Wind is created by the uneven heating of the earth creating temperature, density and pressure differences. In tropical regions there is a net gain of solar radiant energy resulting in heat. In the polar region solar radiation is minimal and we see a net loss of heat. Air at the equator is heated and is raised into the atmosphere. Cooler air from the north replaces the rising warm air. As the warm air loses heat energy it falls back to the earth’s surface at the 30º N and 30ºS latitude. This air is very dry and moves east due to the rotation of the earth. Due to this cycle wind is generated.
Wind turbines have been used for thousands of years to convert the kinetic energy to mechanical energy to allow simple machines to grind grain and pump water. During the 19th century wind turbines contributed greatly to economic development of the U.S. but during the 20th century declined due to the exploitation of fossil fuels. During the energy crisis of 1973 the development of wind turbines to generate electricity resumed. Today wind turbines are used to produce electricity. Only about 0.10 % of the U.S. electrical production comes from wind turbines.6
Modern wind turbines operate with a rotor, transmission, generator, and a control panel. Wind drives the rotor creating a rotation speed of 40-100 rpm’s. The transmission transfers the low revolution to a high speed shaft for electricity production. The control panel monitors wind speed and direction and regulates turbine operation. Turbines are classified as horizontal axis and vertical axis. Horizontal axis machines contain blade resembling an airplane propeller. 6 This type can attain energy conversions efficiencies as high as 45% of the wind energy. Vertical-axis turbines have two to three fixed pitched blades with both ends attached to a rotating vertical tower. They are easier to maintain, accept wind from any direction and do not require protective features to guard against high winds. However, the efficiency is about 10% less than a horizontal unit. 7
Most of the electricity production from wind occurs on large wind farms. These wind farms are predominately owned by independent producers who operate the farms and sell electricity to the utility company for distribution. The Public Utility Regulatory Act (PURPA) requires these producers to sell the electricity at reasonable rate.
Wind energy is a free source of energy. In the use of electricity generation turbines produce no water or air pollution. Wind farms can be inexpensive to build with the right engineering and the land around the farm can be used for other uses (how about crops for biomass energy). Due to the fluctuation of wind patterns wind power can be variable. For optimal electrical production these systems require constant and significant amounts of wind. Planning issue also revolve around wind farms. A common concern is the visual impacts to the landscape.6