Wind turbine blade recycling picks up speed

The small town of Sweetwater, in Nolan County, Texas, sits north of three of the world’s largest onshore wind farms. Some call it the “wind turbine capital of Texas.” On West Alabama Avenue in the town’s southwest corner, its history collides with a more modern legacy. There, across from the Sweetwater Cemetery, where some graves date back to 1880, is a modern graveyard for wind turbine blades.

Hundreds of blades, each cut into thirds, lie there like gigantic white bones stacked on one another. “It’s an eyesore,” says Nolan County attorney Samantha Morrow. The blade boneyard was a hazard for neighborhood children until recently, when the landowners put a fence around it, she says. It remains a breeding ground for rattlesnakes and vermin.

A company called Global Fiberglass Solutions (GFS) started bringing blades to the site in 2017. General Electric (GE) and other turbine manufacturers paid GFS to shred them and use the material to make railroad ties and flooring panels. But the blades keep coming with no removal in sight, Morrow says.

GE filed a lawsuit against GFS last fall for its failure to deliver on its promise. Local officials are talking to state and national legislators, as well as to waste contractors, to remove the blades, according to Morrow. “But it’ll be slow going because of the sheer magnitude and cost involved,” she says.

That’s not the peaceful, green ending one expects for these wind-harnessing behemoths after they have generated clean power for 20–25 years. In addition to languishing in junkyards such as the one in Sweetwater, many thousands of turbine blades are buried in landfills across the Great Plains in Iowa, South Dakota, and Wyoming—a blemish on wind energy’s sustainable image. “We need a way to sustainably dispose of these technologies as they become defunct,” Morrow says.

Turning blades into construction material, as GE and others are doing, is a low-value use for the high-tech composites. It’s one of few available options because the tough resins that hold today’s blades together are almost impossible to break down.

But now, researchers in academia and industry are putting a new spin on blade recycling. Labs around the world are working on novel chemical technologies to separate blades into their building blocks for reuse. Industry leader Vestas is testing a chemical recycling process that could work on today’s blades. Others seek to make tomorrow’s blades with new types of recyclable resins, while some are making the leap to biobased materials.

“Wind turbines are beacons of green energy,” says E. Bryan Coughlin, a chemist at the University of Massachusetts Amherst. Sustainable materials should go hand in hand with renewable energy, he argues. Throwing blades in landfills is a cheap, easy way to get rid of them. “Out of sight, out of mind. But we can’t do that,” Coughlin says. “These wonderful composite materials were designed to perform. We need to think about what to do with them at end of life.”

Chemical breakup

Wind produces almost 8% of the world’s electricity, and the industry is growing rapidly. Over 329,000 turbines are active globally, according to GlobalData.

Modern turbines are colossal. Their blades are more than four school buses in length, which makes them challenging and expensive to transport. And they are built to survive extreme conditions. More than 85% of the materials in wind turbines, including steel, copper wire, and gearing, is recyclable. But the blades aren’t.

Turbine blades are mostly composed of fibers made of glass or carbon set in epoxy resins. To produce blades, layers of fabrics made of dry fibers are vacuum sealed in a mold; a resin is then injected into the mold. Once the resin flows in and infuses the fibers, it is cured for hours in a large and costly oven.

Epoxies are difficult to recycle because they are thermoset polymers, which form 3D cross-linked networks as the resins cure when mixed with amine-based hardeners. In contrast to the thermoplastic polymers we encounter in packaging, epoxy-based thermoset resins do not melt—they burn. And they contain stable C–C, C–N, and C–O bonds, which are hard to break.

So when blades are decommissioned—that’s around 12,000 in Europe and US every year—they are typically cut into sections and sent to landfill. Industry experts predict that roughly 43 million metric tons (t) of blades will be discarded by 2050 (Waste Manage. 2017, DOI: 10.1016/j.wasman.2017.02.007).

“The volume of blade waste is a drop in the bucket of overall industrial waste,” says Tyler Christoffel, a technology manager in the US Department of Energy’s (DOE’s) Wind Energy Technologies Office. But blades take up a lot of space and need to be cut into smaller pieces, so some regional landfills in the US have banned blades. Besides keeping blades out of landfill, “we want to make these materials go farther,” Christoffel says. “There are energy and emissions savings when you reuse materials.”

Mechanical recycling of the sort promised by GFS gives blade materials a second life. For instance, the Danish start-up Continuum separates blades into their fiber, resin, and metal components using mechanical processes such as screening, gravity separation, and optical sorting. The company then blends the components to make composite panels for doors and countertops. The utility service firm Veolia North America shreds blades into pieces for use as raw material and fuel to make cement. Meanwhile, Knoxville, Tennessee–based Carbon Rivers heats composites in an oxygen-deprived environment to decompose the resin into gaseous and liquid fuel and recovers the fibers for reuse.

Many studies use high temperatures or harsh reagents to destroy the epoxies and recover carbon and glass fibers, says Jinwen Zhang, a polymer scientist at Washington State University (WSU). But such approaches often damage fibers and create a caustic waste stream.

