Wind resource assessment

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

History
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.

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
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

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

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

Wind flow modeling
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 Risø 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. meteodyn WT is a CFD wind flow modelling software for wind resource assessment, Annual Energy Production evaluation, site suitability and turbine layout analysis, energy production optimization, maintenance costs and turbines lifespan validation.

Wind farm modeling
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.