Electric cars are a pipe dream

[billvon]

No. When super flywheels fail they are not hard to contain as they are made of thin fibers that turn into dust inside the containment chamber.

It doesn't matter what they turn into. If you have a 24kwhr flywheel and it disintegrates it gives up all that energy at once. If it comes apart over the course of 5 seconds, that's 17 megawatts of power being dissipated in a small space. Small volume + large expenditure of energy = tremendous heat and thermal expansion (i.e. explosion.)

You can't get away from this by clever design as long as you attempt to contain the flywheel. It's basic thermodynamics. You CAN, however, allow the flywheel to experience uncontained failure; that ejects pieces that then dissipate their energy through friction with the outside air. Of course, it would also contain far more energy than an array of shotguns going off, so they better be pointed in the right direction when they blow.

Breaking those super strong carbon fibers into tiny dust specks takes a lot of energy. Some were wound hoops of fibers and others radial brushes of short equal length fibers.

Yep - but it doesn't take megawatts.

Yes you would want to gymbal the flywheel in the "pitch" direction so going up or down a hill would not try to lift the front or back wheels from the ground, but boy would the "corner well" without the car rolling over.

So you'd need a universal joint and a separate gymbal suspension for the flywheel/gearbox assembly, or a suspension, gearbox and motor/generator on a separate gymbaled suspension. Doable but complex.

Also, if you constrain it in yaw, you not only get precessive forces (which is what I figure you're referring to with the 'corner well' comment) but also resistance to turning, which would be problematic.

Once you start thinking of storing wind energy for hours of later delivery, yes you had better put the wheel under ground for safety, but in car or even bus size units they can fail without hurting anyone.

I'd agree for hybrid applications, but for purely flywheel powered vehicles there's just plain too much energy to dissipate.

 

[Billy T]

It doesn't matter what they turn into. If you have a 24kwhr flywheel and it disintegrates it gives up all that energy at once. If it comes apart over the course of 5 seconds, that's 17 megawatts of power being dissipated in a small space. Small volume + large expenditure of energy = tremendous heat and thermal expansion (i.e. explosion.)

You can't get away from this by clever design as long as you attempt to contain the flywheel. It's basic thermodynamics. ...

Let's put some numbers in this "basic thermodynamics":

A well designed for light weight lithium Ion battery can store about 700,000 joules per kilogram*, so let’s say the superflywheel is storing 1,000,000 Joules per kg. There are 3,600,000 Joules per kw hour. So the fly wheel weight is 3.6 Kg for every Kw hour stored. Then your 24Kw hour storage unit weighs 86.4 Kg.

Each 1 joule is 0.239 calories so each Kw hour (3,600,000 Joules) is 860,400 calories, or your 24Kw hour storage units has 20,649,600 calories to heat 86,400 grams. That is 239 calories per gram. If the specific heat of the super fly wheel is 0.5, half that of water, (surely more, 0.7 ?) then the temperature rise of the dust and containment wall it slams into is 478 degrees C on average.

Initially the dust is much hotter – At least glowing a dull red in the vacuum** and the wall temperature rises is not more than 250 degrees C but may rise to a peak of 450C eventually. Not much of a problem, certainly no wall failure, but don’t put your hand on the wall for at least 15 minutes until it cools down some.

* From: http://ask.metafilter.com/141901/What-would-be-a-good-battery-to-use-for-renewable-energy-generation

** Dust is not a good thermal conductor, especially in vacuum, so there is considerable radiative transfer of energy to almost all the chamber wall - relatively uniform heating of it.

BTW they fail completely, I think, in small part of a second - turn to dust at the speed of sound in the fiber. I think when the stress brakes a fiber a shock wave travel along it releasing the strain and makes the dust even before it hits the wall but I am not sure of any of this. Not that it is of any importance, but the peak power is probably >100megawatts, not just your 17 megawatts when strain is turning into heat, mainly, I think, due to the shock wave heating.

 

[ElectricFetus]

I think flywheels are best left to stationary applications, considering the gyroscopic forces they will put on the car, needs for advance even superconducting magnetic bearings to hold significant amounts of energy, and what happens if they fail catastrophically. I once saw a 1 million rcf centrifuge exploded and blow straight up through a science building ceiling and almost into the next floor... well I did not witness the event its self but I saw the damage caused by it at least.

Than again if a fly wheel could be gimbaled such that its gyroscopic forces would prevent a car from tipping it would provide incredible stability to the car, heck would make a motorcycle as stable as a car!

