This Is Why We Don't Recycle Wind Turbine Blades
What should we do with wind turbine blades once they reach the end of their life?
Have you ever wondered how green wind energy really is, especially when you see those vast piles of wind turbine blades dumped in landfills? Social media and articles, like this one from Bloomberg, have raised this question, casting doubts on the sustainability of wind power. Is it actually horrible for the environment?
Wind turbine structure
Most parts of a wind turbine are made from steel, copper, and concrete, and they are recyclable. However, the blades, made mostly of fibreglass and sometimes carbon fibre, present a unique recycling challenge. This challenge is shared with other products like boats, cars, and aeroplanes, Wind turbine blades account for only 5 to 10% of global composite material use. The findings from my rough calculations revealed that if one were to rely on wind power for household electricity over 20 years, the share of composite material waste would be less than that generated by a mountain biking habit.
Understanding the structural design of wind turbine blades is key to grasping why they pose a recycling challenge. Picture a blade as a giant cantilever beam, much like a diving board: fixed at one end, free at the other. Even a 30-meter blade, considered small by today's standards, must withstand extreme wind gusts exerting nearly 200,000 Newtons of force, equivalent to the weight of about four African elephants. These blades must be incredibly stiff to prevent bending into the tower, exceptionally strong to resist breaking, and simultaneously lightweight enough for the tower and bearings to support them.
How composite materials work
The key to being able to achieve this remarkable combination of stiffness, strength and light weight lies in fibre-reinforced materials like fiberglass and carbon fibre. These materials contain fibres that are very strong because they are too thin to contain any defects, but they are floppy, like a rope. Then the fibres are contained in a resin, which is not particularly strong or stiff on its own. But the resin keeps all the fibres in place. Once you put the fibres in resin and the resin cures, the fibres can’t slide past each other anymore and so the composite material becomes very stiff and strong in the direction of the fibres. The composite structure allows for a high degree of strength optimization, concentrating durability where it's needed most while keeping overall mass minimal.
Once the resin hardens, the fibers are fixed in place, making the material stiff and strong where the fibers are aligned.
When manufacturing wind turbine blades, the orientation of fibres is crucial. Most fibres align along the blade's length, ensuring strength and stiffness where it's needed. And they need to be continuous, so wind turbine blades are made in a single piece, layering dry glass fabric in a mold, then infusing it with resin under a vacuum. Once that resin cures, you’re left with a very durable structure – these blades need to withstand exposure to the elements for 20 or 30 years. The fact they can do that is a great engineering feat, but their incredible durability also makes them hard to recycle. As we move on to recycling, keep in mind that the features making these blades robust and efficient also make them tough to repurpose.
Dry glass fabric is layered in a mold and then infused with resin under a vacuum to allow the resin to cure, resulting in a very durable blades that can endure exposure to the elements for 20 to 30 years. Photo source: LM Windpower
Why are they hard to recycle
What does “recycling” actually mean? Is burning the material for energy recovery considered recycling? What about shredding the blades to use them as filler for low-value materials where structural integrity isn't crucial? Does that count as recycling? These recycling methods raise critical questions about sustainability and environmental impact. Burning blades, for instance, introduces CO2 emissions into the equation. Additionally, the process of recycling plastics often consumes more energy than manufacturing from virgin materials. Meanwhile, using shredded materials as fillers poses the risk of squandering the remarkable structural properties inherent in wind turbine blades.
Let’s talk in a bit more depth about fibre reinforced composite materials to find out why. Fibreglass or carbon fibre are a combination of two elements: the fibre and the resin, which are bonded tightly together. The key to recycling composites is separating the fibre from the resin without destroying them.
Separating the resin is the first step to recycling the blade successfully.
The resin, a type of plastic, is composed of long polymers that slide past each other when in liquid form and solidify upon curing. You might be thinking that recycling plastics is a straightforward process, we do it all the time right? PET bottles are recycled into new bottles or into new products, such as trendy workout gear or durable outdoor furniture. Yet, this method can’t be used for materials like wind turbine blades, due to the distinct nature of the resin involved.
The resin used in these blades is a thermoset, which, unlike thermoplastics, undergoes a permanent chemical change upon curing. This change is similar to cooking an egg; once the egg is hard-boiled, it cannot revert to its raw state. Thermosets form a complex cross-linked network, making them impossible to melt down and reshape like thermoplastics, which behave more like cooked spaghetti - easily untangled and reshaped when reheated. This distinction between thermosets and thermoplastics is a key factor in the difficulty of recycling wind turbine blades.
Current wind turbine blades are made with a thermoset resin that permanently hardens, unlike thermoplastics that can be melted and reshaped. This makes recycling the blades challenging.
Existing Recycling Technologies
Creative reuse
The first and simplest method is to creatively repurpose turbine blades for new uses. Given their size and durability, blades can be cut up and used for applications like bike shelters and playground structures or whatever. Instances of such inventive repurposing tend to garner widespread attention and appreciation. However, with over a million wind turbine blades globally, it prompts the question of whether a proliferation of structures resembling wind turbine blades is a desirable outcome.
