Recently, energy systems have experienced a change of paradigm, from a large-scale centr alized approach to the in-situ exploitation of renewabl e sources. Special atte ntion has been paid to microgrids, a particular case of distributed generation where consumer nodes include generation and can be either grid- connected or isolated. This work aims to develop a general model to determine the optimal sizing of an energy system under fixed conditions and to analyze the eff ect of considering different cycle patterns on the solution. The mi xed integer linear programming (MILP) formulation proposes allows determining the best combination of available technologi es that satisfies the demand of a given set of scenarios at minimum total cost. The model has been implemented using AIMMS and applied to a case study consisting of a five-member Mediterranean house. The results obtained reveal the need to select the most convenient time cycles for defining the scenarios of the sizing model