Variable Wind Direction

• The traditional horizontal axis turbines are turned to face the wind in order to work efficiently. The mechanism used to turn horizontal axis turbines, the yaw mechanism, isn't needed on vertical axis turbines. They are equally efficient whatever the wind direction. This means vertical axis turbines are more effective in areas with variable wind directions, such as built-up areas, and they save the difficult maintenance tasks associated with yaw mechanisms.
  
  

Lower Gearbox and Generator

• The gearbox and generator on horizontal axis turbines is located directly behind the rotas at the top of the mounting tower. As horizontal axis turbines need high wind velocities to produce any quantity of electricity the towers are very tall, making maintenance tasks on gearboxes and generators difficult. In vertical axis turbines gearboxes and generators can be mounted at the base of the structure, at ground level, which provides much easier access for the maintenance tasks needed to keep the turbines running efficiently and safely.
  
  

Lower Wind Speeds

• Horizontal axis turbines need large and heavy rotas to produce large quantities of power, and because of this the wind speed needed to keep them moving is high. Areas with low wind speed are just not suitable for horizontal axis turbines. Vertical axis turbines can produce power even from lower wind speeds --- not large amounts of power, but a steady trickle can be produced.
  
  

Noise and Vibration

• There is no getting around the fact that horizontal axis turbines are noisy when they are in full flight. Vertical axis turbines do not suffer from this, and their quietness means they are often cited as more suitable for domestic installations. However there can be issues with noise, and other maintenance problems, created by vibration if the turbines are not mounted very carefully.
  
  

Considerations

• As of 2011, few studies have been done in the efficiency and power output of vertical axis turbines, especially when compared with horizontal axis turbines. Horizontal axis turbines are a proven technology, and while more and more vertical axis turbines are appearing on the market they are often less cost effective than their horizontal counterparts.