Green efficiency deviation in ports: an empirical analysis of scale-greenness trade-offs in Zhejiang, China

As global ports expand, balancing scale with green development grows crucial. While studies on conventional (CPE) and green port efficiency (GPE) is extensive, research on their efficiency deviation (ED) remains limited. Utilizing data from the Zhejiang Province Port Energy Reporting System for 2019–2024, this study evaluated CPE, GPE and the ED in Zhejiang ports using the Super-SBM model, and examines influencing factors through a multilevel regression model. Results indicate that cargo throughput influences ED through mediating and moderating mechanisms, with no direct effect. Cargo throughput’s impact on ED is realized through CPE; it indirectly increases ED by boosting CPE, and port location moderates the relationship between cargo throughput and ED. Large hub ports achieve higher CPE through technological collaboration, regulation-driven initiatives, and efficiency reinvestment, thereby accelerating GPE improvement. These findings offer valuable insights for port managers seeking to balance scale expansion with low-carbon transformation.