The Future of Vertical-Axis Wind Turbines: Opportunities, Challenges, and Sustainability Perspectives

Abstract

This Vertical-axis wind turbines (VAWTs) are emerging as promising alternatives to conventional horizontal-axis wind turbines (HAWTs) for renewable energy generation, particularly in urban and offshore environments. Despite increasing interest, a comprehensive evaluation of their technical, economic, and environmental performance remains limited. This review, based on a targeted literature search, critically evaluates and compares the performance, economic viability, environmental impact, technological advancements, and adoption barriers of VAWTs and HAWTs. VAWTs demonstrate lower aerodynamic efficiency (20–35%) and capacity factors (20–35%) compared to HAWTs (efficiency 40–50%, capacity factors 30–45%), yet offer advantages such as omnidirectional wind capture, simpler ground-level maintenance, lower noise emissions, reduced avian impact, and greater feasibility for space-constrained urban settings. Economic analyses indicate that VAWTs typically have higher levelized costs of energy (60–80 EUR/MWh) than HAWTs (40–60 EUR/MWh), although these are partially offset by reduced operational costs. Environmental assessments favor VAWTs in terms of land use, biodiversity impact, and water consumption. Technological progress, including AI-based aerodynamic optimization, hybrid rotor designs, advanced composite materials, and Maglev bearings, has enhanced the competitiveness of VAWTs. The main adoption challenges are lower power output, scalability constraints, and lack of support from policymakers. While HAWTs remain dominant in large-scale wind energy production due to superior aerodynamic performance and economies of scale, VAWTs offer significant benefits for decentralized, urban, and offshore applications where installation flexibility, noise, and environmental considerations are critical. Continued innovation and more policy support could increase VAWT market penetration and contribute to more diversified, sustainable energy portfolios.

1. Introduction

Implementing sustainable and decentralized energy sources is becoming a key priority in the context of global climate change and the increasing need to reduce greenhouse gas emissions. Wind energy, one of the fastest-growing renewable energy sources with minimal environmental impact, plays a significant role in this process [1,2,3]. Solutions for wind energy utilization have seen advancements in recent years and are becoming more important in the global energy sector. The cumulative energy capacity reached 906 GW in 2023 [4].

Vertical-axis wind turbines (VAWTs) are increasingly gaining attention due to their unique characteristics and potential applications for harnessing wind energy in various environments. Unlike traditional horizontal-axis wind turbines (HAWTs), VAWTs can efficiently utilize wind energy from all directions without requiring realignment. This feature makes them particularly suitable for urban environments, where wind direction and intensity are often variable. They are also suitable for offshore installations as a more compact design can reduce installation and maintenance costs [5].

A comparison of VAWTs and HAWTs highlights technical, economic, and environmental differences. While HAWTs traditionally achieve higher efficiency in stable wind conditions, VAWTs stand out for their simplicity, lower sensitivity to turbulence, and the ability to be installed at lower heights. Economically, VAWTs can potentially reduce production and maintenance costs. In contrast, their environmental advantages, such as lower noise levels and reduced bird impact, make them attractive for urban and ecologically sensitive areas [5]. Significant efforts have been made in recent years to enhance the performance of VAWTs, primarily through optimization and improvements in the design of crucial components, such as wind turbine blades [4].

Technological advances, supported by the application of computational fluid dynamics (CFD) and artificial intelligence (AI), have enabled more detailed analysis and optimization of VAWT designs, thereby improving efficiency and reliability. Research in this area focuses on the development of new materials, innovative blade designs, and advanced control systems to improve the competitiveness of VAWTs in the market [6]. Improvement in VAWT power output can be achieved through optimization of aerodynamic properties. Turbine performance can be optimized by adjusting pitch angle, blade profile, chord-to-radius ratio, number of blades, and rotor height [7]. AI can be utilized to advance blade design and enhance the performance of VAWTs. AI-based optimization is expected to become a standard method for optimizing blade design in wind turbines. Integrating numerical simulations with different AI-optimization methods, such as Multi-Objective Genetic Algorithm (MOGA), Artificial Neural Network (ANN), Genetic Algorithm (GA), and Adaptive Neuro-Fuzzy Inference System (ANFIS), can be utilized to optimize the design of wind turbines [8].

The competitiveness of VAWTs is influenced not only by technical and economic factors but also by their adaptability to specific environmental conditions, such as urban settings and offshore locations. With limited space and unpredictable wind conditions, urban areas present a particularly promising application for VAWTs. On the other hand, offshore installations offer the opportunity to harness strong and stable marine winds while minimizing visual and noise-related impacts on the environment [5].

This study aims to provide an in-depth analysis of the prospects for VAWTs in the context of sustainable energy systems. The research will focus on the following objectives:

• Technical comparison with HAWTs: A comprehensive comparison of VAWTs and HAWTs will be conducted in terms of efficiency, mechanical complexity, and performance in diverse environmental conditions. The comparison will compare the advantages and disadvantages of VAWTs and HAWTs, including their potential applications in both onshore and offshore environments.
• Economic viability and market competitiveness: The study will assess the economic viability of VAWTs, considering factors such as cost per kilowatt, potential market demand, and the competitiveness of VAWTs in comparison with more established technologies.
• Environmental impact and sustainability: The environmental benefits and challenges associated with VAWTs will be evaluated, focusing on their role in contributing to the renewable energy transition. The study will explore how VAWTs reduce carbon emissions, land use, and overall sustainability compared to other renewable energy technologies.
• Innovation and technological advancements: Recent advancements in VAWT technology, particularly optimization techniques, CFD simulations, and AI applications, will be investigated.
• Barriers to adoption of VAWTs: The study aims to address the key barriers to the broader adoption of VAWT, taking into account mechanical complexity, regulatory challenges, market acceptance, and economic feasibility.
• Future directions and outlook: The paper outlines potential applications of VAWTs, particularly in offshore wind farms, including floating farms.

While advancements have been made in VAWT technology, particularly in mechanical, aerodynamic, and optimization methods, a research gap remains in understanding the full potential of VAWTs compared to HAWTs in both onshore and offshore wind farms. This research aims to fill this gap by providing a comparative analysis of VAWTs and HAWTs in various wind environments and addressing the role of advanced technologies in enhancing VAWT efficiency and developing new design variants. Additionally, the study aims to identify barriers to VAWT adoption and propose strategies to improve their competitiveness in the renewable energy market.

2. Materials and Methods

This review conducted a targeted literature search in the indexed databases Web of Science, Scopus, and IEEE to identify recent advances, industry reports, and technical studies related to vertical axis wind turbines (VAWTs), horizontal axis wind turbines (HAWTs), and competing renewables. The initial search was performed using key terms including “vertical axis wind turbine”, “optimization”, “urban wind energy”, and “offshore wind”. To ensure the most relevant and high-impact studies, all results were first screened by title and abstract for subject relevance, focusing on papers published between 2018 and 2025. The latest research published in indexed databases such as Web of Science, Scopus, and IEEE was utilized to analyze the perspectives on the development and application of VAWTs.

Included studies were then evaluated in full text with attention to methodological rigor (e.g., clear technical comparison, reported data and metrics, life cycle assessment integration, or experimental validation). Reports from authoritative agencies (IRENA, NREL) were also incorporated for up-to-date market and policy perspectives. Preference was given to peer-reviewed journal articles; gray literature and non-peer-reviewed data were excluded unless supported by citation in industry standards.

The review protocol emphasized balanced coverage of technical (efficiency, design, advances in CFD/AI), economic (cost, market barriers, competitiveness), and environmental (LCA, biodiversity, siting) aspects. Studies were weighted for inclusion based on the relevance and quality of data presented, with a focus on innovative designs, technological advancements, and comparative metrics. Tables and graphical frameworks synthesize findings for clarity and consistency across sections.

