A wind farm, also called a wind park or wind power plant,Robert Gasch, Jochen Twele (editors). Wind Power Plants: Fundamentals, Design, Construction and Operation. Springer, 2011. p. 11. is a group of wind turbines in the same location used to produce electricity. Wind farms vary in size from a small number of turbines to several hundred wind turbines covering an extensive area. Wind farms may be either onshore or offshore.
Many of the largest operational onshore wind farms are located in China, India, and the United States. For example, the largest wind farm in the world, Gansu Wind Farm in China had a capacity of more than 6,000 MW by 2012,Watts, Jonathan & Huang, Cecily. Winds Of Change Blow Through China As Spending On Renewable Energy Soars, The Guardian, 19 March 2012, revised on 20 March 2012. Retrieved 4 January 2012. with a goal of 20,000 MWFahey, Jonathan. In Pictures: The World's Biggest Green Energy Projects, Forbes, 9 January 2010. Retrieved 19 June 2019. by 2020. As of December 2020, the 1218 MW Hornsea Wind Farm in the UK is the largest offshore wind farm in the world. Individual wind turbine designs continue to increase in power, resulting in fewer turbines being needed for the same total output.
Because they require no fuel, wind farms have less of an effect on the environment than many other forms of power generation and are often referred to as a good source of green energy. Wind farms have, however, been criticised for their visual and landscape effects. Typically they need to be spread over more land than other power stations and need to be built in wild and rural areas, which may lead to "industrialization of the countryside", habitat loss, and a drop in tourism. Some critics claim that wind farms have adverse health effects, but most researchers consider these claims to be pseudoscience (see wind turbine syndrome). Wind farms can interfere with radar, although in most cases, according to the U.S. Department of Energy, "siting and other mitigations have resolved conflicts and allowed wind projects to co-exist effectively with radar".
Siting considerations Location is critical to the overall success of a wind farm. Additional conditions contributing to a successful wind farm location include: wind conditions, access to electric transmission, physical access, and local electricity prices.
Wind conditions
The faster the average wind speed, the more electricity the wind turbine will generate, so faster winds are generally economically better for wind farm developments. The balancing factor is that strong gusts and high turbulence require stronger more expensive turbines, otherwise there is a risk of damage. The average power in the wind is not proportional to the average wind speed. For this reason, the ideal wind conditions would be strong but consistent winds with low turbulence coming from a single direction.
Mountain passes are ideal locations for wind farms under these conditions. Mountain passes channel wind, blocked by mountains, through a tunnel-like pass toward areas of lower pressure and flatter land. Passes used for wind farms such as the San Gorgonio Pass and Altamont Pass are known for their abundant wind resource capacity and capability for large-scale wind farms. These types of passes were the first places in the 1980s to have heavily invested large-scale wind farms after approval for wind energy development by the U.S. Bureau of Land Management. From these wind farms, developers learned much about turbulence and crowding effects of large-scale wind projects, which were previously unresearched, in the U.S. due to the lack of operational wind farms large enough to conduct these types of studies.
Usually sites are screened on the basis of a wind atlas, and validated with on-site wind measurements via long term or permanent meteorological-tower data using anemometers and wind vanes. Meteorological wind data alone is usually not sufficient for accurate siting of a large wind power project. Collection of site specific data for wind speed and direction is crucial to determining site potential in order to finance the project. Local winds are often monitored for a year or more, detailed wind maps are constructed, along with rigorous grid capability studies conducted, before any wind generators are installed.
The wind blows faster at higher altitudes because of the reduced influence of drag. The increase in velocity with altitude is most dramatic near the surface and is affected by topography, surface roughness, and upwind obstacles such as trees or buildings. At altitudes of thousands of feet/hundreds of metres above sea level, the power in the wind decreases proportional to the decrease in air density.
Electricity grid considerations
Often in heavily saturated energy markets, the first step in site selection for large-scale wind projects, before wind resource data collection, is finding areas with adequate available transfer capability (ATC). ATC is the measure of the remaining capacity in a transmission system available for further integration of two interconnected areas without significant upgrades to existing transmission lines and substations. Significant equipment upgrades have substantial costs, potentially undermining the viability of a project within a location, regardless of wind resource availability. Once a list of capable areas is constructed, the list is refined based on long term wind measurements, among other environmental or technical limiting factors such as proximity to load and land procurement.
Many independent system operators (ISOs) in the United States such as the California ISO and Midcontinent ISO use interconnection request queues to allow developers to propose a new generation for a specific given area and grid interconnection. These request queues have both deposit costs at the time of request and ongoing costs for the studies the ISO will make for up to years after the request was submitted to ascertain the viability of the interconnection due to factors such as ATC. Larger corporations who can afford to bid the most queues will most likely have market power as to which sites with the most resource and opportunity are eventually developed. After the deadline to request a place in the queue has passed, many firms will withdraw their requests after gauging the competition in order to make back some of the deposit for each request that is determined too risky in comparison to other larger firms' requests.
