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The network storage capability of district heating systems and gas systems can provide a considerable flexibility in integrated energy systems, increasing the use of volatile renewable energy generation. But the stronger the single energy systems are linked the more complex their operation becomes due to their increased interactions. To ensure a secure and reliable system operation while using the full potential of integrated energy systems, these interactions must be analyzed. Existing power flow calculation methods, however, assume a steady-state behavior of all energy systems in the integrated energy system, neglecting the network storage capability. Hence, this paper presents a joined quasi-steady-state power flow calculation method for integrated energy systems. Our method introduces the dynamic behavior of the district heating system arising from the temperature propagation and the dynamic behavior of the gas system due to the gas compressibility and propagation of hydrogen. In a comparison with a steady-state power flow calculation we show the considerable effect of the network storage on the operation of an integrated energy system. As our method enhances existing steady-state power flow calculation methods, it can be easily used for the same use cases but allowing the full potential of integrated energy systems to be investigated.INDEX TERMS Quasi-steady-state, integrated energy system, power flow calculation, Newton-Raphson method, gradient method.

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To optimally design integrated energy systems a widely used approach is the Energy Hub. The conversion, storage and transfer of different energy vectors is represented by a coupling matrix. Yet, the coupling matrix restricts the configuration of the Energy Hub and the constraints, that can be included. This paper proposes a MILP based optimization framework, which allows a high variability and adaptability and is based on energy flows. The functionality of the developed framework is tested on four use cases depicting different system sizes and Energy Hub configurations. It is shown that the framework is able to simplify the design process of an Energy Hub.

The building sector is responsible for about 7 % of overall greenhouse gas emissions in the US. Cutting the emissions by electrifying heating and cooling supply through heat pumps (HPs) leads to an increase in electricity demand and potential overloading of lines and transformers in electricity distribution systems. Although many studies investigate the maximum potential for HPs in existing distribution systems in Europe, they neglect a potential relieving effect of combining HPs with rooftop photovoltaic (PV) systems as well as the consequence of coupling the electricity and gas system at distribution level. Hence, we investigate the effect of HPs and rooftop PV systems in a representative distribution system in Northeast US and the potential of coupling electricity and gas distribution systems. We show that generally no overloading in average US electric distribution systems occurs even under high realistic HP and PV adoption rates. Moreover, our results show that combining HPs and rooftop PV reduces the impact on the distribution system throughout the year with the greatest reduction in spring and fall. In contrast, the potential for injecting hydrogen on distribution level is technically very limited and not economic. Thus, electrolyzers at distribution level are not able to reduce congestion in the electricity system.