Supercritical CO₂ pumped thermal electricity storage modifications via thermodynamic cycle splitting method

The sCO₂ Brayton cycle pumped thermal electricity storage (PTES) system has attracted considerable attention due to its high cycle efficiency and compact system layout. However, the variation trend of the round-trip efficiency remains unclear, making it challenging to carry out further process reconstruction to enhance system efficiency. The cycle splitting method can be extended to the forward and reverse dual-cycle sCO₂ PTES system, decomposing the complex cycle into a basic host cycle and several equivalent sub-cycles. Three typical modification measures, namely recompression, intercooling, and reheating, can be regarded as subtracting the equivalent recompression sub-cycle (ERC), adding the equivalent intercooling sub-cycle (EIC), and adding the equivalent reheating sub-cycle (ERH) to/from the host cycle. Based on this, a novel combined cycle sCO₂ PTES system is proposed, where partial intercooling measure is adopted to prevent extra heat input. The split equivalent sub-cycles are used to analyze the independent contributions of key parameters for each modification measure in the combined PTES system. The recompression, partial intercooling, and reheating measures achieve round-trip efficiency gains of 15.20, 0.82, and 1.46 percentage points, respectively. The novel combined system achieves a round-trip efficiency of 69.35%, representing a 17.12 percentage-point improvement over the basic host cycle. The conventional exergy analysis method is employed to verify the accuracy of the cycle splitting method results. Compared with exergy analysis method focusing on component-level energy losses, the cycle splitting method can simply and intuitively quantify the independent contributions of each modification measure, providing clear theoretical guidance for sCO₂ PTES system design and efficiency improvement.