Talk:Energy tower (downdraft)

message: It is good to see that you took the effort to improve this section. However I have some concerns about the discussion about capillary action. Specifically, it says that "Capillary action is how trees evaporate water sucked from the ground." AFAIK that is not true. One of the ways trees move water up is by the use of osmotic pressure: Living cells, including cells in the roots of trees, maintain electrochemical gradients across their cell membranes, and they have to spend biochemical energy to do that, see Peter Mitchell (chemist). That way ion concentrations, and hence osmotic pressure, is maintained higher inside the cell than outside, and that difference in osmotic pressure causes water to move across the cell membrane into the cell, and -in the case of trees- up the tree, see Osmosis. Evaporation higher up in the tree keeps the water flowing as long as the difference in osmotic pressure across the cell membranes is maintained. Capillary action alone wouldn't get you very far, and is not sufficient to move water up trees, let alone move it up a 1 km high tower. (Zimmermann U, Schneider H, Wegner LH, Wagner HJ, Szimtenings M, Haase A, Bentrup FW. What are the driving forces for water lifting in the xylem conduit? Physiol Plant. 2002 Mar;114(3):327-335  )
Perhaps it would be possible to mimic what trees do, which is: set up a salt gradient across a semipermeable membrane, and have the water move up the tower by osmosis. That would require a difference in osmotic pressure of 100 atm or so; let me think now, that would require a 4M salt concentration (230 g/l or so); that is a lot of salt right there, a saturated solution even? But even if you get it up the tower that way then it has to evaporate up there; you can't spray it since that would cause you to loose salt, which would have to be replenished to keep the system going. The question then becomes whether you can move enough water by passive evaporation alone; spraying water is a far more efficient to evaporate a lot of water.
Anyway, there is no free lunch here. AFAIK semipermeable membranes are not easy to maintain, and the high salt concentration needed would cause evaporation to slow down. Perhaps a pumping system would be cheaper/easier to maintain after all? JDH 10:58 AM, 27 January 2006
I have to admit I'm no expert when it comes to tree biology, I just remembered being taught back in the day that capillary action is a very important part of how plants and trees function. I also knew the lower the diameter the higher the capillary height, but I guess there is a limit on how thin you can go. It was false to assume that trees use only capillary action, what you wrote it teaches that trees invest some extra chemical energy obtained by photosynthesis to 'pump' their water up. They do this via osmosis gradients, but basically it comes down to spending extra energy to getting the water up there, it won't just climb on its own to then evaporate on top, that mechanism functions only for very small height capillaries. Trees do it with osmosis, but for us, mere mortals, simply pumping with a positive displacement pump could practically give you any height, with fairly good energy efficiency. Sillybilly 02:16, 28 January 2006 (UTC)
thread_title: capillary action?

message: I modified 1/3 of the article extensively for alternative energy at www.pickensplan.com  Hopefully we can get some more ideas, but I do think most of the changes I made are an improvement. From Wikipedia,
This article is about electricity power generation by downdraft created by evaporation of water sprayed at the top of a hollow cylinder, perhaps 100 meters tall.
Sharav Sluice Energy Tower. An energy tower is a method for producing electrical power for consumer consumption, the brainchild of Dr. Phillip Carlson, which has been expanded upon by Professor Dan Zaslavsky from the Technion. An energy tower produces electricity by drawing the energy from the air around it.
An energy tower is a tall hollow cylinder with a water spray system at the top. The water is pumped up to the top of the tower and then sprayed inside the tower which cools the warm air hovering at the top. The cooled air, being denser than the outside warmer air, falls to the bottom of the cylinder which causes a wind turbine at the bottom of the cylinder to spin. The turbine is connected to a generator which produces the electricity. The need for large quantities of water may be solved by choosing a location that is not too far from the coast.
The tower should optimally be situated in a hot dry climate, which thus allows for the greatest extraction of energy from the air. It is a form of solar power that has the peculiar advantage of also working at night. However, power generation by the energy tower is affected by the weather: it slows down each time the ambient humidity increases (such as during a rainstorm), or the temperature falls.
An alternative approach to this is the solar updraft tower, which would require huge (up to 7 or 8 kilometres in diameter) agricultural glass house collectors to capture the solar heated air, to produce 100 megawatts perhaps 5 hours per day.
The down draft tower uses some energy (about 50% of the turbine output) to pump water to the top and pressurizing nozzles. Dry air is continuously drawn at the top from the surroundings.
Some people say that making a tower to test the capacity can be much easier than an up draft tower. This is now being tested in the Netherlands.
Projections made by Altmann[4] and by Czisch[5][6] about conversion efficiency and about Cost of Energy (cents/kWh) are based only on model calculations[7], no data on a working pilot plant have ever been collected. Actual measurements on the 50kW Manzanares pilot solar updraft tower found a conversion efficiency of 0.53%, possibly this could be increased to 1.3% in a large and improved 100MW unit.[8] This amounts to about 10% of the theoretical limit for the Carnot cycle.
You can read more details at Wikipedia. The discussion is also extensive and good. In improvement I suggest is to put the wind turbines 10 or 20 meters above the desert, so ambient wind can carry the cool damp air far from the tower before it is heated by the hot desert sand. Otherwise the air at the top of the tower increases in humidity, thus producing less energy. The output is also reduced by the fact that water vapor has only about half the density of dry air.
Fresh water is typically in short supply in the best locations but salt, or brackish water is often available, but this will corrode the wind turbines, unless the humidity is under 100% at the turbines. That may be possible using very fine spray of computer controlled amounts of water. Ccpoodle (talk) 17:08, 21 August 2008 (UTC)
thread_title:  Wikifying - moved comments from article to here 

