Life Cycle Environmental Impacts of Wind Turbines: A Path to Sustainability with Challenges

: This study aims to evaluate in detail the environmental impacts of the turbines used for electricity generation by wind energy, from a life cycle perspective. For this purpose, a comprehensive literature review is conducted and the life cycle environmental impacts of two sizes of wind turbines, namely 3.6 and 4.8 MW, in Turkey are analyzed. Sustainability studies, especially life cycle assessment (LCA) ﬁ ndings, yield healthy results only if the data used are site-speci ﬁ c. The system has been modeled using GaBi software and the Ecoinvent database. The functional unit is de ﬁ ned as 1 kWh of generated electricity. The impacts have been estimated using the CML 2 Baseline 2001 method. The 4.8 MW turbine has lower environmental impacts than the other turbine. The construction of wind turbines has the greatest share of the environmental impacts of all the options considered. Recycling materials at the end of plant life can reduce unwanted environmental impacts by up to 49%. Similar studies based on site-speci ﬁ c data will help to inform electricity producers and policymakers about wind energy’s current impacts and environmental hotspots. Conducting analogous studies is critical to reducing the environmental impacts of wind energy, which will play an important part in the future of the energy sector.


Introduction
Energy is a critical component for improving societal well-being because it is a basic component of all products and is used in almost every aspect of life.Rapid increases in energy demand are being driven by a variety of factors, including global population growth, urbanization, industrialization, and technological advances [1].Global demand for primary energy increased by 31 EJ in 2021, the largest increase in history, more than reversing the sharp decline seen in 2020.Primary energy consumption in 2021 increased by 8 EJ from 2019.The primary energy consumption of emerging economies has grown by 15 EJ since 2019, with China accounting for the majority of this growth at 13 EJ [2].Meeting the rising energy demand presents a significant challenge for global policymakers, businesses, and societies.
A wide range of technologies are available or in development to provide affordable, dependable, and long-term renewable energy sources [3].Between 2019 and 2021, renewable energy sources accounted for all of the primary energy increases.In this period, the total amount of energy consumed-coal, oil, and natural gas-remained constant [2].The growing population, fast urbanization and industrialization, the finite nature of energy resources, and the potential environmental risks associated with fossil fuel production are all contributing factors to the growing interest in renewable energy sources [4].In 2021, the amount of renewable primary energy (which includes biofuels but excludes hydro) grew by about 5.1 EJ, or an annual growth rate of 15%, which was higher than the 9% growth rate in the year prior and more than any other fuel in 2021.In 2021, there was a sharp increase in solar and wind capacity of 226 GW, almost matching the record increase of 236 GW observed in 2020 [2].China dominated the global markets for concentrating solar thermal power, hydropower, solar PV, and wind power, accounting for nearly half of all installations in recent years [5].
One of the most significant global issues that needs to be resolved in the modern world is the supply of sustainable energy.Climate change, pollution, and energy poverty are among the sustainability impacts of energy production and consumption.The combustion of fossil fuels emits large amounts of greenhouse gases, as well as other harmful gases and solids, into the atmosphere, resulting in climate change, acid rain, and soil and water pollution [6].In 2022, the world's energy-related CO2 emissions increased by 0.9%, or 321 Mt, and hit a record high of over 36.8Gt [7].The fastest growing energy source globally, renewable energy is crucial to achieving net zero emissions worldwide.Using renewable energy sources to generate electricity instead of fossil fuels reduces energyrelated emissions.The technologies and low-carbon energy sources (biofuels, wind, solar, geothermal, hydropower, and carbon capture) required to accomplish rapid and deep decarbonization are currently accessible.
Current trends in the energy sector emphasize the importance of obtaining energy from renewable sources, rather than non-renewable ones.Among renewable energy sources, wind farms yield substantial reductions in unwanted environmental impacts, ranging from global warming and acidification potential to human toxicity [8][9][10][11].Mainly due to these environmental benefits, the number of wind installations has substantially increased, especially over the last decade on a global basis.
