The forthcoming smart-grid is expected to provide advanced energy services more efficiently and eco-friendly with an integrated network of various information such as a smart meter and social networks. As an information model of expressing such an integrated network, a knowledge graph (KG) represents a formal and common specification of concepts and relations in a specific domain. It is essential to leverage KGs for the interoperability, reusability, and scalability of smart-grid applications. However, existing KGs have limitations in accommodating detailed descriptions of energy services. In this paper, we propose an energy knowledge graph, which provides the semantic integration of various energy services. The proposed model also provides the detailed description of a micro-grid community. To verify the proposed model, we present and discuss its use-cases based on energy service scenarios.