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Location Planning A yardstick is used to select locations for wind energy development that is referred to as Wind Power Density (WPD) It is a calculation relating to the effective force of the wind at a particular location, frequently expressed in term of the elevation above ground level over a period of time. It takes into account velocity and mass. Color coded maps are prepared for a particular area describing, for example, ''Mean Annual Power Density, at 50 Meters.'' The results of the above calculation are used in an index developed by the National Renewable Energy Lab and referred to as ''NREL CLASS.'' The larger the WPD calculation the higher it is rated by class. Wind speed A map of available wind power over the United States is available. Color codes indicate wind power density class. As a general rule, wind generators are practical if windspeed is 10 mph (16 km/h or 4.5 m/s) or greater. An ideal location would have a near constant flow of non-turbulent wind throughout the year with a minimum likelihood of sudden powerful bursts of wind. An important factor of turbine siting is also access to local demand or transmission capacity. Usually sites are preselected on basis of a wind atlas, and validated with wind measurements. 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. Local winds are often monitored for a year or more, and detailed wind maps constructed before wind generators are installed. A yardstick used to select locations for wind energy development is referred to as Wind Power Density (WPD) which is further defined under ''Location Planning'' above. To collect wind data, a meteorological tower is installed with instruments at various heights along the tower. All towers include anemometers to determine the wind speed and wind vanes to determine the direction. The towers generally vary in height from 30 to 60 meters. The towers primarily are guyed steel-pipe structures which are left to collect data for one to two years and then disassembled. Data is collected by a data logging device which stores and transmits data for analysis. Great attention must be paid to the exact positions of the turbines (a process known as micro-siting) because a difference of 30 m can nearly double energy production. For smaller installations where such data collection is too expensive or time consuming, the normal way of prospecting for wind-power sites is to directly look for trees or vegetation that are permanently ''cast'' or deformed by the prevailing winds. Another way is to use a wind-speed survey map, or historical data from a nearby meteorological station, although these methods are less reliable. Wind farm siting can be highly controversial, particularly when sites are picturesque or environmentally sensitive, such as having substantial bird life, or requiring roads to be built through pristine areas. Altitude The wind blows faster at higher altitudes because of the reduced influence of drag of the surface and lower air viscosity. 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. Typically, the increase of wind speeds with increasing height follows a wind profile power law, which predicts that wind speed rises proportionally to the seventh root of altitude. Doubling the altitude of a turbine, then, increases the expected wind speeds by 10% and the expected power by 34%. Wind park effect The ''wind park effect'' refers to the loss of output due to mutual interference between turbines. Wind farms have many turbines and each extracts some of the energy of the wind. Where land area is sufficient, turbines are spaced three to five rotor diameters apart perpendicular to the prevailing wind, and five to ten rotor diameters apart in the direction of the prevailing wind, to minimize efficiency loss. The loss can be as low as 2% of the combined nameplate rating of the turbines. In a large wind park, due to ''multifractal'' effects between individual rotors, the behaviour deviates significantly from Kolmogorov's turbulence scaling for individual turbines. Environmental and aesthetic impacts Compared to the environmental effects of traditional energy sources, the environmental effects of wind power are relatively minor. Wind power consumes no fuel, and emits no air pollution, unlike fossil fuel power sources. The energy consumed to manufacture and transport the materials used to build a wind power plant is equal to the new energy produced by the plant within a few months of operation. Garrett Gross, a scientist from UMKC in Kansas City, Missouri states, ''The impact made on the environment is very little when compared to what is gained.'' While a wind farm may cover a large area of land, many land uses such as agriculture are compatible, with only small areas of turbine foundations and infrastructure made unavailable for use. Danger to birds and bats has been a concern in some locations. However, studies show that the number of birds killed by wind turbines is negligible compared to the number that die as a result of other human activities, and especially the environmental impacts of using non-clean power sources. Bat species appear to be at risk during key movement periods. Almost nothing is known about current populations of these species and the impact on bat numbers as a result of mortality at windpower locations. Offshore wind sites 10 km or more from shore do not interact with bat populations. Aesthetics have also been an issue in some areas. In the USA, the Massachusetts Cape Wind project was delayed for years mainly because of aesthetic concerns. In the UK, repeated opinion surveys have shown that more than 70% of people either like, or do not mind, the visual impact. According to a town councillor in Ardrossan, Scotland, the overwhelming majority of locals believe that the Ardrossan Wind Farm has enhanced the area, saying that the turbines are impressive looking and bring a calming effect to the town. Health effects have been reported in many locations. Effect on power grid The intermittency of wind power and other renewable power sources creates issues in power grids, which expect a certain consistency in power output. One proposed solution in Europe is to create a super grid of interconnected wind farms. This large-scale array of dispersed wind farms would be located in different wind regimes, reducing the overall variation in power output. Development To develop a wind farm, a suitable location is first identified. Good locations for wind farms should have fast steady winds and be near transmission lines. Land parcels on which wind turbines will be located then must be leased from the land owners. The wind resource must then be evaluated using data recorded by onsite meteorological towers. The wind farm project must then be financed and constructed. Renewable Energy Products and Services in New Mexico |
