Darrieus Wind Turbine

A Darrieus wind turbine is a vertical-axis wind turbine that generates electricity from curved airfoil blades mounted on a rotating shaft, its blades curved so that at operating speed they experience only tension stress rather than bending, and because its shaft stands upright it works equally well no matter which direction the wind blows, unlike a conventional turbine that must turn to face the wind. French aeronautical engineer Georges Jean Marie Darrieus invented the design and patented it on October 1, 1926. Its blades generate torque the same way an autogyro or a helicopter in autorotation does, the circular motion of each blade creating a small positive angle of attack against the oncoming air, but the design produces pulsing rather than steady power, endures high centrifugal stress, and is difficult to protect from extreme wind and to start on its own, often needing a separate starting motor and mechanical brakes to avoid resonant vibration damage at certain speeds.