News Release
April 15, 2015

No. 2015001

World’s Largest Superconducting Flywheel Power Storage System
Test Machine Completed andTest Operation Started
Railway Technical Research InstituteKubotek Corporation
Furukawa Electric Co., Ltd.
Mirapro Co., Ltd.
Public Enterprise Bureau of Yamanashi Prefecture
The Railway Technical Research Institute (RTRI) has beendeveloping a superconducting flywheel power storagesystem, as a next-generation power storage system,
jointly with Kubotek Corporation, Furukawa ElectricCo., Ltd., Mirapro Co., Ltd. and the Public EnterpriseBureau of Yamanashi Prefecture. This development has
been supported by the New Energy and Industrial
Technology Development Organization as a one of theprojects for “the Technical Development for Safe,Low-Cost, Large-Capacity Battery Systems.”
Now the world’s largest-class superconducting flywheel
power storage system with a superconducting magnetic
bearing was completed and test operation was started.

The superconducting flywheel
power storage system

The flywheel power storage system is capable of storing electricity in the form of kinetic energy byrotating a flywheel, and converting the rotating power again to electricity, if necessary. Since thisrechargeable battery does not deteriorate over time, it can be used for many purposes. For example,
being combined with rather unstable power-generation systems such as photovoltaic or wind-powergeneration, it can help stabilize power supplies. It is also possible to apply this system to railways inorder to prevent regenerative cancellation. For this system, RTRI developed a superconducting magnetic
bearing composed of a high-temperature superconducting coil and high-temperature superconducting
bulk. In this system, the flywheel is levitated by the superconducting magnetic bearing without contact.
Therefore, the power loss is minimal although a large flywheel is used, and it is a very practical system
which enables stable power generation over a long period.
The completed system is the world’s largest-class flywheel power storage system using asuperconducting magnetic bearing. It has 300-kW output capability and 100-kWh storage capacity, andcontains a CFRP (carbon-fiber-reinforced-plastic) flywheel. This flywheel is 2 m in diameter and weighs
4 tons, and is rotated with a superconducting magnetic bearing at a maximum speed of 6,000 RPM.
This is the world’s first superconducting magnetic bearing which uses superconducting material both forNews Release
No. 2015001

April 15, 2015

its rotor and bearing, and is capable of supporting heavy weight, although it is a compact-sized system.
The details of this technical development will be presented at the 91st Cryogenic and Superconducting
Engineering Technical Meeting scheduled on May 27, 2015. Grid-connection tests with amegawatt-class solar power plant will also be started this summer at Komekurayama in Yamanashi
Prefecture.
This system has been developed jointly with Kubotek Corporation, Furukawa Electric Co., Ltd.,
Mirapro Co., Ltd., and the Public Enterprise Bureau of Yamanashi Prefecture, in a project known as “theTechnical Development for Safe, Low-Cost, Large-Capacity Battery System - the Development of theNext-Generation Flywheel Power Storage System” sponsored by the New Energy and Industrial
Technology Development Organization (NEDO).

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April 15, 2015

No. 2015001

Details of the system
1. Characteristics
The larger and heavier the flywheel is, and the faster it
rotates, the larger the amount of energy thepower-storage
systemcanstore.
In
this“superconducting flywheel power-storage system,” thefollowing technical developments have enabled alarge-diameter, heavy-weight flywheel to rotate withhigher speeds and less power loss.
(1) Large-sized CFRP flywheel
For CFRP (carbon fiber-reinforced plastic) flywheels
which have been developed so far, have a 1-meter
diameter has been the upper limit due to restriction instrength and cost. For this system, however, higher
strength and reliability were attained by a better methodof weaving carbon fiber and a 2-meter-diameter
flywheel was developed. This flywheel is made bystacking nine layers of CFRP rotors with a 2-meter
outer diameter, 1.4-meter inner diameter and10-centimeter thickness. With this method, flywheelsof different storage capacities can be made by changing
the number of layers.

World’s largest class CFRP flywheel(2) Superconducting magnetic bearing
The superconducting magnetic bearing of thissystem uses a high-strength, high-temperature
superconducting magnet made of asecond-generation
high-temperature
superconducting wire material containing
yttrium. The rotating shaft also uses
high-temperature superconducting bulk. We
have succeeded in lifting the 4-ton flywheel
without any contact by refrigerating the bearing
to 50 K, that is, -223
and creating a
powerful magnetic field. This technique has
made it possible to rotate the flywheel at aSuperconducting magnetic bearing to support
heavy-weight flywheel

News Release
No. 2015001

April 15, 2015highspeed, with less energy loss. Furthermore, since this system operates at significantly higher
temperatures than 20 K or -253 of the previous superconducting coil, the refrigeration cost can bereduced.
The completed system is the world’s largest-class flywheel power storage system which has 300-kW
output capability and 100-kWh storage capacity by rotating the flywheel which is 2 meters in diameter
and weighs 4 tons.
2. Schedule for grid-connection tests
Basic performance of this machine will be tested and adjusted in confirmation tests and moved to amegawatt-class solar power plant at Komekurayama in Yamanashi Prefecture. There, it will beconnected to the solar power system and the power grid of Tokyo Electric Power Company, andconfirmation testing will be started to help stabilize fluctuating supply of renewable energy.

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April 15, 2015

No. 2015001

Generator motorby RTRI
Converts between rotating energy
and electrical energy tostore/discharge electricity

CFRP flywheel
by Kubotek Corporation
Succeeded in manufacturing world’s
largest-class CFRP flywheel with 2-meter
diameter by unique carbon fiber weaving
methodVacuum vesselby Mirapro Co., Ltd.
Decompresses the airtightvessel to reduce energy loss
by air resistance to flywheel

Connected tomegawatt solarpower system

2 m in diameter

System connection with thesolar power plantby Public Enterprise Bureauof Yamanashi Prefecture
Connects flywheel power storage
system and solar power plant, andstabilizes power supply

Rotating shaft
containing
superconducting bulk

Superconducting
magnetic bearing
by RTRI andFurukawa Electric Co., Ltd.
Succeeded in contactless, low-loss
bearing generating powerful magnetic
field by superconducting coil and bulk
Superconducting
coil (bearing)

System specifications• Output: 300 kW• Storage capacity: 100 kWh• Maximum rotating speed: 6,000 rpm

Confirmation test site

Mega solar power plantin Yamanashi Prefecture.
Output: 1 MW

Output and capacity can be changed
with different combination of the motorand fly wheel, according to differentusages.

System configuration

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April 15, 2015

No. 2015001

Outline of the entire system