Earth magnetic field energy harness

[Stanley514]

If we take in account that magnetic and geographical Earth poles are not completely identical and therefore magnetic poles suppose to rotate around geographical with some speed, could we harness at least a bit of energy from it? For example if you are on the South geographical pole, the South magnetic pole suppose to rotate around you and therefore Earth magnetic field lines suppose to change under some (not a big angle) regarding your position. Is it true?

 

[russ_watters]

They aren't at the same place, but they are roughly stationary with respect to each other.

 

[Stanley514]

They aren't at the same place, but they are roughly stationary with respect to each other.

That's true. However they rotate at a different speed regarding Earth center. For example at equator speed of Earth rotation will be the fastest and the pole the slowest. If we put a wire conductor from the Earth magnetic pole to geographic pole, then one end of it suppose to rotate faster than the other? I suppose Earth magnetic field suppose to penetrate entire Earth globe, not exist only over the surface?

 

[mfb]

The magnetic pole in the northern hemisphere moves with approximately 50 kilometers per year.
Yes in principle it would be possible to get energy out of this, but the energy density of the field is tiny (~1mJ/m^3) and even after a year the fraction you could get out is tiny (let's say 1%). Completely impractical.

You cannot get energy out of the constant field component.

 

[Stanley514]

The magnetic pole in the northern hemisphere moves with approximately 50 kilometers per year.
Yes in principle it would be possible to get energy out of this, but the energy density of the field is tiny (~1mJ/m^3) and even after a year the fraction you could get out is tiny (let's say 1%). Completely impractical.

You cannot get energy out of the constant field component.

I was talking not about that. Earth rotates daily pretty fast.

 

[mfb]

I was talking not about that. Earth rotates daily pretty fast.

Yes, but that does not give you any method to get energy out of the field.

 

[Nugatory]

I was talking not about that. Earth rotates daily pretty fast.

Yes, but we're rotating along with the Earth and its magnetic field, so the magnetic field isn't changing relative to us - and that's what we would need to extract power.

At some point, you are either going to have calculate the amount of power that could in principle be extracted in this way, or take the word of people who have done the calculation.

 

[russ_watters]

That's true. However they rotate at a different speed regarding Earth center. For example at equator speed of Earth rotation will be the fastest and the pole the slowest. If we put a wire conductor from the Earth magnetic pole to geographic pole, then one end of it suppose to rotate faster than the other? I suppose Earth magnetic field suppose to penetrate entire Earth globe, not exist only over the surface?

No. Rotation is in angular speed, not linear speed. In the frame of reference of Earth's surface, they are not moving with respect to each other.

If what you suggest were true, you could spin an entire generator (frame and all) and generate electricity. You can't: you have to hold the generator's frame stationary whill spinning the shaft.

 

[Stanley514]

No. Rotation is in angular speed, not linear speed. In the frame of reference of Earth's surface, they are not moving with respect to each other.

If what you suggest were true, you could spin an entire generator (frame and all) and generate electricity. You can't: you have to hold the generator's frame stationary whill spinning the shaft.

Sorry, maybe my mistake. I just briefly thought about following things:
1) Different points on Earth surface have different speed of rotation:

Now imagine looking down on the Earth from outer space, pretending it’s possible to observe a person standing on the equator while the Earth rotates about its axis. This person would travel a very substantial distance in 24 hours, compared to a person standing at the top of the Earth, who wouldn’t travel at all. The latter person would stand in place as the planet spins below him. The speed of the person at the equator is fast because she covers more distance in the same time span, while the speed of the person at the North Pole is zero because he has no distance to cover. Similarly, the speed of someone standing at the bottom of the Earth, or the South Pole, would also be zero.Now imagine looking down on the Earth from outer space, pretending it’s possible to observe a person standing on the equator while the Earth rotates about its axis. This person would travel a very substantial distance in 24 hours, compared to a person standing at the top of the Earth, who wouldn’t travel at all. The latter person would stand in place as the planet spins below him. The speed of the person at the equator is fast because she covers more distance in the same time span, while the speed of the person at the North Pole is zero because he has no distance to cover. Similarly, the speed of someone standing at the bottom of the Earth, or the South Pole, would also be zero.

http://classroom.synonym.com/earth-rotate-slower-faster-top-17525.html
2) Earth magnetic and geographical poles do not match each other. And therefore suppose to have different speed of rotation.
3) Earth magnetic field doesn't originate at the poles. And instead:

Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from the Earth's interior to where it meets the solar wind, a stream of charged particles emanating from the Sun. Its magnitude at the Earth's surface ranges from 25 to 65 microtesla (0.25 to 0.65 gauss). Roughly speaking it is the field of a magnetic dipole currently tilted at an angle of about 20 degrees with respect to Earth's rotational axis, as if there were a bar magnet placed at that angle at the center of the Earth. Unlike a bar magnet, however, Earth's magnetic field changes over time because it is generated by a geodynamo (in Earth's case, the motion of molten iron alloys in its outer core).

http://en.wikipedia.org/wiki/Earth's_magnetic_field

So, I thought there should be at least slight change in position to magnetic lines from point of view of stationary observer. But I agree that according to logic there should be mechanically separated stator and rotor and therefore it isn't going to work.

 

[mfb]

2) Earth magnetic and geographical poles do not match each other. And therefore suppose to have different speed of rotation.

Different linear speeds, but the same angular velocity.

You could get energy out if you had some magical "anchor" in space, not rotating with Earth (or slower than one orbit per day). A practical realization would look similar to a space elevator. And if we can build that, there are easier ways to get some energy out of it.

 

[zoki85]

Even with satellites orbiting Earth it is not practical.