Power from the Earth's Magnetic Field

On a web forum I frequent, a person asked if it would be possible to extract energy from the Earth's magnetic field. He was told no - static magnetic fields can't transfer energy. For all practical purposes this is true, but in fact we also know that the earth's magnetic field isn't static. It changes from day to day and from year to year - and even second to second. The changes are small over small timescales, but in fact the magnetic poles do drift around and the solar wind does perturb the fields and so forth.

Wikipedia gives a reference saying that typical local variations in the magnetic field at the surface are of the order of 1 nanotesla per second. This is pretty small compared to the total field of perhaps 50 microtesla, but it is measurable with sensitive equipment. Can we extract that energy and free ourselves from reliance on coal and oil? We expect the answer is "no" because otherwise someone would have done it, but we can crunch the numbers to make sure. First, Faraday's law:


Looks bad, but it's not. In this simple physical situation the calculation above will only involve multiplication.

The right hand side says "Make a closed shape out of a bent wire. A square, a circle, a heart, whatever. Now hold it in place and look at the local magnetic field as it passes through the loop. Take that total magnetic flux and look at the rate at which it's changing with time."

The left hand side is just the total potential difference in volts that each electron gains after making one circuit of that loop. It's that number which will tell us something about how useful this might be as a power source.

Magnetic flux is just the magnetic field multiplied by the area of the loop, assuming the field is perpendicular to and uniform within the loop. We're interested in the time rate of change of this flux, and let's say we have a circle with a diameter of 1 meter. The rate of change of the flux is thus (1 nanotesla/second)*(3.14 meters^2).

Which is 3.14x10^-9 volts. Three one-billionths of a volt per square meter of flux-collecting surface. If you tried very hard you might be able to finagle some useful energy out of such a small potential, perhaps with very long superconducting solenoids. But it would be less cost-effective than pretty much any other form of renewable energy by many orders of magnitude.

Still, it was worth a try!

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If you take a long wire, plug both ends in the ground widely separated, and insert a voltmeter, you'll see a voltage. Unbelievable, eh? It's a long time since I did this, but I seem to remember millivolts per kilometer -- easily measurable. What's happening is you have created a giant loop, the return path going deep into the earth. The earth's magnetic field is always fluctuating thru your big loop.

These things are important on the scale of a power grid. Expand your loop to 100 kilometrs by 300 kilometers and you get 100 volts. If this is at very low frequency the DC component of current could present a problem for power transformers.

I once saw a proposal for pulling electricity out of ocean currents. A moving chunck of ocean ater will see changing mag flux due to its motion through the mag field, and seawater is a conductor. So obviously there must be some currents generated as ocean currents interact with the earths EM field. I don't think this is harvestable in any practical way however.

By Omega Centauri (not verified) on 18 Jun 2010 #permalink

Obviously, energy pulled from the earth's magnetic field wouldn't be free, it would be being removed.

If, for the sake of argument, we pretended that a good method of extracting on a commercial scale existed, how much could you pull out before something dramatic happened? Say, the Van Allen belt coming down for a visit? Are we talking "centuries of energy, at current rates of use" or "surprisingly quickly"?

What's the significance of voltage for power generation?

If you had 10^-9 Volts with a sufficiently low impedance source, you could still make a bunch of power (with the appropriate superconducting transformers, etc.). But that's not going to be the case here.

A more interesting (and slightly more challenging) problem is: what's the "capture-able" power per square meter for a loop?

By Anonymous Coward (not verified) on 18 Jun 2010 #permalink

#3: If you could magically dismantle the earth's field and extract the energy, you could get quite a bit. Just a very very rough V*B^2/(2 mu) estimate gives something like 10^21 joules for the first mile in altitude of the earth's atmospheric shell. Collapsing the whole field would probably supply humanity's energy needs for more than a year, but probably well under a century. But this is such a rough guess that it shouldn't be taken seriously without a more careful calculation.

#4: Calculating the possible power directly is a tougher problem. Volts and watts are far from the same thing, but as a "go/no go" estimate for the question of practicality it works pretty well. As a practical matter, turning nanovolts of 1 Hz AC into 120 volts of 60 Hz AC is not something that's feasible in anything resembling these circumstances.

But it would be an interesting calculation to try to find the maximum power directly. Anyone want to give it a shot? If not I'll write it up myself eventually, but as y'all know my posting is sporadic these days due to research responsibilities.

4,5 : Maximum extractable power is pretty easy to compute (though my college EM text has been misplaced and I don't know the units). If you make the loop out of a superconducting wire, then you can induce just enough current that the generated flux through the loop exactly cancels out the flux change from the external field. So this number is exactly calculable (and only undergrad level EM is needed). If you make the superconducting loop big enough you have enough voltage that you could use an inverter to generate AC. The one for my PV system is 94% efficient.

