Harvesting energy from the earth rotation

[Low-Q]

Could a gyro be able to harvest the energy from the Earth rotation? If the gyro is locked in space, it must change position relative to the alignment of the earth. This change in position could be the energy output. A gear mechanism is taking energy from the rotating Earth to keep the gyro spinning. Like a gigant powerball.

What do you say?

Vidar

 

[Andrew Mason]

Could a gyro be able to harvest the energy from the Earth rotation? If the gyro is locked in space, it must change position relative to the alignment of the earth. This change in position could be the energy output. A gear mechanism is taking energy from the rotating Earth to keep the gyro spinning. Like a gigant powerball.

What do you say?

Vidar

I am having difficulty understanding the question. Are we to assume that the gyroscope is in orbit around the earth? Why would there be any need to add energy to keep the gyro spinning? How is it losing energy?

Since a spinning gyroscope does not change the direction of the axis of rotation unless a torque is applied to it, it keeps pointing in the same direction in space. Its position relative to the Earth keeps changing if it is in orbit, so its orientation relative to the Earth does change. But apart from work done by tidal forces due to this change in orientation, which would be very small, no work is done on the gyroscope due to the changing orientation.

AM

 

[AlephZero]

In principle, yes, but the numbers don't stack up too well, because the rotation speed of the Earth is so slow.

Suppse you want an output power of 1 watt, just to prove the idea would work.

Power = torque x angular velocity.

Angular velocity = 1 rev per 24 hours = (2 pi) / (24 x 3600) = 72 x 10^-6 rad/sec

Torque = 14,000 N-m.

Scale that up to something useful like 1 MW of power (i.e. one medium size wind turbine), and the shear force would be about 14 million tonnes on a 1-meter radius shaft, at the start of your gear mechanism.

If you want to get energy from the Earth's rotation, or tidal power is a more practical way to go.

 

[Low-Q]

In principle, yes, but the numbers don't stack up too well, because the rotation speed of the Earth is so slow.

Suppse you want an output power of 1 watt, just to prove the idea would work.

Power = torque x angular velocity.

Angular velocity = 1 rev per 24 hours = (2 pi) / (24 x 3600) = 72 x 10^-6 rad/sec

Torque = 14,000 N-m.

Scale that up to something useful like 1 MW of power (i.e. one medium size wind turbine), and the shear force would be about 14 million tonnes on a 1-meter radius shaft, at the start of your gear mechanism.

If you want to get energy from the Earth's rotation, or tidal power is a more practical way to go.

There has been done experiments on this earlier - by Russians. As far as I know they did not succeed... So I will definitely not make it in my backyard.

 

[Stanley514]

In principle, yes, but the numbers don't stack up too well, because the rotation speed of the Earth is so slow.

Is it possible to harness energy of Earth rotating around Sun?
It speed supposed to be closer to 30 km/sec.

Scale that up to something useful like 1 MW of power (i.e. one medium size wind turbine), and the shear force would be about 14 million tonnes on a 1-meter radius shaft, at the start of your gear mechanism.

What do you meen by that?Force will be to strong for a turbine to withstand?Hard to believe,
but as I know gyroscopes not necessarly should be mecanical.For example there exist some kind of electronic gyroscopes.

 

[Drakkith]

Is it possible to harness energy of Earth rotating around Sun?
It speed supposed to be closer to 30 km/sec.

There is no known feasible way to harness energy from Earths orbital velocity other than to gravitationally assist satellites. And even this wouldn't really count as "harnessing" energy in the sense of power generation.

What do you meen by that?Force will be to strong for a turbine to withstand?Hard to believe,
but as I know gyroscopes not necessarly should be mecanical.For example there exist some kind of electronic gyroscopes.

These would not provide power, but are used to detect rotation via interference of light.

 

[willem2]

If you want to harvest energy from the Earth's rotation, you must slow it down.
Because of conservation of angular momentum, this can only happen if you transfer it to an object not on the earth, such as the moon.
If you can't do this, it's impossible to harvest the rotational energy of the earth.

 

[cmb]

Could a gyro be able to harvest the energy from the Earth rotation?

Already been done [by whoever created the solar system] - it's called the Moon!

The Moon used to go around the Earth closer, and the Earth rotated faster. But the Earth has been losing energy to the Moon, through tides, for billions of years.