This article aims to (1) integrate technical, economic, and sustainability perspectives of VAWT and HAWT technologies using comparative tables and graphical frameworks, (2) summarize the latest innovations in turbine design and control, and (3) analyze the influence of regulatory, environmental, and market dynamics.

The following key areas were identified:

• Historical development, application, and working principles of VAWTs.
• Comparison with competitive technologies in the energy sector: Renewable energy technologies are compared based on key criteria, which are defined in Table 1.
• Comparison of VAWTs and HAWTs: Since HAWTs represent the primary competitor to VAWTs, their comparison is presented in greater detail, focusing on the most important factors specified in Table 2.
• Environmental and human impact: Safety and environmental challenges and implications.
• Barriers to further adoption: Mechanical complexity, economic constraints, regulatory challenges, and the factors that could encourage the wider adoption of VAWTs.

3. Results and Discussion

To better understand the competitive capabilities of VAWTs, the analysis begins with a brief overview of their historical development, highlighting key improvements, followed by an explanation of their working principles and different types of VAWTs.

3.1. Historical Development

VAWTs have evolved significantly over centuries—from early uses in Persia and China for simple mechanical tasks to the invention of the lift-based Darrieus turbine in 1931, which laid the foundation for modern designs. Key milestones include James Blyth’s electricity-generating turbine in 1887, the patenting of the Savonius rotor in 1922, and large-scale prototypes such as Canada’s 64 m turbine in the 1960s. The oil crisis of the 1970s sparked renewed research and commercial deployment, notably Flowind’s installation of over 500 Darrieus turbines in California by 1987, although these eventually faced blade fatigue failures [4,9,10,11,12].

A more recent significant project is the Mariah Energy 2.5 MW turbine (2012), a large-scale VAWT equipped with adaptive blade pitch control, which reduces costs to one-third of those of an equivalent HAWT. Between 2010 and 2020, floating VAWT systems were developed for deep-water applications where traditional HAWTs are not economically viable. For instance, the DeepWind project (EU) utilizes a Darrieus turbine with a vertical rotor mounted on a floating platform [12].

Recent advancements in VAWT technology focus on several key innovations [4,13,14,15,16,17]:

• CFD Simulations: Computational Fluid Dynamics enables detailed airflow analysis around blades, optimizing airfoil profiles (e.g., NACA series) and reducing turbulence.
• Hybrid Designs: Combining Savonius (high starting torque) and Darrieus (high efficiency) rotors addresses limitations such as poor self-starting and low torque. An example is a two-rotor system.
• Advanced Composite Materials: Using carbon fiber reduces blade weight while maintaining structural strength, which is crucial for offshore applications.
• Counter-Rotating Systems: Dual rotors spinning in opposite directions improve wind energy utilization by 15–20%.
• IoT Integration: Smart monitoring systems enable real-time performance tracking and adaptive control of turbine parameters based on weather conditions [18].

VAWT applications have expanded from urban integration to offshore wind farms, where resilience and simplicity offer cost and maintenance advantages. While VAWTs remain a niche technology compared to HAWTs, ongoing technological advancements in design, materials, and control systems continue to enhance their competitiveness and potential market share.

3.2. Operating Principles of VAWT

VAWTs generate electricity by harnessing wind energy through curved or straight blades arranged around a vertical rotor axis. Their operation relies on drag and lift, two primary aerodynamic forces [4,19]:

• Savonius Rotor operates based on the drag force, using concave, cup-shaped blades to capture wind. This creates a pressure difference between the blades, causing the rotor to spin. While simple in design and self-starting, it is less efficient than lift-based designs.
• Darrieus, Giromill, and Gorlov Rotors use airfoil-shaped blades to generate lift as wind flows over them. Lift-induced rotation results in higher efficiency but often requires an external starting torque.

The rotational motion of the blades drives a generator (typically located at the turbine’s base) to produce electricity. The torque is transmitted to the generator via a central shaft. Wind interacts with the blades regardless of direction, eliminating the need for yaw mechanisms. VAWTs are ideal for turbulent or variable wind conditions [4]. Several emerging VAWT concepts incorporate advanced engineering principles to enhance efficiency and reliability:

• MagLev Turbines: Use magnetic levitation bearings to eliminate mechanical friction, improve efficiency, and reduce maintenance [20,21].
• V-VAWT: Features V-shaped blade arrangements to concentrate airflow and enhance lift generation [22].
• Cross-Axis Wind Turbine: This turbine consists of multiple vertical rotors arranged in a cross formation, optimizing wind energy capture from multiple directions [23,24,25].

These innovative designs demonstrate the ongoing evolution of VAWT technology, exploring new ways to enhance performance, reduce mechanical wear, and increase adaptability to various environmental conditions.

3.3. Competitive Technologies in the Electricity Generation Sector

To assess the development potential and application of VAWTs, it is crucial to identify competing technologies in the electricity generation sector. According to the authors, in addition to HAWTs, the main competing technologies include PV technology, hydropower plants, biomass power plants, geothermal power plants, and hydrogen technology.

The key factors considered for comparison include Levelized Cost of Energy (LCOE), capital costs, technology efficiency, contribution to CO₂ emission reduction, impact on biodiversity, land use requirements, operational safety, the lifespan of the power plant, potential for technological improvements, suitability for urban environments, and maintenance costs. The data presented in Table 1 is derived from an analysis of sources [1,18,26,27,28,29,30,31,32]. Literature sources from 2021 onwards were selected to reflect the state of the art in the technologies considered. The authors determined the data range shown in Table 1 through careful examination of the cited literature. When most sources reported the same or a very similar range, that range was adopted. When significant deviations occurred, the authors selected an overlapping interval from literature sources and extended the lower and upper limits as appropriate, based on the individual sources and their own expertise and judgment.

Since HAWTs represent the primary competing wind energy technology, they are not included in Table 1, as they will be examined in greater detail in the following sections.

Table 1. Comparison of VAWT, PV technology, hydropower plants, biomass power plants, geothermal power plants, and hydrogen technology [1,18,26,27,28,29,30,31,32].

Factor	VAWT	PV Technology	Hydropower Plants	Biomass Power Plants	Geothermal Power Plants	Hydrogen Technology
LCOE (EUR/MWh)	80–120	40–60	50–100	60–120	40–170	100–300
Capital Cost (EUR/kW)	1500–3000	750–1200	2000–5000	2500–5000	3000–6000	4000–8000
Efficiency	20–35%	18–20%	80–90%	20–40%	10–20%	18–46%
Impact on Biodiversity	Low	Medium	High	High	Low	Low
Land Use	Low	Moderate	High	Moderate	Low	Low
Contribution to CO2 Reduction	High	High	High	Neutral	Medium	Depends on H2 production method
Water Consumption (m3/MWh)	0.1 to 0.7	0.7–7.5	0.2–2.45	80–27,800	1.9–6.8	9–12
Operational Safety	High	Highest	High	Moderate	High	Moderate
Plant Lifespan (years)	20–25	25–30	50+	20–30	30–50	15–20
Potential for Improvement	Medium	High	Low	Medium	Medium	High
Suitability for Urban Areas	High	High	Low	Moderate	Low	Moderate
Maintenance cost	Low	Lowest	Moderate	Moderate	Low	Moderate

Table 1. Comparison of VAWT, PV technology, hydropower plants, biomass power plants, geothermal power plants, and hydrogen technology [1,18,26,27,28,29,30,31,32].