Do we want all bridges to resemble wind turbine blades? Photo source: https://www.bladebridge.ie/services/
Considering the limitations of the repurposing approach, attention turns to more versatile recycling methods. One option involves cutting the blades into smaller pieces and utilizing them as a form of "composite lumber," akin to traditional wooden planks. While this concept has been explored in various projects, success has proven elusive in my experience. Several challenges emerge, including issues with achieving a consistently flat surface and addressing significant variations in strength based on the material's condition. Those problems are individually solvable but tend to add up to make it not quite worthwhile.
Shredding
Shredding is a key method in recycling wind turbine blades. It involves breaking down the blades into smaller, more manageable fragments which can be used applications where the demanding structural integrity of the original blade isn’t required. For example, the shredded material can be incorporated into products like decking materials, vehicle dashboards, or even for 3D printing.
Cement Co-processing
Another option involves using shredded blade materials in cement production. This process serves a dual purpose—recovering the organic content as energy and integrating the mineral fraction into the cement clinker. One tonne of blade waste can reduce CO2 emissions by 110 kg and save 461 kg of raw materials compared to standard cement manufacturing.
Pyrolysis
Pyrolysis, an advanced recycling method for wind turbine blades, involves heating the material between 400 and 700 °C in a low oxygen environment. This process chemically decomposes the resin into simpler substances, enabling the recovery of fibres for reuse in structural applications. However, the fibres' strength is reduced by as much as 50% after heating, making it impractical for crafting new wind turbine blades. Pyrolysis has drawbacks, including high energy use, CO2 emissions, and the inability to recover the resin.
Heating the blades in a low oxygen environment breaks down the resin into simpler substances, enabling the recovery of fibers.
New Recycling Technologies and Innovations
While the methods mentioned so far offer valuable ways to reuse composite materials, they generally lead to degradation, limiting the materials' use in structurally demanding applications like new blades. This is akin to paper recycling, where each cycle shortens the fibres, gradually reducing the paper's quality from high-grade to lower uses such as cardboard and packing materials.
Moving forward, let's delve into more advanced recycling methods, where the primary objective is to effectively reuse both the fibre and resin in applications that demand structural integrity. The industry is currently pursuing a two-pronged approach: firstly, designing new blades with enhanced recyclability, and secondly, developing methods to repurpose fibre and resin from existing blades to the extent that they can be utilized in the production of entirely new blades.
Redesigning Blades Using Thermoplastics
Remember our discussion earlier on the contrasting recyclability of thermoplastics and thermosets. If wind turbine blades were constructed using thermoplastic resins, the task of recycling would be so much easier. Thermoplastic resins can be melted away from fibres and then recombined into new blades without compromising their structural properties. This approach won’t help recover materials from existing blades but could make future blades fully recyclable. The challenge is that thermoplastic resins usually have much lower structural properties than thermosets, but there has been progress recently in few projects working on new types of thermoplastic resins, and new structural design and manufacturing methods to create fully recyclable thermoplastic blades.
LM Wind Power has recently manufactured its second recyclable wind turbine blade, utilizing Arkema's Elium recyclable thermoplastic resin. With a length of 77 meters, this blade mirrors the dimensions typical of onshore wind turbines. A notable feature of the blade is its shear web – the integral structural element that maintains separation between the two shell sides of the blade – which is constructed from recycled resin. The blade has successfully undergone static testing, a process involving exposure to extreme loads. It is scheduled for fatigue testing in the upcoming months, to further assess its durability and performance.
New recycling methods
The second prong focuses on new innovative methods for recycling existing blades. Significant advancements have been made, enhancing the capabilities of standard recycling processes with high-tech solutions.
There is advanced mechanical recycling like Regen Fiber that converts decommissioned wind turbine blades into reusable materials. This includes their application in the concrete and mortar industries and road construction, where blades are transformed into pencil-like pieces functioning as mini rebar.
Advanced pyrolysis is a multistage process, as discussed by Ryan Ginder from the University of Tennessee. By carefully controlling the temperature of the pyrolysis process, the structural properties of the recovered fibre can be maintained much closer to the virgin material. The recycled glass fibre can be made into nonwoven fabrics, continuous textile yarns, automotive sheet moulding compounds, and plastic injection moulding pellets. A notable application of this technology is the collaboration with TPI Composites, which resulted in the production of continuous fibres and 3D printer filament used to manufacture a drone, showcasing the practical and innovative uses of recycled materials.
Chemical Recycling
In addition to pyrolysis, wind turbine blade recycling incorporates various chemical recycling methods. Solvolysis involves dissolving polymers in a solvent, where controlled temperature and pressure conditions facilitate the breakdown of the polymer matrix, allowing for the separation and recovery of fibres and resins. Another innovative approach is the small molecule-assisted technique, which uses low-molecular-weight compounds to target and decompose the polymers in composite materials. This method operates at lower temperatures and effectively separates the constituent materials for recycling.
Solvolysis involves dissolving polymers in a solvent, where controlled temperature to recover fibers and resins.
