Phase change material-integrated solar heliostat field-driven methane and power cogeneration: Real-data case study optimized by neural networks and swarm optimization from the energy-exergy and techno economic perspective

Solar energy integration with thermochemical processes offers a promising pathway for sustainable fuel production and energy storage. The growing global demand for carbon-neutral energy has increased interest in solar-driven fuel production, especially synthetic methane, due to its storability, compatibility with existing infrastructure, and role in long-term energy storage. This study proposes an integrated solar-thermal hybrid plant combining a Brayton cycle, Organic Rankine cycle- Thermoelectric generator unit, vanadium-chloride thermochemical hydrogen production loop, three-stage methanation process, and a dual thermal-energy storage system (molten salt/phase change material). This setup enables high-temperature power generation, renewable hydrogen production, and continuous synthetic-methane synthesis under varying solar conditions. This novel solar–thermochemical system, assessed thermo-economically and integrated with machine-learning-based multi-objective optimization, enables continuous synthetic methane production and stable power generation under variable solar conditions. A multi-layer perceptron, trained using features from random forest regression (achieving R2 > 0.99), was integrated with a multi-objective particle swarm optimization algorithm to optimize system parameters. The combined framework maximizing energy and exergy efficiency while minimizing product cost. Under optimal conditions, the system achieved a 1.4 MW power output, producing 287 kg h−1 of methane, and a production cost of 29.55 $·GJ−1. In Yuma (Arizona) conditions, the system generates 5.1 GWh of electricity and 999 tons of methane annually, with energy and exergy efficiencies of 42.9% and 53.3%. The thermal energy storage subsystem ensures about 13 h of continuous operation during adverse weather conditions. These results demonstrate the technical and economic viability of solar-driven synthetic methane production as a scalable solution for renewable energy storage and grid stabilization.