Thermodynamic evaluation of electricity and hydrogen cogeneration from solar energy and fossil fuels

A photovoltaics (PV) and methane-steam-reforming hybrid system for efficient and carbon-neutral electricity hydrogen cogeneration from solar energy and fossil fuels is proposed. Middle-wavelength (x-870 nm) sunlight, suitable for PV conversion, is utilized for electricity generation by PV cells, while shorter-and longer-wavelength (280-x nm & 870-4000 nm) sunlight, which is not suitable for PV conversion, is rationally converted to thermal energy and further utilized for hydrogen production. Since electricity and hydrogen are both high-quality and clean energy carriers, the produced electricity and hydrogen could be directly output to users. The solar-to product energy efficiency of the proposed system reaches 56.3%, 42.9% higher than that of the reference system (parallel arranged solar PVT part and solar methane-steam-reforming part). Efficiency improvement is mainly brought by full-spectrum utilization of sunlight and comprehensive utilization of electricity, thermal energy, and chemical energy. Besides, interconversion between hydrogen and electricity can be easily achieved via fuel cells or water electrolysis cells, which enables flexible supply of electricity and hydrogen on demand. When the proposed system only generates electricity, the solar-to-product efficiency is 30.2%, 29.1% higher than that of the reference system; when it only generates hydrogen, the solar-to-product efficiency is 54.5%, 44.5% higher than that of the reference system. In sum, this study offers an efficient, low carbon and flexible route for hydrogen-electricity cogeneration with solar energy and fossil fuels as inputs.