VAWTs

Vertical-axis wind turbines (VAWTs) are wind turbines with a vertical main shaft. The rotor turns around a vertical axis, and the rotor plane is perpendicular to the wind. Because the axis is vertical, the turbine can capture wind from any direction without a yaw mechanism, and the generator and drive train are often located at ground level for easier access.

Two principal families dominate VAWT design: lift-based and drag-based. The lift-based Darrieus turbine uses curved blades and can be efficient, but often requires an initial spin and experiences cyclic loading. The drag-based Savonius turbine uses overlapping scoops to capture wind by drag; it is robust, simple, and has high starting torque but lower efficiency. Hybrid forms like H-Darrieus and helically bladed VAWTs aim to combine strengths and provide smoother torque and better self-starting behavior.

Advantages of VAWTs include omnidirectional wind capture, compact form factors suitable for urban or rooftop installation, and potentially easier access to the drive system. Limitations commonly cited are lower peak efficiency and power density than modern horizontal-axis turbines, larger rotor areas needed for the same output, and pulsating torque in some designs, though helicals reduce pulsations and noise.

Applications include small-scale electricity generation, buildings, remote sites, wind-powered pumping, and experimental installations. In utility-scale wind energy, horizontal-axis turbines dominate; VAWTs are mainly used for distributed generation, education, and niche installations.

History: The Savonius rotor was developed in the 1920s by Finnish inventor S. J. Savonius. The lift-based Darrieus turbine followed in 1931. Since then, hybrids and helicals have been explored, but large-scale deployment remains limited compared with horizontal-axis designs.

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