Wind energy is related to the movement of air masses that move from areas of high atmospheric pressure to adjacent areas of lower pressure, with speeds proportional to the pressure gradient and thus be able to generate energy.

Winds are generated due to non-uniform heating of the Earth's surface due to solar radiation; Between 1 and 2% of the energy from the Sun is converted into wind. During the day, continents transfer a greater amount of solar energy to the air than water masses, causing it to warm and expand, making it less dense and rising. The colder, heavier air that comes from the seas, oceans and large lakes is set in motion to occupy the place left by the warm air.

In order to take advantage of wind energy, it is important to know the diurnal, nocturnal and seasonal variations of the winds, the variation of wind speed with height above the ground, the nature of the gusts in short periods of time, and the maximum values ​​that occurred in historical data series with a minimum duration of 20 years. In order to use wind energy, it is necessary for it to reach a minimum speed that depends on the wind turbine to be used but which usually starts between 3 m/s (10 km/h) and 4 m/s (14.4 km/h), a speed called "cut-in speed", and does not exceed 25 m/s (90 km/h), a speed called cut-out speed.

Wind energy is used through the use of wind machines or aeromotors capable of transforming wind energy into usable mechanical rotation energy, either to directly drive the operating machines or for the production of electrical energy. In the latter case, the most widely used today, the conversion system—which includes an electrical generator with its control and grid connection systems—is known as a wind turbine. In these, wind energy moves a propeller and through a mechanical system the rotor of a generator, normally an alternator, is rotated, which produces electrical energy. For their installation to be profitable, they are usually grouped in concentrations called "wind farms", and these can be on land or offshore.

A wind turbine is a machine that transforms wind energy into mechanical energy using oblique blades attached to a common axis. The rotating shaft can be connected to various types of machinery, whether for grinding grain (mills), pumping water or generating electricity. When used to produce electricity it is called a wind turbine generator. Machines moved by the wind have a remote origin, the oldest being those that functioned as mills.

Wind energy is the energy obtained from the wind or, in other words, it is the use of the kinetic energy of air masses that can be converted into mechanical energy and from it into electricity or other useful forms of energy in daily human activities.[1]​.

Contenido

La energía eólica no es algo nuevo, es una de las energías más antiguas junto a la energía térmica. El viento como fuerza motriz se ha utilizado desde la antigüedad. Así, ha movido a barcos mediante el uso de velas o ha hecho funcionar la maquinaria de los molinos al mover sus aspas. Sin embargo, tras una época en la que se fue abandonando, a partir de los años ochenta del siglo este tipo de energía limpia experimentó un renacimiento.

La energía eólica crece de forma imparable ya en el siglo , en algunos países más que en otros, pero sin duda alguna en España existe un gran crecimiento, siendo uno de los primeros países, por debajo de Alemania a nivel europeo o de Estados Unidos a escala mundial. El auge del aumento de parques eólicos se debe a las condiciones favorables de viento, sobre todo en Andalucía que ocupa un puesto principal, entre los que se puede destacar el golfo de Cádiz, ya que el recurso de viento es excepcional.

First mills

The oldest reference is to a windmill that was used to power an organ "Organ (musical instrument)") in the 15th century.[15] The first windmills for practical use were built in Sistan, Afghanistan, in the 19th century. These were vertical shaft mills with rectangular blades.[16] Devices made of 6 to 8 mill blades covered with cloth were used to grind wheat or extract water.

In Europe

The first mills appeared in Europe in the century in France and England and spread throughout the continent. They were wooden structures, known as mill towers, that were rotated by hand around a central pole to extend their blades to the wind. The tower mill developed in France throughout the 19th century. It consisted of a stone tower topped by a rotating wooden structure that supported the mill shaft and its upper machinery.

These first specimens had a series of common characteristics. A horizontal shaft protruded from the top of the mill. Four to eight blades started from this axis, with a length between 3 and 9 meters. The wooden beams were covered with cloth or wooden planks. The energy generated by the rotation of the shaft was transmitted, through a system of gears, to the mill machinery located at the base of the structure.

Horizontal shaft mills were used extensively in Western Europe to grind wheat from the 1180s onwards. It is enough to remember the famous windmills in the adventures of Don Quixote. There are still machines of this type, for example, in the Netherlands to draw water.[17]​.

Pumping with wind energy

In the United States, the development of wind pumps, recognizable by their multiple metal blades, was the main factor that allowed agriculture and ranching in vast areas of North America, otherwise impossible without easy access to water. These pumps contributed to the expansion of railways around the world, covering the water needs of steam locomotives.[18]​.

Modern turbines

Modern wind turbines were developed in the early 1980s. They began in 1979 with mass production of wind turbines by manufacturers Kuriant, Vestas, Nordtank, Nily Baltazar and Bonus. Those turbines were small by current standards, with capacities of 20 to 30 kW each. Since then, the size of turbines has grown enormously, and production has expanded to many locations around the world.

In order to take advantage of wind energy, it is important to know the daytime, nighttime and seasonal variations of the winds, the variation of wind speed with height above the ground, the nature of the gusts in short periods of time, and maximum values ​​that have occurred in historical data series with a minimum duration of 20 years. It is also important to know the maximum wind speed. In order to use wind energy, it is necessary for it to reach a minimum speed that depends on the wind turbine to be used but which usually starts between 3 and 4 m/s (10-14.4 km/h), a speed called cut-in speed, and does not exceed 25 m/s (90 km/h), a speed called cut-out speed.

Wind energy is used through the use of wind machines (or aeromotors) capable of transforming wind energy into usable mechanical rotation energy, either to directly drive the operating machines, or for the production of electrical energy. In the latter case, the conversion system (which includes an electric generator with its control and grid connection systems) is known as a wind turbine.[19]​.

Wind power reached grid parity (the point at which the cost of wind energy is equal to or less than other traditional energy sources) in some areas of Europe and the United States in the mid-2000s. Falling costs continue to drive down the normalized cost of this renewable energy source: it is estimated that it reached grid parity broadly across the European continent around 2010, and that the same point would be reached across the United States in 2016, due to an additional 12% reduction in costs.[4]​.