Zhang’s team has discovered a new chemical recycling route to deconstruct blade composites. The researchers put pieces of composite into a benign solvent—Zhang isn’t ready to disclose what it is—and add a mild, low-cost acid that serves as a catalyst. The process splits the resins into oligomers that can be reused to make polymers. The separated fibers retain 90% of their original strength and can be recycled into automotive and other parts. After separating the components, the researchers collect and reuse the solvent.

“Our magical solvent enables recycling at moderate temperatures and ambient pressure,” says Zhang’s colleague Baoming Zhao, a chemist at WSU. “We consider our process very green and clean.”

The team is one of 20 to win the first phase of the DOE’s $5.1 million Wind Turbine Materials Recycling Prize. In addition to developing innovative technology that hasn’t been applied to turbine blades before, prize winners demonstrated economic viability by developing a sound business model in terms of secondary markets, partners, and supply chains, Christoffel says.

Another winning team is Coughlin’s group at UMass Amherst, which is partnering with BASF, the world’s largest chemical maker. The team is borrowing from the science of decaffeinating coffee beans to recycle blades. One decaffeination process uses carbon dioxide at high temperature and pressure in a form known as supercritical CO₂, in which the gas behaves like a solvent, helping dissolve and extract caffeine molecules. Turns out that supercritical CO₂ also swells and dissolves in polymers.

The researchers put blade composites into a reactor containing CO₂ and water, then dial up the temperature and pressure. “Water at these conditions is superheated above its boiling point but remains liquid because of pressure,” Coughlin says. “It’s like a pressure cooker in which things cook more quickly.”

Together, the CO₂ and water attack the cross-linked thermosets, breaking them into liquefied resins that can be used as or refined into other useful chemicals. The technology should be easy to scale up because it leverages well-known supercritical CO₂ infrastructure, Coughlin adds.

Toward a closed loop

The wind industry faces increasing pressure to clean up blade waste in Europe, where land is at a premium. A handful of countries have already banned landfilling of blades, and the trade association WindEurope has called for an European Union–wide landfill ban by 2025.

The Danish turbine maker Vestas has been ahead of the curve, says Allan Poulsen, the company’s head of materials and sustainable scaling. Researchers there have been thinking about ways to recycle blades since 2016, he says. “That’s when we started to acknowledge that we needed end-of-life solutions for sustainability and circularity. But good solutions take time.”

Working with Aarhus University, the Danish Technological Institute (DTI), and the US epoxy producer Olin, Vestas has arrived at a two-step process to make existing blade materials mostly recyclable.

In the first step, developed by DTI and Olin, the composite goes into an unnamed “commodity liquid” that separates the fiber and metal parts of the blade from the epoxy matrix, Poulsen says. The second step deconstructs the epoxy using a process developed by polymer specialist Troels Skrydstrup’s group at Aarhus (Green Chem. 2024, DOI: 10.1039/d3gc03707j).

“There is no existing closed-loop recycling for blades,” Skrydstrup says. “We are trying to develop a closed-loop technology that breaks down the epoxy polymer into its original building blocks to rebuild an identical consumer product from those components.”

The method involves exposing the resin to a mixture of fine sodium hydroxide powder and toluene solvent at 190 °C. Sodium hydroxide resists dissolving in toluene, but at that temperature “it’s forced into the solution, and then it’s highly aggressive and it breaks apart the resin,” Skrydstrup says.

After the mixture has done its work, the researchers recover the epoxy building block bisphenol A (BPA) from the solution. The leftover hardener is unusable, but Olin can reuse the recovered BPA to make more epoxies—which at least partially closes the recycling loop and reduces the need for virgin resources, according to Alexander Ahrens, a postdoctoral researcher in Skrydstrup’s lab. “BPA is produced at around 10 million t a year, mostly for polymers,” Ahrens says. “And that’s entirely from fossil feedstocks, so it’s good to be able to reuse BPA.”

Vestas is in the midst of pilot-testing the technology, Poulsen says. “I’m impatient, and I think, Why didn’t we do this yesterday? But we have to figure out how to do it in the most efficient way and also get the most value out of all the materials we separate. We have an ambitious goal of zero-waste wind turbines by 2040. We still have work to do, but we’re on the right track.”

Meanwhile, Skrydstrup’s group is moving ahead on a one-step route to disassemble the entire epoxy-fiber composite. They have found that a ruthenium-based catalyst and the solvents toluene and isopropanol can cleave the C–O bond in epoxies (Nature 2023, DOI: 10.1038/s41586-023-05944-6). The catalyst worked on all sorts of composites: a chunk of carbon fiber-epoxy composite that a student picked up from the garbage, a commercial glass fiber–based laminate, and a piece of a Vestas turbine blade.

