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1. Electricity Storage
On
The Fly

2. How does flywheel energy storage work ?
Flywheel Energy Storage (FES) works by
accelerating a rotor (flywheel) to a very high
speed and maintaining the energy in the
system as rotational energy.

3. The flywheel itself is typically a very heavy
wheel that requires a high degree of force to
set it spinning, and once in motion, a strong
forces is needed to bring it to a stop – in effect
a flywheel is a mechanical battery storing
rotational kinetic energy.
How does flywheel energy storage work ?

4. Adding energy to the system increases the
speed of the spin, while extracting energy
reduces its speed (due to the conservation of
angular momentum).
How does flywheel energy storage work ?

5. “The main characteristics of flywheels are a high cycle
life (hundreds of thousands), long calendar life (more
than 20 years), fast response, high round trip efficiency,
high charge and discharge rates, high power density,
high energy density, and low environmental impacts.
The state of charge can be easily measured from the
rotational speed and is not affected by life or
temperature. On the downside, flywheel self-
discharge at a much higher rate than other storage
mediums and flywheel rotors can be hazardous, if not
designed safely.”

6. FES systems can be either low speed
(typically up to 10,000 rpm) or high
speed (up to 100,000 rpm), with low
speed flywheels being made of
heavier metallic material and are
supported by either mechanical or
magnetic bearings, while high speed
flywheels generally use lighter but
strong composite materials and
typically require magnetic bearings
(to reduce friction losses). They are
typically housed in a vacuum
enclosure to reduce losses due to air
resistance.

7. The technology is capable of transferring large amounts of
power in seconds, with a high roundtrip energy efficiency in
the range of 90%–95%.
It can deliver its stored energy and recharge quickly, in a
matter of seconds. The Sheffield project will combine
flywheel technologies with batteries, which the sponsors
claim will enable the storage system to operate more
efficiently than other systems and reduce costs over the
system’s lifetime.

8. The batteries will be able to take over when the flywheels are either at full
speed or a standstill, only operating for extended periods of frequency
deviation, which will enable the battery-life to be extended versus standalone
chemical battery systems.
Other flywheel energy storage projects
A 2016 report by Grand View Research, Inc projects the
global flywheel energy storage market to reach US$ 478
million by 2024, dominated by the data centres segment
with its requirements for un-interrupted power supplies.
Co-location with distributed generators are also seen as a
significant application of the technology.

9. Various other projects are underway globally. US-based
Beacon Power has a number of Grid-Scale
Flywheel systems in the US.
The company opened its first 20 MW plant in New York in
2011, which has since been performing between 3,000 and
5,000 full depth-of-discharge cycles per year.
The facility comprises 200 flywheels, each with a storage
capacity of 100 kW. A second 20 MW plant was opened in
Pennsylvania in 2014, and most recently, the company has
agreed a 320 kW pilot scheme in Anchorage, Alaska.

10. In early 2016 another US company, Amber Kinetics,
entered the market with a 20-year 20 MW, 80 MWh contract
with Pacific Gas & Electric, which it followed in later in the year with a 25 kWh
flywheel system trial in Hawaii.
The company claims that even with unlimited cycling
during their 30-year lifespan, the systems will suffer no
degradation being 98% steel by weight – this durability
making them significantly more cost effective than
chemical batteries.
 They also pose no risk of fire, chemical explosion or
hazardous materials release.

11. A study by California’s Emerging
Technologies Coordinating Council
found that Amber Kinetic’s solution
provides a cost-effective means of
load-shifting, and recommended its
adoption into California’s Self
Generation Incentive Program
(SGIP).
The study showed that, based on
test data under hypothetical SGIP
economics, the system could
achieve a payback period of
between 2.09 and 3.17 years, and
an internal rate of return of 33-49%.

12. Technology Comparison
Flywheels offer an interesting addition to the electricity storage
portfolio. While the basic technology is well established, the
development of modern construction methods offers the scope
for increased efficiency, with low levels of losses.
This video describes some of the challenges of FES, and the
technological developments aimed at mitigating these – as the
systems become larger and involve greater rotational velocities,
higher levels of containment are needed for safety reasons,
which adds to the cost.

13. Despite focusing on short-duration FES, the paper
makes a favourable comparison with other forms
of mechanical storage:
“Flywheel systems, in comparison to CAES (Compressed Air
Energy Storage), are fairly mature and commercially tested. They
exhibit many advantages over both PHS (Pumped Hydro Storage)
and CAES solutions.
Safety issues associated with these systems can be mitigated but
at a high cost. Both energy and power densities are, on average,
higher than both PHS and CAES and show promise of even
greater improvements with the advent of recent discoveries.” –
S. Sabihuddin et al

14.  Chemical batteries have attracted a huge amount of publicity in recent years, with claims
that they will solve all the problems associated with intermittent renewable energy, yet
the largest chemical battery installation in the world opened this year in California, with
an 80 MWh capability, a size achieved back in 2011 by Beacon Power’s first flywheel
plant.
It is therefore surprising that flywheel energy storage has failed to
generate the same interest given its favourable technical characteristics
and lack of reliance on scarce materials.
Perhaps it’s the fact that it is such old technology that has led to its low
status in the electricity storage arena, but with flywheels delivering
reliable energy in glamorous high-tech applications such as Formula 1
cars and the International Space Station, perhaps it’s time it was taken
more seriously as a grid-level electricity storage solution.

15. FlyWheels
in
Space