Flexibility-oriented robust optimization planning for electro-hydrogen energy storage in high-renewable grids

The large-scale integration of renewable energy sources poses significant challenges to grid stability due to inherent intermittency and volatility. This paper presents a novel robust optimization framework for planning electro-hydrogen energy storage systems (EHESS) that differs from traditional capacity planning by explicitly incorporating flexibility margin indices. We develop a comprehensive electro-hydrogen coupling model that captures the coordinated operational characteristics of battery storage (short-term regulation) and hydrogen systems (long-term shifting). Unlike existing works that treat flexibility qualitatively, we introduce a quantified flexibility margin index to measure the supply-demand gap of ramping capabilities. We formulate a two-layer robust optimization model: the upper layer minimizes investment costs, while the lower layer minimizes operational and flexibility penalty costs under worst-case scenarios. Wasserstein distance-based uncertainty sets are employed to handle the distributional uncertainty of renewable output. Case simulations on a modified IEEE 33-node system validate that the proposed method effectively determines the optimal configuration, reducing total costs by 10.6% compared to baselines by mitigating high-cost flexibility violations.