'Hydricity' Concept Uses Solar Energy to Produce Power Round-the-Clock

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In superheating, water is heated well beyond its boiling point – in this case from 1,000 to 1,300 degrees Celsius - producing high-temperature steam to run turbines and also to operate solar reactors to split the water into hydrogen and oxygen.

"In the round-the-clock process we produce hydrogen and electricity during daylight, store hydrogen and oxygen, and then when solar energy is not available we use hydrogen to produce electricity using a turbine-based hydrogen-power cycle," Tawarmalani said. "Because we could operate around the clock, the steam turbines run continuously and shutdowns and restarts are not required. Furthermore, our combined process is more efficient than the standalone process that produces electricity and the one that produces and stores hydrogen."

The system has been simulated using models, but there has been no experimental component to the research.

"The overall sun-to-electricity efficiency of the hydricity process, averaged over a 24-hour cycle, is shown to approach 35 percent, which is nearly the efficiency attained by using the best photovoltaic cells along with batteries," Gençer said. "In comparison, our proposed process stores energy thermo-chemically more efficiently than conventional energy-storage systems, the coproduced hydrogen has alternate uses in the transportation-chemical-petrochemical industries, and unlike batteries, the stored energy does not discharge over time and the storage medium does not degrade with repeated uses."

Agrawal said, "The concept combines processes already developed by other researchers while also improving on these existing processes. The daytime and night-time systems would use much of the same equipment, allowing them to segue seamlessly, representing an advantage over other battery-based solar technologies."

The research has been funded by the U.S. Department of Energy through the DOE's Center for Direct Catalytic Conversion of Biomass to Biofuels at Purdue's Discovery Park and through a "Solar Economy" project led by Agrawal under the National Science Foundation's Integrative Education and Research Traineeship Program.

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