The tricky part of building a solar tower is building the immensely tall chimney at the centre of the construction.
However, since all the chimney is there for is to guide and concentrate airflow, it doesn't necessarily need to be built from traditional materials.
As soon as the flat part of the solar tower is complete, there ought to be a significant updraft at the centre of the construction.
It ought to be possible to utilise this updraft to lift a kite that supports a flexible material chimney. The longer the chimney, the more powerful the updraft.
As the kite soars higher, more bits of chimney can be sewed onto the bottom, and the kite let out a bit.
Eventually, once the 200MW rated chimney is at full elevation, you can stop sewing on new bits of chimney - or, continue in order to increase the energy rating of your solar flue.-- zen_tom, Nov 22 2006 Solar Tower http://www.visionen...nv/solar_flue.shtml [zen_tom, Nov 22 2006] fill it with this stuff http://www.sprayfoa...s/ahpg.cfm?spgid=12spray polyurathane foam [bleh, Nov 24 2006] to prevent this http://www.bounce-a-lot.co.uk/sky24.jpgor just stitch a car dealerships name on the side and get more funing [bleh, Nov 24 2006] Solar Tower Vortex Generator Solar Tower Vortex GeneratorA sister idea that came to mind in response to points raised by [swyves] [zen_tom, Nov 29 2006] Why sew? Why not start with an accordion?-- ldischler, Nov 22 2006 [ldischler] Constructing an accordion capable of being extended to 1km by a kite might be more of a challenge than sewing on new bits of cloth. It doesn't matter how it's done, the point is that kite-erection is a lot easier than building it out of bricks and mortar. I leave the details of how to actually construct the flimsy flue down to those with better minds than mine.
[21Q] if your tower has an equal diameter at the bottom as it does at the top, the speed of the air flowing through it will be the same at both ends (think of it in terms of a pipe, measure the water going in one end, and then measure the water flowing out of the other, given equal sizes at each end, the flow-rates should be the same)-- zen_tom, Nov 22 2006 Why not use a hot-air balloon instead of a kite?-- angel, Nov 22 2006 [21Q] Ah yes I see - No, I think the purpose of the tower is to create a large temperature difference between the hot air at the surface and the much colder temperatures at high altitudes - it's this temperature difference that produces the airflow.
As for stacking turbines, each turbine will slow the airflow somewhat - I don't know the details, but there must be an optimum turbine/power ratio with 1 turbine operating at a higher velocity producing lots of energy, and lots operating at much reduced velocities, producing less energy per unit. I don't know where that optimum lies.
[angel] Why not? Yes, that would work too - I was just thinking about the automatic updraft formed at the centre of the collection zone and figured a kite would do the job. The problem with the hot air balloon is that they are harder to steer - although, laminar(?) flows around the balloon by the rising air should help keep it in the right place - so perhaps that is a better method.-- zen_tom, Nov 22 2006 I'd never seen solar chimneys before, quite ingenious. Not only would this idea make them more cost effective, and more efficient it being easier to erect far higher and wider chimneys, it also makes the whole plant tantalisingly portable.
Would these work in the Antarctic?-- theleopard, Nov 22 2006 Is it possible to do this without the kite portion restricting airflow enough to significantly lower the power generation capacity?-- NoOneYouKnow, Nov 22 2006 //Would these work in the Antarctic?//Only for 6 months of the year, plus you'd have to keep cleaning off the snow - but, I suppose so.
//Is it possible to do this without the kite portion restricting airflow enough to significantly lower the power generation capacity?// You could try building the chimney out of a solid material like bricks? But seriously, I don't know how much power would be lost suspending a light flue from 1km up - but as long as it's less than say 20% of the total power output, it shouldn't be a problem - it's still effective, and better than using bricks.
What would be *really* cool would be to manage to set up self sustaining vorteces of air that might act as a flue. This way, you don't even need a chimney! Again, that's one for people with better brains than mine.-- zen_tom, Nov 22 2006 A solar tower doesn't use solar panels, just glass (you can put solar panels underneath the glass if you want, but the real energy is produced by the flow of warm air going up the chimney) but yes, you would need to keep it clear of snow, dust, and other light-blocking elements.
Yes, high wind could blow the tower out of shape (twisting the tower so to block off the airflow would pose a problem) or out of alignment - but this problem is something that would effect a static tower (only not as much perhaps) The kite could be steered so as to counteract the forces of the prevailing winds - and perhaps it might be prudent to have guy-ropes attached to the chimney (after it's initial elevation) to help hold it in place.-- zen_tom, Nov 22 2006 //Only for 6 months of the year, plus you'd have to keep cleaning off the snow - but, I suppose so.//
I was thinking you might get a much greater force from the air flow if the hot air was being generated in a cold environment. Probably not worth it then. Poop.-- theleopard, Nov 22 2006 All you need is one long roll of fabric. As you unroll it, you sew the selvedges together to form a tube.-- ldischler, Nov 22 2006 //hot air was being generated in a cold environment. //You're right(ish) but up at 1000m, the temperatures are already pretty (ant)arctic (hence the requirement for the long chimney) I was thinking it might be a good idea though since it should be much easier to control environmental conditions under one of these things, allowing you to transform tracts of previously hostile land into fertile greenhouses.
