back to article Flexible flywheel offers cheap energy storage

Mechanical engineering isn't within the scope of Vulture South, so we'll welcome readers' input about whether this is genius or snake-oil: a Kickstarter project called the Velkess Flywheel hopes to offer low-cost energy storage. Flywheels are good at storing energy, but building them to fine mechanical specifications can get …

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Dynamic Balancing already exists

This is interesting because the ability of a flywheel to store energy is already proven.

Something that deforms will tend to balance if it can deform far enough.

4x4 guys are using dynabeads to dynamically balance tyres that are covered in crap, and it can react to a change in the state of the tyre too.

Maybe manufacture a flywheel with a hollow section so they can use beads to balance the wheel?

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Re: Dynamic Balancing already exists

So if beads will self balance, the off the top of my head it seems to make sense to use a liquid as the major component and water is fairly cheap. Since it's going to be inside an evacuated housing it reduces the danger of a catastrophic failure since some portion will change phase and the liquid will act as a buffering medium for any flying shards from the rotating container that aren't on the outer edge and first to impact. I'm fairly sure there must be reasonable flaws to the idea but nothing comes immediately to mind.

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Re: Dynamic Balancing already exists

The energy stored in a flywheel all depends on storing a lot of mass at the outer edge of the rim, water probably isn't heavy enough. Mercury or molten lead would be good - but might have their own problems

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Re: Dynamic Balancing already exists - FLAW

If the rotor is flexing as it spins then that will absorb energy. Not a problem on a 4x4, you're driving. But in an energy storage device they will be throwing energy away into heating up the rotor as it flexes.

So the question is, does it flex continuously, or does it settle into a shape and stay in that shape? If the latter then only a small amount of energy will be lost. If the former (which I suspect will be the case), then it won't work very well.

Using a fluid as the weight is a bad idea for the same reason - energy will be lost in stirring (thus heating) the fluid. And that will be a continuous loss, not a one-off as it settles into shape.

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Meh

15KWh?

Not sure if this is particularly good or not.

Low tech Lead Acid batteries are good for about 40Wh per kg. So 340kg of lead acid batteries would seem to give a similar amount of storage (~14 kWh) without even looking at other battery tech like Lithium-ion which is far better. I know flywheels have been trialled as storage for bus's etc, but there is always the scary issue of having to deal with the potential for a flywheel to disintegrate following an impact. Not sure from the description how much this is an issue for the deforming flywheel.

Existing battery technology obviously have life-cycle/recharge issues, but new tech like like this flywheel have a habit of not competing with existing technology in the real world due to maintenance and production issues.

Still would love to see if they scale up - I think there is a place for very big (ferris wheel sized) flywheels to absorb wind/solar PV energy and release it. Can this tech scale to store MWh?s Would be cool to see.

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Re: 15KWh?

My take is that the 15KWh figure was selected precisely because it is the same sort of storage density as lead acid batteries; given the choice, a kinetic energy store is preferable to a chemical one, simply because of the toxicity of the latter.

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Re: 15KWh?

You can actually buy UPSs that use this tech. The tend to have much lower running costs than battery which always tend to have a small leakage current. Also there are no annual maintenance and battery swap-out issues.

The ones I've seen are multi kWh, but are normally specified to operate in the deadtime that it takes a diesel generator to spin-up and get to temperature (~1 min). They too run the flywheel in a vacuum, and use a SR motor/generator combo. I saw them put in in a remote location because maintenance was going to be an issue (but as the primary back-up without generator). Another remote location had the same type of set-up, but fuel-cell. THe fuel-cell was very nice in that it jsut sat there doing nothing until needed. The down-side was a life of about 1000 hours on the membrane.

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Re: 15KWh?

What are the efficiency losses for a battery system, though (I have no idea) ?

Would the flywheel provide better performance in terms of the conversion loss for the power going into / out of storage ?

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Re: 15KWh?

This is intended for grid storage, so mass is less of a concern.

To say they will have zero maintenance is naive, they have moving parts, they will need maintenance.

At least inspection.

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Anonymous Coward

Re: 15KWh?

> The tend to have much lower running costs than battery which always tend to have a small leakage current.

The leakage for a battery is approximately 5% per month. The leakage for the flywheel is 2% per day. That alone is enough to increase the running costs. The 2% per day might well be higher since people looking for funding tend to be optimistic with their calculations.

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Re: 15KWh?

Thinking of the mess these things would make if there was an accident (if, say, used in a vehicle).

Those who watched Robot Wars may be familiar with a competitor called Hypno Disk. They used a flywheel which rendered many a solid construction to a pile of twisted metal.

This is an industrial sized version. Mounting one in a car or bus would be asking for trouble.

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Re: 15KWh?

