Modern energy systems combine ICT with electrical and thermal infrastructure. They also interact with other systems like markets and are subject to many regulations. Existing simulation tools are not capable to cover such systems in all of their aspects, hence new languages, methods and tools are necessary. A combination of universal modeling languages and established, domain-specific tools (like grid simulators and telecommunication simulators) is necessary. This leads to hybrid energy systems models, where for instance a multi-agent framework and an electric grid simulator are combined to investigate smart electric vehicle charging algorithms. Also the potential size of such systems poses a challenge for modeling and simulation. And implementing these future cyber-physical systems is another substantial challenge. The designed algorithms need to be compact, computationally inexpensive, potentially self-organizing and intrinsically stable if applied to real energy systems.