Optimization of a Tidal–Wind–Solar System to Enhance Supply–Demand Balancing and Security: A Case Study of the Goto Islands, Japan

Due to the expected increase in electric power demand in the coming decades and the economic and environmental issues caused by power generation from the combustion of hydrocarbon fuels, the integration of renewable energy into the grids of remote islands has attracted attention. Among all renewable sources, tidal stream energy shows potential to contribute positively in areas with strong tidal currents due to the predictability and semi-diurnal periodicity of the resource, which makes it compatible with short-term energy storage. However, its performance in areas with lower available power density has not yet been addressed. In this paper, energy systems for the Goto Islands, Japan which combine solar, offshore wind, and tidal energy are evaluated based on whole-system performance indicators such as the annual energy shortage and surplus and the battery load factor. Without energy storage, an energy mix of 31% solar, 47% offshore wind, and 22% tidal energy provides the lowest values for annual energy shortage (29.26% of total power demand) and surplus (29.26%). When batteries are incorporated into the system, tidal stream energy is the main contributor to reducing these two parameters, with values up to 23.58% and 19.60%, respectively, for the solar and tidal scenario with 30 MW of installed storage capacity. These results show the advantages of tidal stream energy exploitation in stand-alone energy systems, even with relatively low capacity factors (0.33).