The expected usage of this flywheel isn't to spin it up and then put it away in the cupboard with your torches and paraffin lamp for months on end, only getting it out if you suffer a power cut. It's designed to provide overnight power for domestic solar & wind installations - to absorb excess power generated by the the system on a daily basis and then provide it as required throughout the night. Lead-acid batteries could provide that energy storage but they degrade with repeated discharge cycles, especially if the discharge is deep. A flywheel won't suffer that same discharge cycle degradation and it's 2% leakage per day isn't critical unless you live somewhere where you don't receive any sun or wind for weeks at a time.

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Re: 15KWh? - disintegrate following an impact.

Its a huge issue.

in the dim distant past (about '80) i recall being talked at in college about JET, which used a big fuck off flywheel to store energy - all the numbers have long since eveporated (i just recall them being mind boggling), but i do remember that the building was sited so that in the event the flywheel got away, it was far enough away (miles and miles) from any population centres, as a flywheel going through bristol would have killed thousands.

and further why MVA for PV and wind? a couple of kva would do it for britain :-) the sun dont shine and the wind..... well it's never the right _kind_ of wind.....

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Re: 15KWh?

My take is that the 15KWh figure was selected precisely because it is the same sort of storage density as lead acid batteries; given the choice, a kinetic energy store is preferable to a chemical one, simply because of the toxicity of the latter.

My take is that the 15KWh figure was selected precisely because it is the same sort of storage density as lead acid batteries; given the choice, a chamical energy store is preferable to a kinetic one, simply because of the tedium of spending all morning pulling bits of a busted flywheel out of ones face.

potato poe-tah-to i guess

there fixed it for you.

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Re: 15KWh?

> unless you live somewhere where you don't receive any sun

Wow must not been a Brit that wrote that. Oh well look on the bright side (haha) if the UK's weather wasn't so dreadful they might never have had so many colonies.

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Anonymous Coward

Re: 15KWh?

The ones we have are 300kW and 500kW Caterpilar devices.

The flywheels can hold the load for about 30 seconds - long enough to ride out glitches and allow time for the integrated diesels to start.

Contrary to popular belief vacuum-operated flywheels utilising magnetic floating bearings (no contact) do require annual maintenance and during that period we get exposed to the absolutely shitty power feed which led to the UPSes being installed in the first place, so a lot of critical stuff ends up being shut down.

There's certainly an opportunity for some enterprising outfit to sell dual flywheel setups for full redundancy.

The units we have cost about £500k apiece - and paid for themselves in less than 3 months, thanks to

speeding up spacecraft instrument qualification exercises by a factor of 20 (they didn't have to constantly start over). Allow space for a 40 foot shipping container - and they're very quiet while the diesels are running but startup can irritate the neighbours, so placement is important.

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Trollface

Re: 15KWh?

"Thinking of the mess these things would make if there was an accident (if, say, used in a vehicle)."

Cars have had flywheels inside them for about a century now...

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Anonymous Coward

Re: 15KWh?

Car flywheels are only there to maintain the torque between piston firings. They typically weigh less than 10kg and only turn as fast as the engine.

The flywheel in this weighs 340kg and will spin at least one order of magnitude faster than a car flywheel (I could calculate it based on the flywheel size and 15kWh of energy stored but its late and I need sleep).

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Re: 15KWh?

http://inhabitat.com/flybus-new-hybrid-bus-uses-flywheel-instead-of-battery-to-store-kinetic-energy/

Hmm?

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Re: 15KWh?

The problem is that basic lead acid batteries have a very poor duty cycle as they do not like to be discharged. The result is that you have to build a setup where you do not discharge the batteries to much before you charge them up again. For a basic car battery its best for the discharge to be no more that a few percentage points. For batteries that do support depth discharging its still best to only discharge by about 50% if you want to get the most life out of them.

So it you want 15KWh of battery capacity you need to install 30KWh+ of batteries.

A lot of background can be found at http://www.windsun.com/Batteries/Battery_FAQ.htm

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Anonymous Coward

Re: 15KWh? == 13kg TNT

This is called regenerative braking. The bus doesn't use a flywheel for getting from A to B. What it does is use the braking to spin a flywheel up and then when it needs to start again it uses the energy from the flywheel to begin to move. The flywheels are typically heavy with a spin of a couple of thousand rpm.

The flywheel in this project weighs 340kg and will have to spin somewhere between 15,000 and 30,000 rpm depending upon the flywheels size (radius).

Should the unthinkable happen and the flywheel disintegrates it will instantly release the same energy as 13kg of TNT. This is not something I would want outside my home or any home in the vicinity.

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Re: 15KWh?

simply because of the tedium of spending all morning pulling bits of a busted flywheel out of ones face [and other tiresome comments to this effect]

Right, what we need is a perfectly safe energy storage system. Oh, wait, there isn't one, because the point of an energy storage system is to store energy. Any time you have a sharp energy gradient, you have the potential for a Bad Thing. Talking about uncontrolled energy release in qualitative terms, rather than quantitative ones, is just handwaving.

