Assessing Small Cross Flow Wind Turbine for Urban Rooftop Power Generation

Horizontal axis wind turbine is not suitable for urban rooftop power generation. The urban wind environment has issues like low wind velocity conditions and turbulence. Crossflow turbine derived from Banki water turbine is used as its structure is simple. Also, it starts at low wind speeds and possess high starting torque. Therefore, the focus of this study is to understand the flow physics of the crossflow wind turbine. Experimental investigations are carried out with wind velocities varying from 4 to 10 m/s. The performance characteristics of crossflow wind turbine are estimated in terms of coefficient of power (C_p), tip speed ratio (λ) and coefficient of torque (C_t). The relationship between time taken to attain the maximum speed at varied wind conditions is also plotted. The results showed that crossflow wind turbine possess a good self-starting ability at relatively low wind speeds with high starting torque. Peak power coefficient, C_p,max of 0.0485 is obtained for λ = 0.50. As λ is increased further, the C_p value is observed to decrease gradually. C_t value is found to decrease almost linearly from a maximum value of 0.096. Polar plot showed that torque output is almost same at all angles which proves the crossflow turbine to be omni-directional. Hence, regardless of the wind directions, crossflow turbine produces same performance making it a suitable choice for the urban rooftop power generation.