We look at how nanomaterials are allowing for new technological developments in wind turbines.
Nanotechnology in wind energy
Wind power is likely to make a major contribution to the world’s electricity supply in the coming decades, and is a driving force in the renewable energy sector. Currently, the world is faced with the global challenges of climate change, a depleting supply of fossil fuels and the increasing cost of those fuels. Therefore, there are huge opportunities in renewable wind energy.
The global wind turbine manufacturing industry is dominated by a small number of OEMs. The top five OEMs-Vestas, GE, Gamesa, Enercon, and Suzlon-have a combined 62 per yeacent of the global market in 2008. In this growing industry there is increasing interest in manufacturing new types of turbine blades with enhanced properties. It is essential to design and produce blades with good fatigue resistance and good stiffness properties to ensure operational longevity. Polymer matrix composites dominate the wind turbine blade market because of their low-cost, lower weight-to-power ratios, superior fatigue characteristics, high specific strength and modulus, and ability to make complex geometries. And nanomaterials are allowing for great advances in the polymer matrix composites sector.
Wind turbine blade manufacturers are faced with the challenge of constructing technologically increasingly robust, more sophisticated, larger (the total production cost per kilowatt hour of electricity produced decreases with increasing wind turbine size) and stronger blades. Wind turbine blades are designed to meet and withstand complex loadings and harsh operational conditions throughout their operational life. Epoxy composite materials currently used are extremely lightweight, but can be brittle and prone to fracture. To ensure wind energy remains competitive it is essential that production cost is lowered, despite the fact wind power is cheap compared to other sources of renewable power. A number of avenues are currently being explored and different composite materials are being tested to achieve the target of reduction in turbine cost and weight.
To meet these challenges manufacturers are seeking to utilize nanomaterials to eliminate fatigue, tensile and shear failures in turbine blades. Nanomaterials will allow for reduced weight, increased reliability, increased operational life and improved cost/efficiency in turbine blades. This is especially pertinent for cost-effective materials for larger blades used in off-shore wind energy applications.
Nanomaterials allow for the enhancement of mechanical properties of existing materials. Composite additives under development for wind turbine blade applications include nanosilica, carbon nanotubes (CNTs) and graphene. The utilization of these materials allows for significant improvements in tensile strength, tensile modulus, flexural strength, flexural modulus and interlaminar shear strength. Polyurethanes reinforced with carbon nanotubes displays increased fatigue resistance (lasting approximately 8 times longer than epoxy reinforced with fiberglass); they are lighter per volume than carbon fibre and aluminium; display 5 times the tensile strength of carbon fibre and more than 60 times that of aluminium. Hybtonite, developed by Amroy Europe Oy (Herrala, Finland), uses Baytube CNTs from Bayer MaterialScience (Leverkusen, Germany) in their turbine blades. The company claims that with Hybtonite the weight of its smallest blade (2.5m/8.2-ft long) is half that of a comparable fiberglass blade. This permits increased surface area and an aerodynamic design that achieves a coefficient of power (Cp) of 0.47 to 0.50, the highest possible with current turbine designs. CNTs also impart electrical conductivity, which is useful for lightning strike protection.
Also under development are CNT enhanced composites with built-in sensors for structural health monitoring and improved resilience. Incorporation of conductive nanotubes in the blades polymer composite allows for increased sensitivity to deformation. As the CNT is deformed by stress on the blade, a change in conductivity results and relays a signal to the wind turbine control centre. This allows the operator to pinpoint where which blade is stressed and in which area, thus preventing any further stress on the blade.
Nanocoatings are also impacting the wind energy market, with hydrophobic coatings applied to blades to prevent ice formation. This technology is being developed by General Electric. Anti-corrosion coatings are finding application in offshore wind turbines to fight corrosion caused by the conditions at sea. A number of large offshore renewable energy companies are seeking to develop these coatings. Ocean wind and marine energy, a renewable and inexhaustible resource for electricity production, has vast untapped potential, as about 70 per cent of the world is covered by oceans. The European Wind Energy Association expects the market for offshore wind turbines to increase from an annual growth rate of 1.5 GigaWatt (GW) in 2011 to 6.9 GW in 2020. This would mean an increase in annual investments from S$5.8 billion in 2011 to S$15.5 billion in 2020.
With worldwide expenditure on renewable energy breaking through the $trillion barrier in the next few years, nanomaterials are leading the way in reducing costs and making these energy sources increasingly competitive.
The Main Players…
1 General Electric
The company are developing hydrophobic nanocoatings and nanocomposites for wind turbine blades.
The company is developing nanocoatings in collaboration with a number of SMEs and universities.
3 Siemens Energy
Siemens Energy has a number of R&D projects exploring nanomaterials for wind turbine blades.
4 Eagle Wind Power Ltd.
The company is seeking to increase blade performance by using an epoxy resin reinforced with carbon nanotubes .