Looking inside Wind Turbine
There are two promising clean technologies : PV and wind turbine. I’ve researched only on PV. Let’s look into wind turbine.
Horizontal VS Vertical Axis
There are two types of wind turbine : Horizontal Axis Wind Turbine(HAWT) and Vertical Axis Wind Turbine(VAWT). They are defined where rotating axis is installed. In HAWT, rotating axis is parallel with the ground. On the other hand, rotating axis is vertical to ground.
HAWT is more popular in wind power industry, because it is efficient. The wind turbine is vertical to wind direction : it receives power to whole direction. Moreover, tower and blade are located in relatively higher position than VAWT. Wind speed faster in higher altitude.
VAWT is also preferred for some reasons. It can be easily installed with lower cost. It also is not affected by wind-direction. For those reasons, VAWT is adequate in city wind power. Moreover, VAWT is preferred for aesthetic reasons.
Component of Wind Turbine
There are 3 major components for wind turbine: tower, blades,gearbox. According to the picture below, 3 major components account for 61.41% of total wind turbines. There are other components: rotor hub, bearing, generator, yawing, power converter, transformer etc.
- Tower: Diameter of tower is less than 4.3 m difficult. Typcical height of tower range from 30 m to 150m high. Tower height is 2~3 times the blade in HAWT.
- Blades: It rotates and make kinetic energy. Three-blade is system is widely used. The higher blade is located more energy wind turbine can produce(Usually 40m ~ 100m from the ground in HAWT). Light, abundant, fatigue-persistent material is needed : aluminum and composite materials are used in blade.
- Gearbox: blades are connected to a gearbox to the generator. The gearbox converts kinetic energy of the blades to rotations. The rotation rate varies in size and kind of wind turbine.(15 to 1,800 rotations per minute)
- Rotor hub & bearing: Rotor hub & bearing adjust a blade not to pitch from tower.
- Yaw system: Yaw angle is the misalignment between wind and turbine pointing direction(according to wikipedia). Using sensor, yaw system adjust orientation of wind turbine and maximize efficiency and ensure the safety of wind turbine.
Size & Efficiency
Less than 10kw wind turbine is used in home. 10 ~250kw wind turbine is used in community based wind-power. 500 ~ 3MW wind turbine is used in professional windfarm.
Wind turbine works longer than PV : 70–85% of the time. According to Betz’s law, the maximal efficiency of a wind turbine as 59% : typical efficiency is about 30%.
Power in the wind is determined by density of air, turbine blade diameter, velocity of wind and a constant. The constant is composed of different factor such as area, unit conversion.
