PERFORMANCE OF A STAND-ALONE RENEWABLE ENERGY SYSTEM BASED ON HYDROGEN ENERGY STORAGE Abdullah H. Al-Badi, Hassan Yousef, Othman AlAamri , Mohammed AlAbdusalam, Younis AlShidi, Nasser AlHarthy Department of Electrical & Computer Engineering, College of Engineering, Sultan Qaboos University P.O. 33, Al-Khod, Muscat- 123, Sultanate of Oman albadi@squ.edu.om, hyousef@squ.edu.om ABSTRACT In this paper, an ac-linked hybrid electrical energy system comprising of photo voltaic (PV) and fuel cell (FC) with electrolyzer for stand- alone applications is proposed. PV is the primary power source of the system, and an FC–electrolyzer combination is used as a backup and as long-term storage system. A Fuzzy Logic controller is developed for the maximum power point tracking for the PV system. A simple power management strategy is designed for the proposed system to manage power flows among the different energy sources. A simulation model for the hybrid energy has been developed using MATLAB/Simulink. Index Terms— Hybrid energy system, Fuzzy Logic controller, Fuel cell, PV, energy mangment. 1. INTRODUCTION In several countries around the world, the power demand is continuous to increase at the same time the fossil fuel resources are depleting, as a result renewable energy sources (RES) should be utilized to provide secure, reliable, and almost pollution free source for electrical energy production. Wind and Solar power generation are two of the most promising sources in which their growth has exceeded the most optimistic estimation [1]. However, the problems of wind and solar resources are the intermittence of the supply. One way to overcome this is to use energy storage devices, where the excess energy could be stored and used when needed. The storage device can be FC with electrolyzer, batteries, super- capacitor, or superconducting magnetic energy storage (SMES). Battery bank is normally use for short-term energy storage due to its fast charging/discharging and capacity for smoothing the fluctuating of both load and renewable energy sources. For long-term energy storage, batteries alone are not appropriate because of their low energy density. Fuel cells with H 2 storage tank can be used for long-term energy storage to improve the performance of stand-alone RES system. Furthermore, the combination of a battery bank with long-term energy storage such as FC can significantly improve the performance of stand-alone RE systems. A hybrid renewable energy system with fuel cell technology has been suggested by various researchers for small-scale power generation owing to its high efficiency and flexible modular structure [2- 7]. In this paper, a hybrid energy system, consisting of fuel cell with electrolyzer and PV, is proposed to provide the power requirement for stand-alone load. The system is sized to provide reliable energy, in which the PV is the primary power source. In this system the excess energy with respect to load demand is sent to the electrolyzer to produce hydrogen which will be stored and can be used to produce electrical power when there is insufficient solar energy with respect to load requirement. Dynamic modeling for each component of the hybrid system is also discussed. The rest of the paper is organized as follows: The PV model with fuzzy logic controller for maximum power point tracking and the dynamic model of FC with electrolyzer are explained in section III. A simple power management system is discussed in section IV. Discussion of the complete system and simulation results are presented in section V. Conclusions are given in section VI. 2. HYBRID ENERGY SYSTEM A schematic diagram for the hybrid system is presented in Fig. 1. The proposed system consists of a photovoltaic module with maximum power point tracking controller , a proton exchange membrane (PEM) fuel cell with electrolyzer and a DC to AC inverter. The load is fed through a simple power management controller. Fig.1. Schematic diagram for the proposed system 3. SYSTEM DYNAMIC MODELING Dynamic modeling of individual subsystems is explained in this section. 3.1 PV MODEL A mathematical model of the output characteristics for a photovoltaic cell has been discussed in reference [8]. The equivalent circuit of the PV cell is generally modeled as shown in Fig. 2. A photovoltaic cell is usually modeled by the following mathematical equations [9]: I ୗେ െ I ୈ െ I ୱ୦ െ I ୔V ൌ Ͳ (1) where I ୗେ is the current source, I ୈ is the diode current, I ୱ୦ is the shunt current and I ୔V is the current output of the PV model. Power Management Controller LOAD MPPT Control DC/DC DC/AC ELZ Storage Tank (۶૛) Compressor PEMFC DC/DC DC/AC PV array