Wind power generation is recognized as a critical technology for energy security, climate change mitigation, and other environmental impacts.Among other things, the strong growth in today's markets and the prospects for exploiting resource potential contribute to the expectation that wind energy will play an important role in facilitating the transition from fossil-based power generation to renewable energy in the coming decades [12].
Wind is a renewable and sustainable source of energy that has been utilized for centuries, with modern wind turbines being more efficient and reliable than previously.Wind turbines can transform wind energy into electrical or mechanical power.To harness the power of the wind, wind turbines typically consist of blades mounted on shafts and towers.Wind drives the rotor blades on modern wind turbines, which transform kinetic energy into mechanical energy.A shaft carries this mechanical energy to a generator, where it is converted into electrical energy [13].
Wind turbines are promising sources of renewable energy.Since 2000, the use of wind power as a clean, renewable energy source has grown significantly as a result of research and development, supportive legislation, and improvements in efficiency, dependability, and cost [5].Figure 1 presents the global cumulative installed wind power capacity from 2001 to 2023.In 2023, the global installed wind power capacity was estimated to be around 1021 gigawatts [14].Wind power generation reached over 2302 TWh in 2023 [15].After solar photovoltaics, this was the renewable power technology with the second-highest growth [13].
In Turkey, wind power plants generated 34,945 GWh of energy in 2022, accounting for nearly 11% of the country's electricity generation [16].
Although wind energy is among the fastest growing renewable energy sources, it is also known that unwanted environmental effects are generated during the installation, operation, and end-of-life stages of wind farms.One should keep in mind that, apart from the environmental impacts, there are social concerns related to the development of the wind energy sector, as indicated by Chomać-Pierzecka [17].The social impacts of adopting sustainable energy sources, such as quality of life, employment opportunities, accessibility of energy, etc., have been addressed for especially socio-economically disadvantaged societies [18].The relationship between public acceptance and the development of power systems for wind energy has been investigated [19].The impact of green finance on wind power development is also stated in the literature [20].Nevertheless, this study concentrates on the environmental impacts of wind energy.Therefore, by developing strategies to reduce the undesirable environmental impacts caused by wind turbines at their various life stages, it is of importance as well.For this purpose, life cycle sustainability evaluations can be used.The most prominent and critical issue in such evaluations is running a sustainability study on case-specific data, as each case has its own limitations, geographical considerations, etc.In other words, feeding site-specific data will lead to a case-specific appraisal, which is a prerequisite for deriving robust outcomes.This fact is emphasized by [21] in a general sense, especially for countries that have not adopted the life cycle mindset from a sustainability perspective.In this context, the objective of this study is to display the environmental impacts of wind turbines in detail within a life cycle perspective by presenting a comprehensive literature review and analyzing a case study from Turkey.The importance of the quantification of sustainability and case-specific sustainability appraisal are emphasized in this study.Instead of directly transferring the sustainability results obtained from other geographical locations, the significance of case-specific evaluations dealing with various recycling alternatives during decommissioning, the input of energy from different sources, and usage of various materials for construction, etc., are underlined.Running similar studies will make decision-making easier, as addressing the specific hotspots in the life cycle of wind turbines will reduce the efforts required to deal with unwanted environmental impacts.
This study is critical to the future of the renewable energy sector.The LCA methodology is described in detail in this study, and the environmental sustainability of electrical energy from two different turbine sizes, which are expected to be widely used in the future, is examined in conjunction with an extensive literature review on the life cycle environmental impacts of wind energy.

