Beyond design life: What to do with aging wind turbines in Europe?

Wind energy plays a substantial role in the collective global endeavor toward the net-zero target. Countries all around the world have set ambitious wind energy targets, and according to BloombergNEF, about 931GW of wind energy was operational by the end of 2022. By 2023, BloombergNEF has estimated a 102GW installed capacity. More than 93% (959GW) of the generated wind energy has come from onshore wind turbines, and the remaining 74GW has been generated by offshore wind turbines globally.

European countries, especially the EU-27, are among the most ambitious countries to harness wind energy to transition their energy systems. The revised Renewable Energy Directive (REDIII), which has recently come into force, has set the target to increase the share of renewable energy to 45% of the European Union’s gross final consumption of energy by 2030. Wind energy will play a significant role in achieving this target. In the broader European market, wind energy has grown from 123GW of installed capacity in 2013 to 253GW by the end of 2022. BloombergNEF has estimated that Europe installed almost 18GW of wind energy capacity in 2023. In Europe, the largest share (88%) of the wind energy capacity was installed onshore by almost 239GW, and the remaining 12%, that equals to 32GW, was installed in offshore wind farms (see figure 1).

Wind is a renewable and infinite source of energy, but wind turbines have a finite functioning lifetime. The efficient lifetime for wind farms is typically between 20 and 25 years. Regular maintenance is critical for the longevity of wind turbines, as it allows technical issues to be identified and addressed at an early stage before severe malfunction or breakdown occurs. Other determining factors to enhance longevity of wind turbines include manufacturing quality, technological advancements, wind farm location and environmental conditions. The newer and more modern wind turbines could operate more than 30 years if well maintained. However, as new models are evolving toward larger wind turbines to be installed in remote areas, accessibility for operation and maintenance services is becoming more challenging. Furthermore, remote locations typically mean harsher environmental conditions, which could restrict the maintenance service time window due to safety considerations and regulations.

Given the typical 20 to 25 year lifetime efficiency of the installed wind turbines, a large part of the European turbine fleet will reach the end of its operational life over the next 10 to 15 years. On average, Denmark, Spain and Portugal have the oldest wind farms in Europe (see figure 2).

When a wind farm reaches the end of its planned service life, the developer must decide which option is best for the aged wind farm: lifetime extension, repowering, or decommissioning. Technical, economic, and regulatory factors determine which decision is to be taken. Figure 3 portrays an overview of the options that wind farm developers have at the end of life of their assets.

Wind turbines are designed to operate safely for at least 20 years under given operational and environmental loading. In certain circumstances, developers may decide to increase the service life of their wind turbines rather than decommission them. Extension of the service life of the turbines could result in increased revenues from existing projects. In addition to the financial advantages, lifetime extension could be crucial for countries to reach their net-zero targets. If countries only repower and decommission the turbines at the end of their design life, they must substantially increase annual installations to compensate for decommissioned farms with new installations to reach their national wind energy targets. Reaching the targets could become even harder given the huge pressure on materials and scarcity in the supply chain.

Another advantage of lifetime extension is less human-caused disturbance of ecosystems, as lifetime extension delays new construction and installation, which means a longer interval of human disturbance for wildlife. It should also be noted that lifetime extension follows the ‘reduce’ principle of circular economy, as turbines could be used until their real end of life. Therefore, extending the lifetime of turbines could slow the demand for raw materials and key components, so that those resources could be spent more efficiently, resulting in a lower waste stream that could also lighten the recycling load.

For lifetime extension, the structural integrity of the turbines should be thoroughly assessed so that the safety level is not compromised. Safety levels are achieved by verification of ultimate strength and fatigue strength of the materials against loading. Regular, thorough, and high-quality inspection and maintenance routines throughout the entire lifetime of the asset will increase the likelihood that a wind turbine is suitable for lifetime extension.

