Thermo-economic investigation on a novel zeotropic Carnot battery using cascaded phase change material for thermal energy storage

Carnot battery (CB) has emerged as a promising electricity storage technology designed to address the imbalance of renewable energy generation. The application of phase change material (PCM) in CB has been widely investigated to enhance storage performance. However, non-uniform heat flux phenomenon in latent heat storage and poor thermal matching between PCM and CB working fluid impose significant performance limitations. In this study, a novel zeotropic CB using cascaded PCMs as the storage medium (CPCB) is proposed to improve the heat storage/release capacity and heat matching performance. A dynamic mathematical model of the latent heat storage device and a thermo-economic model of CPCB are established. The dynamic behavior of cascaded PCMs and their impact on CPCB's performance are investigated. A case study is conducted to verify the superiority of CPCB over a traditional latent heat storage CB (PCB) and reveal the factors affecting the thermo-economic performance of CPCB. Results show that, compared to PCB, CPCB can achieve a maximum increase of 7.27% in COP and 11.07% in electricity generation. The round-trip efficiency of CPCB is 6.07% higher, and its levelized cost of storage is 11.52% lower than those of PCB. The peak-to-valley duration is found to be the most critical factor affecting the thermo-economic performance of CPCB. The result of this study is conducive to designing a CB using cascaded PCMs with higher comprehensive performance.