Albero: An alternative natural material for solar energy storage by the calcium-looping process

Large-scale thermochemical energy storage (TCES) is gaining relevance as an alternative to current thermal energy storage systems in Concentrated Solar Power plants. Among the different systems, the reversible reaction between CaO and CO2 stands out due to the wide availability and low cost of the raw material: limestone. Direct solar absorption of the storage media would improve the efficiency of solar-to-thermal energy storage due to reduced thermal transfer barriers, but the solar optical absorption of CaCO3 is poor. In this work, we propose the use of a Ca-rich calcarenite sedimentary rock so-called albero as an alternative to limestone. We demonstrate that this reddish material exhibits an average solar absorptance that is approximately ten times larger than limestone. Moreover, the multicycle carbonation/calcination performance under different experimental conditions has been studied by thermogravimetry, and similar values to those exhibited for limestone have been obtained. Besides, the material is cheap (6 €/ton), and simulations showed that the use of this material would significantly improve the overall CaL-CSP efficiency at the industrial level.