Can the Energy Tower design truly generate a positive net energy?

[Unbeliever]

Here might be a very good idea if it could work:

http://inventorspot.com/articles/energy_tower_power_15_Earth's_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?

 

[russ_watters]

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.

 

[FredGarvin]

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."

 

[stewartcs]

They've been working on the concept since 1983, and together have spent more than 150 man-years researching, designing, testing, and analyzing

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

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

http://www.enviromission.com.au/project/technology.htm

 

[Unbeliever]

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.

 

[stewartcs]

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.

It uses air according to the link.

 

[mgb_phys]

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.

 

[Ouabache]

I am glad to see someone bring this up. I also read about this intriguing technology in http://www.israel21c.org/bin/en.jsp?enDispWho=Articles%5El1879&enPage=BlankPage&enDisplay=view&enDispWhat=object&enVersion=0&enZone=Technology , 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.

Thanks! I thought that sounded a bit too good to be true.

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

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?

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?

excerpt from U.S. Patent 6647717:
In accordance with another advantageous feature of the present invention, the water is preferably supplied from an elevated water source. This source can be a natural source of water or a plurality of elevated operational reservoirs capable of storing a volume of water that will allow a water spray distribution with time over a whole week not in conformity with the time distribution of pumping the reservoirs operating only in part of the hours over the week, preferably, when the return or delivered energy is low. A plurality of operational reservoirs may be advantageously mounted within the tower side wall and provide a supply of water lasting in the range of about minutes to fractions of an hour. This is in order to divide the pumping into serial elements and parallel elements, as well as providing other advantages.

 

[stewartcs]

It would be reasonable to assume this technology's net energy exceeds that consumed in pumping water to an elevated reservoir.

Unless I am misunderstanding what you wrote, how do you suppose that the net energy output can ever be greater than the energy input?

 

[Q_Goest]

Unless I am misunderstanding what you wrote, how do you suppose that the net energy output can ever be greater than the energy input?

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?

 

[stewartcs]

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.

 

[Q_Goest]

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.

 

[stewartcs]

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.

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.

As project founder Professor Dan Zaslavsky explains, the Energy Tower works on the basic principle of convection: hot air rises and cold air falls. The 3,000-foot tall tower, with a diameter of 1200 feet, would take advantage of the heavy falling weight of cold air.

Any kind of water - from a sea or drainage ditch - would be added to the top of the tower. The water would cool the hot air at the top, and the heavy cooled air would sink downwards, gathering speed as it falls, and would be used to power turbines at the tower's base. The turbines would be connected to a generator, which produces electricity.

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.

 

[Ouabache]

The reasoning that Q_Goest describes for the net energy gain is correct. This is described in more elaborate detail in the patents cited.

 

[stewartcs]

The reasoning that Q_Goest describes for the net energy gain is correct. This is described in more elaborate detail in the patents cited.

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.

 

[russ_watters]

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

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.

It would be reasonable to assume this technology's net energy exceeds that consumed in pumping water to an elevated reservoir.

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.

 

[russ_watters]

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.

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).

 

[russ_watters]

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.

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...

 

[Q_Goest]

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.

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.

Very good point. Had to research this just a bit. From Wikipedia:

Natural draft, which utilizes buoyancy via a tall chimney. Warm, moist air naturally rises due to the density differential to the dry, cooler outside air. Warm moist air is less dense than drier air at the same temperature and pressure. This moist air buoyancy produces a current of air through the tower.

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.

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!

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.

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.

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.

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.

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.

 

[FredGarvin]

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.

 

[Ouabache]

I believe a healthy amount of personal skepticism is a good thing. However my point for the original poster, is to think concepts through clearly weighing information equally from both sides before drawing any conclusions.

Credibility of the researchers is made with experience. For example my graduate advisor was a respected world-known researcher on electromagnetics. When he spoke or wrote down his thoughts, scientists in the field held his credibility in high regard, compared to an unknown graduate student that I was at the time.

Similary with http://www.technion.ac.il/technion/agr/members/zaslavsky.html began as a blacksmith, then bookbinder and taught himself natural philosophy )

Perhaps a respectful thing is to read his research papers on this and even enlist his comments on our questions posed.

 

[stewartcs]

Perhaps a respectful thing is to read his research papers on this and even enlist his comments on our questions posed.

