Talk:Flywheel energy storage

Gyroscopic force
Since flywheels acts like gyroscopes, what is the impact of earth's rotation on a spinning flywheel? Would that be a source of power drain?
 * If the flywheel was correctly orientated, parallel with the earth's axis of rotation and orbit around the sun, this should not be a serious problem. The impact of gravity is probably a lot more important anyway.  Provided the bearings can impart a counterbalancing force without a friction loss then there can be no energy loss, although the angular momentum may change orientation. -- kiwiinapanic

Superconductors for stability
I'm not sure how this will fit in yet, but I think I'm going to try to add some more on how superconductors are used for keeping flywheels stable. I think it fits in here better than flywheels because everywhere I've seen it been talked about it has been for electricity storage. If I do add it here, it will come from a school paper I wrote on the subject. I'll probably work on it in the talk pages for a few days before adding it to the article itself.Lcolson 03:44, 16 November 2005 (UTC)


 * Finished integration and reorganization. Moved the completed article. Lcolson 21:20, 19 November 2005 (UTC)

"Parasitic losses such as friction, hysteresis and eddy current losses of both magnetic and conventional bearings mean that flywheel energy storage systems can store/deliver power for only a short period, a few seconds or minutes (without recharging).

Further improvements in superconductors may help eliminate eddy current losses in existing magnetic bearing designs. Even without such improvements, however, modern flywheels can have a zero-load rundown time measurable in years." These two sentences are contradictory. How can a flywheel energy storage system only store power for a short period yet have a rundown time measurable in years. I suspect the first statement is erroneous and based on the design of NASA gyroscopes which are designed with these characteristics in mind. &mdash;The preceding unsigned comment was added by 148.197.54.206 (talk &bull; contribs).


 * I see no mention of flywheel energy storage systems "only stor[ing] power for a short period. . ." in the text you quote, nor can I find any contradiction in these sentences. It says: "they could make the things work better; but even without the better-working-ness, energy can be stored for years." -- KyleP 20:57, 5 April 2007 (UTC)

Formula : Disc or Rod
I think that the energy stored, quoted as half (1/2), can't be the same for both the disc and the uniform rod. —The preceding unsigned comment was added by Martin r harris (talk • contribs).


 * I moved this comment from the main article page. Kevin 04:29, 28 April 2006 (UTC)


 * Why not, a disc is simply a very short rod?


 * Correct. There is no such thing as a "disk" in magic physics land. They're both cylinders. These formulas are in any physics text. -- KyleP 20:53, 5 April 2007 (UTC)

interial constants
I was wondering why theres so much about the moment of inertia on this page - Especially why it gives so many random inertial constants. It only makes sense to have the rotor be a solid cylinder, because that should have the greatest strength, and thus greatest possible rotation speeds. Why would you make it, for example, a hollow sphere?? Fresheneesz 21:12, 21 July 2006 (UTC)

The inertial energy depends on the radius as well as the velocity. By having the concentration of mass as far away from the center as possible, you increase I (and thus, kinetic energy), without adding mass, or velocity. -Dan

Surely a discus or elliptoid shape would be stronger than a soild cylinder. Perhaps even a sphere. Anyway, why not include the general integration moment of inertia formula (http://en.wikipedia.org/wiki/Moment_of_inertia), along with cylinder (or any other very common flywheel shapes). Anonymous

Stress
This page needs some math to predict the stresses on a spinning cylinder. I found one equation, but I don't think its correct for this application at least. Fresheneesz 23:22, 30 July 2006 (UTC)

UPS Application: Bearings-weakest link and Premium Power comes at a cost
I've been involved in several R&D projects in the deployment of FES and Motor-Generators at customer sites to provide uninterruptible power to critical loads. The technology performs as advertised in riding through voltage sags and momentary interruptions - especially when integrated with standby power (eg., diesel generator) and an automatic transfer switch (ATS). My company has been involved in the installation of: A Piller UBT flywheel system, an Active Power flywheel system, as well as a Precise Power Rousel Motor-Generator. In each case, the lifetime of the bearings was key to budgeting for longterm maintenance of the systems. Typically we've seen the bearings last 2-5 years. Additionally, it is critical that the greasing mechanism or scheduled greasing is upheld. As you can imagine, technical support for this technology is usually best procurred from the manufacturer. So, the bottom line is that the upkeep is expensive.

