This paper proposes and evaluates an optimized system of tidal turbines as a renewable energy generating unit in New Zealand. A comprehensive simulation model has been set up, using several available commercial software packages to test the performance, capacity and efficiency of the proposed system. Available tidal records have been used to find four regions that are suitable for tidal energy generation and conduct simulation model runs at one of them, Foveaux, to provide the electricity for the isolated area of Stewart Island. Generation of electricity with tidal turbines depends on the water currents and cut-in speed of the tidal turbines. In other words, to reach maximum efficiency from tidal power, the first step is to analyse the water currents of the site where turbine will be located and then estimate the generated power from that turbine. To do it, it is necessary to find the range of water currents and the tidal directions with demonstrating tidal rose and also find how to get maximum power by choosing a proper tidal turbine. Based on tidal flows of the Foveaux straight, two tidal turbines (Schottel 54 kW and 70 kW) with different cut-in speeds are selected. The results indicate that choosing Schottel 54 kW with 0.2 m/s less cut-in speed in comparison to Schottel 70 kW can generate 4.7 times more power.