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The transition from fossil fuels to green renewable resources presents a key challenge: most renewables are intermittent and unpredictable in their nature. Energy storage has the potential to meet this challenge and enables large scale implementation of renewables. In this paper we investigated the dynamic performance of a specific Adiabatic Compressed Air Energy Storage (A-CAES) plant with packed bed thermal energy storage (TES). We developed for the first time a plant model that blends together algebraic and differential sub-models detailing the transient features of the thermal storage, the cavern, and the compression/expansion stages. The model allows us to link the performance of the components, in particular those of the thermal storage system, with the performance of the whole A-CAES plant. Our results indicate that an A-CAES efficiency in the range 60–70% is achievable when the TES system operates with a storage efficiency above 90%. Moreover, we show how the TES dynamic behaviour induces off-design conditions in the other components of the A-CAES plant. Such device-to-plant link of performance is crucial: only through integration of TES model in the whole A-CAES model is possible to assess the benefits and added value of thermal energy storage. To the authors’ knowledge the present study is the first of this kind for an A-CAES plant. [ABSTRACT FROM AUTHOR]

• Proposition of heat-up efficiency to evaluate start-up procedures energetically. • Thermal parameters for electrolysis systems with up to 1 MW el are presented. • Efficiency when only using heating is always lower than partial-load heat-up. • Introduction of a new dimensionless heat-up number for electrolyzers. • Dimensionless heat-up number enables general estimation of time constants. Dynamically-operated water electrolyzers enable the production of green hydrogen for cross-sector applications while simultaneously stabilizing power grids. In this study, the start-up phase of polymer electrolyte membrane (PEM) water electrolyzers is investigated in the context of intermittent renewable energy sources. During the start-up of the electrolysis system, the temperature increases, which directly influences hydrogen production efficiency. Experiments on a 100 kW el electrolyzer, combined with simulations of electrolyzers with up to 1 MW el , were used to analyze the start-up phase and assess its implications for operators and system designers. It is shown that part-load start-up at intermediate cell voltages of 1.80 V yields the highest efficiencies of 74.0 % LHV compared to heat-up using resistive electrical heating elements, which reaches maximum efficiencies of 60.9 % LHV. The results further indicate that large-scale electrolyzers with electrical heaters may serve as flexible sinks in electrical grids for durations of up to 15 min. [ABSTRACT FROM AUTHOR]