Spinning wheels [Storing energy using flywheels, not batteries] | Hacker News Reader

Spinning wheels [Storing energy using flywheels, not batteries]

economist.com

18 pointsigravious32 comments

Take home paragraph: Back on the road, flywheel hybrids that cut both fuel consumption and greenhouse-gas emissions by 30% or more appear to be only three or four years away. When they arrive, today’s coal-fired electric cars will look decidedly dirty by comparison. Roll on the day.

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"the electricity delivered during off-peak periods comes from dirty coal-fired power stations--rather negating the point of having a zero-emission vehicle in the first place."

Except these so-called dirty coal plants are still far cleaner than car exhausts, and more efficient especially if you consider the extraction and refinement processes required for gasoline. Finally, it's much easier to upgrade or replace a power plant on the grid to make it cleaner in the future than it is to get thousands of people to replace their vehicles with ones that are more efficient, cleaner, etc. Nevermind the logistics involved if we wanted to do carbon sequestration.

Off-peak power production depends on where you live. In my region we only have hydro and nuclear, my energy is (relatively) clean 24/7.

Yeah, the main problem with them is that if anything happens the "stored energy" is already kinetic energy and the flywheel can do some pretty serious damage.

The other problem is that they act like gyroscopes. Which means that depending on how you mount them, will either constantly exert a precessional force on your vehical, or really protest you making sharp turns at high speeds.

The second one can be mitigated for the most part by using two flywheels that rotate in opposite directions.

And the first is a problem with anything that stores energy. Gas can explode. Batteries can explode. Etc.

Except some things are more dangerous than others.

I think an accident causes gasoline to burn more often than explode. Even when the tank explodes I don't think it would be as dangerous as a fly wheel shattering with shrapnel flying everywhere.

Flywheels running at high speed are not made of cast iron or other things that turn in to 'shrapnel', they're made of wound filaments of carbon fibre bound with resin, usually they are designed with failure in mind. The bigger problem is dealing with the conversion of the energy in the wheel in to heat.

If we have a flywheel falling on a movable object on the floor I imagine this movable object can attain quite high speeds.

@jacquesm Does the heat problem confine it to providing only bursts of energy?

I meant on destruction of a running wheel, not on normal use.

Right. Except the smallest synchronization error between the two flywheels becomes disaster.

Why ? They don't need to be synchronized at all, as long as they're roughly spinning at the same speeds in opposite directions there is 0 effect. The only effects you'd be left with would be from the difference between the two rotational speeds. If you stop one and the other continues that's a different matter.

Besides, keeping two wheels synchronized is not the hardest thing to do, a car contains a lot of moving, synchronized parts.

Fortunately, composite materials tend to disintegrate quickly to red-hot powder once broken, instead of large chunks of high-velocity shrapnel.[1]

There's also anything built in layers, where the outermost layer will shred, bleeding off massive amounts of energy in relatively low-mass pieces, much more easily contained. Often carbon fiber, but that's just the main material I've seen for this. Dangers associated with flywheels are becoming less and less of a problem, and will only continue to do so with more research.

That said, I'd still be interested in seeing how it reacts to a hard collision. I think that quote mostly refers to over-spinning.

[1] : http://en.wikipedia.org/wiki/Flywheel_energy_storage#Advanta...

> the flywheel can do some pretty serious damage.

There is a solution to this: flywheels that use tightly wound metal tape instead of solid cores. Tape flywheels just unravel inside the casing safely when they break.

Actually, they use wire rather than tape. Powder has also been used and fails very safe but it helps if the material the rim is made of has intrinsic strength.

Such an interesting concept but some key data is missing.

How much energy is lost by using a wheel vs battery? Meaning, how much energy can be extracted from the amount of energy put in? How does that compare to a battery?

How long would a charge on a wheel last (eventually it would spin down on its own) compared with a charge on a battery?

For lead acid batteries, figure 70% of the energy you put in will come back out. Wikipedia tells me that lithium ion batteries are 99.8% efficient, but has no citation and the temperature of my phone charging heavily make me suspicious of that number. Perhaps that is a theoretical maximum.

Motor efficiency is proving elusive on the web. But let's say 90%-95% for brushless DC motors. (square that for in and out)

The trick about batteries is that if you only want to use them for intense bursts you will need a huge energy capacity. You don't normally want to charge at a rate faster than say, 1 hour to get full. If you need to store a 3 second brake stomp and give it back 5 seconds later then you are going to have about 1200 times more batteries than you needed just to store the energy (to support the current).

Here's another post with a picture of what it looks like: http://www.gizmag.com/torotrak-mechanical-kers-system-for-bu...

I can't find any links now, but after Williams created the flywheel kers system, they started talking to the London train system, who was interested in adding it to a trains in the city. Not sure who that ended up.

It's worthy noting, however, that none of the two companies ended up running the flywheel kers in real races last year or this year. KERS was only one of the rule changes for those years, and those teams decided it was best to focus on the other changes instead.

Not related to the post itself, but I think most people here would really love F1. F1 is much more about technology than anything else. I love it.