Engineering the integration of a FES device with a facility's electrical distribution system plays a key role in the successful implementation of the technology as well. From a dead stop, there is typically a considerable amount of inrush current for the motor to spin the flywheel up to speed. The flywheel motor itself adds quite a bit of parasitic load - something that owners are sometimes not aware of when they see their electric bill increase. Bearing replacement will require the unit to be de-energized, and therefore, a maintenance bypass switch would have to be engineered into the system. And of course, while the unit is bypassed, the load is unprotected. Very critical applications may require the consideration of N+1 redundancy. The units give off quite a bit of heat and we've had to engineer a duct system to exhaust the hot air away from one of the installed systems.

In my opinion, the technology is reaching a level of maturity where lessons have been learned and system integrators/developers can diligently plan for "hidden" costs in the implementation of FES. It's a good albeit expensive way to achieve Premium Power.

Aloha, Mark


 * A "flywheel" M-G system was used in the New Zealand (Hamilton-Palmerston North) Microwave Radio system from c1960 with AC mains powered gear until the 1970s when replaced with battery-powered radio systems which did not need a "no-break" supply. They had a motor & generator (1500 rpm) plus flywheel of c3 tons and a diesel on the end which was coupled up when up to speed (though if it didn't start there may have been provision to drop the clutch to start the diesel!). But the M/W stations also had a standby diesel genset as well. John Wilson (NZ)

Application: electric cars?
I got to the "flywheel energy storage" page from the "zero-emission vehicles" page, so I rather hoped there'd be something on the page about their potential for use in cars. A few years ago--I think it was 1997--I remember seeing a presentation by Ben Rosen and his brother, who had developed a hybrid-electric car powertrain using a high-speed flywheel for energy storage. Basically, it was a gas turbine generator, a flywheel for energy storage, and a drive-by-wire electric system with a motor on each wheel, which could reverse for regenerative braking. The flywheel was definitely the gem of the system, though, and used most of the high-tech design elements described in this article--carbon fiber reinforcement, magnetic bearings, magnetic energy transfer, and so on. (A hollow cylinder, if I recall correctly.) I think it represented more or less the state of the art, and they did in fact make a working powertrain out of it. Might make for an interesting addition to the article, anyway, particularly if it's going to be linked from the ZEV page. I'm not sure if it's too specifically commercial, though. I'm new on Wikipedia, so I'm not really comfortable editing articles yet. Emertonom 18:30, 21 August 2006 (UTC)
 * Take a look at Gyrobus MGTom 23:21, 27 September 2006 (UTC)

I think one reason that this will never be a viable application in any kind of vehicle is because in an accident, all of the stored energy could be released instantly. If the flywheel(s) touches the side of the containment vessel, a huge amount of heat is goin to be released instantly. Some of the smaller energy storage flywheels spin at almost 100,000 RPM's. If the intertia of a flywheel spinning that fast is released in an accident, not only will it make a huge amount of heat but debris could fly in all directions at very high velocities...

No you are wrong about that flywheels capable of storing 1 MJ  have been tested on Formula 1 cars. The technology has evolved. —Preceding unsigned comment added by 59.99.9.201 (talk) 09:16, 12 December 2010 (UTC)

Inaccuracy label but no discussion!
There's a "factual inaccuracy" label on one of the sections of this article, but no discussion here on the talk page about why. I'm going to yank it, and hopefully if there really is something wrong with the article the original accuracy questioner will come back and put a note here for us.

Joachim Heck 14:33, 30 October 2006 (UTC)

Automobile flywheel systems from 1970s
I believe Popular Science or Popular Mechanics covered experimental hybrid gas - flywheel systems designed to capture energy on deceleration, as hybrid gas - electric systems do now. —Preceding unsigned comment added by 205.175.225.22 (talk) 11:55, 17 January 2007

Quick Charging?

 * "Quick charging is done in less than 15 minutes."

