Half a croissant, on a plate, with a sign in front of it saying '50c'
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Desert Generator

Here's an idea to harness desert T fluctuations for energy
  (+8)(+8)
(+8)
  [vote for,
against]

Take about 20,000 gallons of water out into the desert, and put it in an enclosed clear tank, with mirrors focused all around it. Have a tube coming up from the tank, with a turbine in it, so that the steam generated by daytime heating turns the turbine, then goes on upward as it expands and cools. It then condenses and collects as liquid water in a tank at the top of the tower. When night falls and no more steam can be collected and condensed, allow the liquid water to fall the 100 feet or however tall it is, through another tube and turbine, and back into the tank at the bottom. Heh, I can just imagine a desert-parched wanderer coming upon this contraption, and thinking,"By golly, they don't make'm like this back home!" in reference to a moonshine still. We'd just have to make sure no curly tubes were showing.
Darknight, Dec 30 2002

(?) Boeing Solar Tower http://www.boeing.c...rgy/powertower.html
Boeing's kinda economic version of the above [FloridaManatee, Oct 04 2004, last modified Oct 21 2004]

(?) To all who doubted my idea, eat this news! http://story.news.y...stralia_tower_col_1
Australian solar tower to be built, 1,000meters high! [Darknight, Oct 04 2004, last modified Oct 21 2004]

The world is turning to dust http://www.unccd.int
Kofi Annan looks really worried on this one. [django, Oct 04 2004]

[link]






       What was the negative vote for?
Darknight, Dec 30 2002
  

       auto-boner does that.
po, Dec 30 2002
  

       Why does it do that?
Darknight, Dec 30 2002
  

       jealous, I think. what do you think?
po, Dec 30 2002
  

       I know not why, but I'd guess that they have it set so that if no one responds, you get a fishy. That sucks!
Darknight, Dec 30 2002
  

       ok, two negatives and no one telling me why. great.
Darknight, Dec 30 2002
  

       Sounds like a good idea to me.
snarfyguy, Dec 30 2002
  

       Any solar device has a maximum of (a quick google later) about 150 Watts per square meter (averaged over a 24 hour period) to play with. What will differentiate one device from another is how much of this the device can capture.   

       I'd have a tendency to create smaller rather than larger devices as you can assemble them as a sealed unit, deliver them en masse and replace them piecemeal should they fail.   

       Sounds like a cute idea, though. Have a sun-baked croissant. I've brushed most of the sand off.
st3f, Dec 30 2002
  

       I like the idea. +
bristolz, Dec 30 2002
  

       Enough power? Uncertain. You might as well throw in a wind station, too, while you're in the desert. The tricky part will be to keep it clean. As far as power transmission, I suppose cables have lived in severe environments without too much difficulty.   

       I'm becoming really curious as to why the Sahara is the way it is. Does it not benefit from any oceanic activity off the west coast?
RayfordSteele, Dec 30 2002
  

       st3f, I don't agree with the calculation, although I can't verify Darknight's assumption either.   

       Con: I guess you're going to have problems with cavitation as the tower is v. high. Also, I agree with st3f that solar charging alone isn't enough.   

       Pro: However, like many renewable energies thermal storage is ultimately dependent on the sun's energy. But like wind and wave power, it can be a fairly concentrated source; you could potentially gather more energy than is reflected onto the tower alone. The power depends on thermal differential, storage capacity, conductance of heat exchanger, etc.   

       Your idea sounds v.similar to Boeing's Solar Tower, but that uses molten salt as an energy storage medium. I guess if water had been easier, they'd have tried that first.   

       Anyway, I wouldn't invest in it, but it's not a bad idea +
FloridaManatee, Dec 30 2002
  

       Solar steam power generation with an array of mirrors in arid regions is a well-baked (if not quite ubiquitous) concept. The notion of condensing the steam at an elevation and generating power from the returning water is interesting, but I think thermodynamically unworkable; otherwise you could use it at any steam-powered generation facility.   

       Also, you whine too much and are way too obsessed with votes. Chill.
egnor, Dec 30 2002
  

       Even better, how about a desert un-generator. Desertification is a major world problem, we could get an army of volunteers to eat tomatoes (or a hardier variety of plant's fruit) and wander around the desert cr*pping all over the place. Plants would grow from the egested seeds until it was a new Eden.   