So [unfortunately] overall it is the Moon that is harvesting energy from the Earth's rotation! But we can intercept some of the work energy that is transferred in that process, by capturing some of the tidal energy.

 

[cmb]

...this can only happen if you transfer it to an object not on the earth, such as the moon...

(Darn - you hit send and beat me to the call, while I went to get my mid-edit drink!)

 

[D H]

Because of conservation of angular momentum, this can only happen if you transfer it to an object not on the earth, such as the moon.

Or to an object that leaves the earth, such as a rocket. Rockets for the most part do "harvest energy from the Earth's rotation." (Satellites launched into retrograde orbits add angular momentum, but not much; most retrograde orbits are only slightly retrograde. So I'll just ignore that minor complication. )

Question: How much mass needs to be launched into geostationary orbit to lengthen a day by one second? Ignore details such as what happens to the exhaust.

 

[LURCH]

I am having difficulty understanding the question. Are we to assume that the gyroscope is in orbit around the earth? Why would there be any need to add energy to keep the gyro spinning? How is it losing energy? ...

AM

It appears from the original post that the gyroscope would be gimbled, and the gimble would be attached to a gearing mechanism which would extract energy. The only way this mechanism could extract energy is if it worked against resistance. This resistance would in turn cause the gyroscope to tumble, which would manifest itself as a type of drag, slowing the gyroscope.

For this reason, I would have disagreed with…

In principle, yes, but the numbers don't stack up too well, because the rotation speed of the Earth is so slow...

… and say that, even in principle, this would not work. The energy needed to keep the gyroscope spinning will always be equal to the energy extracted plus any losses to entropy. I think the Second Law means that this device will end up costing energy, rather than generating it.

 

[Stanley514]

… and say that, even in principle, this would not work. The energy needed to keep the gyroscope spinning will always be equal to the energy extracted plus any losses to entropy. I think the Second Law means that this device will end up costing energy, rather than generating it.

If we are able to harness energy of tides and part of tides energy is purely from Earth rotation, why we can`t harness it in some other way?There exist tidal power plants.
I read to somebodies amateurish mind that in order to increase power output from gyro we need to make it spin as fast as possible and to reduce size of reductor.

 

[willem2]

If we are able to harness energy of tides and part of tides energy is purely from Earth rotation, why we can`t harness it in some other way?There exist tidal power plants.
I read to somebodies amateurish mind that in order to increase power output from gyro we need to make it spin as fast as possible and to reduce size of reductor.

To get energy out, you have to transfer some of the angular momentum of the Earth to an object that isn't on the earth. There's no way to do this with an Earth bound gyroscope.

 

[Stanley514]

Do I understand it right that even there would be no Moon and Sun,some kind of tides or breakers would still take place due to Earth rotation only?
http://www.astronomycafe.net/qadir/q106.htmlIf yes,then you are going to tell we would not be able to capture their enery?Without some outer space object?Are you sure?

 

[nasu]

Do I understand it right that even there would be no Moon and Sun,some kind of tides or breakers would still take place due to Earth rotation only?
http://www.astronomycafe.net/qadir/q106.htmlIf yes,then you are going to tell we would not be able to capture their enery?Without some outer space object?Are you sure?

Where does it say "no Mon and Sun"??

 

[Stanley514]

Where does it say "no Mon and Sun"??

``On a daily basis, we would still have large breakers on the continental west coasts because of the rotation speed of the Earth, and the existence of storms out at sea, and sloping beaches. The waves we are most familiar with from minute to minute are caused by small ripples out at sea caused by storms, which get amplified into majestic breakers by their motion up a sloping beach, and the rotation of the Earth from west to east which gives them added momentum.``
There is only Earth rotation mentioned.

Due to Earth rotation water changes river banks.Do you think Moon and Sun have relation to this?

 

[nasu]

``On a daily basis, we would still have large breakers on the continental west coasts because of the rotation speed of the Earth, and the existence of storms out at sea, and sloping beaches. The waves we are most familiar with from minute to minute are caused by small ripples out at sea caused by storms, which get amplified into majestic breakers by their motion up a sloping beach, and the rotation of the Earth from west to east which gives them added momentum.``
There is only Earth rotation mentioned.

