Osaka Gas and Sonnedix to build BESS at 38.7MW solar PV project in Japan

November 6, 2025
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A Sonnedix project.
Sonnedix Japan has brought online just under 500MW of solar PV in the country. Image: Sonnedix.

Utility Osaka Gas and developer Sonnedix are installing a battery energy storage system (BESS) at the latter’s 38.7MW Oita solar project, which Osaka Gas described as the largest battery storage facility to be co-located with renewable energy generation in Japan so far.

The two companies announced on 4 November that their jointly operated business is constructing a 30MW/125MWh BESS at the Sonnedix solar PV plant in Kyushu, southern Japan.

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Construction began in October 2024, and the partners are scheduled to bring it into commercial operation in November 2026.

Sonnedix said the BESS will be paired directly with the solar PV plant and enable the optimisation of solar generation as “dispatchable, market-responsive power”.

The developer carried out a JPY21.4 billion (US$139.3 million) refinancing of the Oita solar plant, arranged by bank MUFG, which has been a consistent investor in energy storage projects overseas and more recently in Japan.   

Sonnedix Japan has brought online just under 500MW of solar PV in the country, along with 601.5MW of plants in its management. The Oita project is its only one in Kyushu to date, while the BESS retrofit to it marks the developer’s first BESS project in Japan.

US technology provider Tesla will provide its Tesla Megapack BESS solution, likely manufactured at its ‘Megafactory’ in Shanghai, China, from which Tesla’s energy storage division serves markets outside the US.

Engineering, procurement and construction (EPC) duties will be carried out by Japan’s Toshiba Energy Systems & Solutions Corporation. Osaka Gas will carry out route-to-market (RTM) trading and optimisation of the battery asset.

Read the full version of this story on our sister site, Energy-Storage.news.

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