Performance evaluation of a novel vertical axis wind turbine with coaxial contra-rotating concept Djamal Hissein Didane * , Nurhayati Rosly, Mohd Fadhli Zulkafli, Syariful Syafiq Shamsudin Department of Aeronautical Engineering, Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Parit Raja, Batu Pahat, Johor, Malaysia article info Article history: Received 8 March 2017 Received in revised form 21 July 2017 Accepted 26 August 2017 Available online 26 August 2017 Keywords: Aerodynamic performance Contra-rotating technique Vertical axis wind turbine (VAWT) abstract the present work, development and aerodynamic performance prediction of a unique contra-rotating vertical axis wind turbine (VAWT) have been studied. The purpose of this paper is to investigate the effectiveness of employing the contra-rotating concept to a VAWT system while enhancing its conver- sion efficiency. The performance evaluations of the current model were established in terms of key aerodynamic performance parameters such as power, torque, power coefficient and torque coefficient. The systematic analysis of these quantities showed the effectiveness of the contra-rotating technique on VAWT system and the ability to extract additional almost threefold power over the entire operating wind speed ranges covered. The system has also improved the inherent difficulties of the Darrieus rotor to self-start. Moreover, the results of the new concept also demonstrated a significant increase in terms of conversion efficiency for both power and torque compared to a single-rotor system of a similar type. It is anticipated that this current approach will revolutionize wind energy harvesting strategies and will find application in a wide range of wind turbine sites that are characterized by relatively low and moderate wind speed regimes and particularly be useful in the urban environment where turbulence intensity is high. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction The generation of electricity has commonly been accomplished through the combustion of fossil fuels. However, fossil fuel power plants to some extent pollute the environment by producing contaminating emissions and the supplies of these energies have been predicted to finish in a few decades of time. Thus, the use of fossil fuels has to be limited and the use of renewable energies should be encouraged. Renewable energies such as the wind, solar, wave and thermal are abundant and will always be there as long as the world exist. The usage of these energies does not contribute to the pollution problems or to the extinction of the earth natural resources. As such, their implementation is highly favorable for the purpose of saving the world while serving human beings. Wind power, in particular, has been proven to be a promising alternative energy future, due to its free availability and clean character. Hence, it has drawn more attention recently in response to numerous environmental and social challenges [1]. Many studies including Delucchi and Jacobson [2] suggest that in order to address the current significant problems such as climate change, green- house gas (GHG) emission and energy insecurity, there needs to be a major change to energy infrastructure i.e. from fossil fuel based to renewables. Consequently, the recent years witnessed a rapid development of wind power all over the world. A total of 456 GW wind power capacity was achieved across the globe by mid of 2016 and expected to reach 666.1 MW by the end of 2019 [3,4]. Furthermore, a recent projection made by International Energy Agency (IEA) also reported that renewable energy sources sur- passed the coal sources in 2015 and became the largest source of electricity capacity in the world [5]. Over the years, some of the efforts or strategies embraced to enhance the performance of a single rotor wind turbine (SRWT) were by improving blade design, increasing rotor size and/or tower size to access greater wind speeds at higher altitudes or by incor- porating gearbox and lubrication in system [6e9]. However, these approaches involve high engineering costs, as the rotor alone constitutes almost 80% of the total cost of a wind turbine, not to * Corresponding author. E-mail addresses: dhdfils@gmail.com (D.H. Didane), nurhayati@uthm.edu.my (N. Rosly), fadhli@uthm.edu.my (M.F. Zulkafli), syafiq@uthm.edu.my (S.S. Shamsudin). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene http://dx.doi.org/10.1016/j.renene.2017.08.070 0960-1481/© 2017 Elsevier Ltd. All rights reserved. Renewable Energy 115 (2018) 353e361