Which is more efficient, vertical axis or horizontal axis wind turbines?

At present, the efficiency of mainstream three blade horizontal axis wind turbines is much higher than that of vertical axis wind turbines.

This efficiency gap is fundamental. The key indicator for measuring efficiency is the "wind energy utilization coefficient", which represents how much energy a wind turbine can capture from the wind. Modern large-scale horizontal axis fans can achieve an efficiency of 45% -50%, which is close to the theoretical limit (59.3%, known as the Bez limit). In contrast, the efficiency of vertical axis fans is much lower, typically only 15% -40%, depending on their design type.

Why is the efficiency of horizontal axis fans so high?

This is mainly due to its working principle:

All blades simultaneously cut into the wind at the optimal angle: the blades of a horizontal axis fan are designed to resemble the wings of an aircraft (aerodynamic airfoil). When the wind blows, it generates a huge 'lift', which is the main driving force for the rotation of the blades. Due to the fact that the blades always rotate in the same direction, most of the entire blade can continuously and efficiently capture wind energy.

High speed: Horizontal axis fans can achieve very high speeds, which makes it very efficient in driving the generator to generate electricity.

Why is the efficiency of vertical axis fans lower?

The working mode of vertical axis fans (mainly referring to the "Dario type" that looks like an egg beater) is different:

The blades move back and forth in the wind: as they rotate to different positions, their angle with the wind direction constantly changes. Only at certain specific angles can blades efficiently capture wind energy; However, in other positions (such as when turning back to the windward side), the blades will instead generate resistance. This characteristic of 'competing with oneself' fundamentally limits its efficiency.

Poor startup performance: Many vertical axis fans cannot start on their own and require some external assistance.

Although there is a huge gap in efficiency, vertical axis fans are not without their advantages. They possess a series of unique features that make them irreplaceable in certain specific scenarios.

Advantages and disadvantages of horizontal axis fans:

Advantages:

Core advantages: extremely high efficiency and the best economic feasibility for large-scale power generation.

Disadvantages:

Need to align with the wind direction: A complex "yaw system" must be equipped to constantly adjust the cabin to align with the direction of the wind, just like a wind direction marker.

Complex structure and high maintenance costs: Heavy generators and gearboxes are installed at the top of towers tens or even hundreds of meters high, making maintenance and repair very difficult and expensive.

Loud noise: The high-speed rotating blade tip will produce a lot of noise.

High requirements for installation environment: stable and smooth wind conditions are needed, which may not perform well in cities with turbulent and turbulent winds.

Advantages and disadvantages of vertical axis fans:

Advantages:

No need for wind: wind from any direction can make it rotate, eliminating the need for a yaw system.

Simple structure and easy maintenance: The main equipment such as the generator and gearbox are installed on the bottom ground, and maintenance personnel do not need to climb high, resulting in low maintenance costs.

Low noise: The speed is usually slower and the operation is quieter.

Adapt to complex wind conditions: It is very suitable for urban environments with variable wind directions and turbulence, and can be installed on rooftops.

Low startup wind speed: Some types (such as S-type) can start in a gentle breeze.

Disadvantages:

Core disadvantage: Low efficiency.

There is a structural risk: some designs experience high stress at the root of the blades during high-speed rotation, which can easily lead to problems.

So, the final conclusion is:

If you want to build a large wind farm and pursue the maximization of power generation and economic benefits, then "high-efficiency" horizontal axis wind turbines are the only mainstream choice. That's why almost all the windmills we see in the wild have horizontal axes.

But if you need a "not picky, easy to serve" generator for distributed scenarios, such as supplying power to streetlights, buildings, remote base stations, especially in cities with unstable wind directions, then a "low efficiency but sturdy and durable" vertical axis fan may actually be a more suitable choice.

In short, the horizontal axis represents the "top students" who pursue performance and scale, while the vertical axis represents the "talented students" who adapt to specific environments. In terms of pure efficiency, horizontal axis fans outperform.