Green Growth, a Tokyo-based renewable energy developer, has started commercial operation of a battery energy storage system (BESS) co-located with Kagashiya’s high-voltage solar plant in Hita, Oita prefecture.
The project is the first to reach commercial operation under Green Growth’s end-to-end model for battery co-location, which the company first announced in July 2025. The project had previously been targeted for operation in January 2026.
Green Growth said commercial operation began after permitting, grid-connection procedures, and trial operations were completed.
Under the current arrangement, Kagashiya retains ownership of the solar asset while Green Growth manages business planning, project implementation, and ongoing operation and aggregation, according to Green Growth. The company said this separation of ownership and management allows generators without in-house energy expertise to capture more value from their assets.
Green Growth said the project responds to Japan’s shift from its feed-in tariff (FIT) scheme toward feed-in premium (FIP), citing growing curtailment and increased wholesale market volatility as challenges facing renewable energy operators, particularly in Kyushu Electric Power’s service area.
The company said Japan’s curtailment-priority rules are expected to be revised from fiscal 2026 to give FIP generation priority over FIT generation, a change it said would strengthen the case for FIT-to-FIP conversion paired with battery storage.
The battery system has an output of 1,500 kW and a capacity of 4,515 kWh, according to Green Growth. The company said the system will charge during low-price, curtailment-prone daytime hours and discharge during higher-price periods, using an aggregation platform operated by Shizen Connect.
Green Growth said it will act as aggregator for the project, handling generation and price forecasting, trading on the Japan Electric Power Exchange (JEPX) wholesale market, and plan submissions to Japan’s Organization for Cross-regional Coordination of Transmission Operators (OCCTO).
Green Growth said it plans to expand its FIT-to-FIP conversion and battery co-location business, particularly in regions with frequent curtailment, and has additional projects in preparation.
The project comes as Japan winds down its feed-in tariff support for larger solar installations. The government has said feed-in premium auctions for large-scale solar will end after fiscal 2026, while continuing FIT support for smaller systems. As first-generation FIT projects near the end of their guaranteed rates, some solar owners have turned to refinancing and other strategies to adapt to a post-FIT market in Japan.
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