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Fly Wheel on a unimaginable scale!

  1. Jun 2, 2008 #1
    If it was possible to build:

    A vertically mounted fly wheel - over 2 miles in diameter, the largest moving mass ever created by man.

    (half above ground, half below ground)

    Would it work?

    Would it continue to spin any longer because of its mass?

    Could it then be used to generate energy?

    And could it be powered / initially started to spin by man?

    Please please please - could someone put my mind to rest!!

  2. jcsd
  3. Jun 2, 2008 #2


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    A flywheel will only store energy; not 'generate' it. As all good physics pupils know, energy cannot be created.

    You could create such a device, but it would be an incredible feat in engineering; and I'm not quite sure what the point would be. Its large mass would (depending on speed) hold a large amount of energy; but remember; the amount of energy you can get from it will always be a bit less than the amount you put in to get it spinning in the first place.

    Why, what are you thinking?
  4. Jun 2, 2008 #3
    It stems from an idea I cannot get out of my head -

    The egyptians built the pyramids-

    I'd like to build a moving / rotating mass so large - it would almost self propel/maintain its own rotation.

    Once in motion - extract energy from it!
    Advertise on it
    Ride on it
    Learn from it

    It might even have its own gravity.

    What you think ? Please post!

    Ideally I'd like this idea to be developed OR to be torn apart - either way I can gain some peace of mind!! Thanks
  5. Jun 2, 2008 #4
    As brewnog says, energy must be conserved, as given by the second law of thermodynamics. You have to put some in to start it spinning, and the amount you can get out will be less, due to entropy increasing, and unwanted losses such as heat. I don't think there would be much point in doing it...maybe only to show what great feats our engineers can achieve...then again, just let them carry on building 500m high skyscrapers, that actrually serve a practical purpose.

    Since you have invited it, I think this idea won't lead to anything revolutionary.
  6. Jun 2, 2008 #5


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    Nothing magical happens when you build a fly wheel two miles in diameter. The same principles apply as if it were two inches in diameter, you're not going to see perpetual motion or anything.

    And yes, it will have it's own gravity. So do I. So what?
  7. Jun 2, 2008 #6
    Well I'll happily do the former, and rip it appart.

    The flywheel, once in motion, can only store the energy which you put into it. In otherwords, it is moving very fast and has a massive amount of energy BECAUSE you put it there. The wheel won't turn if no force is applied -- once applied, it now has EXACTLY the amount of energy you just applied. When you "extract energy" from it, you're simply taking back the energy you put there in the first place (not to mention you just lost some in the form of heat, so actually you won't even get that back!)
  8. Jun 2, 2008 #7
    At that radius, any known material would explode by the time you got up to a decent speed.
  9. Jun 2, 2008 #8
    Orient it so that it receives it's energy from the rotation of the earth...

    "Free" energy, and I can finally get those 30 hour days I need to get everything done!

    Really though, that's about the only way you could get energy out of it without humans actually putting the energy into it... you could possibly devise a way to utilize geothermal energy as well since you're talking about having it half submerged.
    Last edited: Jun 2, 2008
  10. Jun 2, 2008 #9


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    Albert E. made a statement "Imagination is more important than knowledge", this is a fine example of imagination.

    A wheel this large would only achieve a few RPMs, but that's OK, the two negative resistance sources would be bearing, and air.

    Inside a wheel this size, or any flywheel for that matter, there are ways to design internal energy that is stored and transfered by different methods that have no "negative effect" on the wheels rotation.

    I think it could be engineered, but would be far too vulnerable to natural disasters.
  11. Jun 2, 2008 #10
    Currently excess energy from some solar arrays is stored in black sand heat traps and then extracted at night to drive turbines (maintaining a continuous output across the day/night cycle). maybe a massive flywheel with sufficiently minimal energy losses would be a more efficient storage method?

    just think - with it containing enough angular momentum, you could change out/repair an entire solar facility that feeds into it without losing any power.
  12. Jun 3, 2008 #11
    Flywheels can be an excellent source of short-term stored energy. NASA has used them, there is some company puting them into UPS(uninterruptible power supply) devices for external use with computers and such, and I recall that there are even vehicles that use a special flywheel that replaces a standard combustion engine.
    That's the good, now here's the bad...