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Anonymous Coward

Re: 15KWh?

> Right, what we need is a perfectly safe energy storage system.

There is safe and then there is a 340kg flywheel spinning at somewhere between 15,000 to 30,000 rpm (or even more).

This will have the same energy potential as 13kg of TNT and if it goes wrong it will release all of that energy in an instant. The energy discharge gradient will be vertical, just like TNT.

A battery storage system will not be able to release the stored energy instantly because the speed of discharge is limited by the speed of the reaction within the batteries. It might overheat and catch fire, but it will not be an explosive event.

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In which axis?

Something in my gut says flexible won't scale easily - the dynamic system may well stabilise itself in the plane of rotation, I can't help but think uneven perimeter mass distribution could go critical then catastrophic pretty quickly. Maybe it is having heard my washing machine spin cycle with a pair of jeans, but I suppose I'm thinking being flexible means it's more likely to be off-axis slightly, and bad things happen.

Happy to be proved wrong, of course, but I fear scaling will just amplify the problem exponentially!

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Anonymous Coward

Re: In which axis?

The theory still holds, though - even then it will have changed shape. Permanently..

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Childcatcher

Re: In which axis?

Containment is an issue but if you have containment for a vacuum it will only need small improvements to make it suitable to contain disintegration. I would be more concerned about mounting the device in a vehicle. It would have to be flexible to prevent reaction with the flywheel but then coupling to the power supply is near impossible.

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Happy

Weebles Wobble But Energy Has to Go Somewhere

Interesting. It is a nice idea and I'm very interested to see how they deal with vibration, flex and the inevitable harmonics in the full size model. Just watching the cute little desktop model made my brain dizzy thinking about the forces generated on the frame and bearings. I don't see why the flywheel itself wouldn't be reasonably sound in use but I'm not sure about the affordability of the bearings that can handle dynamic/unpredictable loads they will face. The casing and the foundation/mounting assembly will be interesting as well. Wonky spinning weight will certainly make for some wild noises: Like an inch worm with palsy would be my first guess...

I'm going to send a few bucks their way & see how they do. It's nice to see people actually trying something instead of just ditching the idea because of naysayers & potential problems.

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Unhappy

Re: Weebles Wobble But Energy Has to Go Somewhere

Boo. I didn't realize they already reached their goal.

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Re: Weebles Wobble But Energy Has to Go Somewhere

I agree, the energy has to go somewhere. If the flywheel flexes the energy to flex the flywheel becomes heat.

Suspend the flywheel on magnetic bearings? Permanent magnets? Else more energy lost.

Spin in a vacuum? More energy lost there creating and maintaining the vacuum.

What are you going to do in an earthquake? Vibrations in the floor used to be enough to disturb early hard drives.

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Boffin

Re: Weebles Wobble But Energy Has to Go Somewhere

Some of those problems were solved in the seventies -- a flywheel doesn't have to have the same stability as a hard drive, although you're right that there will be energy loss.

Indeed, even the "flexible" aspect was done in the seventies, although the designs I saw had the fibers spinning radially out from the axis, rather than wrapped around the circumference. Bearings, vacuum containers, yes, this is old technology probably re-written with modern materials.

So probably most of your questions have been dealt with. The main questions are whether, even after all that, will the energy density still be good enough to make this worthwhile.

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It does not work!

(I'm not talking about the flywheel here, but El Reg's streaming method. I have reloaded a bunch of times, and stuff, but nothing comes from it; only the central icon shows a rotating arrow ... ... sitting on Chrome on Linux.)

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Anonymous Coward

Re: It does not work!

Still, the twirly thing is much nicer than the old error three thousand and something that used to come up for all Reg videos.

Chrome / windows 7.

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FAIL

Re: It does not work!

Opera / iOS same... disappointing that a tech site gets details like that wrong.

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Re: It does not work!

"This video does not exist" according to YouTube.

I'm guessing that this is what they wanted to show or possibly this.

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Re: It does not work!

You really aren't missing much in this video. It is 1:17 long, and spends that time telling you that a motor is also a generator, and that it takes energy to make something spin. That it is it. It is wholly generic, except for the last two seconds when the voice-over tells us "we have developed a new way of making fly wheels, then it fades to black.

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Re: It does not work!

Works for me, Firefox 3.6.24 64bit on SUSE 11.3

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Perennial problem

Somebody did this with a motor car-size "motor" a few years ago and got to the stage of having a working prototype but further development collapsed through lack of funds.

The prime mover behind the technology whinged, naturally, that the vested interests did not want to get involved.

Not being an engineer though I bounced this idea of an engineer whose immediate question was "What happens when you want to go up a hill?"