The installation of wind energy requires a considerable initial investment, but subsequently there are no fuel costs.[21]​ The price of wind energy is therefore much more stable than the prices of other, much more volatile, fossil energy sources.[22]​ In 2006, the marginal cost of wind energy, once the plant has been built and is in operation, was generally less than 1 cent per kWh.[23]​ This cost has even been reduced with the technological improvement of the most recent turbines. There are increasingly longer and lighter blades for wind turbines on the market, while improvements are constantly being made in the operation of the machinery of the wind turbines themselves, increasing their efficiency. Likewise, the initial investment and maintenance costs of wind farms have been reduced.[24]​.

By 2004, the cost of wind power had fallen to one-fifth of what it was in the 1980s, and experts believe that the downward trend will continue in the near future, with the introduction to the market of new, increasingly large, mass-produced "multi-megawatt" wind turbines, capable of producing up to 8 megawatts of power per unit.[25] In 2012, the capital costs of wind energy were substantially lower than those of 2008-2010, although they were still above the levels of 2002, when they reached a historical minimum.[26]​ The decrease in the rest of the costs has contributed to achieving increasingly competitive prices. A 2011 report from the American Wind Energy Association stated:

Another report from the British Wind Energy Association estimates an average generation cost for onshore wind of 5-6 cents per kilowatt/hour (2005). $53.10/MWh and that of natural gas at $52.50/MWh.[29] Another government report obtained similar results in comparison with natural gas, in 2011 in the United Kingdom.[30] In August 2011, tenders in Brazil and Uruguay for 20-year purchases presented costs below $65/MWh.

In February 2013, Bloomberg New Energy Finance reported that the cost of generating power from new wind farms in Australia is less than that from new gas or coal plants. When including the current pricing scheme for fossil fuels in the calculations, their estimates indicated costs (in Australian dollars) of $80/MWh for new wind farms, $143/MWh for new coal plants and $116/MWh for new gas plants. This model further shows that “even without a carbon tax (the most efficient way to reduce large-scale emissions) wind power is 14% cheaper than new coal plants, and 18% cheaper than new gas plants.”[31]​.

In April 2023, the levelized cost, without subsidies or subsidies, of onshore wind energy was between $26/MWh and $50/MWh, a higher cost than in 2022 due to inflation, supply chain issues, rising material prices, and financing costs due to rising interest rates.[32]​[33]​.

The wind industry in the United States is currently capable of producing greater power at a lower cost thanks to the use of increasingly taller wind turbines with longer blades, thus capturing greater winds at higher altitudes. This has opened up new opportunities, and in states such as Indiana, Michigan and Ohio, the cost of wind from wind turbines between 90 and 120 meters high can compete with conventional energy sources such as coal. Prices have fallen to even 4 cents per kWh in some cases, and distribution companies are increasing the amount of wind energy in their energy model, progressively realizing its competitiveness.[34]​.

The cost of the unit of energy produced in wind installations is deduced from a rather complex calculation. For its evaluation, various factors must be taken into account, among which it is worth highlighting:

• - The initial investment: the cost of the wind turbine affects approximately 60 or 70%. The average cost of a wind power plant is, today, about 1,200 euros per kilowatt of installed power and variable depending on the technology and brand to be installed (direct drive"), synchronous, asynchronous or permanent magnet generators").

• - The useful life of the installation (approximately 20 years) and the amortization of this cost.

• - Financial costs.

• - Operation and maintenance costs (variable between 1 and 3% of the investment);

• - The global energy produced in a period of one year, that is, the plant factor of the installation. This is defined based on the characteristics of the wind turbine and the characteristics of the wind in the place where it has been located. This calculation is quite simple since the power curves certified by each manufacturer are used and are usually guaranteed between 95 and 98% depending on each manufacturer. For some of the machines that have been operating for more than 20 years, 99% of the power curve has been reached.

En 2022, la energía eólica instalada en el mundo contaba con una capacidad total de 906 GW, un 9 % más que en el año anterior. Los principales mercados del mundo China con un 40 % la potencia terrestre instalada, Estados Unidos con un 17 %, Alemania con el 7 %, la India con el 5 % y España con un 4 % de la potencia mundial.[35]​.

China, Alemania, España, Estados Unidos, India y Dinamarca han realizado las mayores inversiones en generación de energía eólica. Dinamarca es, en términos relativos, la más destacada en cuanto a fabricación y utilización de turbinas eólicas, con el compromiso realizado en los años 1970 de llegar a obtener la mitad de la producción de energía del país mediante el viento. En 2014 generó el 39,1 % de su electricidad mediante aerogeneradores, mayor porcentaje que cualquier otro país, y el año anterior la energía eólica se consolidó como la fuente de energía más barata del país.[36]​.

En 2022, Brasil realizó una fuerte inversión en el desarrollo de su energía eólica, ampliando hasta los 22 GW su capacidad instalada.[37]​.

La siguiente tabla muestra los mayores países productores de energía eólica por capacidad total instalada al final de cada año (en megavatios). Datos publicados por el Global Wind Energy Council (GWEC).[38]​.

Wind energy in Spain

At the end of 2018, Spain had an installed wind energy capacity of 23,507 MW, which represents 22.6% of the capacity of the national electrical system, the country's second source of energy behind the combined cycle with 26,284 MW.[56]​ It is thus ranked fourth in the world in terms of installed power, behind China, the United States and Germany. That same year, wind energy produced 49,570 GWh, 18.4% of electricity demand.[56]​.

On January 29, 2015, wind energy reached a maximum instantaneous power with 17,553 MW,[57]​ covering 45% of the demand.[58]​.

On December 8, 2021, wind energy reached a maximum instantaneous power with 20,034 MW,[59] covering 58.9% of the demand.

At the end of 2021, the accumulated power in Spain was 28,139 MW, covering more than 23% of the country's energy demand and ranking as the first source of electricity generation in that year. That same year, 842.61 MW of wind power were installed.[60]​.

Likewise, the mini-wind sector is growing quite a bit.[61]​ There is a regulation for the manufacture of small wind turbines, from the International Electrotechnical Committee "CEI (Standard IEC-61400-2 Ed2) which defines a small power wind turbine as one whose area swept by its rotor is less than 200 m². The power that corresponds to said area will depend on the quality of the design of the wind turbine, existing up to 65 kW as maximum.[62]​.

Wind energy in the UK

In 2022, wind energy reached an annual generation record, supplying 24.6% of the country's electrical energy. Its wind farms generated a total of 80.2 TWh.[63]​.