    All flywheels must be powered-up from some source of energy. So even vehicles that use them for the sole source of locomotion need to have the flywheels pre-spun before vehicle departure.

    It takes more energy to power-up a flywheel than can be extracted from it afterwards, but this is true for all energy storage devices. Flywheels are an exciting potential alternative to some energy storage applications.

    They can be very expensive if one wants top-notch engineering.

    They can be very dangerous. Whether they are slow-moving(using a very large mass) or very fast (using a smaller mass) the dangers, though different, are significant and potentially lethal.

    Anyway, there is a lot of good info on the web. I would suggest doing a Google search on "flywheels energy storage" without the qoutes, or some similar statement. I did this a couple years ago but I don't recall off-hand the excellent links and info I found.
  13. Jun 3, 2008 #12
    If it was possible to be built and avoiding natural disasters, lets assume the diameter was 500 mtrs - 1000 mtrs (to start with),

    Assuming it was started turning by weight distribution, and 100,000 humans pulling a rope!
    (or some sort of pully/geared system - but human energy)

    Starting a slow rpm

    Its motion was then accelerated/maintained by some sort of thermal rising on one side of the wheel, or internal energy storage.

    Could this result in a renewable energy source?
    And in any way improved by its sheer mass?

    Many thanks for your interest.
  14. Jun 3, 2008 #13

    Vanadium 50

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    You keep asking this, and the answer is still "no". Asking again and again won't change it.
  15. Jun 3, 2008 #14
    As everyone above has said, a flywheel can only act as an energy store, so no it can never be an energy source.

    Also, why do you want to build something so big? assuming it was moving at 1rpm the outer bits of it would be moving at about 700mph! I'd be amazed if it didn't break into bits.

    If for any reason flywheels for energy storage on that scale are required it seems much more sensible and safe to build lots of "small" ones.
  16. Jun 3, 2008 #15
    I have read about using large flywheels to store energy for the purpose of electrical generation. It could be a very good idea, since an EM motor/generator could be utilized for both kinetic energy increases and electricity generation.

    Specifically, what I remember was a proposal to use very large flywheels, about 5-50 meters in height and many meters in diameter to either store excess solar energy or to be used as a backup generator for a large building or facility (no lag time if the power goes out and no expensive batteries to maintain).

    That being said, while large flywheels may one day be used in this manner, it seems unlikely to me that they would be anywhere near the scale you are imagining. There is a certain economy in finding the right scale to implement an energy storage device such as this. A multitude of small flywheels is probably uneconomical, as are extremely large flywheels, not to mention unpractical, given that the entire system would have to be drained of energy to effect repairs.

    My estimate would be that the scale should probably be no larger than one that would be effective to use with the largest turbines currently in existence.
  17. Jun 3, 2008 #16
    What do you mean? I can't think of a single way a flywheel would increase electricity generation. Maybe reduce waste by storing energy that's not being used if you have a situation where demand varies rapidly, but nothing else.
  18. Jun 3, 2008 #17
    I meant that flywheels, hooked up to an electrical grid, could be a superior storage media compared to current methods, like electrical batteries.

    We get a lot of energy from the sun that could be fed into the power grid, but photovoltaic cells could never be implemented as a significant portion of our power grid until we develop electrical substations to store excess energy.

    They are not like nuclear or coal-fired plants, where energy output can be adjusted based on demand. Large scale deployment of photovoltaic cells is going to require a major overhaul of our electrical system, and flywheels seem like a good candidate for an energy storage medium.

    I do not remember writing that they would "increase electricity generation", but I suppose you could look at it that way, if the excess electricity would have been wasted (instead of stored in a flywheel or other medium).
  19. Jun 3, 2008 #18
    I think I see the confusion. I was probably unclear. I meant that one could probably design a device that would double as an electrical motor (to increase the internal kinetic energy of the flywheel during times of excess energy production) and a generator (to create electrical current during times when extra electricity is needed).
  20. Jun 3, 2008 #19
    Do you mean having a shaft from the turbines spinning a flywheel directly rather than by spinning it via electricity to avoid inefficiencies?
  21. Jun 3, 2008 #20


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    The most common system at the moment for storing very large amounts of electricity is a pumped storage scheme - some of these are pretty impressive engineering feats.

    By allowing you to either store unreliable sources of electrcity or balance out base load you can 'save' a lot of energy by using these.
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