Horizontal-axis wind turbines (HAWT)
The main rotor shaft and electrical generator are at the top of the tower, and must be pointed into the wind. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable for generating electricity. Most horizontal axis turbines built today are two- or three-bladed.
Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted up a small amount.
Vertical-axis wind turbines (VAWT)
The main rotor shaft runs vertically. Key advantages of this arrangement are that the generator and/or gearbox can be placed at the bottom, near the ground, so the tower doesn't need to support it, and that the turbine doesn't need to be pointed into the wind. Vertical Axis Wind Turbines offer benefits in low wind situations and they work well no matter which direction the wind is coming from (omni-directional). They also tend to be safer, easier to build, can be mounted close to the ground, and handle turbulence much better. The VAWT is wildlife friendly. Birds view the VAWT as a solid object. Propeller turbines (HAWT), are invisible to birds, causing injury and possible death. Animals are not frightened by the VAWT due to its silent operation.
VAWT in Motion