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# Wind power

### Top 10 Wind power related articles

World electricity generation by source in 2018. Total generation was 26.7 PWh.[2]

Coal (38%)
Natural gas (23%)
Hydro (16%)
Nuclear (10%)
Wind (5%)
Oil (3%)
Solar (2%)
Biofuels (2%)
Other (1%)

Wind power or wind energy is the use of wind to provide mechanical power through wind turbines to turn electric generators for electrical power. Wind power is a popular sustainable, renewable energy source that has a much smaller impact on the environment compared to burning fossil fuels.

Wind farms consist of many individual wind turbines, which are connected to the electric power transmission network. Onshore wind is an inexpensive source of electric power, competitive with, or in many places cheaper than, coal or gas plants. Onshore wind farms have a greater visual impact on the landscape than other power stations, as they need to be spread over more land[3][4] and need to be built in rural areas, which can lead to "industrialization of the countryside"[5] and habitat loss.[4] Offshore wind is steadier and stronger than on land and offshore farms have less visual impact, but construction and maintenance costs are significantly higher. Small onshore wind farms can feed some energy into the grid or provide power to isolated off-grid locations.

Wind power is an intermittent energy source, which cannot be dispatched on demand.[3] Locally, it gives variable power, which is consistent from year to year but varies greatly over shorter time scales. Therefore, it must be used with other power sources to give a reliable supply. Power-management techniques such as having dispatchable power sources (often gas-fired power plant or hydroelectric power), excess capacity, geographically distributed turbines, exporting and importing power to neighboring areas, grid storage, reducing demand when wind production is low, and curtailing occasional excess wind power, are used to overcome these problems. As the proportion of wind power in a region increases, more conventional power sources are needed to back it up, and the grid may need to be upgraded.[6][7] Weather forecasting permits the electric-power network to be readied for the predictable variations in production that occur.

In 2019, wind supplied 1430 TWh of electricity, which was 5.3% of worldwide electrical generation,[8] with the global installed wind power capacity reaching more than 651 GW, an increase of 10% over 2018.[9]

## Wind energy

Wind energy is the kinetic energy of air in motion, also called wind. Total wind energy flowing through an imaginary surface with area A during the time t is:

${\displaystyle E={\frac {1}{2}}mv^{2}={\frac {1}{2}}(Avt\rho )v^{2}={\frac {1}{2}}At\rho v^{3},}$ [11]

where ρ is the density of air; v is the wind speed; Avt is the volume of air passing through A (which is considered perpendicular to the direction of the wind); Avtρ is therefore the mass m passing through "A". ½ ρv2 is the kinetic energy of the moving air per unit volume.

Power is energy per unit time, so the wind power incident on A (e.g. equal to the rotor area of a wind turbine) is:

${\displaystyle P={\frac {E}{t}}={\frac {1}{2}}A\rho v^{3}.}$ [11]

Wind power in an open air stream is thus proportional to the third power of the wind speed; the available power increases eightfold when the wind speed doubles. Wind turbines for grid electric power, therefore, need to be especially efficient at greater wind speeds.

Wind is the movement of air across the surface of the Earth, affected by areas of high pressure and of low pressure.[12] The global wind kinetic energy averaged approximately 1.50 MJ/m2 over the period from 1979 to 2010, 1.31 MJ/m2 in the Northern Hemisphere with 1.70 MJ/m2 in the Southern Hemisphere. The atmosphere acts as a thermal engine, absorbing heat at higher temperatures, releasing heat at lower temperatures. The process is responsible for the production of wind kinetic energy at a rate of 2.46 W/m2 sustaining thus the circulation of the atmosphere against frictional dissipation.[13]

Through wind resource assessment it is possible to provide estimates of wind power potential globally, by country or region, or for a specific site. A global assessment of wind power potential is available via the Global Wind Atlas provided by the Technical University of Denmark in partnership with the World Bank.[10][14][15] Unlike 'static' wind resource atlases which average estimates of wind speed and power density across multiple years, tools such as Renewables.ninja provide time-varying simulations of wind speed and power output from different wind turbine models at an hourly resolution.[16] More detailed, site-specific assessments of wind resource potential can be obtained from specialist commercial providers, and many of the larger wind developers will maintain in-house modeling capabilities.

The total amount of economically extractable power available from the wind is considerably more than present human power use from all sources.[17] Axel Kleidon of the Max Planck Institute in Germany, carried out a "top-down" calculation on how much wind energy there is, starting with the incoming solar radiation that drives the winds by creating temperature differences in the atmosphere. He concluded that somewhere between 18 TW and 68 TW could be extracted.[18]

Cristina Archer and Mark Z. Jacobson presented a "bottom-up" estimate, which unlike Kleidon's are based on actual measurements of wind speeds, and found that there is 1700 TW of wind power at an altitude of 100 metres (330 ft) over land and sea. Of this, "between 72 and 170 TW could be extracted in a practical and cost-competitive manner".[18] They later estimated 80 TW.[19] However, research at Harvard University estimates 1 watt/m2 on average and 2–10 MW/km2 capacity for large-scale wind farms, suggesting that these estimates of total global wind resources are too high by a factor of about 4.[20]

The strength of wind varies, and an average value for a given location does not alone indicate the amount of energy a wind turbine could produce there.

