Wind energy

Wind energy has been a significant energy resource throughout human history, beginning from its use by ancient sailboats to its employment in modern large-scale electrical generators. In the twenty-first century, it is one of the fastest-growing energy sources in the world. Wind energy is a clean, renewable, and free power source that is a viable alternative to fossil fuels, which pollute the environment and promote global warming.

Background

Wind energy has been employed by humans as early as the fourth-century BCE. In this era, Egyptians used the wind to propel sailboats on the Nile River. Shortly afterward, sailing vessels began to appear in the Mediterranean Sea. Another ancient invention was the windmill, a machine that converts wind energy into mechanical energy using sails or blades connected to a rotating shaft. The first documented use of a windmill was in Persia, as shown in a drawing dating from about 500 BCE. Similar windmills became common in areas ranging from the Middle East to China for purposes such as pumping water and milling grain.

During the twelfth century, the first European windmills appeared in England and France. These wooden machines were called post mills, because they had a central vertical post. They employed a horizontal windshaft, had a revolving platform atop the post, and were rotated by hand. In the fourteenth century, a larger and sturdier windmill called the tower mill was developed. The tower mill had a stationary body that supported a rotatable wooden cap, to which the rotor was attached. The blades faced the wind, and there was storage space for the grain at the base. This windmill was popular in Holland, where windmills were used for land drainage. Between 1300 and 1850 CE, windmills provided about 25 percent of Europe’s industrial power. They were used for grinding dyes, spices, and paint pigment as well as for irrigation and grain milling.

In the nineteenth and early twentieth centuries, windmills played an essential role in the development of the western and Great Plains regions of the United States. In 1854, Daniel Halladay designed small, multibladed, and inexpensive windmills that were sturdy enough for the Great Plains. American farmers and homesteaders used windmills to pump underground water to the surface. Windmill-generated water was crucial for livestock, human use, crop irrigation, and steam locomotives. Windmills made the arid Great Plains bloom, opening up the West to towns, farms, and most importantly, the transcontinental railroad. Windmills were responsible for changing cattle ranching from a nomadic to a stable business and transforming the Great Plains into a breadbasket. Between 1880 and 1930, approximately 6 million windmills were installed in the western United States and the Great Plains.

As Europe and the United States became industrialized, the steam engine gradually replaced water-pumping windmills in Europe, and electricity replaced wind power in rural America. The Rural Electrification Act of 1936 provided low-cost federal loans for bringing electricity into rural areas. Low-cost power from town and regional electric generators became available, and power lines were extended to remote areas of the country. In 1935, only 11 percent of the farms in the United States had electric service, but by the early 1970s, about 98 percent did.

Larger windmills called wind turbines were soon developed that could generate electricity. In 1890, in Denmark, P. LaCour built the first windmill capable of generating electricity. In 1941, Palmer Putnam built the world’s largest wind turbine on a windy mountaintop called Grandpa’s Knob in Vermont. This nearly 230-metric-ton generator served an entire town by feeding electric power into the existing local utility grid.

Meanwhile, however, energy from fossil fuels (coal, natural gas, and oil) largely displaced wind power in most applications, including electricity generation. After World War II, nuclear energy also became an option. Nonetheless, some researchers, especially in Europe, continued to develop wind-power technologies. From 1956 to 1957 in Denmark, Johannes Juul built the world’s first alternating current (AC) wind turbine, and the very efficient Gedser wind turbine. The 1973 oil crisis, the environmental movement, and growing concerns about the dangers of atomic energy led to renewed interest in wind power and other renewable energy sources in the late twentieth century. Electricity generated by renewable energy sources is also called “green” power. During the 1990s, wind power was one of the fastest-growing sources of energy. This growth continued into the twenty-first century as global concern over the role of fossil fuels in climate change accelerated.

Wind Energy Technology

When the Sun warms areas of Earth at different rates and the various surfaces absorb or reflect the radiation differently, there are differences in air pressure. As hot air rises, cooler air comes in to replace it. The result is wind, or air in motion. Air has mass, and moving air contains kinetic energy, the energy of that motion.

Windmills convert wind energy into mechanical power or electricity. Modern electricity windmills are called wind turbines or wind generators. In the wind turbine, wind turns two or three propeller-like rotor blades, which are the sails of the system. When the blades move, energy is transferred to the rotor. The wind shaft is connected to the rotor’s center, so both the rotor and shaft spin. The rotational energy is thus transferred to the shaft, which spins an electrical generator at the other end.

