This research paper analyses legal aspects of the application of modern technologies for practical use in the energy sector in the form of a Smart City. The issue of Smart Environment in the light of renewable energy sources was classified as the main research axis. The main goal of the paper, from the methodological point of view, involves decoding the impact and importance of renewable energy sources for the full implementation of the Smart City concept. First, the article presents introductory remarks regarding the general outline of technical, technological and civilization progress. Then, the essence of the Smart City concept and its pillars have been presented. This permitted the authors to move on to identify the most important legal aspects of the issue discussed in this paper and to search for potential problems and suggest possible solutions. The paper ends with a concise summary containing the authors’ observations on the subject and de lege ferenda postulates.