advantages of wind energy
Wind energy is created using kinetic energy into electric power.
What is wind turbine?
Efficiency of a wind turbine
The wind's kinetic energy forces the aerodynamic blades of a turbine to rotate, but air that has passed through the swept area becomes slower and more turbulent.
Because of this, only a proportion of the available wind energy, between 30 to 40%, can be converted into electricity (the efficiency of a wind turbine).
There are very few parts of the world with a constant and useful wind speed, so power generation can be considered only as a local resource. Losses due to friction mean that a minimum wind speed of around 5 m s-1 is needed to start the blades rotating.
With speeds over about 12 m s-1 damage to the turbine might result, so the turbine blades are progressively twisted (feathered) to present a smaller effective area to the wind. The net outcome is that the average power at a well-selected site is only around 30% of a turbine's rated capacity.
The power available to a wind turbine depends on its size and the wind speed.
The kinetic energy of wind is proportional to the mass (m) of air moving through a turbine and the square of its speed (v):
In one second, the mass, m, of air passing through a turbine is given by:
where ρ is the density of air, A is the swept area of the turbine (i.e. the area swept out by the rotating blades) and v is the wind speed.
Therefore, the kinetic energy per second, or the power available to a turbine is:
So, wind power is proportional to the cube of wind speed.
Consequently, the output of a wind turbine varies dramatically with wind speed.
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