Binary medium Carnot battery based on Brayton cycle: thermodynamic and economic analysis

Current large-scale, long-duration energy storage technologies exhibit geographical dependencies, whilst Carnot batteries primarily struggle to balance heat storage temperatures with round-trip efficiency, limiting applications. This study therefore proposes a binary medium Carnot battery based on Brayton cycle. The high heat storage temperature is enhanced by employing the property that N₂ exhibits significantly greater internal energy with increasing pressure compared to CO₂. A high coefficient of performance of heat pump system configuration is achieved, and stored heat drives supercritical CO₂ Brayton cycle for electricity generation. This system achieves heat storage at 873.15 K and a round-trip efficiency of 62.89%. A sensitivity analysis was conducted on key parameters. The impact weight of parameters on system performance was quantified using dimensionless scaled sensitivity coefficients. The synergistic relationships of parameters on multiple system performances were determined, and multi-parameter analysis was carried out for parameters with non-synergistic relationships. In thermodynamic performance-targeted analysis, the energy storage capacity can be maximized by 19.30% to 7.11 MW, this enhancement exceeds round-trip efficiency improvement. But the economic feasibility was compromised. By prioritizing economic performance, the levelized cost of electricity could be reduced by 15.65% to 0.259$/kW·h, while the net present value would increase by 17.17% to 5.66 million$. Based on sensitivity analysis and multi-parameter analysis, the conditions balancing thermodynamics and economic performance were determined, achieving a system round-trip efficiency of 64.91%, energy storage capacity of 6.00 MW, levelized cost of electricity of 0.285$/kW·h, and net present value of 5.79 million$.