The United Kingdom is one of the countries in the world with the most planned wind capacity, thanks to its offshore wind farms located in the waters of the North and Irish Seas:

• - Dogger Bank; 9000MW; North Sea; Forewind * (SSE Renewables, RWE Npower Renewables, StatoilHydro & Statkraft).

• - Norfolk Bank; 7200 MW; North Sea; *Iberdrola Renewables (ScottishPower) & Vattenfall.

• - Irish Sea; 4100 MW; Irish Sea; Central.

• - Estuary of Forth; 3400 MW; Scotland; SeaGreen * (SSE Renewables and Fluorine).

• - Bristol Channel; 1500 MW; Southwest Coast; RWE Npower Renewables.

• - Moray estuary; 1300 MW; Scotland; * EDP Renewables & SeaEnergy.

• - Isle of Wight (West); 900 MW; South; Enerco New Energy.

• - Hastings; 600 MW; South; E.On Climate & Renewables.

According to the British administration, «the offshore wind industry is one of the keys to the United Kingdom's route to a low CO emissions economy.[64]​.

Wind energy in Sweden

At the end of June 2023, Sweden had an annual production capacity of 52,661 GWh, a cumulative capacity of 17,642 MW and 5,826 installed wind generators.[65]​.

• - Wind energy in Croatia.

• - Wind energy in Italy.

• - Wind energy in Romania.

• - Wind energy in Türkiye.

Wind energy in America

The development of wind energy in the countries of Mexico, Central America and South America is in its beginnings, and the combined capacity installed in them, until the end of 2021, reaches 39,447 MW. The breakdown of installed power by country is as follows:[51]​[53]​[66]​[67]​.

• - Brazil: 21,161 MW.

• - Mexico: 7692 MW.

• - Argentina: 3292 MW.

• - Chile: 3137 MW.

• - Uruguay: 1514 MW.

• - Colombia: 510 MW.

• - Peru: 409 MW.

• - Costa Rica: 394 MW.

• - Dominican Republic: 370 MW.

• - Panama: 270 MW.

• - Honduras: 241 MW.

• - Nicaragua: 186 MW.

• - Other countries: installed power less than 185 MW.

• - Central America + Caribbean: 2001 MW.

• - South America: 29,754 MW.

At the end of 2021, Brazil was the world's fourth largest producer of wind energy (72 TWh), behind only China, the US and Germany.[68]​ The country has been preparing to install offshore wind farms by 2030.[69]​ The wind potential of the Patagonia region is considered gigantic, with estimates that the area could provide enough electricity to sustain the consumption of a country like Brazil alone. However, Argentina has infrastructure deficiencies to carry out the transmission of electrical energy from uninhabited areas with a lot of wind to the large centers of the country.[70]​.

Wind energy in Africa

The wind potential of the Africa and Middle East region stands at 59,000 GW, according to data published in October 2020. At the end of that same year, the total installed capacity in the region amounted to 7 GW, representing 0.01% of its estimated potential.[71]​.

In 2022, its installed wind power increased by 453 MW, the lowest figure since 2013.

• - It is a type of renewable energy since it has its origin in atmospheric processes due to the energy that reaches the Earth from the Sun.

• - It is a clean energy as it does not require combustion, so it does not produce atmospheric emissions or polluting waste, thus avoiding an increase in the greenhouse effect and climate change.

• - Reduces dependence on fossil fuels.

• - It can be installed in spaces not suitable for other purposes, for example in desert areas, near the coast, on arid slopes or slopes that are too steep to be cultivable.

• - It can coexist with other land uses, for example meadows for livestock use or low crops such as wheat, corn, potatoes, beets, etc.

• - Creates a high number of jobs in assembly plants and installation areas.

• - Its installation is quick, between 4 and 9 months.

• - Its inclusion in an electrical network allows, when wind conditions are adequate, to save fuel in thermal power plants and/or water in the reservoirs of hydroelectric power plants.

• - Its use combined with other types of energy, usually photovoltaic solar energy, allows the self-powering of homes, achieving autonomy of more than 82 hours and thus ending the need to connect to supply networks.

• - The current dispersed physical situation in countries like Spain makes it possible to compensate for the low production of some wind farms due to lack of wind with high production in other areas. In this way, the waveform produced in electricity generation is stabilized, solving the problems that wind turbines presented as energy producers in their beginnings.

• - It is possible to build wind farms at sea, where the wind is stronger, more constant and the social impact is lower, although installation and maintenance costs increase. Marine parks are especially important in northern European countries such as Denmark.

• - As technology has advanced, the cost of wind energy has decreased significantly, in some cases becoming one of the cheapest ways to generate electricity.

• - Unlike fossil fuels, which can be volatile in terms of price, wind is free, which can contribute to some stability in electricity prices.

• - Wind turbines can be used flexibly and in a variety of configurations ranging from large scale installations to smaller systems for individual or community use.

• - Incorporating wind energy into a country's energy matrix helps diversify its energy sources and can make the energy system more resistant to interruptions or fluctuations in the supply of other sources.

Technical aspects

Due to the natural variability and unpredictability of the wind, in order for wind energy to be used as the only source of electrical energy, it is necessary to store the energy produced when there is wind in order to later use it when there is not. But so far there are no systems large enough to store considerable amounts of energy efficiently, except for pumping stations. Therefore, to address the valleys in the wind energy production curve and avoid widespread blackouts, support from conventional energies such as coal, natural gas, oil or combined cycle thermoelectric plants or reversible hydroelectric plants, for example, is essential. This is a drawback, since when supporting wind power, coal plants cannot operate at their optimal performance, which is around 90% of their power. They have to stay well below this percentage to be able to substantially increase their production when the wind dies down. This is why, when operating in this mode, thermal power plants consume more fuel per kWh produced. Furthermore, by increasing and decreasing its production each time the wind speed changes, greater wear and tear on the machinery occurs. The improvement of the electrical interconnection between France and Spain, scheduled for 2028, with the entry into operation of a 5 GW line, will solve this backup problem. The interconnection with France will allow the European system to be used as a cushion for wind variability.[72]​ The variability in wind energy production has other important consequences:

• - To distribute the electricity produced by each wind farm (which are also usually located in remote natural areas) it is necessary to build high voltage lines that are capable of conducting the maximum electricity that the installation is capable of producing.

