Four Main Types of Wind Turbines
Horizontal Axis Wind Turbine (HAWT) – UpWind
The shafts of the rotor and generator are positioned horizontally and the wind hits the blade before the tower.
Horizontal Axis Wind Turbine (HAWT) – DownWind
The shafts of the rotor and generator are positioned horizontally and the wind hits the tower first then the blades.
Vertical Axis Wind Turbine (VAWT) – Drag based
The generator shaft is positioned vertically with the blades pointing up. The turbines are usually mounted on the ground or a short tower. This type is also called the Savonius turbine, after it’s inventor, S. I. Savonius. It was invented in the 1920’s. It uses drag, like a cup anemometer, to produce torque.
Vertical Axis Wind Turbine (VAWT) – Lift based
The generator shaft is positioned vertically with the blades pointing up. The blades use the lift design. This type is called Darrius or “egg beater”.
Horizontal Axis Wind Turbine
The Horizontal Axis Wind Turbines require a “yaw” mechanism to turn the turbine against the wind direction in order to harvest the wind energy. They are usually installed high up above ground level on a tower in order to harvest the ample wind energy up in the sky. There are 2 types of blades that are used on these turbines. They are the Drag type and Lifting type.
The Drag type blades are typically what you see on an old Dutch wind mill. The blades are generally flat which are hit by the wind to cause the rotation. This type of design is great for operation at very low wind speed and can develop a lot of torque to perform operation. However, they cannot operate at medium to high wind speed.
The Lift type blades are used in most modern wind turbines and on airplanes. The design uses the aerodynamic properties of the blade profile to provide lift force to turn the blades such that the wind turbines can harvest the wind energy at high wind speed. With this design, the rich energy in high wind speed area can then be harvested efficiently.
Vertical Axis Wind Turbine
The Vertical Axis Wind Turbines do not require a “yaw” mechanism to harvest the wind energy. Since the blades rotate 360 degree on the vertical shaft of the wind turbines, wind of any direction can turn the turbine. The turbines are usually installed on or close to the ground level. However, the wind speed is always lower than that in the upper sky. There are also 2 types of blades that are used on these turbines. They are the Drag type and Lift type.
The Drag type blades are used on the Savonius wind turbine. The blades are generally of flat type with large area. They are hit by the wind to cause the rotation. This type of design is good for operation at low to medium wind speed to generate electricity. However, the capacity of this type of wind turbines is limited to small scale because it is difficult to make the large area of blades required.
The Lift type of blades is used on the Darrius or “egg beater” wind turbine. The design uses the aerodynamic properties of the blade profile to provide lift force to turn the blades such that the wind turbines can harvest the wind energy at high wind speed. The blade shapes are different than the lift type used on the Horizontal Axis Wind Turbines.
Choice of wind turbines
There are many wind turbines on the market for you to choose. Horizontal axis wind turbines are most popular nowadays.
Wind turbines have to be mounted up in the sky where wind power is ample. Wind speed is higher up in the sky than near the ground. The ideal site should be far from tall buildings to avoid turbulences, which are the results of changing directions of wind when it hits the obstacles. Horizontal axis wind turbines harvest the wind energy against the direction of wind. The turbulences reduce the wind energy that the wind turbines harvest in that particular direction at that instance.
Some schools or universities choose wind turbines of a few hundred watts capacities. They usually mount them in open areas or roof top of buildings in the campus. What the students can do with these wind turbines are logging operation data for analysis. They have to wait for the wind conditions to happen so that they can take those operation data. They have no control of the wind. What’s more, they cannot change the blade parameters easily either because another set of blades is not available or the wind turbines are mounted on towers that they cannot access.