Tidal power generation is viewed as a leading green energy approach. It is expected that the use of tidal power generation will become a primary method for local-supply-and-local-consumption energy, similar to photovoltaics and wind power. Because the current produced by tides changes with a definite periodicity, it is straightforward to forecast the production of electricity by tidal power generation. However, to cover the supply-and-demand differences in electric power, an accumulation-of-electricity system or a controllable electric power source is required. Hence, in this paper, the cost and electric power quality of an interconnection system constructed with a solid oxide type fuel cell (SOFC), photovoltaics (PV), and tidal power generators are investigated. By accessing the high-speed tidal current in the lake inlets of the Saroma Lake in Hokkaido, the demand of electric power and heat in a surrounding area are provided by the proposed system. As a result of the estimations of numerical analyses, the facility planning, costs, and electric power quality of the proposed system are identified, and the amount of time required to recover the cost versus the present energy cost is expected to be approximately ten years.