Enhanced coupling of low-grade heat sources with Carnot battery through optimal temperature matching

The integration of an external waste heat source into the Carnot battery system holds the theoretical potential to surpass 100% in efficiency. However, achieving significant efficiency requires waste heat sources with relatively high temperatures, limiting the application of Carnot batteries. To address challenge, this paper proposes a novel Carnot battery based on non-phase-change waste heat sources from the perspective of heat transfer temperature matching among waste heat sources, heat pumps, and Organic Rankine Cycles (ORC). The proposal is developed through theoretical modeling and comprehensive energy/exergy analysis, emphasizing the optimization of thermal coupling relationships to enhance system efficiency. On the charging side, Vapor Compression Heat Pump (VCHP) with a small temperature difference for heat absorption is selected to align with the variable temperature characteristics of the waste heat source. To address the narrow temperature range of the VCHP, this study proposes the integration of a Supercritical Extraction Steam Compression Regeneration ORC (SRORC). This cycle markedly elevates the evaporator’s inlet temperature through the compression regeneration process, enabling narrow temperature range heat absorption on the cycle side and enhancing heat exchange matching with the heat storage process. The new system excels in achieving superior temperature matching across each process. Notably, at a waste heat source temperature of 86.4 °C, the power-to-power efficiency of the Carnot battery reaches an optimal 100%, significantly reducing the required heat source temperature. Exergy analysis reveals that the exergy loss in the evaporator on the power generation side is substantially diminished, with the new system’s exergy efficiency reaching 43.41%, surpassing that of a conventional Carnot battery by 13.40%.