Solar power day and night
Concentrating solar power plants use mirrors to concentrate the Sun's heat energy much as a child uses a magnifying lens to start a fire with a piece of paper. The heat is typically used to drive a conventional turbine or engine to create electricity. Storing excess solar heat for release during cloudy or dark conditions significantly increases the efficiency and energy security associated with an intermittent renewable resource. Redox (reduction-oxidation) reactions involving solid oxides are particularly promising for thermochemical energy storage due to their significant capacities for storage and release. EU-funded scientists working on the STOLARFOAM (Thermochemical storage of solar heat via advanced reactors/heat exchangers based on ceramic foams) project made a step-change improvement in the current state-of-the-art solar heat storage concept. Current air-operated solar tower power plants store sensible heat via a temperature change in porous solid ceramic materials like honeycombs. The heat is released during off-sun operation. STOLARFOAM's groundbreaking innovation lies in combining the inherent effective heat transfer of foam structures with the excellent thermochemical cycling of oxide redox pairs for the first time. The team used ceramic foams made partially or entirely from redox oxide materials for heat exchange for the first time. Laboratory screening of redox pair oxides identified a cobalt oxide pair (Co3O4/CoO) as the best candidate. The team focused on Co3O4 honeycomb structures and foams. Porous ceramic honeycombs and foams were tested for sensible heat storage alone and for hybrid sensible/thermochemical heat storage when coated with various loadings of Co3O4. Exploiting the modularity of existing sensible storage systems, the team created the cascaded thermochemical storage concept employing tailored cascades of different porous structures and redox oxide pairs to best optimise heat transfer. An application for intellectual property rights has been filed for this pioneering turboboost to the existing state-of-the-art thermal energy storage system. Significantly extending a solar plant's off-sun operation beyond the current levels paves the way to solar-only power plants and an inestimable contribution to global emissions and climate change.
Keywords
Solar power, thermochemical, energy storage, power plants, redox, oxides, ceramic foams