 

[Billy T]

I think flywheels are best left to stationary applications, considering the gyroscopic forces they will put on the car, needs for advance even superconducting magnetic bearings to hold significant amounts of energy, and what happens if they fail catastrophically. I once saw a 1 million rcf centrifuge exploded and blow straight up through a science building ceiling and almost into the next floor... well I did not witness the event its self but I saw the damage caused by it at least. ...

They are being used in a few F-1 cars now and I think without any gymbals as they don't go up and down hills. They permit up to 30% better fuel use as they recover the braking energy and can increase the acceleration, well above what the motor alone can do, as car comes out of the turn. I also assume, but article I read (link in first post) did not say that on dry race track they may be able to take sharp curves faster without danger of roll over.

I think modest fore/aft (pitch) gymbals would be needed in a car used on streets or bus that climbs hills. Super conducting magnetic bearings, I think, are only used with larger units.

My father was an MD and showed me (as a warning) an oxygen bottle wedged in a second hospital wall - after it had flown thru the first wall. The screw on cap protecting the valve was forgotten or lost and when it was knocked over the valve sheared off (on steel bedpost foot, I think). His plan worked - I always keep any such tanks well chained to a table or vertical water pipe, etc.

 

[ElectricFetus]

They are being used in a few F-1 cars now and I think without any gymbals as they don't go up and down hills. They permit up to 30% better fuel use as they recover the braking energy and can increase the acceleration, well above what the motor alone can do, as car comes out of the turn. I also assume, but article I read (link in first post) did not say that on dry race track they may be able to take sharp curves faster without danger of roll over.

I think modest fore/aft (pitch) gymbals would be needed in a car used on streets or bus that climbs hills. Super conducting magnetic bearings, I think, are only used with larger units.

I did in fact comment on the advantages they could provide and I was already aware of their use in race cars (can read wikipedia like anyone else can thank you very much). The race car Flybrid KERS can store 400 kj or about as much energy as the engine gives off in ~0.6 seconds (~750 kw engines). Certainly that extra acceleration is worth it for a race car from a 25 kg package but is certainly not viable as a power supply on its own. A tesla roadstar consumes ~600 kw per mile and powered by a race car Flybrid KERS would give it a range of 2/3 of a mile. To get 100 miles would require the ability to store 16.7 kwh or 60 Mj.

If we were to make a fly wheel power supply for a car: if it spun at 60,000 rpm, the fly wheel alone would need to weigh 150 kg (assuming 20 cm radius using a cylinder flywheel), this is not included the weight of the vacuum chamber, the power extracting and inserting system or the magic frictionless bearings needed to support what we are assuming is a flywheel with no energy loses.

Now the road system stores 530 kj and weighs 27 kgs, compared against their 400 kj race car system which weighs 25 kg, we can assume very roughly that each extra kg stores 65 kj. If we wanted a system that could power a car for say 100 miles, assuming a very light and efficient car that consumes only 600 kj per mile, than we would need a fly wheel system that weighs ~941 kg.

So in conclusion, fine and dandy for hybrid applications, but much faster flywheels with far less static losses would be needed for applications as a complete powersource in a car.

My father was an MD and showed me (as a warning) an oxygen bottle wedged in a second hospital wall - after it had flown thru the first wall. The screw on cap protecting the valve was forgotten or lost and when it was knocked over the valve sheared off (on steel bedpost foot, I think).

Good now we know what to expect for cars operating on compressed gases, just a note we expect reduce safety problems for battery powered cars verse gasoline or any other alternative. Many batteries in hybrids and EV are not capable of thermal runaway or rapid discharge nor are they as prone to combustion or exploding like diesel, gasoline, natural gas or hydrogen.

 

[Billy T]

To electric fetus et. al. I have never advocated pure super flywheel cars, but do think that is possible with buses which stop and start a lot each mile so would really benefit from an efficient breaking energy recover in unit that can easily run five million cycles with no damage. That would kill even 20 sequential sets batteries. Perhaps every fifth stop is a passenger exchange point where the bus remains a couple of minutes for passengers to transfer between buses. There is a light post like recharge pole at these stops and fact that the rate of recharge of flywheel can be 20 times or more faster than batteries mean that a two minute stop is like recharging a battery for 45 minutes. - Not feasible many times each day for a battery powered bus. Larger flywheel units in buses could be recharged only at each end of the route while driver takes a 15 minute break.

