ResiliEntEE - Resilience of integrated energy networks with a high share of renewable energies
Already today one can observe that complexity of regulation, especially for regulation power and redispatch, is increasing with a rising share of renewable energies in the electricity generation. The reason for this is the sensitivity of the electric system especially towards deviations between production and consumption. This is because there are nearly no buffering effects within the electric network: At the occurrence of small differences between the delivered and the extracted power, the frequency changes which needs to stay within a narrow range to ensure net stability. Therefore, major stability problems are to be expected especially in grids with a high share of renewable energies. One solution is the coupling of the electricity sector with the heat and gas sector. Both sectors are able to provide buffering effects and therefore react considerably slower towards disruptions than the electricity sector. Especially the existing gas infrastructure offers, due to its pipelines and storages, great potential to support the electricity sector. The coupling of the three sectors is complex: each sector consists of different consumers, producers and storages while all of them are coupled by various sector coupling technologies (Fig. 1). This complexity demands an interdisciplinary approach involving especially thermodynamic and electrical engineering experts which will be pursued in this project.
Fig.1: Presentation of the three sectors (black) with producers (blue), conversion technologies (red), storages (green) and consumers (yellow) (PtG: Power to Gas, GT: Gas Turbine, CCGT: Combined Cycle Gas Turbine, Cogen. CCGT: Cogenerated Combined Cycle Gas Turbine, CHP: Combined Heat and Power, FC: Fuel Cells, PtH: Power to Heat
There are several solutions how to integrate renewable energies in the existing energy system. Since the system stability and therefore the supply security are the most important criteria, the main goal is to find economic solutions, which increase the resilience of the system, rather than an only economically driven integration. The term resilience is to be understand as the system's ability to maintain its function after a local disruption. To examine the resilience of the considered energy systems, different scenarios during which the integrated energy system's reaction to different disruptions is analyzed, are investigated. Disruptions can be for example the breakdown of one or more network components or extreme weather conditions. Thus, a detection technique for the reliability of energy supply systems which allows the evaluation of various changes in the system, can be developed.

In the project ResiliEntEE, the TransiEnt Library, which was developed in the preceding project TransiEnt.EE, will be refined. This library uses the programming language Modelica® and is open-source, entirely accessible, expandable and already in use for several research projects. It is suited to perform dynamic simulations of integrated energy systems and to analyze the results according to CO2 emissions and costs. Until recently the focus was on integrating renewable energies. Now the library will be expanded with resilience considerations. Thereby a special focus is put on the electrical grid and its connection to other elements as well as the further development of particular components. Moreover, a suitable regulation for the whole system will be designed which includes the operational planning of consumers and storages as well as the provision of standard benefit, measures of redispatch and reactions to disruptions.

Because of the complexity of the systems, high computing times can occur depending on the geographical scope and the matter of interest. To keep processing times low, methods of model reduction will be evaluated and used. This implies in general and depending on the considered question the neglect of variables which have little influence to the target value.

In TransiEnt.EE the energy system of Hamburg was considered. In ResiliEntEE the system will be gradually enlarged and validated with available data. Thereby the final objective is to model the region of northern Germany. The shares of renewable energy in the considered energy systems and their sectors electricity, heat and gas will be defined differently (60 %, 80 %, 100 %). Whereby the non-renewable share will be provided by gas. The structure of the energy system depends on the considered scenario: There are a decentralized- and a centralized-orientated scenario which investigate many small or rather few big producers and consumers as well as their impact on the resilience of the system. In the scenario "Network Development Plan 2050" the planned grid structure of the network development plans is examined and reasonable adaptions are given to increase resilience.

Overall following questions are to be answered:
- How can the security of supply be guaranteed even with high shares of renewable energies?
- How do disruptions in one sector affect other sectors?
- How can the operation of an integrated energy system be optimized with regard to economic efficiency, environmental compatibility and reliability?
The project is accompanied by a research council which consists of members of different players in the energy system. The project is supported by the Federal Ministry for Economic Affairs and Energy (funding code: 03ET4048, project duration: 01.09.2017 - 28.02.2021).
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