SIEMENS

In the current decade the cost of wind power in many areas is expected to fall below that of electricity generated from coal. Achieving this ambitious goal depends on many factors, including two technological advances: a substantial gain in the energy yield from future wind power plants and lower manufacturing costs. Both represent a major challenge for the materials and production experts in the power generation industry.

A new generation of rotor blades is therefore scheduled to enter large-scale production in the U.S. at the Siemens Wind Power business segment in 2012. Based on so-called ATB (Aeroelastic Tailored Blade) technology, the blades are gently curved like an Arabian scimitar. The curvature means that when a blade bends, it also twists. And thanks to advanced modeling methods, this twisting can be designed so as to reduce the load on the blade. This property represents a major advance compared with today’s rigid blades. Wind turbines on the high seas may be subject to air masses of more than 100 metric tons per second, arriving from different directions. But thanks to their elastic properties, the new blades will be able to accommodate such conditions much better than conventional rotors. As a result, fatigue loads will decrease and service life will increase.

Using this new blade form, larger rotors that produce more energy can be designed without any significant increase in aerodynamic load. “Our new rotor blade is 53 meters long. That’s four meters more than its predecessor, which means a five percent increase in energy yield,” explains Henrik Stiesdal, Chief Technical Officer at Siemens Wind Power. One of Stiesdal’s top priorities regarding the design of the new rotors was to reduce the amount of materials required, so as to cut weight and minimize wind load on the blade. “Compared to its predecessor, the new rotor blade is not only longer but also up to 500 kilograms lighter, depending on final material selection,” he explains.

The engineers’ biggest challenge here was to ensure that the new blade retained the necessary strength, despite the reduction in materials and weight. “It took us some time and effort to develop a process with which to calculate blade strength in all possible wind conditions. Once we had achieved this feat we were able to optimize the rotor design,” says Stiesdal. The improvement in aerodynamic properties was possible largely thanks to computer-based enhancement of the exterior shape of the rotor blades and a large number of tests under real-life conditions.

At the same time, improvements are also being made to the manufacturing process. The entire process of laying out and shaping the many layers of fiberglass and then adding resin is still done by hand, and the whole mixture is cured in huge molds that resemble sandboxes. It is hoped that it will be possible to increasingly automate this process in the future. The goal is to reduce production costs per blade by 40 percent. This will make the plants cheaper, thus ultimately cutting the kilowatt-hour cost of wind power. In addition, wind experts are taking a closer look at the issue of recycling, which will become relevant in bout five years. At present, the number of wind power plants being built worldwide is still greater than the number of plants being dismantled. “One option might be to shred the blades and use the granulate as an additive for concrete,” suggests Stiesdal. ReFiber, a Danish company that works closely with Siemens Wind Power, has developed a pyrolytic process, in which rotor blades are first broken into large pieces and subsequently decomposed in a thermochemical reaction at a temperature of 700 degrees Celsius. This produces a gas, which can be combusted for heating purposes. All that remains is fiberglass, which can be used as insulation for buildings.

Use of new, plant-based materials is also on the agenda. “We’re working with universities in Denmark and the U.S. to investigate whether the wind turbine blades of the future could be genuinely green. For example, they could be based on fiber-composite materials made of plant fibers and held together with bio-resins made of vegetable oils,” says Stiesdal. However, he doesn’t expect to see such rotor blades for another ten years or so. But when such blades do appear on the scene, wind plants will have truly earned their title as the green giants of the power industry.