We have computed various moment of inertia problems during this course. Moment of inertia is important because it allows to compute the energy stored in a rotating body. This has applications:

Source: Cnet:
Beacon Power later this month expects to complete installation of a
flywheel energy storage system on the grid, which the company says is
the largest in the world.

The company said today it plans to host a ceremony for the 20-megawatt
energy storage system in Stephentown, N.Y., where the flywheels supply
short bursts of power to maintain a steady frequency over the grid. The
storage system takes the place of natural gas plants, which grid operators
ramp up and down to create an even match between electricity supply
and demand.

The expected completion of the plant is a milestone for flywheel-based
storage, which has been used for tests and smaller, 1-megawatt systems.
Beacon Power's spinning flywheels, which are made of carbon fiber
and levitated in a vacuum by magnets, absorb energy from the grid and
discharge 1 megawatt for as much as 15 minutes.

The company, which received a  million Department of Energy loan
guarantee for the plant, plans to use the same flywheel-based system for
other energy storage applications, such as buffering power production
from wind farms. Flywheels compete with truck-container-size lithium
ion batteries which have been used on the grid for similar uses.

Beacon Power's business model has helped get the technology onto the
grid. Rather than sell hardware to utilities, it sells grid services,
such as frequency regulation, to grid operators normally supplied by
natural gas plant operators. It owns and runs the plants.

Flywheel storage has been used as backup power for telecommunications
systems but only started being used on the grid in the past few years.
Beacon Power said that 18 megawatts worth of power is now online and
that the system will be fully commissioned later this month. The opening
ceremony is June 12.

Beacon Power on Monday said it has closed a  million loan guarantee
with the Department of Energy for a project to use flywheels to buffer
20 megawatts of power on the grid.

The loan covers 62.5 percent of the estimated  million needed to
construct the flywheel storage plant in Stephentown, N.Y. The New York
Energy Research and Development Authority is also providing  million
in funding for the plant which is now under construction.  A Beacon Power
flywheel spins to store electricity from the grid as kinetic energy where
it can be quickly dispersed back onto the grid for frequency regulation.

A Beacon Power flywheel spins to store electricity from the grid as
kinetic energy where it can be quickly dispersed back onto the grid for
frequency regulation.  (Credit: Beacon Power)

Once done, Beacon Power said that the plant will be the only one of
its kind in the world. Rather than use a large battery, it will use a
network of 200 flywheels to store electricity from the grid as kinetic
energy and disperse it in quick bursts of up to 15 minutes.

Right now, grid operators typically use natural gas power plants to
maintain a balance between supply and demand and keep a steady frequency
of 60 cycles per second. The Stephentown project, expected to be completed
by the end of the first quarter next year, will be able to provide 10
percent of the frequency regulation services in New York needed on a
typical day.

The project is significant step up for the technology, which so far has
been used in smaller-scale installation of about one megawatt of power.

The New York storage installation paves the way for higher penetration
of solar and wind power generation. Since they are variable sources
of power, utilities are looking at different forms of grid storage to
smooth out the delivery of power from renewable sources.

Beacon Power, based in Tyngsboro, Mass., has benefited significantly from
federal and state policies aimed at boosting clean-energy technologies. In
addition to the DOE loan guarantee, which took more than two years to
secure, Beacon Power has received money for technology demonstrations,
such as attached flywheel storage to the Tehachapi wind project in