A vertical axis wind turbine which includes a rotor having three radially extending blades spaced at even intervals about a central axis. Each radially blade having an outer edge that lies on an imaginary circle of a first diameter. Each radially extending blade including a plurality of spaced airfoil sub-blades separated by gaps for the passage of air therethrough. Each of sub-blade having a leading vertical edge, and a trailing vertical edge and being positioned with the trailing vertical edge along a common radius line of the imaginary circle. Each sub-blade is skewed such that its cord line is rotated negative 45 degrees with respect the radius of the imaginary circle. The airfoil sub-blades maximize energy production by creating a secondary wind flow of a higher velocity for impingement upon blades of the rotor, and utilize backpressure during the second half of a rotation cycle to efficiently break the rotor against overspeed.