Finite-time thermodynamic and economic analysis of Rankine Carnot battery based on life-cycle method

Rankine Carnot battery (R-CB) has a great potential in renewable energy-to-grid integration, and the theoretical thermodynamic performance is inaccurate because of the dynamic heat transfer processes and system performance. In this paper, an R-CB system consisting of a heat pump, a heat engine cycle, and a sensible heat storage tank was established. The finite-time thermodynamic model considering the irreversible loss of energy transfer and conversion processes was proposed. Based on the combination of finite-time thermodynamic model and life-cycle method, the levelized cost of energy storage model was established for the combination of economic and energy performance. Furthermore, evaporation temperature, heat storage temperature, temperature difference of shared heat exchanger, and shared heat transfer area were adopted as main variables to conduct the global optimization and parametric analysis of the system. The simulation is based on an R-CB system with a storage capacity of 10 MW/6h, and the results showed the optimized system roundtrip efficiency was 78.1%, and the levelized cost of storage (LCOS) was 0.329 $/kWh with an evaporation temperature of 100 ℃. The roundtrip efficiency increased from 25.6% to 78.1% with the evaporation temperature rising from 60 to 100 ℃, while LCOS decreased by 45.8 %. Reducing the highest heat storage temperature effectively increased the roundtrip efficiency and reduced the heat storage cost, while decreasing the LCOS. The increase in roundtrip efficiency, which was obtained by reducing the shared heat exchange temperature difference and increasing the shared heat transfer area, was the primary factor in reducing the LCOS. The combination of finite-time thermodynamics and the life-cycle method in this paper may provide a more realistic evaluation approach for measuring the technical and economic potential of R-CB systems.