Thermochemical Heat Storage for Baseload Concentrated Solar Power Generation

Kurzfassung

Recent developments in solar-thermal power generation aim as well to achieve higher temperatures to increase the efficiencies of the power cycles as to store the solar energy to enable baseload power generation from a transient energy source. Thermochemical redox processes are an option to store large amounts of solar energy in a compact storage system. The enthalpy effects of these reversible chemical reactions can be exploited. Oxides of multivalent metals in particular, capable of being reduced and oxidized under air atmosphere with significant heat effects are perfect candidates for air-operated Concentrated Solar Power plants since in this case air can be used as both the heat transfer fluid and the reactant (O2) and therefore can come to direct contact with the storage material (oxide). Examples are manganese oxide and cobalt oxide cyclic redox schemes. They can be cycled in the range of 800-1000oC. Porous ceramic structures like honeycombs and foams are favorable for heat exchange applications, the idea of employing such structures either coated with or entirely made of a redox material like Co3O4, as a hybrid sensible-thermochemical solar energy storage system in air-operated Concentrated Solar Power plants has been set forth and tested. At first, small-scale, redox-inert, cordierite foams and honeycombs were coated with Co3O4 and tested for cyclic reduction-oxidation operation via Thermo-Gravimetric Analysis. To improve the volumetric heat storage capacity of such reactors, ceramic foams made entirely of Co3O4 were manufactured. Such foams exhibited satisfactory structural integrity and were comparatively tested vs. the “plain” Co3O4 powder and the Co3O4-coated, cordierite supports under the same cyclic redox conditions. A thermochemical storage system prototype was modeled, built and implemented for the first time in an existing concentrated solar power facility, DLR’s solar tower in Juelich, Germany.