HERCULES introduces a novel breakthrough approach towards thermal energy storage of surplus renewable energy via a hybrid thermochemical/sensible heat storage concept, implemented with the aid of porous media made of refractory redox metal oxides and electrically powered heating elements. The specific redox oxides are capable of reversible reduction/oxidation reactions upon heating/cooling in direct contact with air, accompanied, respectively, by endothermic/exothermic heat effects. The heating elements use surplus/cheap renewable electricity (e.g. from PVs, wind, or other renewable sources) to charge the porous metal oxide-based storage block by heating it to a level exceeding the metal oxide’s reduction onset temperature (i.e. charging/energy storage step). Hence, energy is stored in the porous oxide structure both sensibly as well as thermochemically through the endothermic reduction reaction. Subsequently (i.e. upon demand) the fully charged system can transfer its energy to a controlled airflow that passes through the porous oxide block and initiates the exothermic oxidation of the reduced metal oxide. Thus a hot air stream is produced during this step which can be used to provide exploitable heat for industrial processes. Such redox oxide material-based storage systems not only have much higher energy storage density than conventional sensible-only ones but exhibit a high discharge temperature range (> 500 ºC), do not require gas storage and greatly simplify overall system design and operation. The proposed research will be conducted by an interdisciplinary consortium comprised of leading research centers, universities, innovative SMEs, and large enterprises including ancillary service providers and technology end users.