OK, mostly theoretical and only barely practical questions here.
Could we build a conductive ring around the earth’s magnetic field and propel it in such a way to generate current? It would seem that without the friction normally found in regular devices that the conversion from, say, combuistion to electricity would be more efficient.
Secondly, if we could (and I feel that it should be possible, even if not likely) generate electricity in this manner, are we going to be affecting the earth’s magnetic field or even its spin? It would seem like we would…
Thirdly, could we utilize this electricity in any way? (I guess I mean, forget dollar costs and consider we’ve got a fat or unlimited bankroll to work with).
If you literally mean putting a big ring around the entire earth, there would be quite a few problems to work out re: orbital mechanics.
But let’s say you put up some large number of satellites that orbit in a direction contrary to earth’s rotation, and tethered in pairs by conductive cables in such a manner that they cut across the magnetic lines of force. I think you would generate electricity in this manner. To get it to the ground, you might charge-up batteries, or transmit it by large-array microwave, etc.
BIG HOWEVER: The friction-like interaction between rotor and stator (I think those are the terms) in a dynamo is not just, or even mainly, mechanical friction: the induction process itself works against its own direction of motion. We would have to put energy into those satellites to keep them in orbit…Why not just use that same energy directly to generate power?
As for affecting the earth and its field: not measurably.
Theoretically there is no reason you couldn’t treat the earth as a large magnet and run wire around it in such a fashion that you could generate power. However, I think in practical terms such a thing is nearly impossible.
However, I recall an experiment done by the space shuttle where they were going to trail a VERY long wire as they orbited the earth and see if that could be used to generate electricity (enough to power a satellite). Unfortunately I don’t know the results of the experiment (or if it even happened or was just proposed) and I haven’t figured out a search yet that gets me anywhere near a link I could cite.
Oh, I have no doubt that the current in the windings generate a magnetic field which inhibits the motion. My point is that this is going to happen any time you try and generate electricity from magnetic fields cutting conductors, on the ground or in orbit. Thus, the same energy used here on earth to move physical parts would go a bit farther in space where there aren’t any moving parts…
Also, it would have to be a solid ring, unfortunately, since otherwise you’d be spending a ton of energy just to stay in orbit, nevermind fighting the magnetic fields.
That is interesting about the Space Shuttle… see, I’ve always wondered what the strength of the Earth’s magnetic field is as to how much juice we could hope to get out of it. Also, since the satellites would have to be in orbit anyway having them trail out leads is interesting, but I’m not sure how just hanging out a wire would do anything.
The experiment did happen, and worked all too well. The wire generated enough power that it glowed. Visible on the ground, in fact, if you were in the right place.
Then it burned through, I think. I’ll look for a cite too, but I’m not hopeful.
This page has a bit about tether experiments in space, including a small section on an experiment in which the tether experienced higher than expected voltage and burnt through.
Yes, it could be done. I remember a physics homework problem in which we had to calculate the voltage induce on the fuselage of the space shuttle (wingtip to wingtip) as it orbited earth. IIRC, it was on the order of 10 volts. Our professor said that this really did occur in the shuttle and that the wiring and circuitry had to be designed to deal with the induced voltage.
All you need to do (heh) is run a loop of wire around the earth and start it spinning. Just a simple generator.
Now at first, I thought that it’s unfortunate that the earth’s magnetic poles are so closer to the axis of rotation. I was thinking that if the magnetic poles were on the equator, we could take advantage of the earth’s rotation and we wouldn’t need to spin our wire loop. But on reflection, the loop has to spin relative to the earth, so we’d have to supply that angular momentum after building the loop, no matter how we oriented it.
Drawing electricity from the loop would create a force that would slow the loop down. So to keep generating, you’d have to apply a force to the ring to keep it spinning. Yes, it would be frictionless, so I think it would be reasonably efficient. But resistance in the wire loop would be a huge problem. Perhaps we should specify that our loop be a superconductor.
Would it affect the earth’s magnetic field? No, I don’t think so. Would it affect the earth’s rotation? Yes, the earth would lose the same amount of angular momentum that the ring does. But being more massive, the actual angular velocity of the earth would change much less.
These are just my impressions. It’s been a long time since that physics class, so if I’m mistaken, I hope someone will point it out and educate me.
If you build this ring using materials from the Earth, you’ve changed the Earth’s angular momentum already. When the ring slows down, you’re undoing that earlier change.
With any of these device in orbit, the electric energy you get out comes from the energy used to putting it into orbit in the first place. It’d certainly be more efficient to just to use the launch fuel to boil water and drive a turbine.
Lastly, you don’t need to go into orbit, or a big ring. Just make a wire loop and spin it with the axis perpendicular to the Earth’s magnetic field.
Lenz’s law ("the Sod’s Law of Physics "as my teacher used to say) states that The effect of an induced
emf is such as to oppose the change in flux that produces it; it’s not primarily physical friction that slows a dynamo down, so your spinning loop would slow down until the point at which it isn’t moving (relative to the magnetic field) and no current is being produced.
Maybe yes, maybe no, but that really isn’t the point. After all, if we’re going to be putting rings around planets, I think you can assume we’d be mining asteroids and meteors.
Let me reiterate (if you were addressing me ;)): friction affects the efficiency. I understand, very well, how current and magnetic fields operate Genrating the motion of a ring in orbit is going to have no (almost) friction compared to generating the same thing on the ground. In both cases you fight the current-generated field! In one you hae moving parts. (again, only if this was directed at me)
TheNerd, that is an incredible website. Very interesting indeed. Thanks!
