Siting for Wind Farms

The number of met stations and the time period for data collection to predict the energy production for a wind farm vary depending on the terrain and the availability of long-term base data in the vicinity. In general, numerical models of wind flow will predict wind speeds to within 5% for relatively flat terrain and 10% for complex terrain, which means an error in energy of 15-30%. Therefore, a wind measurement program is imperative before a wind farm is installed. However, if a number of wind farms are already in the region, then 1 year of data collection might suffice.

For complex terrain, you may need one met station per three to five wind turbines. For wind turbines of 500 kW to megawatts, you may need a met station per one or two wind turbines in complex terrain. With more homogeneous terrain, as in the Plains, a primary tall met station and one to four smaller met stations may suffice. The tallest met station should be a representative location on the wind farm area, not the best point.

Contour maps are used for location of wind turbine pads and for roads. In general, the wind turbines will be located on the higher elevations within the wind farm area. Topozone has interactive topography maps (all different scales) online for the entire United States [19]. These maps are very useful in selection of met tower locations, micrositing, roads, and other physical aspects of the wind farm.

The key factors for array siting for the Zond wind farms [20] in Tehachapi Pass were an extensive anemometer data network, the addition of new stations during the planning period, a time frame of 1 year to refine the array plans, a project team approach to evaluate the merits of different siting strategies, and the use of initial operating results to refine the rest of the array. A large number of met stations were needed because the spatial variation of the wind resource over short distances in complex terrain was greater than expected. The energy output from 2 projects, 98 wind turbines and 342 wind turbines, was within 3% of the predicted value. This experience shows it is possible to estimate long-term production from a wind plant with acceptable accuracy for the financial community. One of the key factors is an extensive network of met towers.

In some older wind plants, the lowest producing wind turbines were relocated (these were small wind turbines). The money spent on micrositing is a small fraction of the project cost, but the value of the information gained is critical to accurately estimating the energy production. Many of the problems with low energy production are because of poor siting.

Wind turbines have become larger, with rotor diameters from 60 to 100 m and hub heights of 60 to 100 m. There are very little data at or above these heights; however, NREL had a program for tall tower data [21]. The problem is that any tall tower data collected by wind farm developers are proprietary.

Because of wind shear, wind turbines are located on the higher elevations for rolling terrain, on mesas, and on ridges in complex terrain. In the past, turbulence was considered a big problem for siting at the edges of mesas and ridges. However, with the taller towers, wind turbines are placed on the edges, which are perpendicular to the predominant wind direction. As an example, for wind turbines on mesas in Texas, the north edge of the mesa would have increased winds from northern storms in the winter due to the rise in elevation, and then in the summer with southern winds, there is room for expansion of the wake. Data on turbulence for these sites are proprietary, primarily because it affects operation and maintenance.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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