Preliminary results are presented from an assessment of phased tidal stream energy development in Naru Strait, Nagasaki Prefecture, Japan. Results from a validated 3D hydrodynamic model show that flow speeds exceed 3 m/s in depths ranging between 30 - 60 m within the strait. Tidal stream turbine energy yield is estimated across the strait using mid-depth
ambient flow results from the model. Array scale blockage effects are limited by capping the practical array install capacity below levels shown to reduce turbine power generation in literature. Energy yield estimates are presented for a 45 MW array, built out in four phases. For each phase, rotor swept area and generator rated power are designed to maintain high capacity factor levels. Results show that the 45 MW array in Naru Strait generates an estimated yield of 119 GWh/year. This is equivalent to the average electricity demand of approximately 40,000 households in Japan.