Courtesy : en.wikipedia.org
Green wind energy
Wind power or wind energy is mostly the use of wind turbines to generate electricity. Wind power is a popular, sustainable, renewable energy source that has a much smaller impact on the environment than burning fossil fuels. Historically, wind power has been used in sails, windmills and windpumps but today it is mostly used to generate electricity. Wind farms consist of many individual wind turbines, which are connected to the electric power transmission network.
New onshore (on-land) wind farms are cheaper than new coal or gas plants, but expansion of wind power is being hindered by fossil fuel subsidies.Onshore wind farms have a greater visual impact on the landscape than some other power stations. Small onshore wind farms can feed some energy into the grid or provide power to isolated off-grid locations. Offshore wind farms provide a steadier and stronger source of energy and have less visual impact. Although there is less offshore wind power at present and construction and maintenance costs are higher, it is expanding.
Wind power is variable renewable energy, so power-management techniques are used to match supply and demand, such as: wind hybrid power systems, hydroelectric power or other dispatchable power sources, excess capacity, geographically distributed turbines, exporting and importing power to neighboring areas, or grid storage. As the proportion of wind power in a region increases the grid may need to be upgraded. Weather forecasting allows the electric-power network to be readied for the predictable variations in production that occur.
In 2021, wind supplied over 1800 TWh of electricity, which was over 6% of world electricity and about 2% of world energy.With about 100 GW added during 2021, mostly in China and the United States, global installed wind power capacity exceeded 800 GW.To help meet the Paris Agreement goals to limit climate change, analysts say it should expand much faster – by over 1% of electricity generation per year.
Wind energy
Global map of wind speed at 100 m above surface level.
Roscoe Wind Farm: an onshore wind farm in West Texas near Roscoe
Distribution of wind speed (red) and energy (blue) for all of 2002 at the Lee Ranch facility in Colorado. The histogram shows measured data, while the curve is the Rayleigh model distribution for the same average wind speed.
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},}
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}.}
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 is the movement of air across the surface of the Earth, driven by areas of high and low pressure. 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 thus sustaining the circulation of the atmosphere against friction.
Through wind resource assessment it is possible to estimate wind power potential globally, by country or region, or for a specific site. The Global Wind Atlas provided by the Technical University of Denmark in partnership with the World Bank provides a global assessment of wind power potential.[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.More detailed, site-specific assessments of wind resource potential can be obtained from specialist commercial providers, and many of the larger wind developers have 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. 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. 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
Wind farms
Main articles: Wind farm and List of onshore wind farms
| Wind farm | Capacity (MW) | Country | Refs |
|---|---|---|---|
| Gansu Wind Farm | 7,965 |  China | [25] |
| Muppandal wind farm | 1,500 |  India | [26] |
| Alta (Oak Creek-Mojave) | 1,320 |  United States | [27] |
| Jaisalmer Wind Park | 1,064 | India | [28] |
A wind farm is a group of wind turbines in the same location. A large wind farm may consist of several hundred individual wind turbines distributed over an extended area. 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 systemand 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.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
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.
Induction generators are not 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. Modern turbines 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. Black start is possibleand is being further developed for places (such as Iowa) which generate most of their electricity from wind.
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.
Offshore wind power
The world’s second full-scale floating wind turbine (and first to be installed without the use of heavy-lift vessels), WindFloat, operating at rated capacity (2 MW) approximately 5 km offshore of Póvoa de Varzim, Portugal
Offshore windfarms, including floating windfarms, provide a small but growing fraction of total windfarm power generation. Such power generation capacity must grow substantially to help meet the IEA’s Net Zero by 2050 pathway to combat climate change.
Main articles: Offshore wind power and List of offshore wind farms
Offshore wind power is wind farms in large bodies of water, usually the sea. These installations can utilize the more frequent and powerful winds that are available in these locations and have less visual impact on the landscape than land-based projects. However, the construction and maintenance costs are considerably higher.
