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Energy Tower

  1. Dec 12, 2007 #1
    Here might be a very good idea if it could work:

    http://inventorspot.com/articles/energy_tower_power_15_earths_9102

    My question is: how much energy would it take to pump all that water 3000 feet up? Could this construct have a positive net energy, or is it just more pie in the sky?
     
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  3. Dec 13, 2007 #2

    russ_watters

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    Strange site - they stole the idea, but got it backwards! Quite obviously, as hot air is created by warming from the ground and air cools as it rises, the hot air goes in the bottom and comes out the top. The atmosphere won't allow you to build the device they are trying to build. All they have there is a free convection cooling tower. There are several Israeli popular science magazines that pick up this crap and run with it. Extremely efficient and cheap solar cells are another popular claim.

    Anyway, I'd love to see the look on the turbine designers face (Fred...?) when told they'd have 100% humid air and flakes of salt going through their turbine (wherepon the water would condense onto the turbines)! :rofl:

    And yes, pumping water up to 3000 feet would use a lot of energy.

    Here's the company that is actually working on this (using free convection for power): http://www.enviromission.com.au/project/project.htm

    It's a boondoggle, but at least they built a small prototype.
     
  4. Dec 13, 2007 #3

    FredGarvin

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    I certainly hope they really mean Pelton Wheels and not a real turbine. I really would like to hear what these "researchers" and "inventors" say about that aspect. "We'd make them from stainless steel. Everything would be fine."

    Not only would pumping the water up 3000 ft take a lot of energy, but also pumping the water to the site would too. These are meant to be run in dry/arid areas. There's a reason why they're called "dry."
     
  5. Dec 13, 2007 #4

    stewartcs

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    You would think after spending 150 man-years reseaching , designing, testing, and analyzing they would have realized it didn't work like that. :smile:

    BTW nice link Russ. The technology page has a neat little animation...

    http://www.enviromission.com.au/project/technology.htm
     
  6. Dec 13, 2007 #5
    Thanks! I thought that sounded a bit too good to be true. The one in the animation doesn't use water, though, right? That seems more practical.
     
  7. Dec 13, 2007 #6

    stewartcs

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    It uses air according to the link.
     
  8. Dec 13, 2007 #7

    mgb_phys

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    This is the company behind the Oz one http://www.solarmissiontechnologies.com/ except that their figures look a bit optomistic ( 200MW = 200,000 homes, not if they are running AC is isn't) it seems a sane design.
     
  9. Dec 14, 2007 #8

    Ouabache

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    I am glad to see someone bring this up. I also read about this intriguing technology in Israel21C (a U.S.publication based in Los Angeles) and note it published in EIN Technology Today. This "Energy Tower" technology has been researched and developed under the guidance of Prof. Dan Zaslavsky, a former Chief Scientist for Israel's Ministry of Energy.

    It seems we have already discussed this concept in an earlier thread. At that time there was some issue finding the U.S. patents. I found them. They are U.S Pat # 6,647,717 Nov 18, 2003 and U.S. Pat# 6,510,687, Jan 28, 2003.

    Be careful, not to be swayed so easily. A good rule of science is to be wary of the skeptics.

    Your question was also posed by Artman in our earlier thread. The recent patent cited above, indicate water will be used from a natural or human made elevated reservoir (in conventional hydroelectric power storage, they commonly pump water to elevated reservoirs during non-peak periods of consumption). It would be reasonable to assume this technology's net energy exceeds that consumed in pumping water to an elevated reservoir. Site location of these towers necessitates a nearby source of water.

    How do they get the water up there?
     
    Last edited: Dec 14, 2007
  10. Dec 14, 2007 #9

    stewartcs

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    Unless I am misunderstanding what you wrote, how do you suppose that the net energy output can ever be greater than the energy input?
     
  11. Dec 14, 2007 #10

    Q_Goest

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    Looks like the intent is to use the latent heat of evaporation in water to cool the air, making the air + water vapor denser than the air surrounding the column. So they're not just using the weight of the water alone, they intend to augment that with all the air which is cooled by the water as well.

    I wonder how well this concept compares to the updraft version. Imagine a tower being built at a cost of x, and then having the option of making it either an updraft or downdraft. I wonder which concept, for any given tower, would produce more energy?
     
  12. Dec 14, 2007 #11

    stewartcs

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    Intuitively it doesn't seem like you would have any net energy gain. The amount of energy expended to get the water up there would far surpass any additional effects gained from the latent heat transfer.
     
  13. Dec 14, 2007 #12

    Q_Goest

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    Intuitively, it may be difficult to grasp as you say. Try this...

    The energy required to lift the water is equal to the energy obtained when the water returns back to the ground - less frictional losses or other energy losses. For the moment, let's neglect that. The water doesn't add any energy directly to the system because it obviously takes as much energy to lift it as it produces by falling.

    The other difference is that the column of air in which this water vapor is evaporated in, is cooler and thus weighs more than the surrounding air outside the column.