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Anonymous Coward

Re: Perennial problem

"What happens when you want to go up a hill?"

Personally, I just find a suitable hill to go up on and satisfy my hill ascension urges. YMMV. HTH.

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Re: "What happens when you want to go up a hill?"

It's easier to build the house in situ than it is to build it first and then locate it.

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ql
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Odd for a kickstarter

This is of interest to me as we are off grid. However, given the choice of a passive chemical battery with no moving parts and something that has to run in a vacuum to close tolerances etc.,, I know which option I'll take. Now if they want to work on getting the nickel-iron battery into shape, that seems interesting. But as there is little patent potential (haha!) in it, as it was invented yonks ago, it's unlikely to be developed through the standard western greed model. See http://opensourceecology.org/wiki/Nickel-Iron_Battery

My requirements as one off grid are not necessarily the ability to store power for very long periods of time, just enough time when power from my few solar panels and my small turbine wane. Five days is acceptable. Given what I have learnt about the joys of running the mechanical wind turbine over the different joys of managing the passive lead acid battery, I know I would not choose a dynamic option such as a flywheel. By the way, my battery bank is a smidge over 15kwHrs.

I would much rather have a NiFe battery that can take un-ideal charge states when power comes in, and most of all, I would rather the battery bank did not deteriorate the way lead acid ones do, leading to replacement after 5-7 years even with careful management. I always laugh like a drain when battery how-to's talk about charging a battery using so-many amps at so-many volts when in the real off-grid world you're simply grateful for ANY amps at ANY voltage that flow in.

S

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Re: Odd for a kickstarter

Ah you named your turbine - how sweet!

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Re: Odd for a kickstarter

You're confused, a kickstarter project is not intended to actually work or deliver anything useful, just keep some post grad dicking around with their pet hobby, subsidised by schmucks who think they are changing the world by pledging money from their tablets.

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Re: Odd for a kickstarter

"unlikely to be developed through the standard western greed model"

Fear not. I'm sure the noble Cubans and North Koreans will get around to it Real Soon Now.

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ql
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Re: Odd for a kickstarter

"Fear not. I'm sure the noble Cubans and North Koreans will get around to it Real Soon Now.

House Rules "

Ah - symptomatic binary idiocy. Move along, nothing to see here.

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ql
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Happy

Re: Odd for a kickstarter

"Ah you named your turbine - how sweet!"

It's not what I called it yesterday, up the tower in a breeze! But it does make me wonder what I meant...

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FAIL

Scam Bovine Excrement.

Self balancing fly wheels have been in use since the late 1800s.

look at the mechanism on the end of any large grinding wheel,(small beads in a track).

The orientation of the flywheel is absolutely critical unless in a horizontal East West fixed installation, the Coriolis and Gyroscope effect of large flywheels would damage or destroy the bearings on any type ( magnetic, air or ball-race) .

Look up Coriolis ( http://en.wikipedia.org/wiki/Coriolis_effect ) and (http://en.wikipedia.org/wiki/Gyroscope )

The losses even in a vacuum with magnetic bearings would unlikely be as low as 2 percent as quoted. the sums do not add up !

This concept is just another perpetual motion machine (http://en.wikipedia.org/wiki/Perpetual_motion)

Trev

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You want to know if it'll work?

Ask Williams F1.

Their KERS (Kinetic Energy Recovery System - for those who do not follow F1) solution is a flywheel design and they've spent a lot of time, effort and cash in getting it to work properly. They probably know more about storing energy in high speed flywheels than anyone else around.

IIRC they had to resort to wrapping the things in bonded carbon whiskers as reinforcement to stop them disintegrating[1] and that's on a fairly small object. With that from the real world, I'd be a tad sceptical about a larger object made of anything less puissantly rigid.

[1] Which leads to the other problem. Making a casing strong enough to contain the mess when it does come apart at eye-watering revolutions. Apparently the energy release involved when that happens makes most explosives look rather unimpressive, even on their little device.

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Re: You want to know if it'll work?

You mean it's more impressive than a Trent 900 in a blade-off event? :-)

Ohhhhhhh, I want to see THAT! :-D

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Re: You want to know if it'll work?

Although F1 cars have another couple of pressures (total mass, and total size) which tend to encourage very small flywheels (counter rotating to deal with gyroscopic forces) at very high speeds.

IIRC The Joint European Torus used to use a fairly hefty flywheel to power one of their diagnostic lasers...

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Anonymous Coward

Re: You want to know if it'll work?

"more impressive than a Trent 900 in a blade-off event?"

Shhhhh.

Simon says "no need to tell the workforce anything about it, because it didn't happen". Even though one such incident (Trents have been several in the last few years) made it into the columns of something called the Sun, as well as the usual aviation industry papers.

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