Harnessing Wind Energy
Length: 530 words (1.5 double-spaced pages)
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The earliest known uses of wind power date back to 3000 BC, when people used wind to sail ships. Approximately 4000 years later, windmills were used in Europe to grind tobacco, wheat, and other grains. Later, in the 1700's, windmills were then used to pump water. It was not until the 1900's that wind mills were used for generating electric power. In the United States, windmills were used prior to widespead electrical distribution.
The generation of wind can be traced back to solar energy. It is ultimately a renewable and clean energy source. This is what makes it attractive to many as a source of energy for power plants.
Wind is created as a result of pressure differences in the atmosphere which is caused by temperature differences of radiating solar energy. Other factors that contribute to the flow of air (wind) is the rotation of the earth, and it's terrain. We could expect more wind over bodies of water since water provides less resistance to wind than do objects on the surface of the earth.
If wind is essentially free, why don't we see more windmills? The reason is that wind doesn't blow whenever we need power. Wind energy can only be stored in batteries and much of the energy from wind can not be harnessed into useful energy. The public also views wind generators as an eyesore on the landscape.
Wind, initially is in the form of kinetic energy, thus it has the equation: 1/2mv^2, where m is the mass, and v is velocity of the air. Using the fact that the mass is equal to the volume times the density, we can rewrite the equation for kinetic energy as
k.e. = 1/2Vpv^2, where V is the volume, and p is the density of air.
Furthermore, the volume through a surface is equal to the area of the surface times the velocity of the air, times the time, thus the equation becomes
k.e. = 1/2pv^3At, where A is the area of the surface and t is the time.
Since power is energy per unit time, the available power is
P = 1/2pv^3A
This equation is of interest, since it demonstrates that wind power is a function of the velocity cubed. In fact it would not be practicle to put a wind generator, unless the site averaged at least 14 miles per hour of moving air.
The equation would be the ideal amount of power, in practice the maximum power is about 59% of this value, and of that 59%, 70 percent can be converted to electrical power, the rest is lost to friction, heat, and other irreversibilities. This is one of the draw backs of using electrical power by wind generation.