       We could get the tomatoes from the European Union.   

       I know desert climates don't suit tomatoes, so we would have to start at the margins.   

       Please donate any 'for' votes to DK.
FloridaManatee, Dec 30 2002
  

       I think if you read between the lines this system is a bit more complicated than it appears to be on the outside.
Shz, Dec 30 2002
  

       Most steam systems operate one-way, that is, they only develop power from the pressure of the steam itself. What I'm proposing is a means by which to capture the remaining energy left in the steam, after it condenses. That's the real difference between this and other similar ideas. The Boeing idea is somewhat similar, but would likely be less efficient, since they use more heat exchangers. My idea converts steam directly into kinetic energy by solar energy, rather that using solar energy to heat a medium, to then heat water. Then, with the remaining heat in the steam, it rises into the collection tank at the top, which is quite different, in that it can remain there indefinitely without losing energy, or it can be used as needed in times of peak demand. I think Boeing is on the right track though.
Darknight, Dec 30 2002
  

       I was going to post something similar to this. An array of magnifying glasses, tracking the suns course, which would flash steam the water in clear cylinders to drive pistons. The torque generated would lift a large weight during the day which in turn would generate electricity, or run pumps, or whatever else during the night as it descended.   

       /Question/s/ Would a series of in line magnifying glasses, decreasing in size, each refocusing the previous one's focal point into a smaller and smaller point of light generate more heat than a single magnifying glass? And if so, by slightly tilting the angle of each could you focus a point at ninety degrees from the lights original course?
Anyone?
  

       I'm with [Sleepygrass]. (Well, as long as some troll doesn't come along and tax me for eating it.)   

       I like the thinking/toying with new ideas aspect. Arrays of tracking mirrors I've seen are usually focusing on something a little thicker than water, though.   

       I met this guy in Australian who had a whole system for going bush permanently - he was going to take a large rounded rock, as seem to just stick up out the ground there, build a low wall around it and collect the rainwater (even in dry areas, when it rains you get a lot of water coming off those rocks). Then he'd have a simple wind-driven pump to get water up to a tank, where it could run back down through a turbine when he needed electicity. He was actually an engineer/geologist, so he wasn't just ranting (like me at the moment).   

       A note on the trees/Sahara - pick up Alice Outwater's book WATER for nice description of that (handy for anyone who's experienced the rain that big trees make all by themselves when it's dry everywhere but under the tree).
rowlycat, Dec 31 2002
  

       regarding desert un-generators, the guys at Driwater (look it up, no need to add link) have been planting trees in the Sahara for some time now, using it as an opportunity to both publicise their product and to "re-green" those areas lost to the sands.
cswiii, Dec 31 2002
  

       [Rayford] - //I'm becoming really curious as to why the Sahara is the way it is. Does it not benefit from any oceanic activity off the west coast?// - There are two other deserts that border directly onto ocean - the Atacama (in South America) and the Namibian (in Southern Africa). You could probably include the Californian desert in that list too. It must be something to do with not enough interruption to the airflow, or superheating the airflow, so that it doesn't rain - but now I'm rambling and, oh thanks, yes these cheese nuts are rather nice.
PeterSilly, Dec 31 2002
  

       Peter, Rayford: Deserts generally form to the west of mountains. East coasts tend to be wetter than West coasts. This is due to the Earth's prevalent east-west wind set up by its rotation.   

       Florida: I got the number by googling and took a concensus. It is averaged over a 24 hour period, so should peak at over twice that. If you have a more reliable source (easily possible), drop it in.
st3f, Dec 31 2002
  

       "look it up, no need to add link"   

       No, but it's nice to.
bristolz, Dec 31 2002
  

       //2600 ideas that have no negative votes// I guess now I know exactly how bland my ideas are since 4 of those are mine.
half, Dec 31 2002
  

       Great idea. Takes alot of energy to convert water to steam though. Maybe just solar pump the water to the top as liquid then use the potential energy to drive a generator at constant speed or feedback a control to vary the flow. Would be much easier to construct near a hill so you don't have to build a tower to hold 20k gallons.
daisyifudu, Dec 31 2002
  

       I don't have much faith in my calculations, but I believe them when they say that the gravitational potential energy of the water, even if you do get it all to condense at 100', is absurdly miniscule next to the energy you expended to turn it to steam. If this sort of thing is possible, this is perhaps the reason it isn't widely done -- it's not worth it.
Monkfish, Dec 31 2002
  

