The decarbonisation of the energy system is a major objective of the European Union. The industry's end energy demand is around 25% and therefore represents a logical starting point. Numerous studies prove the economic feasibility and environmental advantages of using industrial excess heat. Up to now, the use of industrial high-temperature excess heat has been predominantly considered. In addition, there is also great potential for industrial low-temperature excess heat and industrial roof surfaces are available for PV systems. These industrial energy potentials can now be used in industry-city energy networks. The temporal incongruity of the urban energy demand and the industrial energy potentials does not permit a complete utilisation. For this reason, more flexibility is needed in industry-city energy networks. Until now, flexibility has focused almost exclusively on the electricity sector. This thesis therefore proposes methods to flexibilize industrial excess heat and PV electricity supply and uses a case study to evaluate the technical, environmental and economic feasibility. The flexibility demand is determined with the help of the discrete Fourier transformation. Based on previous modelling approaches, flexibility options will be integrated in the industry-city energy network. Flexibility options include thermal and electrical storage units, city clusters and load shifting in the industry. In contrast to previous load shifting approaches, with the primary aim of low electricity procurement costs or a reduction of required balancing energy, the industrial processes and thus the supply of industrial excess heat will be postponed in such a way that there will be a better match with urban energy demand. Based on the case study and the assumed framework conditions, the following conclusions could be drawn: The use of industrial energy potentials is reasonable from a technical and ecological point of view, as it can save fossil fuels and thus CO2 emissions. An economic evaluation provides a differentiated picture. From an overall economic point of view, the use of industrial excess heat is reasonable due to positive net present values. In contrast, the use of industrial PV electricity cannot be economically integrated under the assumed framework conditions as no subsidies are included in the considerations. Thermal and electrical storage facilities, city clusters and load shifting in industry were regarded as flexibility options. From an overall system perspective, thermal storage can be integrated in an economically viable way, whereby from a microeconomic point of view a distinction has to be made between different storage designs. Thus, for example, the integration of a long-term thermal storage still leads to an economic presentation, but the net present value is reduced compared to the scenario without flexibility options. The creation of city clusters is the most economical flexibility option. By integrating a second city, the demand is expanded so that the entire industrial energy potential can be fed into the grid and purchased. Load shifting in industry leads to minimal improvements of the technical and ecological indicators, whereby costs and feasibility in practice are difficult to determine. The integration of industrial energy into the urban energy system does not compete with the expansion of renewable energies. The combined use of industrial excess heat and biomass as well as the combination of industrial PV electricity and wind energy is particularly advantageous. When implementing the recommendations in practice, there should be close coordination with all involved stakeholders. In this way, the results can be verified.