The Mechanical Battery Explained – A Flywheel Comeback?

This episode is brought to you by Brilliant
… click the link in the description below. When it comes to energy storage, our first
thought usually is chemical batteries. But what if we went old school … like just
spinning things really fast and capturing that kinetic energy, old school. I thought I’d explain an example of a mechanical
battery: the flywheel. And are they making a comeback? I'm Matt Ferrell. Welcome to Undecided. The versatility and dropping costs of lithium
ion batteries have made them a popular option for not only consumer electronics, but also
grid-scale energy storage. But it’s not the only solution out there. The often overlooked technology of flywheels
has been reinvented and may be a good fit for supporting renewable energy like solar
and wind. High power density, long lifetime, high efficiency,
and being carbon-free has boosted interest in flywheel technology, but how do flywheels
stack up over other energy storage technologies? The world has been shifting from fossil fuels
to renewable energy sources in order to achieve low carbon emissions and maintain cheap prices.

Both electricity consumption and renewable
energy generation have been increasing all over the world in the past few years. In 2018, global energy consumption reached
almost 25,000 TWh (24,738.9 TWh), and of that, solar and wind only accounted for 1,827.8
TWh … or about 5% of the total power generation in the world. Since renewables like solar and wind aren’t
available 24/7, and can't be turned on and off anytime, energy storage systems need to
be placed together with solar and wind farms to make them more widely viable.

But why do chemical battery installations
get all of the buzz right now? Why not flywheels? I mean the first question to ask is probably,
“Flywheels? Really?” Or maybe it's actually: “What are flywheels?” A flywheel contains a dual-function electric
motor to store and generate energy. It operates like an electric motor in an EV
to speed up the flywheel using electricity, so that kinetic energy is stored in the spinning
wheel. Then, when it’s turned off, the dual-function
electric motor operates like a generator, and the mechanical energy stored in the rotating
mass spins the generator's rotor, producing electricity. It’s similar to how regen braking works
in an EV. When it comes down to it, a flywheel can be
considered a big mechanical battery. To get a little nerdy for second and talk
about the Physics, the rotational energy of a rotating mass is directly proportional to
the moment of inertia (rotational mass) and angular velocity.[^formula] For example, imagine
that you spin two car wheels of the same mass, one at 30km/h and another at 100km/h, which
one will be harder to brake? You probably guessed it …

The faster one. That's an example of angular velocity at work. Now, let’s say one of the wheels is 5kg
and the other is 10kg. You speed them up with the same exact velocity,
so they’re both spinning at 30km/h, which one will be harder to stop? If you guessed the heavier one, you got it. And that's an example of rotational mass at
work. Optimizing the shape or increasing the rotational
speed will boost the energy stored in a flywheel. However, speeding up the flywheel increases
the centrifugal forces it's subjected to, and the resistance of the material that it’s
made from limits the amount of energy a flywheel can store. Bottom line: spinning a flywheel too fast
can completely break it apart. Now that's obviously something you want to
avoid, but but as I mentioned earlier, this is something we've been mastering for a long

Flywheels were first used in potter wheels
and spindles in ancient Mesopotamia to produce threads. Later, they played an important role in the
Industrial Revolution, when flywheels were used in engines and machines to smooth out
the power delivered by the driving device. However, the first flywheel used exclusively
for energy storage was built by John A. Howell in 1883 for a military application. In this case, the flywheel installed in the
Howell Mark I torpedo worked as a propulsion source and provided directional balance. And in the 1940s, the concept of flywheels
was used for transportation by the Swiss company Oerlikon, when it released its carbon-free
bus containing a flywheel for energy storage. The Gyrobus used energy from the grid to spin
up a flywheel system, which operated as a generator while on the move. When the flywheel was completely charged (3,000
rpm), the bus could run for 6 km at speeds of up to 50 to 60 km/h. Since then several improvements have been
made to flywheels in order to increase power storage capacity with safe operation.

Flywheel Energy Storage Systems (FESS) are
essentially composed of a few key components besides the flywheel and electric motor: bearings,
an enclosure, and a power electronic converter. FESS have bearings to support the rotor and
resist against forces to maintain its position, which allows it to spin at high velocities. Mechanical bearings require high-performance
lubricants and frequent maintenance to operate properly, and are also sensitive to gyroscopic
forces and the friction it generates. The main losses of flywheels are caused by
friction. To solve for that expensive magnetic bearings
are employed in flywheels that operate at high-speeds in order to reduce maintenance
basically to zero, since they don’t require any lubrication.

It also helps to increase efficiency due to
their minimal losses. FESS also come with a power electronic converter
to control the variable AC frequency and voltage input/output of the electric motor/generator. Flywheel Energy Storage Systems (FESS) fall
into two categories: low-speed and high-speed. Low-speed flywheels are made of steel and
spin at rates up to 10,000 RPM. These are heavy and use the advantage of their
angular mass to increase the stored energy (back to the point that flywheel energy is
linearly proportional to its mass).

