Hydrogen can be produced by coupling high-temperature thermochemical processes with concentrated solar power (CSP), an inexhaustible, greenhouse gas-free energy source. These processes offer the potential to be both more cost-effective and more energy-efficient than even the best solar electric power generation options coupled with conventional electrolysis. However, the high temperatures required and the complication of integrating the chemical processing directly into a concentrating solar plant will require a significant research and development effort over a number of years to bring these options to commercial fruition.

The objective of our ongoing work with the University of Nevada, Las Vegas (UNLV), and General Atomics is to define an economically feasible concept for the production of hydrogen from water using a CSP energy source. Hydrogen production by thermochemical water-splitting—a chemical process that accomplishes the decomposition of water into hydrogen and oxygen using only heat or a combination of heat and electrolysis instead of pure electrolysis—meets these goals. Thermochemical water-splitting cycles have been known for almost 40 years but little U.S. progress has been reported for most of the past 20 years.

Over 100 unique cycles have been proposed in the past, but substantial research has been done on only a few. Recently, there has been a renewed interest in thermochemical water splitting, but none of the recent work has emphasized the unique benefits and challenges of using CSP energy to generate hydrogen.

CSP can be exploited in several different architectures, each with its own thermal characteristics, constraints, and adaptability to thermochemical hydrogen production. In ongoing work, all the existing and proposed cycles will be compared using objective criteria tailored to each solar thermal architecture to determine which cycles can benefit, in terms of efficiency and estimated cost, from the unique high-temperature capabilities of appropriate advanced solar thermal energy source.

Guided by the results of the screening process, one or more cycles will be selected for integration with the best matching CSP system. The required flow sheets will be developed, and preliminary engineering estimates of size and cost will be made for major pieces of equipment. From this information, a preliminary estimate of efficiency and cost will be made, and a preliminary design will be developed for a Phase II demonstration project based on the results of the Phase I study. In Phase III, a full-scale pilot is envisioned, utilizing the data acquired in the first two phases.

Contact:
Rich Diver
rbdiver@sandia.gov
(505) 844-0195