       You're not expending energy turning it to steam, you're capturing energy. It does need a tower, rather than a hill, also, so it can be surrouded by mirrors. Also, it takes advantage of the leftover energy in steam, after it passes through the initial turbine...steam still has enough energy left to rise. In doing so, you can capture that leftover energy. 20,000 gallons held 100 feet in the air comes to 16,691,850ft/lbs of work that can be done. Divide that by the 33,000ft/lbs of work per minute to make one horsepower, and you get 506 horsepower/minute. Multiply that by 750watts per horsepower, and you get 379,360watts/min. Divide that by 60 to determine the watt/hours, and you get 6,323. Reset the units to kilowatts and you get 6.32kw/h from one cycle. One of these alone would generate a fair amount of electricity, but if you take the Boeing approach, and make farms of these, you would have a formidable energy source for desert regions.
Darknight, Dec 31 2002
  

       For "expended", read "captured", or "employed", if you like. The point's that the extra energy captured in this way is insignificant. I agree that the GPE is about 227kJ; but I make the energy you need to capture to turn the water to steam about 1.95PJ, or about eight and a half million times that. This is a lot of effort to increase your [edit begins] total energy capture by 0.00000012% [edit ends] -- and the part about getting all the steam to condense 100' in the air still troubles me.   

       There's a pretty good chance I've made an error somewhere, but I think the problem still exists if I'm off by less than several orders of magnitude (which is possible).
Monkfish, Dec 31 2002
  

       I am just as confident about my calculations as monkfish is about his. The 6.32kw/h is produced over one day/night cycle of heating and cooling, and that's only the leftover energy that the primary turbine couldn't extract. The scale of the tower could be worked out to the optimum size. There's nothing magical about 20,000 gallons and 100 feet high. You could have 50,000gallons perhaps, and 200 feet. Specifics take time to work out. I'm not precisely sure how you came upon the 0.0000085% increase in efficiency, but 6.32kw/h is nothing to waste, when it can be harvested fairly cheap.
Darknight, Jan 01 2003
  

       Erion, that's exactly what I suggested. Collect all the condensation in a tank at the top, and let it fall, once no more can be added to it, through another turbine apart from the first one. You would need different designs for the steam turbine and water turbine anyway. You were right on the money about the southwest US. That's where I first pictured, and felt that this idea would be most beneficial. Looks like we're on the same wavelength.
Darknight, Jan 01 2003
  

       (You seemed to be deliberately missing the point there, Darknight. The size of the tank doesn't matter at all, and, doubts aside, raising the water to arbitrary heights affects things very little. If you're really keen on the extra ten-millionth portion of energy, there would be cheaper ways to get it -- adding a makeup-case mirror to the array, for example.)
Monkfish, Jan 01 2003
  

       I think it's also a fallacy to think you're getting any additional energy by letting the steam condense at altitude. The steam isn't rising of its own accord; it only does that by displacing air, and there isn't any air in your steam pipes. Instead, it's overcoming gravity by use of gas pressure -- and that's pressure you could have harvested in a turbine.
egnor, Jan 01 2003
  

       You all are entitled to your opinions, as I am. Now, 150watts/square meter landing on 100sq meters of collecting mirrors comes to 15,000watts. Now, 15,000watts, in 24 hours is 360kw/hrs. I don't claim that this could power any large city, certainly not one by itself. However, the basic design is fairly simple, which should make it not-too expensive. A group of these could be useful for a mid-sized town. Oh...since the top of the tower would likely be much cooler than the bottom, it would form a low pressure area relative to the bottom. Even with the tower being sealed, the steam would make its way to the top, where it would condense.
Darknight, Jan 02 2003
  

       I thought this was going to be about goats eating everything, they are the best desert generators(makers)   

       The sahara was created by nomadic tribesman and their goats making their way south from babylon or someplace similar.
Trodden, Jan 02 2003
  