• - Technically, one of the biggest drawbacks of wind turbines was the so-called voltage sag. Faced with one of these phenomena, the protections of the wind turbines with squirrel cage motors caused the disconnection of the network to avoid being damaged and consequently new disturbances in it, in this case, lack of supply. In January 2007, the REE published a series of response requirements for these voltage gaps. The wind turbines installed from that date on already met these requirements, as well as an adaptation to those previously installed.[73]​.

• - In addition to the obvious need for a minimum wind speed to be able to move the blades, there is also a higher limitation: a machine can be generating at maximum power, but if the wind speed exceeds the specifications of the wind turbine, it is mandatory to disconnect it from the grid or change the inclination of the blades so that they stop rotating, since its structure can be damaged by the stresses that appear on the axis. The immediate consequence is an obvious decrease in electricity production, despite there being abundant wind, and represents another factor of uncertainty when it comes to having this energy in the consumer electrical network.

Although these problems seem unique to wind energy, they are common to all energies of natural origin:

• - A solar panel will only produce energy as long as there is enough sunlight.

• - A hydroelectric plant can only produce as long as water conditions and rainfall allow the release of water.

One of the ways to alleviate the lack of control over renewable resources (wind, solar radiation) are the so-called hybrid systems, where energy sources are combined with storage. There is a trend towards the creation of renewable plants that involve wind, solar generators and battery storage (usually lithium ion). In countries such as Australia or the United States, their use is being regulated and specific rates are even defined for the injection of energy from these plants that are beginning to compete on equal terms with plants based on fossil fuels, given that they begin to have a generation forecast of one day ahead or more.

Environmental aspects

• - Generally, although not always, it is combined with thermal power plants, leading some people to consider that they do not really save too many carbon dioxide emissions. However, it must be taken into account that no type of renewable energy allows, at least on its own, to cover all the demand and production of electricity, but nevertheless its contribution to the electrical network is clearly positive from the point of view of emissions savings.

• - There are wind farms in Spain in protected areas such as SPA (Special Protection Area for Birds) and SCI (place of community importance) of the Natura 2000 Network, which represents a natural impact—although reduced—due to human activity.

• - At the beginning of its installation, the places selected for it coincided with the routes of migratory birds or with areas where birds take advantage of hillside winds, which causes the wind turbines to come into conflict with birds and bats. Fortunately, mortality levels are very low compared to other causes such as accidents, although this statement is questioned by independent experts. Currently, the environmental impact studies necessary for the recognition of the wind farm plan take into consideration the ornithological situation of the area. Furthermore, since current wind turbines are low rotation speed, the bird strike problem is being significantly reduced.

• - The landscape impact is an important note due to the arrangement of the horizontal elements that compose it and the appearance of a vertical element such as the wind turbine. They produce the so-called "disco effect": this appears when the sun is behind the windmills and the shadows of the blades are regularly projected onto the gardens and windows, flickering in such a way that people called this phenomenon the "disco effect." This, together with noise, can lead people to a high level of stress, with considerable effects on their health. However, the improvement in the design of wind turbines has made it possible to progressively reduce the noise they produce.

• - The opening of wind farms and the presence of operators in them means that human presence is constant in places that until then were little traveled, which also affects fauna.

The installation of large wind turbine plants is often criticized for the landscape impact it has on small municipalities and natural landscapes. In the image, a wind plant affecting the views of the Montserrat mountain in Rubió, Catalonia.

Microgeneration of wind energy consists of small generation systems of up to 50 kW of power.[74]​ In remote and isolated communities, which have traditionally used diesel generators, their use is a good alternative. It is also increasingly used by households that install these systems to reduce or eliminate their dependence on the electrical grid for economic reasons, as well as to reduce their environmental impact and carbon footprint. These types of small turbines have been used for several decades in remote areas along with battery storage systems "Battery (electricity)").[75]​.

Small wind turbine generators connected to the electrical grid can also use what is known as on-grid storage, replacing energy purchased from the grid with locally produced energy, when this is possible. The excess energy produced by domestic microgenerators can, in some countries, be poured into the grid for sale to the electricity company, generating income for the owner of the installation who pays off the installation.[76][77]​.

Off-grid systems can adapt to wind intermittency, use batteries, photovoltaic systems or diesel generators to complement the energy produced by the turbine. Other equipment, such as parking meters, illuminated traffic signs, public lighting, or telecommunications systems, can also be powered by a small wind turbine, generally together with a photovoltaic system that charges small batteries, eliminating the need for connection to the grid.[78]​.

Mini wind turbines could generate electricity cheaper than the grid in some rural areas of the United Kingdom, according to a study by the Carbon Trust organization), published in 2010.[79] According to that report, mini wind turbines could generate 1.5 TWh of electricity per year in the United Kingdom, 0.4% of the country's total consumption, avoiding the emission of 600,000 tons of CO. This conclusion is based on the assumption that 10% of homes to install mini wind turbines at prices competitive with those of the electricity grid, around 12 pence (about €0.17) per kWh.[74] Another report prepared in 2006 by Energy Saving Trust, an organization dependent on the United Kingdom Government, ruled that microgeneration (of different types: wind, solar, etc.) could provide up to 30% or 40% of electricity demand around the year. 2050.[80]​.

Distributed generation from renewable energies has increased in recent years, as a result of greater awareness about the influence of humans on climate change. The electronic equipment required to allow the connection of renewable generation systems to the electrical grid may also include other grid stability systems to ensure and guarantee the quality of the electrical supply.[81]​.

Wind farms and wind energy by country

• - Renewable energies in Germany.

• - Wind energy in Spain.

• - Annex: Wind farms in Spain.

• - Wind energy in Argentina.

• - Wikimedia Commons hosts a multimedia gallery on Wind Energy.

• - World Wind Energy Council (GWEC).

• - The World Wind Energy Association (WWEA).

• - About the origin of the wind and its use.

• - Remapping the World, world map of wind intensity.

• - Wind energy contributes to Spain's first trade surplus.

• - Translation into Spanish of the work published by Albert Betz in 1926 Wind-Energie und ihre Ausnützung durch Windmühlen ("Wind energy and its use through windmills").

• - Notions of wind energy for students and teachers new to the subject.

• - Introduction to the theory of wind turbines.

• - What is Mini Wind Energy? APPA.

• - Wind Regulation of Electric Vehicles (REVE).

• - Cost of a wind farm.

