Development plans in the energy sector of European countries assume modifications almost in all fields of energy systems. Global use of renewable energy sources is expected to achieve the primary purpose of energy sector development plan — reduction of greenhouse gas emissions into the atmosphere. Towards that goal, national energy development plans intend to implement a huge number of renewable energy sources and to reduce the capacity of, or shut down, fossil fuel power plants. However, the results of the latter action are not well researched. For timely reaction to avoid any accidents in the future, there is a need for comprehensive assessment of the impact of the above power plants on the power system in a long-term perspective. This article focuses on the reasonableness of conventional power plants in the energy systems of the Baltic countries in 2050.