A key challenge when it comes to replacing a turbine’s damaged parts is the scarcity of spare parts, which makes the components difficult to replace. The scarcity of components for older models is a major concern as wind turbine manufacturers are constantly designing and building new turbine models that are more efficient than their predecessors. Therefore, spare parts for old wind turbines could be very difficult to find on the market if manufacturers cease the production lines for these components. It is also unclear whether there will be enough trained technicians to perform the maintenance of the old turbine models.

In addition to the technical suitability of wind turbines for lifetime extension, the profitability of the turbines needs to be assessed. Wear-out of components means more frequent maintenance services and downtime, and higher related costs. The costs could be more significant for offshore wind farms as their operating expenditures are higher than for onshore wind farms. This is mainly due to marine logistics and the environmental conditions of the site. Therefore, a cost-benefit analysis is needed to determine if lifetime extension makes a viable business case. This becomes even more important as developers in most European countries can no longer benefit from different sorts of wind energy support schemes and guaranteed feed-in tariffs, as these policy instruments do not cover the period of lifetime extension. Developers will then have no choice but to sell their generated electricity on the spot market, competing with power plants that may produce electricity with lower variable costs, or secure a Power Purchase Agreement (PPA). In general, new business models need to be developed as the revenue model and cost structure will be different after the lifetime extension.

Regulatory requirements are another important aspect to address when taking a decision on lifetime extension.

For one, developers need to make sure that they are allowed to continue operating their asset beyond the licenced operational period. The consent process can be very lengthy and unclear. In general, the requirements for lifetime extension are country-specific and there is currently no international or EU regulation. In Germany, for example, the current relevant law allows for a lifetime extension of up to 10 years if the regulatory authority expects no subsequent use for the site and if the grid connection is available. However, given Germany’s ambitious wind targets for 2050, authorities will likely be inclined to decommission smaller and older turbines to make way for the installation of larger turbines.

In addition to the land leasing consent process, the regulatory regime for transmission assets is another determining factor for the lifetime extension of wind turbines. For instance, in Germany, the transmission system operators (TSOs) build and operate the offshore transmission infrastructures, not the wind farm developers. In the UK, on the other hand, wind farm developers are allowed to build the offshore transmission infrastructure, but they are not allowed to own it, so they must sell the asset to the offshore transmission owner (OFTO). The lifetime of the grid connections is limited, and there is no clarity on whether the lifetime of the transmission infrastructure will be extended, or whether the assets will be decommissioned. The situation is further complicated by the fact that usually several wind parks with different lifetimes and end-of-life plans are connected to the same TSO convertor platform. Therefore, a decision to extend the lifetime of a wind farm also depends on alignment between the parties’ target lifetimes and the consensus among the wind park developers, TSOs and governments.

If lifetime extension is not opted for at the end of life of a wind turbine, repowering or decommissioning comes into play. Repowering is essentially done in three ways. First, developers may decide to maintain the tower and foundation, but replace the old turbine with a new but lower-capacity turbine. In this case, the new turbine may generate less power, but it puts less load on the tower, which could result in a longer service life (less fatigue) and lower maintenance costs. Given countries’ ambitious wind targets, this type of repowering does not seem to be widely favored.

The second repowering option is to preserve the old tower and foundation, but replace the turbine with a new, higher capacity turbine. Although the turbine could produce more electricity, this repowering option is usually not favorable as it places greater loads on the tower and foundation, increasing the risk of structural failure or damage.

The first two options are referred to as partial repowering, but there is a third option, referred to as full repowering. This consists of replacing the whole turbine, tower, and foundation with an entirely new, higher capacity wind turbine platform. Both partial and full repowering, if done at the end of the operation permit, could be subject to the challenges of transmission infrastructure availability described earlier. The complexity increases when repowering is planned to increase capacity, as the grid connection will also need to be upgraded. Despite these challenges, 4.31GW of wind power capacity (both onshore and offshore) has been repowered in Europe between 2013 and 2022 (see figure 4).

