6.2 Energy and power in the wind
The energy contained in the wind is its kinetic energy, and in accordance with basic physical principles the kinetic energy of a moving mass (moving air in this case) is equal to half the mass, m, (of the air) times the square of its velocity, V:
It can also be shown that the power in the wind passing through a wind turbine rotor is proportional to:
- the density of the air
- the area of the rotor
- the cube of the wind velocity.
The density of air is lower at higher elevations (e.g. in mountainous regions), and average densities in cold climates may be significantly higher than in hot regions. Also, wind velocity has a very strong influence on power output because of the ‘cube law’. For example, a wind velocity increase from 6 ms–1 to 8 m s–1 will increase the power in the wind by a factor of more than two.
The power contained in the wind is not in practice the amount of power that can be extracted by a wind turbine because losses are incurred in the energy extraction/conversion process.
There are various different types of wind turbine, as you’ll see in the next section.
