In this work, a mixed integer linear mathematical model for the energy storage devices dispatch in an interconnected power system is proposed. This model was implemented in a computer program written in C++ that outputs a linear program in LP format to be solved in any commercial or free solver. A case study of Brazil's Northeastern Power System is presented to evaluate the impact of the use of energy storage devices on the operational cost of a system with renewable variable energy sources, such as wind and solar, as well as hydroelectricity. Alternative scenarios were considered, where the amount of wind energy was changed in order to assess the impact of wind energy growth on system performance. Simulation results show that up to 15% O&M cost reduction is attainable in this scenario. (C) 2017 Elsevier Ltd. All rights reserved.