Thermodynamic Modelling of Thermal Energy Storage Systems

This paper presents a novel methodology for comparing thermal energy storage to electrochemical, chemical, and mechanical energy storage technologies. The underlying physics of this model is hinged on the development of a round trip efficiency formulation for these systems. The charging and discharging processes of compressed air energy storage, flywheel energy storage, fuel cells, and batteries are well understood and defined from a physics standpoint in the context of comparing these systems. However, the challenge lays in comparing the charging process of these systems with the charging process of thermal energy storage systems for concentrating solar power plants (CSP). The round trip efficiency and the levelized cost of energy (LCOE) are the metrics used for comparison purposes. The thermal energy storage system is specifically compared to vanadium redox, sodium sulphur, and compressed air energy storage (CAES) systems from a large scale storage perspective of 100's of MWh. The rationale behind this analysis was to develop an electrical storage efficiency for molten salt thermal energy storage systems, such that it can be compared to battery energy storage technologies in the context of comparing CSP with thermal energy storage to solar photovoltaic with battery storage from a utility scale perspective. The results from the modelling using Andasol 3 CSP plant as a case study yield a storage efficiency of 86% and LCOE of $216/MWh. The results of this modelling will facilitate the future generation of a thermal energy storage roadmap.