Wind Energy
Authors: Carpentier Monique 
Published: March 2010

Wind energy comes originally from the sun. The sun heats the atmosphere unevenly and creates air movement between hot and cold regions: Approximately 2% of the energy from the sun is transformed into "kinetic" from the air. Some 35% of the kinetic energy is dispersed in an atmospheric layer, one kilometre thick. If only 1O% of the available wind energy is produced on the earth's surface, there is a potential of 1.3 × 1014 W for the whole planet. If this power were harnessed and made available, the energy produced on a yearly basis would be equivalent to 10 to 15 times the actual energy consumption of the world; obviously, it is not possible to harness all the wind energy on the surface of the earth, not to mention oceans. Nevertheless, these numbers show the potential importance of wind energy among the "renewables". In Canada alone, there is a potential of at least 50 000 MW in a radius of less than one hundred miles from existing transmission lines.

Unfortunately, wind energy has to be taken "where is and as is". It cannot be transported, accumulated, or concentrated in its original form. Nevertheless, wind energy has obvious advantages; it is inexhauslible and is not influenced by political borders.

Energy and Power from the Wind

A mass moving at a certain speed had a kinetic energy of 1/2 m V2. If the flow is moving at a speed V, perpendicular to the surface S, the mass of air going through the surface per second is given by: Ms = SVp, where p is [he air density (p = 1.25 kg/m3). The kinetic energy available per second which is the power, is equal to:

(Equation in full paper)

With S in m2, p in kg/m3 and V in m/sec., P is in watts. If one doubles the wind speed, the wind power will go up by a factor of eight. However, no energy transformation is perfect. If all the kinetic energy in the air approaching a wind turbine were extracted by the spinning blades, the air would stop. But the air cannot stop. If it did, all the rest of the air behind it would have to spill around the rotor. Betz has shown that maximum conversion "Betz efficiency" is about 59.3%. "Cp" is the ratio of the power that a wind turbine can extract from the total power contained in the flow (Cp max, = 0.593). Every type of wind turbine has its own characteristic C" (Fig. 1).

Principle of Wind Turbine Operation

There are two major wind turbine families-drag machines (Savonius rotor) and lift machines (Darrieus rotor).

Drag machines generally use the wind to rotate a horizontal axle with vertical blades attached to it. Each blade has a different drag coefficient* for its concave and convex surface (C concave**, C convex). The difference in drag forces (F concave*** - F convex) makes the system rotate (Fig. 2).led. Windfarm developers lease or purchase wind rights on a suitable tract, purchase wind turbines from various manufacturers, contract for the installation of the equipment, negotiate power sales contract with one of the California utility companies, and arrange financing through limited partnerships.

The impetus for this activity is due to three factors:Substantial U.S. energy tax credits are available to individual investors who enter into limited partnership agreements with a wind farm developer.