What’s left at the end is a liquid from which the researchers separate the BPA, unscathed glass fibers, and the shiny piece of metal mesh that is used in blades to protect them from lightning strikes. The process takes around 3 days and relies on expensive ruthenium, but the team is trying to make the method more practical.

“The catalyst is not fast,” Skrydstrup says. “But it’s like Pac-Man—it chews its way through the epoxy, liberating the BPA and the glass fibers. Nothing like this has been seen before.”

Resin redesign

While many researchers are chipping away at today’s epoxy blades, others are taking a fresh look at materials for next-generation blades. By using tough resins that can be degraded on command, they want to design blades that are inherently recyclable.

Some efforts center on making new degradable epoxies that contain carefully placed chemical groups with breakable bonds. For instance, the Recyclamine epoxy made by Connora Technologies, which the Indian firm Aditya Birla bought in 2019, uses an amine hardener with acetyl or ketal bonds. An acetic acid–catalyzed hydrolysis reaction easily snips those bonds, says Harald Stecher, a blade materials engineer at the Spain-based turbine maker Siemens Gamesa, which has already sold around 300 blades made with the recyclable epoxy.

Mechanical tests on a recyclable blade 115 m long have shown that it behaves the same as a traditional blade, Stecher says. Recycling involves immersing blade pieces in a bath of heated recycling liquid for a few hours. “Then the glass is filtered out and fiber mesh and metal parts recovered,” he says. “The process breaks down the 3D thermoset network and converts it to a thermoplastic with very good mechanical properties similar to polycarbonates or polyamides.”

The thermoplastic is not fluid enough for the vacuum-based molding process used to make blades. But Stecher says it could be compounded with thermoplastics such as polyethylene to make industrial parts. Siemens Gamesa is now also using a similar recyclable thermoset made by Taiwan-based Swancor.

The French specialty materials manufacturer Arkema is ditching thermoset epoxies altogether. The company has developed a thermoplastic resin called Elium that depolymerizes and liquefies when heated, so it easily separates from the fiberglass in a blade. Purifying and treating the liquid resin restores its original properties so it can be remade into blades, according to Arkema.

The company is part of a consortium called ZEBRA (Zero Waste Blade Research), which is now putting two full-scale Elium blades, one 62 m and the other 77 m in length, through a battery of structural and recycling tests.

Mechanical engineer Robynne Murray and her colleagues at the US National Renewable Energy Laboratory (NREL) did early validation tests on Elium thermoplastic composites and found that a 13 m blade made of the new thermoplastic resin performed just as well as a traditional thermoset blade of the same size. Because the thermoplastics don’t need to be cured, she says, “even if Elium resin is more expensive than traditional epoxy, the blade turns out to be on par because of these facility cost reductions.”

A few years ago, the NREL team decided to develop its own recyclable resin. The researchers set out to look for a low-viscosity resin that works in today’s vacuum-based blade-making process. Then they went a step further.

“We wanted to decarbonize these materials, so we wanted to use biobased building blocks,” says NREL chemical and biological engineer Nicholas Rorrer. “Among all the recyclable chemistries, epoxy-anhydride chemistry came to the forefront. You initiate it like epoxy-amine chemistry, but it yields a material with esters as its main linkage instead of amines. And we’ve been studying how to depolymerize esters for a very long time.”

The resin, which the NREL group calls Polyester Covalently Adaptable Network (PECAN), is made from plant-derived chemicals such as sorbitol and butanediol (Matter 2024, DOI: 10.1016/j.matt.2023.10.033). PECAN manufacturing emits 40% less greenhouse gases than processes for making traditional epoxy resins. Tests show that fiberglass-PECAN composite pieces remained stiffer and deformed less over time—a material’s tendency to deform over time is called creep—than conventional epoxy blades. And the researchers could make a 9 m prototype PECAN blade using traditional wind blade manufacturing practices.

What’s more, the team has now showed that heating the composite in methanol deconstructs it, yielding all the fiberglass and the anhydride hardener for reuse (Science 2024, DOI: 10.1126/science.adp5395). Even if the resin cannot be reused for now, “we’re still talking about 80% of wind blade manufacturing being closed loop,” Rorrer says.

He is positive about the market potential of the new resin. “We challenged the classic assumption that you can’t use recyclable-by-design materials in robust world applications,” Rorrer says. “In fact, we show that sometimes they perform better. PECAN creeps less than Elium, so if Elium has a pathway to market I’m not worried about PECAN. I tell everyone, ‘Be like Nike and just do it.’”

All these collective research efforts will help eliminate waste and decarbonize the wind energy sector as it grows. That won’t come free, of course. “Recycling is going to be more expensive than the normal production of blades,” Aarhus’s Skrydstrup says.

But without recycling, companies will eventually have to pay to send blades to landfill—and that option might become unavailable as more landfilling bans take effect. So even if players aren’t convinced by the business case for reprocessing, policy could be the tailwind that pushes recycling of turbine blades. Companies may as well start investing in recycling technologies, Skrydstrup says. “We’re going to have to pay somehow.”