Abstract
High-temperature thermal energy storage enables concentrated solar power plants to provide base load. Thermochemical energy storage is based on reversible gas–solid reactions and brings along the advantage of potential loss-free energy storage in the form of separated reaction products and possible high energy densities. The redox reaction of metal oxides is able to store thermal energy at elevated temperatures with air providing the gaseous reaction partner. However, due to the high temperature level, it is crucial to extract both the inherent sensible and thermochemical energies of the metal-oxide particles for enhanced system efficiency. So far, experimental research in the field of thermochemical energy storage focused mainly on solar receivers for continuously charging metal oxides. A continuously operated system of energy storage and solar tower decouples the storage capacity from generated power with metal-oxide particles applied as heat transfer medium and energy storage material. Hence, a heat exchanger based on a countercurrent moving bed concept was developed in a kW -scale. The reactor addresses the combined utilization of the reaction enthalpy of the oxidation and the extraction of thermal energy of a manganese–iron-oxide particle flow. A stationary temperature profile of the bulk was achieved with two distinct temperature sections. The oxidation induced a nearly isothermal section with an overall stable off-gas temperature. The oxidation and heat extraction from the manganese–iron oxide resulted in a total energy density of 569 kJ/kg with a thermochemical share of 21.1%.
Highlights
A thermochemical energy storage (TCS) is able to complement concentrated solar thermal power plants (CSP) to allow for renewable base load supply
Metal oxides are a suitable candidate for thermochemical energy storage for CSP, since the redox reaction of metal oxides occurs at elevated temperatures [3,4], which are necessary to reach high efficiencies
Since the heat transfer of thermal and thermochemical energy can overlap in the moving bed reactor, the temperature and pressure dependence of the reaction rate of the redox reaction of the manganese–iron-oxide particles is decisive
Summary
A thermochemical energy storage (TCS) is able to complement concentrated solar thermal power plants (CSP) to allow for renewable base load supply. The principle of thermochemical energy storage is based on a chemically reversible gas–solid reaction. The thermal energy is either released in the form of reaction enthalpy (discharging), absorbed by the reverse endothermic reaction (charging), or stored in the chemical bond by the separation of the gas and solid phases. Metal oxides are a suitable candidate for thermochemical energy storage for CSP, since the redox reaction of metal oxides occurs at elevated temperatures [3,4], which are necessary to reach high efficiencies. The considered system (Figure 1) is based on metal-oxide particles as thermochemical energy storage material and heat transfer medium to expand the CSP operation time into evening hours or to compensate weather instability
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