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Containment systems are also used to enhance the performance of the flywheel. The
containment vessel is often placed under vacuum or filled with a low-friction gas such as
helium to reduce the effect of friction on the rotor. Figure 8 illustrates a typical system
packaging approach.
Figure 8
System Packaging Includes All Power Conditioning, Controls And Switchgear (Courtesy
Of Caterpillar)
Features and Limitations
The advantages and disadvantages of flywheel systems relative to other energy storage
systems were listed in Table 1. The specific features and limitations of flywheel systems
are examined in the sections below.
Power Capacity
As noted above, the energy stored by a flywheel is determined solely by the mass and
speed of the rotor, while the maximum power is determined more by the characteristics
of the motor-generator and power electronics. This means that the energy and power
characteristics of a flywheel system are more or less independent variables, allowing
optimization of both characteristics independently. This is in contrast with most other
energy storage devices. In batteries, for instance, both energy and power are determined
by the size and shape of the battery electrodes.
Because of this independence, flywheel systems can, in theory, be designed for any
power and energy combination. In practice, technical limitations such as rotor strength
and weight, and resource limitations such as cost limit design characteristics.
Flywheel systems are typically designed to maximize either power output or energy
storage capacity, depending on the application. Low-speed steel rotor systems are
Flywheels Page 10