This paper presents latest results and outcomes of a research project about the decentralized feed-in of solar thermal energy into district heating networks. While solar heat exemplarily stands for any other heat source (as waste heat) the focus is on smaller distributed solar thermal heating plants rather than large central systems. The idea is to use the district-heating system as thermal source and sink to ensure the supply of the local heat consumers as well as the transmission of solar heat to other customers. This approach is supposed to minimize investment costs and increase the solar share, thus substituting fossil fuels. Analyses and investigations were done based on computational DH system simulations. A special version of the TRNSYS-simulation program was applied to calculate transient operation of a 3^rd generation DH network (following IEA-DHC Annex X classification, see [1]). Several feed-in substations have been integrated into the model. Heat consumption and load profiles of the consumers have been estimated using the Typical-Day Method. This approach allows to adapt any measured data (daily load profiles) to a specific weather data set and to scale heat load profiles of the same type according to a given peak load or daily heat consumption. The simulation offers the opportunity to have a look to any internal state of the system as local pressure, fluid temperature or mass flow. With this information component stress can be analyzed very well. The paper presents findings of the recently finnished project "Dezentrale Einspeisung in Nah- und Fernwärmesysteme unter besonderer Berücksichtigung der Solarthermie"¹ and the ongoing research project "Kostenreduktionspotential beim Ausbau der Solarisierung von Fernwärmenetzen durch Standardisierung"². It is based on the German publications [2] and [3].