Vertical axis windmill: Performance evaluation and estimation of energy output with Darrieus turbines

The growing demand for renewable energy resources gave rise to practically rediscovering the Darrieus wind turbine in the sixties. The economic feasibility of its utilization however is dependend upon the local wind energy and the knowledge of the performance of the turbine under different operating conditions. Several turbines have been tested in this research for different values of the solidity, which is related to the mass of the turbine blade. A method has been developed to determine the performance of small wind rotors, which can be done in small wind tunnels. This methodology significantly reduces testing time and research costs, besides providing a continuous function for the power coefficient, that is, the fraction of the wind energy that can be extracted by the turbine. By using power coefficient and wind velocity data, a numerical simulation of the performance of the turbines is carried out for one year period, under a constant speed operating condition; for two cities in Brazil. The equipment operates in this condition with simple controls and generates electric energy at constant frequency. The experimental performance data were found to closely fit those of Blackwell, Sheldahl and Feltz.