WIND
POWER
Power generation
Wind power is commonly exploited as wind is available
everywhere, especially in coastal areas. Turbine generators are used to harness
this energy and convert it into electricity. The propeller is attached to a
main shaft, which in turn is attached to a gear box and then a generator (see Fig 2). The gear box allows the shaft to
rotate at a faster angular velocity (with a lower torque output) compared to
the high torque, low speed propellers of about 40rpm [2]. This allows a “generator rotation speed of 1000 or 1500
revolutions per minute” (Steisdal, 1999) [3]. As stated in Faraday’s Law,
with greater rotation speeds, a larger voltage will be produced.
Fig
2 – The basic mechanism
behind a wind turbine, showing the gear box, shafts and generator (http://www.petervaldivia.com/technology/energy/image/wind-turbine.jpg)
Location
It is more advantageous to position a wind turbine in
a windier location as then larger rotational speeds will be generated. Once a
certain wind speed is reached, however, the power output of the generator will
remain constant (see Fig 3). The
maximum power output can be achieved at a particular angular speed. If the wind
speed is too high, then the wind turbine will automatically shut down [2]. A location which is too windy,
therefore, will become a disadvantage.
Fig
3 – It can be seen that
there’s a limit in wind speed at which there is maximum power output for
a typical wind turbine. (http://www.talentfactory.dk/en/tour/wres/pwr.htm)
Generators
Some wind turbines house two separate generators
– one with a lower power output, and one with a higher output. This
allows electricity to be generated at lower wind speeds, when the rotational
speed of the shaft is too low to utilise the larger generator [2].
Effect of
blade shapes
The blades are shaped like a plane wing, and have similar
aerodynamic properties. As the wind passes over the longer side of the blade,
it travels faster than it does on the shorter side (according to
Bernoulli’s principle). This causes a higher pressure on the shorter
side, producing a force, with the longer side on the leading edge (see Fig 4) [4]. Therefore,
with longer blades, a greater torque will be produced from the bigger force,
leading to greater rotational speeds, and a higher energy output. “A
turbine’s power output is proportional to the square of the length of its
blades” (Edwards, 2008) [5].
As a result, many countries are funding research into much bigger wind
turbines, with over 100m long blades, which would be capable of power outputs
of 20 Megawatts. The first wind farm in the
Fig
4 – The aerodynamics behind
the shape of turbine blades (http://www.awea.org/faq/basicop.html)
Disadvantages
There are several problems associated with using wind
power. The major concern is that it is not guaranteed that there will be enough
wind for the generator to work, and so the power output will fluctuate
randomly. Local residents are also not happy with the sight of turbines, or the
noise they produce.