This has nothing to do with the absence of the Sun.
I am afraid you did not read the text carefully. Starting with the title.
"If it did not have Moon" means exactly this: everything else but the Moon stays.
Besides the semantics, how would you account for the seasons, mentioned in the text, in the absence of the Sun?

 

[cmb]

If we are able to harness energy of tides and part of tides energy is purely from Earth rotation, why we can`t harness it in some other way?There exist tidal power plants.

Basically, the Earth's rotation is too slow. You could, indeed, spin up a gyroscope with its axis orthogonal to that of the earth's. You'd then observe a rotation of that gyroscope relative to an earthbound observer - it would rotate once per day. Now, if you could figure out a way to efficiently extract energy from a device with a [relative] gyroscopic precession rotation rate of once per day whilst simultaneously feeding in energy enough to keep a big flywheel rotating at many rpm continuously, then maybe you could progress with the idea?

 

[Stanley514]

Basically, the Earth's rotation is too slow. You could, indeed, spin up a gyroscope with its axis orthogonal to that of the earth's. You'd then observe a rotation of that gyroscope relative to an earthbound observer - it would rotate once per day. Now, if you could figure out a way to efficiently extract energy from a device with a [relative] gyroscopic precession rotation rate of once per day whilst simultaneously feeding in energy enough to keep a big flywheel rotating at many rpm continuously, then maybe you could progress with the idea?

I don`t know.If idea principally working and we would be able to obtain netto energy from Earth rotation then,I guess, the same idea could be extrapolated and we would be able to obtain energy from Earth movement around the Sun (this motion is much faster).Gyroscope not necessarily should be mechanical,I think.Maybe it`s possible to do something based on purelly electronic cycles?Then we may avoid some problems associated with strenghts of materials?

 

[cmb]

I think it is going to be worse than that. There is something about the physics of such an arrangement that will always mean the energy in is greater than the energy out, I'm afraid. You have to keep turning the flywheel to generate the rotation - it's a perpetual motion machine by another definition, and like all perpetual motion machines, you have to put energy in in a manner more efficient that taking it out.

 

[Drakkith]

I think it is going to be worse than that. There is something about the physics of such an arrangement that will always mean the energy in is greater than the energy out, I'm afraid. You have to keep turning the flywheel to generate the rotation - it's a perpetual motion machine by another definition, and like all perpetual motion machines, you have to put energy in in a manner more efficient that taking it out.

It's not a perpetual motion machine, it's just very inefficient due to the long rotation time of the Earth for what you are wanting to do. The energy you might be able to extract from it comes directly from slowing the Earth down slightly, so energy is conserved.

 

[cmb]

The energy you might be able to extract from it comes directly from slowing the Earth down slightly

right, but you only slow down the Earth a little so long as the gyroscope is still rotating. Once you stop the gyroscope, you speed the Earth back up again. This is a bit like accelerating your car eastwards. naively, you have slowed the Earth down, so you must've generated some energy? Not really, because you have to stop the car sometime and you put exactly that energy back into the Earth.

So the physics says that you have to put [at least] the same energy in as you'd get out.

 

[Drakkith]

right, but you only slow down the Earth a little so long as the gyroscope is still rotating. Once you stop the gyroscope, you speed the Earth back up again.

What? I don't think this is correct. Once you extract the energy it is gone unless you intentionally give it back to the Earth.

This is a bit like accelerating your car eastwards. naively, you have slowed the Earth down, so you must've generated some energy? Not really, because you have to stop the car sometime and you put exactly that energy back into the Earth.

No, the gyroscope would apply a torque against Earth's motion. Once stopped it would NOT apply a torque in the opposite direction. You would have to purposely input energy and reverse the gyroscope to make this happen.

 

[cmb]

the gyroscope would apply a torque against Earth's motion. Once stopped it would NOT apply a torque in the opposite direction. You would have to purposely input energy and reverse the gyroscope to make this happen.

So, if you were to extract some energy out of the slow rotation of the gyroscope, then let the gyroscope spin down under its own friction to standstill, then after all that the Earth would be rotating slower that it was before? Right?

OK... so to what was the angular momentum transferred, or does this defeat conservation of angular momentum?

