Analysis of a thermochemical energy storage system based on the reversible Ca(OH)2/CaO reaction

The development of novel energy storage technologies is crucial for the massive deployment of large-scale renewable energy systems. This paper presents the conceptual study of an integrated system for the large-scale storage of solar thermal energy in the form of thermochemical energy based on calcium hydroxide. Calcium oxide-based storage media are very promising because they are an abundant and inexpensive resource with high energy density and the possibility of storage under ambient conditions. The equilibrium temperature of the reaction is around 500 °C, so the integrated system operates in a temperature range similar to that of concentrating solar power plants and molten salt storage, being able to reach higher temperatures in power production depending on the partial pressure of the steam generated in the reaction. The study discusses the technological challenges of the system, highlighting the importance of recovering the latent heat from condensation of the steam generated in the dehydration reaction, which represents 38% of the solar thermal energy entering the reactor during the charging phase, and proposes recovery mechanisms. The analysis shows the potential competitiveness of the technology as a large-scale energy storage system. By considering the full recovery of the latent heat of the steam, the system achieves a round-trip thermal efficiency of more than 80%, an overall thermal-to-electrical efficiency of 40% and LCOE values of 100 USD/MWhe.