An energy management system to minimize the operation cost of a microgrid is presented in this work. The microgrid is composed of the technologies more used as renewable energies and storage systems, as well as active consumers which demand depends on price. The proposed model is based on linear programming with the operating cost as the objective function and the operating limits as constraints. The model has two phases. The first phase does the optimal dispatch of generating units in function of the forecasting demand and the offers made by generators. The second phase minimizes the differences between the planning values obtained in the first phase and the real data, because there are differences as consequence of the uncertainties of renewable energies and the consumers’ behaviour.