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Special Feature
Newsletter "SEI WORLD" Vol. 461

Large-scale storage battery system Redox flow battery

Principle and features of the redox flow battery


Have you heard in the news of cell phone batteries igniting? A similar accident should never occur in a large-scale electricity storage system, which is tens of thousands of times larger.
→The redox flow battery is made only from non-combustible materials.

Long service life

Repeated charging and discharging may shorten the service life of batteries.
→The redox flow battery has no limitation in recharging cycles, allowing stable operation for 20 years.


Have you ever experienced a sudden shutdown of your PC despite a still remaining battery level of 10% or so? Actually, it is quite difficult to measure the battery’s level while using it.
→The redox flow battery with its flowing characteristic enables accurate measurement of remaining power in real time.

Principle of the redox flow battery

Why are they needed?

Electric generation from renewable sources such as solar energy and wind power, which we are currently adopting on a global scale, depends on natural conditions and is hard to control. So far the generation capacity of renewable energy has been relatively small in comparison with overall generation capacity, and therefore, the fluctuation has been covered by hydraulic and thermal power plants. To expand the use of renewable sources further, we must solve two problems, (1) surplus power and (2) frequency variation. As a solution, storage batteries are attracting attention.

Problems in increasing capacity of renewable energy

(1) Surplus electric power

Power generation capacity of renewable energy is not adjustable. Therefore, the difference from the required capacity is covered by electric generators using other sources. Increasing volume of renewable energy widens the variation and decreases the electricity produced by other generators. Thermal power plants may not be feasible if the generation capacity is substantially reduced. Once stopped, it takes time to resume the operation. Therefore, a battery with a large storage capacity is required to charge surplus electricity and discharge in power shortage.
►The requirement is high-capacity.

(2) Frequency variation

Distribution of sunrays to the ground is not constant even in a day. Electricity generated by renewable energy is unstable even in a very short period of time. Fluctuation in electricity, surplus and shortage, within a short period of time causes frequency variation and may stop electrical equipment. Therefore, a storage battery with quick charging and discharging capacity is required to compensate the opposite function of the power generation by renewable energy and suppress any sudden fluctuation.
►The requirement is quick charging and discharging response and durability under repeated use.

The world's largest-scale flow battery system operates in Hokkaido.

In FY2015, in a joint development with Hokkaido Electric Power Co., Inc., we started the operation of a large-scale storage battery system at Minami-hayakita Substation. This is the world’s largest-scale demonstration project (15 times larger than the redox flow battery in our Yokohama Works), attracting the attention of the rest of the world.

Schematic of the demonstration project
Building that houses the battery system
Building that houses the battery system
Electrolytic tank in the building
Electrolytic tank in the building
Storage battery capacity
  • Output 15 MW, capacity 60 MWH
  • * It is equivalent to the electricity consumption of 6,000 households for a day.
Verification test period
December 2015 to March 2019 (planned)
Verification test items
  • ●Development of control methods to suppress frequency variation by using a storage battery as a power supply to control the variation
  • ●Development of operational procedures to address surplus (shortage) power by using a storage battery
  • ●Evaluation of performance of the redox flow battery

A new container type battery, which substantially reduces on-site construction, will be released in FY2016.

The system is currently being tested at the Osaka Works. The first commercial product will be installed and operated at the Yokohama Works next summer.

Features of the container type

Electrolytic tank is included
in the container.
  • ・No on-site piping work for electrolyte.
  • ・Easy on-site installation of instrumentation and assembly work.
  • ・Reduction in transportation costs.
Higher output of battery unit (cell)
【double output density】
・Reduction in size and cost.

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