Modeling and simulation are essential for the development and assessment of new technologies for complex cyber-physical systems, both in academia and industry. One particular instance of such complex systems are novel energy systems. They comprise a variety of heterogeneous physical domains (electricity, thermal, gas, etc.), modeled as time continuous dynamic systems, and time discrete communication and control systems. Tools and solutions based on co-simulation concepts for such cyber-physical energy systems (CPES) have been developed in recent years. This paper focuses on the need for real-time hardware integration into CPES simulation, identified from recently conducted research projects. From those projects – presented as use cases – relevant actors are identified and their interaction and data exchange is discussed. Resulting requirements are presented for the CPES simulation and the hardware to be integrated. The handling of heterogeneous laboratory hardware is discussed and a simplification in the form of a hardware abstraction layer is proposed.