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

摘要

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 solarto-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 (T-hot from 700 to 1100 degrees C) and low O-2 partial pressure (p(O2) 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 p(O2 )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-delta) is evaluated for specific storage and overall solar-to-electric efficiency in a subsystem using vacuum pumping or N-2 sweep gas for the reducing environment in the receiver. Vacuum pumping parasitics increase proportionally to changes in oxygen non-stoichiometry (Delta delta) and are prohibitively high for Delta delta 0.1. Sweep-gas parasitics to separate N-2 from air asymptote to smaller constant values at large Delta delta. Thus, a sweep gas subsystem has lower balance-of-plant parasitics at Delta delta 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 p(O2) and increasing T hor can achieve the same energy storage for either inert sweep gas or reversible vacuum-pump systems with solar-to-electric efficiencies above 35%.