Wind is created by temperature gradients , created by differences in heat received on the surface of the earth as a result of incoming radiation from the Sun. These gradients depend on the angle of the incident sunlight, as well as the characteristics of the terrain and are vital for the formation of specific regional climates. Land and water masses have different heat capacities which lead to an uneven heating of the planet’s surface.
As there are different temperatures in different regions due to the aforementioned reasons, bulk motion of air molecules is created as the density of air changes with temperature, leading to concentration gradients and pressure gradients. These pressure gradients are what is we call “wind”. A fluid in a pressure differential will move from higher to lower pressure areas at different speeds, as the pressure gradient changes over time.
Major components of the creation and behavior of wind is the rotating motion of the Earth around itself, known as the Coriolis Effect, which is negligible along the equator due to Earth’s radius being larger, and boundary layers formed when air comes into contact with the Earth’s surface.
Fig 1. Wind Circulation System (Hadley Cell) ,
Source : https://www.fas.org/irp/imint/docs/rst/Sect14/Sect14_1c.html
Wind as a renewable energy source
Wind power is very environmental friend energy source, as it emits no carbon dioxide (except for the process of turbine creation). It is a clean and relatively accessible power source with high scalability from small to large applications.
Although the wind is stochastic in nature, with a lot of unpredictability over the span of a few minutes, on an annual basis is very dependable with little variations of total extractable power.
Wind energy is the sum of kinetic energy of the air molecules due to pressure differentials.
and power is Energy per unit time ,where, in both equations, A is the area of a disc, ρ is the density of air and U is the velocity.
It is clear from the above equations that wind power is proportional to the cube of the incoming wind speed, thus areas with higher wind speeds are optimal for wind energy capture.
Total Amount of Extractable Power
The wind as a resource is greater than our current energy usage from all different sources. Studies conducted by Axel Kleidon in Germany concluded that there is an extractable amount of power between 18TW and 68 TW. These studies where done by calculating the incoming solar energy that creates the temperature gradients.
Other studies by Christina Archer and Mark Jacobson found that there is an extractable amount of 1700 TW of power at 100 meters above sea level (although they were not based on actual measurements of wind speeds, like Kleidon’s). As they stated, something between 72 and 170 TW could be extracted with practical and financially viable means. In their paper, Jacobson et al, 2012 later estimated...