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Long-term wind speed data for thirteen meteorological stations, measured over a five-year period, were statistically analyzed using the two-parameter Weibull distribution function. The purpose of this study is to reveal for the first time the wind power potentials in Chad and to provide a comprehensive wind map of the country. The results show that the values of the shape and scale parameters varied over a wide range. Analysis of the seasonal variations showed that higher wind speed values occur when the weather condition is generally dry and they drop considerably when the weather condition is wet. It was also observed that the wind speed increases as one moves from the southern zone to the Saharan zone. Although the wind power at each site varies significantly, however, the potentials of most of the sites were encouraging. Nevertheless, according to the PNNL classification system, they are favorable for small-scale applications only. A few stations in the middle of Sudanian and Sahel regions are found to be not feasible for wind energy generation due to their poor mean wind speed. The prevailing wind direction for both Saharan and Sahel regions is dominated by northeastern wind, while it diverged to different directions in the Sudanian zone.

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This paper describes the study of a small vertical axis wind turbine (VAWT) with a combined design of Darrius and Savonius counter-rotating rotors. The main purpose of this study is to improve the extraction capabilities of a single-rotor VAWT by using two distinct rotor designs while adopting the counter-rotating technique. Given that the conversion capabilities and operational speed of the existing wind turbines are still limited, the current technique is used to enhance the efficiency and expand the operating speed range of the VAWT. The Darrius and Savonius counter-rotating rotors were exposed to a similar upstream wind speed using a centrifugal blower. It was found that the Savonius-Darrius counter-rotating rotor was able to operate effectively particularly at the low-speed wind. By looking at the individual performance of the rotors, it was observed that the conversion efficiency of the H-type rotor increases as the wind speed increases. However, in the case of the S-type rotor, it is higher at lower wind speed and tends to decreases as the operating speed increases. Thus, the maximum efficiency of the S-type rotor was achieved at low-speed, whereas the H-type rotor has achieved its maximum efficiency at the highest operating wind speed. The average efficiency of the present Savonius-Darrius counter-rotating rotor has been improved to reach almost 42% more efficiency in terms of torque.

This paper describes the study of a small vertical-axis wind turbine (VAWT) with a combined design of Darrius and Savonius counter-rotating rotors. The main purpose of this study is to improve the extraction capabilities of a single-rotor VAWT by using two distinct rotor designs while adopting the counter-rotating technique. Given that the conversion capabilities and operational speed of the existing wind turbines are still limited, the current technique is used to enhance the efficiency and expand the operating wind speed range of the VAWT. The Darrius and Savonius counter-rotating rotors were exposed to a similar upstream wind speed using a centrifugal blower. It was found that the Savonius-Darrius counter-rotating rotor was able to operate effectively, particularly at the low-speed wind. By looking at the individual performance of the rotors, it was observed that the conversion efficiency of the H-type rotor increases as the wind speed increases. However, in the case of the S-type rotor, it is higher at lower wind speed and tends to decrease as the operating speed increases. Thus, the maximum efficiency of the S-type rotor was achieved at low speed, whereas the H-type rotor has achieved its maximum efficiency at the highest operating wind speed. The average efficiency of the present Savonius-Darrius counter-rotating rotor has been improved to reach almost 42% and 30% more efficiency in terms of torque and power, respectively. Highlights • The effectiveness of combining S type and H type on a counter-rotating VAWT has been studied. • The new combined design was able to enhance the performance of the system significantly and was able to operate in a low-speed wind condition. • An average power coefficient and torque coefficient of up to 30% and 42% were, respectively, achieved using this technique.

The wind is an energy source that has the properties of a clean, free, and readily available energy source. However, the efficiency of the existing rotors used to harness wind power is still not satisfactory. Thus, in this current study, the development and aerodynamic performance investigation of ten NACA airfoils comprising of five symmetrical and five non-symmetrical airfoils have been analyzed through the computational fluids dynamic (CFD) simulation approach. The main motive of this study was to investigate the aerodynamic performance of NACA airfoils to be used on a vertical axis wind turbine (VAWT), which will assist in further understanding the physics of the interaction between airflow and the wind turbine blades. The simulation was performed using two-dimensional computational models based on an unsteady state K-omega Shear Stress Transport (SST) turbulence model. This study covers a parametric study based on the variations of tip-speed ratios and constant wind velocity. The aerodynamic performances are evaluated in terms of torque, torque coefficient, and also power coefficient. The performance of NACA0018 was found to be the best among the other airfoils with a power coefficient of 0.3. NACA0010 displayed the lowest power coefficient among the other airfoils but had a more extensive operating range compared to the other airfoils. However, for non-symmetrical NACA airfoils, NACA2421 scored the highest power coefficient, followed by NACA4412. It was also found that most of the non-symmetrical NACA airfoils can operate at a higher range of tip-speed ratios compared to the symmetrical NACA airfoils.

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