By Omega Centauri (not verified) on 18 Jun 2010 #permalink


The harnessing of the electric power associated with space weather storms is discussed. A simple system based on a large-scale coil located at high latitudes is devised and the power output of the system for a sample storm is calculated. It is shown that independently of the resistances of the conductors used in the coil and the number of turns in the system the maximum output of the system is restricted to the 1â10 MW range, which is comparable to the maximum output of a single large wind turbine.

#6: I think I'd just calculate the Poynting vector. We know B and dB/dt, so Maxwell's equations can give us E. From there you have P = (1/mu)E x B, so that'll give the power per area and can be multiplied by the area of the collecting surface.

@ΩC: There is a good reason not to use large conducting loops to extract energy from variations in the geomagnetic field, namely that sometimes those variations are much larger than average. If you aren't careful with your circuit breaker limits, then sooner or later you will get a repeat of the 1989 Hydro-Qu&eactue;bec power grid collapse.

By Eric Lund (not verified) on 19 Jun 2010 #permalink

What, no mention of the power generated from a long cable in orbit? And the proposal that you can change orbits by pumping current into the cable?

I'm very disappointed.

here's another one for you: how much power could you get out of the earth's electric field?

and what about this: we have thousands of radios transmitting all kind of waves out there. I knew a guy who lived 2 km from a 100 KW TV tower and at his home, fluorescent lamps were always lit without any power. A small light but definitively a light. Would it be possible to build some kind of coil or multiple coils to get power from all these waves? cellular, tv, radio, microwave, etc.?

Another reason why this is a potentially bad idea.
I've read some papers claiming the earths magnetic field is caused by currents running though columns of iron heavy molten rock due to eddies in the core of the earth, these eddies are caused by the earths rotation.
So it's possible that harvesting energy from the earths magnetic field would load the iron in the core and somehow slow down the earths rotation, since the power source for the magnetic field is the rotational potential energy of the planet.

Just a thought...
Like how about sending a stream of helium balloons & magnets through a coil say 100m high?
Using air pressure / density to generate power?
Probably not enough to overcome magnetic forces? Depends on size of balloon. Difficult to set up i'd say.

@14 - sure, any extraction of energy from the magnetic field necessarily will tend to slow the convection currents driving that field. But the convection currents are driven by heat, which comes partly from heat when the earth originally coalesced, and party from nuclear reactions in the heavier elements in the core. So ultimately it's safe geothermal and nuclear power.

Last week (first week of June 2010) spaceweather.com said the sun had plasma jets antipodally. I have since read
The Black Hole at the Heart of Astronomy (electric universe) and a pic from that site:
shows a similarity. Is the magnetic field of our sun collapsing?

By katesisco (not verified) on 11 Jul 2010 #permalink

Typically, people think a time-varying flux is needed to induce current flow in an inductive loop, and while this is accurate for conventional conductors, I suggest (since superconductors can have DC surface currents induced by their spontaneous rejection of all incident magnetic fields) that a superconductive coil assembly can have a net DC current induced by a properly conditioned static magnetic field. Making use of power electronics, this DC current could then be directed through a diode into a charged capacitor, extracting energy from the static magnetic field. A repeated cycle of short circuiting (to refresh the current in the superconductive coil) and open circuit off-loading into a charged load capacitor or battery could enable power extraction from earth's magnetic field.

Further, computer-based partial differential equation simulations have shown that a two piece ferromagnetic antenna with the superconductive coil situated in the air gap can greatly (numerous orders of magnitude) intensify the flux operating such a coil (Up to even 1 Tesla local flux density). See www.magneticharvest.com for more detail on this...

Interesting post, thanks. I've often wondered why we don't harness lightning, or the ionosphere, for 'free' power. More on topic, how much current in the core is induced there from current flowing in the ionosphere, and just how much current flows through the ionosphere?

An Amazing thought taking energy from the earths magnetic field, yet the Holy one who gathers and distributes the energy of earths positioning and rotation would be some what disturbed over taking anything for the use of maintaining the earths orbit and its rotation! For proof that the Lords mystery has been finished Rev:10:7 and His code/keys being given Rev:1:18 making the way straight for His now return in this Generation of Destiny.. go to the proof in the news and science page and on the about page and services page on His gathering website... http://www.adamandeveseedgatheringministry.com the contact page is for questions and asking for proofs/truths of this Epic day...Good thinking on trying to find new ways for energy, but that one source "i" believe must be ignored...much respect r.p.berry / Elijah paul Moses

the earth's core which may be a single iron crystal is a giant magnet and rotates slightly faster than the rest of the planet. A superconducting wire around the earth may generate a large amount of current.

This is a pretty interesting post. The problem with the Earth's magnetic field is that the variations in the flux are very slow, thus producing very little current output. You could however, use it somehow to increase the peak power of an existing variating field. Just a thought - let me know what you think (I was thinking of doing the same sort of thing with the earth's gravitational field - you get a small motor to spin large blades on the end of which are permanent magnets. You get a coil to run around it and theoretically gravity's contribution to the movement of the magnets should create more output than input.)


