Wind power

8.4.18
Outline the basic features of a wind generator.
2
A conventional horizontal-axis machine is sufficient.
8.4.19
Determine the power that may be delivered by a wind generator, assuming that the wind kinetic energy is completely converted into mechanical kinetic energy, and explain why this is impossible.
3

8.4.20
Solve problems involving wind power.
3

8.4.18 - Outline the basic features of a wind generator

  • What is a wind generator
  • Types of wind generator
  • Features of wind generator


What is a wind generator?


- A wind generator is often named as wind turbine. The wind turbine looks like a fan, and it works the opposite of a fan. Unlike a fan, producing wind by spinning the blades with electricity, wind generator produces mechanical power or electricity by using wind. There are varieties of wind generators, and each type has different feature and purposes. In general, small turbines are used to produce mechanical power for certain tasks (e.g. grinding grain or pumping water). Then, big turbines are often used to produce bulk power to the electical grid.

windpower.jpg
Wind turbine #1


- In most cases, a wind generator does not stand alone to produce electricity. Unless a wind generator is used to produce mechanical power for farmer, at least two or more turbines are planted to produce more electricity. The place where wind turbines are crowded is called, 'Wind farm'. In wind farm, individual turbines are interconnected with power collection system and communications system. Obviously, the most important part of deciding place for wind farm is whether there is constant and powerful wind blowing in the region. The region does not necessarily have to be in land, but it may be in ocean or mountain.

180px-Windmills_D1-D4_-_Thornton_Bank.jpg
Wind Farm located in north sea of Belgium

Source: http://en.wikipedia.org/wiki/File:Windmills_D1-D4_-_Thornton_Bank.jpg

wind-farm.jpg
Basic Features of Wind Farm

Source: http://www.alternative-energy-news.info/technology/wind-power/wind-farms/


Types of wind generator


- There are two types of wind turbines. The first one is 'horizontal axis turbine' and this model is the most frequently used one. Another type is called, 'vertical axis turbine'.

1) Horizontal-axis wind turbine (HAWT)
- Feature: HAWT has its main motor and electricity generator on top of its tower. The most vivid feature is that the blades head toward the wind. Most of them have gear box which changes slow rotation into fast rotation.

- Advantage: High efficiency because blades always move perpendicularly to the wind. Tall tower of HAWT allows the turbine to contact with stronger wind. Therefore, it increases the wind speed by 20% which is related to increase in power output (37%). Finally, the angles of blades are adjustable, these maximizes the total amount of power achieving from same wind.

- Disadvantage: It is very expansive to build a tall HAWT since it needs huge blades and supportive tower. Because of the size, the cost of transportation increases. Therefore, the installation is the problem.

e-126-wind_turbine.jpg
Largest HAWT in World

Source: http://tothewindmills.wordpress.com/2008/03/10/eponymous/

2) Vertical-axis wind turbine (VAWT)
- Feature: VAWT has its main motor spinning vertically to the direction of wind. Even though HAWT is the basic model of wind turbine in this world, VAWT is used in variety of places where wind changes frequently and wind blows fast in lower attitude.

- Advantage: VAWT is not massive compare to HAWT, therefore, it does not cost as much as VAWT. Also, since it does not need tower to support gear box and generator (most of VAWTs have their gear box and generators on the ground), it is easy to construct and to change parts. Finally, VAWT is not as noisy as HAWT.

- Disadvantage: Not as efficiency as HAWT(only 50% efficiency). Also, because wind speed near ground is not too fast, the power produced by VAWT is not as great as the one of HAWT

Darrieus-windmill.jpg
Picture of VAWT

Source: http://en.wikipedia.org/wiki/File:Darrieus-windmill.jpg


Features of wind generator

<Inside and outside of the wind turbine (HAWT)>
EERE_illust_large_turbine.gif
Inside of horizontal axis turbine
- Anemometer: This device measures and transmits wind speed data to the controller.
- Blades: The most important part of turbine. Most turbines have two or three blades. The wind makes the blades to lift and rotate.
- Brake: Used to stop blade if there is an emergency
- Controller: Controller starts the generator at wind speed between 8 to 16 MPH. It stops the generator when the speed is over 55 mph because it may damage the device.
- Gear box: Gear box is connected to low/high speed shafts in order to increase the speed from 30~60 rpm to 1000~1800rpm. Because gear box is the expansive part of turbine, it is still required to find an alternative method for gear box
- Generator: Device that produces electricity
- High/Low speed shaft: Shaft that rotates to drive the generators.
- Nacelle: Nacelle is basically the container of devices in wind generator.
- Tower: Tower is the part that supports nacelle.
- Wind vane: This device measures wind direction.
- Yaw motor/drive: Yaw drive keep the rotor to face the wind direction. Yaw motor powers the drive.

Source: http://en.wikipedia.org/wiki/File:EERE_illust_large_turbine.gif

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