The article is concerned with systematizing the concept of «renewable energy sources» and their classification, exploration of the world energy reserves to assess prospects for modernization of the energy sector in the context of sustainable development. Sustainable development leads to introducing the renewable energy sources as an alternative to the resource-intensive obsolete technology. This significantly improves the quality of life of population and reduces of degradation of the natural environment. The article systematizes the renewable energy components, proposes various options for classification in accordance with both the physical and the economic bases. The research results provide a basis for a consistent and thorough statistical estimation of prospects for development of the energy sector in general, as well as the renewable sources of energy in particular, in the context of sustainable development. Also a comparison of the energy reserves with the general energy of the solar radiation has been provided.