This makes no sense in the context of the article. What is quick charging? Charging of what, the flywheel's momentum, or of a battery, or of the generator? A battery within the system, or any external battery? 15 minutes has no relevance if it is not related to another quantity. Is this "charge" always a certain amount of Joules, Coulombs, Volts, etc.? -- KyleP 20:37, 5 April 2007 (UTC)


 * I replaced the sentence with a quote from ScienceNews; I hope this helps. &mdash; Sebastian 16:27, 31 May 2007 (UTC)

Vancouver bus flywheel demonstration?
The reference for the line "flywheels were used in buses..." says nothing about such a project! —Preceding unsigned comment added by 74.67.57.245 (talk) 18:34, 21 December 2007 (UTC)

Nourbey Gulia
I removed the following paragraph from the "Applications" section, since it doesn't even mention applications. This might make sense in a history section, but I'm not sure how big that would get if we dedicated a paragraph to every researcher of the last 30 years. It may make more sense to create an article for the redlink. &mdash; Sebastian 16:22, 31 May 2007 (UTC)

In the 1980s Soviet engineer Nourbey Gulia had been working on flywheel energy storage. His work resulted in many original solutions for wheel suspension, vacuum chamber sealing, rotation rate decline compensation, and hydraulic transmission. However, his primary advance was the composite flywheel capable of rotation rates exceeding 40,000 rpm, running unloaded for up to a week, and resistant to explosive destruction. Gulia's "super flywheels" were tightly wound with metal or plastic tape. These had tensile strength higher than that of molded steel, and in the case of failure simply unwind inside the chamber, filling it and grinding to a stop. Gulia's first wheels were made of steel tape, but the latest models used Aramid filament (Kevlar or Twaron), wound not unlike a bobbin of thread.

Electricity is not needed
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. -- Good! The energy is converted back to electricity by slowing down the flywheel. -- Eh??

Where does this "electricity" assumption come from? You can store energy in a flywheel without ever having any electricity anywhere! This is maybe a bad example, but just to illustrate the point http://www.xtrac.com/pdfs/Torotrak_Xtrac_CVT.pdf describes a formula one race car flywheel energy storage. "The energy is converted back to electricity by slowing down the flywheel" is complete rubbish. Kinetic energy was put into the flywheel during braking and the flywheel puts kinetic enery back into the car on acceleration.

Is this an article on Flywheel energy storage, or about somebody's particular product with a specific application?

Crysta1c1ear 15:59, 7 June 2007 (UTC)


 * I changed the headline to clarify the good point you are making. I will also change the article to include this technology. &mdash; Sebastian 19:35, 7 June 2007 (UTC)

Difference from Compulsator
Can someone please explain the difference between FES and a Compulsator? Thanks! &mdash; Sebastian 08:06, 1 September 2007 (UTC)


 * DGMWINE but I think the terms are not rigorously distinct.


 * My understanding is that "compulsator" is used when the unit unloads it's energy electrically in the form in which the electricity is needed (voltage, cycle, capacity, etc.) whereas this link is not so close for a FES - it just unloads electricity.


 * Also, when talking about the assembly that includes the flywheel itself (and maybe its immediately neighbouring components), and your interest is primarily in the energy storage characteristics and how thise are achieved, you are more likely to refer to the FES. On the other hand, if you are talking about the entire assembly and are principally interested in its electrical characteristics rather than how it is built/engineered to deliver those, you are more likely to refer to the compulsator.


 * However I wouldn't consider myself expert enough to edit based on this. Martin 08:25, 4 September 2007 (UTC)

Gyroscopes in opposite directions?
"Strictly speaking, they would exert a huge torqueing moment around the central point, trying to bend the axle. However, if the axle were sufficiently strong, no gyroscopic forces would have a net effect on the sealed container, so no torque would be measured externally."

Can anyone explain how this is true?

If there's a torque on the axle, how does one isolate that from the outside world? The axle has to be connected to the car in some way, so would there not be a torque on the car, too? —Preceding unsigned comment added by Pediddle (talk • contribs) 17:00, 16 September 2007 (UTC)

I think what was meant, was that if you had two flywheels, spinning in opposite directions, attached to the same axis/axle, spinning at the same speeds, they would cancel each other out externally as long as the axis is strong enough, but when the axle was rotated, the two flywheels might try to bend the axle in the middle? -69.87.203.168 (talk) 02:24, 24 November 2007 (UTC)

You would think this was addressed in any aircraft with contra-rotating propellers or blades (Soviet military aircraft specifically). While not specific to flywheel energy storage, I always enjoy this link http://www.dself.dsl.pipex.com/MUSEUM/LOCOLOCO/brennan/brennan.htm Bottom of linked page relevant to discussion. And http://en.wikipedia.org/wiki/Gyro_Monorail Curious —Preceding unsigned comment added by 220.147.241.183 (talk) 02:30, 27 January 2008 (UTC)