message: Solar towers can be very large when measured across, but 30 kilometers seems a little excessive! I assume the author meant 30 meters? 69.221.13.64 08:09, 11 March 2006
:The planned glass warehouse associated with the Solar Tower has indeed a diameter of 30 km. The tower itself has a diameter of 100m or so. To anyone who is not caught up in the hype of this Solar Tower project it is clear that this is totally ridiculous. The Solar Tower has one fundamental flaw, and that is that its yield is pathetic; 2% or so. As a consequence it needs those oversized collector areas.  JdH 13:24, 14 May 2006 (UTC)
thread_title:  Solar tower diameter 

message: The huge greenhouse situated at the base of a solar tower looks very vulnerable to weather.  What wind speeds could the system tolerate.  Other potential problems I have in mind would be hailstorms, snowstorms(Canada), duststorms in deserts etc..  There can't be many suitable sites in the world where such problems do not exist?
Patj 17:28, 5 August 2006 (UTC)
thread_title:  Longevity of a solar updraft tower 

message: "Water Spray Convection Energy Tower" is a ridiculous misnomer. To begin with: This is a downdraft tower, not an updraft tower as is implicated by the word convection. It is wrong, plain and simple.   The new name is also against the Wikipedia  convention to use common names, and not invent new names, and certainly not new names that are wrong to begin with.  Surfing around it turns out that there are several common names in use for Dan Zaslavsky's Energy Tower. Most commonly used is "Aero-electric power station" or "Aero-electric power plant", "Aero-electric power tower", "Aeroelectric tower" or "S.N.A.P. tower"; "S.N.A.P." stands for SNeh Aero-electric Power, Sneh is the Hebrew word for ‘Burning Bush’. Zaslavsky also uses the name "Sharav Sluice Energy Tower" I would appreciate some input on this issue and reach a consensus, to avoid further misnomers like the present one. JdH 13:50, 2 March 2007 (UTC)
replies: text: I would like to have a name that is easier to remember than the ones you listed and describes it more.  Since the energy in the hot air got there because of the sun, it is really a solar power system.  Because there is a solar updraft tower it seems natural to call this other one a "solar downdraft tower".  I put in a redirect so that  solar downdraft tower works.  I fully support a move to this name (which would make a redirect from here to there)  but in the meantime a redirect from that name to here lets me start using the potential new name.  Vincecate 19:31, 3 March 2007 (UTC)
replies: text: Please have a look at Wikipedia:Naming conventions. In particular, where possible we should avoid neologisms. Solar updraft tower was not a neologism when it was proposed, since that was already used in Jörg Schlaich's paper , but your proposed name certainly is a neologism. Furthermore, solar downdraft tower does not accurately reflect the fact that for it to work it needs hot, dry air. The required hot, dry weather can be found at the Horse latitudes or Subtropical High of the subtropical latitudes between 30 and 35 degrees both north and south, and is caused by descending air of Hadley cell circulation. The system would not work in the hot, humid climate of the Intertropical Convergence Zone, so solar radiation alone does not suffice. Aeroelectric power goes all the way back to Carlson's original patent , so it certainly has a long track record, even longer than Energy tower introduced by Dan Zaslavsky. But it might not meet Wikipedia's convention to use common names where possible. So perhaps it would be best to revert to the old name Energy tower, even though that has the problem that it is not very precise. But that may be addressed by using disambiguation, such as Energy tower (aeroelectric) or Energy tower (downdraft). JdH 08:42, 4 March 2007 (UTC)
replies: text: To me Aeroelectric power just sounds like wind power, so I don't like that.  I think it is easier to remember names that are a bit more on target.  I agree that Solar downdraft tower is a neologism, but a far better one than the Water Spray Convection Energy Tower neologism this article currently has, so at least an improvement. Google does not find that anywhere outside of Wikipedia.  But I think the disambiguation Energy tower (downdraft) seems best, since we are not supposed to make any new names.  It fits the Wikipedia way of doing things.  So you have my agreement on that.  Vincecate 11:16, 4 March 2007 (UTC)
thread_title:  Requested move 