Wind energy is related to the movement of air masses that move from areas of high atmospheric pressure to adjacent areas of lower pressure, with speeds proportional to the pressure gradient and thus be able to generate energy.

Winds are generated due to non-uniform heating of the Earth's surface due to solar radiation; Between 1 and 2% of the energy from the Sun is converted into wind. During the day, continents transfer a greater amount of solar energy to the air than water masses, causing it to warm and expand, making it less dense and rising. The colder, heavier air that comes from the seas, oceans and large lakes is set in motion to occupy the place left by the warm air.

In order to take advantage of wind energy, it is important to know the diurnal, nocturnal and seasonal variations of the winds, the variation of wind speed with height above the ground, the nature of the gusts in short periods of time, and the maximum values ​​that occurred in historical data series with a minimum duration of 20 years. In order to use wind energy, it is necessary for it to reach a minimum speed that depends on the wind turbine to be used but which usually starts between 3 m/s (10 km/h) and 4 m/s (14.4 km/h), a speed called "cut-in speed", and does not exceed 25 m/s (90 km/h), a speed called cut-out speed.

Wind energy is used through the use of wind machines or aeromotors capable of transforming wind energy into usable mechanical rotation energy, either to directly drive the operating machines or for the production of electrical energy. In the latter case, the most widely used today, the conversion system—which includes an electrical generator with its control and grid connection systems—is known as a wind turbine. In these, wind energy moves a propeller and through a mechanical system the rotor of a generator, normally an alternator, is rotated, which produces electrical energy. For their installation to be profitable, they are usually grouped in concentrations called "wind farms", and these can be on land or offshore.

A wind turbine is a machine that transforms wind energy into mechanical energy using oblique blades attached to a common axis. The rotating shaft can be connected to various types of machinery, whether for grinding grain (mills), pumping water or generating electricity. When used to produce electricity it is called a wind turbine generator. Machines moved by the wind have a remote origin, the oldest being those that functioned as mills.

Wind energy is the energy obtained from the wind or, in other words, it is the use of the kinetic energy of air masses that can be converted into mechanical energy and from it into electricity or other useful forms of energy in daily human activities.[1]​.

Contenido

La energía eólica no es algo nuevo, es una de las energías más antiguas junto a la energía térmica. El viento como fuerza motriz se ha utilizado desde la antigüedad. Así, ha movido a barcos mediante el uso de velas o ha hecho funcionar la maquinaria de los molinos al mover sus aspas. Sin embargo, tras una época en la que se fue abandonando, a partir de los años ochenta del siglo este tipo de energía limpia experimentó un renacimiento.

La energía eólica crece de forma imparable ya en el siglo , en algunos países más que en otros, pero sin duda alguna en España existe un gran crecimiento, siendo uno de los primeros países, por debajo de Alemania a nivel europeo o de Estados Unidos a escala mundial. El auge del aumento de parques eólicos se debe a las condiciones favorables de viento, sobre todo en Andalucía que ocupa un puesto principal, entre los que se puede destacar el golfo de Cádiz, ya que el recurso de viento es excepcional.

First mills

The oldest reference is to a windmill that was used to power an organ "Organ (musical instrument)") in the 15th century.[15] The first windmills for practical use were built in Sistan, Afghanistan, in the 19th century. These were vertical shaft mills with rectangular blades.[16] Devices made of 6 to 8 mill blades covered with cloth were used to grind wheat or extract water.

In Europe

The first mills appeared in Europe in the century in France and England and spread throughout the continent. They were wooden structures, known as mill towers, that were rotated by hand around a central pole to extend their blades to the wind. The tower mill developed in France throughout the 19th century. It consisted of a stone tower topped by a rotating wooden structure that supported the mill shaft and its upper machinery.

These first specimens had a series of common characteristics. A horizontal shaft protruded from the top of the mill. Four to eight blades started from this axis, with a length between 3 and 9 meters. The wooden beams were covered with cloth or wooden planks. The energy generated by the rotation of the shaft was transmitted, through a system of gears, to the mill machinery located at the base of the structure.

Horizontal shaft mills were used extensively in Western Europe to grind wheat from the 1180s onwards. It is enough to remember the famous windmills in the adventures of Don Quixote. There are still machines of this type, for example, in the Netherlands to draw water.[17]​.

Pumping with wind energy

In the United States, the development of wind pumps, recognizable by their multiple metal blades, was the main factor that allowed agriculture and ranching in vast areas of North America, otherwise impossible without easy access to water. These pumps contributed to the expansion of railways around the world, covering the water needs of steam locomotives.[18]​.

Modern turbines

Modern wind turbines were developed in the early 1980s. They began in 1979 with mass production of wind turbines by manufacturers Kuriant, Vestas, Nordtank, Nily Baltazar and Bonus. Those turbines were small by current standards, with capacities of 20 to 30 kW each. Since then, the size of turbines has grown enormously, and production has expanded to many locations around the world.

In order to take advantage of wind energy, it is important to know the daytime, nighttime and seasonal variations of the winds, the variation of wind speed with height above the ground, the nature of the gusts in short periods of time, and maximum values ​​that have occurred in historical data series with a minimum duration of 20 years. It is also important to know the maximum wind speed. In order to use wind energy, it is necessary for it to reach a minimum speed that depends on the wind turbine to be used but which usually starts between 3 and 4 m/s (10-14.4 km/h), a speed called cut-in speed, and does not exceed 25 m/s (90 km/h), a speed called cut-out speed.

Wind energy is used through the use of wind machines (or aeromotors) capable of transforming wind energy into usable mechanical rotation energy, either to directly drive the operating machines, or for the production of electrical energy. In the latter case, the conversion system (which includes an electric generator with its control and grid connection systems) is known as a wind turbine.[19]​.

Wind power reached grid parity (the point at which the cost of wind energy is equal to or less than other traditional energy sources) in some areas of Europe and the United States in the mid-2000s. Falling costs continue to drive down the normalized cost of this renewable energy source: it is estimated that it reached grid parity broadly across the European continent around 2010, and that the same point would be reached across the United States in 2016, due to an additional 12% reduction in costs.[4]​.