Certainly small super flywheel units could be in hybrid cars, instead of batteries but I think there is a chicken and egg problem - they would only be economically attractive if produced in large volume. For this reason and because I want more people to use buses in the city I lend to support sugar cane alcohol for fewer and smaller multi-fuel cars in the city as that is slightly negative net CO2 production when only sugar cane alcohol is used and gives jobs to many in the third world who are unskilled and currently unemployed (no or little cash earned) - converts them into customers of higher tech goods.

Converting an existing car to be triple flex fuel (alcohol, natural gas or gasoline) is much cheaper than making a new battery hybrid car like the Volt. I think the subsidies ($7500 + more from some bankrupt states) are taking the US down the wrong path. Better to use that taxpayer's money to make buses free at off peak hours and tax more low efficiency and non flex fuel cars to make free buses at off peak nearly tax-neutral if that is feasible. (I have not tried to evaluate that.) At least get 90+% of the growing retired population off of public transport during peak hours.

PS I did not try to check you numbers but think (from reference given) that you can store a million joules per Kg in a super flywheel.

 

[adoucette]

Better to use that taxpayer's money to make buses free at off peak hours and tax more low efficiency and non flex fuel cars to make free buses at off peak nearly tax-neutral if that is feasible. (I have not tried to evaluate that.) At least get 90+% of the growing retired population off of public transport during peak hours.

NO.

Buses are not only very impractical as a solution but are HIGHLY inefficient turning in the worst passenger miles per gallon of any solution.

 

[Billy T]

... I was already aware of their use in race cars (can read wikipedia like anyone else can thank you very much). ...

MY source was The Economist at http://www.economist.com/blogs/babbage/2010/07/techview_electric_cars_crossroads

I rarely search for information - usually just post from memory or recent articles that have been sent to me. I still have not read what wiki said on super flywheel. As I mentioned in earlier post all of my enthusiasm for them comes from personnel contact with one of their pioneers, a colleague and friend about 30 years ago.

 

[Billy T]

NO.

Buses are not only very impractical as a solution but are HIGHLY inefficient turning in the worst passenger miles per gallon of any solution.

Not the supper flywheel buses I spoke of - they have infinite passenger mpg. Did you read any of my posts recommending them? I also mentioned, more than once, that they should be free during off peak hours - that helps put more people on them - increases their passenger miles/ mile.

BTW, buses can be very practical. I don't own a car (wife does however). I use the bus or metro. The buses have special lanes and even with their stops are much faster than driving your car in even partial rush hour in Sao Paulo - As well as are free to anyone over 60 years of age. Taxi cabs with passenger can use the bus lanes too. I, being somewhat liberal, like what it says on the side of most buses.Translated that is something like: "Transportation is the citizen's right and the government's duty."

It is not unusual to see a dozen buses, one immediately behind the other in the bus lanes. They are color coded by areas served so you immediately know if a frequent user which is yours. Also many of the stops have electronic displays that tell you by bus number the buses that will arrive in the next few minutes. - This lets the people order them selves to be on the curb only if their bus is one of the next to come and speeds boarding. There are so many that if I am only going a km or so, one I can use will arrive in less than a minute. You can not park your car that quick - very practical and free to me (as is the metro).

 

[adoucette]

Not the supper flywheel buses I spoke of - they have infinite passenger mpg

Not possible.

BTW, buses can be very practical.

They can be if where/when you need to go is where/when they are going.
Trouble is that is frequently not the case for much of the population.
In our Suburban based population the bus stops simply can't be very convenient because the population density doesn't support it.
Which means you have to drive to a bus parking lot to then ride the bus in, but once people are in their car they are much more likely to just drive in.
Worse, the buses have to keep running fairly frequently even well past rush hour because while most people get off from 4 to 6 (causing you to need to buy and staff a lot more busses than you normally need), there are some who won't get off all the way till past midnight, causing your average passengers per trip to drop down into the single digits.

The buses have special lanes and even with their stops are much faster than driving your car in even partial rush hour in Sao Paulo -.

And thus you prove you are wrong.
If buses WERE practical there wouldn't be a rush hour.
And even though the state increases the traffic on the car lanes by dedicating an entire lane to buses, people still, by a HUGE margin, opt for the car because it is so much more practical/convenient.

As for efficiency, they suck.

Portland, which has relatively high usage still only came out at 38.8 Pass-mi/gal, easily exceeded by any Hybrid car with only one passenger and blown away if you carpool with just one other person.

http://saveportland.com/Car_Vs_Tri-Met/energy-cost-death-02d.htm


http://en.wikipedia.org/wiki/Fuel_efficiency_in_transportation#cite_note-37

 

[Billy T]

To adoucette:

I will certainly admit it is possible, even easy in a rich society, to structure the society so that buses are impractical - not attractive as they don't go often (as low ridership) or near the suburban sprawl of homes that makes the US by far the greatest consumer of gasoline per capita - I don't see how you, concern with passenger mpg can call that efficient.

