Vertical Axis vs. Horizontal Axis Wind Turbines

Typical shape of a horizontal axis wind turbine.

Both vertical axis wind turbines (VAWTs) and horizontal axis wind turbines (HAWTs) generate electricity from wind power. However, the VAWT is less efficient, less durable and does not work as well as the HAWT.

Physics

Wind blows faster when it is farther from the ground. VAWTs are usually built at ground level, making their overall energy output less than a HAWT, which is erected higher in the air.

Efficiency

HAWTs use a propeller design to generate energy. The propeller can be turned to face the wind. A VAWT uses the eggbeater shape so that it always faces the wind. However, although the VAWT can produce energy this way, efficiency is lost through not having its entire blade shape always against the wind.

Stress

In the design for an HAWT, the greatest stress put on the blade by the wind is at the base of the blade, where it is strongest. In a VAWT design shaped like an eggbeater, the greatest stress is put on the center of the curved blades, where it is weakest.

Structure

HAWTs rest on towers that hold them up. VAWTs may need guy cables running from their top to the ground, which can be impractical for farming areas.

Maintenance

When replacing the rotor on an HAWT, it can be removed from the shaft. When replacing the rotor on a VAWT, the entire machine must be taken down.

References

• Danish Wind Industry Association: Wind Turbines: Horizontal or Vertical Axis Machines
• "Mother Earth News;" Wind Power: Are Vertical Axis Turbines Better?; Alison Rogers interview with Mick Sagrillo; February/March 2008