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 stationsSmall onshore wind farms can feed some energy into the grid or provide power to isolated off-grid locations. Offshore wind farms deliver more energy per installed capacity with less fluctuations and have less visual impact. Although there is less offshore wind power at present and construction and maintenance costs are higher, it is expanding. Offshore wind power currently has a share of about 10% of new installations
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 electricitand about 2% of world ener 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
Regions in the higher northern and southern latitudes have the highest potential for wind power. Installed capacity has reached 650 GW in 2019. In most regions, wind power generation is higher in the winter when PV output is low. For this reason, combinations of wind and solar power are recommended.
Wind energy
Global map of wind speed at 100 m above surface level.
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. 1⁄2 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
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 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-capabilitiesModern 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 possibland 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 use 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 energyIn 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.