To assess prospective wind power sites a probability distribution function is often fit to the observed wind speed data.[21] Different locations will have different wind speed distributions. The Weibull model closely mirrors the actual distribution of hourly/ten-minute wind speeds at many locations. The Weibull factor is often close to 2 and therefore a Rayleigh distribution can be used as a less accurate, but simpler model.[22]

## Wind farms

Large onshore wind farms
Wind farm Capacity
(MW)
Country Refs
Gansu Wind Farm 7,965  China [23][24]
Muppandal wind farm 1,500  India [25]
Alta (Oak Creek-Mojave) 1,320  United States [26]
Jaisalmer Wind Park 1,064  India [27]
Shepherds Flat Wind Farm 845  United States [28]
Roscoe Wind Farm 782  United States
Horse Hollow Wind Energy Center 736  United States [29][30]
Capricorn Ridge Wind Farm 662  United States [29][30]
Fântânele-Cogealac Wind Farm 600  Romania [31]
Fowler Ridge Wind Farm 600  United States [32]
Whitelee Wind Farm 539  United Kingdom [33]

A wind farm is a group of wind turbines in the same location used for the production of electric power. A large wind farm may consist of several hundred individual wind turbines distributed over an extended area. Wind turbines use around 0.3 hectares of land per MW,[35] but the land between the turbines may be used for agricultural or other purposes. For example, Gansu Wind Farm, the largest wind farm in the world, has several thousand turbines. A wind farm may also be located offshore.

Almost all large wind turbines have the same design — a horizontal axis wind turbine having an upwind rotor with 3 blades, attached to a nacelle on top of a tall tubular tower.

In a wind farm, individual turbines are interconnected with a medium voltage (often 34.5 kV) power collection system[36] and communications network. In general, a distance of 7D (7 times the rotor diameter of the wind turbine) is set between each turbine in a fully developed wind farm.[37] At a substation, this medium-voltage electric current is increased in voltage with a transformer for connection to the high voltage electric power transmission system.[38]

### Generator characteristics and stability

Induction generators, which were often used for wind power projects in the 1980s and 1990s, require reactive power for excitation, so electrical substations used in wind-power collection systems include substantial capacitor banks for power factor correction. Different types of wind turbine generators behave differently during transmission grid disturbances, so extensive modeling of the dynamic electromechanical characteristics of a new wind farm is required by transmission system operators to ensure predictable stable behavior during system faults (see wind energy software). In particular, induction generators cannot support the system voltage during faults, unlike steam or hydro turbine-driven synchronous generators.

Induction generators aren't used in current turbines. Instead, most turbines use variable speed generators combined with either a partial- or full-scale power converter between the turbine generator and the collector system, which generally have more desirable properties for grid interconnection and have Low voltage ride through-capabilities.[39] Modern concepts use either doubly fed electric machines with partial-scale converters or squirrel-cage induction generators or synchronous generators (both permanently and electrically excited) with full-scale converters.[40]

Transmission systems operators will supply a wind farm developer with a grid code to specify the requirements for interconnection to the transmission grid. This will include the power factor, the constancy of frequency, and the dynamic behaviour of the wind farm turbines during a system fault.[41][42]

### Offshore wind power

Offshore wind power refers to the construction of wind farms in large bodies of water to generate electric power. These installations can utilize the more frequent and powerful winds that are available in these locations and have a less aesthetic impact on the landscape than land-based projects. However, the construction and maintenance costs are considerably higher.[43][44]

Siemens and Vestas are the leading turbine suppliers for offshore wind power. Ørsted, Vattenfall, and E.ON are the leading offshore operators.[45] As of October 2010, 3.16 GW of offshore wind power capacity was operational, mainly in Northern Europe. Offshore wind power capacity is expected to reach a total of 75 GW worldwide by 2020, with significant contributions from China and the US.[45] The UK's investments in offshore wind power have resulted in a rapid decrease of the usage of coal as an energy source between 2012 and 2017, as well as a drop in the usage of natural gas as an energy source in 2017.[46]

In 2012, 1,662 turbines at 55 offshore wind farms in 10 European countries produced 18 TWh, enough to power almost five million households.[47] As of September 2018, the Walney Extension in the United Kingdom is the largest offshore wind farm in the world at 659 MW.[48]

World's largest offshore wind farms
Wind farm Capacity
(MW)
Country Turbines and model Commissioned Refs
Walney Extension 659  United Kingdom 47 x Vestas 8MW
40 x Siemens Gamesa 7MW
2018 [48]
London Array 630  United Kingdom 175 × Siemens SWT-3.6 2012 [49][50][51]
Gemini Wind Farm 600  The Netherlands 150 × Siemens SWT-4.0 2017 [52]
Gwynt y Môr 576  United Kingdom 160 × Siemens SWT-3.6 107 2015 [53]
Greater Gabbard 504  United Kingdom 140 × Siemens SWT-3.6 2012 [54]
Anholt 400  Denmark 111 × Siemens SWT-3.6–120 2013 [55]
BARD Offshore 1 400  Germany 80 BARD 5.0 turbines 2013 [56]

### Collection and transmission network

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Wind Power in Serbia

In a wind farm, individual turbines are interconnected with a medium voltage (usually 34.5 kV) power collection system and communications network. At a substation, this medium-voltage electric current is increased in voltage with a transformer for connection to the high voltage electric power transmission system.

