Transcritical CO2 Carnot Battery: Part A - Numerical Framework and Parametric Optimization

With the global transition to renewable energy, the demand for large-scale energy storage such as Carnot Batteries is getting intensified. This study presents a numerical framework developed in Python to evaluate the performance of transcritical CO2 Carnot Batteries. The research identifies inherent modeling challenges related to Carnot Batteries, specifically the thermal mismatches and mass flow bottlenecks involved in multi-tank thermal energy storage (TES) systems, and proposes solutions to resolve them. The modeling framework uses a discretized heat exchanger (HEX) modeling approach to accurately identify internal pinch point violations caused by the non-linear thermophysical properties of supercritical CO2 (sCO2) near the critical point. The model was validated against the 1 MW Mercangöz pilot plant, achieving Round-Trip Efficiency between 51% and 53%. Crucially, the study utilizes the Round-Trip Efficiency with cooling metric to account for system thermal asymmetry, revealing that parasitic cooling loads can reduce efficiency by 7–8% (in case the of Mercangöz pilot plant). These results demonstrate that ???????? ???????????? serves as the primary key performance indicator for maximizing the net electricity delivered to the grid. The central contribution of this work is an extensive parametric modeling study evaluating over vast number of cycle configurations, identifying optimal pressure ranges for the charge cycle (28–34 bar low-side; 122–154 bar high-side) and discharge cycle (35–41 bar low-side; 120–152 bar high-side). To verify the accuracy of this parametric study, a detailed baseline cycle, configured according to the optimal medium-scenario parameters, was modeled. This verification model successfully achieved the prescribed efficiency ranges and slightly outperformed the nominal commercial plant proposed by Mercangöz et al. Moreover, the new concept of Thermal Energy Ratio (TER) is introduced to quantify the thermal asymmetry between the charging and discharging cycles, which, alongside the back-work ratio, is found to be a critical factor in determining the parasitic cooling requirements and overall system performance. The findings underscore the importance of precise pressure and temperature selection in maximizing the performance of transcritical CO2 Carnot Batteries, providing a comprehensive roadmap for future design and optimization efforts in this field.