german
AutoGrid

Opportunities and risks of grid-independence in Germany

Project state
Started
Schematic representation of the studies in the framework of the project AutGrid | © Fraunhofer ISE

The energy supply system in Germany is changing, from a previously centrally dominated towards a more decentralised structure. In the course of the transition and with the increase in distributed generation systems such as PV systems and wind turbines, there are regional efforts, particularly in rural communities, municipalities and counties, to meet the demand for energy through self-generated renewable electricity.

Grafik der Energiesystemanalyse. Ausgehend von einem Basisszenario soll ein Simulationsmodell in ein Optimierungsmodell einen möglichst effizienten Netzausbau ermöglichen. Dieses Szenario kann mit einer integralen Opimierung verglichen werden.
Schematic depiction of the energy system analysis; the self-sufficiency scenarios are compared with a cost-minimising basic scenario | ©Fraunhofer ISE

These objectives are usually stipulated in local climate protection programmes. These can include expansion targets for renewable energy technologies, efficiency improvements, sustainable transport restructuring, CO2 emission reduction targets or other measures necessary for implementation. As a consequence, an accelerated expansion of renewable energy sources is taking place within the "100ee" (100 renewable energy) regions, resulting in an increased use of the decentralised potential.

This raises the question as to how these self-sufficiency efforts will impact on the energy system. Will the potential for renewable energy be maximised or could this even incur additional costs, for example through an increased need to expand the grid as a result of individual regions leaving the grid? This also depends, in particular, on the degree of energy self-sufficiency which is striven for. Previous efforts at a decentralised level have mostly focussed on achieving balanced electricity independence. What would happen, however, if the regions go a step further and start striving towards full power self-sufficiency? To what extent would such systems deviate from the most cost-effective system? What impact would the size of a self-sufficient region have on the overall system costs? And what are the opportunities and risks that arise from electricity self-sufficiency?

Depiction of the reduced German transport grid (159 nodes, 262 transmission lines); the illustrated grid provides the basis for the load flow and grid expansion calculations (depending on the scenario, the basis will be supplemented with planned lines from the grid development plan 2014, 2nd draft (NEP)) | ©Fraunhofer ISE

Based on the existing energy supply system in Germany, this research project is concerned with optimising the expansion of the electricity grid that is integral to the transformation of the energy supply system towards increasingly decentralised renewable electricity generation. For this purpose, an interdisciplinary research team is depicting Germany's electricity system to a high regional resolution in an optimisation model used for the grid expansion planning, and is analysing and evaluating the grid expansion and operation in interaction with factors that are also outside the technical system.

The power and energy self-sufficiency of grid regions in Germany will be analysed and assessed with regard to their system-relevant effects. In particular, the focus is on analysing the grid expansion, operation and supply security, as well as the effects on the overall electrical system and the quantification of costs. To support the project, a cross-impact balance analysis is being conducted to generate various consistent scenarios and qualitatively assess the plausibility for developing different forms of self-sufficiency and their interaction, also with social and ecological factors. This research project is aiming to quantify – by means of optimisation – the grid expansion and operation in conjunction with the technology mix of renewables, conventional energy sources and storage systems. In addition, the effects of power and energy self-sufficiency are being evaluated comprehensively on different regional scales in regards to the German energy supply system, security of supply and system costs. Summing up, the risks and opportunities involved in increasing the number of power-independent regions during the course of the energy transition in Germany will be determined for the entire system, and in particular for the transmission grid.

So far it has been possible to determine during the course of the project as to where the regions are localised at the present time, which goals are they pursuing and until when, and how these are being promoted. The results are published in Senkpiel et al: "Concept of evaluating chances and risks of grid autarky", EEM Porto 2016.

The linear optimisation model has been developed in such a way that the costs for the technology development (renewable energy, conventional generation, storage and grids) and their operation are minimised. The created database not only enables the regions to be mapped up to a resolution at the county level in the model but also to be aggregated flexibly in order to reduce the solution problem. In addition to the optimisation model, an algorithm has been developed which can reduce the transmission grid according to selected model regions (see Figure 4). The influence of this network reduction is currently being assessed quantitatively. Initial test runs for Baden-Württemberg have already been successfully calculated.

In addition, a separate load flow solver and grid expansion optimiser has been developed so that the results of the overall optimisation model can be compared with the separate grid planning. Work is currently being carried out to integrate different grid expansion possibilities and different depths of detail into the model in order to identify the best relationship between the accuracy and duration of the optimisation problem.

In addition, expert interviews have been conducted with representatives from renewable energy regions in order to identify the factors that have an impact on the regional objectives. These were discussed in an expert workshop and arranged in a sequence in order to determine the most important factors.

Depiction of the reduced German transport grid using the developed reduction algorithm | ©Fraunhofer ISE

The project is being carried out by the  Fraunhofer Institut für Solare Energiesysteme (ISE) and the  Zentrum für interdisziplinäre Risikoforschung (ZIRIUS) at the University of Stuttgart. Fraunhofer ISE is responsible for energy system analyses, grid flow calculations and grid expansion optimisations. ZIRIUS are following the CIB approach to determine plausible grid-independent scenarios that will be used in the optimisation measures developed at Fraunhofer ISE.

Project duration

05/2015 – 04/2018

Contact

Charlotte Senkpiel
Project coordinator
Fraunhofer-Institut für Solare Energiesysteme (ISE)
Heidenhofstr. 2
79110 Freiburg im Breisgau
Germany
+49 761 4588-5078
+49 761 4588-9078

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