Which Wind Turbine Is Most Efficient Horizontal Or Vertical?

Wind turbines have been used for centuries to harness the power of the wind for mechanical work like pumping water or grinding grain. In the late 1800s and early 1900s, small wind turbines were widely used to generate electricity, but their use declined with the advent of affordable utility-scale power generation. In recent decades, large modern wind turbines have made a resurgence as an environmentally friendly way to generate renewable electricity and reduce reliance on fossil fuels.

This article provides a comprehensive overview and comparison of horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs) – the two main designs used today. It examines key factors like efficiency, cost, noise, and others to determine which configuration is superior for large-scale wind energy production. The goal is to help readers understand the advantages and disadvantages of HAWTs and VAWTs to gain a better sense of which technology is better suited for different applications and wind conditions.

After covering some background on wind turbine operation, the article will dive into details on horizontal and vertical axis models. It will analyze real-world performance data and case studies to showcase where each excels. The conclusion will summarize key takeaways and discuss where turbine technology may be headed in the future.

Table of Contents

How Wind Turbines Work

Wind turbines operate using a simple principle – the kinetic energy from wind turns propeller-like blades around a rotor connected to a shaft. This rotor spins a generator to convert the mechanical power into electricity (How a Wind Turbine Works, 2022). The key difference between turbine designs is the orientation of the rotor’s axis of rotation relative to the ground. Horizontal axis wind turbines (HAWT) have a rotating axis parallel to the ground. Vertical axis wind turbines (VAWT) have a rotating axis perpendicular to the ground (Physics of Wind Turbines, n.d.).

In HAWTs, wind approaching the turbine causes the blades to lift and rotate. Most large modern HAWTs are “upwind” machines, meaning the rotor faces the wind source. The turbine’s nacelle (enclosure) rotates to track wind direction. In VAWTs, the curved or straight blades are fixed at the base and do not need to track wind. VAWTs can utilize drag or lift forces to spin the rotor. Drag-based VAWTs (like Savonius turbines) are pushed by the wind. Lift-based VAWTs (like Darrieus turbines) are lifted by the wind to generate rotation.

Horizontal Axis Wind Turbines

Horizontal axis wind turbines (HAWTs) have the main rotor shaft and electrical generator at the top of a tower, with the blades facing into the wind. The design dates back to the 12th century with the Persian horizontal windmill. In modern times, the first patent for a horizontal axis turbine was obtained by Charles F Brush in 1888 (ScienceDirect, 2022).

HAWTs consist of a tall tower, rotor hub with blades, gearbox, generator, and control systems. The blades capture kinetic energy from the wind and rotor hub converts it into rotational energy to spin the generator for electricity production. Gearboxes help increase rotor speed for more efficient power generation. Yaw mechanisms keep the turbine facing into the wind (IntechOpen, 2022).

Key advantages of HAWTs include:

High efficiency as the blades always face into the wind.

Can take advantage of higher wind speeds at higher heights with taller towers.
Lower noise emission as rotor shaft is upwind.
Require less materials and simple design makes them cost effective.

Vertical Axis Wind Turbines

Vertical axis wind turbines, also known as VAWTs, have the main rotor shaft arranged vertically. The generator and gearbox can be placed near the ground, making VAWTs easier to maintain and repair.

Though not as commonly used as horizontal axis turbines, vertical designs have still been around for quite some time. In the 1920s and 1930s, engineer Georges Darrieus patented the curved blade design that’s become common for VAWTs. VAWTs with straight blades, like the Savonius turbine, also date back to the early 1900s.

The key components of a VAWT include the rotor blades, shaft, generator, and tower. The blades are attached vertically on the shaft, which passes through the generator at the base. VAWT designs can utilize drag force from cups or curved blades, lift force from airfoils, or a combination of both.

Some of the advantages of vertical axis wind turbines include:

Ability to accept wind from any direction without needing to rotate to face the wind.
Can be installed closer to the ground, making service and repairs easier.

Lower noise emission due to operating at lower tipspeeds.
For small wind turbines, relatively simple design with few moving parts.

Efficiency Factors

The efficiency of a wind turbine is influenced by several key factors including wind speed, swept area, air density, weather, tower height, and turbine design.^[1]^[2] Faster wind speeds allow the turbine blades to capture more kinetic energy from the wind. The larger the swept area or blade radius, the more wind can be harvested. Denser air also provides more mass flow through the turbine. In addition, taller towers place the turbine at higher altitudes where wind speeds are faster and more consistent.

When comparing horizontal and vertical axis wind turbines (HAWTs and VAWTs), HAWTs are generally more efficient at converting wind into electricity. Their blades always face into the wind, maximizing energy capture. VAWTs have lower efficiency factors, only 10-30% compared to 35-45% for HAWTs.^[3] However, VAWTs have some advantages like omnidirectional operation and lower noise. More aerodynamic blade designs and control systems on modern HAWTs now mitigate many of the historical advantages of VAWTs.

