News Release
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-storagesystem
canstore.
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.
(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 a

World’s largest class CFRP flywheel

Superconducting 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.

News Release
April 15, 2015

No. 2015001

Generator motor
by 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 solar
power system

2 m in diameter

System connection with thesolar power plantby Public Enterprise Bureau
of 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

News Release
April 15, 2015

No. 2015001

Outline of the entire system