Wind tunnel experiments of a newly developed two-bladed Savonius-style wind turbine Sukanta Roy, Ujjwal K. Saha ⇑ Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India highlights  Benchmark wind tunnel experiments on a novel Savonius-style wind turbine (SSWT).  Analysis on the performance and starting characteristics of the newly developed wind turbine.  Comparative examination of the newly developed turbine with other tested models.  Discussion on the influences of Reynolds number and tip speed ratio.  Estimation of overall efficiency and payback period for the wind energy conversion system (WECS). article info Article history: Received 17 May 2014 Received in revised form 5 October 2014 Accepted 6 October 2014 Keywords: Savonius-style wind turbines Power coefficient Torque coefficient Static torque coefficient Tip speed ratio abstract Wind tunnel experiments have been conducted with a newly developed two-bladed Savonius-style wind turbine specifically meant for a small-scale energy conversion. This novel shape of the turbine blade is evolved from a series of experiments with different types of blades in the recent past. The developed two-bladed turbine is tested in an open type test section and its performance is assessed in terms of power and torque coefficients. Experiments have also been conducted with other standard blades such as semi-circular, semi-elliptic, Benesh and Bach types in order to have a direct comparison. In this study, all the reported experimental data are inclusive of wind tunnel blockage corrections. Further, the effects of Reynolds number on the dynamic and static characteristics are also discussed. The present investiga- tion demonstrates a gain of 34.8% in maximum power coefficient with the newly developed two-bladed turbine. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Recent instabilities in the world energy market due to depletion of fossil fuel sources, global warming threats and increasing price of fossil derivatives necessitate the need of harnessing the clean and renewable sources of energy. In this context, research in the field of wind energy is becoming particularly important [1–6]. Although considerable progress has been achieved in the area of horizontal axis wind turbines, the available technical designs of vertical axis wind turbines are not yet satisfactory for the develop- ment of low cost reliable wind energy converters for conditions corresponding to the off-grid power generation at low wind speeds. Thus, attention is being paid to the small-scale wind tur- bines for distributed energy systems [4–10]. The Savonius-style wind turbine (SSWT) appears to be promising for such conditions, however, it possesses a lower efficiency as compared to its coun- terpart. This class of wind turbines patented by Savonius S.J. in 1920s is a modification of Flettner’s cylinder used to propel the ships [11]. The maximum efficiency reported by Savonius was 31%, though this claim was not agreed by subsequent investigators [12–14]. For a conventional SSWT, the maximum conversion effi- ciency as reported by Sandia laboratory was found to be 24.4% [15]. Apart from this efficiency factor, SSWTs deliver a number of advantages over other wind turbines targeting small-scale energy conversion such as design simplicity, ease of fabrication, ease of installation in confined spaces like rooftops, buildings or above the communication towers. Further, they can operate at low wind speeds causing lesser wear and tear, and their operation is inde- pendent of wind direction thereby avoiding the need of a yaw mechanism. [13,14,16–21]. Looking at these advantages, it can clearly be said that if a higher efficiency can be achieved, these SSWTs would make an attractive source of power generation. http://dx.doi.org/10.1016/j.apenergy.2014.10.022 0306-2619/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +91 361 2582663; fax: +91 361 2690762. E-mail address: saha@iitg.ernet.in (U.K. Saha). Applied Energy 137 (2015) 117–125 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy