Green Growth and K2 Partner on Rooftop Solar FIT-to-FIP Conversions with Battery Storage, Plan New Projects
November 20, 2025
Green Growth and K2 Holdings have announced a partnership focused on renewable energy and battery storage solutions. The collaboration will start with a retrofit and scheme conversion of a rooftop solar power plant in Tagawa City, Fukuoka Prefecture.
The 490 kWAC / 578 kWDC facility, currently operating under a feed-in-tariff (FIT) contract at 36 yen per kWh valid until April 2035, will be upgraded with a 1.5 MWh battery energy storage system (BESS) and converted to the feed-in-premium (FIP) scheme. Green Growth will act as the project aggregator and manage the retrofit and conversion, while K2 Holdings subsidiary Kyushu Kiden will handle engineering, procurement, and construction (EPC) for the battery system.
The upgraded plant is expected to begin operations under the FIP scheme in fiscal year 2026. Following this project, the companies plan to retrofit other K2 Energy solar plants and offer support to third-party asset owners seeking similar upgrades. METI data indicates K2 Holdings owns four additional high-voltage rooftop solar power plants totaling 3.2 MWAC / 3.8 MWDC, all located in Fukuoka Prefecture within the curtailment-prone Kyushu TSO area, operating under early FIT contracts at 36 or 40 yen per kWh depending on certification year.
In addition, Green Growth and K2 Holdings aim to jointly develop new rooftop solar projects under the FIP scheme, leveraging K2 Energy and Kyushu Kiden’s networks of factories, warehouses, and commercial facilities. The scheme, introduced in October 2025, allows rooftop asset owners to operate under higher FIT/FIP prices during the early stages of their contracts, enabling faster return on investment.
Green Growth began providing FIT-to-FIP conversions and BESS retrofits in July 2025 with a 1.5 MWAC / 1.8 MWDC solar project owned by Kagashiya. Since then, the company has also partnered with Nankyu on two facilities in Kagoshima Prefecture.
K2 Energy joins a growing number of Kyushu solar plant owners seeking to mitigate the impact of curtailment on returns and maximize asset value through battery retrofits.
