Keywords

1 Introduction

1.1 Wind Farms Installation in Europe

The wind energy market is growing in Europe, making wind turbine waste significant in quantity and of importance in future scenarios of circular economy. It is crucial to understand how and where wind technology was and is spreading in order to locate potential sources of materials to be collected, treated and reused. The typology and quality of materials also require attention, especially if they will be addressed to the construction sector.

In 2022, the total installed wind power capacity in Europe amounted to 255 GW, mainly attributable to onshore plants (88%) [1]. But in the decade 2013–2022, offshore installations recorded an annual growth rate of 15.7%, higher than onshore farms (7%).

Two-thirds of the total wind capacity is installed in six countries, such as Germany (66 GW), Spain (30 GW), the United Kingdom (29 GW), France (21 GW), Sweden (15 GW), and Turkey (12 GW) [2].

The 67% of onshore wind capacity is installed in seven countries: Germany (58.95 GW), Spain (29.8 GW), France (20.65 GW), United Kingdom (14.6 GW), Sweden (14.4 GW), and Turkey (12 GW). Significant shares come from Italy (11.8 GW), Poland (7.86 GW), the Netherlands (6.22 GW), Portugal (5.67 GW), Finland (5.60 GW), Denmark (4.97 GW), Greece (4.8 GW) and Ireland (4.61GW) [1].

Offshore wind capacity counts 30.1 GW, of which 97% is installed in five countries: the United Kingdom (13.9 GW), Germany (8.0 GW), the Netherlands (2.8 GW), Denmark (2.3 GW) and Belgium (2.2 GW). The remaining 3% share is distributed in other European countries, among which France (0.48 GW) and Sweden (0.19 GW) stand out [1, 2]. Figure 1 shows the percentages of installed wind power capacity in the European countries.

Fig. 1.
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European countries with the highest share of wind power: (a) onshore; (b) offshore.

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Taking into account wind generators, the nominal capacity increased by an annual average of 5.50% for onshore and 7.45% for offshore turbines. This trend highlights how wind turbines are getting larger and larger and more powerful. Sweden and Finland have the most powerful onshore wind turbines, with an average capacity of 5.7 MW and 5.6 MW, respectively. The lowest average capacity is held by Portugal (2.2 MW) and Poland (2.8 MW) [1].

Moreover, knowing the year of installation of wind turbines is a critical information to manage their life cycle and to estimate the amount of waste to be disposed of. More and more wind farms in Europe are reaching the end of their life cycle. In 2022, 14 GW of wind farms were nearing the end of life (EoL) and about 78 GW will reach 20 years of age in 2030. The oldest wind turbines are installed in Spain with an average age of 13.4 years, followed by Portugal (13.3 years), Italy (11.4 years), Germany (11.3 years), the UK (8.7 years), and France (8.0 years) [1]. The decommissioning of air generators is a challenge for the future. The study presented in [3] predicts that Germany will be the largest producer of onshore wind waste in 2050, with an estimated 67.6 tons of wind turbine blades to be disposed of. Sweden, the United Kingdom, Ireland, Italy, and Eastern Europe will follow with a significant amount of waste. A moderate increase is expected in Spain, France, Finland and central Greece, while a slight increase is predicted in the Baltics, northern UK, northern France, and Poland. The UK is projected to become the largest producer of offshore wind waste by 2050 with a waste generation rate of approximately 40%. The Netherlands is predicted to record the second largest production rate of 8%, followed by Belgium (5%) and Ireland (2%).

1.2 Potentialities of Wind Energy in Circular Economy and Constructions

Life cycle assessments (LCAs) demonstrated that the materials used for the manufacture of turbines constitute 70–80% of the impact. As a consequence, an effective recycling at EoL can provide economic and environmental benefits.

In particular, the study conducted in [4] considered a cradle-to-gate life cycle inventory analysis of materials of a 60 MW wind park. The saved energy was estimated to be approximately 81 TJ, and the reduction in emissions equal to 7351 tons of CO2.

