One of the main priorities of the modern energy development is the transition from modern hydrocarbon energy to energy using renewable energy sources (RES) (wind, solar, etc). The relevance of this step is explained by such factors as saving organic fuels (coal, gas, fuel oil, etc.) and reducing environmentally harmful emissions into the atmosphere, which lead to climate change on Earth. However, at the same time, the influence of RES on the controllability of the electric power systems (EPS) operation modes and the reliability of their functioning remain completely unexplored. An excessive increase of wind power plants (WPP) and solar power plants (SPP) the share in the structure of the EPS generating capacities begins to manifest itself in a sharp decrease of operation reliability. The scientific novelty of the article consists in the development of an economic and mathematical model to study the influence of WPPs and SPPs on the reliability and stability of the power plant operation in emergency situations arising from faults in the backbone networks, as well as in the study of the specific share of the installed power of WPPs and SPPs in the total installed power of EPS. The implementation of the proposed model makes it possible to economically justify the strategy and scale of renewable energy implementation in EPS.