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

Abstract

Pumped-thermal electricity storage has the advantages of high energy storage density, no geographical restrictions and low costs, making it the most promising large-scale electricity storage technology. In this paper, a numerical model of the Brayton-like pumped-thermal electricity storage based on packed-bed latent heat/cold stores is established and a recuperator is added between the hot store and the expander. The rated power of the system is 150 kW and the charging/discharging time is 4 h. The dimensionless analysis is applied to the energy storage units including transient temperature, charging/discharging time as well as axial position. Moreover, based on the finite element method, an extensive thermodynamic analysis is carried out in MATLAB. It is concluded that compared with the non-recuperated system, the total input power of the recuperated system can be reduced by 18.1 kW in the charge duration and the energy density of the system using PCMs instead of sensible heat storage materials can be improved from 202.4 kWh/m3 to 267.4 kWh/m3. The roundtrip efficiency of the system could reach 0.55. In addition, detailed exergy flow and exergy loss of each component are studied. It is found that the total exergy loss of the recuperated system is 52.27 kW, a 22.4 % decrease compared to that of the non-recuperated system and the compressor has the largest exergy loss, accounting for 36 % of the total loss, which can be ameliorated by improving the level of industrial manufacturing in the future.