Horizontal Wind Turbine:
Vertical and Horizontal Designs Vary
In Efficiency and Reliability
The horizontal wind turbine or HAWT is the design used most frequently in wind-farms and in the smaller home-use turbines. The blades rotate on a horizontal axis.
In the VAWT or vertical axis turbines, the main rotor shaft is arranged vertically. The advantage is that the turbines do not need to be pointed
in a specific direction in order to
capture the wind’s energy.
This is an advantage in areas where the prevailing winds vary greatly. But, there are numerous disadvantages.
The VAWT designs are sometimes referred to as eggbeaters, because that’s kind of what they look like. The appearance is interesting and the energy created is usable.
One of the problems is the ripple torque created by the shape, which puts added stress on the tower. That makes them somewhat unreliable.
Another problem is that some kind of external motor must be used to get the rotor turning. Unless the prevailing winds are strong and regular, there may be a continuous need to restart the rotor.
Overcoming Disadvantages of the "Eggbeater"
Other VAWT designs have been created to overcome the disadvantages of the eggbeater. Examples include the Giromill and the Savonius designs. Straight or scoop-shaped blades are used respectively to increase reliability and reduce torque, but the efficiency ratings of all VAWTs are lower than those of the HAWT designs.
Design of A Wind Turbine:
Factors Affecting Efficiency
The design of a wind turbine is only one of the things affecting efficiency. First, there must be enough wind present on a regular basis to make the cost of installation worthwhile. A feasibility study is usually conducted before the turbines are installed. No turbines are efficient in all areas.
Second, the height of the tower is a factor that has nothing to do with the actual turbine’s design. The necessary height of the tower is determined to a small extent by the length of the blades.
But in small turbines, such as the ones designed for home use, the only factor used to determine how high the tower needs to be is the height of surrounding obstacles. The tower needs to be tall enough to ensure that the wind reaches the blades unobstructed.
Wind Turbine Generator and Gearbox
Another efficiency factor that has nothing to do with the design of a wind turbine is the generator component. The generator is typically a gearbox. Some gearboxes are more efficient than others.
For example, the adjustable-speed drive may be more efficient than the continuous variable transmission. Designers have differences of opinion about which gearbox is best.
Most designers agree that the horizontal wind turbine is the best choice for homeowners and wind-farms alike.
Only a few of the VAWT designs are currently in operation.
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