Transient simulation and thermodynamic analysis of pumped thermal electricity storage based on packed-bed latent heat/cold stores

Abstract Pumped thermal electricity storage is a promising large-scale electricity storage technology that uses thermodynamic cycles and thermal energy storage to achieve electricity storage and release. At present, for pumped thermal electricity storage based on the Joule-Brayton cycle, packed beds filled with sensible heat storage media are widely adopted as the thermal store, while they usually suffer from low energy storage densities and large volumes. In this paper, the thermodynamic feasibility of packed-bed latent heat/cold stores is explored to replace the packed-bed sensible heat/cold stores in pumped thermal electricity storage. A numerical model of a 10.5 MW/5 h storage system based on packed-bed latent heat/cold stores is established. The energy and exergy analysis of components is carried out. The effect of compression ratios, porosities, isentropic efficiencies, and inlet velocities on the systematic thermodynamic performance is investigated and optimal conditions are also investigated. It is concluded that the energy storage density of the system increases from 232.5 kWh/m3 to 245.4 kWh/m3 when packed-bed sensible heat/cold stores are replaced by latent ones. Furthermore, the power density of the system based on packed-bed latent heat/cold stores is 216.5 kW/m3, and the round-trip efficiency reaches 84.7%, which is competitive in large-scale electricity storage technologies.