Abstract
Energy Storage Systems (ESSs) are an important source of flexibility in power systems with high penetration of Renewable Energy Sources (RESs). When installed at transmission-distribution interface nodes, shared ESSs can support both Transmission System Operators (TSOs) and Distribution System Operators (DSOs), but their long-term planning remains challenging because investment decisions depend on coordinated operation under uncertainty and battery degradation over time. This paper proposes a degradation-aware planning framework for shared battery ESSs in coordinated TSO-DSO operation. The problem is formulated as a bi-level stochastic optimization model in which the upper level determines siting, sizing, and staged investment decisions under investment-cost uncertainty, while the lower level evaluates these decisions through coordinated system operation. To preserve tractability, the framework combines Benders' decomposition for long-term planning with an Alternating Direction Method of Multipliers (ADMM)-based decentralized coordination mechanism for short-term operation. The framework is evaluated on integrated IEEE transmission-distribution test systems over a 15-year planning horizon. Relative to uncoordinated operation, coordinated operation with shared ESSs reduces operating costs by up to 18.25% and RES curtailment by up to 92.16% in the later years of the planning horizon, while eliminating voltage violations. The results also show that degradation materially affects ESS valuation and that temporal discretization can influence siting and sizing decisions.

Abstract
Blending green hydrogen into gas networks is subject to strict quality regulation. As Europe diversifies its Liquefied Natural Gas supply, existing literature often ignores the extreme chemical variability of these sources by assuming a static composition. This study proposes a nonlinear steady-state optimization model, strictly adhering to European standards, to maximize hydrogen injection across eight real-world LNG profiles. Results reveal severe sensitivity to the carrier gas: lean gas (Trinidad and Tobago, USA) restricts maximum hydrogen integration to 8.89% and 11.40% by volume due to insufficient heavy hydrocarbons. Conversely, carbon-rich gas (Nigeria) allows up to 20.10%, although inert gases degrade this capacity. Ultimately, this 20.10% maximum blend yields only a 6.77% emission reduction. The imported chemical profile dictates absolute limits, proving that static universal hydrogen quotas are thermodynamically unachievable year-round without continuous dynamic quality tracking.