A comprehensive review of green hydrogen hubs: Technologies, services, challenges, and future perspectives

The global energy system is undergoing a profound transition from fossil fuels to renewable energy sources (RESs). Within this context, green hydrogen has emerged as a promising energy carrier for enhancing large-scale renewable utilization and mitigating wind and solar curtailment. Driven by technological progress, environmental imperatives, and evolving economic conditions, green hydrogen technologies are increasingly recognized as a foundational pillar of future low-carbon energy systems. Building upon these motivations, this paper provides a comprehensive review of Green Hydrogen Hubs (GHHs) by emphasizing critical technologies and service functionalities spanning from the component level to the system level of GHHs. The core principles and conversion mechanisms of GHHs are elucidated to establish the technical foundations, followed by an in-depth examination of the diverse grid support services and auxiliary services delivered through intrinsic functional mechanisms and global demonstration projects. Major technical challenges and recent advances in GHH integration are further synthesized in light of current pilot projects and evolving regulatory landscapes. Finally, the prospects of GHHs in strengthening system flexibility and accelerating the low-carbon energy transition are discussed, underscoring the necessity of continued technological innovation and supportive policy frameworks to achieve cost-competitive and sustainable deployment.