Sumitomo Electric Industries has delivered its redox flow (RF) battery to a grid-connected energy storage plant built by Shin-Demitsu Co., Ltd. in Nagasu, Tamana County, Kumamoto Prefecture. The plant was completed in October 2026 and will enter full commercial operation on 1 November 2026.
System specifications
The installed RF battery has a capacity of 8,000 kWh and an output of 2,000 kW, equivalent to four hours of discharge at rated power. Sumitomo Electric says that is roughly the daily electricity consumption of about 900 ordinary households.
The project is the first in which Sumitomo Electric has supplied an RF battery to a scheme supported by the Ministry of Economy, Trade and Industry / Agency for Natural Resources and Energy's grid-scale storage subsidy — formally the fiscal 2024 programme supporting the introduction of grid-connected storage batteries and water electrolysers, for which the Environmental Symbiosis Initiative is the public applicant body.
Safety and longevity drove the technology choice
According to Sumitomo Electric, the RF battery was selected not only because of its extremely low fire risk but also because of its long service life and the very small capacity degradation it shows in long-term operation.
The electrolyte is non-flammable and components use flame-retardant materials, so the system does not fall under the Fire Service Act's designation of hazardous materials. That means no hazardous-materials installation permit is required and no hazardous-materials handler needs to be permanently on site — a meaningful operational simplification for a grid asset.
Sumitomo Electric notes that the electrolyte does not degrade with charge and discharge, and that performance loss tied to cycle count is extremely small. The electrolyte is reusable, with a track record of reuse, while 99% of equipment materials can be recycled with appropriate separation under a Ministry of the Environment industrial waste wide-area certification.
Responding to Kyushu curtailment
The backdrop is renewable curtailment. Maximising renewable energy use is essential to achieving carbon neutrality by 2050, but in regions with heavy solar build-out such as Kyushu, output is being curtailed during hours when generation exceeds demand. Shin-Demitsu built the Kumamoto plant to help put that surplus energy to work and to stabilise the power system.
Sumitomo Electric says it aims to contribute to supply-demand balancing, more effective use of renewables and greenhouse gas reduction through wider deployment of its RF batteries.
This article was assisted by AI analysis. Please refer to the original source for official information.