Optimization and 4E analysis of a hybrid solar-methane system for hydrogen and freshwater production with enhanced waste heat recovery from a compressed air energy storage system

Compressed air energy storage (CAES) systems based on the gas turbine cycle produce significant waste energy during charging and discharging, which has not been effectively utilized in multi-generation systems. This study proposes a novel system that recovers waste heat during the charging period using two trans-critical CO2 Rankine cycles coupled with a reverse osmosis desalination system, and during the discharge period using a domestic hot water heat exchanger, an absorption chiller, a proton exchange membrane electrolyzer, and a steam Rankine cycle (SRC). The system is powered by hybrid energy sources—a solar power tower and a methane-based combustion chamber—to overcome the limitations of each energy source when used individually. Comprehensive energy, exergy, exergy-economic, and environmental analyses are conducted, with parametric studies examining key factors such as high pressures and temperatures in the CAES system and the heat recovery steam generator temperature in the SRC. Multi-objective optimization, performed by linking EES software with MATLAB and employing artificial neural networks (ANNs) to reduce computational time, reveals an exergy round trip efficiency of 37.8 % and a unit cost of 128.65 $/GJ. ANNs, trained with about 2000 randomly generated data points, enable accurate and efficient predictions of system performance, ensuring a robust design process.