Abstract
Wind is an important resource for generating renewable energy. To effectively estimate wind energy potential, Weibull, lognormal and gamma distribution functions have been widely used. However, when the distribution is bi-modal these conventional distribution functions are not suitable. Since Narakkalliya is affected by both monsoon seasons to varying degrees, the wind speed data show a bi-modal behaviour. A study was conducted at Narakkalliya in 2001 to calculate the energy generated from wind using the conventional Weibull distribution. The objective of this study was to show that energy calculation could be carried out more accurately using mixture distribution. Thus in this study, mixture Weibull distributions, mixture lognormal and Weibull distribution, mixture gamma and Weibull distribution were considered to model the wind speed frequency distribution (WSFD). Parameters of the above mentioned distributions were calculated using maximum likelihood method. The goodness-of-fit of the distributions was compared using K-S error, Chi-square test and root mean square error. Mixture Weibull distribution had the lowest error followed by the mixture lognormal and Weibull distribution. The fitted mixture Weibull distribution and the power curve data for the Narakkalliya wind turbine were used for energy calculation. According to the analysis mixture Weibull estimates 83.2 % of the actual energy while Weibull estimates 75.9 % of the actual.
Highlights
Sri Lanka experiences two distinct monsoonal wind seasons, which are the Northeast (NE) Monsoon from December to February and the Southwest (SW) Monsoon from mid-May to September
In Sri Lanka a study has been carried out to model the wind speed data and for energy calculation at Narakkalliya using the Weibull distribution (Fernando, 2010). This seems to be a reasonable approximation, it is critical to note that the Weibull distribution does not show a high accuracy in modelling wind speed frequency distribution (WSFD) in locations, which are strongly affected by both monsoons, displaying a dual peak scenario
The present study shows that energy calculation could be carried out more accurately using mixture distributions
Summary
Sri Lanka experiences two distinct monsoonal wind seasons, which are the Northeast (NE) Monsoon from December to February and the Southwest (SW) Monsoon from mid-May to September. The present study has been carried out to model the WSFD using hourly wind speed data at 40 m mast height for the year 2001 at Narakkalliya. In Sri Lanka a study has been carried out to model the wind speed data and for energy calculation at Narakkalliya using the Weibull distribution (Fernando, 2010). This seems to be a reasonable approximation, it is critical to note that the Weibull distribution does not show a high accuracy in modelling WSFD in locations, which are strongly affected by both monsoons, displaying a dual peak scenario. IDD E D eIsEtiDmaEEted using the maximum likelihood method that maximises the logarithm of likelihood function which is given by:
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