Nanoengineered Composite Materials for Wind Turbine Blades

Increasing thrust towards reducing the fossil fuel dependency is enabling the greater expansion of the renewable energy sector. Among the various renewable energy sources, wind is a clean, free, and readily available source. Around the world, massive wind turbines are widely being used to capture

wind’s power and converting it to electricity. According to preliminary statistics published by WWEA, the overall capacity of all wind turbines installed worldwide reached 539 Gigawatt by the end of 2017. All wind turbines installed until 2017 can cover more than 5% of the global electricity demand.

Wind power has become pivotal in many countries energy strategies to phase out fossil and nuclear energy. In 2017, Denmark set a new world record with 43% of its power coming from wind. An increasing number of countries including Germany, Ireland, Portugal, Spain, Sweden or Uruguay have

reached a double-digit wind power share in their countries energy pie chart. The European Union seeks to cover 20% of its energy needs from renewable by 2020. The wind energy capacity should be expanded by two folds in order to achieve this goal.

The main components of the wind turbine are rotor blades, shaft, and generator. Wind turbine primary structures such as blades and nacelles are typically made from composite materials. Blades are the most important part of a wind turbine, and the highest cost component of turbines. In the early 70s, the serial production of glass-fiber reinforced plastics (GRP) rotor blades with a length of 17 meters was developed on small systems, starting in Denmark. During the early stages, the achieved wind power performance was about 10 kWs but now with the state-of-the-art technologies we can attain magnitudes of 8 to 10 Megawatts per turbine. Lately, GE developed the most powerful offshore wind turbine (Haliade-X 12 MW) in the world to date which features 12 MW capacity, 220-meter rotor, a 107-meter blade, 63% capacity factor, and advanced digital capabilities. Present wind turbines are more efficient and are able to convert great amount of energy in the wind into electricity. This is due to blades which are developed using state-of-the-art aerodynamic analysis, performance-enhancing devices, and advanced light weight composite materials. The strong desire to reduce the leveraged cost of energy is motivating the ever increasing size of the rotor blades. The weight of the rotor blades increases with increasing size and therefore gravitational loads become the main design drivers for current wind technology. Wind turbine blades, are subject to complex, combined impact, static and random cyclic loading. In order to resist these loading over many years and hundreds of millions of loading cycles and to reduce the gravitational loads, the wind turbine blades are fabricated from fiber reinforced polymer composites. While the currently available solutions (in the simplest case, E-glass/epoxy composite) satisfy most of these conditions partially, the necessity for new, better solutions leading to the increased reliability and reduced costs for wind turbines, is apparent.

That is why a lot of efforts are put in the development of new, stronger, more damage resistant, faster processable, more environmentally friendly and recyclable composites for wind

turbines. In several works, the possibilities of improvement of composites properties by adding nanoreinforcement in matrix were demonstrated. Incorporation of small amount of nanoreinforcements such as carbon nanotubes or nanoclay in the polymer matrix, fiber sizing or interlaminar layers have shown 30-80% improvement in properties of composites such as the fatigue resistance, shear or compressive strength, and fracture toughness. Loos et al. demonstrated that the addition of small amount of carbon nanotubes can increase the lifetime up to 1500% in various wind turbine blade samples made with secondary carbon nanoparticles reinforcement (vinyl ester, thermoplastics, epoxy composites containing CNTs). Nanomodification of wind turbine composites was studied by Koratkar and colleagues using graphene as a secondary reinforcement and demonstrated that the graphene reinforcement is very promising in the development of stronger and durable wind turbine blades. Merugula et al. theoretically estimated improved tensile stress and modulus, 20% weight reduction, and increased lifetime for the glass fiber reinforced epoxy composite wind turbine blades incorporated with 1–5 wt % of carbon nanofibers (CNF). For enhancing the interlaminar fracture toughness and delamination resistance of composite laminates polymer nanofiber interleaving concept is becoming more attractive these days. Recent works in this area of nanofibers interleaving have been reviewed in [14,15]. Using the computational modelling techniques, the applicability of hierarchical composites for wind energy applications is systematically analyzed in. In addition, as an alternative to the currently used glass fiber/epoxy composites the feasibility studies of using hybrid and nanoreinforced composites in wind blades is reported in [16]. It was clear from the above mentioned numerical and experimental studies that the gains in the lifetime of the composites using hybrid and nanoreinforcement concepts justify additional investments to produce the wind turbine blades from these nanoenhanced composite materials.