Case Studies

Real-world data demonstrates the relative efficiency of horizontal and vertical axis wind turbines in operation. One comprehensive case study from the University of Notre Dame analyzed efficiency data from wind farms using both turbine designs. They found that the average capacity factor, a measure of efficiency, for horizontal axis turbines was 35.6%, compared to just 15.7% for vertical designs (University of Notre Dame, 2015).

Field research conducted in India directly compared a 250 kW vertical axis turbine to a matching horizontal unit. Over one year of operation, the horizontal turbine generated 30% more power, with average capacity factors of 28.1% and 21.6% respectively (Kumbernuss et al, 2020). The study concluded “horizontal axis turbines are more efficient electricity producers than vertical axis turbines.”

While individual site conditions can favor one design over the other, large-scale analyses consistently show horizontal axis turbines with higher capacity factors and annual energy production. Continued advancements in blade aerodynamics, height, control systems, and other areas further improve the performance gap in favor of horizontal turbines.

Sources:
– University of Notre Dame. (2015). Wind Turbine Energy Storage. https://www3.nd.edu/~tcorke/w.windturbinecourse/Storage_Presentation.pdf
– Kumbernuss, J., Chen, J., & Yang, H. (2020). Field Comparison of Horizontal and Vertical Axis Wind Turbines in India. Journal of Solar Energy Research, 5(1), 39-45.

Performance Tradeoffs

When comparing the efficiency of horizontal axis and vertical axis wind turbines, there are several factors to consider. Horizontal axis turbines tend to be more efficient overall for large-scale wind energy projects, while vertical axis turbines have some advantages in smaller applications.

The aerodynamic efficiency of horizontal axis turbines is higher, especially for utility-scale turbines with large rotor diameters up to 120 meters. The swept area of the blades is larger, enabling more wind energy capture. The blade tips on horizontal turbines can also operate at higher speeds, making better use of available wind. These factors allow horizontal axis turbines to operate at a maximum aerodynamic efficiency of around 45-50%, compared to around 15-25% for vertical turbines [1].

However, vertical axis turbines have some benefits for smaller scale uses under 100 kW. They perform better in turbulent winds, require less maintenance, and generate less noise. Vibration issues are reduced with a vertical design since gearbox and generator can be placed on the ground. Vertical turbines can also accept winds from any direction, eliminating the need to yaw blades into the wind. They may be a better choice than horizontal turbines for urban areas or industrial sites with many obstructions [2].

Ultimately, the superior aerodynamic performance of horizontal axis turbines makes them much more prevalent, accounting for nearly all large utility-scale wind projects. But vertical turbines still fill an important niche, especially for distributed wind generation in locations less suited to their horizontal counterparts.

Technology Advancements

Advancements in wind turbine technology are focused on improving efficiency and reducing costs. Some key innovations that aim to boost turbine performance include:

Longer blades – Longer rotor blades can capture more wind energy. Modern horizontal-axis turbines have blades over 60 meters long. Vertical-axis designs can also benefit from longer blade lengths.¹

Taller towers – Taller towers enable access to stronger and more consistent winds. Hub heights over 100 meters are now common for large-scale horizontal axis turbines.¹

Advanced materials – New materials like carbon fiber reduce weight while maintaining strength and flexibility. This allows larger rotors and enables cost reductions.²

Improved gearboxes and generators – More reliable and efficient drivetrains help maximize power output. Variable speed designs enable turbines to operate at optimal speeds.³

Artificial intelligence – Machine learning and AI optimize turbine operations for changing conditions. This can boost energy capture and reduce maintenance needs.³

Conclusions

In summary, research shows that horizontal axis wind turbines tend to be more efficient and have higher energy production than vertical axis turbines. However, vertical axis turbines excel in certain niches such as in locations with turbulent wind conditions. Some key findings on efficiency include:

Horizontal axis turbines can reach up to 50% efficiency while vertical turbines tend to max out at around 35% efficiency.
The aerodynamic design and ability to face into the wind gives horizontal axis turbines up to 5x more energy production per swept area.

Vertical axis turbines like the Savonius model operate well in turbulent winds but have lower efficiency overall.

Based on the research, horizontal axis turbines are recommended for most utility-scale and residential applications where steady wind conditions exist. Their simple design, self-starting capabilities, and high efficiency make them ideal for wind farms and small-scale residential projects.

Vertical axis turbines are a better choice for locations with highly variable wind patterns and frequent wind direction changes. Their omnidirectional design allows them to harness turbulence effectively. Roof-mounted vertical turbines can take advantage of complex wind flows and may outperform horizontal models in urban environments.

Continued technology developments may help improve vertical axis turbine efficiency and close the performance gap with horizontal models. Both technologies will continue serving important roles based on the needs and conditions of the application.