The ability to generate electricity is measured in units of power called watts. A kilowatt represents 1,000 watts, a megawatt is 1 million watts, and a gigawatt represents 1 billion watts. Electricity and production are described in kilowatt-hours. Multiplying the number of kilowatts by the number of hours equals the kilowatt-hours. One kilowatt-hour equals the energy of one kilowatt produced or used for a period of one hour.

The turbine’s size and the speed of the wind through the rotor determine the output of the turbine. By the early 2020s, large offshore wind turbines could exceed a power rating of 10 megawatts, with some prototypes even approaching 20 megawatts. Onshore wind turbines tend to be rated under 10 megawatts. Wind turbines can generate electricity for an individual building or for widespread distribution by connecting to an electricity grid or network.

Wind Farms

A wind farm or wind power plant is a group of large wind turbines (660 kilowatts and up) installed in the same location to jointly capture wind and produce electricity. There can be up to about one hundred individual modules or turbines sited far apart and covering an extended area of hundreds of square kilometers. Turbines can be added as the need arises. Individual modules connect with a medium-voltage (usually 34.5-kilovolt) power collection system. Then a substation transformer increases the medium voltage of electrical current for connection with a high-voltage transmission system.

Wind farms are best located in areas with consistent, strong, and unobstructed winds, such as high plains, mountain passes, and coastlines. In rural, agricultural areas, the land between the turbines can still be used for farming. Wind farms can also be sited in the ocean, where there tend to be stronger and more consistent winds than on land. Such installations are known as offshore wind power.

Advantages and Disadvantages

The first advantage of wind energy is that the fuel is free. The main costs of generating electricity from wind are those of installation, operation, and maintenance. Proponents note that these costs have dropped in many cases as the wind power industry has grown and matured, making wind energy more competitive with fossil fuels. Supporters also suggest that wind power can help promote energy independence from expensive imported energy, and thus reduce national economic and security risks. Developing the wind industry can create net job growth at the local and national levels.

Environmentalists also point out that wind energy has significant long-term benefits for the environment, human health, and global climate change. Wind is a clean, renewable energy resource that is inexhaustible and easily replenished by nature. Wind power plants do not pollute the air or need waste cleanups like fossil-fuel and nuclear-generation plants, and wind turbines do not emit greenhouse gases or cause acid rain. While critics have argued that installation of wind turbines can be environmentally disruptive and turbine blades can threaten birds and other wildlife, most scientists suggest these concerns can be mitigated and are ultimately less damaging than continued reliance on fossil fuels.

A significant disadvantage is that wind is inconsistent and intermittent. It is variable power that does not always blow at times of electrical demands. To be cost-effective, wind sites are located where both strong winds and land are available, usually in remote locations, far from large population centers where consumer demand is the greatest. For instance, many of China’s major wind-energy resources are located in the Northern China wind belt, including the sparsely populated Xinjiang Uygur and the windy grasslands of Nei Monggol. Even in locations where winds are strong, there are wide differences in wind velocities over relatively short distances.

To meet these challenges, storage of surplus wind energy and electrical distribution systems to transmit this energy to consumers are necessary. Wind power can be stored in batteries, and technology already exists that can convert wind energy into fuels such as ethanol and hydrogen. However, economic feasibility is a major consideration. Enhanced electrical transmission systems improve reliability for consumers, relieve congestion in existing systems, and provide access to new and remote wind-generation sources. Typically, large wind plants are connected to the local electric utility transmission network. There have also been proposals for super grids of interconnected wind farms to alleviate supply and demand issues.

On a smaller scale, distributed energy is a viable solution. Consumers can make their own wind power with a private wind turbine and batteries as backup. As more communities or individual consumers use distributed energy, they can also help lower the costs of central wind power plants and transmission systems. Applications of small-scale wind power include offshore platform lighting, remote homes and cabins, utility-connected homes and businesses, water pumping, and telecommunications. In such situations, wind generators often work as part of a hybrid wind-solar battery-charging system. Also, small domestic turbines can complement power from a larger electrical power system, with utility companies buying back any surplus electricity.

There are also aesthetic and environmental concerns surrounding the large-scale implementation of wind energy. Local residents and public advocacy groups have often opposed wind farms because of the rotor noise, visual impact, and potential harm to property values and local wildlife and its habitats. In some cases, technological advances and the appropriate siting of the wind generators away from populated areas have mitigated the problems.

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