UPS steady-state losses
The UPS section needs a dose of honesty, in conjunction with the disadvantages section. What sizes of UPS storage systems are practical for flywheels? And for such systems, if they sit around day after day fully charged, but never utilized, how much energy do they consume total, just to stay charged and operational? It looks like they are much worse than batteries on this important parameter, quite important in such applications -- let's have some facts! -69.87.203.168 (talk) 02:46, 24 November 2007 (UTC)

Advantages vs Disadvantages
"One of the primary limits to flywheel design is the tensile strength of the material used for the rotor. Generally speaking, the stronger the disc, the faster it may be spun, and the more energy the system can store."

This statement is very misleading. You can also have a heavy (say 500 lbs.) flywheel spinning at a much slower rotational speed that can store the same energy as a lighter faster spinning flywheel. We should be specific when discussing stationary versus non-stationary applications. —Preceding unsigned comment added by 220.147.241.183 (talk) 02:45, 27 January 2008 (UTC)


 * Flywheel mass is not a design limit. You can always make a heavier flywheel by making it bigger. However tensile strength is a design limit. Once you have worked your way up to carbon fibre composites you are near the current limits set by available materials. And while it may be possible to find new materials with higher tensile strength, all that will do is to set the limit higher. So the statement is not misleading.


 * In any case, doubling the mass of a flywheel doubles the energy stored but doubling the rotational speed or the radius of the flywheel quadruples the energy stored. Hence the speed/radius has a much bigger effect on energy stored than mass does. And maximum speed/radius is absolutely dependent on tensile strength. People aren't interested in using a more massive material for the flywheel when you can get a far bigger increase in energy storage by using a stronger material. In fact if you do the maths it shows that the highest energy storage is achieved by the material with the highest strength-to-weight ratio.


 * Sure, you can always store more energy by using a heavier flywheel but that's not the way to go if you intend to have flywheel powered cars, boats or planes. -- Derek Ross | Talk 21:03, 23 May 2008 (UTC)


 * Why isn't this included in the article? The article itself is not very clear about this, as it says nothing about the mass of the flywheel. It seems (from the article) that mass is irrelevant.


 * What about the case of miniaturization of the FES? If you wanted to make a very small FES would it still be best to use strongest as opposed to denser, but less strong material? Waydot (talk) 21:39, 18 January 2009 (UTC)

Physical characteristics
It would be nice to have some discussion about the lifetime of the energy storage: I'd imagine that due to friction etc. storage efficiency would degrade over time. it would be good to know the longest timespan storage that flywheels currently operate at: days weeks? hours? --naught101 (talk) 00:33, 21 February 2008 (UTC)


 * If the flywheel is magnetically beared and kept in vacuum, there's only very little friction during storage, mostly caused by Eddy_current. I'd think most degeneration of material is caused when energy is added (wheel is accelerated) or drawn. Then you get massive distortions throughout the material which probably cause microfractions over time. Thus I would assume that the lifetime of a flywheel mostly is dependant on how often it gets accelerated and deccelerated and not so much on how long the energy is stored in particular. For the latter I'd say a superconducting magnetic bearing could hold a flywheel for years without much energy loss for the upkeep cost for the superconductivity of course :) --84.56.197.45 (talk) 16:09, 3 March 2008 (UTC)

The flywheel is good company in the world

Use in Aircraft Carriers
There is an article in Popular Mechanics about replacing the steam launcher on aircraft carriers with electric-flywheel technology. This can handle much larger loads and recharge much faster and requires a huge amount of less maintenance. —Preceding unsigned comment added by 41.112.146.254 (talk) 10:42, 20 May 2010 (UTC)

Use for power grid regulation
Very surprised to see no discussion of the use of flywheels for matching variations in generation to variations in usage in commercial power grids - ie for grid energy storage. ciphergoth (talk) 12:01, 28 January 2011 (UTC)


