Optimal Capacity of Renewable Energy and Methanation System in a Remote Island Model Considering Frequency Fluctuation

Abstract

This paper optimizes renewable energy and methanation system capacities while considering frequency fluctuations for the remote island of Tsushima in Nagasaki Prefecture, Japan. On remote islands, power systems are small-scale, and introducing renewable energy sources, whose output varies with weather conditions, can cause significant frequency fluctuations. Therefore, when introducing variable renewable energy sources, it is necessary to select appropriate countermeasures; however, specific investigations and quantitative evaluations are lacking. Moreover, when optimizing facility capacity, numerous constraints must be considered, such as the annual supply-demand balance, which increases the problem’s scale, resulting in excessive computation time and making it impossible to solve. This paper employs hierarchical clustering to group annual data into a manageable dataset and solves the optimization problem. By incorporating frequency fluctuations as a constraint, we propose a method for determining the renewable energy and methanation capacities that minimize both CO2 emissions and facility costs. The proposed approach demonstrates a reduction of over 10% in total costs and more than 15% in CO2 emissions compared to conventional methods. Furthermore, the proposed method helps identify internal combustion power generators that can be decommissioned, supporting the transition towards cleaner energy sources in remote island power systems.

Keywords: renewable energy, methanation, frequency fluctuation, optimal equipment planning, remote island