Flywheels come up every once in a while (I remember seeing them for the first time about 20 years ago).... but I wager they'll never become mainstream. The problem is the more energy they store, the more explosive they become.

http://en.wikipedia.org/wiki/Flywheel_energy_storage#Advanta...

Same kind of thing with the Dymaxion car (1930) - a 3 wheeled car that could transport 11 passengers @ 30mpg, reach speeds of 120mph and do a U-turn in it's own length. Sounds brilliant.. except what happens when something happens to one of the tires.

http://en.wikipedia.org/wiki/Dymaxion_car

Why do you state that when the article linked clearly says: "The cause of the accident was not determined, although Buckminster Fuller reported that the accident was due to the actions of another vehicle that had been following the Dymaxion closely.".

It's a pity investors bailed on the project, it seems like it was well ahead of its time, prototype failures are usually experienced behind the scenes, not in front of an audience that large and I think that they investors probably were on the money pulling out because of public perception, even if they blamed the tech, it was not the wheels that had anything to do with this, but more likely a lack of reinforcement of the main structure of the car.

As for flywheels: http://afstrinity.com/ that company (a merger of American Flywheels and Trinity Power) is probably right at the cutting edge.

Anything storing a significant amount of energy is prone to accidents, from batteries to rocks on the tops of mountains.

Flywheels are one of the few technologies that can store signficant amounts of energy and can be engineered to fail with relative grace, as opposed to say a fuel tank blowing up. Another strategy is to use many relatively small flywheels in parallel, each in their own containment vessel.

This also helps with some other engineering difficulties involving flywheels. Flywheels are ancient tech, at least 50 years old but probably much older, and if you count them as storage devices in a purely mechanical context as well then you can go back in to history quite a bit, about a thousand years.

the AFS Trinity website only mentions their car with ultracapacitors. Know of a link where they're working with flywheels?

And I feel I should point out that the accident of the Dymaxion was in a prototype with a canvas roof. The death of the driver is probably the main reason it was abandoned at the time, that's pretty bad PR-mojo.

That's the 'trinity' portion of the company, they make the control circuitry. The AFS bit is mostly research and patents, but they do engineering of composite flywheels as well.

It looks like they're 'pivoting' away from using flywheels in favor of ultracapacitors and Lithium-Ion batteries.

An older article on the topic:

http://www.wired.com/wired/archive/8.05/flywheel.html?pg=2&#...

> you can go back in to history quite a bit, about a thousand years.

What about 5000? http://en.wikipedia.org/wiki/Potter%27s_wheel

> Why do you state that when the article linked clearly says: > "The cause of the accident was not determined, although > Buckminster Fuller reported that the accident was due to > the actions of another vehicle that had been following the > Dymaxion closely.".

For the obvious reason why 3 wheel vehicles have never become mainstream.... If you work with computers you should know about Single Point of Failure. If you are cruising on the highway and get a flat with 1 of your 4 tires it's no Big Deal. How do you think that would figure with only 3.

Or another example. Why so many wheels on an 18-wheeler. Wouldn't it be awesome if a truck could do a u-turn in it's own length? Those things blow out tires all the time. But it doesn't matter because they have 18. SPOF. 3 wheel vehicles will never catch on in the mainstream. They'll only ever be the equivalent of glorified motorcycles - the ultralights on the road.

You could get all the advantages of a tadpole configuration and mitigate the risk of blow-out considerably by using two wheels at each spot side-by-side, that's fairly simple engineering and this is used on plenty of lightweight fly-over trailers.

The tadpole configuration has stability issues though, rolling it over is fairly easy if the vehicle has a high center of gravity.

The Reliant Robin solved that for the most part by reversing the arrangement putting the single wheel in front, but they still tend to overturn quit easily.

The accident mentioned above during the demonstration probably really was caused by that other car, but the ease with which a three wheeled configuration turns over most likely contributed to the severity, and in the long run would have had to be solved using tricky engineering such as a single wheel for low speed maneuvering and two wheels for higher speeds.

Here is a Reliant Robin doing what it does best:

http://www.youtube.com/watch?v=xr8SvdSzs7c

I think there is a topgear episode where they try to improve the Reliant Robin by putting training wheels on it.

Moreover, supplies of the metal are far from abundant, and are located in countries not necessarily friendly to America: the biggest reserves are in Bolivia, China and Russia.

Yeah, it's a good thing countries with all the oil for our gas-powered cars are so friendly.

That's actually in relation to Lithium, nothing to do with flywheels per-se.

Canada, Saudi Arabia and Mexico are unfriendly?

The only unfriendly countries which supply a significant amount of oil to the US are Venezuela and Russia.

http://www.eia.doe.gov/pub/oil_gas/petroleum/data_publicatio...

I read about this about 13 years ago in Discover:

http://www.mega.nu/ampp/bitterly.html

Seemed like a fantastic idea at the time, but the problem then was that the wheel would explode at high speeds. Apparently these are very challenging to manufacture.

This has been done before, there was a bus i read about on boingboing that used only kinetic energy to power it, if i remember the wheel was some 20tons.

I see your spinning wheel in a vacuum and raise you a battery drive and the dirt road behind my house.

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