Wind Energy and Life Cycle Sustainability
It is a known fact that quantifying sustainability in an objective and robust manner is of importance.With growing environmental awareness, renewable energy sources have gained importance as energy sources.Assessing an energy system's direct environmental effects, however, does not solve the issue.The environmental effects of renewable energy sources, such as wind energy, can differ greatly based on several variables, such as the materials used, transportation, plant capacity, and maintenance needs [22].Because of this, evaluating environmental sustainability should be conducted by using a life cycle approach.Life cycle assessment (LCA) is an environmental management tool based on this approach.The LCA method investigates the potential impacts on the environment of a product, process, or service, from raw material extraction to production, transportation, use, and waste management [23].LCA evaluates the impact on the environment of all relevant inputs (raw materials, water, energy, and land use), as well as emissions into the air, water, and land.ISO 14040 [24] describes the "principles and framework for LCA", whereas ISO 14044 [25] "specifies requirements and provides guidelines" for LCA.
Wind energy has emerged as one of the world's most important renewable energy sources due to its rapid growth, significant contribution to electricity generation, and potential for future expansion [26].Although their operational phase has resulted in a reduction of greenhouse gas emissions, it is imperative to evaluate the environmental impact of their manufacturing and installation processes in order to determine their overall sustainability.Some studies in the literature have been conducted by using the LCA method to assess the environmental impacts of producing electricity using wind energy.This section of the paper examines studies that use the life cycle analysis method to evaluate onshore wind energy systems' environmental effects.
When the literature review is considered as a whole, it becomes clear that there are LCA studies on the life cycle sustainability of wind turbines in the literature.Figure 2 compares energy life cycle analysis studies and wind life cycle analysis studies in the literature by year.Figure 3 presents the current state of LCA for wind energy studies in the literature.In a thorough literature search of the Web of Science database, the number of scientific articles discovered with the keywords (wind energy and life cycle assessment) were examined and the results revealed that there has been a significant increase in the number of studies prepared in this field.The decrease in 2023 was caused by articles that were still in the publication process.In the first month of 2024, 14 articles containing these keywords were published.
Selected LCA studies related to wind energy are tabulated in Table 1.This table presents the locations of the wind turbines, types and sizes, functional units adopted, and environmental impact categories investigated.As evident from Table 1, both onshore and offshore turbines with sizes ranging from big to small and micro turbines are covered.Although different scopes are identified for the studies, the majority are from cradle to grave.
There are LCA studies dealing with various components of wind turbines as well.Jiang and Xiang [47] investigated the environmental burdens of the gearbox by adopting the LCA methodology.The results show that the main source of impacts is the manufacturing phase.Reusing components at the decommissioning stage is devoted to lowering the impacts by 10%.
Similar to all other energy sources, wind farms have a limited lifetime.The turbines reaching their end-of-life stage should be handled in a proper way to lower their unwanted environmental impacts.There are studies in the literature related to this issue.In the study performed by Nagle and Delaney [53], composite wind turbine blade wastes generated from the decommissioning stage of a wind farm were investigated in terms of alternative scenarios of co-processing in cement kilns and landfilling via LCA.Another study on Chinese wind turbine blades at the end-of-life stage with various disposal scenarios was performed Cong and Song [65].
The challenges associated with blade waste from on-shore wind farms were examined by Nagle and Delaney [53].In the aforementioned study, repurposing blades into second-life structures was evaluated via LCA.Not clearly stating the assumptions, calculations, and conversions applied to LCA studies involving wind farms is quoted as a problematic issue by Davidsson and Höök [75].The uncertainties related to the decommissioning stage of wind farms is emphasized by Mello et al. [72].
Arvesen and Hertwich [22] mentioned certain points to focus on for future perspectives on the LCA of wind energy as geographical areas other than Europe; large turbines; offshore technologies; construction and operation; and maintenance phases of the life cycle.

Case Study: Life Cycle Environmental Impacts of a Wind Turbine
The LCA methodology followed here is the ISO 14040/44 methodology [24,25].Accordingly, iterative steps of goal and scope definition; inventory analysis; impact assessment; and interpretation are conducted [23,24].The goal, boundaries, and functional unit of the study are all clearly defined in the goal and scope definition step of the process.This is followed by the life cycle inventory phase, which entails gathering data on all inputs (such as energy and raw materials) and outputs (such as emissions and waste) throughout the product's life cycle.In the life cycle impact assessment phase, these data are analyzed to determine their potential environmental impacts, which are classified and characterized into impact categories such as global warming potential and resource depletion.The final phase is interpretation, which involves analyzing the results to identify significant impacts, drawing conclusions, and making recommendations for reducing environmental burdens [76].
One of the primary benefits of LCA is its ability to provide a comprehensive perspective, identifying significant environmental hotspots and facilitating informed decisionmaking for sustainable product design, process optimization, and policy development.However, conducting an LCA is frequently data-intensive and resource-intensive, necessitating extensive data collection and technical expertise, which can be expensive and time-consuming [77].
The LCA modeling was carried out in GaBi Software version V10.8 [78] and the CML (Centre of Environmental Science at Leiden University) 2001 impact assessment method [79] was used to estimate the environmental impacts.GaBi is a widely used tool for conducting LCA.It offers comprehensive solutions for modeling, analyzing, and optimizing the environmental performance of products and processes.GaBi software provides significant benefits, including comprehensive and up-to-date databases, detailed modeling, and support for a variety of impact assessment methods.However, the use of the software can be resource-intensive, necessitating significant time and financial investment [80].The CML method is a widely used LCA approach.This method distinguishes itself by focusing on midpoint indicators, which represent environmental impacts at an intermediate point in the cause-effect chain, rather than endpoint indicators, which reflect long-term effects on human health, ecosystem quality, and resource availability [81].
The following sections define the research's goal and scope, as well as its data and assumptions

