Green Growth has announced a strategic partnership with K2 Holdings to convert solar power plants under the Feed-in Tariff (FIT) scheme to the Feed-in Premium (FIP) mechanism, with the installation of battery storage systems. The first pilot project involves a rooftop solar plant with a capacity of 490kWAC/578kWDC located in Tagawa, Fukuoka Prefecture.
The site, currently operating under a FIT contract at JPY36 per kWh valid until April 2035, will be equipped with a 1.5MWh battery storage system. The project is scheduled to begin operations under the FIP regime in fiscal year 2026. Green Growth is responsible for project management and will act as the aggregator, while K2 Holdings’ subsidiary Kyushu Kiden will provide engineering, procurement and construction for the storage system.
Extension planned to other assets
The two companies plan to extend this type of conversion to other rooftop solar plants owned by K2 Energy, as well as third-party assets. K2 currently owns four other high-voltage rooftop solar plants in Fukuoka Prefecture, totalling 3.2MWAC/3.8MWDC. These installations are all located within the area of Kyushu’s transmission system operator (TSO), known for production constraints, and benefit from initial FIT tariffs ranging from JPY36 to JPY40 per kWh.
This partnership comes as asset owners under legacy FIT regimes seek to mitigate the impact of production curtailment on profitability by integrating storage solutions and accessing more flexible tariff schemes.
Development of new FIP projects
In parallel with conversions, Green Growth and K2 Holdings will jointly develop new rooftop solar plants under the FIP scheme. The projects will leverage the industrial and commercial network of K2 Energy and Kyushu Kiden, including factories, warehouses and other buildings available for photovoltaic installations.
This development aligns with a new scheme effective since October 2025, allowing rooftop plant owners to benefit from higher FIP tariffs in the early years of the contract. The measure aims to support faster return on investment for newly installed or converted assets.
Since July 2025, Green Growth has supported several asset owners in this transition. Following an initial contract with Kagashiya for a 1.5MWAC/1.8MWDC plant, the company has also signed agreements with Nankyu for two installations in Kagoshima Prefecture.
