Efficient Hydrogen Production System with Complementary Utilization of Methane and Full-Spectrum Solar Energy

Solar hydrogen production by integration of photovoltaic cells (PV) and electrolytic water splitting offers the ability to simultaneously store intermittent solar energy and produce hydrogen. However, the solar-to-hydrogen efficiency is limited by the inability of PV cells to utilize solar energy in the long-wavelength spectrum. On the other hand, solar energy in the short-wavelength spectrum with high activation ability is underutilized in solar thermochemical methane steam reforming (MSR). To address these issues, this paper proposes a hydrogen production system that integrates electrolytic water splitting with a thermochemical MSR and employs a Rankine Cycle (RC) for balancing electricity and heat for water electrolysis. This system enables the efficient conversion of full-spectrum solar energy into hydrogen while minimizing the underutilization of high-grade solar energy. The thermodynamic and environmental performances of the proposed system are evaluated and compared with those of a reference system - a full-spectrum solar hydrogen production system without fossil fuels. Results show that the proposed system produces 2.21-2.71 times more hydrogen than the reference system when solar direct normal irradiance (DNI) ranges from 200-1000 W/m2. It exhibits higher energy efficiency, exergy efficiency, and solar-to-hydrogen efficiency than the reference system. Furthermore, the proposed system can reduce approximately 15.0 kg of CO2 emissions when producing 1 kg of hydrogen. This study provides a promising approach to efficiently using solar energy and fossil fuels for generating hydrogen.