Energy Storage Systems Episode 2 : Flywheels for cheap energy storage

4년 전

What’s up Steemates, hope you’re all A-Okay and enjoying life! As for me, I'm doing great as I am back with another Episode in my Energy Storage Systems series:

Flywheel Energy Storage Systems

Ok so you might be thinking: WTF, this isn’t a flywheel!. And you would be right by saying so, this isn’t a flywheel but please bear with me on this one.

One of the main reasons I chose this shot over another is that a Flywheel Energy Storage System – AKA FESS – is ugly:

I mean look at that! UG-LY. And that's the best one out there! So yeah, I've decided to go with the roller-coaster picture.

The Technology

What's a FESS?

Simply put, a FESS is the whole system and the flywheel is the rotor. When the flywheel is set in motion, the energy is maintained as angular kinetic energy - AKA rotational energy. The force to set in motion the rotor can either be done mechanically - in a water mill - or electrically - using the excess energy of solar panels. To extract energy from the FESS, the speed of the flywheel is reduced
Usually a flywheel necessitates and important amount of force to set it in motion as it is heavy, however, once it begins its spin, stopping it requires an approximately equal amount of force.

FESS have been around for thousands of years and are one of the first mechanical energy storage systems. A perfect example is the potter’s wheel whereby pressing a pedal, a cylinder is set in motion which enables a craftsman to mold his pot.
Fast forward thousands of years later between the 60s and 70s some attempts have been made to use FESS in electric vehicles, for space missions or as stationary power backup.

Although the technique and materials have evolved, the underlying principle remains the same. In order to understand the magic regarding flywheel technology, we need to take a quick detour and look at the physics behind it:

Kinetic Energy

E = ½m

Does it ring any bells? Ok and if I say that E is the energy, m the mass of the object and v its velocity? Still doesn’t? This formula is what we use to determine the kinetic energy an object moving in a straight line creates.

For rotating objects, the idea remains the same but this time we have:

E= ½lω²

  • l is the moment of inertia which is a measure of how hard it is to get an object rotating. Therefore, it is equivalent to the mass for an object moving in a straight line. However, equivalent does not mean equal and when rotating an object, the distribution of the weight also plays an important role. Therefore, the moment of inertia considers both the weIght and its ditribution. Think of figure skaters:

When a figure skater puts their arms out, some of their mass is further from the center of their body (the point of rotation) so they have a higher moment of inertia. If they're spinning quickly with their arms out but then suddenly bring their arms in to the center, they instantly reduce their moment of inertia.

So, if we apply this to a FESS, a very heavy flywheel with a large diameter will have a moment of inertia more important than a much smaller flywheel of the same weight.

  • ω is the angular velocity – aka the rotational speed. It is worth noting that both in linear and rotational movements, the energy is much more sensitive to a variation in velocity or angular velocity as the relation is squared.

Think about a dynamo lamp, the faster you turn the handle, the brighter the light.

Newton’s first law of motion

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

In the case of flywheels this unbalanced force comes from:

  • Air resistance - greatly reduced by sealing the flywheel inside a vacuumed cylinder.
  • Friction because of the bearings – eliminated by using superconducting magnets.

The Business Opportunities

Why use do we have for Flywheels today?

Do you remember the shot of the roller coaster? Well guess what, it's The Incredible Hulk roller coaster at Universal's Islands of Adventure and it uses FESS in order to give the ride the extra boost it needs. Indeed, the ride features an uphill launch which requires a brief but intense current to reach the speed of 40mph. To enable this incredible feat, the park uses large flywheels which release an important amount of energy when needed. Without this technology, the park would have 2 choices: invest in a new substation or brownout the local energy grid at each launch.

There are many more uses! NASA are trying to implement FESS in their satellites as they are more durable and do not necessitate to be changed every couple of years.
Volvo’s hybrid V60 KERS is another example, it uses flywheels to improve by 25% its fuel economy. The flywheel slows down the vehicle when needed and stores the energy which can be released when an extra kick is needed.

And the list could go on!

So, in conclusion Flywheels have numerous advantages when compared to your classical batteries- including Lithium-ion batteries:

  • They last much longer, some flywheels from the industrial revolution are still in operation.
  • Produce no carbon dioxide and do not contain hazardous chemicals.
  • Their energy efficiency can be as high as 90%.

However, as we’ve learn throughout our lives, nothing is perfect. The weight of flywheels is a real buzzkill as it makes it too heavy to use as the main energy storage system in a vehicle – especially cars. Not only is the weight bothering but the material that is used in a FESS has a breaking point, meaning that if the force applied on the flywheel is too great it might shatter.

Energiestro case Study

As I’ve explained in my first article of the series, Episode 0, renewable energies are intermittent and as I’ve explained in my previous article, Episode 1, one of the issues with Lithium-ion batteries is it cannot stand conditions of extreme heat, something quite problematic in solar power plants.

So why not use flywheels? That is the logic behind the creation of French startup Energiestro which has created a flywheel made out of concrete.


Let me explain, as one of the co-founders puts it:

Storage is not a technological problem but one related to economics. We know how to store electricity in batteries, but we don’t know how to do it profitably.

Indeed, the estimated cost of storing energy in batteries is 10 cents per kilowatt-hour, and although solar energy is the cheapest form of energy at 2 cents per kilowatt-hour, storing it in such devices makes it more expensive than coal, gas and nuclear.

The real idea behind this startup is the use of concrete as it is at least 10 times cheaper than steel and almost 20 times cheaper than carbon. Just like that, storing energy costs 2 cents per kilowatt-hour. And, as we all know 2 + 2 = 4 and 4 cents per kilowatt-hour is the price of the second cheapest source of energy: coal.

So how does it work?

When excess energy is produced, it is redirected to a motor which sets the flywheel in motion - it can reach up to 1000 km/h - and the energy can be stored for a long period of time . To use this excess energy, you just have to reverse the process: the flying wheel activates the motor which sends electricity back to the grid.

I highly recommend to take a look at their TedX pitch:

A few other companies such as Amber Kinetics are also trying to revolutionise the storage industry with, at this point in time they seem to attract much less investors than Lithium-ion batteries.

Aaaand that's it for today!

Hope you've all enjoyed this Article, please leave a comment if you feel like it and an upvote if you like what you've felt! Resteems are also greatly appreciated!

You can also take a look at Episode 0 and Episode 1, I'll be releasing the next one in the series soon!

1ArticleExplain That Stuff
3ArticleThe Guardian
4Company siteAmber Kinetics
5Company siteEnergiestro
1The Incredible Hulk
2Flywheel 1
3Figure Skating

Fun Battery Fact:

The Ouarzazate Solar Power Station is located in Morocco and is the largest Solar Power Station in the world covering 450 Hectares and producing 2635 kWh/m²/yr.

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