Technical and economic evaluation of a novel liquid CO2 energy storage-based combined cooling, heating, and power system characterized by direct refrigeration with phase change

Abstract

Energy storage systems combining cooling, heating, and power have higher flexibility and overall energy efficiency than standalone systems. However, achieving a large cooling-to-power ratio in direct-refrigeration systems without a phase change and in indirect refrigeration systems driven by heat is difficult, limiting the energy output of the system. Therefore, this study proposes a novel combined cooling, heating, and power system based on liquid CO2 energy storage. Using direct refrigeration with a phase change, the system has a large cooling capacity and can achieve a wide range of cooling-to-power ratios through the mass flow regulation of the refrigeration branch. Energy, exergy, and economic analyses were conducted based on models of the proposed system. Adjusting the split ratio of the system splitter S1 can realize a wide range of changes in the cooling- and heating-to-power ratios of the system and can flexibly meet the demand for cooling, heating, and power generation. The system with the best overall performance was obtained by optimizing the levelized cost of storage as the objective function, where the system’s power efficiency, exergy efficiency, energy efficiency, levelized cost of storage, and energy storage density were 0.56 %, 18.15 %, 319.76 %, 0.10 $/kW·h, and 19.17 kW·h/m3, respectively. The proposed system in the standalone power-storage mode has technical and economic performance advantages, as compared to other systems reported in the literature.