    We don't obtain any additional energy from the water column weight. That actually consumes energy. We do however, gain energy from the heavier column of air. So we can calculate the maximum amount of energy output (assuming 100% efficiency) by neglecting the water and only considering the cooling affect of the water on the air.
     
  14. Dec 14, 2007 #13

    stewartcs

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    The article didn't mention using the falling water for any reason, unless I missed that somewhere. I assumed it was used only for evaporation.

    So the purpose seems to be to use the cold, denser air, to drive wind turbines located at the base of the tower. A byproduct of the evaporation is the desalination of the water which, as the article states, could be used for another purpose. However, it didn't state it was to drive a hydro-turbine.

    If the water isn't used (or even if it is) I still don't think you'll have a net energy gain.
     
  15. Dec 14, 2007 #14

    Ouabache

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    The reasoning that Q_Goest describes for the net energy gain is correct. This is described in more elaborate detail in the patents cited.
     
  16. Dec 14, 2007 #15

    stewartcs

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    Well that is quite a long read. Interesting, but long.

    Anyway, it still seems that once you consider all of the losses, including the motor/pump system losses, friction loss in the falling fluid, etc, if you did get any kind of net energy gain would it be appreciable?

    Considering if you used the electrical energy generated by this machine to power the machine itself, the amount left over would have to be sufficient enough to be used elsewhere. If so, from an economic view, how long would it take to recover the cost associated with building this machine to begin with?

    Maybe that's why I don't see any popping up all over the place. :rolleyes:
     
  17. Dec 14, 2007 #16

    russ_watters

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    That's a terrible rule of science! The correct/appropriate rules of science here are that extrordinary claims require extrordinary evidence and the burden of proof is on the person claiming the new discovery/invention.
    Since that is the primary claim, it is not something to be taken for granted. It must be proven.

    Gullible people often take the position 'they wouldn't try it if it didn't work', or worse, 'they wouldn't write an article about it if it didn't work'. But that really is just gullibility.
     
  18. Dec 14, 2007 #17

    russ_watters

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    That sounds nice except that we already know it isn't true. Cooling towers are an extrordinarily well-researched device and we already know that if you spray water in the top of a cooling tower, air will flow up, out of the cooling tower.

    But it gets worse. Air at higher altitude is already cooler than air at lower altitude, and yet it is less dense. Why? Because of the altitude!

    But it still gets worse. Since air at higher altitude is cooler than air at lower altitude, evaporation is less efficient and may even be impossible.

    But it still gets worse. Water vapor is less dense than air and so evaporating water into it may actually decrease its density (I need to check the calcs on that, but in any case, there wouldn't be as much of an increase as they may think).
     
  19. Dec 14, 2007 #18

    russ_watters

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    Skimming the patents, I don't see the basic psychrometric calculations required to prove their claim. Please note that the patent office doesn't necessarily require that the claim will work, patents are simply designed to protect new/unique ideas. Anyway, the calculations aren't that difficult and I may go through them later...
     
  20. Dec 14, 2007 #19

    Q_Goest

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    Hi Russ,
    I guess the point here is the question of whether or not the idea presented in the OP is physically possible. To be fair, let’s address the issues surrounding the problem of feasibility.
    Very good point. Had to research this just a bit. From Wikipedia:
    A cooling tower is trying to cool hot water which produces moist warm air. Heat from the water is actually sufficient to warm the air, hence this is not applicable. We need to do an energy balance which is applicable.
    Not sure what the point here is. The same applies to all air both inside and outside the tower. So if the tower pressure at the top is the same as the pressure outside the tower at the top, then the pressure at the bottom of the tower, if the air is denser, will be at a higher pressure.
    True. But how high are the towers? I don’t suppose they are proposing the towers be built more than a few thousand feet high, so I don’t see why this should matter. Air pressure is still going to be 13 psia, give or take, at the top of the tower.
    Very good point. As mentioned earlier, we need to do an energy balance on this to determine the feasibility. Draw a control volume around a differential, horizontal layer of air at the top of the tower. Into this control volume, we find dry, atmospheric air and liquid water entering. There’s no reason to assume they are at different pressures or temperatures, though that could be changed also to try and improve the efficiency. Exiting this control volume is the mixture of air and water vapor. The question then is, is the air entering the CV higher or lower in density than the air leaving.

    For this CV, the first law reduces to the sum of the enthalpy for the water and air in equating to the enthalpy of the air/water vapor mixture leaving.

    This turns into a long, boring problem…

    I did some quick calcs using a database I have which indicate a rise in density of something like 3 to 7 percent, indicating the concept is feasible. Granted, I didn’t do all the math here, but I’m not inclined right now. If you do it, I’d be interested in what you come up with.
     
  21. Dec 15, 2007 #20

    FredGarvin

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    I'm personally not buying it without seeing some real numbers. One thing I have not seen mentioned is the insulation required to eliminate heat transfer from the surroundings. I am not sure how conceivable it is to expect a building that size to be perfectly insulated. I have a sneaky suspicion that the heat gained by simple conduction through the walls would be a show stopper.
     
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