Science Applications International and the Florida Solar Energy Center of the University of Central Florida have teamed to develop an advanced solar thermochemical water splitting cycle for hydrogen production that utilizes the “quantum boost” effect of sunlight. This is a $5M, 4 year program funded by the U.S. Department of Energy that began in 2007. The objectives are to cost effectively generate hydrogen at above 40% efficiency.
The project is divided into three phases. In the first phase, thermodynamic and chemical equilibrium analyses of the potential solar thermo-chemical cycles are being conducted. Next, a bench-scale solar concentrator and reactor system will be designed and constructed for on-sun validation. Finally, a fully-integrated pilot-scale solar hydrogen production system will be fabricated.
FSEC has identified a hybrid cycle for which the reactions are as follows:
(1) SO₂ + 2NH₃+H₂O --> (NH₄)₂SO₃ (aqueous, ~300K, chemical absorption)
(2) (NH₄)₂SO₃ + H₂O --> (NH₄)₂SO₄ + H₂ (aqueous, ~350K, photocatalytic)
(3) (NH₄)₂SO₄ + ZnO --> 2NH₃ + ZnSO₄ + H₂O (solid/gas, ~550K, thermochemical)
(4) ZnSO₄ --> ZnO +SO₂ + ½ O₂ (solid/gas, ~1125K, thermochemical)
This paper provides a comparative analysis of this cycle to several other competing processes for solar water splitting. Specific characteristics of the cycle are described. The SAIC/FSEC development program, sponsored by the US Department of Energy, has a goal of producing an operating pilot-scale plant for production of hydrogen at the end of the four-year program. The program will be reviewed and progress to date will be summarized.