Factor	VAWT	PV Technology	Hydropower Plants	Biomass Power Plants	Geothermal Power Plants	Hydrogen Technology
LCOE (EUR/MWh)	80–120	40–60	50–100	60–120	40–170	100–300
Capital Cost (EUR/kW)	1500–3000	750–1200	2000–5000	2500–5000	3000–6000	4000–8000
Efficiency	20–35%	18–20%	80–90%	20–40%	10–20%	18–46%
Impact on Biodiversity	Low	Medium	High	High	Low	Low
Land Use	Low	Moderate	High	Moderate	Low	Low
Contribution to CO2 Reduction	High	High	High	Neutral	Medium	Depends on H2 production method
Water Consumption (m3/MWh)	0.1 to 0.7	0.7–7.5	0.2–2.45	80–27,800	1.9–6.8	9–12
Operational Safety	High	Highest	High	Moderate	High	Moderate
Plant Lifespan (years)	20–25	25–30	50+	20–30	30–50	15–20
Potential for Improvement	Medium	High	Low	Medium	Medium	High
Suitability for Urban Areas	High	High	Low	Moderate	Low	Moderate
Maintenance cost	Low	Lowest	Moderate	Moderate	Low	Moderate

Based on the data in Table 1, the following conclusions can be drawn:

• LCOE and Capital Costs: VAWTs have a similar LCOE to hydropower plants and biomass power plants (although their LCOE tends to increase, while VAWTs’ LCOE is declining). The capital cost is higher than that of PV technology but lower than that of other technologies.
• Efficiency: VAWTs have similar efficiency to other technologies, except for hydropower plants, which are significantly more efficient.
• Impact on Biodiversity: Most technologies have low environmental impact, except hydropower plants, which can have a moderate impact.
• Land Use: VAWTs require 50–70% less land area than PV systems for an equivalent energy output, reducing land acquisition costs.
• Water Consumption: VAWTs have the lowest water consumption, which is a significant advantage.
• Operational Safety: Most technologies have high safety standards.
• Lifespan: Hydropower plants have the longest lifespan, while other technologies have a similar life expectancy. Competing PV technology has a slightly longer lifespan than VAWTs. However, unlike PV technology, VAWTs do not experience efficiency degradation over time.
• Potential for Improvement: Hydrogen and PV technologies have the greatest potential for future improvements, but VAWTs also have considerable room for enhancement.
• Suitability for Urban Areas: VAWTs and PV systems are the most suitable for urban environments. VAWTs can be integrated into rooftops or building façades to harness wind energy in cities, reducing transmission losses and infrastructure costs [5]. VAWTs produce <45 dB of noise at wind speeds of 12 m/s, making them ideal for urban areas sensitive to noise pollution [5,6,32,33].
• VAWTs can provide a more stable energy output in regions with more consistent winds than PV systems.

This comparison reveals that each technology has its advantages and disadvantages, and the choice ultimately depends on the specific needs and site conditions. Table 1 also shows that PV technology is the biggest competitor to VAWT, as it has a lower LCOE, lower investment costs (CapEx), and high security of use.

3.4. Comparison of HAWT and VAWT

The primary competitor of VAWT is HAWT. This chapter provides a detailed comparison of these two technologies to understand their advantages and disadvantages to assess the development potential and application prospects of VAWT. The characteristics criteria for comparison are illustrated in Figure 1.

The comparison criteria are further classified into subcategories shown in Table 2.

Table 2. Comparison criteria of WAVTs and HAWTs.

A. Technical Characteristics	B. Economic Characteristics	C. Environmental and Human Impact
A1. Wind turbine efficiency coefficient and Cp coefficient	B1. Levelized Cost of Energy (LCOE)	C1. Land and space occupation
A2. Simplicity of design and installation	B2. Capital investment cost	C2. Impact on birds and wildlife
A3. Scalability	B3. Payback period	C3. Impact on humans and technology (noise, shadow flicker, electromagnetic interference)
A4. Operational adaptability, minimum and maximum wind speeds for operation	B4. Maintenance costs and ease of maintenance	C4. Operational safety (blade failure, tipping over, ice formation on blades, vibrations, etc.)
A5. Ease of plant operation and control
A6. Lifespan of the power plant
A7. Capacity utilization factor
A8. Potential for technology improvement

Table 2. Comparison criteria of WAVTs and HAWTs.

A. Technical Characteristics	B. Economic Characteristics	C. Environmental and Human Impact
A1. Wind turbine efficiency coefficient and Cp coefficient	B1. Levelized Cost of Energy (LCOE)	C1. Land and space occupation
A2. Simplicity of design and installation	B2. Capital investment cost	C2. Impact on birds and wildlife
A3. Scalability	B3. Payback period	C3. Impact on humans and technology (noise, shadow flicker, electromagnetic interference)
A4. Operational adaptability, minimum and maximum wind speeds for operation	B4. Maintenance costs and ease of maintenance	C4. Operational safety (blade failure, tipping over, ice formation on blades, vibrations, etc.)
A5. Ease of plant operation and control
A6. Lifespan of the power plant
A7. Capacity utilization factor
A8. Potential for technology improvement

3.4.1. Technical Characteristics

The comparison of HAWT and VAWT in the technical characteristic category is shown in

Table 3. Technical characteristics of HAWTs and VAWTs.

Category	HAWT	VAWT	References
Efficiency coefficient (%) and Cp (Power coefficient)	Higher Cp (45–50%), closer to the Betz limit (59.3%). Overall efficiency exceeds 70% under optimal conditions. Higher efficiency due to their lift-driven blade design, optimized airfoil profiles, and ability to align with wind direction.	Lower Cp (30–45%) due to aerodynamic losses. New designs (e.g., helical blades) improve efficiency. Efficiency is typically 50–60%.	[4,35,36]
Simplicity of design and installation	More complex design and installation process. Yaw mechanism needed to keep the rotor facing the wind direction. The installation process often involves more time and resources.	The generator and key components are located at ground level. Installation without the need for cranes. Yaw mechanisms are not needed.	[36,37,38]
Scalability (maximum dimensions)	Utility-scale projects (1–26 MW turbines) dominate.	Limited scalability. Most designs are under 100 m in height. Typical power 1–10 MW.	[4,36,37,38,39]
Operational adaptability (Wind Speed Ranges)	Optimal performance (3–4 m/s). “Cut-out” app. 25 m/s.	Operational speeds range from 2 to 20 m/s.	[4,35]
Ease of operation and control	Active yaw mechanisms required.	Easier management.	[4,35]
Lifespan of the power plant	Typically 20–25 years.	Typically 15–20 years.	[4,35]
Capacity factor	Higher capacity factor (~30–45%).	Lower capacity factor (~20–35%).	[4,35]
Potential for technology improvement	Continuous advancements in materials and design.	Limited potential for significant improvements.	[6,33]

and explained in more detail in this subchapter.

• A1. Efficiency coefficient (%) and Cp (Power coefficient)

The efficiency coefficient measures the overall efficiency of a turbine in converting wind energy into electrical energy. In contrast, the Cp coefficient represents the ratio of actual power extracted to the theoretical maximum power available in the wind. The efficiency coefficient includes all losses (mechanical, electrical), whereas Cp focuses on aerodynamic efficiency [35,36].

HAWTs generally have a higher efficiency coefficient than VAWTs, often exceeding VAWT efficiency by approximately 25% under similar conditions [40]. Due to design limitations, VAWTs tend to have lower Cp [41].

• A2. Simplicity of design and installation

HAWTs typically have a more complex design and installation process. The main components, including the generator, gearbox, and rotor, are housed in a nacelle at the top of a tall tower. This configuration requires the installation of specialized equipment, such as cranes, especially for larger turbines. HAWTs require a yaw mechanism to maintain the rotor’s orientation in the wind direction, which adds to their complexity. The installation process often involves more time and resources due to the height and weight of components [37].

