The wind industry has set installation records over the last couple years. That trend may continue with global wind capacity predicted to double in the next five years, according to the Global Wind Energy Council. This growth trend is thanks, in part, to a developing offshore wind market and larger wind turbines with longer blades.
“The wind industry has been increasing blade length approximately 6.5 feet per year over the last 10 years,” said Mark Kirk, CCT, Wind Energy Sales Manager at Composites One. “This increase in length has allowed the industry to increase production by using larger turbines and, therefore, lower the cost of energy.”
However, the longer the blade, the more reliability and stability come into question. Kirk attributes materials and manufacturing for letting turbine blades keep up with ever-growing towers. “Because of composite materials, blades can spin faster and capture winds at lower velocity. Composites offer wind manufacturers strength and flexibility in processing with the added benefit of a lightweight material,” he says.
Composites are made of two or more materials with different physical or chemical properties that when combined, do not fully blend but together become stronger and more durable. Materials for the wind-turbine blade market include resins of glass fiber reinforced polyester, glass fiber reinforced epoxy, and carbon fiber reinforced epoxy.
“Combining glass fibers with a resin matrix results in composites that are strong, lightweight, corrosion-resistant, and dimensionally stable. They also provide good design flexibility and high-dielectric strength, and typically require lower manufacturing costs,” says Kirk, who points out that high-strength composite materials, such as carbon fiber and epoxies, are now also being used for high-performance blades.
“Today’s turbine blades and components must meet strict mechanical properties, such as high rigidity and resistance to torsion and fatigue. In addition to these mechanical properties, the finished product must offer excellent corrosion resistance and a high-temperature tolerance. Composite materials can offer greater stiffness in many instances, and reduced weight on finished parts,” he adds.
But that’s not all. Because of their flexibility, composites materials make repairs easier for wind technicians and provide for a longer blade life. The materials can also be used for other turbine components. “The move to composite nacelle covers, composite spinners, and in some cases more advanced close molding of these composite components, has also reduced the over all weight of the units over traditional steel and aluminum so turbine costs are coming down.”
Materials make up more than 90% of the manufacturing costs of a blade, so if turbines are to successfully grow in size, reduced costs are key. “The challenge for today’s wind industry is clear,” says Alexis Crama, LM Wind Power’s Vice President of Offshore Development. “The industry must increase annual energy production, and reduce costs through innovation in material use and manufacturing technologies, all the while considering reliability and the efficient servicing of turbines during operation.”
He says that as turbine blades get longer and more offshore projects develop, the demand for higher reliability and lower costs will only increase from wind-farm developers. “Building larger blades presents new design challenges, which in many ways involve re-thinking the materials, structure, and other characteristics. Rotor blades are arguably one of the most influential pieces in terms of the cost of energy.”
Along with building the world’s longest blade to date (at 88.4 meters — the blade is currently undergoing testing for product validation in Denmark), LM Wind Power recently unveiled research into a modular blade-molding concept to increase flexibility in production when making larger and longer blades. The new process extends the rotor diameter by attaching variable tip lengths, without the added expense of building a new blade mold.
This process enables separate manufacturing of the blade and tip, followed by a traditional joining technique that permanently assembles a blade, explains Crama. “Through a combination of reduced production costs, increased rotor size, and optimized wind-farm output, these modular products are expected to cut the cost of energy for offshore blade applications by about 6 to 8%.”
He adds: “Ultimately, the winners of tomorrow’s wind industry will be those who can adapt, innovate, and expand at the lowest cost.”