On the path toward day and night continuous solar high temperature thermochemical processes: A review

High temperature solar thermochemical processes for fuels and chemical commodities production have been studied for decades and their feasibility is now proven. However, industrial deployment is limited and one of the main reasons is that the variability of solar energy hinders a priori day and night continuous solar process operation. Nevertheless, solar intermittence is now very well managed for Concentrated Solar Power (CSP) electricity production. Indeed, thermal storage up to 600 degrees C is demonstrated and CSP electricity is base-load capable. However, far beyond electricity, heat supply is the major need in industry. This work reviews the recent works published or patented in the field of continuous operation of high temperature solar thermochemical processes (>600 degrees C). There is currently a strong commitment toward day and night solar processes operation since it could improve durability, quality of the products, efficiency and economics of such technologies. Indeed, industrial processes are mainly continuous, and daily start up and shut down strongly limit the production capacity of the solar-driven processes, which represents a major lock for scale up. For the first time in this paper, day and night continuous high temperature solar processes are reviewed and categorized. The reported works show the great innovation activity in this field and the various options investigated to date. The main outcomes show that continuous heat supply is possible thanks to hybridization or thermal energy storage.