Civil Engineering Reference
In-Depth Information
can be discharged with no hardship on the power electronics, or other
components of the system.
As to the number of charge-discharge cycles the flywheel can withstand,
the fatigue life of the composite rotor is the limiting factor. Experience indi-
cates that the polymer fiber composites in general have a longer fatigue life
than solid metals. The properly-designed flywheel, therefore, can last much
longer than the battery and can discharge to a much deeper level. Flywheels
made of composite rotors have been fabricated and tested to demonstrate
more than 10,000 cycles full charge and discharge. This is an order of mag-
nitude more than any battery presently available.
10.10.3
Flywheel Benefits Over Battery
The main advantages of the flywheel energy storage over the battery are as
follows:
•
high energy storage capacity per unit of weight and volume.
•
high depth of discharge.
•
long cycle life, which is insensitive to the depth of discharge.
•
high peak power capability without overheating concerns.
•
easy power management, as the state of charge is simply measured
by the speed.
•
high round trip energy efficiency.
•
flexibility in designing for a given voltage and current.
•
improved quality of power as the electrical machine is stiffer than
the battery.
These benefits have the potential of making the flywheel the least-cost
energy storage alternative per Wh delivered over the operating life.
10.11
Compressed Air
The compressed air energy storage system consists of:
•
air compressor.
•
expansion turbine.
•
electric motor-generator.
•
overhead storage tank or an underground cavern.
The energy stored in compressed air is given by the following derivations.
