Wind turbine blade recycling in Washington: a feasibility study

Matthew Booth; Hari Nath

doi:10.7273/000007016

As of mid-2023, there are approximately 1,822 operational wind turbines in Washington sited at roughly 21 commercial wind farms, stretching between the coast near Aberdeen to the far eastern Palouse. These wind farms may be owned directly by a local utility, such as Puget Sound Energy’s Wild Horse and Skookumchuck developments; by an out-of-state utility, such as Portland General Electric or the Los Angeles Department of Water and Power (LADWP); or by a private development firm such as Avangrid and Iberdrola. According to the United States Energy Information Administration (EIA), these assets provided more than 9.1 gigawatt hours of energy in 2022, or enough to power more than 850,000 homes. While the most significant growth of our state’s wind energy fleet occurred in the late 2000’s, the late 2020’s are poised to see another spurt of growth as utilities are mandated to reduce the carbon intensity of energy generation in line with the Clean Energy Transformation Act, a landmark effort by the state of Washington to decarbonize the electricity sector by 2045. The Energy Facility Siting Council, an executive division of the state government, notes two active applications for new utility scale wind, and many of the currently active wind farms. In addition, utilities such as Puget Sound Energy and Avista have indicated their intention to expand generation through wind in the coming years, whether from repowering a retiring turbine site with larger units or from the development of new resources. Avista is developing new resources in Whitman County, and PSE is expanding operations in central Washington. With over 23% of Washington’s electricity currently being generated by fossil fuels, further deployment can be expected as utilities decarbonize in advance of CETA deadlines. A wind turbine is a seemingly simple concept that is underpinned by complex technologies. When the wind blows, an airfoil is moved, which in turn spins a generator to make electricity. While there are a variety of manufacturers, they all follow similar design utilizing similar materials. There are three main components visible from the outside: the tower, typically a hollow steel and concrete structure over 100 feet tall; the nacelle, a bean or box-shaped shroud at the top of the tower holding electronic and mechanical equipment as well as servicing areas; and the blades, generally three long (100 foot +) fan vanes made of a complex mix of fiberglass, balsa wood, and carbon fiber. The blades have more in common with an airplane wing than a traditional windmill blade or fan blade, with a focus on strength, durability, and weight reduction that leads to using similar materials and design processes. With the differing technologies, materials, and operating stresses for the components, they experience different levels of wear and often have different lifetimes. Towers are relatively simple and made of strong, sturdy materials. They’re more resistant to the vibration and oscillation that’s inherent in a large, spinning structure than some of the other components. There have not been many reports of structural issues or wear from typical service, and similar structures such as bridge piers may last 50-100 years without needing major work. Towers also contain ladders and wiring to move people and electricity up and down, which will likely not require extensive refurbishing and maintenance for decades. When these towers do reach the end of life, the components are readily recyclable utilizing existing channels; metal scrap of that quality will be eminently valuable and concrete from the foundation can be turned into fill. The nacelle has some of the more wear-intensive parts in a wind turbine. Generally, the entirety of the gearboxes, bearings, and generating equipment can be readily recycled utilizing existing metal waste, and the vast majority of industrial lubricants have approved safe disposal methods. The blades, or airfoils, are a seemingly simple but extremely complex piece of engineering. They are massive, typically between 150 and 300 feet long, and made of layers of fiberglass, adhesive, and sometimes structural foam or lightweight balsa wood. They’re typically hollow, with the thin fiberglass skin providing a lightweight, slightly flexible structure. There are some metal fittings to attach the airfoil to the hub of the turbine, as well as some wiring for lightning protection, but they’re otherwise almost entirely made of a composite. Composites such as fiberglass and now carbon fiber are formed by stacking layers of lined-up fiber on top of each other at an angle and use a resin to bind these layers together. Most airfoil manufacturers utilize a glass substrate woven like a piece of cloth to impart more rigidity to the structure, and most of the resins known to be used in the industry (especially historically) are most similar to a two-step epoxy, with a chemical process “activating” the resin to turn it solid. While exact proportions of epoxy to fiber differ from manufacturer to manufacturer, they’re typically in the 40% resin to 60% glass ratio. Similarly, binding resins may vary from manufacturer to manufacturer, but chemically-set epoxies have been historically used. During manufacture, the glass cloth is wrapped around a form for the blade shape and the resin is rolled on, much like paint would be. During this process, foam or balsa blocks are added to areas requiring extra strength, such as the leading edge of the airfoil. Additional adhesive is used on most trailing edges to add extra support to the sharpest edge of the blade, where flexing can cause the most damage from deformation. Due to the nature of fiberglass or carbon fiber composites, recycling and disposal is extremely difficult with existing technology. While glass fiber may be infinitely recyclable, and many of the resins used may have a secondary life, they must be separated prior to material recovery. The fiberglass construction process fully enrobes the glass fibers in resin with a chemical bond, which is both extremely strong and extremely hard to break down. Composites that have not been broken down with chemical or physical processes are not able to be recycled, but some limited reuse opportunities do exist. The majority of retired blades so far have been landfilled, as costs for recycling are too high to be recovered through recycled material sales. Most manufacturers have determined their airfoils should last for roughly 20 years, and many of them offer equipment guarantees that reflect this.

Wind turbine blade recycling in Washington: a feasibility study

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