Goal and Scope
The main goal of the study is to determine the environmental impacts associated with 3.6 MW and 4.8 MW onshore wind turbines installed in Turkey.Another objective is to provide recommendations for future energy planning by comparing the environmental impacts of wind turbines of different sizes.
As shown in Figure 4, the scope of the study is from cradle to grave, and it includes the following stages: The functional unit is 1 kWh of electricity generated from selected onshore wind turbines.

Inventory Data
The data used in this analysis were obtained from a variety of sources and 2022 has been selected as the time reference.The wind turbine capacity factors used in the assessment are based on wind-installed capacity and wind-based electricity generation in Turkey in 2022 [16].
In this study, two different sizes of onshore wind turbines are modeled and their environmental effects are assessed.Table 2 presents the technical specifications of the 3.6 MW and 4.8 MW wind turbines selected for this study.The 3.6 MW onshore wind turbine is chosen as it is the average size of wind turbines in Turkey in 2022, while the 4.8 MW onshore wind turbine is selected considering it has recently become the most popular turbine size in the country.The inventory data for onshore wind turbines are taken from Atilgan and Azapagic [43].3. The primary data were gathered from government and industry reports, as well as the academic literature.The background life cycle inventory data were obtained from Ecoinvent but were modified for the model conditions.
The construction stage includes the raw material extraction and processing of materials such as the concrete, aluminum, steel, and glass fiber required to manufacture the fixed (tower and basement) and moving parts (rotor, nacelle and hub, yaw, and mechanics), turbine manufacturing, all transportation, and installation.The transportation stage considers the transportation systems required to provide raw materials for the production of the various wind turbine components, the transportation of turbine components to the specific wind farm site, and transportation during operation.For fair comparisons, it is assumed that the turbines are manufactured in Germany and installed in Canakkale, Turkey.The operation stage is concerned with turbine maintenance, which includes oil changes, lubrication oil, and transportation of people during the maintenance.When the wind turbine is no longer in service, the decommissioning process begins.The current scenario involves recycling some components (see Table 3 for the details).The raw materials for turbine parts made in Germany are transported 100 km by road and 150 km by rail.The turbine is shipped to Turkey (2500 km by rail and 150 km by road), and 150 km of railroad and 100 km of road transportation are used to deliver the raw materials needed for the fixed part to the installation location.
The turbines under investigation have different capacity factors.The environmental impact values are obtained per functional unit.Elevated turbine sizes are expected to result in fewer negative environmental effects compared to smaller sized ones.Similar findings have been reported in the literature for various renewable energy sources [42].Another main finding of this paper is that the construction phase is the main contributor to the environmental impacts.Moreover, as can be observed in Figure 6, unwanted environmental impacts are reduced by recycling for all the impact categories by up to 49%.Therefore, it is recommended to apply recycling as much as possible during the decommissioning stage.It should be noted that impacts arising from the transportation of materials are considered within construction.As presented in Figure 6 and Table 4, the wind turbine construction stage is almost entirely responsible for the ADP elements caused by the use of metals.The ADP fossil fuels produced for both sizes of turbine were primarily due to the energy used in the extraction and processing of construction materials.The emissions of SO2 (around 72%) and NOx (around 25%) from the production of the metal parts contribute almost all the acidification potential.The EP of electricity from the wind turbines examined in this study came from the plant construction stage, particularly from phosphate emissions to freshwater (58%).The FAETP and MAETP for both sizes of turbines are primarily caused by metal emissions into fresh water during construction and decommissioning.The biggest contributors to GWP are the construction and operation of the power plant, due to the CO2 (>91%) and CH4 (>7%) emissions.Construction is responsible for nearly all of the HTP and TETP, primarily due to chromium emissions into the air and water.The most significant contributors to the ODP and POCP are the construction and operation of the wind turbines.
When the results from the literature are examined, a wide range of values are reported for each effect.This is primarily due to differences in background data and assumptions regarding geographical regions, installed capacities, capacity factors, recycling rates, and lifetimes.When our results are compared to those in the literature, we can see that they are within the expected range.
The annual environmental impacts from wind energy-based electricity generated in Turkey have been estimated using the impacts per kWh from the 3.2 MW onshore wind turbines and the total wind energy electricity generated from wind turbines in 2022 (34,945 GWh); the results are shown in Table 4.   Turkey's total greenhouse gas (GHG) emissions as CO2-equivalent (eq.) for the year from wind-powered electricity are 0.13 million tonnes (Mt).The greenhouse gas inventory results revealed that overall GHG emissions as CO2-eq.for the year 2021 compared to the previous year increased by 7.7% to 564.4 Mt in Turkey.Total GHG emissions per capita were calculated at 4 tonnes CO2-eq.for 1990, 6.3 tonnes CO2-eq.for 2020 and 6.7 tonnes CO2-eq.for 2021.In 2021, the energy sector had the largest share of total GHG emissions with 71.3%.The energy sector was followed by the industrial processes sector, the agriculture sector, and the waste sector, with 13.3, 12.8, and 2.6% shares.The energy sector emissions were calculated as 402.5 Mt CO2-eq. in 2021, which increased by 188.4% compared to 1990 and also increased by 9.8% compared to the previous year.Similarly, emissions from the industrial processes and product use sector were calculated at 75.1 Mt CO2eq. in 2021, which increased by 228.7% compared to 1990 and also increased by 10.6% compared to the previous year [82].

