In ancient times, wind was used to move the sails of the ships. In this chapter, we will see how wind energy is used to generate electricity.
A turbine converts the kinetic energy of the wind to useful mechanical energy. This energy could be used in mechanical form or turn generator turbines and provide electricity. Just like in the hydropower systems, wind energy is harnessed through conversion of the wind kinetic energy to mechanical energy.
The wind turbines are largely classified into two types- Horizontal Axis Wind Turbines and Vertical Axis Wind Turbines. Large areas installed with wind turbines, that is, wind farms are increasingly emerging today.
There are general characteristics of wind while others are more specific to the site. Some of the site specific characteristics include −
Mean wind speed − This estimates the annual wind yield though it does not give the distributions.
Wind speed distribution − There are three aspects namely annual, diurnal and seasonal characteristics. Understanding the wind speed variations and the spread is necessary when choosing a site.
Turbulance − This is the chaotic movement of wind in unpredictable patterns. Turbulance results from continuously changing properties of wind motion that impact on energy production and fatigue on blades.
Long term fluctuation − Irregular wind causes unpredictable energy supply. Before a wind turbine is set, the area should be studied for a constant wind flux.
Distribution of wind direction − This is more significant in positioning of the blades especially for horizontal axis types.
Wind shear − Shear is change in wind direction, speed or the height at which the maximum velocity occurs.
Wind patterns are important and are often analyzed using a wind spectrum. A high value of the wind spectrum represents a large change in the wind speed at the given time interval. If represented on a graph, the peaks depict turbulences that occur with time.
There are three distributions −
Diurnal − Caused by the difference between temperatures during the day and at night.
Depressions − Occur with four-day intervals along the coastal region.
Annual − Distribution is latitude dependent.