Mid-temperature solar fuel process combining dual thermochemical reactions for effectively utilizing wider solar irradiance

The conversion of solar energy into chemical fuels is becoming more attractive and can be used for flexibly generating power; however, the poor annual solar-to-fuel efficiency severely hinders the application of the solar fuel process in the power system. Here, we study a mid-temperature solar fuel process having synergetic dual thermochemical reactions, in which solar heat at around 300 °C provides heat to drive methanol steam reforming and decomposition successively with a variation in the solar irradiance. At solar irradiance below 400 W/m2, the low-grade solar heat is used to drive methanol steam reforming, at solar irradiance above 400 W/m2, the solar heat is combined with methanol decomposition. The solar thermochemical performances of the proposed solar fuel process were analyzed for typical days and a full year. In contrast to the individual solar-driven methanol decomposition process which mainly utilize solar irradiance above 400 W/m2, the annual average solar-to-fuel efficiency in the synergetic process, which can utilize wider solar irradiance from 100 to 1000 W/m2, is improved to 60%, and the annual average solar-to-electricity efficiency is improved to 21%. The promising results can offer a possibility of greatly improving the annual average performance of the solar fuel process, especially for enlarging the effective utilization of lower solar irradiance.