In the case of VAWTs, the generator and key components are located at ground level, enabling installation without the need for cranes. A simpler design, omnidirectional operation, and lower height reduce installation complexity, making VAWTs particularly suitable for urban or confined spaces with turbulent or shifting wind conditions [36]. VAWTs can capture wind from any direction without requiring yaw mechanisms, which reduces mechanical complexity and minimizes the need for operational adjustments [36,38].

• A3. Scalability (maximum dimensions)

Utility-scale projects (1–26 MW turbines) dominate in the case of HAWTs due to higher efficiency and proven technology. The trend is a continuous increase in rotor diameter, which expands the swept area, enabling greater energy capture [33]. China’s most extensive offshore HAWT, with a 26 MW capacity, a rotor diameter of approximately 310 m, and a tower height of around 185 m, is being built [39].

VAWTs are associated with limited scalability, as most designs are under 100 m in height, with smaller rotor diameters (~50 m), resulting in typical power ratings of 1–10 MW. However, innovations like coaxial counter-rotating systems and MagLev bearings aim to enhance their capacity [4,36,38].

CFD-based optimization studies have demonstrated that hybrid VAWT designs, which combine lift- and drag-based rotors, can extend the operational range and improve scalability [42]. Recent research shows that VAWTs have potential for scalability in grid-connected systems, especially in hybrid configurations incorporating solar PV and energy storage [43,44]. Research from Pagnini et al. showed that VAWTs have potential for small-scale distributed generation and can attract attention for both standalone and grid-connected configurations, supporting their scalability for local grids and integration with the broader electricity network [45].

• A4. Operational adaptability (Wind Speed Ranges)

VAWTs perform better in turbulent or variable wind conditions. Operational speeds range from 2 to 20 m/s [4]. HAWTs require more stable wind conditions for optimal performance (3–4 m/s), with “cut-out” being app. 25 m/s [35].

• A5. Ease of operation and control

The management of VAWT is easier as it captures wind from any direction without adjustment [4]. HAWT requires active yaw mechanisms for alignment with the wind direction, which increases operational complexity [35].

• A6. Lifespan of the power plant

The lifespan of VAWT is typically 15–20 years, though advancements in materials and design are extending the lifespan [4]. HAWT is proven technology with a typical lifespan of 20–25 years [35].

• A7. Capacity factor

VAWTs have a lower capacity factor (~20–35%), limited by lower efficiency in converting wind energy into electricity. One disadvantage of VAWT is that they must be installed close to the ground. Since the wind blows at a higher speed and evenly at greater heights, an installation not on a mast loses lots of efficiency [4]. HAWTs have higher capacity factor (~30–45%), depending on location and wind conditions [35].

• A8. Potential for technology improvement

VAWTs have limited potential for significant improvements. Technology improvements are associated with the development of magnetic bearings, modular systems, and contra-rotating rotors [6]. For HAWTs, continuous advancements in materials and design are being undertaken. Optimization through AI and smart grid integration is also one of the potentials for technology improvement [6,33].

3.4.2. Economic Characteristics

The comparison of HAWTs and VAWTs in the economic characteristic category is shown in

Table 4. Comparison of economic characteristics of HAWTs and VAWTs.

Parameter	HAWT	VAWT	References
Levelized Cost of Energy (LCOE)	40–60 EUR/MWh Lower due to higher efficiency and economies of scale	60–80 EUR/MWh Higher due to lower efficiency and maintenance costs Competitive in urban areas	[4,35,36]
Capital Investment Cost (EUR/MW)	1.0–1.5 million EUR/MW High tower costs complex components	1.0–2.0 million EUR/MW Simpler design Lower profitability per MW due to lower power coefficient (Cp)	[4,35,36,40]
Payback period	~5–10 years Shorter payback period Higher energy production and lower LCOE	~10–15 years Longer payback period Lower efficiency and higher costs per unit of energy produced	[4,35,36]
Maintenance costs	Frequent maintenance of components mounted atop tall towers (up to 150+ m) Specialized equipment and safety protocols needed Increased operational complexity	20–30% lower maintenance costs as most components are ground-level Simplifying access and repair work Housing of critical components near the base, reducing downtime This design eliminates the need for climbing tall towers, a significant operational advantage in urban or remote settings [38] Simplified Gear Systems: direct-drive systems reduce mechanical wear and maintenance frequency	[4,38,46]

and explained in more detail in this subchapter.

• B1. Levelized cost of energy (LCOE) (EUR/MWh)

VAWTs generally require a higher material mass per swept area unit than HAWTs. For example, large Darrieus VAWTs exhibit a specific mass (kg/m²) up to 10 times higher than equivalent HAWTs due to structural reinforcements needed to handle cyclic loads and blade fatigue [47].

The varied designs of VAWTs (e.g., Savonius, Darrieus, helical) demand specialized fabrication for components like curved blades and magnetic levitation (MAGLEV) systems, increasing labor costs. For instance, MAGLEV VAWTs require precision aligning neodymium magnets and custom rotor brackets, often necessitating advanced 3D printing or CNC machining [32,48]. Lack of standardized components (e.g., blade profiles, support arms) further complicates mass production, unlike HAWTs, which benefit from aviation-derived modular designs [47,48]. HAWTs use lightweight composite materials (e.g., carbon fiber) optimized for lift-driven blades, reducing mass and material costs per MW capacity [47]. Standardized three-blade designs and automated manufacturing processes lower labor costs (economies of scale). HAWT blade production leverages established aerospace techniques, enabling cost-effective mass production [4,48].

• B2. Capital investments cost (EUR/MW)

VAWTs incur 15–25% higher initial rotor costs due to material mass and fabrication complexity, but savings in drivetrain and maintenance costs partially offset this. VAWTs often require larger foundations due to ground-level generator placement, increasing installation costs in soft soils or urban settings. However, their compact design allows installation in constrained spaces (e.g., rooftops), reducing land use expenses [48]. HAWTs require tall towers (up to 150+ m offshore) and active yaw systems to align with wind direction, increasing material and labor expenses. Offshore installations face additional challenges like marine infrastructure and crane logistics [4,47]. Large-scale HAWT farms need extensive electrical infrastructure, whereas VAWTs can integrate into decentralized urban grids with lower upfront costs.

HAWT requires frequent maintenance of components mounted atop tall towers, necessitating specialized equipment and safety protocols, increasing operational complexity [38]. On the other hand VAWT requires lower maintenance costs (20–30%) as most components are ground-level, simplifying access and repair work [4]. VAWTs house critical components like generators and gearboxes near the base, reducing downtime and making maintenance easier. This design eliminates the need for climbing tall towers, a significant operational advantage in urban or remote settings [38]. Many VAWTs use direct-drive systems (e.g., magnetic levitation bearings), which reduce mechanical wear and maintenance frequency compared to HAWTs’ complex gearboxes [38,46].

3.4.3. Environmental and Human Impact

The comparison of HAWT and VAWT in land occupancy, bird/wildlife impact and human impact is shown in

Table 5. Comparison of HAWT and VAWT in environmental and human impact categories.

Category	HAWT	VAWT	References
Land Occupancy (km2/MW)	0.23–0.4 km2/MW	0.01–0.03 km2/MW	[1,36,49]
Bird/Wildlife Impact	Higher mortality, migratory risks	Lower mortality, less risk	[4,36,48,49,50]
Human Impact	Noise, shadow flicker, EMI, house price loss	Quieter (<45 dB), less flicker, lower EMI, better suited for urban environments, possible aesthetic concerns	[4,35,40]

and explained in detail below.

