Abstract
Increasing knowledge on wind shear models to strengthen their reliability appears as a crucial issue, markedly for energy investors to accurately predict the average wind speed at different turbine hub heights and thus the expected wind energy output. T his is particularly helpful during the feasibility study to abate the costs of a wind power project. The ext rapolation laws were found to provide the finest representation of the wind speed according to heigh ts, thus avoiding installation of tall towers, or e ven more expensive devices such as LIDAR or SODAR. The proposed models are based on theories that determine the vertical wind profile from implicit r elationships . However, these empirical extrapolation formulas have been developed for specific meteorolo gical conditions and appropriate sites for wind turbines; reason that several studies have been mad e by various authors to determine the best suited formula to their own conditions. This study is aime d at proceeding the research issue addressed within a previous study, where some extrapolation models were tested and compared by extrapolating the energy resources at different heights. However, comparable results are returned by the power law and the log law which indeed proved to be preferable. In this c ontext, this study deals the assessment of several wind speed extrapolation laws (six laws), by comparing t he analytical results obtained with real data for t wo different meteorological Sites, different roughness , different altitudes and different measurement per iods. The first site studied is an extremely rough site w ith daily measurements of March 2007, wind speed measurements are available at four different height s of Gantour/Gao site, obtained by the water, energ y and environment company Senegal. The second site studied is a feeble rough site with monthly measurements for 2005, wind speed measurements are available at three different heights of Kuujjuarapi k Site obtained by Hydro-Quebec Energy Helimax Canada. The study aims to determine the effectiveness and concordance between the extrapolation laws and the real measured data. The results show that the adjusted law is efficiently adequate for an extreme ly rough site and the modified laws with two other laws are efficiently adequate for a feeble rough si te. The experimental results and numerical calculat ions exploited for the evaluation of the Weibull paramet ers fall the shape factors k greater than 9. The increase in altitude often causes an increase in the Weibull parameters values, however, our results show that the shape factor k can take lower values to those estab lished in the reference altitude.
Highlights
Winds are large-scale movements of air masses in the atmosphere
This study deals the assessment of several wind speed extrapolation laws, by comparing the analytical results obtained with real data for two different meteorological Sites, different roughness, different altitudes and different measurement periods
The increase in altitude often causes an increase in the Weibull parameters values, our results show that the shape factor k can take lower values to those established in the reference altitude
Summary
Winds are large-scale movements of air masses in the atmosphere. These movements of air are created on a global scale primarily by differential solar heating of the Earth’s atmosphere. Wind power can be thought of as an indirect form of solar energy. The differential heating of the sea and land causes changes to the general flow. The nature of the terrain, ranging from mountains and valleys to more local obstacles such as buildings and trees, has an important effect. The result is that the wind varies continuously, with height, roughness and over hills
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