Review of Carbonate-Based Systems for Thermochemical Energy Storage for Concentrating Solar Power Applications: State-of-the-Art and Outlook

Thermochemical energy storage (TCS) systems are receiving increasing research interest as a potential alternative to molten salts in concentrating solar power (CSP) plants. In this framework, alkaline-earth metal carbonates are very promising candidates since they can rely on wide availability, low cost, high volumetric density (>1 GJ m-3), relatively high operating temperatures (>800 °C), nontoxic and noncorrosive chemical nature, and no occurrence of any side reactions involving the production of undesired byproducts. Therefore, their reversible calcination/carbonation reaction with CO2 can be used to store/ release energy in CSP plants. However, in spite of these promising features, the TCS research field is relatively new, and most of it is still limited to the lab-scale. Therefore, great research efforts are needed to bridge the gap from fundamental research to real-scale application and implementation of TCS-CSP systems. This manuscript reviews the state-of-the-art of carbonate-based systems for TCS in CSP plants. In particular, the literature has been analyzed in-depth, paying attention to (i) the materials development, with a focus on the solutions available to improve the durability of the materials (namely, the ability to withstand repeated carbonation/ calcination cycles); and (ii) the design of the reactor configuration for both the solar-driven endothermic calcination and the exothermic carbonation reaction, focusing on the optimization of the reactor concept, based on the physicochemical properties and working temperatures of the reagents.