 * 'Tis actually there as Frequency regulation (Flywheel energy storage), and has been for at least a year, but I guess that little section isn't particularly obvious, and hasn't got a link to grid energy storage. It looks a bit like someone saw the news about a usage of FES and thought they'd add it to this article without realising that the reason for frequency fluctionations is because of mismatched supply and demand (is that correct?).
 * The article could really do with a re-write, or rather a restructure. The intro talks about rotational speeds and carbon filaments (which should be in a Desciption section), but doesn't mention what they really are (ie a form of electro-mechanical battery, apart from the non-electrical versions).  Oh, I had several of those back in the 1960s, where you push the toy car along a little, and it continues on its own (from the flywheel), although they didn't have magnetic bearings or indeed any bearings at all.
 * I say it could do with a restructure, with a proper description which might flesh out the way they work a bit better, particularly with respect to electrical versions (which appear to be the majority). I'd also tend to split applications between electrical and other, and move it down below Advantages and disadvantages.
 * In the meanwhile, I've renamed that section to Grid energy storage with a tag. Tim PF (talk) 18:51, 28 January 2011 (UTC)

New non-KERS application of flywheel energy storage for racing
As per http://www.wired.com/autopia/2010/02/porsche-builds-a-competition-caliber-hybrid/. Should probably be added to motorsports section with citation. — Preceding unsigned comment added by 98.149.135.239 (talk) 03:06, 2 June 2011 (UTC)


 * I believe Williams have been developing their own flywheel-based KERS system; however AFAIK all current KERS systems use electrical storage. Mr Larrington (talk) 14:59, 15 August 2011 (UTC)

Added this
I added this: Flywheels have also been proposed for use in continuously variable transmissions. Punch Powertrain is currently working on such a device.

If it isn't upto standard, improve the information. — Preceding unsigned comment added by 91.182.91.212 (talk) 11:25, 13 September 2012 (UTC)

Concrete flywheels, failure modes?
I'm not seeing very many web references to concrete flywheels. Are they used? Apparently it should be possible to construct them inexpensively, using an outer high-tensile cover for compression against fracture.

It's unclear what the failure mode would be of a concrete flywheel. If the release energy is high enough, it may fracture all the concrete from the sand, resulting in a powdered cloud of debris that may contain the failure kinetic energy about as well as an all-composite filament wheel.

--DMahalko (talk) 06:53, 19 December 2012 (UTC)


 * Using Concrete for flywheels wouldn't make a lot of sense. Concrete is strong in compression but weak in tension, hence its use in building columns, with steel reinforcing handling the tension. The stresses in a flywheel are all tensile.--Graham Proud (talk) 10:38, 18 January 2014 (UTC)

Vacuum pump needs
Hi, I was thinking this page need a discussion of the vacuum pump requirement for the vacuum systems.

My experience with vacuum comes from UHV systems, where the pressure will rise considerably if there is no active pumping of the system for prolonged time, even with all the specially-designed fittings.

But for the purely mechanical properties of vacuum, there are much less strict requirements than UHV. Does anyone know whether it is feasible for a flywheel system to simply pump down the pressure and disconnect the pump? Would such a system keep vacuum for years on end?

If not, the pump system should be seen as an integral part of the flywheel. Therefore the power consumed by the pump and its maintenance requirement should be brought in for a fair comparison with batteries and other power storage devices. MigB (talk) 11:14, 22 March 2014 (UTC) — Preceding unsigned comment added by MigB (talk • contribs) 10:33, 22 March 2014 (UTC)
 * Looking at the Beacon Power product, they are vacuum sealed. Certainly vacuum equipment would be required in the factory but not within the device.--Graham Proud (talk) 15:06, 22 March 2014 (UTC)

AC or DC
Some of these systems - eg for physics labs - generate DC, others might generate AC. Some have separate motors and generators. It would be great to have more detail on this. Duration of input/output and typical storage times might be interesting ? Some are optimised for peak power output (charging at lower power). - Rod57 (talk) 14:16, 7 December 2015 (UTC)

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Externally mechanically supported kinetic energy storage?
Are there any concepts externally mechanically supported? Like launch loop or "maglev trains" going in circles. F = m⋅a = m⋅v^2 /r = 2K/r so K=F⋅r/2 is about the energy stored.(F the force the system can carry) If the strength of the disc is also still used can roughly add that. Or just not hearing about that because negatives not reported?(indeed, afaics, none seem to be sufficient, launch loop is fast enough, but requires that large radius)2001:984:6FB5:1:8A4B:AF78:1B75:1ECD (talk) 00:09, 24 March 2016 (UTC)