Although the assumption is that wind turbines will be repowered at the end of their life, sometimes developers decide to repower their wind parks sooner. There are three main reasons for early repowering, including scarcity of suitable wind sites, technological advancements, and market demand for secondhand wind turbines.

Repowering is important to accelerate the pace at which wind energy targets can be achieved. It could play a particularly important role for countries with limited suitable sites for wind parks. Land scarcity could be compensated with higher capacity repowering, allowing countries to increase their installed capacity, and meet their targets. In addition, power rating and capacity factors of new turbines have increased over the last decade. Such technological advancements make repowering an attractive option. The third major driver for early repowering is the development of the market of secondhand wind turbines. Secondhand wind turbines are usually purchased when the buyer faces dimension restrictions due to permitting or logistical restraints, such as when the wind farm is located at higher altitudes where it is difficult to transport bigger turbines to the site.

Another important reason for installing a secondhand turbine is economic. The installation of secondhand turbines requires lower capital expenditure compared to new turbines, and it is a key factor in the financial decision-making process, especially when the interest rate is high. A critical issue with early repowering is that although it could increase the electricity production of existing wind farms, if not well managed in terms of circularity, it could add to the waste volume of the sector. Consideration of the full life cycle of renewable energy technologies, including wind turbines, should be at the core of early repowering decisions if a sustainable energy transition is to be achieved.

In addition to technical and economic feasibility, supportive national and European regulatory frameworks for repowering projects are essential. Within the European Union, regulations are already in place to streamline the permit-granting process for repowering renewable energy projects. For example, in December 2022, the European Council adopted emergency measures that include regulations to shorten and accelerate the permit-granting process for renewable energy projects, as well as for the grid and infrastructure needed to integrate renewable energy into the energy system.

These emergency measures complement the provisions of the revised Renewable Energy Directive (REDIII), which came into force in November 2023. Repowering is endorsed in REDIII as a good strategy that can ensure the continued use of existing wind farms while reducing the need to designate new land for renewable energy projects. REDIII highlights two key advantages of repowering: the likelihood of increased public acceptance and knowledge of environmental impacts.

REDIII introduces a stable and permanent regulatory regime to streamline the permit-granting process for renewable energy production, including repowering projects in the region. According to REDIII, permit-granting procedures for the repowering of renewable energy power plants with an electrical capacity of less than 150 kW located in renewables acceleration areas shall not exceed six months for onshore projects and 12 months for offshore projects. If the repowering projects are located outside the renewable acceleration areas, the permitting process shall not exceed 12 months for onshore and 24 months for offshore plants. REDIII also states that the permit-granting procedure, including environmental assessments and screening, for the repowering projects should only be limited to the potential impacts resulting from the changes compared to the original project.

Decommissioning puts an end to the operation of a turbine at a specific location. When lifetime extension or repowering is not technically, legally, or financially feasible, wind turbines are dismantled and removed from the site. The land may be used for full repowering or restored to its original environmental conditions prior to the initial installation of the turbine. European countries decommissioned 4.95GW of wind power capacity over the last decade (see figure 5). WindEurope expects more than 13GW of existing wind capacity to be decommissioned between 2023 and 2030, while their expectation for repowered capacity over the same period is limited to 9GW.

When a wind turbine is dismantled, the blades, nacelle, and tower are first disassembled and removed by a crane. Subsequently the lower sections, including the foundation, are disjoined. Decommissioned wind turbines can have different fates. If the turbine is still in good technical condition, it could be resold to other farms for electricity generation. If it needs repair, it might be refurbished and then resold. Even if there is no buyer for the whole turbine, different elements of the turbine could be sold on the secondhand spare part market. Finally, if for some reason the turbine does not end up on the secondhand market, various components of the turbine could be sent for repurposing, recycling, incineration, or landfill.

