It is basically a drag force driven wind turbine with two cups or half drums fixed to a central shaft in opposing directions. Each cup/drum catches the wind and so turns the shaft, bringing the opposing cup/drum into the flow of the wind. This cup/drum then repeats the process, causing the shaft to rotate further, thus completing a full
rotation. This process continues all the time the wind blows and the turning of the shaft is used to drive a pump or a small generator. Though typical values of maximum power coefficient for other types of wind turbines vary between 30% to 45%, those for the Savonius turbines are typically not more than 25% according to most investigators [6]. This type of turbine is suitable for low-power applications and they are commonly used for wind speed instruments.