Well - it IS nice to kick over a hornet's nest, from time to time...
I like this table (posted earlier):
Table 12.1 Energy-storage data.
Maximum energy-storage capability of various materials
W-hr/lbm kJ/kg Material
14,900 118,250 Hydrogen
5,850 46,430 Gasoline
2,760 21,900 Methanol
208 1,650 Silver-zinc-battery
85 675 Lead-acid-battery
14 111 Flywheel
10 79 Compressed gas and container
1 8 Rubber bands
0.06 0.5 Springs
Quite the illustration. Trick is, the infrastructure is a good bit simpler for
the flywheel than for the H2 or even gas and MeOH. Also, this figure for a
flywheel assumes... something. Likely a figure for a cast iron simple disc.
There are better ways of building a flywheel.
In fact, comments about fragmentation issues from other flywheel projects bring
up the materials issue - modern ultra-high speed flywheels use carbon fiber
wraps. There is a limiting factor involving the ratio of density to tensile
strength and modulus - carbon fibers kick steel's butt in the modulus area.
Allows much higher rotational speeds. Look at the wheels on those supersonic
cars - no Goodyears there. Similar construction - velocity of the outside
diameter of the tires for these cars reaches mach 1. Heeluva flywheel.
Especially since (look at the posting with the formulae) kinetic energy in a
flywheel is, IIRC, proportional to the *square* of the rotational velocity.
I'll stay out of the polar moment thing for now.
In another post this thread someone mentioned using Concrete and thin water
film bearings. I was reminded of a few neat toys one can occasionally find.
Seems one can polish a 1 meter granite sphere and a mating socket well enough
that a few psi water pressure can float the many-tons ball such that a small
child can get it spinning - with effort. Stopping it, well... This is likely a
better solution than mags and a vacuum bottle. The bottle (which I didn't think
of before) is only really required with ultra-high speed wheels - the multi-ton
concrete job wouldn't spin too fast (couldn't, really - no good in tension) to
store some good HP-Hours.
Boku lo-tech...
Pax,
Tony
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