Moreover, LCA analyses demonstrated that 342 kg of CO2 can be saved for every tonne of blade waste used. Substitution of blades of steel and concrete products was found to provide the most impacts [5].

Despite the clear benefits, the recycling of composite materials from wind turbines requires high costs and limited volumes of waste are available. Repurposing blades into second life structures appears an increasing and suitable alternative, but difficulties occur: a perceived lower quality of used materials, uncertainty on residual structural properties, lack of end markets for recycled materials [6]. In addition, it should be considered that wind turbines use rare earth components in depletion and their recovery could be of significant importance [7].

1.3 Aim of the Study and Methodological Note

The aim of this paper is to illustrate the state-of-the-art in how wind turbines components can be reused in urban environments and buildings following the concept of a circular economy and sustainable energy transition.

In particular, the research questions that inspired the study are:

  • what are the potentialities of wind turbines materials to be applied in the circular economy of buildings?

  • are there applications developed in research or on-site that constitute reference examples?

For answering these questions, the information presented was extracted from a collection of documents merging different sources: journal and conference papers from the Scopus database, reports and websites of European institutions, and datasheets of companies. The variety of the documentation allows a larger view of the topic considering both the scientific developments and the real case studies.

2 Materials from Wind Turbines

A wind turbine is basically made up of a foundation, a lattice or tubular tower, a generator (or nacelle), and blades. These components include numerous materials:

  • Fiberglass or carbon fibre reinforced composites are commonly used for turbine blades due to their strength, flexibility, and lightweight properties;

  • Steel is a common material for wind turbine towers, providing the necessary strength to support turbine components;

  • Steel and alloys are often used for gearbox and generator components because of their durability and ability to withstand mechanical stress;

  • The nacelle, which houses the turbine gearbox and generator, is typically made of steel or aluminium.

According to a report from the National Renewable Energy Laboratory [8], the composition of wind turbines varies based on their make and model. Generally, wind turbines consist mainly of steel, representing 66–79% of the total turbine mass. Other important components include fiberglass, resin, or plastic (11–16%); iron or cast iron (5–17%); copper (1%); and aluminium (0–2%).

Wind turbine blades are considered attractive components that can be reused in the construction sector due to their valuable mechanical and durability properties [9].

Moreover, ongoing research focuses on developing advanced materials to enhance the efficiency and durability of wind turbines. Innovations include the use of new alloys, hybrid materials, and smart materials that can respond to changing conditions.

The authors collected data provided by Vestas company, a global leader in the design, manufacture, and sale of wind turbines [10]. The company is committed to reducing the environmental impact of its products and provides, for 20 onshore and 3 offshore wind turbine models, the percentages of the materials used [11]. These data were used to make it clear how different types of materials, such as steel, iron, aluminium, copper, polymers, glass and carbon fibres, change according to the turbine capacity. The analysis excluded electrical and electronic components, lubricants, and fluids due to minor interest in constructions and cities. Figure 2 shows the percentages of materials used in onshore and offshore wind turbines.

Fig. 2.
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Source Vestas [11].

Percentages of materials used in the construction of onshore and offshore wind turbines.

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Steel and iron materials are the most used materials in both onshore (83% to 88% by weight) and offshore wind turbines (about 82%). Aluminium and alloys account for 1–2% of offshore wind turbines. The 2 MW turbine has an aluminium percentage of 1.57%, whereas turbines with higher rated power, with the exception of the 6 MW turbine (1.50%), have values below 1.50%. For offshore wind turbines, aluminium and alloys vary between 1.3%–1.5%. The amount of copper and alloys used in onshore wind turbines varies between 0.57% and 0.60%. In offshore wind turbines, the amount of copper decreases with the capacity (from 1.45% to 0.90%). Onshore wind turbines contain a percentage of polymeric materials (epoxy resins, glass and carbon fibres, and thermoplastic polymers) that varies between 2.60% and 4.70%. This value varies according to the rated power of the turbine; in fact, the 2 MW turbine has a percentage of polymeric materials of 4%, similar to the 7 MW turbine (4.05%). Offshore wind turbines, on the other hand, have a percentage of polymeric materials of 1.45% for 7 MW turbines and a value of 0.90% for the 15 MW turbine. On average, the amount of glass/carbon composite materials vary between 6.0% and 9.0% in onshore wind turbines and between 7.25% (9 MW) and 9.5% (15 MW) in offshore wind turbines.

