In reality, wind energy is a converted form of solar energy. The sun’s radiation heats different parts of the earth at different rates-most notably during the day and night, but also when different surfaces (for example, water and land) absorb or reflect at different rates. This in turn causes portions of the atmosphere to warm differently. Hot air rises, reducing the atmospheric pressure at the earth’s surface, and cooler air is drawn in to replace it. The result is wind.
Air has mass, and when it is in motion, it contains the energy of that motion (“kinetic energy”). Some portion of that energy can converted into other forms mechanical force or electricity that we can use to perform work.
A wind energy system transforms the kinetic energy of the wind into mechanical or electrical energy that can be harnessed for practical use. Mechanical energy is most commonly used for pumping water in rural or remote locations- the “farm windmill” still seen in many rural areas of the U.S. is a mechanical wind pumper – but it can also be used for many other purposes (grinding grain, sawing, pushing a sailboat, etc.). Wind electric turbines generate electricity for homes and businesses and for sale to utilities.
There are two basic designs of wind electric turbines: vertical-axis, or “egg-beater” style, and horizontal-axis (propeller-style) machines. Horizontal-axis wind turbines are most common today, constituting nearly all of the “utility-scale” (100 kilowatts, kW, capacity and larger) turbines in the global market.
Electricity generated by a utility-scale wind turbine is normally collected and fed into utility power lines, where it is mixed with electricity from other power plants and delivered to utility customers. Today turbines with capacities as large as 5,000 kW (5 MW) are being tested.
Source: The American Wind Energy Association, 2008