Techno-economic analysis of a modular thermochemical battery for electricity storage based on calcium-looping

Electricity storage is becoming one of the main challenges for the massive deployment of renewables. Thermal energy storage is gaining momentum, with molten salts-based systems being the state-of-the-art technology. As an alternative, Thermochemical Energy Storage (TCES) is a promising system that can increase the system performance in terms of energy storage density, maximum heat discharge temperature and long-term storage capacity. This work proposes and preliminary evaluates the performance of a novel modular Thermochemical Energy Storage (TCES) system based on the Calcium-Looping (CaL) process. The modularity allows its integration with multiple renewable energy sources into different high-temperature applications, including hard-to-decarbonise applications. Heat for the charging stage is provided by electrical heaters connected either to a Photovoltaic (PV) facility or directly to the grid. Limestone particles are heated, and once they reach their decomposition temperature (∼930 °C at 1 bar), the released CO2 is removed from the reactor, cooled, compressed, and stored. When the stored energy discharge is required, CO2 is supplied to the reactor to produce calcium carbonate and release the stored heat (∼ 400–875 °C). In the proposed concept, the solids remain in the reactor, and CO2 is added or removed depending on the stage. As cases of study of the concept, energy storage systems integrated with PV plants of 0.5 and 20 MWe and grid-based storage are considered. An hourly simulation throughout the year is performed. Results show an energy density above 1 GJ/m3, higher than current molten-salt-based systems. The levelized energy storage cost is below 100 €/MWh for the grid-based storage, highlighting its potential to contribute significantly to the global energy transition.