Design of coupled systems for the energy transition: Green Hydrogen Storage, Compression and Conversion

Hydrogen is regarded as the most promising clean energy vectors in the Power-to-Gas-to-Power (PtoGtoP) concept. However, this strategy faces several challenges, like intermittent inflows of energy, high costs, and rather low energy efficiency due to the losses during conversion and storage. In the frame of the project HyReflexS (Hydrogen-based emergency power supply with integrated control power plant through flexible sector coupling and metal hydride storage), funded by the German Federal Ministry of Economics and Climate Action, and the project Digi-HyPro (Digitalized hydrogen process chain for the energy transition), funded by dtec.bw – Digitalization and Technology Research Center of the Bundeswehr (German Armed Forces), a design of systems for the energy chain transition is proposed. In the case of HyReflexS, the aim of the project is to develop a demonstrator for an emergency power supply (10 kW for 8 h) and peak shaving with a dynamic behavior of +/-1 kW/min as a model system for a depot for electric buses with grid-supporting behavior. For this purpose, a metal hydride storage system able to store more than 10 kg of hydrogen is under development to be coupled with an electrolyzer (EL) and a fuel cell (FC). The subcomponents EL and FC should be integrated on several levels within both electrical and gas grids. On the electrical side, various converters are required to ensure grid-parallel as well as island operations (emergency power operation). The components are electrically coupled at a DC voltage level and controlled in terms of power or voltage via several DC/DC converter topologies. The grid connection is carried out via an inverter, which is controlled and executed depending on the operating mode, grid following, grid supporting or grid forming. To study the dynamic behavior and to establish a higher-level control logic for multiple operating scenarios, such as peak shaving, emergency power operation, and the overall heat integration, the system is simulatively developed and investigated. Subsequently, a demonstrator will be manufactured as a prototype to realize the functionality of the entire system. The Digi-HyPro project aims to develop a decentralized and scalable system for clean energy demands spreading across different locations. A SET-Unit (Smart-Energy-Transform-Unit) is designed to optimize the connections between renewable sources and the current power and gas grid demands. Applying this concept, hydrogen generated by an EL can be stored compactly and safely in a metal hydride storage system or fed into the natural gas grid. Inversely, hydrogen can be taken from the grid, separated from the natural gas and stored in the metal hydride system. Once the metal hydride storage is filled with hydrogen, the FC can convert the energy into electricity to support the power grid or charge electric vehicles. A specially developed metal hydride compressor can also provide hydrogen at high pressure for the mobility sector. In both projects, component and system level simulations are performed to design, develop and optimize the individual components and overall integrated system performance. These digital models are based on critical data from experiments and are validated using prototype setups. This multidisciplinary investigation involves the optimization of systems for the transition of the whole energy sector to the use of renewables with experimental demonstrations in kWel ranges. Final scalability studies in the industrially relevant MWel range can pave the way to an efficiently networked green energy system