Just like solar power, wind power is another renewable energy source with zero carbon emissions. This is only if you consider the entire life cycle of the wind farm to be carbon emissions free. A group of wind turbines together are called as a wind farm. Remember, a windmill when used for electricity generation is called as a wind turbine. There are two kinds of windfarms: offshore and onshore. As self-explanatory it is, offshore windfarms are on land while those are not are on the sea. The first onshore windfarm was built in 1980 in the USA and first offshore windfarm in the UK, eleven years after.
Stuff that makes a wind turbine:
A wind turbine can rotate either about a horizontal axis or a vertical axis. What you see these days are horizontal axis wind turbines. Following are the parts/stuff that are needed to make a horizontal axis wind turbine:
- Rotor blades or simply blades
- Shaft: High speed shaft and Low speed shaft
- Nacelle : House of the Generator and the Gear Box/Transmission
- Anemometer and Wind vane
- Yaw drive and Yaw motor
Let’s look at them one by one:
Rotor blades: These are just like the one in a helicopter but placed in a different way. When wind flows, it creates a low pressure area behind the blade which pulls it and makes it turn. The blades keeps turning as long as the wind keeps flowing. Most wind turbines have two or three blades. Wind turbines with two bladed designs are cheaper and efficient than three bladed designs. But two bladed designs are noisy and hence are suitable for offshore windfarms. The shape of these blades is guided by aerodynamic studies. These blades have to be long, light, thin, strong and cost effective. Material of construction (MOC) for blades include glass fiber and carbon fiber. Aluminum and wood are also considered as MOC but mainly for small scale wind turbines. From afar, the blades will seem to be moving at a very slow speed. It is around 20 rpm http://www.ecw.org/windpower/web/cat2a.html (revolutions per minute). The tip of the blade though is running at 150 mph (miles per hour) or 241 kph (kilometre per hour). Look at this video and see what a speed of 150 mph means.
Shaft: There are two kinds of shafts in a wind turbine, high speed and low speed. In the horizontal axis wind turbines, these shafts align with the direction of the wind. The low speed shaft is connected to the center of the rotor, the point where the blades meet. The blades transfer their rotational energy to mechanical energy here. The high speed shaft drives the generator.
Nacelle: This section contains the generator and the gear box. The generator is what produces electricity. The capacity of the generator varies according to its application. It uses the principle of electromagnetic induction. It is a conductor (a coiled wire) surrounded by magnets. When one moves with respect to another, it induces voltage in the conductor, which in turn generates current flow. The gear box is an assembly of parts similar to a wrist watch i.e. a set of gears. It connects the two shafts together. This amplifies the incoming speed to a much larger speed suitable for power generation. Now we have the mechanical energy converted into electrical energy.
Tower: All horizontal axis wind mills have a tower. It takes the blades to the desired altitude. This year GE launched a new kind of tower called the space frame tower. Have a look at it here. The most widely used material for tower construction is steel. It is a lattice framework like the one by GE and is covered up by other materials like PVC.
Anemometer and Wind vane: Anemometer measures wind speed and a wind vane measures wind direction. Both these data are transferred to the controller which then makes sure the wind turbines works efficiently no matter what the wind speed or direction is.
Controller: It knows when to start a wind turbine and when to shut it off. Too much wind and there is a fear of damage to the wind turbine.
Break: Stops the wind turbine during emergencies.
Pitch: It helps rotor speed within operational limits. It is guided by the controller.
Yaw drive and yaw motor: These keep the rotor facing the wind direction wherever the wind blows.
Base/Foundation: This is the structural support on which the wind turbines stand tall and fixed to the ground. It is made of cement.
Paint/color: Wind turbines are colored white for aesthetic purpose.
Have a deeper look at the wind turbine by clicking here.