Dharik S. Mallapragada

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

Significance Diminishing fossil fuel resources and increasing atmospheric greenhouse gases present a compelling case for transitioning to a sustainable economy where all human needs can be met by using abundant solar energy. In this paper, we introduce “hydricity,” a paradigm that proposes synergistic coproduction of solar thermal power and hydrogen. We realize hydricity by judiciously integrating solar water power cycle, solar thermal hydrogen production techniques, and turbine-based hydrogen power cycle and by suitably improving each one for compatibility and beneficial interaction. The proposed hydricity concept presents a potential breakthrough solution for continuous and efficient power supply and also an exciting opportunity to envision and create a sustainable economy to meet all the human needs—namely, food, chemicals, transportation, heating, and electricity. 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.

GWh Level Renewable Energy Storage and Supply using Liquid CO2

Abstract A novel energy storage system is proposed to deliver GWh or more of electric energy from an intermittently available energy source. The system is a closed loop cycle that transforms carbon atoms between liquid carbon dioxide and liquid methane. Methane is associated with the highest energy content per mole carbon. Therefore, for a given power, it requires the least amount of carbon circulation in the cycle. Both carbon dioxide and methane are stored as liquids, thereby avoiding the challenges associated with storing gases. In each case, the electrical power required for liquefaction is minimized by integrating the vaporization and liquefaction steps of carbon dioxide and methane. This means that the refrigeration available from vaporizing liquid carbon dioxide is used in the liquefaction of methane and the refrigeration available from vaporizing liquid methane is used in the liquefaction of carbon dioxide.

Energy Systems Analysis for a Renewable Transportation Sector

Abstract In a fossil-fuel deprived world, it is likely that all the basic human needs will be met by renewable sources like solar energy. Among the needs, transportation offers the greatest challenges, owing to its high energy-density fuel requirements, which have traditionally been met by fossil-based liquid hydrocarbon fuels. Here, we present a detailed systems analysis of the transportation sector, from which emerges an energy efficient roadmap, based on the use of renewable carbon sources like biomass and atmospheric CO2, solar energy in the form of H2, heat and electricity, in conjunction with novel processes for producing liquid fuels. The proposed roadmap is illustrated using the US transportation sector as a case study.

Continuous baseload renewable power using chemical refrigeration cycles

Abstract We propose a cycle to store and supply GWh of electricity from intermittent renewable energy by transforming carbon atoms between carbon dioxide and methane. Among hydrocarbons, methane is associated with the highest energy content per mole of carbon. Therefore, for a given electricity supply, it requires the least amount of carbon circulation. To minimize storage volumes, both carbon dioxide and methane are stored as liquids. When renewable energy is available, methane is synthesized from vaporizing carbon dioxide, and subsequently purified, liquefied and stored. When renewable energy is unavailable, liquid methane is vaporized and oxidized for electricity supply. The produced carbon dioxide is purified and liquefied for storage and subsequent usage. In each case, the electricity required for purification and liquefaction is minimized by integrating the vaporization and liquefaction steps of carbon dioxide and methane. The cycle can achieve ∼55% storage efficiency with much reduced storage volumes compared to other options.