A transmission line is required to bring the generated power to (often remote) markets. For an offshore station, this may require a submarine cable. Construction of a new high voltage line may be too costly for the wind resource alone, but wind sites may take advantage of lines already installed for conventional fuel generation.

One of the biggest current challenges to wind power grid integration in the United States is the necessity of developing new transmission lines to carry power from wind farms, usually in remote lowly populated states in the middle of the country due to availability of wind, to high load locations, usually on the coasts where population density is higher. The current transmission lines in remote locations were not designed for the transport of large amounts of energy.[57] As transmission lines become longer the losses associated with power transmission increase, as modes of losses at lower lengths are exacerbated and new modes of losses are no longer negligible as the length is increased, making it harder to transport large loads over large distances.[58] However, resistance from state and local governments makes it difficult to construct new transmission lines. Multi-state power transmission projects are discouraged by states with cheap electric power rates for fear that exporting their cheap power will lead to increased rates. A 2005 energy law gave the Energy Department authority to approve transmission projects states refused to act on, but after an attempt to use this authority, the Senate declared the department was being overly aggressive in doing so.[57] Another problem is that wind companies find out after the fact that the transmission capacity of a new farm is below the generation capacity, largely because federal utility rules to encourage renewable energy installation allow feeder lines to meet only minimum standards. These are important issues that need to be solved, as when the transmission capacity does not meet the generation capacity, wind farms are forced to produce below their full potential or stop running altogether, in a process known as curtailment. While this leads to potential renewable generation left untapped, it prevents possible grid overload or risk to reliable service.[59]

## Wind power capacity and production

### Growth trends

[34]

In 2019, wind supplied 1430 TWh of electricity, which was 5.3% of worldwide electrical generation,[8] with the global installed wind power capacity reaching more than 651 GW, an increase of 10% over 2018.[9] Wind power supplied 15% of the electricity consumed in Europe in 2019. In 2015 there were over 200,000 wind turbines operating, with a total nameplate capacity of 432 GW worldwide.[60] The European Union passed 100 GW nameplate capacity in September 2012,[61] while the United States surpassed 75 GW in 2015 and China's grid-connected capacity passed 145 GW in 2015.[60] In 2015 wind power constituted 15.6% of all installed power generation capacity in the European Union and it generated around 11.4% of its power.[62]

World wind generation capacity more than quadrupled between 2000 and 2006, doubling about every 3 years. The United States pioneered wind farms and led the world in installed capacity in the 1980s and into the 1990s. In 1997 installed capacity in Germany surpassed the United States and led until once again overtaken by the United States in 2008. China has been rapidly expanding its wind installations in the late 2000s and passed the United States in 2010 to become the world leader. As of 2011, 83 countries around the world were using wind power on a commercial basis.[63]

The actual amount of electric power that wind can generate is calculated by multiplying the nameplate capacity by the capacity factor, which varies according to equipment and location. Estimates of the capacity factors for wind installations are in the range of 35% to 44%.[64]

Top 10 countries by added wind capacity in 2019[65][66]
•   China: 26,155 MW (43.3%)
•   United States: 9,143 MW (15.1%)
•   United Kingdom: 2,393 MW (4.0%)
•   India: 2,377 MW (3.9%)
•   Germany: 2,189 MW (3.6%)
•   Spain: 1,634 MW (2.7%)
•   Sweden: 1,588 MW (2.6%)
•   France: 1,336 MW (2.2%)
•   Mexico: 1,281 MW (2.1%)
•   Argentina: 931 MW (1.5%)
•   Rest of the world: 11,324 MW (18.8%)
Top 10 countries by cumulative wind capacity in 2019[65]
•   China: 236,402 MW (36.3%)
•   United States: 105,466 MW (16.2%)
•   Germany: 61,406 MW (9.4%)
•   India: 37,506 MW (5.8%)
•   Spain: 25,224 MW (3.9%)
•   United Kingdom: 23,340 MW (3.6%)
•   France: 16,643 MW (2.6%)
•   Brazil: 15,452 MW (2.4%)
•   Italy: 10,330 MW (1.6%)
•   Rest of the world: 105,375 MW (16.2%)
Number of countries with wind capacities in the gigawatt-scale
10
20
30
40
2005
2010
2015
2019
Growing number of wind gigawatt-markets
Countries above the 1-GW mark
•  2018 2017 2016 2015 2012 2011 2010 2009 2008 2006 2005 2004 1999 1997 1995 1986
Countries above the 10-GW mark
•  2018 2016 2015 2013 2009 2008 2006 2002
Countries above the 100-GW mark
•  2019 2014
External video
Growth of wind power by country, 2005-2020

