  Evaluating new technological developments for energy systems is becoming more
and more complex. The overall application environment is a continuously growing
and interconnected cyber-physical system so that analytical assessment is
practically impossible to realize. Consequently, new solutions must be
evaluated in simulation studies. Due to the interdisciplinarity of the
simulation scenarios, various heterogeneous tools must be connected. This
approach is known as co-simulation. During the last years, different approaches
have been developed or adapted for applications in energy systems. In this
paper, two co-simulation approaches are compared that follow generic, versatile
concepts. The tool mosaik, which has been explicitly developed for the purpose
of co-simulation in complex energy systems, is compared to the High Level
Architecture (HLA), which possesses a domain-independent scope but is often
employed in the energy domain. The comparison is twofold, considering the
tools' conceptual architectures as well as results from the simulation of
representative test cases. It suggests that mosaik may be the better choice for
entry-level, prototypical co-simulation while HLA is more suited for complex
and extensive studies.
