The Energy System Ontology: A conceptual framework for energy transition research

The energy transition is characterized by the increasing complexity and interdependence of technological, economic, policy, environmental, and social dimensions. While a large and rapidly growing body of literature addresses these aspects, differences in terminology, conceptual scope, and analytical focus hinder the integration of findings across studies and the alignment of diverse modeling approaches. This paper presents the Energy System Ontology (ESO), a comprehensive conceptual framework developed to bridge these gaps and support the structured organization and synthesis of knowledge related to energy systems and energy transition. ESO is constructed through a systematic, multidisciplinary review of the energy transition literature combined with ontology engineering principles to ensure robustness. The framework identifies and formalizes core relationships across energy technologies, markets, policies, and environmental contexts, enabling a consistent representation of the energy nexus while preserving vital disciplinary distinctions. The resulting ontology provides a domain-wide reference that supports comparative analysis, semantic interoperability across heterogeneous energy-system representations, and the systematic exploration of transition pathways. The current evaluation provides requirements-based verification and application-oriented evidence rather than independent external validation. By offering an explicit and extensible structure, ESO contributes to greater transparency and provides a robust framework for the analysis of socio-technical systems within the energy transition.