The wind power industry set new records in 2014 – more than 50 GW of new capacity was installed. Another record-breaking year occurred in 2015, with 22% annual market growth resulting in the 60 GW mark being passed.[68] In 2015, close to half of all new wind power was added outside of the traditional markets in Europe and North America. This was largely from new construction in China and India. Global Wind Energy Council (GWEC) figures show that 2015 recorded an increase of installed capacity of more than 63 GW, taking the total installed wind energy capacity to 432.9 GW, up from 74 GW in 2006. In terms of economic value, the wind energy sector has become one of the important players in the energy markets, with the total investments reaching US$329bn (296.6bn), an increase of 4% over 2014.[A][69] Although the wind power industry was affected by the global financial crisis in 2009 and 2010, GWEC predicts that the installed capacity of wind power will be 792.1 GW by the end of 2020[68] and 4,042 GW by end of 2050.[70] The increased commissioning of wind power is being accompanied by record low prices for forthcoming renewable electric power. In some cases, wind onshore is already the cheapest electric power generation option and costs are continuing to decline. The contracted prices for wind onshore for the next few years are now as low as US$30/MWh.

In the EU in 2015, 44% of all new generating capacity was wind power; while in the same period net fossil fuel power capacity decreased.[62]

### Capacity factor

Since wind speed is not constant, a wind farm's annual energy production is never as much as the sum of the generator nameplate ratings multiplied by the total hours in a year. The ratio of actual productivity in a year to this theoretical maximum is called the capacity factor. Typical capacity factors are 15–50%; values at the upper end of the range are achieved in favorable sites and are due to wind turbine design improvements.[71][72][B]

Online data is available for some locations, and the capacity factor can be calculated from the yearly output.[73][74] For example, the German nationwide average wind power capacity factor overall of 2012 was just under 17.5% (45,867 GW·h/yr / (29.9 GW × 24 × 366) = 0.1746),[75] and the capacity factor for Scottish wind farms averaged 24% between 2008 and 2010.[76]

Unlike fueled generating plants, the capacity factor is affected by several parameters, including the variability of the wind at the site and the size of the generator relative to the turbine's swept area. A small generator would be cheaper and achieve a higher capacity factor but would produce less electric power (and thus less profit) in high winds. Conversely, a large generator would cost more but generate little extra power and, depending on the type, may stall out at low wind speed. Thus an optimum capacity factor of around 40–50% would be aimed for.[72][77]

A 2008 study released by the U.S. Department of Energy noted that the capacity factor of new wind installations was increasing as the technology improves, and projected further improvements for future capacity factors.[78] In 2010, the department estimated the capacity factor of new wind turbines in 2010 to be 45%.[79] The annual average capacity factor for wind generation in the US has varied between 29.8% and 34% during the period 2010–2015.[80]

### Penetration

Country Year[81] Penetrationa
Denmark 2019 48%
Ireland 2020[82] 36.3%
Portugal 2019 27%
Germany 2019 26%
United Kingdom 2020[83] 24.8%
United States 2019 7%
aPercentage of wind power generation
over total electricity consumption

Wind energy penetration is the fraction of energy produced by wind compared with the total generation. Wind power's share of worldwide electricity usage at the end of 2018 was 4.8%,[85] up from 3.5% in 2015.[86][87]

There is no generally accepted maximum level of wind penetration. The limit for a particular grid will depend on the existing generating plants, pricing mechanisms, capacity for energy storage, demand management, and other factors. An interconnected electric power grid will already include reserve generating and transmission capacity to allow for equipment failures. This reserve capacity can also serve to compensate for the varying power generation produced by wind stations. Studies have indicated that 20% of the total annual electrical energy consumption may be incorporated with minimal difficulty.[88] These studies have been for locations with geographically dispersed wind farms, some degree of dispatchable energy or hydropower with storage capacity, demand management, and interconnected to a large grid area enabling the export of electric power when needed. Beyond the 20% level, there are few technical limits, but the economic implications become more significant. Electrical utilities continue to study the effects of large-scale penetration of wind generation on system stability and economics.[C][89][90][91]

A wind energy penetration figure can be specified for different duration of time but is often quoted annually. To obtain 100% from wind annually requires substantial long-term storage or substantial interconnection to other systems that may already have substantial storage. On a monthly, weekly, daily, or hourly basis—or less—wind might supply as much as or more than 100% of current use, with the rest stored, exported or curtailed. The seasonal industry might then take advantage of high wind and low usage times such as at night when wind output can exceed normal demand. Such industry might include the production of silicon, aluminum,[92] steel, or natural gas, and hydrogen, and using future long-term storage to facilitate 100% energy from variable renewable energy.[93][94] Homes can also be programmed to accept extra electric power on demand, for example by remotely turning up water heater thermostats.[95]

### Variability

Wind power is variable, and during low wind periods, it must be replaced by other power sources. Transmission networks presently cope with outages of other generation plants and daily changes in electrical demand, but the variability of intermittent power sources such as wind power is more frequent than those of conventional power generation plants which, when scheduled to be operating, may be able to deliver their nameplate capacity around 95% of the time.

