The energy grid is currently undergoing a historic change of state from the traditional structure where a utility owns the generation, transmission and distribution services into an integrated smart grid in a monopolistic market which introduce consumers as active players in managing and controlling the power. This evolution adds more complexity to the energy scene as it requires an unprecedented partnership of different fields and technologies to establish successful integration of components with a bidirectional transfer of information and energy. The Smart Grid Interoperability Panel (SGIP) was incorporated in late 2009 to oversee the efforts in defining a set of standards and interoperability layers to ensure a secure integration and operation of various elements of the system. This paper discusses the smart grid concept as a system-of-systems (SoS); analyzes the interoperability framework models developed by SGIP and the European Union Smart Grid Cooperation Group respectively; presents the stakeholders as domains and zones associated with the interoperability layers; and illustrates other architectural concepts such as fault-tolerance, software integration platform and design characteristics of smart grid as an elegant system.