Progress
Vestas, in collaboration with Circular Economy for Thermoset Epoxy Composites (CETEC), two Danish universities, and epoxy resin supplier Olin, is spearheading the commercialization of a solvolysis recycling process. They achieved a lab-scale proof of concept in early 2022 although the progress on scaling up this technology remains uncertain. Although still in the developmental stages compared to mechanical and pyrolysis processes, the successful implementation of solvolysis could be a way to recycle epoxy resin, which the other methods are not able to. This would be a significant step towards achieving the "holy grail" of wind turbine blade recycling, which entails the capability to reclaim both resin and fibre for incorporation into new blades.
DecomBlades have recently successfully produced recovered fibres that are viable for manufacturing new wind turbine blades. Their process involves using pyrolysis to extract the glass material from old blades, which is then ground into a powder. This powder is subsequently melted down to create new fibres, a process that was actualized at 3B’s glass fibre manufacturing plant in Norway last September.
Old wind turbine blades undergo pyrolysis to produce powder than can replace 5% of virgin glass in new blades. Photo source: https://decomblades.dk/index.php/2023/04/20/632/
DecomBlades reports that their technique can replace up to 5% of virgin glass in new blades. Admittedly, this figure might seem modest at first glance. However, it's important to consider the current dynamics of blade production and decommissioning. Currently, the industry is producing a significantly higher number of new blades compared to the quantity of old blades being decommissioned. Therefore, even substituting a small percentage, such as 1-5%, of the raw materials in new blades with recycled materials, is sufficient to utilize all the decommissioned blades available at present. It’ll be decades before the number of retiring blades catches up with the number of new blades being produced, and by then other methods will hopefully have progressed to the point where most of that can be covered by recycling.
Is recycling blades worth it?
The critical issue behind the exploration of wind turbine blade recycling is the rationale behind the desire to recycle blades. Did you notice how complicated all these processes are? As efforts inch closer to the ideal scenario of transforming old wind turbine blades into new ones, the complexity escalates. This progression leads to an increase in the number of processes involved and necessitates more transportation between facilities, raising questions about the energy consumption of these activities.
This question was addressed in a 2018 study by Liu et al, which found that the energy needed to process 1 kg of wind turbine blade waste was 0.26MJ to put blades in landfill – that’s a little under 0.1 kWh – and around 20MJ for the various chemical processes. That’s nearly 100 times more energy for advanced recycling compared to simply landfilling! Incineration with energy recovery generates rather than consumes energy, however it releases CO2 in the process, so only really a good outcome if it is replacing a fossil fuel energy source such as in a cement kiln, or if it includes carbon capture, which so far it does not.
Table 4 from Liu, Meng, Barlow 2018 study shows that landfilling only uses 0.26 MJ to process 1 kg of wind turbine waste, far less than recycling methods
It's important to note that even the most energy-intensive recycling processes for wind turbine blades consume only about as much energy as the blades would have generated in a few days of their operational lifespan. This perspective is crucial to avoid misconceptions about the energy efficiency of recycling. The energy used in recycling these blades does not surpass the total energy generated by the turbine throughout its lifetime.
The most energy-intensive recycling processes use only as much energy as the blades would generate in a few days of operation.
However, if the primary goal is to minimize energy use and emissions from decommissioned wind turbine blades, the most efficient approach would be to avoid transporting, processing, or burning them, especially without carbon capture. Burning the blades releases CO2, as carbon atoms bound in the resin are liberated into the atmosphere. This approach ensures that the carbon atoms currently sequestered in the resin of the blades are not released as CO2, thus minimizing the environmental impact of their disposal.
End of life energy use and emissions aren’t the only concern, the full lifecycle matters. This was the topic of another recent study by Diez-Cañamero and Mendoza. If you consider the whole life of the wind turbine blade, then using recycled materials in new blades will offset some of the energy and emissions needed to produce virgin materials. The more that can be recovered and the better its quality, the less virgin materials are needed. In this study, even though it has the second highest emissions from end of life processing, solvolysis emerged as the most effective in terms of circularity and full lifecycle CO2 emissions, significantly outperforming other methods such as pyrolysis and landfilling, and with potential to improve further if the process can be developed to improve material quality of the recycled material and if efficiencies can be maintained as the process is scaled from lab to commercial scale.
Conclusion
The current state of wind turbine blade recycling presents an overall positive outlook. The only downer left is the issue of cost, which no one likes to talk about and is really hard to estimate for something like solvolysis that still needs to be scaled a long way. Will we be happy to pay more for recycled or recyclable wind turbine blades? It might take regulatory mandates to shift the market towards these more sustainable options.
A key motivator for wind turbine manufacturers in addressing this issue stems from public perception. Images of wind turbine blades being disposed of in landfills have garnered significant attention and criticism. This negative publicity undermines attempts to rationalize landfilling as an environmentally sound decision, despite any logical arguments to its favour.
Looking ahead, the progress in the field of blade recycling is anticipated with keen interest. The combination of technological advancements and growing environmental consciousness suggests a promising direction for solving the challenges associated with wind turbine blade recycling in the coming years.
Watch “This Is Why We Don't Recycle Wind Turbine Blades” on Engineering with Rosie on YouTube.