A solar source for the production of green hydrogen is envisioned by researchers from Massachusetts Institute of Technology, University of Waterloo (Canada) and Ewha Womans University (South Korea). This solar thermochemical hydrogen process is expected to use up to 40% of solar heat for green fuel generation, a significant improvement over the 7% utilization rate achieved by existing systems.

As in other solar thermochemical hydrogen routes, the conceptual system can be built around an existing concentrated solar plant, absorbing the receiver’s heat and directing it to split water and produce hydrogen. What differentiates the new technology is a novel two-step thermochemical reaction system wherein water in the form of steam is exposed to a metal, which serves to remove oxygen and separate out the hydrogen. The metal is reheated in a vacuum to reverse the oxidation process and regenerate itself, enabling it to again produce more hydrogen in a process that can be repeated hundreds of times.

Process efficiency stems from its train-like design, with box-shaped reactors running on a circular track. Each reactor in the train would house the metal repeatedly going through different thermochemical stations. The system can also recover most of the process heat used by allowing reactors on opposite sides of the circular train-like track to exchange heat through thermal radiation. A second set of reactors circles around the first train, moving in the opposite direction and operating in cooler temperatures to allow removal of oxygen from the hotter inner train without the need for energy-consuming mechanical pumps.

The researchers plan to construct a prototype of the system described in Solar Energy in the coming year.