In future energy scenarios with a high share of renewable energies within the electricity system, power-to-heat technologies could play a crucial role for achieving the climate goals in the heating sector. District heating systems can integrate volatile wind and photovoltaic energy sources and resolve congestions within the electricity grid, leading to curtailment of renewable electricity generation. This paper presents a design approach for setting up system-beneficial power-to-heat-based district energy systems. Within the scope of the project QUARREE100 an existing district in the provincial town Heide in Northern Germany is examined. A linear investment and unit commitment optimization model is applied. By considering local dynamic emission factors for grid-sourced electricity, which contain information on local wind energy curtailment as well as the emission intensity of the overall electricity generation, a renewable and system-beneficial design can be derived. With this method, the minimal rated power and capacity of energy converter and storage units can be determined to achieve emission reductions with respect to minimum costs. The approach of using different methods for the consideration of the emissions of grid-sourced electricity is analyzed based on different scenarios. By using a dynamic emission factor for grid-sourced electricity, lower emissions with fewer costs can be achieved. It is shown that a dynamic assessment leads to different design decisions and far-reaching deviations in the unit commitment. The results clearly show that a constant emission factor is no longer an option for grid-sourced electricity in urban energy system models.

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Existing districts pose a particular challenge within the transition into a renewable energy system. Especially the heat supply requires innovative concepts. In many districts, renewable energy resources are limited, and district heat supply relies on energy imports from the upstream energy infrastructures, especially the gas and electricity grid. These upstream infrastructures are in an ongoing process of transformation into a renewable energy system with uncertain speed and depth. To design future-proof heat supply concepts, this work presents a scenario-based design approach considering different scenario paths for the upstream energy infrastructures as well as the development of the existing building stock. Therefore, a mixed-integer linear programming model is set up to optimize the energy converter and storage capacities of a generic district heat supply with respect to costs and emission. Additionally, three different refurbishment scenarios are considered for the existing buildings stock. From the results of the different scenarios, future-proof heat supply concepts are derived. The analysis shows that heat-pump capacities in combination with a thermal storage is of great importance for a future carbon-neutral heat supply. A combined heat and power unit helps to reduce emissions in short term. However, only if the gas network has a high share of renewable energies, this technology will compete with electricity based heating via heat-pumps. The results show that electrolysis is at least in short term not a viable option for designing a cost-efficient carbon-neutral district heat supply.