Energy Efficiency Assessment of Four Designs of Vertical Axis and Drag Differential Wind Turbines

In the present study was compared the energy efficiency of four different designs of vertical axis and drag differential wind turbines maintaining the same height and diameter. Besides the classical two bladed Savonius model were studied two of its derivates (Schulz and Benesh), as well as the almost unknown Lenz turbine. In a laboratory were determined the power curves versus the tip speed ratio exposing the turbines to wind speeds between 1 and 7 m/s. To prevent any difference of frictions between the different tests for the 4 models was used the same base including the alternator and the gear. The Lenz turbine had a widely outstanding result with a maximum power coefficient of 32.5 %, followed by the models Benesh with 21.4 %, Savonius with 18 % and Schulz with 13 %.