The use of renewable energy sources is an urgent task in the territories with decentralized energy supply. The introduction of new digital technologies allows one to analyze the possibility and expediency of implementing energy technologies in specific territorial conditions. Currently, one of the main trends of digital energy transformation is Digital Twins, which in some cases are considered synonymous with the digitalization of the energy sector. Whereas the technology of Digital Twins is actively developing, there is no single standard for the development of software tools. The article presents the previous stages of research on the design of architecture and components of the digital twin and the corresponding approach based on the application of ontological modeling. The presented study introduces aspects of designing software tools that are part of the Digital Twin architecture. The agent-service approach is used in the design of components of the Digital Twin architecture. The design of software tools is based on examples of tasks relevant to isolated power systems (solar power plant and wind farm) as an energy system with a relatively small set of parameters. The experience gained will be further extended to other energy systems.