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Abstract

A photoelectrochemical system and method utilizing the photons having energies above the bandgaps of a p-type semiconductor photocathode and an n-type semiconductor photoanode with redox couples having fast electron transfer kinetics to keep overpotentials under 0.15 volts, and redox potentials energetically located within the band gaps, for storing energy in photodriven oxidation and reduction reactions separated by less than 1.6 volts using a redox flow battery configuration, are described. The photoelectrochemical system can also store heat in the flow battery generated from the inefficiencies of the photoredox reactions and from impinging photons having energies below the band gaps. Redox flow batteries contain fluid electrolyte and tanks for storing the redox equivalents, which can be used to store the solar energy not used to drive the photoredox chemistry for hot water and space heating applications. The present hybrid photoelectrochemical/thermal system may be used store excess grid electricity when electrical demand is low, or as a conventional redox flow battery in a distributed energy system, if the redox electrolyte volume was increased above that needed for solar load leveling on a daily or weekly time scale. Heat generated from the discharge of the redox battery would also be captured and stored.

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