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Wind Energy
Wind Energy
Wind Energy is the conversion of wind energy into a useful form, such as electricity, using wind turbines. At the end of 2008, worldwide nameplate capacity of wind-powered generators was 121.2 gig watts (GW). Wind power produces about 1.5% of worldwide electricity use, and is growing rapidly, having doubled in the three years between 2005 and 2008. Several countries have achieved relatively high levels of wind power penetration, such as 19% of stationary electricity production in Denmark, 11% in Spain and Portugal, and 7% in Germany and the Republic of Ireland in 2008. As of May 2009, eighty countries around the world are using wind power on a commercial basis.
Large-scale wind farms are typically connected to the local electric power transmission network; smaller turbines are used to provide electricity to isolated locations. Utility companies increasingly buy back surplus electricity produced by small domestic turbines. Wind (and solar) energy as power sources is favored by environmentalists as an alternative to fossil fuels, because they are plentiful, renewable, widely distributed, clean, and produce no greenhouse gas emissions; however, the construction of wind farms is not universally welcomed due to their visual impact and other effects on the environment.
Wind power, along with solar power, is non-dispatch able, meaning that for economic operation all of the available output must be taken when it is available, and other resources, such as hydropower, must be used to match supply with demand. The intermittency of wind seldom creates problems when using wind power to supply a low proportion of total demand. Where wind is to be used for a moderate fraction of demand, additional costs for compensation of intermittency are considered to be modest.
Electricity generated by a wind farm is normally fed into the national electric power 
transmission network. Individual turbines are interconnected with a medium voltage (usually 34.5 kV) power collection system and communications network. At a substation, this medium-voltage electrical current is increased in voltage with a transformer for connection to the high voltage transmission system. The surplus power produced by domestic micro generators can, in some jurisdictions, be fed back into the network and sold back to the utility company, producing a retail credit for the consumer to offset their energy costs.
Induction generators, often used for wind power projects, require reactive power for excitation so 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: Low voltage ride through). In particular, induction generators cannot support the system voltage during faults, unlike steam or hydro turbine-driven synchronous generators (however, properly matched power factor correction capacitors along with the electronic control of resonance can support induction generation without a grid). Doubly-fed machines—wind turbines with solid-state converters between the turbine generator and the collector system—generally have more desirable properties for grid interconnection. 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 power factor, constancy of frequency and dynamic behavior of the wind farm turbines during a system fault.
As of 2008, Europe leads the world in development of offshore wind power, due to strong wind resources and shallow water in the North Sea and the Baltic Sea, and limitations on suitable locations on land due to dense populations and existing developments. Denmark installed the first offshore wind farms, and for years was the world leader in offshore wind power until the United Kingdom gained the lead in October, 2008 with 590 MW of nameplate capacity installed. The United Kingdom planned to build much more extensive offshore wind farms by 2020.[50] Other large markets for wind power, including the United States and China focused first on developing their on-land wind resources where construction costs are lower (such as in the Great Plains of the U.S., and the similarly wind-swept steppes of Xinjiang and Inner Mongolia in China), but population centers along coastlines in many parts of the world are close to offshore wind resources, which would reduce transmission costs.
On 21 December 2007, Q7 (later renamed as Princess Amelia Wind Farm) exported first power to the Dutch grid, which was a milestone for the offshore wind industry. The 120 MW offshore wind farm with a construction budget of €383 million was the first to be financed by a nonrecourse loan (project finance). The project comprises 60 Vistas V80-2MW wind turbines. Each turbine's tower rests on a monopole foundation to a depth of between 18–23 meters at a distance of about 23 km off the Dutch coast.
Transporting large wind turbine components (tower sections, nacelles, and blades) is much 
easier over water than on land, because ships and barges can handle large loads more easily than trucks/lorries or trains. On land, large goods vehicles must negotiate bends on roadways, which fixes the maximum length of a wind turbine blade that can move from point to point on the road network; no such limitation exists for transport on open water. Construction and maintenance costs per wind turbine are higher for offshore wind farms, motivating operators to reduce the number of wind turbines for a given total power by installing the largest available units. An example is Belgium's Thornton bank Wind Farm with construction underway in 2008, featuring 5 MW wind turbines from Repower, which were among the largest wind turbines in the world at the time. In 2009, the first floating wind turbine was launched by Statoil Hydro. The 2.3 MW turbines can be anchored in water 120–700 m deep. It will be tested off the coast of Norway for two years.