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 degrees C provides heat to drive methanol steam reforming and decomposition successively with a variation in the solar irradiance. At solar irradiance below 400 W/m(2), the low-grade solar heat is used to drive methanol steam reforming, at solar irradiance above 400 W/m(2), 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/m(2), 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. (C) 2016 Published by Elsevier Ltd.