Overview of Demonstration Project Aimed at Harnessing Renewable Energy on Remote Islands

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Okinawa Prefecture is located at the southernmost tip of the Japanese archipelago, comprising a vast expanse of sea spanning 1,000 kilometers east to west and 400 kilometers north to south, consisting of approximately 160 islands of various sizes. Among these, there are 37 inhabited islands where 1.46 million people reside.

Okinawa Electric Power Company (OEPC) is a vertically integrated electric utility company engaged in all generation, transmissions, and distribution. The OEPC supplies electricity to all inhabited islands in Okinawa Prefecture. The prefecture has 11 independent power systems, and due to the small scale of the island grids other than the main island of Okinawa, diesel power generation serves as the primary source.

The OEPC has been forward-thinking in integrating solar and wind from the perspectives of climate change countermeasures and fuel cost reduction on the islands. However, on small grids, the widespread integration of intermittent renewable resources such as solar and wind power can pose technical challenges regarding energy balance, subsequently affecting grid frequency. To cope with this, the company has focused on developing battery control technology to stabilize grid frequency by mitigating solar and wind power fluctuations.

Moreover, as renewable energy increases, diesel units face operational challenges, with decreased output levels reducing negative headroom and necessitating corrective action through suppressing renewable energy output. As a substitute for diesel units, while maintaining grid support capability, OEPC has developed a motor-driven generator powered by renewable-charged batteries, known as an MG set. The MG set comprises generators, AC induction motors, and batteries, addressing the negative headroom issue. Additionally, the MG set allows for battery charging during periods of excess electric supply, particularly when operating in regenerative charging mode. In 2020, on Hateruma Island, all diesel generators were provisionally stopped, and this grid, alongside wind power, MG sets, and batteries, achieved a 100% renewable energy supply for around ten continuous days.

This webinar showcases two demonstration projects: 1) a Grid stabilization project with advanced battery controls on Miyako Island and 2) a 100% renewable energy supply project using the MG set on Hateruma Island.