The Savonius rotor is a drag-based vertical axis wind turbine and is used as an alternative source in small-scale energy generation. Design simplicity, low-cost, easy installation, good starting ability, relatively low operating speed and independent to wind directions are the main advantages of this rotor. However, because of its low efficiency and high negative torque produced by the returning blade, this rotor concept rarely gained popularity. Over the last few decades, although a number of investigations around the world have reported performance gains of the Savonius rotor, the available technical design is still not able to fulfill the demand of efficient small-scale wind energy converter at low wind speeds. Until now, various design changes have been proposed to meet a growth in power output through optimization of influencing variables like aspect ratio, overlap ratio, blade material, and so forth. Investigations have also been carried out by installing additional devices like curtain design, deflector plate, nozzle and ducts, multi-staging, guide-box tunnel and windshields. Installation of these devices considerably reduced the negative torque as well as improved the starting performance of the rotor. As a result, the power output of the rotor is also improved. Several researchers have reported increased power coefficients for various rotor designs based on their different testing parameters. Power coefficients for the conventional Savonius rotors have been mostly reported in the range of 0.12–0.18 and by optimizing its design, it can reach as high as 0.38. This article attempts to discuss the various influencing parameters as well as the augmentation techniques. This would offer an overall idea on the progress that has taken place to improve the design and performance of the Savonius rotor.
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