Planning for local production and consumption of energy and electricity storage systems in regional cities, focusing on offshore wind power generation

In this study, an energy localization system in a local city focusing on large-capacity offshore wind turbines was proposed and the impact of expensive energy storage devices is clarified. The economics of the proposed system was clarified determining the payback period using the discounted cash flow (DCF) method. The proposed system comprises a power generation unit with offshore wind power and other renewable energy sources, an energy storage unit with storage batteries or hydrogen storage systems, a transmission unit, a distribution unit, and an energy demand unit. A power transmission network (Southern Hokkaido offshore wind power transmission network: SHOT) is being developed to supply electricity to Hakodate City (240,000 inhabitants, 677.9 km²) from the currently planned Southern Hokkaido offshore wind power generation (1720 MW) and Toi onshore wind power generation (160 MW). The payback periods for SHOT with a hydrogen storage system and redox flow batteries were 7–8 and 10–12 years, respectively. This was because hydrogen storage systems can be combined with small-capacity water electrolyzers, inexpensive large-capacity hydrogen tanks, and small-capacity fuel cells at a lower cost, whereas the cost of storage batteries is based on their storage capacity. Economic feasibility study showed that income tax relief could effectively speed up the payback period for SHOT investments. As the periodic replacement of expensive equipment accounted for 13 %–25 % of the total project expenditure, technological innovations to extend the service life of the targeted equipment can be effective in reducing the payback period.