Optimal Design of Electrolysis-based Hydrogen Hubs: Impact of Different Hydrogen Demand Profile Assumptions on System Flexibility and Investment Portfolios

Green hydrogen (H2) produced from renewable energy sources (RES) through electrolysis offers a promising solution to decarbonize hard-to-abate sectors, paving the way for H2 hubs. The agility of electrolyzers, especially proton-exchange membrane (PEM) technology, can be leveraged to provide flexibility to future integrated electricity and H2 systems. More flexibility can be unlocked by optimizing the designs of H2 hubs, which generally consist of electrolyzers, H2 storage tanks, H2 liquefiers, and battery energy storage systems (BESSs). This paper introduces a generic optimization framework for finding the least-cost designs of H2 hubs that also minimizes system operating costs under arbitrary H2 demand profiles. The proposed electrolyzer model incorporates a variable efficiency to avoid overestimating the power consumption and the true size of electrolyzers. In RES-rich countries like Australia, envisaged H2 export demand may constitute a significant source of demand flexibility. The proposed framework is therefore demonstrated on a case study involving the Australian National Electricity Market (NEM) under a future large-scale green H2 export scenario, assessing the impact of three different H2 export profile assumptions on H2 hub investment costs, system operating costs, and system flexibility. These profiles include: (a) a realistic one based on historical liquefied natural gas (LNG) ship schedules and a pilot H2 export project, (b) an inflexible constant demand across the year, and (c) a flexible monthly target without intraday and interday restrictions. Numerical analysis demonstrates that the optimal H2 hub designs obtained under the more realistic H2 export profile assumptions enjoy the lowest system operating costs and the highest flexibility, the latter of which is evidenced by a substantial increase in availability of reserves.