Decoupling the heating and reduction processes in solar-driven two-step thermochemical cycle by coupling it with thermal power generation

Solar-driven H2O/CO2 splitting via two-step thermochemical cycle is a promising path for renewable fuel production. However, the energy losses caused by the high solar thermal temperature and the significant technical challenges in oxygen carrier heat recovery have long hindered its efficiency improvement. In this work, the two-step cycle was proposed to couple with a thermal power generation process to recover the process heat, and the electricity generated was proposed to be used in the reduction step, for which the solar heating and reduction processes can be decoupled. Thermodynamic evaluation shows that an efficiency advantage over the traditional cycling mode can be expected even when the solar thermal temperature is 50 K lower. It is 16.1 % at Tred = 1773 K and Tsolar = 1723 K, significantly higher than that of the traditional cycle working at Tred = 1773 K with 95 % gas heat and 40 % solid heat recovered (13.6 %). The novel cycling mode not only provides a practical heat recovery strategy, but also creates a completely new space for further lowering the solar thermal temperature and brings about obvious engineering advantages. It is supposed to be of important implications in promoting the practical application of the technology.