Innovative Carbon Fiber Materials Enable Longer Blades, Greater Energy Capture than Traditional Fiberglass

Study blows a hole in the theory that wind turbine manufacturers have avoided carbon fiber materials because of their high cost

The wind industry operates in a cost-driven market, meaning developers, manufacturers, and customers focus on bottom-line costs and how to do more but spend less. By contrast, the aerospace industry operates in a performance-driven market, where the focus is on high performance, with cost being important but secondary.

An example of how cost vs. performance can drive decisions in these two industries lies in the primary structural material each one uses to manufacture its products. Fiberglass is the primary structural material used in wind turbine blade manufacturing, whereas
the aerospace industry uses carbon fiber materials in its military applications and airplanes.

Carbon fiber has well-known benefits for reducing wind turbine blade mass because of its significantly enhanced properties of stiffness and strength compared to fiberglass. However, the high relative cost of carbon fiber materials, originally developed for the aerospace industry, has prohibited broad adoption of their use within the cost-driven wind industry.

Now, the Optimized Carbon Fiber Project, funded by WETO—and implemented by researchers at DOE’s Sandia and Oak Ridge National Laboratories and Montana State University—has demonstrated the commercial viability of novel, cost-competitive, carbon fiber composites derived using precursor material from the textile industry. The project also found system-level benefits for using carbon fiber composites to reduce the levelized cost of wind energy resulting from the lower mass and ability to design long, slender wind turbine blades.

“As wind turbine blades get longer, they become much more massive,” said Brandon Ennis, principal investigator at Sandia. “Controlling blade mass is critical to allowing further growth in rotor size and reduction in the levelized cost of wind energy. Carbon fiber is an enabling technology for accomplishing these objectives, which will support increased wind energy deployment across the United States.”

Ennis said the team’s research demonstrates the significant opportunity for innovation in carbon fiber development to produce materials better suited for the unique loading demands of wind turbines.

“The textile carbon fiber material we studied performed at a higher value compared to existing commercial materials, and this type of material would enable broader adoption of carbon fiber into wind turbine blade designs, creating a larger market for fiber manufacturers,” he said.

In the Optimized Carbon Fiber Project, researchers compared a novel, heavy-tow carbon fiber (i.e., more carbon filaments in each bundle of fibers), a baseline commercial carbon fiber material, and fiberglass. The study characterized each of these materials using a validated cost model and mechanical testing (for static tensile and compressive strengths and fatigue) in 3-MW and 10-MW land-based and offshore reference wind turbine models.

Compared to the commercial baseline carbon fiber, mechanical testing results show that the heavy-tow carbon fiber material:

• Performs with similar stiffness but at nearly 40% reduced tensile strength
• Is similar in compressive strength—with only a 20% reduction.

When compared on a cost-specific basis to the commercial baseline carbon fiber, the heavy-tow carbon fiber material:

• Has 100% more stiffness
• Performs with 56% more compressive strength.

In wind turbines, compressive strength matters more than tensile strength and drives demand for the type of material used; regardless of material performance, the final cost is typically the determining factor for material selection by the wind industry.

The study also revealed a 25% blade mass reduction when spar caps were made using either of the carbon fiber materials rather than fiberglass, highlighting the value of carbon fiber materials. The spar cap material costs for wind turbine blades with spar caps using the heavy-tow textile carbon fiber are 40% less than blades whose spar caps were made from the baseline commercial carbon fiber.

Download a copy of the project report to learn how the study was conducted and read more about its results. Visit the Sandia website to learn about the broad range of research the lab is conducting on blade reliability and composite materials.

Spring 2020 R&D Newsletter

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