1 Abstract: Technologies to harness ocean current energy are at an early developing stage, and only a few prototypes and demonstration units have yet been tested. Ocean currents are potentially significant and currently untapped resource of energy. Ocean currents thus contain an abundant source of energy that can be captured and converted to a usable form. This paper discusses the performance of three different types of Savonius rotors used as water current turbines. Rotors design and test results in a tow tank are presented. All three rotors have same cross sectional area. Test results shows that double stage rotor has lower cut-in speed and produces higher torque when compared to single and three stage rotor design. These rotors were tested to determine a suitable water current turbine for a micro seafloor power generation system. Keywords: Savonius rotor; Water current turbine; Hydro kinetic turbine; Free flow turbine. I. INTRODUCTION Ocean energy is one promising renewable resource that might be tapped to meet needs for electric power. Energy conversion from marine currents is quite similar to that of wind energy conversion but there are also several differences between them. The underwater placement of a Marine Current Energy Converter (MCEC) gives some advantages such as no noise disturbance for the public, low visual exposure and little use of land space but also adds some challenges like the need for water and salt proof technology, difficult and costly maintenance etc. Ocean currents are relatively constant and flow in one direction only, in contrast to the tidal currents closer to shore where the varying gravitational pulls of the sun and moon result in diurnal high tides. Ocean current speeds are generally lower than wind speeds. This is important because the power contained in flowing bodies is proportional to the cube of their velocity. Also another important factor is that seawater is about 835 times denser than wind, so for the same area of flow being intercepted the available power in the seawater current is 835 times more than wind of same speed. Thus, ocean currents represent a potentially significant, currently untapped, reservoir of energy. The total worldwide power in ocean currents has been estimated to be about 5,000 GW, with power densities of up to 15 kW/m 2 .Ocean current generated energy technologies have many favorable characteristics, including the following: • Water currents always have a relatively high energy density. • Ocean currents are relatively constant in location and velocity, leading to a large capacity factor (fraction of time system is actively generating full power) for the turbines. • Water current turbines have minimal visual impact because they are installed beneath the water’s surface. II. WATER CURRENT TURBINE To date there are only a few technologies that have progressed [1] as far as the full-scale deployment and testing.When designing a rotor for marine current generation there are two types of rotors to consider. These are the Savonius rotor and the propeller rotor each with its own unique characteristics. The reasons to choose Savonius rotor over other types are stated below: • Simple and low cost design • A Savonius rotor cannot rotate any faster than the fluid rotating it, hence it is safer for fish • A Savonius rotor accepts flow from any direction and they are easier to install • Generator may be above the water level • High starting torque helps to start at lower speed. • Maintenance to have a clean leading edge is not necessary The above advantages outweigh its low efficiency and slow running speed makes it an ideal economical choice to meet small-scale power requirement [6]. Agreement on the efficiency of the Savonius turbine apparently has finally been reached a half century after its development [3,4]. Savonius claimed an efficiency of 31 per cent in the wind tunnel and 37 per cent in free air. However, he commented [5] “The calculations of Professor Betz gave 20 % as the highest theoretical maximum for vertical air wheels, which under the best of circumstances could not produce more than 10% in practical output.” Submerged Water Current Turbines Md.Nahidul Islam Khan, M.Tariq Iqbal, Michael Hinchey Faculty of Engineering and Applied Science, Memorial University of Newfoundland Email: nahidul@engr.mun.ca 978-1-4244-2620-1/08/$25.00 ©2008 IEEE Authorized licensed use limited to: Memorial University. Downloaded on October 18,2021 at 16:22:45 UTC from IEEE Xplore. Restrictions apply.