Evaluating thermodynamic performance limits of thermochemical energy storage subsystems using reactive perovskite oxide particles for concentrating solar power

Concentrating solar power with cost effective and efficient thermal energy storage (TES) has the potential to achieve high dispatchability and enable high penetration of other renewable energy sources. However, levelized cost of electricity of integrated CSP systems remains prohibitively high, and new storage subsystems with higher specific energy storage (kJ kg-1) and overall solar-to-electric efficiencies are needed to lower the costs of dispatchable electricity from CSP. This paper explores the potential for increased specific energy storage and solar-to-electric efficiencies of a TES subsystem that combines sensible and chemical energy storage (i.e., thermochemical energy storage - TCES) using a redox cycle of reducible perovskite oxide particles. The TCES subsystem stores energy through sensible heating and endothermic perovskite reduction in a concentrated solar particle receiver at high temperature (Thot from 700 to 1100 °C) and low O2 partial pressure (pO2 from 10-2 to 10-4 bar). Stored energy is recovered as needed in a particle reoxidation reactor/heat exchanger fed by air. Energy parasitics to lower pO2 for perovskite reduction in the receiver by vacuum pumping or inert sweep gas generation depend on system design and operating conditions. In this work, TCES with the perovskite strontium-doped calcium manganite (Ca0.9Sr0.1MnO3-δ) is evaluated for specific storage and overall solar-to-electric efficiency in a subsystem using vacuum pumping or N2 sweep gas for the reducing environment in the receiver. Vacuum pumping parasitics increase proportionally to changes in oxygen non-stoichiometry (Δδ) and are prohibitively high for Δδ>0.1. Sweep-gas parasitics to separate N2 from air asymptote to smaller constant values at large Δδ. Thus, a sweep gas subsystem has lower balance-of-plant parasitics at Δδ needed for high specific TCES. Improvements in vacuum pump efficiencies from current commercially available values to >10% could reduce pumping parasitics and achieve solar-to-electric efficiencies approaching 35%. Various combinations of reducing pO2 and increasing Thot can achieve the same energy storage for either inert sweep gas or reversible vacuum-pump systems with solar-to-electric efficiencies above 35%.