Japan is storing electricity in the hulls of decommissioned ships — turning retired vessels into grid-scale floating 500 megawatt-hours battery banks anchored in Tokyo Bay.

 

Japan is storing electricity in the hulls of decommissioned ships — turning retired vessels into grid-scale floating battery banks anchored in Tokyo Bay.

Japan has one of the largest commercial shipbuilding and shipping industries in the world — and consequently one of the largest flows of ships retiring from service each year. A decommissioned bulk carrier or container ship represents thousands of tonnes of structural steel, intact electrical systems, and existing marine infrastructure — and in a country where land for industrial facilities is scarce and expensive, it also represents a floating platform that can be moored offshore without land acquisition, planning permission, or community opposition from onshore residents.

Mitsui O.S.K. Lines and Mitsubishi Heavy Industries have jointly developed the MV StorageShip concept — a decommissioned 50,000-tonne bulk carrier with its cargo holds converted to house containerised lithium-ion battery modules, its onboard electrical systems upgraded for grid-scale charging and discharging, and its mooring adapted for permanent anchorage with submarine power cables connecting to the Tokyo metropolitan area distribution network. Each converted vessel holds approximately 500 megawatt-hours of battery capacity — equivalent to one of the largest shore-based grid storage installations in Japan.

Three vessels are in conversion as of 2024, with a combined capacity of 1,500 megawatt-hours targeting commissioning in Tokyo Bay by 2026. The conversion cost is approximately 60% of an equivalent shore-based facility, and the floating location eliminates land cost entirely — a significant factor in Tokyo Bay where industrial land commands premiums that make conventional battery storage economically marginal. Japan has always been innovative about using its marine territory to compensate for land scarcity. Floating battery storage is the latest chapter in a very long maritime tradition.

Source: Mitsui O.S.K. Lines & Mitsubishi Heavy Industries — MV StorageShip Floating Battery Programme Report 2024

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