Upon concluding its intended operational lifespan, a wind farm developer faces the task of choosing among various alternatives for the aged facility, i.e. extending its lifetime, opting for repowering (partial of full repowering), or proceeding with decommissioning (reuse, recycle, incinerate, landfilled). The determination of the most appropriate action is influenced by technical, economic, and regulatory considerations.

Additionally, efforts are being made to repurpose entire turbine blades as structural components in various applications. These applications range from bike sheds in Denmark, noise barriers for highways in the US, and ‘glamping pods’ scattered throughout festival sites in Europe to their incorporation into civil engineering projects like pedestrian footbridges in Ireland [12].

3 Reusing of Wind Turbines in Constructions

Current recycling processes for fibre-reinforced polymers cannot provide high-quality materials. It seems more viable reusing segmented parts of turbines as construction elements. Moreover, reflection on the consequences for the initial design of composite products is still missing [13].

The combination of fibres and polymers, also known as glass fibre reinforced polymer (GFRP) composites, represents the majority of the material composition of the blades (60–70% reinforcing fibres and 30–40% resin by weight) [5].

3.1 Wind Turbines Reuse in Cities

Examples of recycling of wind turbines in urban environment are increasing. The information collected by the authors demonstrates that blades and towers can be included in infrastructures such as bridges, barriers with different functionalities, and urban and domestic furniture [13, 14].

Pedestrian, bicycle, and vehicle bridges that use wind turbine blades as their primary load-carrying structural members are evaluated in the project “Re-wind Network blade repurposing solutions” [15].

The Re-Wind Network repurposed wind blades as poles of different types:

  • Power line poles for distribution and transmission lines;

  • Cell phone towers;

  • Lighting poles;

  • Sign support poles.

Depending on the size of the wind turbine blade, they can be used in urban or suburban neighbourhoods.

Barrier structures designed from wind blades can perform various uses:

  • construction site boundary barriers;

  • noise barrier;

  • traffic barrier (Jersey barrier).

These constructions can also be used for wave and wind attenuating and sea-wall barriers. Barrier dimensions vary depending on the size of the blades and design requirements to replace timber or steel and save material (see Fig. 3).

Fig. 3.
figure 3

Examples of reuse of wind turbines in urban environment. Sources: (a) and (b) from [15], (c) from [16], (d) from [17], (e) from [22], (f) from [23].

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Noise attenuation barriers made of recycled fiberglass are proposed by the Danish company Miljøskærm [16]. A section of the wind turbine blade would be used as small grain partition walls, replacing concrete walls, or as traffic barriers [6]. Superuse Studios Rotterdam designed playground blades [17, 18] and street furniture [19] using discarded wind turbines. Turbine blades are also used for bus and bike shade, canopies, roofing parking-lot. Bike shade installations are well located in Aalborg and Almere Port (Denmark). The installations were promoted by Siemens Gamesa Renewable Energy S.A [20] and Superuse Studio [21].

3.2 Wind Turbines Reuse in Buildings

Decommissioned wind turbines can also be transformed into building components. According to the study conducted in [24], developing projects to reuse disused wind turbines could benefit the coastal areas in Mexico's Yucatan province (see Fig. 4). The homes of the region, built with low-quality masonry blocks, are vulnerable to hurricanes and severe flooding. The reuse of wind turbine blades, both intact and dissected, assumes a key role in the enhancement of these components in the structural field, helping to meet the challenges associated with extreme weather events. The study considered a 2 MW wind turbine blade, representative of the technology of the 2000s, and proposed an innovative solution consisting of raising the houses with the section of the wind turbine closest to the hub, appropriately cut into segments suitable for the size of domestic houses. The sections can be cylindrical or elliptical, and installed in the ground and filled internally with rubble.