The installation of wind energy requires a considerable initial investment, but subsequently there are no fuel costs.[21]​ The price of wind energy is therefore much more stable than the prices of other, much more volatile, fossil energy sources.[22]​ In 2006, the marginal cost of wind energy, once the plant has been built and is in operation, was generally less than 1 cent per kWh.[23]​ This cost has even been reduced with the technological improvement of the most recent turbines. There are increasingly longer and lighter blades for wind turbines on the market, while improvements are constantly being made in the operation of the machinery of the wind turbines themselves, increasing their efficiency. Likewise, the initial investment and maintenance costs of wind farms have been reduced.[24]​.

By 2004, the cost of wind power had fallen to one-fifth of what it was in the 1980s, and experts believe that the downward trend will continue in the near future, with the introduction to the market of new, increasingly large, mass-produced "multi-megawatt" wind turbines, capable of producing up to 8 megawatts of power per unit.[25] In 2012, the capital costs of wind energy were substantially lower than those of 2008-2010, although they were still above the levels of 2002, when they reached a historical minimum.[26]​ The decrease in the rest of the costs has contributed to achieving increasingly competitive prices. A 2011 report from the American Wind Energy Association stated:

Another report from the British Wind Energy Association estimates an average generation cost for onshore wind of 5-6 cents per kilowatt/hour (2005). $53.10/MWh and that of natural gas at $52.50/MWh.[29] Another government report obtained similar results in comparison with natural gas, in 2011 in the United Kingdom.[30] In August 2011, tenders in Brazil and Uruguay for 20-year purchases presented costs below $65/MWh.

In February 2013, Bloomberg New Energy Finance reported that the cost of generating power from new wind farms in Australia is less than that from new gas or coal plants. When including the current pricing scheme for fossil fuels in the calculations, their estimates indicated costs (in Australian dollars) of $80/MWh for new wind farms, $143/MWh for new coal plants and $116/MWh for new gas plants. This model further shows that “even without a carbon tax (the most efficient way to reduce large-scale emissions) wind power is 14% cheaper than new coal plants, and 18% cheaper than new gas plants.”[31]​.

In April 2023, the levelized cost, without subsidies or subsidies, of onshore wind energy was between $26/MWh and $50/MWh, a higher cost than in 2022 due to inflation, supply chain issues, rising material prices, and financing costs due to rising interest rates.[32]​[33]​.

The wind industry in the United States is currently capable of producing greater power at a lower cost thanks to the use of increasingly taller wind turbines with longer blades, thus capturing greater winds at higher altitudes. This has opened up new opportunities, and in states such as Indiana, Michigan and Ohio, the cost of wind from wind turbines between 90 and 120 meters high can compete with conventional energy sources such as coal. Prices have fallen to even 4 cents per kWh in some cases, and distribution companies are increasing the amount of wind energy in their energy model, progressively realizing its competitiveness.[34]​.

The cost of the unit of energy produced in wind installations is deduced from a rather complex calculation. For its evaluation, various factors must be taken into account, among which it is worth highlighting:

• - The initial investment: the cost of the wind turbine affects approximately 60 or 70%. The average cost of a wind power plant is, today, about 1,200 euros per kilowatt of installed power and variable depending on the technology and brand to be installed (direct drive"), synchronous, asynchronous or permanent magnet generators").

• - The useful life of the installation (approximately 20 years) and the amortization of this cost.

• - Financial costs.

• - Operation and maintenance costs (variable between 1 and 3% of the investment);

• - The global energy produced in a period of one year, that is, the plant factor of the installation. This is defined based on the characteristics of the wind turbine and the characteristics of the wind in the place where it has been located. This calculation is quite simple since the power curves certified by each manufacturer are used and are usually guaranteed between 95 and 98% depending on each manufacturer. For some of the machines that have been operating for more than 20 years, 99% of the power curve has been reached.

En 2022, la energía eólica instalada en el mundo contaba con una capacidad total de 906 GW, un 9 % más que en el año anterior. Los principales mercados del mundo China con un 40 % la potencia terrestre instalada, Estados Unidos con un 17 %, Alemania con el 7 %, la India con el 5 % y España con un 4 % de la potencia mundial.[35]​.

China, Alemania, España, Estados Unidos, India y Dinamarca han realizado las mayores inversiones en generación de energía eólica. Dinamarca es, en términos relativos, la más destacada en cuanto a fabricación y utilización de turbinas eólicas, con el compromiso realizado en los años 1970 de llegar a obtener la mitad de la producción de energía del país mediante el viento. En 2014 generó el 39,1 % de su electricidad mediante aerogeneradores, mayor porcentaje que cualquier otro país, y el año anterior la energía eólica se consolidó como la fuente de energía más barata del país.[36]​.

En 2022, Brasil realizó una fuerte inversión en el desarrollo de su energía eólica, ampliando hasta los 22 GW su capacidad instalada.[37]​.

La siguiente tabla muestra los mayores países productores de energía eólica por capacidad total instalada al final de cada año (en megavatios). Datos publicados por el Global Wind Energy Council (GWEC).[38]​.

Wind energy in Spain

At the end of 2018, Spain had an installed wind energy capacity of 23,507 MW, which represents 22.6% of the capacity of the national electrical system, the country's second source of energy behind the combined cycle with 26,284 MW.[56]​ It is thus ranked fourth in the world in terms of installed power, behind China, the United States and Germany. That same year, wind energy produced 49,570 GWh, 18.4% of electricity demand.[56]​.

On January 29, 2015, wind energy reached a maximum instantaneous power with 17,553 MW,[57]​ covering 45% of the demand.[58]​.

On December 8, 2021, wind energy reached a maximum instantaneous power with 20,034 MW,[59] covering 58.9% of the demand.

At the end of 2021, the accumulated power in Spain was 28,139 MW, covering more than 23% of the country's energy demand and ranking as the first source of electricity generation in that year. That same year, 842.61 MW of wind power were installed.[60]​.

Likewise, the mini-wind sector is growing quite a bit.[61]​ There is a regulation for the manufacture of small wind turbines, from the International Electrotechnical Committee "CEI (Standard IEC-61400-2 Ed2) which defines a small power wind turbine as one whose area swept by its rotor is less than 200 m². The power that corresponds to said area will depend on the quality of the design of the wind turbine, existing up to 65 kW as maximum.[62]​.

Wind energy in the UK

In 2022, wind energy reached an annual generation record, supplying 24.6% of the country's electrical energy. Its wind farms generated a total of 80.2 TWh.[63]​.

