Pultruded carbon fiber spar caps, supplied prefabricated and ready to install, offer wind turbine blade manufacturers opportunities to reduce production time whilst increasing quality, helping to lower the cost of electricity produced by wind energy.
Wind energy is one of the fastest growing industries in the world. In Europe alone, wind energy now meets 11% of electricity demand and this figure is set to reach 25% by 2030. One of the key challenges of wind power has always been that it must compete with other forms of electric power generation on a cost basis. The industry has matured rapidly and over the last 10 years innovations in turbine design, increased performance and advanced operations have dramatically reduced the cost of wind energy. One key focus area is the turbine rotor blades, where developments target improved design, production and materials to maximize power at minimum cost.
Bigger blades, more carbon fiber
Wind turbines have a service life of 20 years or more, and their blades can make 10 million rotations during that time. To provide the exceptional performance and reliability required for this application blades have primarily been manufactured from glass fibre reinforced composites, but improved designs are necessitating the use of carbon fibre.
One way to generate more power from the wind is to increase blade length. Today, the world’s longest commercial blade is 88.4 m, manufactured by LM Wind Power to power an 8 MW offshore turbine. Blades of more than 100 m in length are now on the drawing board. Onshore, with fewer favorable high-wind speed sites available, turbines with longer and lighter blades are crucial to exploiting regions with lower wind speeds. And blades are not only getting bigger, they are also getting slimmer. Blades with a more slender profile have better aerodynamics and require less material to build.
To enable these longer, slimmer designs manufacturers have started to convert structural areas of the blade from glass to more expensive carbon fiber. The higher stiffness and lower density of carbon fiber results in a longer, lighter and stiffer blade, and a more efficient turbine. Using lighter blades also means less robust turbine and tower components are needed. Together the cost savings achieved pay for the extra cost of the carbon fiber.
Carbon fiber is currently used in the spar cap – the main load-carrying element of the blade which runs from the root to the tip to impart stiffness. For these critical structures it is essential that the unidirectional fiber employed is straight and perfectly aligned. At the moment spar caps are mostly manufactured using infusion or prepreg processes, but they are an ideal application for pultrusion.
Higher quality at lower cost
Evolutions in blade design and materials bring challenges in production. Manufacturers need processes to enable the production of longer blades with better quality, at lower cost. Ways to facilitate and speed up the production process, still a largely manual operation, are imperative. Pultruded spar caps, delivered prefabricated and ready to install in the blade, promise reduced production time, leading to cost savings, as well as higher quality parts with superior mechanical properties. With these advantages within reach it's not surprising that all the leading turbine producers are studying pultruded spar caps.
Pultrusion is an efficient, cost-effective manufacturing process for composite profiles. A continuous process, pultrusion ensures products with a consistent, high quality. The precise unidirectional fiber alignment, high fiber volume fraction and controlled resin content achieved with pultrusion deliver consistently better overall properties than other composites manufacturing processes. In infusion and prepreg spar cap production the fibers can wrinkle, which means less accurate fiber alignment and suboptimal mechanical properties.
Spar caps – whether manufactured in E-glass, carbon or high modulus glass fiber – are not the only potential application for pultruded parts. Root section profiles and other structural parts are further areas where the benefits of prefabrication can be realized.
A leader in carbon pultrusion
Offering design capabilities based on 50 years of experience in the composites industry Exel has supplied tailored solutions to the wind energy industry for more than two decades. Our expertise encompasses all material combinations, including glass and carbon fiber, and vinyl ester, epoxy and polyurethane resin. We have designed and manufactured carbon fiber profiles for demanding applications in a wide range of markets. Our production capabilities ensure the high speed pultrusion of high quality parts and the most efficient use of material, helping to make carbon fiber profiles more cost effective than ever before.
With eight factories on three continents, supported by local R&D teams, Exel Composites is ready to support global growth in the wind energy market. The recent acquisition of a Chinese composites manufacturer expands our capacity and sales and product development network in Asia. This further milestone in Exel Composites' growth strategy will enable us to capitalize on the growing demand for composites in Asia, and better meet the needs of the region's fast developing wind energy market.
To find out how Exel Composites can create a competitive edge for your business please contact Henrikki Honkanen, Product Business Owner - Wind Energy.