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Proc Natl Acad Sci U S A. 2015 Dec 29;112(52):15821-6. doi: 10.1073/pnas.1513488112. Epub 2015 Dec 14.

Round-the-clock power supply and a sustainable economy via synergistic integration of solar thermal power and hydrogen processes.

Author information

1
School of Chemical Engineering, Purdue University, West Lafayette, IN 47907;
2
Industrial Process and Energy Systems Engineering Group, École Polytechnique Fédérale de Lausanne, CH-1951 Sion, Switzerland;
3
Krannert School of Management, Purdue University, West Lafayette, IN 47907.
4
School of Chemical Engineering, Purdue University, West Lafayette, IN 47907; agrawalr@purdue.edu.

Abstract

We introduce a paradigm-"hydricity"-that involves the coproduction of hydrogen and electricity from solar thermal energy and their judicious use to enable a sustainable economy. We identify and implement synergistic integrations while improving each of the two individual processes. When the proposed integrated process is operated in a standalone, solely power production mode, the resulting solar water power cycle can generate electricity with unprecedented efficiencies of 40-46%. Similarly, in standalone hydrogen mode, pressurized hydrogen is produced at efficiencies approaching ∼50%. In the coproduction mode, the coproduced hydrogen is stored for uninterrupted solar power production. When sunlight is unavailable, we envision that the stored hydrogen is used in a "turbine"-based hydrogen water power (H2WP) cycle with the calculated hydrogen-to-electricity efficiency of 65-70%, which is comparable to the fuel cell efficiencies. The H2WP cycle uses much of the same equipment as the solar water power cycle, reducing capital outlays. The overall sun-to-electricity efficiency of the hydricity process, averaged over a 24-h cycle, is shown to approach ∼35%, which is nearly the efficiency attained by using the best multijunction photovoltaic cells along with batteries. In comparison, our proposed process has the following advantages: (i) It stores energy thermochemically with a two- to threefold higher density, (ii) coproduced hydrogen has alternate uses in transportation/chemical/petrochemical industries, and (iii) unlike batteries, the stored energy does not discharge over time and the storage medium does not degrade with repeated uses.

KEYWORDS:

electricity; hydrogen; process synthesis; solar; solar thermal power

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