  Composed of a large variety of technologies and applications with
unprecedented complexity, the smart grid, as a cyber-physical energy system,
needs careful investigation of the interactions between the various domains
involved, especially the coupling between the power and information systems. In
this paper, two modern ways of modeling and simulating complex cyber-physical
energy systems are considered: Co-simulation and Power-Hardware-in-the-Loop
experiments. An analysis of these two approaches shows that a complementary and
joint setup with realistic behaviors of hardware equipment under a variety of
complex environments, co-simulated by several simulators from different
domains, create a complete and high performance environment to achieve a
holistic approach for smart grid validation and roll out. In the scope of
coupling these two techniques, major technical challenges are identified and
advanced solutions are outlined.