       Ahhh, but you're forgetting. You could build a tower of this size or smaller using steel tubing, perhaps, rather than I beams and the like. Or, you could downsize the tower to say 50 feet, and triple the square meters to 300. That gives you the equivalent in 8 hours of 150watt/100sq meter for 24hours, while reducing the cost of the tower by at least half or more. Granted, you'd need more mirrors, but they're not as generally expensive(or shouldn't be) as tower-building. It would take more ground space, but come on, 17.3x17.3 meters is not that much room to give up for such a cause. The very essense of my idea is to find a way to capture the power from those huge changes in temperature during a day/night cycle. When I think of all the power that strikes our deserts each day and is not put to use, it sickens me in an age where we claim that we need/want to make use of newer and cleaner power sources. To make something like this work, you have to be willing to fail a time or two. Boeing is trying a similar approach. Apparently they're not too scared, and they see some potential. I saw the potential, too, before I even found out about Boeing's tower. The only real difference between mine and Boeing's approach, is how we store extra energy for later use.
Darknight, Jan 02 2003
  

       Why all the hostility? (By the way, I am fully capable of determining the weight of a given volume of water. That's part of what I used in my initial calculations.)It is possible, and probably a good idea, to re-evaluate the geometric design of a tower for such a situation as this. It doesn't have to be tall and skinny. You can triangulate as well.
Darknight, Jan 02 2003
  

       Read the last link provided.
Darknight, Jan 04 2003
  

       Darknight, I've got no idea why you think the story you linked has anything to do with this idea.   

       About which: Setting aside the source of the energy for a moment, there's a steam turbine here like any other. Existing turbines don't force steam into collection towers. They directly capture the remaining energy -- the heat of the steam, which in this design is escaping out into the desert. (Looking back, I think this is also more or less what egnor's annotations say.)
Monkfish, Jan 04 2003
  

       It has everything to do with my idea. The only difference is that mine attempts to increase overall efficiency through recycling the condensation.
Darknight, Jan 04 2003
  

       This is all very interesting, but since when does a halfbakery idea have to make sound business sense in order to be accepted?
Seems to me that the fact the thread has taken this turn is a good indication that the idea has some practical merit and is worth investigating further. So [DK], don't view the in-depth analysis going on here as hostility, if these guys hadn't had their imaginations captured by this idea then I'm sure they wouldn't have bothered taking it further.
egbert, Jan 04 2003
  

       (Speaking for myself, egbert, I don't think the idea -- though interesting -- does have practical merit; and any further investigation by its author should begin by thinking about the reasonably polite annotations to it without the attitude of blind denial or the weird, delusional triumphalism. I don't see that the economics of hypothetical solar power facilities are very relevant either, though.)
Monkfish, Jan 04 2003
  

       Well, yes, that's a different question isn't it?
egbert, Jan 05 2003
  

       [UB] //Electricity retails for around 11c/kwh ... Issuing 25 year Utility Bonds yielding 4.5%//   

       Oh-oh; now you've done it. You've wandered into FloridaManatee's territory. For the past 7 years, I've been buying, selling and financing power plants (Project Finance magazine deal of the year, etc.) and I am a semi-specialist in renewable and distributable generation.   

       (-) Cost of financing is very high: A new-technology, renewable energy generator simply could not be financed at 4.5%. Even the long end of the Utility Benchmark is trading at a yield of 7.9826%. Plus you've got a huge spread for merchant risk if you are pricing relative to on-grid tariffs (e.g. Mirant and AES debt is trading in the double digits) and then there's documentation costs and up front fees. Debt guarantees would be needed and that'll push your cost of funding up to your cost of equity.   

       (+) The marginal cost of supply in desert areas is way more than urban areas: The cost of financing is (almost) moot in locations where both grid supply and fuel transport are infeasable, e.g. China's Inner Mongolian desert, where the Asian Development Bank have been financing the 37MW Dabancheng wind farm. In these areas, the only question is "What's the cheapest method of electrification and can it be afforded at that price (after factoring subsidies)?"   

       Hence, [DK's] idea will likely only have to compete against existing wind and solar technologies. The first step is a fesibility study, as has been done here, but on more detailed basis, followed by a pilot plant.   

       I wish him luck. If he needs a little friendly advice on how to go about it, I can be contacted at the email address on my profile page.
FloridaManatee, Jan 05 2003
  

       [UB] I think that remark was aimed at me. If so, let me clarify: I know, I was addressing [DK]'s perception of hostility not your serious discussion. If it wasn't aimed at me, then please forgive my overactive ego gland.
egbert, Jan 06 2003
  

       I've kept an eye on this topic for a few days now. In addition to the already noted concerns for feasibility, there's a factor that hasn't been addressed *much*.