The United Kingdom is one of the countries in the world with the most planned wind capacity, thanks to its offshore wind farms located in the waters of the North and Irish Seas:

• - Dogger Bank; 9000MW; North Sea; Forewind * (SSE Renewables, RWE Npower Renewables, StatoilHydro & Statkraft).

• - Norfolk Bank; 7200 MW; North Sea; *Iberdrola Renewables (ScottishPower) & Vattenfall.

• - Irish Sea; 4100 MW; Irish Sea; Central.

• - Estuary of Forth; 3400 MW; Scotland; SeaGreen * (SSE Renewables and Fluorine).

• - Bristol Channel; 1500 MW; Southwest Coast; RWE Npower Renewables.

• - Moray estuary; 1300 MW; Scotland; * EDP Renewables & SeaEnergy.

• - Isle of Wight (West); 900 MW; South; Enerco New Energy.

• - Hastings; 600 MW; South; E.On Climate & Renewables.

According to the British administration, «the offshore wind industry is one of the keys to the United Kingdom's route to a low CO emissions economy.[64]​.

Wind energy in Sweden

At the end of June 2023, Sweden had an annual production capacity of 52,661 GWh, a cumulative capacity of 17,642 MW and 5,826 installed wind generators.[65]​.

• - Wind energy in Croatia.

• - Wind energy in Italy.

• - Wind energy in Romania.

• - Wind energy in Türkiye.

Wind energy in America

The development of wind energy in the countries of Mexico, Central America and South America is in its beginnings, and the combined capacity installed in them, until the end of 2021, reaches 39,447 MW. The breakdown of installed power by country is as follows:[51]​[53]​[66]​[67]​.

• - Brazil: 21,161 MW.

• - Mexico: 7692 MW.

• - Argentina: 3292 MW.

• - Chile: 3137 MW.

• - Uruguay: 1514 MW.

• - Colombia: 510 MW.

• - Peru: 409 MW.

• - Costa Rica: 394 MW.

• - Dominican Republic: 370 MW.

• - Panama: 270 MW.

• - Honduras: 241 MW.

• - Nicaragua: 186 MW.

• - Other countries: installed power less than 185 MW.

• - Central America + Caribbean: 2001 MW.

• - South America: 29,754 MW.

At the end of 2021, Brazil was the world's fourth largest producer of wind energy (72 TWh), behind only China, the US and Germany.[68]​ The country has been preparing to install offshore wind farms by 2030.[69]​ The wind potential of the Patagonia region is considered gigantic, with estimates that the area could provide enough electricity to sustain the consumption of a country like Brazil alone. However, Argentina has infrastructure deficiencies to carry out the transmission of electrical energy from uninhabited areas with a lot of wind to the large centers of the country.[70]​.

Wind energy in Africa

The wind potential of the Africa and Middle East region stands at 59,000 GW, according to data published in October 2020. At the end of that same year, the total installed capacity in the region amounted to 7 GW, representing 0.01% of its estimated potential.[71]​.

In 2022, its installed wind power increased by 453 MW, the lowest figure since 2013.

• - It is a type of renewable energy since it has its origin in atmospheric processes due to the energy that reaches the Earth from the Sun.

• - It is a clean energy as it does not require combustion, so it does not produce atmospheric emissions or polluting waste, thus avoiding an increase in the greenhouse effect and climate change.

• - Reduces dependence on fossil fuels.

• - It can be installed in spaces not suitable for other purposes, for example in desert areas, near the coast, on arid slopes or slopes that are too steep to be cultivable.

• - It can coexist with other land uses, for example meadows for livestock use or low crops such as wheat, corn, potatoes, beets, etc.

• - Creates a high number of jobs in assembly plants and installation areas.

• - Its installation is quick, between 4 and 9 months.

• - Its inclusion in an electrical network allows, when wind conditions are adequate, to save fuel in thermal power plants and/or water in the reservoirs of hydroelectric power plants.

• - Its use combined with other types of energy, usually photovoltaic solar energy, allows the self-powering of homes, achieving autonomy of more than 82 hours and thus ending the need to connect to supply networks.

• - The current dispersed physical situation in countries like Spain makes it possible to compensate for the low production of some wind farms due to lack of wind with high production in other areas. In this way, the waveform produced in electricity generation is stabilized, solving the problems that wind turbines presented as energy producers in their beginnings.

• - It is possible to build wind farms at sea, where the wind is stronger, more constant and the social impact is lower, although installation and maintenance costs increase. Marine parks are especially important in northern European countries such as Denmark.

• - As technology has advanced, the cost of wind energy has decreased significantly, in some cases becoming one of the cheapest ways to generate electricity.

• - Unlike fossil fuels, which can be volatile in terms of price, wind is free, which can contribute to some stability in electricity prices.

• - Wind turbines can be used flexibly and in a variety of configurations ranging from large scale installations to smaller systems for individual or community use.

• - Incorporating wind energy into a country's energy matrix helps diversify its energy sources and can make the energy system more resistant to interruptions or fluctuations in the supply of other sources.

Technical aspects

Due to the natural variability and unpredictability of the wind, in order for wind energy to be used as the only source of electrical energy, it is necessary to store the energy produced when there is wind in order to later use it when there is not. But so far there are no systems large enough to store considerable amounts of energy efficiently, except for pumping stations. Therefore, to address the valleys in the wind energy production curve and avoid widespread blackouts, support from conventional energies such as coal, natural gas, oil or combined cycle thermoelectric plants or reversible hydroelectric plants, for example, is essential. This is a drawback, since when supporting wind power, coal plants cannot operate at their optimal performance, which is around 90% of their power. They have to stay well below this percentage to be able to substantially increase their production when the wind dies down. This is why, when operating in this mode, thermal power plants consume more fuel per kWh produced. Furthermore, by increasing and decreasing its production each time the wind speed changes, greater wear and tear on the machinery occurs. The improvement of the electrical interconnection between France and Spain, scheduled for 2028, with the entry into operation of a 5 GW line, will solve this backup problem. The interconnection with France will allow the European system to be used as a cushion for wind variability.[72]​ The variability in wind energy production has other important consequences:

• - To distribute the electricity produced by each wind farm (which are also usually located in remote natural areas) it is necessary to build high voltage lines that are capable of conducting the maximum electricity that the installation is capable of producing.