Electric power generated from wind power can be highly variable at several different timescales: hourly, daily, or seasonally. Annual variation also exists but is not as significant. Because instantaneous electrical generation and consumption must remain in balance to maintain grid stability, this variability can present substantial challenges to incorporating large amounts of wind power into a grid system. Intermittency and the non-dispatchable nature of wind energy production can raise costs for regulation, incremental operating reserve, and (at high penetration levels) could require an increase in the already existing energy demand management, load shedding, storage solutions, or system interconnection with HVDC cables.

Fluctuations in load and allowance for the failure of large fossil-fuel generating units require operating reserve capacity, which can be increased to compensate for the variability of wind generation.

Presently, grid systems with large wind penetration require a small increase in the frequency of usage of natural gas spinning reserve power plants to prevent a loss of electric power if there is no wind. At low wind power penetration, this is less of an issue.[96][97][98]

GE has installed a prototype wind turbine with an onboard battery similar to that of an electric car, equivalent to 60 seconds of production. Despite the small capacity, it is enough to guarantee that power output complies with the forecast for 15 minutes, as the battery is used to eliminate the difference rather than provide full output. In certain cases, the increased predictability can be used to take wind power penetration from 20 to 30 or 40 percent. The battery cost can be retrieved by selling burst power on demand and reducing backup needs from gas plants.[99]

In the UK there were 124 separate occasions from 2008 to 2010 when the nation's wind output fell to less than 2% of installed capacity.[100] A report on Denmark's wind power noted that their wind power network provided less than 1% of average demand on 54 days during the year 2002.[101] Wind power advocates argue that these periods of low wind can be dealt with by simply restarting existing power stations that have been held in readiness, or interlinking with HVDC.[102] Electrical grids with slow-responding thermal power plants and without ties to networks with hydroelectric generation may have to limit the use of wind power.[101] According to a 2007 Stanford University study published in the Journal of Applied Meteorology and Climatology, interconnecting ten or more wind farms can allow an average of 33% of the total energy produced (i.e. about 8% of total nameplate capacity) to be used as reliable, baseload electric power which can be relied on to handle peak loads, as long as minimum criteria are met for wind speed and turbine height.[103][104]

Conversely, on particularly windy days, even with penetration levels of 16%, wind power generation can surpass all other electric power sources in a country. In Spain, in the early hours of 16 April 2012 wind power production reached the highest percentage of electric power production till then, at 60.5% of the total demand.[105] In Denmark, which had a power market penetration of 30% in 2013, over 90 hours, wind power generated 100% of the country's power, peaking at 122% of the country's demand at 2  am on 28 October.[106]

Increase in system operation costs, Euros per MWh, for 10% & 20% wind share[6]
Country 10% 20%
Germany 2.5 3.2
Denmark 0.4 0.8
Finland 0.3 1.5
Norway 0.1 0.3
Sweden 0.3 0.7

A 2006 International Energy Agency forum presented costs for managing intermittency as a function of wind energy's share of total capacity for several countries, as shown in the table on the right. Three reports on the wind variability in the UK issued in 2009, generally agree that variability of wind needs to be taken into account by adding 20% to the operating reserve, but it does not make the grid unmanageable. The modest additional costs can be quantified.[7]

The combination of diversifying variable renewables by type and location, forecasting their variation, and integrating them with dispatchable renewables, flexible fueled generators, and demand response can create a power system that has the potential to meet power supply needs reliably. Integrating ever-higher levels of renewables is being successfully demonstrated in the real world:

In 2009, eight American and three European authorities, writing in the leading electrical engineers' professional journal, didn't find "a credible and firm technical limit to the amount of wind energy that can be accommodated by electric power grids". In fact, not one of more than 200 international studies, nor official studies for the eastern and western U.S. regions, nor the International Energy Agency, has found major costs or technical barriers to reliably integrating up to 30% variable renewable supplies into the grid, and in some studies much more.

Solar power tends to be complementary to wind.[109][110] On daily to weekly timescales, high-pressure areas tend to bring clear skies and low surface winds, whereas low-pressure areas tend to be windier and cloudier. On seasonal timescales, solar energy peaks in summer, whereas in many areas wind energy is lower in summer and higher in winter.[D][111] Thus the seasonal variation of wind and solar power tend to cancel each other somewhat.[108] In 2007 the Institute for Solar Energy Supply Technology of the University of Kassel pilot-tested a combined power plant linking solar, wind, biogas, and hydrostorage to provide load-following power around the clock and throughout the year, entirely from renewable sources.[112]

### Predictability

Wind power forecasting methods are used, but the predictability of any particular wind farm is low for short-term operation. For any particular generator, there is an 80% chance that wind output will change less than 10% in an hour and a 40% chance that it will change 10% or more in 5 hours.[113]

However, studies by Graham Sinden (2009) suggest that, in practice, the variations in thousands of wind turbines, spread out over several different sites and wind regimes, are smoothed. As the distance between sites increases, the correlation between wind speeds measured at those sites, decreases.[E]

Thus, while the output from a single turbine can vary greatly and rapidly as local wind speeds vary, as more turbines are connected over larger and larger areas the average power output becomes less variable and more predictable.[39][114] Weather forecasting permits the electric-power network to be readied for the predictable variations in production that occur.[115]

Wind power hardly ever suffers major technical failures, since failures of individual wind turbines have hardly any effect on overall power, so that the distributed wind power is reliable and predictable,[116] whereas conventional generators, while far less variable, can suffer major unpredictable outages.

