Green hydrogen-enabled power-to-methane energy storage in a biomass-solar hybrid system: A 4E assessment and multi-objective optimization

This study presents a novel biomass-solar hybrid energy system designed to store renewable energy through hydrogen-enabled power-to-methane conversion. The system integrates municipal solid waste-based biogas production, anaerobic digestion, Organic Rankine Cycle (ORC), Proton Exchange Membrane (PEM) electrolysis, and methanation. Hydrogen produced via solar-powered PEM electrolysis is combined with CO 2 captured from the system to synthesize methane—providing a storable, dispatchable energy carrier and contributing to long-duration energy storage. A detailed 4E (energy, exergy, economic, and environmental) analysis is conducted, followed by a multi-objective optimization using machine learning techniques and the Grey Wolf Optimizer under three scenarios. In the base case, the system delivers 1215 kW of electricity and 0.18 kg/s of methane, achieving an emission index of 0.0016 kg/kWh. With energy pricing assumptions of 0.14 $/kWh for electricity and 4 $/kg for methane, the system shows a payback time of 5.75 years. Optimized scenarios further enhance system performance—achieving 19.06% exergy efficiency, 1.59 kg/s of methane output, and a product cost of 52.89 $/GJ. The results confirm the effectiveness of integrating hydrogen pathways into renewable energy storage systems, enabling cleaner fuel production and improving the economic and environmental sustainability of energy systems. • A Cogeneration using biogas, solar energy, and methanation was proposed. • Technical, economic, and environmental analyses were conducted. • Multi-criteria and grey wolf optimization were employed. • Optimal exergy efficiency (19.06%) and cost (52.89 $/GJ) were achieved.