In recent years the oceanic energy has received special attention mainly due to technological improvement, resulting in increasingly competitive costs. In Brazil, ocean energy appears as a strategic alternative and in the upcoming decades can make a significant contribution to the country's energy matrix. The greatest amplitudes and tidal velocities are found in the north and northeast of the country, making this energy resource an option to be considered in small isolated systems. However, there are few studies that present viable solutions for the use of this extractable potential. The availability of kinetic energy from tidal currents is directly influenced by the lunar cycle, making it necessary, in the case of isolated systems, a storage system to guarantee continuity in the power supply. In this paper is discussed the problem of sizing isolated system based on tidal currents. Considering the generating source variability during the lunar cycle, this paper aims to support the establishment of adequate criteria for sizing of a tidal current micro-plant, considering system installation costs and O&M. Sensitivity analysis studies are also carried out to verify the impact of system cost and capacity factor.