• C1. Land occupancy (km²/MWh)

HAWTs require large spacing (typically 5–10 rotor diameters apart) to minimize wake interference, which reduces turbulence and efficiency losses between turbines. In general, the total area of a wind farm includes the perimeter surrounding all the turbines, consisting of the direct impact area, the undisturbed land between turbines, and the buffer zone for residential buildings [1]. It is important to note that wind farm turbines can be arranged in different layouts, such as long rows, several irregular rows, parallel rows, or separate power plants. Each configuration results in land occupancy per installed MW of turbine capacity [1].

VAWTs can be clustered more densely (3–4 rotor diameters apart) due to omnidirectional operation and reduced wake effects, enabling higher energy density per unit area [36,49]. VAWTs are particularly suitable for constrained spaces (e.g., urban rooftops and mountainous terrain) where land availability is limited [36].

• C2. Impact on birds and wildlife

Large HAWT farms fragment habitats and displace wildlife, and their placement in migratory bird corridors leads to significant risks—especially for raptors and other sensitive species [51,52]. Empirical research, including a study in Karnataka, India, found an annual animal fatality rate of 0.26 per turbine, with raptor declines linked to cascading ecosystem impacts, such as increased prey populations [48,50,53].

VAWTs, by contrast, can be installed in urban and agricultural zones with minimal land disruption, and their lower height and slower blade speeds generally reduce avian and wildlife collisions. Studies by Roy et al. and Thaxter et al. have shown that when VAWTs are deployed in dispersed clusters and outside migration corridors, they pose a lower risk to birds and wildlife. Nonetheless, no wind turbine is impact-free; effective siting, selective curtailment, and local risk assessment remain essential for both VAWT and HAWT projects. VAWTs typically offer reduced bird collision and disturbance rates, but these benefits are context-dependent and require ongoing ecological monitoring. [51,52].

VAWTs, when deployed in smaller, more dispersed clusters, show reduced collision rates per unit energy produced and lower aggregate wildlife disturbance. Research from Roy et al. indicates that, while overall infrastructure-related bird mortality can be significant, VAWTs—due to their lower height, slower blade speeds, and flexibility in siting—can be placed in urban/agricultural areas, as well as outside major migration corridors, further mitigating the risk [52].

However, it is essential to note that no wind energy technology is entirely free from impacts on wildlife. The literature suggests site-specific risk assessments and best-practice mitigation—such as selective curtailment during peak migration and informed siting—remain necessary for both HAWT and VAWT projects. Claims of reduced impact must always be contextualized: VAWTs generally exhibit lower bird collision rates and ecosystem disturbance across a range of installations, but local effects depend on turbine density, landscape, and species composition. Monitoring programs, adaptive management, and further ecological research are needed to validate these benefits under diverse regional conditions [51].

• C3. Impact on people and technology

VAWTs operate at lower rotational speeds (~60 rpm vs. HAWTs at 10–20 rpm, but with higher tip speeds), reducing aerodynamic noise and making them preferable for noise-sensitive areas [54,55]. VAWTs produce lower noise at low-to-moderate wind speeds (5–8 m/s). For example, a 200 kW VAWT emits ~94.1 dBA at 6 m/s, compared to HAWTs of similar capacity (~96.7–100.2 dBA) [56]. HAWTs generate higher noise due to blade-tip vortices and mechanical components. Larger HAWTs (>1 MW) generate >100 dBA at rated wind speeds [56]. The installation of wind turbines can affect house prices in the vicinity, causing potential loss of revenue. Research by Dröes and Koster [57] showed that constructing a wind turbine leads to a 1.8% decrease in local house prices. A turbine taller than 150 m decreases prices within 2 km by 5.4%, while the effect of small turbines (<50 m) is statistically insignificant. Also, the impact of tall wind turbines does not extend significantly beyond 2 km. Wind farms should be placed carefully, as the total loss in housing wealth can increase if turbines are built too close to residential properties [57].

• C4. Life cycle perspective

Although wind turbines are recognized as a clean and renewable source of electricity generation, the challenges of the energy required for manufacturing and their environmental impact remain. Wind turbines do not produce emissions during their operational stages; however, emissions are generated during manufacturing, transportation, and disposal [58]. Life cycle analysis (LCA) is a method that quantifies the energy use, emissions, and environmental impacts of a product, system, or process throughout its life cycle stages, encompassing the extraction of materials, transportation, manufacture, installation, and disposal, as well as recycling [58].

Martínez et al. conducted an LCA study of a 2 MW wind turbine. The results showed that the manufacturing process of wind turbine components is the greatest contributor to environmental impact [59]. Tremeac and Menuier compared a 4.5 MW and 250 W wind turbines and conducted a sensitivity analysis. The results showed that energy use primarily occurs at the manufacturing stage, accounting for 75% for the 4.5 MW wind turbine and 96% for the 250 W wind turbine, respectively [60]. Similarly, the results of the LCA performed on a large-scale (400 MW) offshore wind farm with large wind turbine units (5 MW) in China showed that manufacturing contributes the most to the environmental impact, which is in accordance with the results published in other studies [61,62,63].

Rashedi et al. conducted an LCA of three types of 50 MW wind farms: onshore-HAWT, offshore-HAWT, and VAWT. The results showed that VAWT generated the lowest impact per unit of electricity, followed by offshore-HAWT and onshore-HAWT. The impact of onshore- and offshore-HAWT on human health was 1.72 and 1.54 times higher compared to the onshore VAWT farm. Similarly, ecosystem quality onshore and offshore values were 1.27 and 1.14 times higher compared to VAWT, with a similar trend observed in the resources category. The results showed that offshore HAWT exhibits higher impact values than onshore HAWT [64].

On the other hand, the capacity factor of offshore HAWT is almost 50% higher than that of onshore HAWT per unit electricity profile, making it more eco-friendly and cost-effective than onshore HAWT [64]. Uddin and Kumar performed an LCA of VAWT and HAWT for three potential applications in Thailand, analyzing the life cycle embodied energy, emissions (air and water), environmental impacts, energy payback time, and performance indexes. Research has shown that VAWT is more energy- and emission-intensive compared to HAWT for base case system design. The environmental impact could be reduced using thermoplastics or fiberglass turbines, with an average reduction in more than 15% [58]. The findings are supported by recent research from Cao et al., which emphasizes that the capacity factor significantly influences the environmental performance of offshore wind plants, followed by the importance of site selection and maintenance of offshore wind farms. Results from scenario-based dynamic modeling suggest that selecting glass fiber-reinforced plastic and carbon fiber-reinforced plastic as materials could significantly reduce global warming potential and other environmental impacts [63].

LCA is an instrument for assessing environmental performance and decision support; however, it only considers environmental impact. Sustainability assessment also includes social and economic performance. In decision-making, different considerations play important roles, and products or activities should be economically viable, environmentally benign, and socially just to be qualified as the most sustainable [65]. Talluri et al. [66] conducted a techno-economic and environmental analysis of installing two VAWT on the deck of a ship in conjunction with conventional power plants. The results showed that the installation of the WAVT is still not profitable for all the routes, given the current policy and fuel prices. The environmental gain is significant, but considering the economic features, it is still not recommended for routes that do not experience strong wind conditions. Results showed that the installation of the VAWT could be advantageous when carried out on vessels that travel the Atlantic Ocean [66]. Recently, Ramalho et al. [67] researched the externalities associated with wind energy. Even though the environmental advantages are significant, the wind turbines may alter the environment, create noise pollution, cast shadows, and cause flashing. The negative effects are felt mainly by inhabitants living closer to the wind turbines [57,67,68].

Kouloumpis et al. [69] investigated developing a smaller-scale VAWT to mitigate climate change. The results showed that most impacts are accredited to the supporting infrastructure, especially the mast and the foundations. The turbine itself accounted for only 30% of the global warming potential impact category. The results showed that environmental performance is susceptible to the fluctuations of the capacity factor.