 

[Drakkith]

So, if you were to extract some energy out of the slow rotation of the gyroscope, then let the gyroscope spin down under its own friction to standstill, then after all that the Earth would be rotating slower that it was before? Right?

Yes.

OK... so to what was the angular momentum transferred, or does this defeat conservation of angular momentum?

To the gyroscope and then to whatever you are using to get power out of it.

 

[cmb]

To the gyroscope and then to whatever you are using to get power out of it.

Let's say it fed some high-geared generator that charged up a battery. Now the generator has stopped too, and so the only difference before-to-after is that I've got a charged up battery and a slowed down Earth. Does this not defeat conservation of angular momentum?

 

[Drakkith]

I don't believe so. If it did, then someone should have pointed it out immediately. I recently tried out an example at the local Sci-Port where that had a wheel on an axle that you spun up with your hand. Then you sat in a chair that could turn and rotated the wheel and axle around perpendicular to it's rotational axis. This caused the chair and myself to turn one way. As the wheel spun down I did not return to my original direction.

 

[willem2]

I don't believe so. If it did, then someone should have pointed it out immediately. I recently tried out an example at the local Sci-Port where that had a wheel on an axle that you spun up with your hand. Then you sat in a chair that could turn and rotated the wheel and axle around perpendicular to it's rotational axis. This caused the chair and myself to turn one way. As the wheel spun down I did not return to my original direction.

It does violate conservation of angular momentum, and is therefore impossible. A gyroscope that you let rotate freely won't slow down the earth, or produce any energy. The only way to slow down or speed up the Earth with such a gyroscope, is to let it point more or less in the direction of the Earth's spin. The gyroscopy will have it's lowest energy state when it's spinning in the same direction of the earth, and you can't get any energy out of it anymore.

 

[Drakkith]

It does violate conservation of angular momentum, and is therefore impossible. A gyroscope that you let rotate freely won't slow down the earth, or produce any energy. The only way to slow down or speed up the Earth with such a gyroscope, is to let it point more or less in the direction of the Earth's spin. The gyroscopy will have it's lowest energy state when it's spinning in the same direction of the earth, and you can't get any energy out of it anymore.

Alright, I just re-read the thread again. I guess that it is impossible. Not sure why I was thinking it would work...perhaps I was remembering another thread.

 

[cmb]

The only way to slow down or speed up the Earth with such a gyroscope, is to let it point more or less in the direction of the Earth's spin. The gyroscopy will have it's lowest energy state when it's spinning in the same direction of the earth, and you can't get any energy out of it anymore.

[EDITED OUT A SECTION HERE]... I don't think what I just wrote then was correct. I was discussing that a gyroscope with its axis perpendicular to the Earth's axis would slow the Earth down. I think that's not true, because it would have no component of angular momentum about the same aXIs as the earth, so the two would not interact in that way - is that correct??...

Gyroscopes' behaviour tends to defeat human's intuition (hence a load of 'anti-gravity' devices try to exploit gyroscopes, due to misconceptions on how they work). I suspect that this is, in part, because we have evolved with the 'lizard' parts of our brain never needing to intuitively comprehend gyroscopic motions, as nothing in the natural world behaves in such a way to need that intuitive comprehension.

 

[Simon Bridge]

I'm guessing Low-Q is thinking of one of these:
http://www.lhup.edu/~dsimanek/museum/advanced.htm

BTW: I'm with LURCH.

 

[K^2]

Angular momentum is still a conserved quantity. Meaning you cannot slow Earth's rotation down without either a) drastically altering it's moment of inertia or b) expelling mass.

In particular, you cannot use a gyro to extract energy from Earth's rotation, because the torque would cause the gyro to tip, until its axis of rotation is aligned with Earth's.

 

[D H]

Angular momentum is still a conserved quantity. Meaning you cannot slow Earth's rotation down without either a) drastically altering it's moment of inertia or b) expelling mass.

In particular, you cannot use a gyro to extract energy from Earth's rotation, because the torque would cause the gyro to tip, until its axis of rotation is aligned with Earth's.

Exactly. It's a perpetual motion machine.

Using a gyro or a flywheel as an energy storage device is okay. One of the many problems with renewable energy is that it is not available. Solar power needs to be stored during the daytime for use at nighttime, wind power needs to be stored when the wind blows for use when the winds aren't so strong. This isn't perpetual motion; it's just a storage device. And it's lossy, as are all real energy storage devices.

