Techno-economics of solids-based thermochemical energy storage systems for large scale, high-temperature applications

Journal article, 2024

This work evaluates the techno-economic feasibility of the three most promising solids cycling systems (carbonates, thermally-reduced and chemically-reduced metal oxides) for thermochemical energy storage when deployed for large-scale applications with high-temperature operation. For each system, a specific material is selected (Ca, Co and Fe, respectively) and two process layouts are formulated: one focused on energy storage and one co-generating additional high-value byproducts (to offer CO2 capture to nearby processes, production of pure O2 and production of H2 respectively). The study compares deployments sized to absorb 100 MW of solar power with an intermittency period of 12 h and dispatch it continuously as a constant high-temperature energy discharge. For each process layout, mass, energy and exergy balances are solved and the cost structure is calculated using a bottom-up approach. The technical assessment shows the Co-based system to have the best performance (electrical efficiency up to 45 %) for sole energy storage due to its higher extent of reaction and energy density. The results show that the generation of valuable byproducts (to offer CO2 capture and pure O2, respectively) is done at the expense of electrical efficiency and dispatchability, although the Fe-based process with co-production of an energy carrier (H2) reaches high energy efficiencies (>80 %). Nevertheless, the generation of valuable byproducts tends to improve the economic performance (reduction in breakeven electricity selling price - BESP) in all three systems. The results indicate that the deployment of chemically-charged (Fe-based) layouts involves up to 10 times larger costs than thermally-charged ones (Ca and Co) due to the cost of the reducing agent. Despite this, when involving production of H2, the Fe-based process offers a significantly lower BESP than all other layouts. If high plant costs represent a financial barrier, Ca-based layout with CCS at the largest size investigated (250 MW) presents the lowest BESP among the rest of layouts investigated. Additionally, a parametric study reveals that the cost structure of the Ca-based process is the most robust to the variations considered in the study (costs of solid material, cooling water and heat input, as well as product selling prices).