Key aspects of wind turbine implementation, that should be considered for the reduction in life cycle environmental impact are shown in

Table 6. Key LCA takeaways.

Aspect	Key Takeaways	References
Geographical location	Deployment of is advantageous for remote, off-grid areas with adequate wind resources. Proximity to residential areas can negatively affect property values, necessitating careful site selection for sociotechnical compatibility.	[57,60,64]
Material substitution	Substituting copper with aluminum alloys in wind farm systems (especially cables, generators, transformers) yields reductions in mass, costs, and life cycle impacts (up to 30%) without compromising operational performance.	[64]
Blade structural innovation	Employing sandwich structures with green composite facesheets and biodegradable cores in blade design enhances both structural performance and sustainability across the lifecycle.	[64]
Recycling—end-of-life blades	Advancing and optimizing recycling techniques, particularly mechanical recycling, remains imperative for turbine blade waste. Metal component recycling markedly decreases environmental burdens at end-of-life.	[58,60,61,70]
Sustainable EoL supply chains	The integration of sustainable supply chain designs, including efficient cutting and sectioning technologies for turbine disposal. Tailoring these operations to site and project-specific requirements enhances circularity and resource conservation.	[71]
Transportation	Transportation of components should be as limited as possible. When large transportation distances are necessary, a boat or train should be the preferred method of transportation.	[60]

.

Recycling can be challenging as wind turbine blades are made from composite materials. In line with circular economy approaches, new circular value chains must be designed, and cutting and sectioning operations should be integrated into the value chain. Lund et al. [71] applied multicriteria decision-making methodologies (MCDM) for sustainable decision-making to assess different technologies for the sectioning of wind turbines. The study identified that an excavator with a diamond saw blade is the preferred technology for sectioning wind turbine waste for later transportation and processing. Paulsen and Enevoldsen identified recycling through co-processing to produce cement as the most suitable method for handling end-of-life (EoL) wind turbine blades based on the current technology readiness level (TRL) of the various recycling methods [72]. Recently, Xu et al. [70] identified pyrolysis and chemical solvolysis as promising recycling methods for waste wind turbine blades to recover glass fibers for further use as reinforcing materials for structural components.

For all turbine types, the choice of recycling method (mechanical, co-processing for cement, pyrolysis, or chemical solvolysis) influences total life cycle emissions and waste management challenges. Moreover, LCA results are sensitive to the capacity factor, site selection, and maintenance frequency, which vary with turbine design and installation environment. Recent dynamic modeling indicates that optimizing glass or carbon fiber composites, in conjunction with operational and maintenance protocols, can reduce the global warming potential for both onshore and offshore wind farms. Continued improvements in blade design, material innovation, and recycling are essential for optimizing life cycle sustainability of both VAWTs and HAWTs. An integrated approach addressing technical, economic, and circularity aspects can significantly improve the long-term environmental profile of vertical-axis wind technologies.

• C5. Operational Safety

Operational safety is assessed through several factors, shown in

Table 7. Assessment of operational safety for HAWTs and VAWTs.

Parameter	HAWT	VAWT	References
Blade breakage and structural failure:	Larger HAWT blades. experience higher centrifugal forces. blade failures remain a critical safety concern, especially in high-wind conditions.	lower rotational inertia. Composite materials lower stress.	[1,38,73]
Ice throw and projectile hazards:	High tip speeds pose risks to nearby infrastructure and personnel. Ice detection systems and deicing technologies are crucial.	Vertical design limits ice accumulation.	[38,73]
Tower overturning and foundation stability	are more susceptible to extreme wind gusts and foundation instability. Offshore HAWTs require complex floating platforms.	lower center of gravity, and compact designs (e.g., monopile foundations) to improve resistance to overturning.	[38,73,74,75]

.

• Blade breakage and structural failure:

VAWTSs are characterized by lower rotational inertia, and proximity to the ground reduces the risk of catastrophic blade failure. However, composite materials like carbon fiber-reinforced polymer (CFRP) significantly lower stress (150 MPa vs. 215 MPa in structural steel) and fatigue damage (0.12 fatigue ratio vs. 0.21 in steel), enhancing blade durability [73,74]. Dynamic stall effects and turbulent wind conditions near the ground can increase cyclic loads, accumulating fatigue over time. Structural optimizations mitigate these risks by improving stress distribution uniformity (88% in optimized designs) [74,76]. Larger HAWT blades (up to 100+ m) experience higher centrifugal forces and bending stresses, increasing the likelihood of blade fractures or delamination [1]. Blade failures in HAWTs can spread debris over large areas due to their height [38]. Advanced materials and pitch-control systems reduce risks, but blade failures remain a critical safety concern, especially in high-wind conditions [38,73].

• Ice throw and projectile hazards:

VAWTs’ lower tip speeds (typically 15–30 m/s) reduce the distance ice or debris can be thrown. Their vertical design also limits ice accumulation on blades in turbulent urban or marine environments [73]. HAWTs’ high tip speeds (60–90 m/s) can propel ice fragments over 300 m, posing risks to nearby infrastructure and personnel. Ice detection systems and de-icing technologies are mandatory for HAWTs in cold climates [38,73].

• Tower overturning and foundation stability:

VAWTs’ lower center of gravity and compact designs (e.g., monopile foundations) improve resistance to overturning. Structural simulations show monopiles reduce deflection by 30% compared to piled foundations under dynamic loads [74]. Offshore VAWTs benefit from reduced wave-induced stresses, with fatigue damage ratios 20% lower than HAWTs in marine environments [74]. HAWTs’ taller towers (80–150 m) are more susceptible to extreme wind gusts and foundation instability. Offshore HAWTs require complex floating platforms, increasing overturning risks in rough seas [38,73]. It can be concluded that HAWTs dominate in efficiency and capacity, but VAWTs offer advantages in urban areas [75].

3.5. Improvement Opportunities for VAWT

Based on recent scientific literature, advancements in VAWT focus on enhancing efficiency, operational range, and adaptability to diverse environments. This section identifies and discusses the most promising avenues for improvement, supported by relevant research findings. The scheme of improvement opportunities is shown in Figure 2.

3.5.1. Aerodynamic Design Optimization

• Variable Blade Pitch Systems: Adjusting blade angles dynamically during rotation improves lift-to-drag ratios and mitigates dynamic stall. Sinusoidal and cycloidal pitch adjustments have increased power coefficients by 30–78.6%, depending on wind conditions [7,77].
• Hybrid Rotor Designs: Combining Savonius (drag-based) and Darrieus (lift-based) rotors enhances self-starting capabilities and efficiency. Dual-rotor configurations achieve 25–35% higher power output in low-wind urban environments [3,4,74,75].
• Blade Geometry and Surface Modifications: The application of AI and CFD has recently become a powerful tool for optimizing configuration or flow conditions in renewable energy applications [6]. Studies by Hassanpour and Azadani, Yoo and Oh, and Hashem and Zhu proposed optimizing the blade shape of an H-Darrieus rotor using a genetic algorithm approach. Optimizing blade profiles (curved blades) and introducing surface features such as holes or fins can reduce drag and increase torque, particularly at low wind speeds [78,79,80]. CFD studies indicate that Savonius VAWTs with perforations achieve 10–15% higher output power at 10 m/s than conventional designs [18,81].

