Analysis of height variations of sodar-derived wind speeds in Northern Spain

• Published in: Journal of wind engineering and industrial aerodynamics Vol. 92; no. 10; pp. 875 - 894
• Main Authors: Pérez, I.A., Garcı́a, M.A., Sánchez, M.L., de Torre, B.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-08-2004
• Subjects: Sodar; Weibull statistics; Wind characteristics; Wind data; Wind speed distribution; Europe, Iberian Peninsula; Spain; Wind speed distribution; Wind characteristics; Wind data; Sodar; Weibull statistics
• ISSN: 0167-6105; 1872-8197
• DOI: 10.1016/j.jweia.2004.05.002

The Weibull distribution has been widely used in wind speed analysis. Ten-min averages from a sodar placed in an extensive plateau in the North of Spain were considered. The measuring period was April 2001. Daily wind speed evolution has been analysed and a sharp contrast between day and night has been obtained. Contrasting behaviour between surface and more distant levels has also been seen. The strong convection during the day and the stratification stability during the night were responsible for this well-defined pattern. Four wind speed intervals for a typical wind turbine were considered. Low wind speeds showed no directional character, although moderate winds came from two prevailing directions due to the synoptic weather systems affecting the Iberian Peninsula with a 5–6 day period. Ground influence was present only at lowest levels. As a result, the behaviour of wind speed derived from surface data must be avoided. Although moderate winds were frequent, a persistence analysis revealed the low number of lasting runs. The wind speed power law was also analysed and the usual one-seventh expression was proved not to be valid. The Weibull parameters were calculated by four methods: linear regression by cumulative frequency, moments, maximum likelihood and quartiles. The equivalence was in general clear. Finally, height analysis revealed that the shape parameter was around two whereas major differences were reached for the scale factor. A successful fit with the height was proved for the latter. Finally, a well-defined daily evolution was obtained, indicating that selection of a site for energy generation purposes must be preceded by a temporal study based on direct height measurements.