Piezo energy harvesting progress

Discussion in 'Physics' started by #12, Mar 18, 2014.

  1. #12

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  2. strantor

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    I remember a discussion quite a while back about powering street lamps with piezo electric mats (not this new technology specifically, but previously existing piezo tech) on the sidewalks. IIRC it got pretty heated, but in the end there was a consensus that while walking on a normal hard surface, all (nearly all) of the energy that you expend results in propelling you forward. Adding some energy harvesting (robbing) device under your feet would cause you to expend more energy to walk the same distance, as nothing is free - it isn't harvesting unused energy, it is robbing you of energy that you wouldn't have to expend otherwise. I believe it was likened to walking on loose sand; much harder to do.

    Then more recently there was a discussion about wind farms actually killing the wind. The turbines rob energy out of the wind and slow it down, so downstream areas receive less wind than they would have normally.

    Now this guy is talking about powering the world from ocean waves; Should I go to the beach and enjoy the waves while they still exist?
     
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  3. inwo

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    Just when we get these killer storms rolling too. :D Now someone will kill the wind and waves.:(
     
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  4. #12

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    You guys are silly!

    (I like silly :D)
     
  5. Alec_t

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    LOL.
    Actually, in areas where there is rapid coastal erosion it would make sense to install a barrage of devices to harvest the wave energy. Double bonus.
     
  6. MrChips

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    Another tax on the working class!

    What I great idea! I am hooked up to a CPAP machine while I sleep at night to prevent obstructive sleep apnea.
    Perhaps someone can devise a way of harvesting the energy as we breath while we are sleeping.
     
  7. Alec_t

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    Perhaps, in the case of apnoea, the body is already diverting energy away from breathing activity?
     
  8. strantor

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    To take the silliness a step further, ponder this:

    Waves are caused by tides; the moon orbiting the earth, pulling the ocean along with its gravitational field. If we sap energy from the waves, do we not therefore sap energy from the tides that created them? And if we sap energy from the tides, do we not therefore sap energy from the moon? With our wave power leeches, can we actually succeed in putting a drag on the moon, causing it to slow down and eventually fall out of orbit, crashing into the earth?
     
  9. MrChips

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    Good point. If we harvest energy from Niagara Falls, don't we slow down the water flow down the falls?
     
  10. #12

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    Bill Marsden said this about our planet in a sticky over-unity thread:

    "Let's spin this sucker down!"

    On the serious side, the moon gets farther away when you slow it down. I don't remember where I read that, but the observation goes like this:

    A very long time ago, the moon was much closer than it is now and almost geosynchronous. The tides were a thousand times as high as they are now. That energy expended as tidal forces caused the moon to slow down, and that's is why is is now farther away and lags the spin of the planet by about one orbit per 28 days.
     
  11. Wendy

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    It is tidal coupling. It is why one side of the moon always faces earth, the same effect is occurring in reverse. However, as the earths spin slows down, it imparts this momentium to the moon, which means every year the moon is several inches further out. Eventually (so I've read) the moon will wander off when it gets too far, but I think there is a chance the sun will engulf us in its red giant phase first.
     
  12. Alec_t

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    That will convince the doubters of global warming :)
     
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  13. #12

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    Are you saying my interpretation was backwards?
     
  14. shortbus

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    Do we have to call you #21 now?
     
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  15. #12

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    It's entirely possible :D

    I think Neil Armstrong wrote a book about how objects act in space, but I haven't read it.
    The results are often not what you'd expect.
     
  16. strantor

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    So you're saying I'm actually on to something? I was just joking. Maybe if I joked more often, I would sound smarter.
     
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  17. Wendy

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    Naw.......
     
  18. THE_RB

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    I'm not sure you are right. The moon/earth movement puts a fixed amount of energy into the tides, energy which is normally dissipated chaotically into the shores etc.

    If you extract some energy from that there will be less energy dissipated on the shores etc but I doubt that would increase the total energy input.

    In fact if you "dampen" the oceans enough it may reduce the energy input. In the same way if you block off a ducted fan's air path it seems like you're adding more load but in reality it reduces the coupling of source to load and there will be less energy taken from the fan.
     
  19. poopscoop

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    For the record, higher speed = higher kinetic energy = higher orbit. If the moon moved more slowly it would be closer to, not farther from, earth. Think back to the "gravity well" in physics.

    An interesting effect of this is seen in orbital docking between spacecraft. If the target vehicle is in front of you, ahead in the orbit, and you 'mash the gas' to catch up, you increase your kinetic energy, thus drifting to a higher orbit. In your new orbit, your relative speed is slower, and the target object seems to accelerate away.

    During the Gemini missions, the capsule crew actually had to slow their speed, thus dropping to a lower orbit with a faster relative speed, until they caught up with (and passed) the target vehicle. Then and only then could they rise to the target orbit.
     
  20. Wendy

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    As the earths spin slows down the moons orbit speeds up. The earth is trying to tidal lock with the moon, where one face of earth always faces the moon, but the process is so slow lots of other stuff will happen first.

    In the early days of earth the moon was much closer to earth, not tidally locked (had its own spin), and the earth's day was much shorter (16 hours or so?).

    One theory suggests the moon was created from the earth by a truly cataclysmic collision in the early days of the solar system, so was very close indeed.
     
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