There is a way to harvest energy from the Earth's rotation without a) drastically altering it's moment of inertia or b) expelling mass. That way is to piggyback of an existing external torque on the Earth. This tidal station, for example, generates 254 MW of power.

 

[K^2]

There is a way to harvest energy from the Earth's rotation without a) drastically altering it's moment of inertia or b) expelling mass. That way is to piggyback of an existing external torque on the Earth.

The lunar tide is definitely expelling mass. The Moon. :p The solar tide also results in Sun being "pushed", but calling that one "expelling mass" would be a bit of a stretch, I agree.

 

[Low-Q]

Maybe we could harness the energy that separates the continents. What about having a long rod between America and Europe. The rod is attached to America, while in Eurpoe the rod moves a few centimeter a year. Connect that movement to a flywheel or some sort of generator... That was off topic, but an interesting idea I think :-)

Vidar

 

[Simon Bridge]

You only need to put the rod across a rift. Attach to one end and rest the other end on rollers - use it to drive a wheel.

You saw the analysis of the torque needed to turn the Earth's sloww rotation into useable energy? Do the same for the much much slower continental drift.

 

[LURCH]

The lunar tide is definitely expelling mass. The Moon. :p The solar tide also results in Sun being "pushed", but calling that one "expelling mass" would be a bit of a stretch, I agree.

This is a good point, and shows one of the changes of view that makes the tidal generator a worthwhile idea. The Moon's mass is being expelled anyway. The tides come in and go out and generate (when taken as a whole) an almost unimaginable amount of energy. Even though the tides come and go relatively slowly, these motions represent an small movement of the entire ocean, which is a tremendous amount of mass. So the energy is being expended whether we put it to use or not.

Likewise with continentle drift. The continents are moving slowly, but with tremendous overall force. The amount of energy it would take to stop the continents from drifting is the amount of energy available to tap; the engeneering challenge would be in gearing down the generator at the end of the rod. But the energy is already moving from one place to another. We can briefly divert that flow to our own use if we are clever about it.

 

[Stanley514]

In particular, you cannot use a gyro to extract energy from Earth's rotation, because the torque would cause the gyro to tip, until its axis of rotation is aligned with Earth's.

If you could speed up a powerball by rotating it with your hand then why you cannot speed up hyro with the Earth rotation?Of course, the Earth makes fewer number of rotations per 24 hours, but theoretically?If you could speed up something then you could harness energy by taking part of energy out and keeping the same speed.Still absolute speed of Eath rotation is not too low.It`s close to 100 meters/sec.

 

[Simon Bridge]

When you speed up the powerball by twisting with your hand, you also have an equal and opposite torque on your hand, and yourself. You muscles provide a counter-torque in reaction - keeping you from rotating. You can do this because your body is braced against the Earth ... so the counter-torque is transferred to the Earth (imparting a small angular momentum to the Earth). Thus - the energy to the ball comes, at least partly, from the rotation of the Earth.

Note: you cannot take energy out of a rotating object without changing the speed that it rotates at.

To exploit the rapid surface tangential speed of the Earth, you need to find some place to stand that is stationary wrt the rotation - and remains stationary under Newton's 3rd Law.

So I can imagine a big gear at the north pole which turns with the Earth and meshes with another gear that, therefore turns the other way. But what is the other gear attached to?

To make it work, I'd have to hold the second gear by the axle and walk round and round the drive gear on the ground. If I go around once a day, the axle I'm holding is now stationary wrt the rotation of the Earth and, indeed, the gear is turning and generating power.

It can take a while to get your head around rotating reference frames and the misconceptions that arise from the common approximation that the Earth is stationary.

 

[mfb]

Without moon, we would have waves from storms (independent of Earth's rotation) and tides from sun. It is possible to extract power from both.

A direct way to harvest energy from Earth's rotation would be given with a space elevator. Lifting mass to geostationary orbit requires energy, but if you keep lifting the object the centrifugal force (in rotating coordinates) will give you energy.

 

[Simon Bridge]

A direct way to harvest energy from Earth's rotation would be given with a space elevator. Lifting mass to geostationary orbit requires energy, but if you keep lifting the object the centrifugal force (in rotating coordinates) will give you energy.