3.5.2. Active Flow Control Technologies

• Plasma Actuators: Applying time-varying waveforms (e.g., sinusoidal, cosine) to blades delays flow separation and suppresses vortices. This method boosts energy output by 35–43% compared to non-actuated turbines [82].
• Guided Vanes and Deflectors: Omni-directional guide vanes (ODGVs) redirect wind toward blades, accelerating airflow. Studies report 20–30% power augmentation in Savonius turbines with optimized deflector placements [18,75]. Qasemi and Azadani examined the impact of flat plate deflectors on the power performance of a Darrieus VAWT based on the Taguchi orthogonal array L16. When optimal deflector settings in terms of size, orientation, and position were used, an efficiency increase of 16.42% was achieved compared to a turbine without deflectors [76]. Ansaf et al. optimized the design of a Darrieus H-rotor VAWT combined with fixed guiding walls surrounding its rotor. The design of the guiding walls was analyzed using various geometric parameters. The results of the surrogate model were compared with CFD results, leading to the selection of the optimal solution. A comparison between the open Darrieus model and the optimized Darrieus model with guiding walls demonstrated a significant improvement in the power coefficient of up to 177% at λ = 3 due to the increased airflow velocity [83].

3.5.3. Advanced Control Systems

• AI-Driven Pitch Optimization: Genetic algorithms identify optimal blade pitching kinematics and tripling power coefficients while reducing load fluctuations by 77% at off-design conditions [77].
• Adaptive Tip Speed Ratio (TSR) Control: Adjusting rotational speed based on real-time wind data maximizes energy capture. Counter-rotating systems increase power density by 30% in clustered urban installations [11].

3.5.4. Material and Structural Innovations

• Magnetic Levitation (MagLev) Bearings: Eliminating mechanical friction reduces startup wind speeds to 1.5–2 m/s and extends lifespan by minimizing wear [18,75].
• Lightweight Composite Blades: Carbon fiber and polylactic acid (PLA) reduce blade mass by 40%, enhancing responsiveness to low winds while maintaining structural integrity [18,75].
• 3D-printed blades and recycled polymers are being increasingly used for small-scale VAWTs [11,18].

3.5.5. Urban Integration and Scalability

• Building-Integrated VAWTs: Modular designs enable rooftop and façade installations, leveraging urban wind acceleration effects. Hybrid wind-solar systems achieve energy yields 15–25% higher than those of conventional systems in constrained spaces [75].
• Floating Offshore VAWTs: Their low center of gravity and omnidirectional operation make them suitable for deep-water platforms. Prototypes show 20% cost savings in foundation logistics compared to HAWTs [18].

3.5.6. Counter-Rotating VAWT

Counter-rotating VAWTs (CR-VAWTs) represent a significant advancement in VAWT technology, addressing key limitations of conventional VAWTs through innovative dual-rotor configurations. The key features that will be discussed are shown in Figure 3.

Design and Operational Principles

CR-VAWTs feature two co-axial rotors rotating in opposite directions, enabling higher energy capture and torque stability. Key design parameters include:

• Axial Gap: The distance between rotors (e.g., 0.1–0.3 rotor diameters) optimizes wake interaction and minimizes turbulence losses [84,85].
• Blade Geometry: Curved or helical blades reduce cyclical stress, while hybrid designs (e.g., Savonius-Darrieus) enhance self-starting capabilities [86,87].
• Drivetrain Efficiency: Counter-rotation doubles the relative angular velocity of the generator, allowing smaller, cost-effective generators to achieve equivalent power outputs [85,87].

Performance Enhancements

• Increased Power Output: CR-VAWTs achieve 14% higher power coefficients than conventional VAWTs at optimal tip-speed ratios (TSR ≈ 2.5) due to reduced wake interference and improved torque uniformity [84,87].
• Low-Wind Adaptability: Dual-rotor systems maintain stable performance in turbulent or low-speed winds (3–5 m/s), with hybrid configurations (e.g., Savonius outer rotor + Darrieus inner rotor) achieving 30% higher efficiency in urban settings [86,87].
• Noise Reduction: Opposing blade rotations cancel out high-frequency vortices, lowering noise emissions by 5–10 dB compared to single-rotor VAWTs, making them suitable for residential areas [85,87].

Key Innovations

• Taguchi-CFD Optimization: Studies using Taguchi methods and CFD identified blade height as the most critical parameter (contributing ~45% to power output), followed by axial gap and turbine diameter. Optimal configurations increase energy density by 20% [84,85].
• Actuator Line Modelling (ALM): Advanced simulations reveal that CR-VAWTs mitigate dynamic stall by redistributing aerodynamic loads across both rotors, reducing blade fatigue [85,88].
• Modular Scalability: Smaller, coaxial rotors simplify manufacturing and transportation compared to large single rotors, enabling cost-effective deployment in decentralized systems [85,87].

Applications and Case Studies

• Urban Integration: Compact CR-VAWTs are installed on rooftops and building façades, leveraging turbulent urban winds. A study in Malaysia demonstrated a 25% increase in annual energy yield for hybrid CR-VAWTs in city environments [87].
• Offshore Floating Platforms: CR-VAWTs with helical blades show promise in marine environments, where their low center of gravity and omnidirectional operation reduce foundation costs by 15–20% compared to HAWTs [85,86].
• Agrivoltaic Systems: Dual-rotor designs coexist with crops, minimizing land use conflicts. Experimental setups in Italy achieved 10–15% higher energy density per hectare than standalone solar or wind systems [85].

Challenges and Future Directions

• Design Complexity: Balancing rotor interactions (e.g., torque synchronization) requires advanced control systems, increasing initial costs [84,85].
• Scalability: Most CR-VAWTs are limited to <100 kW, though prototypes like the 30 kW co-axial Darrieus turbine demonstrate potential for medium-scale grids [87].
• Research Frontiers: Bio-inspired designs (e.g., fish-swimming kinematics) and AI-driven pitch control are under investigation to further optimize efficiency and durability [85,86].
• Adoption of AI in optimization of VAWTs: AI-powered design optimizations—like rotor blade shapes tailored to local wind conditions—can enhance turbine efficiency, leading to quicker returns on investment and greater long-term profitability [89]. The primary risk of applying AI to wind turbines lies in the potential bias and discrimination within algorithms, which could result in unpredictable and potentially harmful outcomes. Additional risks include cyberattacks, ethical concerns, system complexity, and liability issues in the event of accidents [6].

Summary of CR-VAWT Advantages

CR-VAWTs are positioned as a technology for niche markets. A summary of key CR-VAWT advantages is shown in

Table 8. Summary of CR-VAWT Advantages.

Aspect	CR-VAWT vs. Conventional VAWT	Key Studies
Power Coefficient	14% higher at optimal TSR	[86,87]
Noise Levels	5–10 dB reduction	[85]
Urban Suitability	25% higher energy yield in turbulence	[87]
Offshore Viability	15–20% lower installation costs	[85,86]

. For further details, reader is referred to experimental validations in [87] and design frameworks in [85].

3.5.7. Short-Term Opportunities (1–5 Years)

Urban and Suburban Areas

• VAWTs are well-suited for cities due to their compact design, low noise levels, and ability to operate in turbulent winds. They can be integrated into buildings, parking lots, highways, or public spaces for localized energy production [49].
• Application in “smart cities” for powering street lighting, EV charging stations, or small-scale infrastructure [90].

Hybrid Systems and Off-Grid Solutions

• Combination with solar panels or battery systems for a stable energy supply in rural/remote areas (e.g., telecom relays, agricultural sensors) [91].
• Ideal for small-scale projects where easy installation is crucial [91].

Experimental and Niche Projects

• Pilot projects in communities with limited space or environmental requirements (e.g., tourist destinations, protected areas) [90].
• Use in industrial zones to reduce energy costs [90].

Decentralized Energy Solutions

• Supporting the energy transition through distributed networks, particularly in regions with unstable electrical infrastructure [91].