Almost 85% to 90% of a wind turbine is recyclable today, especially the metallic components. However, cost-efficient recycling of blades is more challenging. Wind turbine blades are made up of several layers of materials. These are mainly balsa wood or polyethylene terephthalate (PET) foam combined with glass and/or carbon-fiber-reinforced polymer and infused with epoxy resins for structural strength and integrity. Recycling such composites is not straightforward, as separating the resin from the other materials is particularly challenging and not yet attractive due to the lack of valuable metals and minerals in the composite. It is not yet an economically attractive business model. That is why the blades have been mostly landfilled or incinerated until now. However, landfilling is becoming an unacceptable practice, especially in Europe. Several European countries including Austria, Finland, Germany, and the Netherlands, have already landfill bans in place for composites, including wind turbine blades. WindEurope has also called for a Europe-wide landfill ban for decommissioned wind turbine blades by 2025. Another alternative to landfilling is to incinerate the blades, which can produce heat and electricity, but the energy content is not robust and burning the blade emits hazardous flue gases that could contain small glass fiber spares and dioxins, especially if PVC is used in the blades.

Several technologies are available to recycle the composite materials of the blades, but most technologies are not yet widely commercialized or fully cost-competitive with virgin materials. One of the well-known end-of-life options is cement co-processing. In this process, the blades are burned in kilns where the glass fiber can partially replace cement raw materials such as silica. The organic fraction of the composite is burned to generate heat, but the problem of the hazardous flue gases needs to be addressed.

Recycling could be more successful if cradle-to-cradle was considered in the design process. For this reason, the world’s largest turbine manufacturers, such as Siemens Gamesa and Vestas, have made efforts to produce recyclable blades. This is becoming increasingly important for turbine manufacturers’ sales as non-price criteria, including circularity, are becoming an integral part of the requirements in countries’ wind energy tenders, especially in Europe. Incorporating recyclability into the design process could help address one of the key challenges within the (blade) recycling supply chain, which is the uncertainty of available blade waste material. This is key to scaling up blade recycling and improving the cost-competitiveness of recycled materials. Incentives should also be provided to use recycled blade materials in the manufacture of new blades. Currently, recycled materials are not cost competitive with virgin raw materials. Moreover, waste transportation and treatment regulations need to be amended to ensure the flow of the blade waste materials.

In addition to blade recycling, there have been initiatives to repurpose decommissioned blades. Examples include the creation of a playground in the Netherlands, bridges in Ireland, a bike shelter in Denmark, and park benches in the US. However, it’s not a scalable and circular solution and should not be considered ‘the’ solution to decommissioning challenges.

The European Union is determined and ambitious to transition its energy system into a sustainable one, and European countries are betting big on wind energy. By the end of 2022, Europe had installed 253GW of wind energy capacity, with many projects in the pipeline. However, many of Europe’s wind turbines will reach their end of life in 10 to 15 years, which requires action. Wind park developers have several options for dealing with their aged turbines. These include lifetime extension, repowering and decommissioning. Technical, economic and regulatory factors drive the decision-making process, and each option has its own advantages and challenges. What is critical is that along with the innovative technologies needed to mature each option, regulations (e.g., waste treatment and transportation, landfill bans, etc.) must be adopted and adapted in a way that supports and incentivizes the market to develop viable business cases for end-of-life solutions.

So far, development of wind energy projects has been driven mainly by the goal of reducing greenhouse gas emissions and increasing energy independence. In the slipstream of these ambitions, the increasing number of aging wind turbines in Europe represents a growing environmental challenge that needs to be addressed in a sustainable way to avoid solving one problem by creating another. As the current president of the European Commission, Ursula von der Leyen, put it, "the future of our clean tech industry has to be made in Europe", but the future of wind energy end-of-life product treatment lies in Europe as well. This includes ensuring that decommissioned European turbine blades are not landfilled or burned in non-European countries. It is also an essential strategy to secure the critical raw materials that Europe needs for its renewable energy production. And it is the responsible, sustainable way to deal with the waste generated in Europe.