Wind power

Devices that use wind as an energy source are the oldest known devices engineered specifically to produce power. From ancient grain mills to today’s complex wind turbines, wind has provided humanity with an important power source. As the world’s demand for energy has increased at an accelerating rate, the use of wind power as an alternative energy source has earned much attention.

Early Uses

The wind has long been used by humans as a source of energy. A sailboat was likely the first device designed to use wind power to replace human energy; sailing craft have been in use since prehistoric times. It was obvious long before the development of modern science and engineering that if the wind could push increasingly large sailing craft, then it could be harnessed for other tasks as well. A full thousand years after the first sailing craft, the first wind systems were planned for use in Babylonia to pump water through an irrigation system, although there is no evidence that they were ever built. The construction techniques to bring about such systems did not fully materialize until about 1000 CE, when wind power was used widely in the Middle East.

Aside from sailing, the first widespread use of the wind for power was to grind grain, with windmills turning grindstones. Around the same time came the development of wind-powered pumps, put to work lifting water from wells and irrigation canals and to drain fields (most famously in Holland, now the Netherlands). Just before the beginning of the Industrial Revolution, wind-powered devices were in use across the world, with other applications including sawing lumber and even turning carousels. Yet the limits of using wind power—chiefly that the wind does not always blow—were well known, and its use typically was neglected in favor of more reliable energy sources when available. Water power, for example, which operated with few interruptions, was usually more consistent than wind power. Water-powered devices were generally smaller and required less investment in equipment. Because the wind shifts direction and velocity, windmills needed to be engineered to operate under a wide range of conditions. But even with its limitations, wind was often the only choice for power, and tens of thousands of wind-powered systems were constructed around the world.

Reevaluation as Energy Source

Just before the turn of the nineteenth century came the discovery of new and widespread uses for electricity. Not long after, Moses G. Farmer was issued a patent for a wind-powered generator. After four thousand years of providing mechanical power for humankind, the wind finally became linked with electricity. Yet, with the onset of the Industrial Revolution, steam power became the energy means of choice. Soon thereafter, petroleum, cheaply priced oil, and internal combustion engines all but drove to extinction the use of wind power, with the exception of the iconic farm windmill, which continued to be used for pumping water.

Beginning in the early 1970s, however, wind power was recognized as a potentially important world power source. Global energy prices increased as the Organization of Petroleum Exporting Countries (OPEC) forced world oil prices up from $3 to $32 per barrel in seven years. During that oil crisis, many Western nations realized how dependent they were on foreign energy sources and how closely energy prices were linked to economic health. Indeed, the free and abundant flow of cheap energy was recognized as directly related to the economic vitality and well-being of any country. Therefore, measures were taken to reduce dependency on foreign energy sources. The most significant step taken was the encouragement of energy conservation, and second to it was the improvement and development of alternative and renewable energy sources, which include wind power, solar power, hydroelectric power, biofuels, and geothermal energy.

In the United States, President Jimmy Carter described the energy crisis of the late 1970s as the “moral equivalent to war.” Congress responded and passed the Wind Energy Systems Act of 1980, which would provide an eight-year, $900 million program to develop cost-effective wind power systems across the United States. California responded immediately and launched a full-fledged effort to harness the power of the wind. By 1990, wind power contributed 1 percent of California’s energy needs, or more than 1,000 megawatts (million watts, or Mw). That power could supply 400,000 households and save 4 million barrels of oil each year. By 2023, the state estimated that wind power accounted for 11.17 percent of the total state power mix of about 31,399 gigawatt-hours (GWh; a gigawatt is one thousand megawatts). California continued to increase its efforts to harness wind power. In 2022, the California Energy Commission set targets for the state to produce 25 gigawatts of power from offshore wind by 2045.

The California experience, however, represents only a fraction of the possible wind-generating power capacity in the United States. Various federal incentives continued to support renewable energy sources nationwide into the twenty-first century. While California was an early adopter of wind power technology, several other states have surpassed it in wind energy production. By 2023, the top four wind power–generating states were Texas, Iowa, Oklahoma, and Kansas, according to US Energy Information Administration (EIA) statistics. This helped wind power's share of total US electricity generation increase from below 1 percent in 1990 to approximately 11 percent in 2023.

