Sonnedix Japan announced it broke ground in October on its first battery energy storage system, set to retrofit its 30MWAC/38.6MWDC solar power plant in Oita Prefecture. The project will add 125MWh of storage capacity to the site, signalling a significant evolution in the company’s Japanese asset portfolio.
An industrial partnership focused on technology integration
The battery energy storage system (BESS) will utilise Megapack units supplied by Tesla. Toshiba Energy Systems & Solutions will oversee engineering, procurement, and construction (EPC), while Osaka Gas will be responsible for market trading optimisation. The BESS is scheduled to enter commercial operation in November 2026.
The solar plant, owned by the special purpose entity Oita Solar LLC, has been operational since March 2020 under a feed-in-tariff (FIT) agreement of 40 JPY/kWh, valid until February 2040. As part of the retrofit, the facility will transition to the feed-in-premium (FIP) scheme, a mechanism offering market-based remuneration with additional premiums.
Structured financing and network constraint context
The project underwent a refinancing process aimed at optimising its capital structure. Sonnedix secured a non-recourse credit facility totalling JPY21.4bn ($142mn) from MUFG Bank. The funding is intended to support both the financial viability of the site and the capital requirements for battery system integration.
Among Sonnedix Japan’s 25 operational solar assets, the Oita plant is the only one located in the Kyushu transmission zone, known for its high curtailment risks. This marks the company’s second battery storage facility under construction globally, following an 18MW/72MWh hybrid generation-plus-storage project underway in Italy.
