Vertical-axis wind turbines (VAWT) are a type of wind turbine where the main rotor shaft runs vertically. Among the advantages of this arrangement are that generators and gearboxes can be placed close to the ground, and that VAWT do not need to be pointed into the wind. Major drawbacks for the early designs (savonius, darrieus, giromill and cycloturbine) included the pulsatory torque that can be produced during each revolution and the huge bending moments on the blades. Later designs like turby, quietrevolution and aerotecture solved the torque issue by using the helical twist of the blades, similar to Gorlov's water turbines.
Drag-type VAWT, such as the Savonius rotor, typically operate at lower tipspeed ratios than lift-based VAWT such as Darrieus rotors and cycloturbines.