### Energy storage

Typically, conventional hydroelectricity complements wind power very well. When the wind is blowing strongly, nearby hydroelectric stations can temporarily hold back their water. When the wind drops they can, provided they have the generation capacity, rapidly increase production to compensate. This gives a very even overall power supply and virtually no loss of energy and uses no more water.

Alternatively, where a suitable head of water is not available, pumped-storage hydroelectricity or other forms of grid energy storage such as compressed air energy storage and thermal energy storage can store energy developed by high-wind periods and release it when needed. The type of storage needed depends on the wind penetration level – low penetration requires daily storage, and high penetration requires both short- and long-term storage – as long as a month or more. Stored energy increases the economic value of wind energy since it can be shifted to displace higher-cost generation during peak demand periods. The potential revenue from this arbitrage can offset the cost and losses of storage. For example, in the UK, the 2 GW Dinorwig pumped-storage plant evens out electrical demand peaks, and allows base-load suppliers to run their plants more efficiently. Although pumped-storage power systems are only about 75% efficient, and have high installation costs, their low running costs and ability to reduce the required electrical base-load can save both fuel and total electrical generation costs.[117][118]

In particular geographic regions, peak wind speeds may not coincide with peak demand for electrical power, whether offshore or onshore. In the U.S. states of California and Texas, for example, hot days in summer may have low wind speed and high electrical demand due to the use of air conditioning. Some utilities subsidize the purchase of geothermal heat pumps by their customers, to reduce electric power demand during the summer months by making air conditioning up to 70% more efficient;[119] widespread adoption of this technology would better match electric power demand to wind availability in areas with hot summers and low summer winds. A possible future option may be to interconnect widely dispersed geographic areas with an HVDC "super grid". In the U.S. it is estimated that to upgrade the transmission system to take in planned or potential renewables would cost at least US$60 bn,[120] while the social value of added wind power would be more than that cost.[121] Germany has an installed capacity of wind and solar that can exceed daily demand, and has been exporting peak power to neighboring countries, with exports which amounted to some 14.7 billion kWh in 2012.[122] A more practical solution is the installation of thirty days storage capacity able to supply 80% of demand, which will become necessary when most of Europe's energy is obtained from wind power and solar power. Just as the EU requires member countries to maintain 90 days strategic reserves of oil it can be expected that countries will provide electric power storage, instead of expecting to use their neighbors for net metering.[123] ### Capacity credit, fuel savings and energy payback The capacity credit of wind is estimated by determining the capacity of conventional plants displaced by wind power, whilst maintaining the same degree of system security.[124][125] According to the American Wind Energy Association, production of wind power in the United States in 2015 avoided consumption of 280 million cubic metres (73 billion US gallons) of water and reduced CO 2 emissions by 132 million metric tons, while providing US$7.3 bn in public health savings.[126][127]

The energy needed to build a wind farm divided into the total output over its life, Energy Return on Energy Invested, of wind power varies but averages about 20–25.[128][129] Thus, the energy payback time is typically around a year.

## Economics

Onshore wind is an inexpensive source of electric power, competitive with or in many places cheaper than coal or gas plants.[131] According to BusinessGreen, wind turbines reached grid parity (the point at which the cost of wind power matches traditional sources) in some areas of Europe in the mid-2000s, and in the US around the same time. Falling prices continue to drive the Levelized cost down and it has been suggested that it has reached general grid parity in Europe in 2010, and will reach the same point in the US around 2016 due to an expected reduction in capital costs of about 12%.[132] According to PolitiFact, it is difficult to predict whether wind power would remain viable in the United States without subsidies.[133]

### Electric power cost and trends

Wind power is capital intensive but has no fuel costs.[135] The price of wind power is therefore much more stable than the volatile prices of fossil fuel sources.[136] The marginal cost of wind energy once a station is constructed is usually less than 1-cent per kW·h.[137]

The global average total installed costs for onshore wind power in 2017 was $1477 per kW, and$4239 per kW for offshore, but with wide variation in both cases.[138]