Meanwhile, supportive government policies in several European countries, as well as technical improvements, helped drive strong growth in wind energy at the global level as well. By 1998, the cost of wind-generating capacity had dropped to one-third of what it was in 1981 and became more competitive with other energy sources. In 1990 only about sixteen countries generated substantial wind power, for a total of around 3.6 billion kWh; by 2022, those figures had increased to 127 countries and 2.9 trillion kWh, according to the EIA. One major growth market was China, which directed significant investment into becoming the leading generator of wind-powered electricity in the world.

Wind-Powered Generators

The laws of physics determine the capabilities and efficiencies of wind-powered generators. The physical realities of wind power are as follows: Wind force varies with the square of its velocity; the power, however, varies with the cube of the velocity; the wind’s ability to do work is limited by its flux, or the amount of energy that can be created by a cross-sectional area of wind traveling at a given velocity; and a perfect system can extract only 60 percent of the total wind power available. Realistically, after electrical conversion systems and (in some systems) storage, the conversion efficiency drops to between 20 and 50 percent. Therefore, one needs to garner a large area of wind to produce significant power. That equates directly into a very large wind turbine required to produce a relative modicum of electrical power.

A typical wind generator sits atop a tower about 35 meters off the ground and sports a blade approximately 60 or 70 meters in length. This device will generate about 660 kilowatts of power. Wind farms may occupy hundreds of acres, populated with many (perhaps several hundred) of these wind turbines.

The typical wind generator consists of a tower, a generator, gears, the rotor, the axis system, and speed control. Some wind generators have batteries for power storage and inverters to convert power states. Wind generators must be placed on towers to enable them to capture optimal wind states. Generators placed too close to the ground will be adversely influenced by obstructions to a steady wind flow located on the ground, such as buildings, hills, and trees. The tower must be high enough to allow clearance for large, efficient rotors.

The rotors of the modern wind generator (also known as propellers, blades, or turbines) are quite unlike the windmills of the past. They come in many forms, depending on the task they are required to perform. The generator task itself is principally determined by the kind of generator mounted on the tower. Typically, the rotors are based on one of two designs. The most common wind-power-generator design is the horizontal axis rotor system. In this system, the shaft of the rotor is aligned horizontally with the ground, with the rotor blades mounted perpendicular to the rotor shaft. This design requires that the generator be mounted at the top of the tower. The disadvantages include that installation and maintenance must be done high above the ground. These rotors look much like aircraft propellers—they are designed along some of the same aerodynamic principles. The other type of design is called the vertical axis system. In this design, the shaft is mounted vertically, with the rotors placed alongside the shaft. The rotor designs for these wind generators are not propeller types; one design looks like an eggbeater and is called exactly that. In these designs, the wind rotates the rotor and shaft, which are mounted vertically. That allows the generator to be placed at the bottom of the assembly on the ground. Often there are no requirements for a tower to be constructed. Other vertically mounted designs are called paddle vanes and s-rotors.

Refinements to Generators

With few exceptions, in wind-power systems, the wind cannot turn the generator shaft fast enough to generate power. Therefore, gear systems are required to “step up” the system from the turning rotor to the generator. A typical blade rotation speed of 200 to 400 rotations per minute (RPM) must be geared up to 1,800 to 3,600 RPM for the generator to deliver adequate power. These gearing systems require that more force be delivered to the turning rotor than if there were no gears between the rotor and the generator shaft. Consequently, gear systems limit the minimum amount of wind necessary to turn the rotor and deliver power from the generator.

