System integration of large-scale green hydrogen production: Conceptualization, challenges, and opportunities

Power-to-X (PtX) and X-to-Power (XtP) conversions are increasingly recognized as vital pathways for decarbonizing hard-to-abate sectors. Hydrogen exemplifies these processes, with power-to-hydrogen achieved through renewable-powered electrolysis and hydrogen-to-power enabling emission-free fuel cell-based reconversion. Integrating large-scale green hydrogen production with the electric grid, however, presents both challenges and opportunities. This review clarifies definitional ambiguities of the topic and systematically identifies eight major challenges, such as grid integration, system optimization, power/energy market operation, spatial deployment, early-stage technology, stack degradation, and cost competitiveness. It also highlights eight key opportunities, ranging from ancillary services (frequency regulation, voltage support, congestion relief) to seasonal storage and cogeneration, all contributing to improved grid flexibility and system resilience. Representative studies are analyzed to evaluate recent advances in grid-connected hybrid renewable-hydrogen systems, converter topologies, AI/ML-based renewable power generation and hydrogen demand forecasting, fault detection, and operational control strategies. A comparative perspective with batteries and pumped hydro underscores hydrogen’s superior scalability and long-duration storage potential, while also emphasizing flexibility-degradation trade-offs that affect technical and economic performance. Building on these insights, the review develops a structured research roadmap, emphasizing advanced electrolyzer modeling, PHIL-based validation, degradation-aware operation, and control. By bridging technical and techno-economic perspectives, this review provides a critical synthesis and strategic guidance for researchers, system operators, industry, and policymakers to accelerate the effective integration of green hydrogen into future low-carbon energy systems.