Steam takes up anywhere between 1600 to 1800 times as much volume as liquid water. For the sake of discussion, let us use the figure 1650 (conservative? yes, but let us presume that the gods are in a good mood today). In a closed system containing 20,000 gallons as described, if we plan to gather the steam throughout the day and hold it in "queue" for condensation by the temperature drop after nightfall, this would necessitate a volume of 2673 cu. ft. for liquid, and an additional 4,411,469 cu. ft. for steam storage. I arrive at these figures because re-compressing the steam for storage or to aid condensation would significantly hinder the turbine's performance (thus negating the whole premise of the idea, and causing the proverbial shooting of one's own foot), combined with the consideration that the typical car here in the Sonoran desert can achieve and maintain an interior temperature of over 230 degrees during the day (*without* intentionally focused energy), so one shouldn't count on the steam re-condensing in any appreciable amount until after dark, especially with mirrors focused around the structure's base.

With the aforementioned footprint of 17.3m x 17.3m, this structure would need to be a minimum of 1370.2 ft. in height to contain the steam and liquid volumes alone (not including the power generating equipment, plumbing, or building materials involved, or even the "100 feet" or so needed to give the falling water enough energy to power the second turbine). Not only will we have made quite a "nifty" use of the desert environment, but we will also have built one of the top five tallest buildings in the world on a rock base that has limited conventional construction endeavors in the region to a mere 31 stories, as well as achieving a "hands down win" with regard to the largest height-to-footprint ratio (in excess of 50:1). This ratio would make most engineers "a bit apprehensive", to say the least.

Then again, I suppose it would be foolish of anyone to suspect that you haven't already worked this out.
X2Entendre, Jan 06 2003
  

       Store the steam in a balloon.
egbert, Jan 06 2003
  

       A really, really big balloon, no?
X2Entendre, Jan 06 2003
  

       I was hoping for 'Dessert Generator,' powered by the fluctuations in my waisteline...
RayfordSteele, Jan 06 2003
  

       Yes, but easier to construct than a really, really big tower, no?   

       Thinking went: ratio of 50:1 might present problems as a normal structure, but would not be excessive as a tie. How could it work as a tie? If the steam were contained in LtA vessel. Hence balloon.   

       I'm not a balloon expert, but I know there are a few around here so I thought I'd throw it open to the floor to see how it was received.
egbert, Jan 06 2003
  

       OK [egbert], I'm willing to consider the merits of that, but it may deserve a new heading. I nominate you (if you would be so kind, sir) to enlist the services of such an expert to post for us the idea and specifications for the "REALLY, REALLY BIG Balloon".
X2Entendre, Jan 06 2003
  

       Isn't this just sort of an open-sytem diurnal heat exchanger? Instead of cooling towers, the cold of night is used instead?
rapid transit, May 10 2003
  

       all these comments are a year old. When do they get taken off the site? I'd like something current to discuss. Interesting idea, by the way, but I don't think power in the dessert is the first priority for renewable energy systems.
izumi, Oct 21 2003
  

       May was five months ago, not a year. And your comment brings this idea up to date. There are plenty of new ideas at the bakery if you will only take the trouble to look for them. Old ideas don't dissapear unless they are marked for deletion (and this one isn't) so don't get your panties in a twist. Vote, say something constructive, or just go away.   

       + to the idea.
k_sra, Oct 21 2003
  

       I like this idea, even if it isn't feasible.   

       You could build towers at the shores, and work your way inland towards the desert. Build a small canal of salt seawater alongside the towers. Desalinate the seawater in your tower (first cycle), then use the salt as a heating medium (the Boeing tower) and collect the fresh water to combat desertification. Work your way through the desert. Also, you could use part of the salt as an ingredient to make glass (plenty of sand in the desert), glass which you use to build the heating element of your solar-thermal tower.   

       It could work, knowing they're building this huge tower in Australia.   

       See link: the world is turning to dust.
django, Jun 16 2004
  

       Use a stirling engine (heat difference engine) to pump cold water (cold side of engine) from deep below and the intense heat of the desert would be the hot side of the engine. The thermal transfer would make it workl.
daniel_bingamon, Mar 09 2007
  
      
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