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Wind energy is a plentiful, renewable, alternative energy source to fossil fuels that does not produce greenhouse gases. Wind energy or wind power is the harnessing of the natural wind flow created by the uneven heating of the earth’s atmosphere by the sun, the earth’s rotation, and surface irregularities in the earth. The motion of the wind, or its kinetic energy, can be processed into electricity or into mechanical power to perform tasks such as pumping water. Harnessing the power of the wind is a promising way to meet the growing demand for electricity while avoiding harmful environmental impacts.
Humans have used the energy of the wind for centuries. Wind powered sailing ships along the Nile River by 5000 B.C. in Egypt, and by 200 B.C., the Chinese used windmills to pump water and the Persians used them to grind grain. In the Middle Ages, food production, particularly the milling and grinding of grains, was powered by windmills in both the Middle East and Europe. Windmills powered pumps to drain lakes and marshes in northern Europe. Immigrants to the United States used the same technology to pump water on farms for livestock and irrigation, as well as for steam locomotives. Wind turbines produced electricity in the areas of the rural United States in the first half of the 20th century that were not connected to the central power grid, until the Rural Electrification Administration brought nearly every household into the power grid in the 1950s. The price increases and shortages from the oil embargo of 1973 provoked private and public groups to invest in wind energy again. Small-scale turbines for home and community use appeared on the market in the late 1970s and the first commercial wind farms and wind power plants appeared in Europe and the United States in the 1980s. Wind power is now the fastest-growing energy resource in the world.
The kinetic energy of the wind is converted into electric energy by the turbine. Wind moves the blades of wind turbines, which in turn spins a shaft connected to a generator that makes electricity. There are two types of wind turbines: horizontal-axis and vertical-axis turbines. The more common horizontal-axis turbines have two to three blades and most commonly face upwind. Vertical axis turbines, which resemble eggbeaters, do not have to face upwind and are therefore suitable for sites with more variable winds. The size and electrical output of wind turbines depends on their use. Turbines used by utility companies can generate anywhere from 100 kilowatts to several megawatts of electricity. Small turbines that generate under 100 kilowatts are used to power homes and water pumps on farms.
Wind farms, or wind parks, are groups of wind turbines set in one location that provide electricity for the utility grid. These wind farms can have hundreds of turbines spread over thousands of acres of land that produce hundreds of megawatts of electricity. To determine whether a site is a good candidate for a wind farm, meteorological data about the site’s wind speed and direction must be recorded for one year or longer from a tower near to the proposed site. Suitable sites need an average wind speed of 10 miles per hour or greater, a constant windflow, and should not be subject to sudden strong bursts of wind. Favorable wind sites include high altitudes, sites near lakes, bays, or the ocean, and areas far from upwind obstacles such as trees and buildings. Sites should also have easy access to transmission capacity for the electricity produced.
The wind over the ocean reaches higher velocities than onshore wind and lacks obstacles such as buildings, mountains, and trees to slow its flow. Offshore wind farms take advantage of these constant, high velocity winds. Many countries have installed offshore wind farms in shallow coastal waters. Research is underway to reinforce tower foundations and account for increased wind speed and turbulence over deeper waters. Current offshore wind farms consist of turbines attached to a tower and support structure that are anchored by piles driven into the ground below the ocean. As with onshore wind turbines, offshore turbines convert the wind’s kinetic energy into electricity via generators. The electricity generated is sent to a transformer via undersea cables. The energy is converted to high voltage and send to substations. Offshore wind turbines are modified to withstand the harsh conditions offshore, such as the salty sea air and wave surges, and are built with special access platforms for maintenance. Offshore wind turbines are also larger than onshore turbines to take advantage of the higher and steadier winds.
Small-scale use of wind energy, or “small wind”, is the use of wind energy to power individual homes, businesses, or communities. Small wind turbines are different than large turbines in more than size. Small turbines can be “on grid” or “off-grid”, meaning they can be connected to the existing electrical grid or not. Systems that are “on grid” use power from the turbine when available and from the grid when supplemental power is necessary. Some small turbines use induction generators that produce AC electricity that is compatible with the existing grid. Others must use inverters to convert DC energy to grid-acceptable AC energy, step-up transformers, and other equipment to connect safely and efficiently. Many utility companies “buy back” excess energy from small wind turbines that is not used by the owner, which results in lower electricity bills when the owner does use electricity from the grid. “Off-grid” systems usually include a storage device, such as batteries, that stores excess electricity generated during windy periods for use during calm periods or when supplemental power is needed.
Commercial wind turbines cost approximately $3.5 million, including installation. Small turbines that power individual homes cost $35,000 to $50,000. For owners of small wind systems, financial benefits include tax savings, revenue for excess energy produced, and money saved by not purchasing electricity from the grid.
In many areas, wind generated electricity is on-par or cheaper for consumers than traditionally derived electricity. Cost per kilowatt hour is difficult to calculate for wind and other sources and many experts disagree on the true cost of each form of energy. The cost of energy takes into account the total cost of the project and its installation, recurring operation and maintenance costs, administrative costs, and annual energy production. These figures do not take taxes, tax breaks, and other incentives into account. Wind energy supplies electricity at the rate of 4 to 6 cents per kilowatt hour, although some experts state a price as high as 9.9 cents. The cost of hydroelectric power ranges from 5.1 to 11.3 cents per kilowatt hour, and solar power from 15 to 30 cents per kilowatt hour. The cost of electricity from these renewable sources is expected to decline with technological advances. Power from traditional sources is currently cheaper, although environmental regulations make the construction of coal and nuclear power plants difficult in many countries. Gas-fired electrical plants produce power at the rate of 3.9 to 4.4 cents per kilowatt hour. That cost is variable and fluctuates with the cost of fuel. Coal-fired electrical plants supply energy at the rate of 4.8 to 5.5 cents per kilowatt hour, although new high efficiency and low-environmental impact plants have a price as high as 11 cents. Nuclear power plants supply energy at the rate of 11.1 to 14.5 cents per kilowatt hour, although that price can rise to as high as 25 cents in a newly constructed plant.
Wind energy is desirable for its low environmental impact. Wind energy does not produce air emissions because there are no combustible fuels involved in the electricity’s generation. Turbines do not discharge water or generate solid waste, although turbines in areas with rainfall insufficient to clean them will require water for cleaning dirt and insects from the turbine blades. Wind turbines require large amounts of land onshore, although this land can be used for agriculture or for livestock grazing. There is no adverse impact on the land when wind turbines are removed. Wind farms do pose a threat to birds and bats, although the extent of this danger is still under study and new technologies are being developed to mitigate the threat to wildlife.
The future of wind energy is bright, as energy demand and environmental concern grow and the prices of fossil fuels rise. The global wind capacity is projected to grow exponentially with new on- and off-shore installations. Research into deep-water off-shore wind farms and in land-based systems that can operate with lower wind speeds is underway. On- and off-shore turbines are growing in capacity and efficiency. The United States Department of Energy estimates that increasing the percentage of electricity generated by wind from 1 percent to 20 percent is feasible, reliable, and affordable.
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