Government Incentives and Subsidies

• Many governments are implementing policies and incentives to promote renewable energy technologies, including VAWTs. This support can help offset initial installation costs and encourage adoption among homeowners and small businesses looking to reduce their carbon footprint [91].

3.5.8. Long-Term and Opportunities (5+ Years)

Technological Advancements

Ongoing research and development in VAWT technology are expected to enhance its efficiency and reliability significantly. Innovations such as improved blade designs, fixed guiding walls, materials that reduce wear and tear, and advanced control systems can lead to greater energy capture and lower operational costs over time [7]. These advancements will make VAWTs more competitive against HAWTs in larger applications.

Offshore Applications in Deep Waters

VAWTs can be competitive in floating offshore wind farms due to their simple construction and resistance to changes in wind direction. They are well-suited for deep waters where HAWTs are not cost-effective [75,92,93,94].

Integration into Smart Grids and Sustainable Cities

• Synergy with future energy systems (smart grids, hydrogen economy) to optimize energy consumption [90].
• Architectural integration into buildings as part of an “active energy skin” [90].

Global Markets with Specific Conditions

• Application in areas with frequent variable wind directions (e.g., tropical regions) or extreme weather conditions.
• Expansion into developing countries with a growing demand for decentralized energy.

Environmental and Regulatory Advantages

• Reduced impact on birds and ecosystems compared to HAWTs, which may attract subsidies or incentives [75].

3.6. Main Barriers to the Greater Adoption of VAWTs

The greater adoption of VAWTs faces several obstacles that hinder their widespread use in the renewable energy market. The main barriers identified are shown in Figure 4 and discussed in this section.

3.6.1. Lower Efficiency and Technical Limitations Compared to HAWTs

VAWTs have a significantly lower Cp than HAWTs, especially under high wind speed conditions. This is due to airflow turbulence, dynamic stall, and large vortices generated downstream of the rotor, which reduce the overall energy the turbine can extract from the wind [7,18]. This inefficiency makes VAWTs less attractive for large-scale energy production, particularly in competitive commercial markets where HAWTs dominate due to their higher efficiency and well-established technology [92]. Additionally, self-starting issues at low wind speeds limit their applicability in areas with variable wind conditions [18].

3.6.2. Mechanical Complexity and Design Challenges

Despite advancements in variable designs (e.g., adjustable blade pitch), mechanisms for adapting parameters during operation (such as active angle-of-attack control) increase structural complexity. These systems require high structural strength and resistance to mechanical fatigue, which raises maintenance costs and reduces reliability. Due to cyclic loading, sinusoidal blade pitch adjustment systems can lead to material failure [7].

3.6.3. Market Perception and Acceptance

Market perception plays a crucial role in the adoption of any technology. VAWTs have historically been viewed as less effective than HAWTs, leading to a lack of confidence among investors and stakeholders in their viability for large-scale applications. Additionally, concerns about noise pollution and aesthetic impacts can lead to local opposition in urban settings, further complicating their acceptance [75,92].

3.6.4. Cost Competitiveness

While VAWTs can be cheaper to install and maintain, their overall cost-effectiveness is often overshadowed by HAWTs due to the economies of scale achieved by larger wind farms. The initial investment in VAWT technology can still be significant, particularly when considering the need for advanced materials and designs to overcome existing limitations. This cost competitiveness issue is a barrier that needs addressing through innovation and potential subsidies or incentives [7,18,92].

3.6.5. Regulatory and Financial Barriers

Regulatory frameworks often favor established technologies, such as HAWTs, making it difficult for newer technologies, like VAWTs, to gain traction. Funding for renewable energy projects can also be limited, particularly in regions with less developed financial markets. These economic barriers can restrict investment in VAWT technology, resulting in fewer research projects and slowing its development [92].

Recent multi-country econometric analysis clearly demonstrates that government intervention, including fiscal incentives, direct subsidies, and strategic planning, has a strong causal relationship with both renewable energy adoption and the pace of technology innovation in wind power. Where policy is proactive, wind energy consumption rises substantially, and new turbine architectures—including VAWTs—are more likely to be pursued, tested, and scaled. In contrast, weak government support correlates with stagnation in technology portfolios and reduced investor confidence in emerging systems [95]. The research from Hvelplund et al. highlights the critical importance of guaranteed grid access, simplified licensing, stable feed-in tariffs, and coordinated policy mandates as elements directly linked to expanded market competitiveness and investment. A dual track-incentive system for both wind power and its integrating infrastructure is necessary [96].

A large-scale policy analysis by Azhgaliyeva et al. [97] identified tax reliefs, strategic grants, and long-term planning as the most effective interventions for scaling wind energy, especially when paired with clear market signals and investor protections. However, the study also underscores that prevailing incentives and regulatory practices typically favor established technologies, erecting considerable barriers for new entrants like VAWTs. Without targeted reforms, the current structure of subsidies and adoption policies risks maintaining the status quo, rather than advancing next-generation turbine solutions.

4. Conclusions and Future Research Directions

Vertical-axis wind turbines (VAWTs) offer a competitive pathway for renewable energy, particularly in niche applications such as urban, decentralized, and offshore environments. Their competitiveness hinges on striking a balance between aerodynamic efficiency, operational flexibility, and cost-effectiveness. Recent innovations, including variable—pitch blades, plasma actuators, AI-driven pitch optimization, and hybrid rotor designs, demonstrate significant potential gains in energy performance, urban integration, and cost reduction, as summarized in

Table 9. Summary of key advancements for VAWT.

Area	Innovation	Performance Gain
Aerodynamics	Variable pitch blades	Up to 78.6% CP increase
Flow Control	Plasma actuators	35–43% energy boost
Smart Systems	AI-driven pitch optimization	3× power coefficient
Urban Integration	Helical hybrid rotors	30% efficiency in cities
Offshore Applications	Floating VAWTs	20% cost reduction

.

However, despite these advancements, VAWTs face critical limitations that must be acknowledged. Major unresolved engineering challenges include dynamic stall management, scaling to larger turbine sizes, improving self-starting characteristics, and optimizing long-term material durability. These technical gaps, particularly in scalability and performance consistency, currently restrict VAWT competitiveness relative to conventional horizontal axis wind turbines (HAWTs). Additionally, market adoption is hampered by regulatory and financial barriers arising from existing policy incentives that favor more established HAWT technologies.

Long-term opportunities for VAWTs will hinge on continued research and development in aerodynamics, smart control systems (especially AI and machine learning for adaptive operation), multi-objective optimization for efficiency and sustainability, and integration with advanced energy storage solutions. Policy support and market innovation will be instrumental in overcoming adoption hurdles and fostering investment in next-generation VAWT technologies.

The global energy landscape shifts towards sustainability, and VAWTs continue to evolve as a promising alternative to traditional wind energy solutions. While they currently face challenges related to efficiency, scalability, and cost competitiveness, ongoing advancements in aerodynamics, materials, and smart energy integration pave the way for broader adoption. Future research efforts will be crucial in optimizing VAWT performance, making them more viable for urban, decentralized, and offshore applications. Key areas of research include:

• AI and Machine Learning—Developing predictive models for wind pattern mapping and real-time turbine adaptation to enhance efficiency and responsiveness.
• Multi-Objective Optimization: Using genetic algorithms to balance efficiency, cost, and environmental impact.
• Energy Storage Integration: Pairing VAWTs with hydrogen storage or batteries to stabilize grid output.

In conclusion, while VAWTs have considerable promise for a sustainable energy transition, realizing their full potential requires addressing persistent engineering constraints, a more balanced regulatory environment, and targeted research priorities. Future work should focus on the empirical validation of design advances, robust comparative analyses with HAWTs, and fostering interdisciplinary collaboration among technical, economic, and policy domains.