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# Maglev Energy Storage Cars

Energy Storage on a Large Scale
 (+6, -2) [vote for, against]

This is a very similar concept to a flywheel except that instead of levitating a rotor on magnetic bearings, we use robotic maglev cars speeding around a track instead. The track would be several kilometres in diameter and would be heavily banked to resist centrifugal forces.

The cars have regenerative brakes that release energy whenever required. Likewise whenever excess energy is available to the grid, they are sped up.

To further reduce idling losses it would be beneficial to enclose the whole track in a vacuum. This would also allow a higher maximum speed.

The energy stored would obviously be our friend œmv².

The best way to store a lot of energy would be to maximize V since total energy stored is proportion to V squared.

The limiting factor to speed is probably the forces exerted on the track by the hurtling cars..

So lets say we have 100 cars running round the track each weighing 100,000 kg (about 220, 500 lbs). Lets be optimistic and estimate the speed to be 3,600 kph/2,237 mph/1000 m/s (I know!). So our energy stored is 100 x 0.5 x 10^5 x (10^3)^2 = 0.5 x 10^2 x 10^5 x 10^6 = 5 x 10^12 Joules / 3.7 x 10^12 foot pounds.

(Or 1.2 Kilotons of TNT, but why would we measure this in Kilotons...)

This is equivalent to 1.4 million Kwh. So quite a lot of leccy. If the turnaround efficiency was 100%. Which it wouldn't be..

Someone is going to tell me they can't go that fast. I just know it..

The centripetal force would be

F = mv²/r

So given a radius of 2 km, the force would be:

F = 10^5 x (10^3)^2 / (2x10^3) F = 5 x 10^10/(10^3) F = 5 x 10^7 Newtons

F = 50 MN / 11.24 million lbs

Uh.. thats actually quite a lot.. and the cars would be dealing with a force of ~50g.

 — DrWotsit, Jun 14 2007

Extra options to make it marketable Naked_20women_20sho...20naughty_20monkeys
[methinksnot, Jun 14 2007]

Kiritimaticentrifugomobile Kiritimaticentrifugomobile
Don't break a finger trying to type it [methinksnot, Jun 14 2007]

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As far as I know, the limiting factor for flywheels is rim speed and not rpm. But I think you are safe as this is a little bit faster than a maglev could travel.
 — Ling, Jun 14 2007

 The limiting factor, indeed, isn't the top speed. Over a radius of several km I think the maglev track wouldn't be too difficult to engineer to restrain forces of cars passing at 1000m/s.

Maintaining a hard vacuum may well be your limiting factor. And I don't know what kind of magnetic drag you can expect at that speed.
 — elhigh, Jun 14 2007

 Simple!!?? This is the half bakery, man! If anything this idea is too simple.

Needs more monkeys.
 — Galbinus_Caeli, Jun 14 2007

 .. genetically engineered pirate monkeys.

Feed 'em custard.
 — Custardguts, Jun 14 2007

mokeys, yes. Naughty monkeys.
Needs some shopping for shoes and a coupla naked wenches and we're all set.
 — methinksnot, Jun 14 2007

I believe you are thinking too small. Increase the radius until the centripetal force is within acceptable limits (I'm thinking we could use this contraption as the base running track of the kiritimaticentrifugomobile! See second link).
 — methinksnot, Jun 14 2007

1000m/s is pretty much the rim speed of the best flywheels using composites etc.
But it raises an interesting question: A flywheel is limited because the material in tension is also rotating, so you can't add more material to make it 'stronger'. Your Maglev doesn't have this constraint- simply build a bigger mountain behind the rails.
 — Ling, Jun 15 2007

don't maglev trains use a huge amount of power to fly?
 — TIB, Jun 15 2007

The friction problem with not getting a complete vacuum could be mostly removed if you stretched a cover between the rear of each car and the front of the one behind it. So it would look sort of like a flywheel except with no middle. A sort of reverse flywheel.
 — Semley, Jun 15 2007

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