Climate change mitigation and the EU2020 strategy foster energy efficiency in Europe’s future manufacturing landscape. These challenges make high demands to SMEs as well to MNCs. The paper gives insight to an approach on Eco-factories based on the EU-funded FP7 project EMC2. Eco-factories will enable the quantum leap in integrating environmental issues in brownfield and greenfield factory planning and factory operation. The paper focuses on the identification, structuring and definition of requirements for Eco-factory simulation approaches. Requirements for developing a simulation environment for integrating energy and material flows for detailed analysis but also wide user spectrum is presented. The paper shows that demands are twofold requesting integrated, modular and detailed simulation solutions as well as emphasize on user-friendliness and low complexity.