# Harvesting energy from the earth rotation

1. Dec 10, 2011

### 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

2. Dec 10, 2011

### Andrew Mason

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

3. Dec 10, 2011

### 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.

4. Dec 16, 2011

### Low-Q

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.

5. Jan 30, 2012

### Stanley514

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

6. Jan 30, 2012

### Drakkith

Staff Emeritus
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.

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

7. Jan 30, 2012

### willem2

If you want to harvest energy from the earths 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.

8. Jan 30, 2012

### cmb

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.

9. Jan 30, 2012

### cmb

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

10. Jan 30, 2012

### D H

Staff Emeritus
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.

11. Jan 31, 2012

### LURCH

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…

… 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.

12. Feb 23, 2012

### Stanley514

If we are able to harness energy of tides and part of tides energy is purely from Earth rotation, why we cant 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.

Last edited: Feb 23, 2012
13. Feb 23, 2012

### willem2

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.

14. Feb 23, 2012

### 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?

15. Feb 23, 2012

### nasu

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

16. Feb 23, 2012

### Stanley514

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?

Last edited: Feb 23, 2012
17. Feb 23, 2012

### nasu

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?

18. Feb 23, 2012

### cmb

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?

19. Feb 24, 2012

### Stanley514

I dont 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?

20. Feb 24, 2012

### 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.