Fig. 4.
figure 4

Examples of reuse of wind turbines in buildings structure. Sources: (a) from [24], (b), (c), (d) from [15].

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Other solutions are offered by Re-Wind Design [15] (see Fig. 4). The company made the idea of construction of small shelters including blades of wind turbines that have reached the EoL. Shelters can be arranged on prefabricated containers and used for both domestic and industrial use. Another use is to build fixed camping tents called Glamping Pods using the wind blades as a wall or roof because of they are stronger and have a longer life span than wooden trusses or sheet metal.

3.3 Repowering of Wind Turbines

Repowering involves replacing or upgrading older turbines with newer, more efficient models. This may include using advanced technology, larger rotor blades, and more powerful generators. Repowering can significantly increase the overall energy production capacity of a wind farm and improve its economic viability. It also contributes to technological advancements in the industry.

Repowering offers numerous advantages, including a nearly three-time increase in the electricity output of a wind farm, achieved with a 25% reduction in the number of turbines on the same site. Older wind farms, typically located in ideal locations, often feature less efficient turbines. Upgrading to more powerful turbines makes logical sense. Additionally, repowering allows local communities to continue to maintain the benefits of their wind farm, such as local taxes and community projects.

Repowering wind turbines requires checking components that will not be replaced. It is important to evaluate these components if they are to stay in service with the repowered turbine. There are several challenges to be considered here regarding the structural components of wind turbines. In general, towers and foundations are over designed and have a high safety factor. However, it is necessary to evaluate the remaining useful life, including fatigue analysis, serviceability and strength. Blades can contain cracking and pitting of the leading edge of the blade. In the case of tower bed frames, this is a high-cost item and often the last item to wear out.

An interesting example considering repowering is the CRAIL Wind Project [25], which illustrates how repowering can be successfully executed with attention to regulatory compliance, technical expertise, comprehensive services, and long-term support. By repurposing an existing turbine and adapting it to current standards, the project contributes to sustainable energy initiatives while fostering community participation and long-term environmental benefits. The refurbishment process, overseen by former Vestas engineers, encompassed a complete disassembly, meticulous inspection of all components, and refurbishment in strict adherence to the original manufacturers’ specifications and tolerances. As part of this process, the turbine height was reduced from 45 to 35 m to comply with planning permission requirements. Additionally, the turbine's power output was derated from 500 kW to 400 kW to comply with limitations imposed by grid connections. Beyond the refurbishment itself, the supplier not only delivered, but also handled the construction and commissioning of the turbine. The supplier also demonstrated commitment by providing a 5-year warranty, coupled with a 5-year operations and maintenance agreement for ongoing support.

Another successful example is in Germany, such as the Düngstrup Wind Farm in Lower Saxony, where eight 1,3 MW turbines were replaced by four new 3 MW turbines on the same site [26]. While the old wind farm produced 12 GW hours per year, the new turbines produce 35 GW hours. In general, repowering initiatives are expected to increase power output four times and three times in terms of installed capacity.

4 Conclusions

The production of waste from wind farms is estimated to be growing. From the analysis performed, we can state that the materials used in the design phase will also change varying the power of onshore and offshore wind turbines. In particular, copper or polymeric materials record a higher percentage of weight in offshore wind turbines.

Current recycling processes are unable to provide high quality materials, and the reuse of segmented parts of EoL products as construction elements has been demonstrated to provide effective alternatives.

Several companies and design studios proposed and built examples of small infrastructures in urban environments, and also researchers conceptualised possible integrations of wind turbine sections as a part of buildings, such as roofs and foundations.

In summary, wind farm developers should weigh several options for aging facilities, including extending their operational lifespan, considering either partial or full repowering, or choosing decommissioning with subsequent actions such as reuse, recycling, incineration, or landfill disposal.