BMI lead engineer, says. "We want to design blades that not only won't break in high winds, but will last 20 to 30 years. Currently, blades are sufficiently strong, but they cost too much. As commercial machines get bigger, this could be even more of a problem."
Wind turbine blades are most often fabricated by hand using multiple layers of fiberglass cloth. The traditional method is for the sheets to be cut to shape, laid down in a mold by hand, sprayed or rolled with resins, and finally cured.
"This method has been used to fabricate many types of composite structures, such as boats and car bodies, but it tends to create small imperfections that cause premature failures of wind turbine blades," Ashwill says.
Ashwill is studying alternate manufacturing methods that use automated processes and advanced molding techniques to build better blades cheaper.
Ashwill says that a blade design study this year will look at issues associated with very large blades. A sub-scale design, an eight-meter blade, will be produced that incorporates advanced materials and architectures. Using the new design, a contractor will build new blades that will be tested at Bushland. Results of this testing will be used to design and build large turbine blades. Depending on DOE funding, such blade testing will occur in the next one to three years.
"We are confident that we can come up with new blade designs that will be more reliable and efficient than existing ones and that will be attractive to large turbine manufacturers and the utility industry," Ashwill says.
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