The wind-power generator must operate in a very wide range of conditions, considering a constantly variable wind speed and direction. To deliver a consistent energy output, the generator shaft should ideally turn at a more or less constant RPM. In most commercial generators, that is accomplished in a variety of ways. The pitch of the rotor is selectively changed along the entire length, or the rotor is selectively pitched at the tip. Some rotors have flaps, much like an aircraft wing, to change the degree of aerodynamic lift provided by the rotor. The degree of aerodynamic lift ultimately determines the power output of the rotor. Some generators change the angle at which the system is facing the wind to increase or decrease the amount of impinging wind energy. As important as it is to maintain a maximum effective energy output by regulation, it is also necessary to allow energy to go to waste if the wind speed exceeds the levels the system can tolerate. There are also systemic control mechanisms relating to aspects other than speed control. Among them are braking systems to slow or stop the generator in the event of dangerous winds or system failure. Wind systems need to be shut down in the event that the wind speed is too low, a condition that can deliver unacceptably low or inconsistent power to the regulatory mechanisms.

While the most familiar wind-power generators operate at the utility scale, some wind systems have been designed for home use, and there are homes around the world whose sole or partial power source is wind power. These homes rely on small wind power–generation systems nearly identical to their commercial counterparts. Typically, they rely on direct current (DC) generators that feed banks of batteries storing the power from the wind generator, which allows for a constant supply of power to the home even when the wind is not blowing. These homes use direct current for many purposes, and many have special DC appliances. Some appliances do not operate on DC, so these homes have devices called inverters, which change direct currents to alternating currents (AC). During the storage and conversion process, however, there is energy loss, so the wind-power system becomes less efficient at each stage.

Disadvantages as an Energy Source

The same problems associated with wind-power generation encountered by prehistoric humans still exist. Generating power from wind flow is fraught with myriad difficulties. Consistency and direction of the wind remain key hurdles. In addition, the storage of wind power is necessary for use in windless conditions or at times when the wind is so strong that the generators have to be shut down for their protection. In a large utility system, the power demand varies considerably from hour to hour and day to day; therefore, the utility must maintain backup generating capacity.

Environmental concerns also plague the use of modern wind-power devices. While many environmentalists applaud the non-polluting nature of wind-power generation, some people complain that the devices themselves are a blight on the landscape. Offshore wind farms, with turbines sitting in the shallow water of the ocean, have been especially controversial for this reason. Local residents' objections to the effect on the view and, in some locations, concerns about the possible impact on tourism have blocked attempts to build offshore wind farms in a number of countries. Other complaints lodged against wind farms have included the dangers posed to migrating birds (and sea life, in the case of offshore wind farms), noise from the rotors, and the environmental impact of constructing wind farms, especially in sensitive areas such as mountain ridgelines.

Advantages as an Energy Source

Although wind power is unlikely to fully replace other energy sources in the near future, it remains an important resource. When public utilities adopt wind energy efficiently, it offers a great number of social advantages. It is available (to a variable degree) nearly everywhere. The necessary equipment is well understood and relatively simple compared to other types of power plants. Most importantly, it is renewable and nonpolluting, a factor that has become all the more highly valued as the negative impacts of climate change—driven heavily by fossil fuel consumption—have increasingly come into focus.

The additional development of standard home interfaces for wind power could effectively decrease domestic use of other nonrenewable energy resources, pending the likely requirement of a technological advance in power storage technology. A combination of locally available energy, such as wind and solar power, with maximal use of conservation techniques could result in a decline or stabilization in the energy requirement by the private sector. As the free flow and abundance of energy are the life’s blood of any economy, such developments serve to benefit society as a whole.

Principal Terms

aerodynamic lift: a measure of the degree of wind force acting on a rotor, which is translated into power to a generator in a wind-power machine

axis system: the vertical or horizontal orientation of the power shaft of a wind-power machine

power flux: the amount of energy that can be obtained from a cross-sectional area of the wind at a given velocity

power grid: the mechanical power distribution system of a social structure, and its independent power distribution systems

rotor: the bladed system on a wind-power machine that is set into motion by the wind and translated into power to a generator

step-up gearing: a gear system that increases the revolutions of the downstream shaft (generator) over the revolutions of the upstream shaft (rotor)

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