High Efficiency Solar Production of Hydrogen from Water

ABSTRACT

In February 2007, Science Applications International, Corp. (SAIC) embarked on a project to develop a solar concentrating system to supply high temperature heat and photonic energy to a thermo-chemical reactor being developed by the Florida Solar Energy Center (FSEC) of the University of Central Florida (UCF) to produce hydrogen. The results presented in this paper are the initial work performed under a $5M, 4 year U.S. DOE project.

This project has as its primary goal the development of a viable solar high-temperature thermo-chemical water-splitting cycle that not only uses solar flux for heating but also includes a “solar boost” from photon absorption in the chemical process. This approach has the potential to be more energy efficient and therefore more cost-effective than cycles that only use thermal energy for production of hydrogen from water. The FSEC developed cycle can be as high as 45% efficient. In contrast, using solar energy from photovoltaics to electrolyze water to produce hydrogen is about 10% efficient.

SAIC developed the concept of the solar concentrating system to supply the energy to the water splitting reactor and designed the system integration technique. We are performing specific field tests on an existing solar dish in Phoenix, Arizona to verify the concept, revise the system specifications and design and develop an economic evaluation to prove that the cost goals can be realized.

The project is divided into three phases. In the first phase, laboratory testing and evaluation are being conducted. Thermodynamic and chemical equilibrium analyses of the potential solar thermo-chemical cycles that include a photo-assisted step are being performed. The results will be combined with preliminary economic analyses to select a preferred cycle for further development. In the second phase, a bench-scale solar concentrator and reactor system will be designed and constructed for on-sun validation of the selected process. Finally, the third phase will include the fabrication of a fully-integrated pilot-scale solar hydrogen production system including an optimized solar dish concentrator and solar reactor (with recycle loops included). The pilot-scale system will be operated to demonstrate the complete solar water-splitting process with a net reaction of water + sunlight ® hydrogen and oxygen. Economic analyses will be completed to verify feasibility of the system to deliver hydrogen at less than $3 per kilogram.