• - Technically, one of the biggest drawbacks of wind turbines was the so-called voltage sag. Faced with one of these phenomena, the protections of the wind turbines with squirrel cage motors caused the disconnection of the network to avoid being damaged and consequently new disturbances in it, in this case, lack of supply. In January 2007, the REE published a series of response requirements for these voltage gaps. The wind turbines installed from that date on already met these requirements, as well as an adaptation to those previously installed.[73]​.

• - In addition to the obvious need for a minimum wind speed to be able to move the blades, there is also a higher limitation: a machine can be generating at maximum power, but if the wind speed exceeds the specifications of the wind turbine, it is mandatory to disconnect it from the grid or change the inclination of the blades so that they stop rotating, since its structure can be damaged by the stresses that appear on the axis. The immediate consequence is an obvious decrease in electricity production, despite there being abundant wind, and represents another factor of uncertainty when it comes to having this energy in the consumer electrical network.

Although these problems seem unique to wind energy, they are common to all energies of natural origin:

• - A solar panel will only produce energy as long as there is enough sunlight.

• - A hydroelectric plant can only produce as long as water conditions and rainfall allow the release of water.

One of the ways to alleviate the lack of control over renewable resources (wind, solar radiation) are the so-called hybrid systems, where energy sources are combined with storage. There is a trend towards the creation of renewable plants that involve wind, solar generators and battery storage (usually lithium ion). In countries such as Australia or the United States, their use is being regulated and specific rates are even defined for the injection of energy from these plants that are beginning to compete on equal terms with plants based on fossil fuels, given that they begin to have a generation forecast of one day ahead or more.

Environmental aspects

• - Generally, although not always, it is combined with thermal power plants, leading some people to consider that they do not really save too many carbon dioxide emissions. However, it must be taken into account that no type of renewable energy allows, at least on its own, to cover all the demand and production of electricity, but nevertheless its contribution to the electrical network is clearly positive from the point of view of emissions savings.

• - There are wind farms in Spain in protected areas such as SPA (Special Protection Area for Birds) and SCI (place of community importance) of the Natura 2000 Network, which represents a natural impact—although reduced—due to human activity.

• - At the beginning of its installation, the places selected for it coincided with the routes of migratory birds or with areas where birds take advantage of hillside winds, which causes the wind turbines to come into conflict with birds and bats. Fortunately, mortality levels are very low compared to other causes such as accidents, although this statement is questioned by independent experts. Currently, the environmental impact studies necessary for the recognition of the wind farm plan take into consideration the ornithological situation of the area. Furthermore, since current wind turbines are low rotation speed, the bird strike problem is being significantly reduced.

• - The landscape impact is an important note due to the arrangement of the horizontal elements that compose it and the appearance of a vertical element such as the wind turbine. They produce the so-called "disco effect": this appears when the sun is behind the windmills and the shadows of the blades are regularly projected onto the gardens and windows, flickering in such a way that people called this phenomenon the "disco effect." This, together with noise, can lead people to a high level of stress, with considerable effects on their health. However, the improvement in the design of wind turbines has made it possible to progressively reduce the noise they produce.

• - The opening of wind farms and the presence of operators in them means that human presence is constant in places that until then were little traveled, which also affects fauna.

The installation of large wind turbine plants is often criticized for the landscape impact it has on small municipalities and natural landscapes. In the image, a wind plant affecting the views of the Montserrat mountain in Rubió, Catalonia.

Microgeneration of wind energy consists of small generation systems of up to 50 kW of power.[74]​ In remote and isolated communities, which have traditionally used diesel generators, their use is a good alternative. It is also increasingly used by households that install these systems to reduce or eliminate their dependence on the electrical grid for economic reasons, as well as to reduce their environmental impact and carbon footprint. These types of small turbines have been used for several decades in remote areas along with battery storage systems "Battery (electricity)").[75]​.

Small wind turbine generators connected to the electrical grid can also use what is known as on-grid storage, replacing energy purchased from the grid with locally produced energy, when this is possible. The excess energy produced by domestic microgenerators can, in some countries, be poured into the grid for sale to the electricity company, generating income for the owner of the installation who pays off the installation.[76][77]​.

Off-grid systems can adapt to wind intermittency, use batteries, photovoltaic systems or diesel generators to complement the energy produced by the turbine. Other equipment, such as parking meters, illuminated traffic signs, public lighting, or telecommunications systems, can also be powered by a small wind turbine, generally together with a photovoltaic system that charges small batteries, eliminating the need for connection to the grid.[78]​.

Mini wind turbines could generate electricity cheaper than the grid in some rural areas of the United Kingdom, according to a study by the Carbon Trust organization), published in 2010.[79] According to that report, mini wind turbines could generate 1.5 TWh of electricity per year in the United Kingdom, 0.4% of the country's total consumption, avoiding the emission of 600,000 tons of CO. This conclusion is based on the assumption that 10% of homes to install mini wind turbines at prices competitive with those of the electricity grid, around 12 pence (about €0.17) per kWh.[74] Another report prepared in 2006 by Energy Saving Trust, an organization dependent on the United Kingdom Government, ruled that microgeneration (of different types: wind, solar, etc.) could provide up to 30% or 40% of electricity demand around the year. 2050.[80]​.

Distributed generation from renewable energies has increased in recent years, as a result of greater awareness about the influence of humans on climate change. The electronic equipment required to allow the connection of renewable generation systems to the electrical grid may also include other grid stability systems to ensure and guarantee the quality of the electrical supply.[81]​.

Wind farms and wind energy by country

• - Renewable energies in Germany.

• - Wind energy in Spain.

• - Annex: Wind farms in Spain.

• - Wind energy in Argentina.

• - Wikimedia Commons hosts a multimedia gallery on Wind Energy.

• - World Wind Energy Council (GWEC).

• - The World Wind Energy Association (WWEA).

• - About the origin of the wind and its use.

• - Remapping the World, world map of wind intensity.

• - Wind energy contributes to Spain's first trade surplus.

• - Translation into Spanish of the work published by Albert Betz in 1926 Wind-Energie und ihre Ausnützung durch Windmühlen ("Wind energy and its use through windmills").

• - Notions of wind energy for students and teachers new to the subject.

• - Introduction to the theory of wind turbines.

• - What is Mini Wind Energy? APPA.

• - Wind Regulation of Electric Vehicles (REVE).

• - Cost of a wind farm.