That won't generate energy you didn't give it getting it there.

 

[StephenofCaly]

Nah, we live here. Screw up someone else's backyard. Let's harvest energy from the orbital velocity of Jupiter. So Jupiter's orbit comes in a kilometer or so - who's to care? Somebody do the math.

 

[Simon Bridge]

Jupiter has a big effect on things like keeping the asteroids in their belt.
How about Saturn or Neptune.

But the question remains: how?

 

[mfb]

That won't generate energy you didn't give it getting it there.

It will. In rotating coordinates, the potential is given by V(r)=-1/3mωr^3 - GmM/r. As you can see, this does not have a lower bound, it goes to minus infinity for r→infinity (and has a maximum at geostationary orbit). In practice, the strength of the cable would limit the maximal radius of the space elevator.

 

[Simon Bridge]

Do you mean to say that all you have to do is spin around to get free energy?

 

[mfb]

All you have to do is to build a space elevator and lift material high enough to extract rotational energy from Earth (and find some way to transfer this energy to places where you need it). It is not really free, it slows the rotation of earth. The total energy is 2*10^29 J, so 10GW over 100 years (3*10^19 J) would not influence it in a significant way. But you can see that other energy sources are probably better.

The extracted rotational energy 1/3~m\omega r^3_{final} will go to:
- potential energy of the lifted mass (close to GmM/r_earth)
- kinetic energy of the lifted mass 1/3~m\omega^2 r^2_{final}
- work done to your payload, which you can extract with a dynamo or similar devices

 

[Buckleymanor]

http://mb-soft.com/public2/earthrot.html
The idea has been around for some time and some research done I have other links somewhere if posters are interested.

 

[mfb]

The proposed idea there violates basic laws of physics. As the author does not plan to emit anything to space or at least raise it by significant amounts, the moment of inertia of Earth would not increase. However, the rotational energy is linked to energy by 2E=I\omega^2 = \frac{L^2}{I}. L is fixed in closed systems, so if you want to extract energy, you have to increase I or link the Earth to systems with a larger I.
The author repeats over and over that energy conservation would not be violated, but apparently he never heard about angular momentum.

C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago

Apart from that, he is a bit optimistic about the energy content. Lengthening the day by 1 billionth would give a maximal amount of 4*10^21 J, that is about 10 times the current world energy consumption.

Well, the whole site seems to be very close to the crackpot-region with a lot of CAPS and repeated complaints that nobody cares about things which are impossible or too small to use them.

 

[StephenofCaly]

The proposed idea there violates basic laws of physics...Well, the whole site seems to be very close to the crackpot-region with a lot of CAPS and repeated complaints that nobody cares about things which are impossible or too small to use them.

I enjoy that remark. The problem here seems to be in imagining the movement of objects on a fixed radial vector from the Earth's center, passing through a continuous spot on the Earth's surface at the equator, and sweeping into space. An imaginary clock hand, as it were, and one that can lock things somehow to its line, so that stuff must slide up and down the vector.

At about 24,000 miles, this vector touches an orbit called the geosynchronous orbit. Objects orbiting at this height require the proper angular momentum to remain stable on the vast imaginary vector.

Objects locked onto the vector at a closer distance lack the angular momentum to stay at that distance, and will tend to fall back down the vector. Objects locked onto the vector at a further distance would tend to RISE, as the vector - if it can lock onto the object - sweeps it higher and higher like a xistera - the jai-alai thingy - does to a jai-alai ball.

It takes a certain amount of work to go from the Earth's surface to geosynchronous orbit - which then could somehow harvest the work of going from geosynchronous to infinity.

My guess is that it's a lose - it takes more work to get up to the zero-point than could be harvested, even by flinging something off into west of eternity.

PS: I shall leave it off there, as it seems that personal theories and the commenting upon them is suspect.

 

[mfb]

It is possible, and I already mentioned and evaluated it, just read page 3 of this thread.

My guess is that it's a lose - it takes more work to get up to the zero-point than could be harvested, even by flinging something off into west of eternity.

It is not, see my previous posts.

PS: I shall leave it off there, as it seems that personal theories and the commenting upon them is suspect.

This is not a personal theory, it is just an application of Newton's Laws of motion and gravity.