Wind energy applications — the road ahead
By Don Rosato

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Note: This is the fourth article of a four-part series covering wind energy (1) trends, (2) material advances, (3) process technologies and (4) applications.

INDUSTRY PULSE

Which is the most promising emerging application development in wind energy?
  • 1. Floating offshore wind turbines
  • 2. Intelligent blades that adapt to wind conditions
  • 3. Lightweighted rotor sails
  • 4. Architectural fabric wrapped around space frames

Wind energy is providing significant growth opportunities for plastic composite materials. The global market for plastic composite materials in wind turbine production is projected to reach $3.95 billion by 2014. Carbon fiber and other advanced composites are expected to play an increasing role in wind blade production, owing to the expansion of offshore installations and the adoption of larger scale turbines that call for stiffer and lighter materials.

Offshore wind energy is extending the breadth of wind generated power. Land-based wind farms are limited by their impacts on the landscape, large seasonal wind variability and fewer available places for construction. Winds over the ocean are more reliable, attain higher speeds and are less turbulent than winds over land, and no landforms block accessibility of the wind over the ocean.

Even though offshore winds generally offer a better wind resource, installing and operating turbines in harsh ocean environments is very challenging. Initial costs for offshore wind energy are high because of the challenges of transporting materials to remote locations and installing them underwater, as well as constructing the foundations so they can sustain the harsh, often unpredictable conditions beneath the waves. High offshore-installation costs are pushing development of supersized turbines to achieve economies of scale.

Floating wind turbines are an attractive option for offshore installations. Floating installations help to address the high offshore-foundation costs that can compose nearly a third of the overall costs associated with offshore wind farm construction. They can be positioned beyond the horizon (approximately 12 miles out), where spinning turbines will no longer be visible, thus eliminating the "not in my backyard" problem. Floating wind farms also more readily accommodate local concerns about fishing and shipping lanes. Mounting wind turbines on floating structures also allows the turbine to generate electricity in water depths where bottom-mounted towers are not feasible.

While large offshore turbines can be very effective, a key challenge is how to get them out into the ocean. WindFlip AS proposes to transport fully assembled turbines in a near horizontal position from onshore to the final installation location far off-coast.

Gigantic floating turbines delivered to offshore site.

Under a new agreement reached last year, the U.K. and U.S. will collaborate in the development of floating wind technology designed to generate power in deep waters currently off limits to conventional turbines, but where the wind is much stronger. Part of this joint development will focus on intelligent blades that adapt to wind conditions and will provide a leap in energy yield.

Elsewhere of note, Project NOVA (Novel Offshore Vertical Axis), a public/private U.K. consortium is testing a 50-kilowatt vertical axis wind turbine (VAWT) demonstrator, the Aerogenerator X, built by Wind Power Ltd. at Cranfield University. NOVA is sponsored by the U.K. Energy Technologies Institute and the Engineering & Science Research Council, with financial support from the European Regional Development Fund.

The fully working 50 kW prototype will demonstrate Project NOVA's new concept 10-megawatt offshore, double-arm VAWT. The first machine will be built next year following two years of prototype testing. The ultimate aim is to build a 10 MW Aerogenerator X off-shore wind turbine farm providing 1 gigawatt of power by 2020.

10-megawatt Aerogenerator X Concept.

The 50 kW scaled-down prototype is equipped with embedded structural strain and air pressure monitoring. The demonstrator will allow the NOVA project team to gain an understanding of the engineering performance and aerodynamic behavior of the design in use and extensively test in offshore operational conditions the composite materials selected.

Urethane acrylate structural adhesive, Crystic Crestomer 1152PA supplied by Scott Bader Co. Ltd, provides lightweight structural bonding of the various carbon fiber and glass fiber epoxy composite parts for the prototype's two 10-by-1.9-meter rotor sails. Prototype rotor-sail weight was significantly reduced by using the structural adhesive, which had the added benefit of also providing lower overall manufacturing costs compared to a jointed sectional and mechanical assembly design.

The structural approach used for the rotor sails is similar to a large commercial aircraft wing. The sail central box components were manufactured from multidirectional carbon-fiber fabrics and epoxy resin using a vacuum infusion molding process. To the central box is added glass fiber-reinforced leading and trailing edge components. The fully commercialized 10 MW offshore wind turbine will have two 160-meter arms supporting two 80-meter long V-shaped sails. When built, it would be the heaviest composite construction in the world, weighing about 160 metric tons.

Finally from an application standpoint, a new approach to manufacturing horizontal axis wind turbine (HAWT) blades could facilitate production of blades exceeding 130 meters and reduce production costs by up to 40 percent. Traditionally, producing the stiff fiberglass blade of the largest turbines requires the use of million-dollar molds. Also, moving these huge blades — which span half the length of a football field — from the factory to the wind farm also requires custom cranes, oversize rigs, hours of careful route and traffic planning and expert drivers to execute precarious turns.

A research group led by GE including Virginia Polytechnic Institute & State University and the National Renewable Energy Laboratory is looking to use architectural fabric wrapped around a fishbone-shaped space frame to produce very large, low-cost and lightweight wind turbine blades. The project has received nearly $4 million in funding from the U.S. Advanced Research Projects Agency for Energy. Fabric would be tensioned around ribs that run the length of the blade and specially designed to meet the demands of wind blade operations. The blade space frame will be similar to the spars and ribs used in airplane wings.

Fabric composite wind blade section concept.

Instead of polyester typically used in architectural fabric, glass-based fabrics will be used to increase durability. The fabric will be infused with a soft, rubbery resin to allow the fabric to retain some flexibility. The new design will eliminate the need for large expensive molds, allow blades to be made in a more automated fashion and eliminate restrictions on blade size.

Dr. Donald V. "Don" Rosato serves as president of PlastiSource, Inc. a prototype manufacturing, technology development and marketing advisory firm located in Concord, Mass., and is the author of the Vol 1 & 2 "Plastics Technology Handbook".