Design Turbine spacing A major factor in wind-farm design is the spacing between the turbines, both laterally and axially (with respect to the prevailing winds). The closer the turbines are together, the more the upwind turbines block wind from their rear neighbors (wake effect). However, spacing turbines far apart increases the costs of roads and power cables, and raises the amount of land needed to install a specific capacity of turbines. As a result of these factors, turbine spacing varies by site. Generally speaking, manufacturers require a minimum of 3.5 times the turbine's rotor diameter of clear space between each adjacent turbine's respective spatial envelope.
Closer spacing is possible depending on the turbine model, the conditions at the site, and how the site will be operated. Airflows slow as they approach an obstacle, known as the 'blockage effect', reducing available wind power by 2% for the turbines in front of other turbines.
Onshore
The capacity of the world's first wind farm was 0.6 MW, produced by 20 wind turbines rated at 30 kilowatts each, installed on the shoulder of Crotched Mountain in southern New Hampshire in December 1980.
+ World's largest onshore wind farms Wind farm Present capacity (MW) Country Notes Gansu Wind Farm 30,000 China Zhang Jiakou21,235ChinaUrat Zhongqi, Bayannur City2,100ChinaM'Intyre & Herries Range QLD2,023AustraliaMarkbygden Wind Farm2,000SwedenHami Wind Farm2,000ChinaDamao Qi, Baotou City1,600China Muppandal Wind farm 1,500 India Alta (Oak Creek-Mojave) 1,320 United States Terra-Gen Press Release , 17 April 2012Complexo Eólico Lagoa dos Ventos 1,112 Brazil Jaisalmer Wind Park 1,064 India Complexo Eólico Rio do Vento 1,038 Brazil Hongshagang, Town, Minqin County1,000ChinaKailu, Tongliao1,000ChinaChengde1,000China Shepherds Flat Wind Farm 845 United States Meadow Lake Wind Farm 801 United States Roscoe Wind Farm 781.5 United States Horse Hollow Wind Energy Center 735.5 United States Capricorn Ridge Wind Farm 662.5 United States Fântânele-Cogealac Wind Farm 600 Romania Fowler Ridge Wind Farm 599.8 United States Sweetwater Wind Farm 585.3 United States Complexo Eólico Chuí 582 Brazil Zarafara Wind Farm545Egypt Whitelee Wind Farm 539 United Kingdom Buffalo Gap Wind Farm 523.3 United States Dabancheng Wind Farm 500 China Panther Creek Wind Farm 458 United States
Onshore turbine installations in hilly or mountainous regions tend to be on ridges generally three kilometres or more inland from the nearest shoreline. This is done to exploit the topographic acceleration as the wind accelerates over a ridge. The additional wind speeds gained in this way can increase energy produced because more wind goes through the turbines. The exact position of each turbine matters, because a difference of 30 metres could potentially double output. This careful placement is referred to as 'micro-siting'.
Offshore
Europe is the leader in offshore wind energy, with the first offshore wind farm (Vindeby) being installed in Denmark in 1991. As of 2010, there were 39 offshore wind farms in waters off Belgium, Denmark, Finland, Germany, Ireland, the Netherlands, Norway, Sweden, and the United Kingdom, with a combined operating capacity of 2,396 MW. More than 100 GW (or 100,000 MW) of offshore projects are proposed or under development in Europe. The European Wind Energy Association set a target of 40 GW installed by 2020 and 150 GW by 2030.
, The Walney Wind Farm in the United Kingdom is the largest offshore wind farm in the world at 659 MW, followed by the London Array (630 MW) also in the UK.
Offshore wind turbines are less obtrusive than turbines on land, as their apparent size and noise is mitigated by distance. Because water has less surface roughness than land (especially deeper water), the average wind speed is usually considerably higher over open water. Capacity factors (utilisation rates) are considerably higher than for onshore locations.
The province of Ontario, Canada is pursuing several proposed locations in the Great Lakes, including the suspendedOffshore wind development hits a snag in Ontario Alberta Oil Magazine, April 2011. Retrieved 29 September 2011. Trillium Power Wind 1 approximately 20 km from shore and over 400 MW in size. Other Canadian projects include one on the Pacific west coast. In 2010, there were no offshore wind farms in the United States, but projects were under development in wind-rich areas of the East Coast, Great Lakes, and Pacific coast; and in late 2016 the Block Island Wind Farm was commissioned.Installation and service / maintenance of off-shore wind farms are a challenge for technology and economic operation of a wind farm. , there are 20 jackup vessels for lifting components, but few can lift sizes above 5 MW. Service vessels have to be operated nearly 24/7 (availability higher than 80% of time) to get sufficient amortisation from the wind turbines. Therefore, special fast service vehicles for installation (like Wind Turbine Shuttle) as well as for maintenance (including heave compensation and heave compensated working platforms to allow the service staff to enter the wind turbine also at difficult weather conditions) are required. So-called inertial and optical based Ship Stabilization and Motion Control systems (iSSMC) are used for that.