Siemens and Vestas are the leading turbine suppliers for offshore wind power. Ørsted, Vattenfall, and E.ON are the leading offshore operators. As of November 2021, the Hornsea Wind Farm in the United Kingdom is the largest offshore wind farm in the world at 1,218 MW.
Collection and transmission network
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.
Wind power resources are not always located near to high population density. 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.
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.
One of the biggest current challenges to wind power grid integration in some countries is the necessity of developing new transmission lines to carry power from wind farms, usually in remote lowly populated areas due to availability of wind, to high load locations, usually on the coasts where population density is higher.Any existing transmission lines in remote locations may not have been designed for the transport of large amounts of energy. In particular geographic regions, peak wind speeds may not coincide with peak demand for electrical power, whether offshore or onshore. A possible future option may be to interconnect widely dispersed geographic areas with an HVDC super grid.
Wind power capacity and production
Main articles: Wind power by country and Wind power industry
Growth trends
Log graph of global wind power cumulative capacity (Data:GWEC)
Wind energy generation by region over time
In 2020, wind supplied almost 1600 TWh of electricity, which was over 5% of worldwide electrical generation and about 2% of energy consumption. With over 100 GW added during 2020, mostly in China, global installed wind power capacity reached more than 730 GW. But to help meet Paris Agreement goals to limit climate change analysts say it should expand much faster – by over 1% of electricity generation per year. Expansion of wind power is being hindered by fossil fuel subsidies.
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%.
Wind generation by country
| Number of countries with wind capacities in the gigawatt-scale102030402005201020152019Growing number of wind gigawatt-marketsshow Countries above the 1-GW markshow Countries above the 10-GW markshow Countries above the 100-GW mark |
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. Online data is available for some locations, and the capacity factor can be calculated from the yearly output.
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.
Penetration
Share of electricity production from wind, 2021
In 2021, wind and solar power reached a record 10% of global electricity. Shown: 20 leading countries.
Wind energy penetration is the fraction of energy produced by wind compared with the total generation. Wind power’s share of worldwide electricity usage in 2021 was almost 7%, up from 3.5% in 2015.
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.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 stabilit and economics.
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,steel, or natural gas, and hydrogen, and using future long-term storage to facilitate 100% energy from variable renewable energy. Homes can also be programmed to accept extra electric power on demand, for example by remotely turning up water heater thermostats.
Variability
Main article: Variable renewable energy
Further information: Grid balancing
Wind turbines are typically installed in windy locations. In the image, wind power generators in Spain, near an Osborne bull.
Roscoe Wind Farm in West Texas
Wind power is variable, and during low wind periods, it may need to 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.
Utility-scale batteries are often used to balance hourly and shorter timescale variation, but car batteries may gain ground from the mid-2020s. Wind power advocates argue that periods of low wind can be dealt with by simply restarting existing power stations that have been held in readiness, or interlinking with HVDC. 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.
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.
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Seasonal cycle of capacity factors for wind and photovoltaics in Europe under idealized assumptions. The figure illustrates the balancing effects of wind and solar energy at the seasonal scale (Kaspar et al., 2019).
Solar power tends to be complementary to wind.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. Thus the seasonal variation of wind and solar power tend to cancel each other somewhat.Wind hybrid power systems are becoming more popular.
Predictability
Main article: Wind power forecasting
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.
In summer 2021 wind power in the United Kingdom fell due to the lowest winds in seventy years – smoothing peaks by producing hydrogen may help in future when wind has a larger share of generation.
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. Weather forecasting permits the electric-power network to be readied for the predictable variations in production that occur.
It is thought that the most reliable low-carbon electricity systems will include a large share of wind power.
Energy storage
Main article: Grid energy storage
See also: List of energy storage projects
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. 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.
Fuel savings and energy payback
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 CO2 emissions by 132 million metric tons, while providing US$7.3 bn in public health savings.
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 20–25Thus, the energy payback time is typically around a year.