In Sao Paulo the buses are almost always jam packed - ~60 seated and 40 or more standing in the isle.* With one following closely behind another there are more more people moved on the main roads by buses than cars do, by far.

You can not dam buses in general because the US is stupidly set up for energy efficient transportation. Probably the US uses more fuel per passenger mile than any other country in the world and as that was YOUR standard of comparison, where does that rank the US?
-------------------
* I almost always get on as I enter by the exit door - quasi permitted as I don't need to pass the fare collector. Some people may not get on and must wait 2 or 3 minutes for the next bus they can use as even the stair wells are packed with 6 or 7 people standing in each. Sometimes, but rarely, people can't get thru the packed isle in time to get off at the stop they wanted. Most know to start heading for the door a few stops early. I don't think there is any road surface transport that moves more people or passenger miles per gallon of diesel fuel than the buses of Sao Paulo do.

 

[adoucette]

I will certainly admit it is possible, even easy in a rich society, to structure the society so that buses are impractical - not attractive as they don't go often (as low ridership) or near the suburban sprawl of homes that makes the US by far the greatest consumer of gasoline per capita - I don't see how you, concern with passenger mpg can call that efficient.

Our houses are where they are and they can't be moved and so you have to deal with "What Is", not what you wish it to be.
With things that cost so much and last as long as housing (and all the related infrastructure like schools, shops, hospitals, fire, police, entertainment centers built nearby to support these homes) and with our rapidly growing population it isn't likely to change any time soon and so while Buses can work for some people in certain high traffic corridors, it is not a very workable solution for transportation in a Suburban oriented population.

In Sao Paulo the buses are almost always jam packed - ~60 seated and 40 or more standing in the isle.* With one following closely behind another there are more more people moved on the main roads by buses than cars do, by far.

Not seeing it Billy, indeed it seems very auto centric.

http://www.der.sp.gov.br/servicos/mapaonline.aspx

 

[Billy T]

Our houses are where they are and they can't be moved and so you have to deal with "What Is", not what you wish it to be.
With things that cost so much and last as long as housing (and all the related infrastructure like schools, shops, hospitals, fire, police, entertainment centers built nearby to support these homes) and with our rapidly growing population it isn't likely to change any time soon ...

Yes. That is unfortunately true. Gasoline will be $20/gallon* before the US can get to even European average population density. That is why I have often posted that the US is poorly set up for the high cost fuel era that is coming.

Americans will eventually pay very dearly for having had gasoline cost $2/gallon when the rest of the world was paying the equivalent of $5/gallon and thus buying smaller cars, living more in urban high rises, building rapid transit systems and passenger railroads.
------------
* In current value dollars. Much more in nominal dollars of the era - Perhaps $50 to $150/gallon. Exactly how much depends on how much of the QEx printing press dollars can be removed. (Holders of them will not just give them up for nothing so I expect most will eventually be in the circulating money supply. )

 

[adoucette]

Americans will eventually pay very dearly for having had gasoline cost $2/gallon when the rest of the world was paying the equivalent of $5/gallon and thus buying smaller cars, living more in urban high rises, building rapid transit systems and passenger railroads.

Not likely.
The things we have been discussing in this thread will eventually cap the price of transportation.
Probably at not much more per mile than we are paying today and quite possibly less as we move more on to an electrical infrastructure.

Arthur

 

[billvon]

Each 1 joule is 0.239 calories so each Kw hour (3,600,000 Joules) is 860,400 calories, or your 24Kw hour storage units has 20,649,600 calories to heat 86,400 grams. That is 239 calories per gram. If the specific heat of the super fly wheel is 0.5, half that of water, (surely more, 0.7 ?) then the temperature rise of the dust and containment wall it slams into is 478 degrees C on average.

Right, that's if you can transform it all into heat. By comparison, a pound of TNT releases only about 2 megajoules compared to the 86 megajoules you're releasing here - but you certainly wouldn't want to be in the car when a pound of TNT is detonated inside. The key is:

but the peak power is probably >100megawatts

Peak power gives you rate of expansion of heated material, which is what causes the shockwave in an explosion. So IF you can transform all that energy safely into heat, then it's not a problem. But transforming all that kinetic energy into heat while containing the resultant "event" is not a trivial problem.

