Ocean Giants: Wind of Change

“Cold Hawaii” is the name that wind surfers have given the 55-kilometer stretch of coast in northern Denmark that extends from Hanstholm in the north to Agger in the south. Here, in the Thy National Park, there is a steady and strong westerly wind that the surfers love. Thirty kilometers farther east is a hotspot for wind fans of a very different kind. At the test center in Østerild, seven huge wind turbines are being tested for their offshore use. The biggest of them, a model from Siemens Gamesa, is exactly 271.40 meters tall. As a result, it has replaced the 254-meter-high Storebælt Bridge as Denmark’s tallest structure. Since November, the turbine has been undergoing preparations for its commercial use, which is scheduled to begin in 2024.

Such demands can only be met with well-founded research. “The rotor blades, for example, are becoming bigger and bigger,” says Christian Schmidt, who heads the Crosslinkers business line at Evonik. “That poses new challenges, not only during transport and construction but also earlier on, during production. We’ve developed customized products to deal with this.”

Rotor blades are now technological high-performance products made of a variety of materials. Most of them are made in two half-shells. Each half of a blade is made of fiberglass mats impregnated with VESTAMIN® IPD. This resin provides the rotor blades with the required mechanical stability and ensures that the finished turbines have a long service life. The composite structure’s service life can be extended further by applying silicon dioxide particles directly to the mats or mixing them into the impregnating resin. These particles are called NANOPOX® and were developed by Evonik. If 2,500 were piled on top of one another, they would be as thick as a human hair. The reinforced blade halves are connected to one another by carbon-fiber bars. This produces hollow spaces, which are then filled with foam. Weight is the most crucial aspect here. Evonik has developed the structural foam ROHACRYL™, which requires minimal amounts of resin and has a low density that enables it to be customized to meet the wind turbine industry’s requirements and thus make weight-saving designs possible.

The last thing to be applied is the coating. Storms, hail, sand, and airborne salt—the rotors especially have to be protected against these extreme influences. To do this, many manufacturers use coatings that contain fumed silica from Evonik. This silica ensures that the protective coat can be applied to the blades with uniform thickness. In addition, it contains special crosslinkers that accelerate the drying of the coatings and make them more resistant to the effects of weather.

A blade’s corners and edges are especially critical. The leading edge sweeps through the air at speeds of up to 400 kilometers per hour. A foam-like protective coating consisting of polyurethane is therefore applied to this edge. Additives from Evonik’s toolkit ensure that this coating has the right structure. Without these protective coating, the rotor blades would be damaged in no time.

But that’s not the only place where the offshore giants have to work well, because wind farms are currently being built at sea all over the world. In 2021 alone, the amount of offshore wind power generated worldwide increased by more than 25 percent to a total of 130.6 terawatt-hours. The Siemens-Gamesa turbine that is currently being tested in Denmark will go into operation in the Sofia Wind Farm on Dogger Bank off the northeastern coast of the UK. Beginning in 2024, a total of 100 such turbines will be installed here, boasting a total rated capacity of 1.4 gigawatts, which is the equivalent of a nuclear power plant. Additional projects will be implemented close by on this shoal, which connects Great Britain with the European continent.

The thought of floating wind turbines might sound absurd, given the height and weight of these titans. However, a variety of concepts are already being tested. One such idea is to put each wind turbine on top of a huge submerged buoy. The upper part of the buoy is filled with air in order to give it buoyancy, while the bottom contains a counterweight to the wind turbine. Such structures have been used for more than four years at a wind farm around 25 kilometers off the Scottish coast. Due to their size, they can only be assembled out on the high seas. 

The new options for offshore facilities also make the use of wind power attractive for countries that until now have been unable to access renewable sources of energy. The International Energy Agency (IEA) and the International Renewable Energy Agency (IRENA) expect the amount of electricity from offshore wind turbines to increase immensely in the future. The global capacity might rise to 2,000 gigawatts by 2050, compared to slightly over 35 gigawatts at the end of 2020.

These goals are considered ambitious. “Offshore wind power in the western hemisphere has never seen anything like this,” said Mike Jacobs, senior energy analyst at the Union of Concerned Scientists. To date, the USA has only seven offshore wind turbines—five in a wind farm off Rhode Island and two more set up as tests in Virginia. Bonnie Tully, who manages Evonik’s business activities in the USA, now expects the program to provide the world’s biggest economy with a substantial boost. “Wind energy will have pretty dynamic effects. It helps to keep costs low in supply chains, production, and the construction sector.”

China, the world’s second-largest economy, has been using wind power for some time, and its installed capacity is twice as large as that of the USA. Moreover, the People’s Republic of China has been achieving new expansion records year after year. The Bloomberg news agency has calculated that China added around 58 gigawatts to its wind power capacity in 2020 alone. That’s more than half of the facilities that were put into operation worldwide in that year. The country’s wind energy sector is correspondingly important, and seven of the world’s top ten wind turbine manufacturers are from China.

Evonik responded to this growth early on and opened an isophorone diamine plant in Shanghai in 2014. The company has extensive experience with isophorone chemistry, which has been in use for 60 years and serves as the main technological basis for preventing materials in wind turbines from becoming brittle or fragile. Today Evonik manufactures isophorone products on three continents. In addition to the facility in Shanghai, these products are also manufactured in Marl and Herne (Germany), Antwerp (Belgium), and Evonik’s biggest US location, in Mobile, Alabama. Recently the company also began to make these products from renewable raw materials. Evonik has developed a procedure for turning such materials into the precursor product acetone. This is part of Evonik’s “eliminate CO₂” mass balance approach, which aims to substitute fossil carbon with renewable or recycled carbon.

Iris Zhen, who manages Evonik’s crosslinker business for China and Southeast Asia from the location in Shanghai, expects further growth. “China wants to become carbon-neutral by 2060. The first step toward achieving this goal is to generate a large part of the electricity from emission-free and renewable sources and thus accomplish the transition to sustainable and clean energy sources and a carbon-free economy.” Zhen also thinks that wind will play a crucial role in a clean energy future, and she expects “Asia, and China in particular, to continue to dominate the global wind energy sector.”

There’s no doubt that the carbon-free electricity from wind power benefits the environment. But how durable are wind turbines and how are they disposed of? “Our wind turbines are designed to last at least 25 years,” says Gerhardt. A turbine’s service life is mainly determined by its rotor blades. “We have made progress here with new concepts and materials that have considerably improved durability under the harsh offshore conditions.” The recycling of steel, concrete, and metal is already no problem, adds Gerhardt. However, the recycling of the rotor blades is more difficult. The rotors consist of a mixture of plastic and carbon fibers as well as of balsa wood. These materials can be separated from one another only with great difficulty. “However, we recently launched a truly green rotor blade on the market for offshore use: the RecycableBlade,” says Gerhardt.

Creavis, the strategic innovation unit at Evonik, has the same aim and is now pooling the expertise from a variety of business lines in order to make wind power a part of the circular economy. The structural foam ROHACRYL™ is already reusable. As a result, Martin Gerhardt’s plans for the future might become a reality. “Our goal for 2040 is to build only turbines that are fully recyclable,” he says. Once that goal is achieved, it won’t just be the huge rotors that will go in circles for as long as possible, but also the materials that they are made of.