Conclusions
The following conclusions are driven from this study and put forth the environmental impacts of wind turbines from a life cycle sustainability standpoint.
Similar to all sorts of energy-generating installations, addressing specific environmental factors within the life cycle of wind energy facilities will guide strategy development for handling and reducing the unwanted environmental impacts.
The use of wind energy is one of the ways that will bring humanity to sustainability.Then again, there are obstacles to be tackled on the road.The most significant challenge can be quoted as the use of site-specific data to obtain a clear picture of environmental impacts.In this sense, location-specific issues such as geographical considerations, matters related to transportation, end-of-life recycling alternatives, various energy sources and materials used for, i.e., construction, etc., gain importance.The use of location-specific data is essential to achieve a sound case-specific evaluation.
The examples presented in this study indicate that the environmental impacts per functional unit are decreased by more than 63% in cases using 4.8 MW onshore wind turbines instead of 3.6 MW ones.
The construction phase contributes the main share of all environmental impacts.Recycling reduces all unwanted environmental impacts by up to 49%.
It is recommended to conduct similar studies with site-specific data for each wind installation.Also, future focus should be given to (i) large turbines; and (ii) the construction, operation, and maintenance phases of the life cycle.
A sustainability assessment that takes into account the life cycle environmental impacts, economic costs, and social aspects of these options will assist the energy sector in identifying and implementing the most sustainable energy solutions.Future studies should consider both the economic and social impacts, as well as the environmental impacts.

Figure 2 .
Figure 2. Comparison of the publications in the WoS database (Keywords: energy and life cycle assessment; wind and life cycle assessment).

Figure 3 .
Figure 3. Results of searching for publications in the WoS database (Keywords: wind and life cycle assessment).

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extraction and processing of raw materials; • manufacture and installation of the turbine; • operation and maintenance over the lifetime of the system; • decommissioning of the turbine; and • all transportation.

Figure 5 .
Figure 5. Environmental impacts from selected wind turbines.

Figure 6 .
Figure 6.Distribution of environmental impacts for various life stages.

Table 1 .
Selected LCA studies related to wind energy supply.

Table 2 .
Technical specifications of the assessed wind power turbines.

Table 3 .
Assumptions and summary of inventory data (per kWh).

Table 4 .
Distribution of environmental impacts for various life stages.
Table 5 outlines the environmental impacts generated from wind-based electricity in Turkey for the whole year of 2022.

Table 5 .
Annual environmental impacts from wind-based electricity in Turkey in 2022.