I don't see how what Russ said about the direction of air flow is debatable.

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.

So maybe the good Dr. could explain that first.

BTW, I also just worked on a project with a guy with a PhD from MIT in the particular subject matter of the project. I was no more impressed with his abilities as compared to some of the other guys I work with who have just a BS.

 

[Ouabache]

Just noticed there is a good Energy Tower video clip that describes a few more particulars. Their information is my source in my replies below. There is also a contact, (may be found towards the bottom of http://www.energybytower.com/50379/%D7%94%D7%A7%D7%A9%D7%A8%2D%D7%94%D7%99%D7%A8%D7%95%D7%A7 ) in case anyone here has specific questions.

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.

These aren't conventional cooling towers as Envromission are planning, which operate while the sun is shining. These towers are to make use of the Hadley Cell circulation that naturally causes a downward flow of air. By increasing the density of the descending air with evaporating water, the air will accelerate down the tower, a process similar to wind shear.

The downdraft in the Hadley Cells are +/- 30 degrees from the equator, which is where the Energy Towers are designed to be constructed. The Hadley air movement is 24hrs/day so the Energy Towers may potentially operate around the clock.

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?

They've calculated 45% net energy (33% consumed for pumping water to the top of the tower, 22% other system losses).

Some more detailed descriptions for the Energy Tower, may be read at http://www.iset.uni-kassel.de/abt/w3-w/projekte/new_et-brochure_zaslavsky.pdf. They express the thermodynamics of the design in section 1.3

 

[Artman]

There are several real world problems making this design nearly impossible to build with current levels of construction materials and methods:

1. Weight of the water in the amount required. Based on calculation I made before on a similar post, this tower will require close to 155,000 GPM to operate. Moving at 14 FPS up a 3000 ft tower requires about 4 x 155,000 = 640,000 Gallons in the piping to span the entire length of the tower, 640,000 x 8.33 gal/lb = 5,331,200 lbs of water alone. Divide that by even 200 pipes to carry it up and that is still 26,656 lbs of water sitting in the pipe. They will need to use some sort of basin arrangement because I doubt they will be able to support the full weight from the bottom. This means multiple pump sets.

2. That would require 200 5" pipes 3000' long each. At the bottom of each pipe the static pressure is nearly 1300 PSI.

3. The working conditions to build or maintain the top of that tower would be incredibly harsh (and frightening).

4. The tower creates wind, if it does so as it is designed, the amount of wind could be horrendous, this will be a problem at the top and the bottom. I can see this thing sucking many a worker from his or her perch and tossing them down a 3000 foot high chute.

5. They will run out of money long before they get this thing built, long before they uncover the problems with the design just from unknown conditions in creating a structure this big.

My figures may be off a little (I estimated several times), but the problems do still exist, just maybe not to the magnitudes I describe.

 

[stewartcs]

They've calculated 45% net energy (33% consumed for pumping water to the top of the tower, 22% other system losses).

Some more detailed descriptions for the Energy Tower, may be read at http://www.iset.uni-kassel.de/abt/w3-w/projekte/new_et-brochure_zaslavsky.pdf. They express the thermodynamics of the design in section 1.3

The first thing I noticed in that report was this statement:

Question series no.1 - Computation of the net power production and desalination output

...Unfortunately, many attempts to compute the net deliverable power made by reviewers were intuitive, and short of physical and engineering reasoning.

And that's in their own report! :rofl:

How on Earth can anyone say there is a net energy increase of 45% when they are "guestimating"?

 

[Ouabache]

Artman i like your thought process. Perhaps we can run these numbers by the engineers on this project and get some feedback.

stewartcs you probably will want to reread that reference again, as you've misinterpreted that section. That section has to do with potential reviewers of this design. The project team determined a 45% net energy after considerable calculation and statistical analysis of their data. One sidenote, the government of India has made their own independent review of this project, with a positive outcome. They are committing to a collaborative effort with the Israeli team, in construction of the Energy Tower. There is another good reference, this one by http://www.ecmwf.int/about/special_projects/czisch_enrgy-towers-global-potential/report_2006_extended.pdf that elaborates on analytical considerations in determining net energy from the Energy Tower design, (beginning on page 5).