Vertical-Axis Wind Turbine: All You Wanted to Know

Wind energy is one of the best alternatives to traditional sources of energy. For one, it has a minimal carbon footprint. Furthermore, it is a self-reliant energy source and will enable you to get off the grid.

Now there are two types of wind turbines, and we are going to be looking at one of them: the vertical-axis wind turbine. 

VAWTs, as they are often called, are easy to maintain, have low transportation and maintenance costs, and offer lots of convenience. That doesn’t even begin to cover it, though – read on to find out more about vertical-axis wind turbines.

Vertical-Axis Wind Turbines vs Horizontal-Axis Wind Turbines

There are two main types of wind turbines: horizontal-axis wind turbines and vertical-axis wind turbines. The two types have several differences, but the one that distinguishes them is the positioning of the shaft relative to the ground: either horizontal or vertical.

Horizontal-axis turbines have a shaft that is positioned horizontal to the ground, and feature all of the components (blades, generator, shaft) on top of a tall tower. On the other hand, vertical-axis turbines have a shaft that is positioned vertical to the ground, and all the main components are near to the ground.

Horizontal-axis wind turbines are designed and built to always face into oncoming wind. Vertical-axis wind turbines don’t need to be pointed into the wind.

The advantages of horizontal-axis turbines include:

  • Most have the ability to self-start.
  • Tall tower gives them access to stronger winds, especially on sites which have wind shear.
  • Tall tower allows installation on uneven land or in offshore locations.
  • Ability to pitch rotor blades in a storm and thus minimize damage.
  • Ability to wing warp, which ensures the turbine blades have the best attack angle.
  • Stability since blades are positioned to the side of the turbine’s center of gravity.

The advantages of vertical-axis turbines include:

  • Ease of maintenance.
  • Reduced construction and transport costs.
  • Don’t need to be pointed into the wind.

Disadvantages of horizontal-axis wind turbines include:

  • Difficult to operate near ground winds.
  • Needs tall cranes and skilled operators to install.
  • Difficult to maintain.

Disadvantages of vertical-axis wind turbines include:

  • Less efficient.
  • The blades often spin back into the wind, and that causes drag.
  • They operate at a physically lower level where there is more turbulent wind.
  • They have a low starting torque and may need energy to begin turning.

Vertical-Axis Wind Turbine Design

VAWTS feature a main rotor shaft which is positioned vertically. Thanks to this arrangement, the turbine does not have to face the wind for it to be effective. This comes as a plus on sites where the wind direction varies a lot – for instance when integrated into a building.

The main disadvantage of this arrangement is lower rotational speed, which results in higher torque, which consequently leads to a higher cost of the drive train.

Thanks to the vertical axis, the gearbox and generator can be positioned close to the ground. This enhances accessibility for maintenance.

What Makes Vertical-Axis Wind Turbines Better

For a vertical-axis wind turbine, the shaft it set transverse to the wind and its main components are found at the turbine’s base. This arrangement enables the gearbox and generator to be positioned near the ground.

As a result, maintenance/servicing and repair is much easier compared to horizontal-axis turbines where the key components are located high atop a tall tower. This reduces not just the costs but also the environmental impact.

Unlike horizontal-axis wind turbines (HAWT), vertical-axis wind turbines (VAWT) are omni-direction and therefore do not have to be pointed in the direction of incoming wind. As a result, they do not need the wind-sensing and orientation mechanisms used in HAWT structure.

VAWTs are able to function better than HAWTs in the event of gusty, turbulent winds. Furthermore, HAWTS are unable to harvest turbulent winds efficiently, and that causes accelerated fatigue for them. The gearbox of a VAWT experiences far less fatigue than the gearbox of a HAWT.

VAWTs allow closer grouping in wind farms, and that leads to an increase in power generated per unit of land area. Furthermore, in a HAWT wind farm, you can install VAWTs below the existing HAWTs and thus increase/supplement power output.

Challenges of Vertical-Axis Wind Turbines

The main disadvantage is that VAWT blades experience rapid, cyclical variations in angle of attack and relative airspeed – that can result in dynamic stall. Dynamic stall can make the turbine less efficient, and cause vibrations and noise.

Furthermore, the VAWT’s blades are prone to fatigue due to wide variation in applied forces in the course of each rotation. Modern composite materials – or design improvements – can help overcome this problem.

Such design improvements include using aerodynamic wing tips which give the spreader wing connections a static load.

VAWT blades may twist and bend during each turn, and that puts them at the risk of breaking apart.

Traditionally, VAWTs are not as reliable as HAWTs. However, modern designs have been able to overcome many of the problems associated with the early designs.

Types of Vertical-Axis Wind Turbines

1. Savonius Wind Turbine – An easy to build, simple in shape wind turbine, but which has limited speeds. Savonius turbines are not ideal for industrial use, but are okay for small-scale projects.

2. Darrieus Wind Turbine – It is oval in shape, and able to achieve high speeds. Darrieus turbines are ideal and popular for large-scale energy production, thanks to the high speeds. They are more complex than Savonius turbines.

3. Helical Wind Turbine – They are helical-shaped, and are quite popular in the residential wind market. A helical wind turbine can generate electricity even with a small wind. You do not have to position them very high. They have a complex design.

Final Verdict

Vertical-axis wind turbines are able to catch the wind from all directions and do not need yaw mechanisms. They are far easier to maintain since the main components are positioned close to the ground.

However, they are not self-starting. Furthermore, the high variation of winds experienced by the blades can cause blade fatigue.

If you are attached to HAWTs, note that you can still install VAWTs in the same area since VAWTs are positioned closer to the ground than HAWTs.

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