Storage for grid connected electricity generators
This article could talk about the technical and economic viability of flywheels for grid connected electricity generators, particularly intermittent renewable sources such as solar and wind. — Preceding unsigned comment added by Jray310 (talk • contribs) 08:10, 22 October 2016 (UTC)

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Comparison to electric batteries
The comparison to electric batteries section suggests only one way in which flywheels are not superior to electric batteries is limited flexibility in terms of shape. However, the use of batteries seems far more prevalent than flywheels, would suggest there must be some other advantages to battery storage. Is this section really capturing the whole picture, or is it overly biased in the direction of flywheels? —Salton Finneger (talk) 18:07, 28 February 2017 (UTC)


 * The application makes a world of difference, for small or portable, or flat as in a EV, batteries have no competition from flywheels, as the size of the battery industry proves. For the much rarer stationary applications it's all about cost, when a UPS is small, it will use a battery, when the storage gets to hundreds of kW, a kWh of spinning steel is cheaper than a kWh of chemical battery, when storage becomes even larger, a kW of falling water is cheaper than a kW of spinning steel. The "Comparison_to_electric_batteries" leaves out the little detail that there aren't small flywheels for storage. Dougmcdonell (talk) 21:02, 1 March 2017 (UTC)

The last two sentences are unsupported (and in my experience working in this field, wrong) "that flywheels don't need maintenance because they are are sealed". Seals would then need replacement, especially in high speed flywheels and this is one of the limiting factors of flywheels that they are difficult to keep sealed. I do agree that low speed flywheel designs are low maintenance and some batteries are not, but when was the last time you did anything to the battery in your car? Or a battery in a cell tower? It seems very design specific and does not make a comparison between electric cells and flywheels. The other "a flywheel at a minimum must occupy a fixed square surface area and volume", confuses me as flywheel energy has nothing to do with surface area or volume, but mass and speed. Again, power and energy density vary (a good comparison of the state of the art could be made in this regard) There are advantages and disadvantages, but these aren't them. Wiredrabbit (talk) 11:21, 18 March 2019 (UTC)

Possible error in specific energy equation?
I was taking a look at the specific energy equation found in this article and, as far as I can tell, this equation is not dimensionally consistent. For it to be dimensionally consistent K should have dimensions corresponding to (L)^-2. I'm sorry if this is not the correct format to submit my doubt. 213.99.46.50 (talk) 14:46, 3 May 2017 (UTC)

I also believe there is something wrong with that equation. Even the left side "specific energy" is supposed to be Joules per KILOGRAM, not Joules per 'moment of inertia'. The units don't net out to zero either. It (to me) doesn't make sense that equation takes 'rotor material density' as an input variable, when 'rotor material density' is already implied in the 'moment of inertia'. 2600:1700:4CA1:3C80:69CA:CA42:B778:1237 (talk) 17:56, 20 October 2018 (UTC) Yes, this is completely wrong - so wrong that I corrected it from E/I to E/m - as flywheels are nearly all cylindrical, perhaps someone can substitute in for the shape factor K to give a reasonable numerical estimate for an isotropic material? — Preceding unsigned comment added by 2A00:23C4:1585:DF00:A181:8E11:7B16:DE8B (talk) 11:01, 7 June 2020 (UTC)

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Chernobyl Disaster
was a result of an x-time repeated experiment to use the residual enegy of the heavy turbine rotors as flywheel uninterruptible power supplies. To spare the huge, expensive and leaking accumulators. And they have been very close to solve the generator exciter regulation problem, unfortunately the necessary integrated circuits have been under US technological embargo at this time :( 85.216.197.77 (talk) 19:57, 18 July 2021 (UTC)

Helically Symmetric Experiment flywheels
I'm not sure how to use references, but I was curious about: The Helically Symmetric Experiment at the University of Wisconsin-Madison has 18 one-ton flywheels, which are spun to 10,000 rpm using repurposed electric train motors. https://news.wisc.edu/one-of-a-kind-fusion-experiment-comes-online/

Does anyone have more information about this hardware? 50.5.47.22 (talk) 03:22, 28 November 2021 (UTC).

PG&E grid storage update
Per a 2018 Planet Money (NPR) episode, PG&E's 2016 agreement with a California company to construct a flywheel energy storage system in Fresno did not yield usable results. Nieuwe Nederlander (talk) 00:55, 23 February 2022 (UTC)