Journal of Mechanical Science and Technology 31 (11) (2017) 5089~5097 www.springerlink.com/content/1738-494x(Print)/1976-3824(Online) DOI 10.1007/s12206-017-1002-7 Hydraulic design and performance analysis on a small pump-turbine system for ocean renewable energy storage system † Patrick M. Singh 1 , Zhenmu Chen 1 and Young-Do Choi 2,* 1 Graduate School, Department of Mechanical Engineering, Mokpo National University, Muan-gun 58554, Korea 2 Department of Mechanical Engineering, Institute of New and Renewable Energy Technology Research, Mokpo National University, Muan-gun 58554, Korea (Manuscript Received April 6, 2017; Revised July 19, 2017; Accepted August 21, 2017) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract Korea has a myriad of islands in the south western coast that extensively rely on diesel generators for power production, which in- crease cost and environment pollution. The small hydro pump-turbine system for ocean renewable energy storage system is a kind of hybrid system that can reduce the usage of diesel generators and help to contribute to the environment in a positive manner by helping to reduce carbon emissions. The study focuses on initial hydraulic design and numerical analysis of a 30 kW-class pump-turbine system for energy independent islands in South Korea. The purpose of the study is to propose an ocean renewable energy storage system using a small pump-turbine system working with seawater. A 30 kW-class pump-turbine does not require a large head; approximately 30 m is sufficient for the design and application. Several other renewable energy systems like wind turbines, tidal turbines, wave energy convert- ers and solar energy could be used to make a hybrid system with pump-turbine. The initial design achieved more than 85 % efficiency in both pump and turbine modes. However, further optimizations of the impeller blade shape and number of guide vane and stay vanes could improve the overall efficiency of the system. Keywords: Small hydro pump-turbine; Ocean renewable energy storage; Hydraulic design; Performance ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction Renewable energy and ESS (Energy storage systems) can be combined to effectively replace or reduce diesel power generation in small outer islands that are far from the main land [1]. It can be a very promising new business that can be advanced into both domestic and overseas markets, especially the island nations in Asia and the South Pacific Ocean can benefit from this type of power generation systems. There are around 50 thousand islands in the world with a to- tal area of over one sixth of global land area [2, 3], with the islands inhabiting more than 740 million people according to Geographic information system (GIS) analysis [4]. Korea’s Jeonnam province (Shinan-gun) alone consists of more than 1000 islands where 270 are inhabited islands, among which 107 islands are not connected to the electricity grid. These islands heavily rely on diesel power generation. Korea Electric Power Corporation (KEPCO) supplied diesel to 30 inhabited islands in the region in the year 2014 that accounts to ap- proximately 13223 kL (136.3 billion KRW) and the numbers keep rising every year. The local government administration operating in this region also consumes diesel that accounts approximately 14000 kL (165 billion KRW) [5]. Although the islands face severe energy insecurity, renew- able energy sources are abundantly available in the form of wind, solar, wave, biomass, and hydropower enabling clean renewable power conversion opportunities [6, 7]. Usually, each island is blessed with at least one renewable energy source. With the increasing demand for low-emission genera- tion and rapid development of sustainable energy technologies, the utilization of renewable energy presents promising pros- pects for island power hybrids. It is quite feasible to eliminate fossil fuels with renewable energies in islands from economi- cal and technical aspects [8, 9]. There are some energy inde- pendent islands in Korea, such as in Gasado and Sammado, with wind and solar hybrid systems that store excess electric- ity using batteries which were developed in October 2014. Other prospective islands include Geochado, Jodo, Sapsido and Geomundo [10]. Shin et al. conducted a study on the ca- pacity design and operation planning of a hybrid PV-wind- battery-diesel power generation system in the case of Deok- jeok Island in Korea. The study was conducted for optimal design of Hybrid power generation system (HPS) in which * Corresponding author. Tel.: +82 61 450 2419, Fax.: +82 61 452 6376 E-mail address: ydchoi@mokpo.ac.kr This paper was presented at the ISFMFE 2016, LOTTE City Hotel, Jeju, Korea, October 18-22, 2016. Recommended by Guest Editor Hyung Hee Cho. © KSME & Springer 2017