Vorwerk, Daniela

The coupling of the three energy grids electric power, gas and heat, via sector coupling devices such as fuel cells or electrolyzers enables the increase of the share of renewable energies in consumption beyond the electricity sector. Correct modeling is crucial for the physically correct description of the behavior of fuel cells and effects on the energy grids, especially regarding transients caused by switching processes or during plant faults. In the paper presented here, the proton exchange membrane fuel cell is introduced as a component for its use in the “Extended Node Method”. It allows a suitable integration into the grid-based energy systems electricity, gas and heat based on node equations. For this purpose, the fuel cell is described as a multi-energy component. Also, for gas and heating grids, electrical analogies are used. The associated systems of equations are constructed in such a way that they can be applied to different topologies. Exemplary operating points are shown for a sample configuration. The results are partly compared with other calculation methods and software and discussed.

In a future renewable energy system, electrolyzer, as coupling elements between power and gas systems, convert renewable electricity into storable hydrogen, which can be used in further consumption sectors. The general scope of this investigation is a controlled proton exchange membrane electrolyzer at a low voltage grid. For this, the proton exchange membrane electrolyzer as well as the power electronics for grid connection are developed as components for the "Extended Node Method" based on electrical equivalent circuit diagrams. It is shown how these components are especially defined for this method, how their topology affects the node definitions and how the AC/DC and DC/DC transitions are realized. As a study case, a sample model of a 40 kW stack is considered. The setpoints for electrolyzer current as well as reactive power are adjusted and transient calculations are carried out. The results are compared with models in Simulink/Simscape and show general agreement.

In the context of a multi-energy-grid, the consideration of various energy carriers on the same level is beneficial. This work shows the development of heating network components in electric analogies for their definition and usage in the node-based Extended Node Method. The method enables an efficient iteration algorithm for finding of stable steady-state operation points, even for extended network topologies. Three different thermal equivalent circuit diagrams, a ladder-, Pi- and T-model, describing the thermal behavior of heating pipelines are presented. They simultaneously fulfill the thermodynamic energy balance as well as the electrical equivalent circuit diagram correlations. The influence of the spatial resolution is tested using a single-line model. Moreover, a steady state calculation is also performed for an 18-node sample network. All results are compared with Simulink/Simscape and show satisfactory agreements.

In order to make our energy grid future-proof an integrated grid planning approach for the energy sectors electric power, gas and heat is being pursued focusing on the industrial metropolis Hamburg. To this end, it is necessary to develop a coordinated scenario framework that is accepted by and useful for all participating grid operators. This work contributes using a concept called “Neutral Cell Areas” offering a regionalization approach by describing spatially limited regions. The framework is developed from scratch, meaning that existing energy grids are deliberately disregarded to ensure that “Neutral Cell Areas” provide indeed a neutral point of view and leaving degrees of freedom of the exact power supply open (cf. greenfield approach). Several approaches like city districts, statistical areas, land use plan areas and grid patterns as well as hexagons as evenly shaped cell areas are presented. The “Neutral Cell Areas” are characterized by Key Values based on various indicators and combinations thereof. The indicators hail from a variety of fields. They enable comparability and interaction between the cell areas as well as facilitate assumptions about specific future predictions in the context of energy grid planning.

To meet ever-stricter climate targets and achieve the eventual decarbonization of the energy supply of German industrial metropolises, the focus is on gradually phasing out nuclear power, then coal and gas combined with the increased use of renewable energy sources and employing hydrogen as a clean energy carrier. While complete electrification of the energy supply of households and the transportation sector may be the goal, a transitional phase is necessary as such massive as well as rapid expansion of the electrical distribution grid is infeasible. Additionally, German industries have expressed their plans to use hydrogen as their primary strategy in meeting carbon targets. This poses challenges to the existing electrical, gas, and heating distribution grids. It becomes necessary to integrate the planning and developing procedures for these grids to maximize efficiencies and guarantee security of supply during the transition. The aim of this paper is thus to highlight those challenges and present novel concepts for the integrated planning of the three grids as one multi-energy grid.

Optimized integration of fuel cells into grids or on-board power supplies is necessary to facilitate replacement of conventional energy producers by a reliable and plannable power generation technology. Due to the interdependency between fuel cell current and voltage, integration of fuel cells requires a power conditioning system, which increases integration weight and cost. For this reason, integration of electric field modifier electrodes into the setup of proton exchange membrane fuel cells is a new approach to control the output voltage in order to minimize the subsequent power conditioning system. This approach considers the physics of proton transport through the electrolyte membrane and could offer a lever to control the ohmic resistance. In this paper, a fuel cell model is implemented in MATLAB and extended by electric field modifier electrodes, allowing control of the ohmic resistance through an externally applied voltage. The concept of boosting and attenuating fuel cell voltage is presented along with different setups to enable this behavior. Furthermore, an electrical equivalent circuit for electrically controllable fuel cells is developed and implemented in MATLAB/Simulink. A method to parameterize the developed MATLAB and Simulink models by first experimental results is presented.