Wind FARM

wind farm or wind park also called a wind power station or wind power plant 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 can be either onshore or offshore.

Part of the United States with a turbine under construction

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. However, at higher altitudes, the power in the wind decreases proportionally to the decrease in air density. Rendering significantly less efficient power extraction by the wind turbines, requiring a higher investment for the same generation capacity at lower altitudes.

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 over 6,000 MW by 2012, with a goal of 20,000 MW by 2020. As of September 2018, the 659 MW Walney 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.

Wind farms tend to have much less impact on the environment than many other power stations. Onshore wind farms are also criticized for their visual impact and impact on the landscape, as typically they need to take up more land than other power stations and need to be built in wild and rural areas, which can lead to “industrialization of the countryside”, habitat loss, and a drop in tourism. Critics have linked wind farms to adverse health effects (see wind turbine syndrome). Wind farms have also been criticized for interfering with radar, radio and television reception.

Many 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 opportunities get to be developed upon. After the deadline to request a place in the queue has passed, many firms will withdraw their requests after gauging the competition to make back some of the deposit for each request that is determined too risky in comparison to other larger firms’ requests.

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 generation without significant upgrades to transmission lines and substations, which have substantial costs, potentially undermining the viability of a project within that area, 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.

How closely to space the turbines together is a major factor in wind farm design. 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 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 3.5 times the rotor diameter of the turbine between turbines as a minimum. Closer spacing is possible depending on the turbine model, the conditions at the site, and how the site will be operated. Airflows slow down as they approach an obstacle, known as the ‘blockage effect’, reducing available wind power by 2% for the turbines in front of other turbines.

 

Map of available wind power over the United States. Color codes indicate wind power density class

The location is critical to the success of a wind farm. Conditions contributing to a successful wind farm location include wind conditions, access to electric transmission, physical access, and local electricity prices.

Usually, sites are screened based on a wind atlas and validated with on-site wind measurements via a 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. The collection of site-specific data for wind speed and direction is crucial to determining site potential 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.

Mountain passes are ideal locations for wind farms under these conditions. Mountain passes channel wind blocked by mountains through a tunnel-like pass towards areas of lower pressure and flatter land. Passes used for wind farms like 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 a lot about turbulence and crowding effects of large-scale wind projects previously unresearched in the U.S. due to the lack of operational wind farms large enough to conduct these types of studies on.

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 they risk damage. The average power in the wind is not proportional to the average wind speed, however. 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 towards areas of lower pressure and flatter land. Passes used for wind farms like 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 a lot about turbulence and crowding effects of large-scale wind projects previously unresearched in the U.S. due to the lack of operational wind farms large enough to conduct these types of studies on.

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