A carbon-negative solar fuel production method with enhanced solar contribution and superior CO2 reduction capacity: Experimental and system investigation

With the continuous growth in energy demand, multi-energy hybrid utilization plays a significant role in optimizing energy structures and promoting low-carbon transformation. Solar energy and natural gas thermochemical hybrid utilization, by converting concentrated solar thermal energy into high-quality fuel chemical energy, helps mitigate the impact of solar irradiation variability on energy supply stability and reliability. Existing research primarily focuses on solar-driven dry/steam reforming of methane (DRM/SRM), converting solar energy into chemical energy in the form of syngas. However, these processes are fundamentally constrained by the thermodynamic properties of reforming and reaction thermal effects, resulting in low solar contribution, limited fossil fuel substitution, and insufficient CO2 utilization capacity. To address these challenges, this study proposes an innovative carbon-negative solar fuel production method with enhanced solar share and CO2 reduction capacity via chemical looping conversion. In this approach, oxygen carriers are employed to mediate the chemical looping reactions, restructuring the conventional CH4–CO2 reforming process into two separate steps, CH4 oxidation and CO2 reduction, enabling the production of high-purity CO. Concentrated solar energy is utilized to provide the heat required for reduction reaction. This pathway significantly increases the overall reaction thermal demand, enabling a higher fraction of solar energy to be converted into chemical energy stored in product CO-rich syngas. Experimental validation of the feasibility of this method is conducted in this study. Based on this approach, a carbon-negative solar fuel production system is developed and its performance is systematically evaluated through thermodynamic modeling and parametric analysis. Promising results show that the proposed system increases the solar share to 28.44 %, representing a 7.19 percentage point improvement over the most efficient solar-driven SRM system reported in literature. Furthermore, the system enhances the CO2 reduction per unit of CH4 to 2.84, which is 2.12 times higher than that of the conventional DRM process (0.91 mol-CO2/mol-CH4). Life-cycle assessment further confirms the carbon-negative characteristics of the SE-CL system, with total emissions of −0.69 kg CO2-eq/kg-CO. These findings offer an effective solution to enhance the share of renewable energy in the energy structure and provide new pathways for utilizing CO2 with high value.