This paper, outlines the results of various scenarios for optimizing Poland's future energy system up to 2050. The objective of the study was to demonstrate through the use of models how the level of binding targets for the share of renewable energy (RES) in final energy consumption would impact the evolution of the Polish energy sector. The differences in the compared scenarios consist of the level of RES (renewable energy sources) targets while assuming the same ETS (emissions trading system) CO2 reduction pathways. These scenarios of differing RES targets are compared with other ones where the level of RES obligatory for 2020 has not been increased in the 2020-2050 period. The lack of increasing RES targets applies no preference for any particular technology, and the resulting energy mix is cost-optimal. Potential variations in the energy mix are shown, addressing the fuel and technological structure of electricity production. The analysis presents the costs of electricity generation in the examined scenarios and the level of capital expenditures for the development of new capacities. It examines how RES technologies may develop in Poland with and without the national RES targets after 2020, and the consequences for coal as well as the development of clean coal technologies. (C) 2015 Elsevier Ltd. All rights reserved.