Wind Energy Basics

Since wind is a converted form of solar energy, wind energy and solar energy go hand in hand. The radiation from the sun heats the various parts of the earth at differing rates. This occurs because the different surfaces of the earth, e.g. water and land, absorb or reflect the sun’s radiation at different rates. Consequently, sections of the atmosphere warm differently. As hot air rises, the atmospheric pressure at the earth’s surface is reduced, causing cooler air to be drawn in to replace it; the result of which is wind.

The energy that the wind then produces can be transformed by a wind energy system into mechanical or electrical energy, which can then be harnessed for functional use. Mechanical wind energy is most often used to pump water in the form of a farm windmill found in rural locations. The farm windmill is one example of a mechanical wind pumper which can be used for many other purposes as well, such as sawing, grinding grain, and pushing a sailboat. Electrical wind energy is generated through the use of electrical turbines, which create electricity for homes and businesses and to sell to utilities.

Electrical wind turbines come in two basic designs: vertical-axis, or “egg-beater” style, and horizontal-axis, or “propeller” style. The horizontal-axis wind turbines constitute almost all of the “utility-scale” turbines in the global market, which consequently makes them the most common type of wind turbine used today.

Utility-scale wind turbines used on land-based wind farms are available in a variety of sizes. The rotor diameters of these turbines range from 50 to 90 meters with towers of roughly the same size. A turbine that has a 90-meter rotor and a 90-meter tower for a total height of approximately 135 meters would definitely fall on the large end of the size spectrum for wind turbines. Offshore turbine designs, however, are currently under development to have even larger rotors.

Turbines that are intended to be used for homes or small business are much smaller. The rotor diameters of these turbines are typically 8 meters or less and are placed on towers measuring 40 meters or less in height.

The electrical output of a wind turbine depends on both the size of the turbine and the speed of the wind through the rotor. Wind turbines manufactured today have a range of power ratings from 250 watts to 5 megawatts. Not surprisingly, wind speed is a crucial factor in determining the efficiency of a turbine. For small turbines, an annual average wind speed that is greater than 9 miles per hour is required, while utility-scale turbines necessitate a minimum speed of 13 miles per hour.