By Antoine Vandenheste (not verified) on 07 Apr 2011 #permalink

i cant agree for these information that i got , in my veiw point, how the earth got magnetic power. if it has magnetic power only ,it got magnetic feild.
a wellknown the answer , but the apt answer from this , i l wait for this.
but am sure that, what m thinking the answer s right. i need the answer from you.........

By soumyanath.m.s (not verified) on 23 Aug 2011 #permalink

I watched a program tonight, it said there was and area above south america with a weakened magnetic field. If you were to launch a large coil above ths spot and spin it would that generate a sufficient current? And what would a reasonable outlay be (KW to $ over life span)?

Remember Nikolai tesla and his experiment with the electric car - wasn't that based on the same principle ?
#antoine - did you try it out?

By Somnath.biswas… (not verified) on 10 Oct 2011 #permalink

What about if we were using the magnetic field of Jupiter which is about a million times more powerful than ours? It would seem likely future space missions and far future colonies in the Jovian system would want to take advantage of that energy in order to make up for the lower solar energy available. It might even be considered as a possible energy source for undiscovered alien life forms beneath Europa to feed off in the way those recently discovered marine lifeforms feed off heat from subsea volcanos.

By Jim in Texas (not verified) on 17 Nov 2011 #permalink

What and use a huge transformer to transfer the energy across millions of miles?

how about a superconductor laid throughout over the equator...or circular coils of 1km radius at the poles .....would they induce currents..?

I believe you can extract energy from earth using coils. I knew a person in school who built a coil and put it under high tension lines and picked up power then the goverment came in and told him he had to move this coil he said it was on his fathers land but he still had to move it.Dont beleive what sicentest say can and cant be done.The germans didnt listen to them they did things there own way and were way more advanced Than us.Also always be aware of your surroundings and the people around you.

By mike skorich (not verified) on 17 Jan 2012 #permalink

I find it amazing that, being an ex electronics engineering student (finished my degree) that last night I dreamt the first half of the above formula (first post) and have never seen it before in my life! Seen and worked with similar, but we were specifically conducting tests over an area of the earth with a weak field; attempting to bend and artificially lengthen the earths own magnetic field to produce a larger sub-artificial coil for the purposes described in these posts.

I know it's an old thread, but HOW the heck did I see this formula in a dream, jot it down in my phone, then find this forum which dictated the same concept? Very strange; I have always been interestedin alternate sources for energy (nuclear fission, solar) but last nights dream just blew me away!

Was a bit unhappy (to say the least) that my dream was disrupted by some pack of wild boars we were hunting for food...got the better of me :)

Hey Folks,

nice threat. Here are my thoughts. 1. It is possible to
use everything around us to convert it into useful energy.
Including the earths magnetic field. All ya have to do is go further in expanding your thoughts and remove flaws.
As a fact there isnt simply the earths magnetic field, its
an electro-magnetic field. I believe the rotation is a reaction to
the cause and not vice versa. Else how could it have been continous for ages. Take our atmosphere as a large plasma belt (single coil) around the globe, charged by the solar winds. What ya get is a never depleting source of energy as long as our star is running.
The earth just reacts to it in building the electro-magnetic field and even sending EM-waves into space.
The little "radio-freak" (no harm folks) knows that EM-waves can be picked up and be converted back into electric energy. Doing so on manmade EM-waves and fields is simple robbery, doing it on the earths sources its free. On how to possibly use the earths magnetic field, well the answers are in the net. Just need to combine them and extract the right clues. Studying Nikola Teslas work and others gives some strong direction.
They just werent able to build some of their technology due to alot of materials and technologies needed to do it were not in place yet at their time.
I believe in 20 years, we all can get rid of fossil or nuklear energy sources and to say it with Nikola teslas words "Connect to the forces wich drive the solar system and planets itself"(I cant recall the right words, but thats the meaning I picked out of it)

Good luck everyone in their findings.

@30 Please do yourself a big favor and read Jung on the collective unconsious. Our dreams will lead us if we listen. Can any one comment on Tesla's work?

By George Andrews (not verified) on 17 Feb 2012 #permalink

One key point to remember in any such plan is to be sure (somehow) that the energy you're "extracting" isn't man-made in origin.

eg radio waves, domestic earth-based return loops (ie SWER power system) etc.
If we were all to lose power due to massive solar storm or similar, you might find your so called free power source to suddenly read 0v. LOL...

Nicola Tesla powered an electric car without the use of a battery, drawing power apparently from the earth's electro-magnetic field. J.P. Morgan, the oil king, would have none of it and would not finance the invention. I don't know, however, why Nicola did not go elsewhere to get another backer. It's so sad. We had free energy back in the thirties but we are still slaves of the oil companies.