 

[adoucette]

The paper discusses failure modes for composite high speed flywheel-rotors for
energy storage application and an optimization of the energy distribution between
rotational and translational energy of the debris

http://www.aspes.ch/publications/EnerComp2.pdf

Also:

http://www.voxsolaris.com/flywheel.html

funny:

The reader is probably familiar with washing machines that walk. If a flywheel had as much as a gram more on one side than the other, the battery would do more than walk. It would run like a bat out of hell and as it did so, it would teach the jackhammer a thing or two about how to be a proper jackhammer.

 

[Billy T]

Right, that's if you can transform it all into heat. By comparison, a pound of TNT releases only about 2 megajoules compared to the 86 megajoules you're releasing here - but you certainly wouldn't want to be in the car when a pound of TNT is detonated inside. ...

Glad you accept my analysis. More important is the experimental observations that the stored energy is converted into heat before the dust even hits the wall. Presumable this is due to shockwave traveling in the fibers as the strain is released. The stronger the fibers are, the better the wheel is for storing energy AND the greater the shock heating when it fails:

Please read page 169 at this link: http://books.google.com/books?id=nt...=onepage&q=failure of super flywheels&f=false

It speaks of my APL/JHU colleague and friend’s early (1969 & later) experiment on super flywheel failures. Because it is a .pdf file, I cannot copy the Nov 1974 Popular Mechanics text but here are a few parts I re-typed:

“…even if all the fibers of a super flywheel were to fail at the same time there would be no explosion…”

“failures were accompanied by a sudden flash of heat of several hundred degrees…”

“As Rabenhorst hoped, when filaments of his super flywheel fatigued and shattered, they were reduced to dust before they hit the wall …

SUMMARY: Both the analysis I presented in post 1964 and dozens of experimental "spin to destruction" observations show that containment of total immediate failure of a fiber type super flywheel is not difficult.

PS in the explosion of TNT, the energy is released in a gas to produce a huge immediate pressure increase. That pushes most every thing near it out of the way. In the fibers that fail the energy is released in the fibers by shock heating of them that also turns them to dust.

 

[Stoniphi]

I read a Sciam article many years ago that went on about San Francisco's having a fleet of flywheel - powered buses, unless my memory has failed me again.

It was a big deal due to the regenerative braking for power recovery.....it may have been when Billy's friend was doing that research and the US was looking at flywheels as a static storage solution for solar generated electricity.

 

[Billy T]

“… On May 20, 2011, Royal Dutch Shell made its final investment decision on the world’s first floating liquefied natural gas (FLNG) vessel, a development that promises to open up a large number of stranded natural gas fields to development. … Advertised as the longest floating structure in the world, Shell’s first FLNG facility will span more than four soccer fields, weigh more than six times as much as the world’s largest aircraft carrier and tower seventeen stories above the water. {BT comment: Almost certain it is the largest thing that ever floated, except for ice}

By cooling natural gas to minus 260 degrees Fahrenheit at a liquefaction facility, it condenses into a liquid that’s roughly 1/600th its original size. In this form, large amounts of natural gas can be safely transported overseas in specially designed ships. Re-gasification terminals warm the LNG to return it to its gaseous state before pipelines transmit the product to end users. …”
From: http://www.investingdaily.com/tes/1...gx=d.kac,stid.6544,sid.250664,lid.12,mid.3720

Here is Shel's video on it: http://www.youtube.com/watch?v=nVs9qjF5Uzo&feature=relmfu

BT comment: Forget about EVs – the car of the future runs on Natural Gas, which given the way electric power is now and for decades to come produced, is less polluting.

If not that then electric motor and super flywheel which can do 10,000 deep discharge cycles with no lose of capacity and has higher energy density than a battery, more rapid recharge capacity, and is made from cheaper materials like carbon fibers, steel and copper for the motor, plus could absorb all the energy in a panic stop from high speed - no battery can do that without making lots of battery destructive heat for very low, if any percentage energy recovery.

Question: What is best "working fluid" for an engine operating between ambient water at 32F or above and about -245F? (273 & 119.26K) So max efficiency is 1-(119/273) = 56%, better than a fossil fuel power plant but efficiency is not much important when the "fuel heat" is free. Efficiency is better >60% in the summer when water is not with ice in it. High efficiency does reduce the capital cost for any fixed max power level.

 

[1337spb]

Hopefully some fusion power to charge up the batteries.

Petrol stations could also be modified to supply the batteries so instead of charging them up you swap them (I know they are heavy but a robot fork lift could do it or you could use the power of the car - drive over a battery and it clicks round and swaps somehow not that tricky really) .