A transition plan for conventionally structured generation portfolios dominantly based on coal fired plants has been offered through four models. The models are primarily focused on elevated penetration of facilities based on intermittent renewable sources and CO2 emission reduction by at least 20% compared to the initial state, accordingly addressing balancing output power variation problems and social aspects of the considered society. These models are: Flexible generation portfolio model, which can provide balancing power by itself; Open system model that provides balancing power at the balancing market; Hybrid system model with hybrid plants based on wind, hydro and solar energy, having the ability to store, convert and use this energy for balancing purposes; Mix model that includes options from the previous three. The models are elaborated on an arbitrary conventional power system and simulated applying International Atomic Energy Agency's software tools. Considering chosen technical, economic, environmental and social parameters, conducted analyses resulted with the Mix model as the most suitable option for a sustainable development of the treated power system type. Due to similarities between generation portfolio structures in developing countries, the model can provide guidelines for sustainable planning and contribute to a low carbon future. (C) 2017 Elsevier Ltd. All rights reserved.