Comparing the thermodynamic potential of alternative liquid metal oxides for the storage of solar thermal energy

The relative potential of liquid multivalent metal oxides for the storage of thermal energy as sensible, latent and/or thermochemical storage energy in a liquid chemical looping thermal enerrgy storage (LCL-TES) is reported. This LCL-TES cycle comprises a reduction reactor, an oxidation reactor, two reservoirs for storing the hot and cold medium and a heat recovery unit. The materials were assessed on the basis of their melting temperature, Gibbs free energy, reaction temperature and thermal storage capacity. Ellingham diagrams were used to identify regimes with a potential for application in a LCL-TES, while phase diagrams were used to identify processes which combine sensible, latent and thermochemical heat storage. Based on these criteria, the oxide of CuO/Cu2O was found to have the greatest thermodynamic potential for use in a LCL-TES system with a total enthalpy of 404.67 kJ/mol for thermal storage. However, the high temperature of ∼1200 °C and corrosive nature of molten copper and its oxides will make this cycle challenging to implement. Lead, on the other hand has a lower total enthalpy of 250.09 kJ/mol, but is molten at lower temperatures.