However, the estimated average cost per unit of electric power must incorporate the cost of construction of the turbine and transmission facilities, borrowed funds, return to investors (including the cost of risk), estimated annual production, and other components, averaged over the projected useful life of the equipment, which may be more than 20 years. Energy cost estimates are highly dependent on these assumptions so published cost figures can differ substantially. In 2004, wind energy cost 1/5 of what it did in the 1980s, and some expected that downward trend to continue as larger multi-megawatt turbines were mass-produced.[139] In 2012 capital costs for wind turbines were substantially lower than 2008–2010 but still above 2002 levels.[140] A 2011 report from the American Wind Energy Association stated, "Wind's costs have dropped over the past two years, in the range of 5 to 6 cents per kilowatt-hour recently.... about 2 cents cheaper than coal-fired electric power, and more projects were financed through debt arrangements than tax equity structures last year.... winning more mainstream acceptance from Wall Street's banks... Equipment makers can also deliver products in the same year that they are ordered instead of waiting up to three years as was the case in previous cycles.... 5,600 MW of new installed capacity is under construction in the United States, more than double the number at this point in 2010. Thirty-five percent of all new power generation built in the United States since 2005 has come from wind, more than new gas and coal plants combined, as power providers are increasingly enticed to wind as a convenient hedge against unpredictable commodity price moves."[141]

A British Wind Energy Association report gives an average generation cost of onshore wind power of around 3 pence (between US 5 and 6 cents) per kW·h (2005).[142] Cost per unit of energy produced was estimated in 2006 to be 5 to 6 percent above the cost of new generating capacity in the US for coal and natural gas: wind cost was estimated at $56 per MW·h, coal at$53/MW·h and natural gas at $53.[143] Similar comparative results with natural gas were obtained in a governmental study in the UK in 2011.[144] In 2011 power from wind turbines could be already cheaper than fossil or nuclear plants; it is also expected that wind power will be the cheapest form of energy generation in the future.[145] The presence of wind energy, even when subsidized, can reduce costs for consumers (€5 billion/yr in Germany) by reducing the marginal price, by minimizing the use of expensive peaking power plants.[146] A 2012 EU study shows the base cost of onshore wind power similar to coal when subsidies and externalities are disregarded. Wind power has some of the lowest external costs.[147] In February 2013 Bloomberg New Energy Finance (BNEF) reported that the cost of generating electric power from new wind farms is cheaper than new coal or new baseload gas plants. When including the current Australian federal government carbon pricing scheme their modeling gives costs (in Australian dollars) of$80/MWh for new wind farms, $143/MWh for new coal plants, and$116/MWh for new baseload gas plants. The modeling also shows that "even without a carbon price (the most efficient way to reduce economy-wide emissions) wind energy is 14% cheaper than new coal and 18% cheaper than new gas."[148] Part of the higher costs for new coal plants is due to high financial lending costs because of "the reputational damage of emissions-intensive investments". The expense of gas-fired plants is partly due to the "export market" effects on local prices. Costs of production from coal-fired plants built-in "the 1970s and 1980s" are cheaper than renewable energy sources because of depreciation.[148] In 2015 BNEF calculated the levelized cost of electricity (LCOE) per MWh in new powerplants (excluding carbon costs): $85 for onshore wind ($175 for offshore), $66–75 for coal in the Americas ($82–105 in Europe), gas $80–100.[149][150][151] A 2014 study showed unsubsidized LCOE costs between$37–81, depending on the region.[152] A 2014 US DOE report showed that in some cases power purchase agreement prices for wind power had dropped to record lows of $23.5/MWh.[153] The cost has reduced as wind turbine technology has improved. There are now longer and lighter wind turbine blades, improvements in turbine performance, and increased power generation efficiency. Also, wind project capital expenditure costs and maintenance costs have continued to decline.[154] For example, the wind industry in the US in early 2014 was able to produce more power at lower cost by using taller wind turbines with longer blades, capturing the faster winds at higher elevations. This has opened up new opportunities and in Indiana, Michigan, and Ohio, the price of power from wind turbines built 90–120 metres (300–400 ft) above the ground can since 2014 compete with conventional fossil fuels like coal. Prices have fallen to about 4 cents per kilowatt-hour in some cases and utilities have been increasing the amount of wind energy in their portfolio, saying it is their cheapest option.[155] Some initiatives are working to reduce the costs of electric power from offshore wind. One example is the Carbon Trust Offshore Wind Accelerator, a joint industry project, involving nine offshore wind developers, which aims to reduce the cost of offshore wind by 10% by 2015. It has been suggested that innovation at scale could deliver a 25% cost reduction in offshore wind by 2020.[156] Henrik Stiesdal, former Chief Technical Officer at Siemens Wind Power, has stated that by 2025 energy from offshore wind will be one of the cheapest, scalable solutions in the UK, compared to other renewables and fossil fuel energy sources if the true cost to society is factored into the cost of the energy equation.[157] He calculates the cost at that time to be 43 EUR/MWh for onshore, and 72 EUR/MWh for offshore wind.[158] In August 2017, the Department of Energy's National Renewable Energy Laboratory (NREL) published a new report on a 50% reduction in wind power cost by 2030. The NREL is expected to achieve advances in wind turbine design, materials, and controls to unlock performance improvements and reduce costs. According to international surveyors, this study shows that cost-cutting is projected to fluctuate between 24% and 30% by 2030. In more aggressive cases, experts estimate cost reduction of up to 40% if the research and development and technology programs result in additional efficiency.[159] In 2018 a Lazard study found that "The low end Levelized cost of onshore wind-generated energy is$29/MWh, compared to an average illustrative marginal cost of $36/MWh for coal", and noted that the average cost had fallen by 7% in a year.[160] ### Incentives and community benefits U.S. landowners typically receive$3,000–\$5,000 annual rental income per wind turbine, while farmers continue to grow crops or graze cattle up to the foot of the turbines.[161] Shown: the Brazos Wind Farm, Texas.
Some of the 6,000 turbines in California's Altamont Pass Wind Farm aided by tax incentives during the 1980s.[162]

