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How does a Savonius rotor use semicircular blades to capture wind energy?

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Rows of white wind turbines with spinning blades stand on a dry, grassy landscape at a wind farm near Tehachapi, California. — turbine Wind turbines near Tehachapi, California.

The Savonius rotor is a type of vertical-axis wind turbine invented by Finnish engineer S.J. Savonius in 1922. It captures wind energy through a design consisting of two semicircular blades, which are often constructed by cutting an oil drum in half along its vertical axis.1

These blades are welded together with an offset from the central axis to form an open "S" shape. This configuration allows the rotor to capture wind effectively from any direction, as the concave side of the blades catches the wind while the convex side offers less resistance, creating the rotational force necessary to generate power.1