//All you need is one long roll of fabric// Yep, that would do it - plus if it did blow away in a gale, you can just roll out another one - not an option with a bricks-and-mortar flue.-- zen_tom, Nov 22 2006 ...and at sunset each day...?-- ConsulFlaminicus, Nov 22 2006 It takes time for something to cool down, if we have objects with a high thermal capacity beneath the collector, we can stretch-out the energy transfer between the sunlight and the air in the system - If we can stretch it out to 12 hours, then we have a day and night system. If we can't, we might be able to switch off the turbine and, assuming it is no longer sapping the airflow of its speed, maintain enough airflow to keep the system afloat. Again, if we say 20% of the energy is needed to maintain the chimney (which, I think is quite a generous estimate), then we only have to worry about the cooling effect of night-time for a mere 2 and a half hours.-- zen_tom, Nov 22 2006 Unless I've missed something, this idea is pure genius.-- jtp, Nov 22 2006 after going through all annotations, I am still struggling to understand how the flimsy material would keep itself upright & not get twisted/ pressed out of cylindrical shape due to wind pressure.-- vedarshi, Nov 23 2006 Could this not be acheived by having light wieght tubular rings sewn into the fabric of the shaft to maintain it's cylindrical structure?-- theleopard, Nov 23 2006 Yeah, a ribbed structure would maintain its cylindricality - and indeed, we would need some stiffening in place to stop narrowing of the tube due to Bernoulli's Principle.
The alternative is to use the kite to hoist an initial (operational) soft flue, around which, harder, more robust materials can be secreted, in order to build the chimney proper (over a period of years if necessary).
I think projects like these would be best built in the long-term (maybe even generational?) by people on a self-sustaining basis, using the collector as a greenhouse capable of sustaining the population - like a kind of technological kibbutz. As it gets bigger, it becomes capable of sustaining more people, who are then able to support the building effort. The remaining problem for this sustainable build effort is to find a way to create the collector glass (or other transparent, or semi-transparent material) on site, using locally available materials.
Available materials might be the earth on which it's built, items that can be grown in the greenhouse, or derivatives of those powered by energy generated by the formulative tower.
It would be interesting to figure out what seed materials you would need to plonk somewhere, in the middle of the desert to be able to start off one of these constructions that would, eventually, be able to support a large self-sustainable, and non-polluting population.-- zen_tom, Nov 23 2006 I missed all the Solar Tower ideas until now. My favourites are the bouyant gas inflatable ones - hot air or helium. I like the self-erecting idea but think it should still be based on bouyant gas.
To make it more useful initially, it could be used for cooling and ventilation until it was big enough to produce significant power.
Putting the turbine at the top: this would pressurise the chimney which would be good for stopping it collapsing, but could make the hot air inside denser, reducing the bouyancy that powers the airflow.-- caspian, Nov 24 2006 i cant help but picture those side of the road inflatable ad guys who use a leaf blower and fabric to shoot up, then fall down, the shoot up agan, all the whle waving their arms wildly (linky). seems like this may have a similar problem.
how about a double layer fabrc, erected by kite or balloon, so that once erect, it could be filled with a hardening foam (great stuff or that fast settng insulation foam {linky}) to prevent flapping. run a tube up two sides, and distribute the two foam components from the aforementioned 'ribbed' rings so that the foam has time to fill all the points before it sets.-- bleh, Nov 24 2006 How about building the flue up the side of a mountain, rather than straight up into the air? Regardless of how rigid the flue is, it solves problems of rigidity and building cost.
Incidentally, as I'm at over 3000m altitude as I write this and I'm wearing a t-shirt, I'd disagree with the assertion that temperatures at 1000m are "pretty antarctic".
And I'm not sure that it would be so easy to control the environmental conditions in the collector -- doesn't the temperature get to about 60°C down there, with strong, dry winds at all times?-- swyves, Nov 24 2006 I love it, but I'm sure there's a problem: if structural strength isn't keeping it up there, then lift is doing it. You don't get lift for nothing - the wibbly tower is an energy sink. I'm too tipsy (and stupid) to do the sums, but I have this nagging feeling that the net energy sum wouldn't end up in your favour.
However, the buoyant gas variation gets my vote easily. Apart from the cost, there's a lot of energy embedded in steel and concrete, and a fairly strong power law applies to the amount you need versus the height of the tower. Again, too tipsy. Must... find... Roark...-- whennightfalls, Nov 25 2006 The reason more turbines aren't put higher up is because put simply, it wouldn't work.
The maximum power you can get from airflow is speed times opposing force, I think. Adding another turbine is simply adding more opposing force, which you could have done by simply increasing the force of the original turbine. You can think of the airflow as being divided up among all the turbines, so you really might as well just have them at the base.-- ihope127, Nov 26 2006 //Incidentally, as I'm at over 3000m altitude as I write this and I'm wearing a t-shirt, I'd disagree with the assertion that temperatures at 1000m are "pretty antarctic".// But it's not just you at 3000m is it? There's all that earth you're standing on that's being warmed in the sunshine, and the accompanying warm layer of air laying over it like a duvet. If you were to climb a pole up another 1000m, I'm pretty sure it would be considerably colder than it is close to the ground.
//And I'm not sure that it would be so easy to control the environmental conditions in the collector -- doesn't the temperature get to about 60°C down there, with strong, dry winds at all times?//
I was thinking about this over the weekend and it ought to be possible to solve the humidity by having water that should naturally collect at the centre of the tower, fed back out to the extremities, to evaporation tanks along the perimeter. This ought to keep a steady humidity going. If anything, as long as your water extractors are working properly (and they shouldn't have to work hard since they've got a full km column of air to work on) the system should act as a moisture trap - it's just a matter of drawing off water collected at the centre off to the sides. Then there's the question about the winds - undoubtedly yes, it's going to get a bit blowy, but - and this is what sparked another idea, the windspeed (and pressure) should increase as you approach the centre. At the extremities, the windspeed would remain reasonably low.
So, with that in mind, you should still have a majority of your collector area available for cultivation.-- zen_tom, Nov 27 2006 random, halfbakery