Performance investigation of a standalone renewable energy system using response surface methodology (RSM): 4E analysis and multi-objective optimization

Abstract

This study aimed to identify and present novel findings in the field of hybrid renewable energy systems tailored for off-grid operation through a numerical-experimental investigation. The objective of the research was to contribute to the current knowledge of energy systems by addressing critical aspects of energy, exergy, economic, and environmental (4E) evaluations. The system described in the study is designed to meet the electricity demands of a telecom tower by integrating various components, including a photovoltaic (PV) unit, proton exchange membrane electrolyzer (PEME), proton exchange membrane fuel cell (PEMFC), and battery storage unit. An organic Rankine cycle (ORC) is also incorporated to efficiently recover waste heat from the PEMFC. The PV unit serves as the primary power source, with excess solar power directed to the PEME during periods of high solar irradiation. The PEME generates hydrogen and oxygen, while the PEMFC is fueled by hydrogen stored in metal hydride tanks. This setup ensures consistent power generation year-round. The study employs response surface methodology (RSM) to create regression equation models and utilizes the desirability function approach for multi-objective optimization. The optimal parameters identified include a 12:35 PM time setting, PEMFC current density of 0.693 A/cm2, PEME inlet water temperature of 326.2 K, and ORC turbine inlet pressure of around 580 kPa. These parameters result in impressive 4E outcomes: 50.9 % energy efficiency, 54.7 % exergy efficiency, a $0.53 levelized cost of energy, and a sustainability index of 2.1.