On the other hand, modern flywheels that feature
high power density and efficiency can reach 100,000 RPM, which makes it store more energy
since flywheel energy is proportional to the square of angular velocity. You still with me? Because I’m not sure I am. Advanced flywheels are housed in a vacuum
enclosure to reduce aerodynamic drag. They also have air or magnetic suppression
bearing technology to reach high speed and are made of materials with a high strength-to-weight
ratio, like carbon and fiberglass. In practice, flywheels have a fast response
to frequency changes, making them a good solution to stabilize the grid frequency when unstable
variations occur. In addition to that, they can be completely
charged within a few milliseconds, have a considerably longer lifetime of about 20 years
compared to other technologies, high efficiency (about 95%), and high power density so it
can store more energy in a smaller space. All these advantages make flywheels a suitable
option for several applications. They’ve been used as Uninterrupted Power
Supplies (UPS) in industrial and commercial applications to provide power backup for essential

Flywheels have also been used as Control Moment
Gyros (CMG) in spacecraft, like in the International Space Station (ISS) to hold the space station
at a fixed attitude relative to the Earth's surface. In motorsports they’ve been used as hybrid
propulsion systems for regenerative braking, like in the Audi R18 e-Tron LMP1s that won
at Le Mans in 2012, 2013 and 2014. And they’ve also been used in the electrical
grid to support the increasing spread of renewables.

FESS have also been used in grid applications
in order to provide ancillary services, such as frequency regulation and power fluctuation
support. Similar to how Tesla’s Hornsdale Power Reserve
has been used in Australia. Some examples are the Beacon Power 20 MW units
installed in Stephentown, New York and Hazle Township, Pennsylvania to support frequency
imbalances in the grid. These plants were commissioned in 2011 and
2014. Beacon's flywheel rotor is made of a carbon
fiber composite rim. Its flywheels spin up to 16,000 rpm and can
completely charge and discharge for 175,000 cycles. Another company playing this game in order
to spread flywheels over other renewable energy storage applications is Amber Kinetics.

Their all-steel M32 model can provide 8kW
power for four hours, achieves efficiency higher than 86%, and offers 11,000 cycles. In 2018, the company in partnership with West
Boylston Municipal Lighting Plant (WBMLP) commissioned a 128kW/512kWh flywheel energy
storage system in Massachusetts. This project is integrated to a grid connected
solar array, and it has already discharged 116MWh. Amber Kinetics also installed another storage
system, but now in China, to operate with a 60 MW solar power power plant in order to
store energy and improve grid stability. Since its commission in 2018 it has already
stored 75.6MWh with no gas emission . But, how do flywheels stack up over other
energy storage systems? Compared to batteries, flywheels are made
of environmentally friendly materials that can be reused, and may have higher capacity
than lithium-ion and flow batteries. In addition to that, batteries need to be
recycled and replaced more frequently than flywheels, which have a much longer life cycle. In comparison to other mechanical energy storage
systems, such as compressed air and pumped hydropower, flywheels reach higher efficiencies.

So, what’s the catch with flywheels? Why haven't we seen them popping up in solar
and wind farms everywhere? The latest technology provides energy just
for a few hours and flywheels have a high energy installation cost. According to the Electricity Storage and Renewables:
Costs and Markets to 2030 report, in 2016, FESS costs varied from $1500/kWh to $6000/kWh,
and expected installation costs by 2030 will range from $1000/kWh to $3900/kWh. On the other hand, lithium-ion battery storage
systems for utility-scale applications varied from $200/kWh and $1260/kWh in 2016, and it’s
expected by 2030 to see a reduction to between $77/kWh and $574/kWh. Flywheels are also beaten out by flow battery
technology, which may reach between $108/kWh and $576/kWh by the same year. Another interesting analysis is the Levelized
Cost of Storage (LCOS), which is directly comparable to LCOE but for storage systems. The article Projecting the Future Levelized
Cost of Electricity Storage Technologies shows that, for short discharge duration and frequent
cycles, the Mean LCOS for flywheels might reach about $520/MWh in 2050, while Li-ion
and Vanadium redox-flow batteries might have Mean LCOS of $280/MWh and $220/MWH, respectively.

Flywheels need to have a big cost reduction
and performance boost, along with the development of new materials with high strength and low-density
rotor materials, as well as improvements on the electrical motor/generator. This means a lot of money and time spent on
research and development, which is why flywheels have been overlooked in favor of the latest
battery technologies . But there is an interesting hybrid approach. But before I get to that, I'd like to thank
Brilliant for sponsoring this video. If you’d like to learn more about physics
and kinetic energy, check out the Science Essentials course at Brilliant. Physics was never my strong suit, so brushing
up on potential energy and kinetic energy really helped me wrap my head around flywheels. Even if physics makes your brain spin with
an angular velocity that's hard to stop, Brilliant has over 60 courses in other topics like mathematics,
science, and computer science. They teach all of the concepts through fun
and interactive challenges, which help you understand the "why" of something …

just the "how." It helps to develop your intuition, which
is my favorite part about Brilliant and taps into the way I learn. Go to to sign
up for free. The first 200 people will get 20% off their
annual premium membership. Thanks to Brilliant and to all of you for
supporting the channel. Now, back to the hybrid approach…Some recent
studies and projects have been developed to verify the feasibility of integrating flywheels
with batteries for hybrid energy storage systems. One example is the AdDHyStor project, operated
by Schwungrad Energie, that has already received about €3 million EU-funding for trailing
a 1.0 MW battery-flywheel hybrid energy storage system to support dynamic grid stabilization
in Rhode, Co. Offaly [24] [25]. Another recent example is the 8.8MW lithium-ion
battery set integrated with a 3MW flywheel system in Almelo in the Netherlands that will
assist the integration of green power sources to the grid. This looks to be a promising solution and
may be making a bit of a comeback. Jump into the comments and let me know what
you think about old school mechanical batteries, and if there other types I should take a look

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