Bimodal versus Weibull Wind Speed Distributions: an Analysis of

W IND E NGINEERING VOLUME 28, N O . 2, 2004
PP
225–234
225
Bimodal versus Weibull Wind Speed Distributions:
an Analysis of Wind Energy Potential in La Venta,
Mexico
O. A. Jaramillo* and M. A. Borja
Instituto de Investigaciones Eléctricas
Calle Reforma113, Col. Palmira.
Gerencia de Energías No Convecionales, Ed. 18 P.A.
Cuernavaca Morelos México 62490
Tel. (+52) (777) 3183811 Fax (+52) (777) 3182436
*e-mail ojs@iie.org.mx
ABSTRACT
The International Standard IEC 61400-12 and other international recommendations suggest
the use of the two-parameter Weibull probability distribution function (PDF) to estimate the
Annual Energy Production (AEP) of a wind turbine. Most of the commercial software uses
the unimodal Weibull PDF as the default option to carry out estimations of AEP, which in
turn, are used to optimise wind farm layouts. Furthermore, AEP is essential data to assess the
economic feasibility of a wind power project. However, in some regions of the world, the use
of these widely adopted and recommended methods lead to incorrect results. This is the
case for the region of La Ventosa in Mexico, where the frequency of the wind speed shows a
bimodal distribution. In this work, mathematical formulations by using a Weibull PDF and a
bimodal distribution are established to compare the AEP, the capacity factor and the
levelised production cost for a specific wind turbine. By combining one year of wind speed
data with the hypothetic power performance of the Vestas V27-225 kW wind turbine, it was
found that using the Weibull PDF underestimates AEP (and thus the Capacity Factor) by
about 12%.
Keywords: Wind Energy; Wind characteristics; Weibull wind speed distribution; Bimodal
wind speed distribution; Levelised production cost; La Ventosa Mexico.