Modelling and Evaluation of CO2-based Electrothermal Energy Storage System

Abstract

The use of renewable energy sources as a solution to the energy dependency on fossil fuels requires innovative solutions to the issue of energy storage. Among the solutions suggested in the literature, electrothermal energy storage comprised of a heat pump and a heat engine using transcritical CO2 cycles, water as a thermal energy storage (TES) fluid to store sensible heat and ice as a cold storage medium to store latent heat, appears promising. In this paper, a steady state mathematical model of the system is developed using Aspen Plus V11, validated and compared against results available in the literature. The validated model’s performance is then studied utilizing parametric sensitivity analysis by exploring the effect of different parameters on multiple efficiency metrics, with the best case achieving improvement on the round-trip efficiency (?R-T) of 7.64 %. The hydraulic turbine inlet temperature and the heat engine minimum pressure are found to contribute the most to the ?R-T improvement, with the minimum pressure being the one that can be further decreased by using cold TES mediums with lower freezing points. Finally, the effect of alternative cold TES mediums (with lower freezing temperature than ice) on the performance of the system is evaluated. It was concluded, that the ?R-T of the model decreases as the freezing temperature declines, from 46.90 % at 0 °C to 44.90 % at -20.19 °C. As a result, no benefit related to the ?R-T of the model can be deduced by choosing cold TES mediums with lower freezing p than ice.