Wind resource assessment is the process by which wind power developers estimate the future energy production of a wind farm. Accurate wind resource assessments are crucial to the successful development of wind farms.

Modern wind resource assessments have been conducted since the first wind farms were developed in the late 1970s. The methods used were pioneered by developers and researchers in Denmark, where the modern wind power industry first developed.

Government agencies publish maps of estimated wind resources for most areas with active wind power development. Wind prospecting can begin with the use of such maps, but the lack of accuracy and fine detail make them useful only for preliminary selection of sites for collecting wind speed data. With increasing numbers of on-site measurements, as well as operating data from built wind farms, the accuracy of wind resource maps should improve over time, but these maps are unlikely to eliminate the need for on-site measurements.

To estimate the energy production of a wind farm, developers must first measure the wind on site. Meteorological towers equipped with anemometers, wind vanes, and sometimes temperature, pressure, and relative humidity sensors are installed. Data from these towers must be recorded for at least one year to calculate an annually representative wind speed frequency distribution.

Since onsite measurements are usually only available for a short period, data are also collected from nearby long-term reference stations (usually at airports). These data are used to adjust the onsite measured data so that the mean wind speeds are representative of a long-term period for which onsite measurements are not available.

Calculations that are performed include: - correlations between onsite meteorological towers - correlations between long-term reference stations and onsite meteorological towers - shear to extrapolate wind speeds to turbine hub height - wind flow modeling to extrapolate wind speed changes across a site - energy production using a wind turbine manufacturer's power curve

Wind power developers use various types of software applications to assess wind resources.

Wind data analysis software assist the user in removing measurement errors from wind data sets and perform specialized statistical analysis. Popular applications are Windographer and WindRose.

Wind flow modeling software aims to predict important characteristics of the wind resource at locations where measurements are not available. The most commonly used such software application is WAsP, created at Risų National Laboratory in Denmark. WAsP uses a potential flow model to predict how wind flows over the terrain at a site. WindSim is a similar application that uses CFD calculations instead, which are potentially more accurate.

Wind farm modeling software aims to simulate the behavior of a proposed or existing wind farm, most importantly to calculate its energy production. The user can usually input wind data, height and roughness contour lines, wind turbine specifications, background maps, and define objects that represent environmental restrictions. This information is then used to design a wind farm that maximizes energy production while taking restrictions and construction issues into account. There are four wind farm modeling software applications available: openWind, WindPRO, WindFarmer, and WindFarm.

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)