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.
-- macrumpton, May 14 2004

Flywheel ideas http://home.earthli...adella/homepage.htm
[kbecker, Oct 04 2004, last modified Oct 05 2004]

For any reasonable energy storage in the wheel your batteries would still see multi-g forces so their construction would be really expensive.
-- kbecker, May 14 2004


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.

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.

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.
-- ConsulFlaminicus, May 15 2004


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.

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.
-- macrumpton, May 15 2004


[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!
-- ConsulFlaminicus, May 16 2004


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.
-- macrumpton, May 17 2004


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.
-- PainOCommonSense, May 17 2004


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.
-- Freefall, May 17 2004


Doesn't a flywheel wear down?
-- DesertFox, May 17 2004


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.
-- kbecker, May 17 2004


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...

Not to mention that the bearings needed to cope with the higher speeds are very expensive and sophisticated.

Of course figuring out what to do with 10 rpm of nearly unstoppable force is a challange.
-- macrumpton, May 18 2004


Kinetic energy:
E = .5 x moment of inertia x (angular speed) ^2

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)

This gives us:
E = .25 x pi x R^2 x h x density x (R^2 + r^2) x (angular speed)^2

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.

Of course, the more mass you use the more energy you'll waste in your bearings.
-- Worldgineer, May 18 2004


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).
-- oxen crossing, May 19 2004


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.
-- Kirkmcloren, Aug 14 2006


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.
-- betaray, Sep 13 2006



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