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Wind power is the conversion of wind energy into a useful form, such as electricity, using wind turbines. Wind power produces about 1.5% of worldwide electricity use,and is growing rapidly, having doubled in the three years between 2005 and 2008. The size of wind machines varies widely. Small turbines used to power a single home or business may have a capacity of less than 100 kilowatts. Some large commercial sized turbines may have a capacity of 5 million watts, or 5 megawatts. There are two types of wind machines used today based on the direction of the rotating shaft (axis):
- horizontal–axis wind machines
- vertical-axis wind machines.
Horizontal-axis
Most wind machines being used today are the horizontal-axis type. Horizontal-axis wind machines have blades like airplane propellers. A typical horizontal wind machine stands as tall as a 20-story building and has three blades that span 200 feet across. The largest wind machines in the world have blades longer than a football field! Wind machines stand tall and wide to capture more wind.
Vertical-axis
Vertical–axis wind machines have blades that go from top to bottom and the most common type (Darrieus wind turbine) looks like a giant two-bladed egg beaters. The type of vertical wind machine typically stands 100 feet tall and 50 feet wide. Vertical-axis wind machines make up only a very small percent of the wind machines used today.
For a wind turbine to work efficiently, wind speeds usually must be above 12 to 14 miles per hour. Wind has to be this speed to turn the turbines fast enough to generate electricity. The turbines usually produce about 50 to 300 kilowatts of electricity each. Once electricity is made by the turbine, the electricity from the entire wind farm is collected together and sent through a transformer. There the voltage is increase to send it long distances over high power lines.
The main advantage of wind energy is the zero emission of pollutants substances and greenhouse gases.The production of wind energy does not involve any kind of waste.
The main disadvantages are relatively limited energy resource, the inconstancy due to wind speed variation and the reduced number of possible locations. Few places on Earth offer the possibility to produce enough electricity using wind energy.