The wind industry in the United States generates tens of thousands of jobs and billions of dollars of economic activity.[163] Wind projects provide local taxes, or payments in place of taxes and strengthen the economy of rural communities by providing income to farmers with wind turbines on their land.[161][164] Wind energy in many jurisdictions receives financial or other support to encourage its development. Wind energy benefits from subsidies in many jurisdictions, either to increase its attractiveness or to compensate for subsidies received by other forms of production which have significant negative externalities.

In the US, wind power receives a production tax credit (PTC) of 2¢/kWh in 1993 dollars for each kW·h produced, for the first 10 years; at 2¢ per kW·h in 2012, the credit was renewed on 2 January 2012, to include construction begun in 2013.[165] A 30% tax credit can be applied instead of receiving the PTC.[166][167] Another tax benefit is accelerated depreciation. Many American states also provide incentives, such as exemption from property tax, mandated purchases, and additional markets for "green credits".[168] The Energy Improvement and Extension Act of 2008 contains extensions of credits for wind, including microturbines. Countries such as Canada and Germany also provide incentives for wind turbine construction, such as tax credits or minimum purchase prices for wind generation, with assured grid access (sometimes referred to as feed-in tariffs). These feed-in tariffs are typically set well above average electric power prices.[169][170] In December 2013 U.S. Senator Lamar Alexander and other Republican senators argued that the "wind energy production tax credit should be allowed to expire at the end of 2013"[171] and it expired 1 January 2014 for new installations.

Secondary market forces also provide incentives for businesses to use wind-generated power, even if there is a premium price for the electricity. For example, socially responsible manufacturers pay utility companies a premium that goes to subsidize and build new wind power infrastructure. Companies use wind-generated power, and in return, they can claim that they are undertaking strong "green" efforts. In the US the organization Green-e monitors business compliance with these renewable energy credits.[172] Turbine prices have fallen significantly in recent years due to tougher competitive conditions such as the increased use of energy auctions, and the elimination of subsidies in many markets. For example, Vestas, a wind turbine manufacturer, whose largest onshore turbine can pump out 4.2 megawatts of power, enough to provide electricity to roughly 5,000 homes, has seen prices for its turbines fall from €950,000 per megawatt in late 2016, to around €800,000 per megawatt in the third quarter of 2017.[173]

## Small-scale wind power

Small-scale wind power is the name given to wind generation systems with the capacity to produce up to 50 kW of electrical power.[174] Isolated communities, that may otherwise rely on diesel generators, may use wind turbines as an alternative. Individuals may purchase these systems to reduce or eliminate their dependence on grid electric power for economic reasons, or to reduce their carbon footprint. Wind turbines have been used for household electric power generation in conjunction with battery storage over many decades in remote areas.[175]

Recent examples of small-scale wind power projects in an urban setting can be found in New York City, where, since 2009, several building projects have capped their roofs with Gorlov-type helical wind turbines. Although the energy they generate is small compared to the buildings' overall consumption, they help to reinforce the building's 'green' credentials in ways that "showing people your high-tech boiler" cannot, with some of the projects also receiving the direct support of the New York State Energy Research and Development Authority.[176]

Grid-connected domestic wind turbines may use grid energy storage, thus replacing purchased electric power with locally produced power when available. The surplus power produced by domestic microgenerators can, in some jurisdictions, be fed into the network and sold to the utility company, producing a retail credit for the microgenerators' owners to offset their energy costs.[177]

Off-grid system users can either adapt to intermittent power or use batteries, photovoltaic, or diesel systems to supplement the wind turbine.[178] Equipment such as parking meters, traffic warning signs, street lighting, or wireless Internet gateways may be powered by a small wind turbine, possibly combined with a photovoltaic system, that charges a small battery replacing the need for a connection to the power grid.[179]

A Carbon Trust study into the potential of small-scale wind energy in the UK, published in 2010, found that small wind turbines could provide up to 1.5 terawatt-hours (TW·h) per year of electric power (0.4% of total UK electric power consumption), saving 600,000 tons of carbon dioxide (Mt CO2) emission savings. This is based on the assumption that 10% of households would install turbines at costs competitive with grid electric power, around 12 pence (US 19 cents) a kW·h.[180] A report prepared for the UK's government-sponsored Energy Saving Trust in 2006, found that home power generators of various kinds could provide 30 to 40% of the country's electric power needs by 2050.[181]

Distributed generation from renewable resources is increasing as a consequence of the increased awareness of climate change. The electronic interfaces required to connect renewable generation units with the utility system can include additional functions, such as the active filtering to enhance the power quality.[182]