message: I read over the deletion policy and don't see anyplace where it says articles can not talk about things that have not been built yet.  So grounds for deletion seem invalid.   Please discuss first.  If there is no consensus for deletion then it does not go through.  I don't consent. Vincecate 00:52, 9 March 2007 (UTC)
thread_title:  Theoretical not grounds for deletion 

message: This article first appeared with "brainchild of Professor Dan Zaslavsky" as the credit and was finally corrected by Krysith to give credit to Carlson for the original patent. It has been and still is an attempt at promoting Sharav Sluice's (partially owned by Dan Zaslavsky) promotion.
Theoretical was not the reason for AfD. Promotional while attempting to secure funding is reason for deletion. The original sock of the article did not give proper credit and it still proposes that there was an improvement by Dan Zaslavsky. I would think that if a pilot plant was built the article should stay, until then it's only purpose is to promote an attempt at securing funding. —The preceding unsigned comment was added by Rohar1 (talk • contribs) 01:11, 9 March 2007 (UTC)
thread_title:  Promotional is grounds for deletion 

message: Just wondering whether it is known if rain would mess up such a tower, what it's effects would be (positive maybe? due to water hitting the turbine?). Would it flood at the bottom? does anyone have any ideas as to the effects on the operation of it? not that it rains often in the desert, just asking. (212.46.56.195 16:50, 23 March 2007 (UTC)
replies: text: That would most certainly mess it up. These power plants work only in a hot, arid climate. The idea is you "harvest" hot dry air, and cool it down by allowing water to evaporate at the top of the tower in order to generate a downdraft of cool humid air. When it rains the ambient humidity goes way up, and as a result evaporation comes to a grinding halt. JdH 18:38, 23 March 2007 (UTC)
thread_title:  Would rain mess it up? 

message: Solar energy resources span from the heat and light of the sun over to wind, waves and the products of photosynthesis. These are resources but solar technology is something else. A wind or wave turbine is not a solar power technology. Burning wood is not a solar energy technology because fire is its own separate thing with no direct connection to the sun. Although the downdraft tower, in a similar way to evaporative coolers, clearly uses a solar resource I don't think either of these technologies are properly described as solar energy/solar power technologies. I've edited out the reference to solar power. Mrshaba (talk) 16:11, 20 March 2008 (UTC)
thread_title:  Powered by a solar resource but not solar power 

message: Hang on, wouldn't the energy required to pump all that water against gravity to cool the air at the top off set any electricity produced by the tower?? --Pavithran (talk) 08:46, 6 June 2008 (UTC)
replies: text: No.  The sun is heating up the air outside putting in energy.   It is not a closed system.  It really works.  :=)  Vincecate (talk) 11:53, 6 June 2008 (UTC)
thread_title:  Principle of COnservation of Energy gone bust? 

message: So then is the actual output power only half as much? I think this could be stated more clearly either way. — NRen2k5(TALK), 04:47, 29 April 2009 (UTC)
replies: text: I think you should assume that the margin of error is much larger than a factor of 2 in those estimates and just not take them too seriously.  Vincecate (talk) 19:15, 1 May 2009 (UTC)
thread_title:  Actual output 

message: Concept summary
An energy tower (also known as a downdraft energy tower because the air flows down the tower) is a tall (1,000 meters) wide (400 meters) hollow cylinder with a water spray system at the top. 
Alternatively, temperature decreases uniformly with positive changes in altitude at a rate of ~ 16° C per mile. Therefore, should it be possible to tether heat conducting cables up through the inside of a convection chimney to a sufficient altitude above the top, could enough heat be drawn out of the air in the chimney to sustain a sufficient downdraft to power turbines 24 / 7 ? A flexible base would permit the tower to tilt. Regular lift maintenance balloons would be released to rise up the cables to the top..
Or, in the other direction, as long as the thermal inversion properties of the ocean hold up shielding the lower, colder depths from the circular flow of using the surface as a heat sink, why not have a 3D lattice of carbon nano tube elements inside the Downdraft chimney to cool the air so it falls and place the units off shore?  — Preceding unsigned comment added by William Hale (talk • contribs) 00:02, 28 July 2013 (UTC)
thread_title:  Proposed Concept summary upgrade 

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