h a l f b a k e r yNumber one on the no-fly list
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The big challange in energy storage is to
increase the storage density of the
medium.
Batteries are not so great
compared to other mediums like gas or
lpg, and flywheels are pretty good, but you
have to use really high (read expensive)
speeds to get high efficiency.
Making a flywheel
out of batteries adds
the efficencies of each. The Flywheel
would have to be pretty slow, but the
great weight would make up for that.
Flywheel ideas
http://home.earthli...adella/homepage.htm
[kbecker, Oct 04 2004, last modified Oct 05 2004]
[link]
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For any reasonable energy storage in the wheel your batteries would still see multi-g forces so their construction would be really expensive. |
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Flywheel batteries are actually becoming widely accepted in UPS situations and are not that expensive (when compared to the value of the equipment, data and businesses they protect). Their weak point is in the timing of the 'kick in' and the too-rapid decay of their output - they are fine for 'ripple protection' but may not be adequate where there are extended (90 seconds plus) brown or black outs. |
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It is extraordinarily clever of you to make the leap to seeing that the spinning mass could somehow be designed to carry stored chemical potential in addition to its stored kinetic potential, so please accept this pastry medal. |
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There would be issues with composition of the chemical mass - suggest that any electrolyte-based system would have far too much viscous drag and impair the potential and efficiency of the flywheel, but concentric rings of solid-type battery materials (many options here) with the connections made through soft brushes when discharge is required..... and issues with constructing the thing so that it didn't fly apart. |
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Thanks for the pastry medal, I know just
where to hang it!
It occours to me that rather than a
battery, perhaps a super-capacitor
model would be better, as it would be
better for structural (no sloshing
electrolytes) as well as favorable high
charge/discharge rates. |
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Re: the multi-G forces, the more
massive the flywheel the more energy it
stores per revolution, so this massive
design would be a fairly slow (low G)
design.
The Big challange would be the
bearings. |
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[macrumpton] The Big Challenge with a massive, slow rev design would lie more in convincing each of your clients to buy an adjoining block of land to house the thing. The 'massive' option is the result of removing your idea too early from the oven! |
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I am not saying it needs to be large, just
that it would likely be more massive
than a typical flywheel storage device. If
anything it would be smalller than a
regular battery pack since it has more
capacity. My point is that if you already
have a battery, you can increase its
storage capacity by adding kinetic
energy storage to its existing chemical
storage. |
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I knew we hadn't explored all the Flywheel capablilities.
Hey just make sure you make a nice solid room to house these dangerously explosive devices. |
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Interesting idea, but in order to make the flywheel useful at all, you need the high speed. Slowing it down to the point where current chemical storage devices could cope with the loads would defeat the purpose of having a flywheel in the first place. |
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Doesn't a flywheel wear down? |
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Recent models usually run in sealed vacuum containers and have magnetic bearings. There is absolutely no wear. Of course some electronic components can still break down, but the wheel itself has no wear. |
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Re the need for speed:
I am no physicist, but it seems to me
that a 1 lb flywheel going 10000 rpm
stores the same energy as a 200lb
flywheel going 500 rpm, or a 1000lb
flywheel going 10 rpm. Hardly an
explosive danger... |
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Not to mention that the bearings
needed to cope with the higher speeds
are very expensive and sophisticated. |
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Of course figuring out what to do with
10 rpm of nearly unstoppable force is a
challange. |
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Kinetic energy:
E = .5 x moment of inertia x (angular speed) ^2 |
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Moment of inertia for a hoop of height h, inner radius r and outer radius R:
Izz = .5 x pi x R^2 x h x density x (R^2 + r^2) |
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This gives us:
E = .25 x pi x R^2 x h x density x (R^2 + r^2) x (angular speed)^2 |
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So if we hold the dimensions of our hoop constant, then the stored energy is proportional to density and the square of speed. A doubling the density without changing geometry or a doubling of mass in the axial direction (larger h) would store double the energy for a given speed. A doubling of the speed will yield four times the energy. |
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Of course, the more mass you use the more energy you'll waste in your bearings. |
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You are right about the big
challenge being the bearings. I
love the idea of a really massive
slow flywheel, but I checked with
my cousin the bearing engineer,
and he says, "no way." The
extreme cost of merely
maintaining the bearings makes
this unfeasible; even a small
amount of wear screws up the
efficiency too much (according to
him). |
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Slow no
The real performers in inertial storage are called a compulsator. I think the University of Texas built one that contains 130 kilowatt hours of energy. They are experimenting with multi shot armor piercing cannon. I think like 5 shots a second. Tank killers. |
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Everyone seems to be thinking about using for Earth Based equipment. I think the idea would be genius for a space based weapon. Slowly charge the flywheel and the batteries with Solar power, and use the sudden discharge to power your Gauss rifle, gigawatt laser, or what have you. |
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