Thermodynamic analysis and evaluation of a novel composition adjustable Carnot battery under variable operating scenarios

Abstract

Discontinuity of production resulting in supply imbalance is the main problem hindering renewable energy development. Carnot battery (CB) is a recently emerged large-scale power storage technology to solve the supply imbalance of renewable energy power generation. Improving the component performance of CB under variable operating conditions is crucial to guarantee the life-span performance of the CB. In the present study, a composition-adjustable CB is proposed. The application and optimization of the zeotropic mixture improved the heat match in the heat transfer component. The composition adjustment is conducted to relieve the excess operating parameter deviation of mechanical components. Thermodynamic analysis and optimization models are formulated, and a genetic algorithm is applied to solve the models. Case studies under several operating scenarios are conducted to verify the superiority of the proposed composition-adjustable CB over a conventional CB and a zeotropic CB. Results show that under a benchmark operating scenario, compared with conventional CB, the round-trip efficiency and exergy efficiency of CB using zeotropic working fluid are improved by 22.40% and 16.78%. Considering the limitation of the mechanical components under variable operating scenarios, composition-adjustable CB has the largest operating range. Three CBs demonstrate different operating strategies to maintain the flexible and efficient operation of the mechanical components, among which the operating performance of composition-adjustable CB is the best. During the discharging process, the exergy efficiency of the expander in composition-adjustable CB is up to 18.19% and 0.94% higher than that of zeotropic CB and conventional CB, respectively. Overall, compared with conventional CB and zeotropic CB under variable operating scenarios, the average round-trip efficiency of composition-adjustable CB is improved by 56.34 % and 26.98 %, respectively; the average exergy efficiency of composition-adjustable CB is improved by 51.26 % and 25.21 %, respectively.