Firms capturing energy from wind are finding ways to use thermoplastic resins in turbine blades, but thermosets remain the material of choice.
The topic was discussed during the Society for the Advancement of Material and Process Engineering's show, SAMPE 2002, held May 12-16 in Long Beach. SAMPE is based out of Covina, Calif.
Thermoplastics potentially can be used to mold trailing- and leading-edge portions separately before they are attached to a blade, said George Dohn, director of industrial products with Baltek Corp. in Northvale, N.J.
``I think we could reduce the labor hours by concentrating on smaller areas with thermoplastics,'' he said.
Baltek and competitor Diab AB supply PVC core materials and balsa wood for wind blades.
``We are seeing quite a few composites made with thermoplastics as opposed to thermosets,'' said Jeff Bassman, president of epoxy formulator Jeffco Products of San Diego. Jeffco is building a 30 million-pound-a-year epoxy plant this year in Dallas, specifically to serve the industry.
He said concerns remain about thermoplastics.
``They typically tend to be softening at 160° F or 175° F,'' Bassman said. ``It is possible to enhance these temperatures, but not remain in a cost-competitive situation.''
Another problem for thermoplastics is that they require higher resin-to-glass ratios, while wind blades need the higher reinforcement content that thermosets can deliver, said Martin Zvanik, national distribution manager with Owens Corning's composites solutions business in Toledo, Ohio.
A suitable modulus is needed to avoid buckling and twisting, Zvanik said, and thermosets have higher modulus numbers than thermoplastics.
``[Fiber placement] could be used to make these blades with thermoplastics,'' said William Benjamin, president of Benjamin Diversified Consulting Inc. of Gilbert, Ariz. Fiber placement can cut labor costs by 70-80 percent, vs. hand layup.
Components using carbon fiber include blades, spinners or hubs and nacelle covers, and more uses are being considered. The upper and lower surfaces of most blades are bonded, and selective use of unidirectional carbon fiber makes sense for torsional strength. Ski and snowboard makers use the concept now.
During 2001, ``only about 2 percent of the potential for carbon fiber in wind applications was being realized,'' said Dayton Griffin, engineering project manager with Global Energy Concepts LLC of Kirkland, Wash., an engineering and technology consultant.
Griffin identified three possible models for carbon fiber's use in wind blades: full replacement of glass fiber, selective use in conventional designs and innovative design of more-slender blades and related platforms.
Wind energy faces increasing hostility because of the not-in-my-backyard attitudes, said market analyst Anne-Marie Howe of Santa Ana, Calif. But she hopes the growing need for renewable energy might mollify some opposition.
European countries, especially Germany and Spain, dominate global production of wind energy. The principal players are expanding into the Western Hemisphere. Howe said Vestas Wind Systems A/S of Ringkobing, Denmark, and Enercon GmbH of Aurich, Germany, were the largest suppliers of wind turbines in 2001. LM Glasfiber A/S of Lunderskov, Denmark, is the biggest maker of wind blades. Vestas and Enercon also make blades.
Of interest to the industry is General Electric Co.'s approach through GE Power Systems, already a major supplier of power-generation technology. GE bid about $358 million to acquire the Tehachapi, Calif.-based wind energy unit of Enron Corp. through a bankruptcy sale, which is pending. The Enron operation makes large wind turbines.
The United States is showing more interest in stimulating domestic production. In March, a federal tax credit for wind energy production was extended through December 2003. Both the Senate and House want to extend the tax credits to 2006. In addition, the Senate wants to establish target requirements for several renewable energy sources, including wind.
Separately, a Washington conference committee will need to resolve differences in pending federal energy bills, said Jon Chase, assistant director for legislative affairs with the American Wind Energy Association of Washington.