If you don't know the solar tower yet, please take a look at the chimney [link]. This idea is only a modification of that great electricity generating technology.

The tall chimney of the planned solar tower in Australia will be made from concrete and steel. It's quite expensive (1/2 of the total cost of the project; that's US$ 200 million). And the thought alone that it will be 170 metres in diametre, 1 kilometre high, but only 25 centimeters thick, and located in an open desert.... I'm not an engineer, this just sounds very fragile (it's probably very much not so).

The idea is to forget about the tower, and use a "plastic" inflatable tunnel instead. This tunnel would be attached to a mountain slope (there are plenty of canyons, mountain ridges and 1km high hills in the Sahara) and easily bridge a sufficient altitude and temperature difference. (Say you find a good 1km high hill, with a slope of 20%, you'll need a few kilometres of high strength UV-resistant plastic for the tube, but I think it's still far cheaper than a steel-concrete tower).

It would be very difficult to build an inflatable tower, but an inflatable tunnel on a mountain slope would be feasible, I think. You can use a tiny part of the generated energy to keep the tunnel pressurised.

For the rest, the process behind the solar tower remains the same: heat the air at the bottom of the tunnel in the large greenhouse, and it will travel up the tunnel, at the base of which a turbine is located.

I don't know... [it's only a modification of an existing idea] but this sounds a lot cheaper than a concrete tower. But then, engineers would have thought about this long ago, if it where a realistic option...
-- django, Jun 17 2004

The planned solar tower in Australia http://www.enviromission.com.au/
[django, Oct 04 2004, last modified Oct 05 2004]

Map of (southern) Algeria http://www.lib.utex...a/algeria_rel01.jpg
Indicating lots of hills and mountain ridges. [django, Oct 04 2004, last modified Oct 05 2004]

Mountainside Solar Chimneys http://www.halfbake..._20Solar_20Chimneys
but not inflated [FarmerJohn, Oct 04 2004, last modified Oct 05 2004]

FarmerJohn, yep, thx a lot for this link. I'll leave my idea for what it is. :-(

[Still, an inflatable plastic chimney may be a cheap alternative].

[to others: no need to fishbone or croissant this idea: see FarmerJohn's link].
-- django, Jun 17 2004


I'd say this is a very valid improvement/variation on the Mountainside Solar Chimney. It certainly sounds a lot cheaper, though not as durable. I imagine you'd have to replace the plastic tube at least once a decade or so and do occational repairs as well.

If you build it with the turbines at the bottom of the hill, it won't work because the pressure in the tube will be less than the outside pressure, causing the tube to collapse, but it you mount the turbines at the top of the hill, there will be higher pressure inside the tube, keeping it inflated. You probably will need to use a fan at the bottom to initially inflate the tube.

The biggest problem I see is the possiblity that plasitc tube might not be insulated well enough, so the air would cool to ambient temperature before reaching the top, wasting a lot of the potential energy. This may be improved somewhat by using a double layer of plastic with air space between, and/or have a shiny mylar inner coating to slow down radiated heat loss.

Of course if you run this up a tall mountain, the environmentalists might complain about you dumping all that hot air up there and melting the glaciers. Hmm, I wonder if you built a large enough one if you could moadify the local weather patterns. perhaps you could cause a lot of rain in what was previously a rain shadow area, or cause someplace that previously got a lot of rain to be drier. Of course these issues apply to the Mountainside Solar Chimey as well.
-- scad mientist, Jun 17 2004


scad mientist, yes, I agree, the inflatable tube would have to be well insulated. But it is a double layered tube, rigid from the bottom upwards to the top.

If you use black plastic for the outer layer at the bottom, the air inside the double layered tube would expand, making it quite rigid, and keeping the both the pressure and the temperature at a good level. Moreover, the air which passes the tube (and it's air filled fingerlike extensions) is also heated, making it a rigid structure.

I was thinking of putting the turbine at the bottom of the tube, but after your comments, I'll have to rethink this. :-)

It has been suggested that the best option, if you want to work with cheap materials, is to find a good cliff or a canyon ridge, somewhere in the desert, to which you can attach the inflatable structure. This would be much more economical than building a one kilometre high, freestanding tower.

(By the way, I think we both agree that "mountain" in this idea, doesn't refer to what we normally think of as mountains; it's more rock formations in the desert. I've taken a thorough look at my atlas and found plenty of suitable sites. Especially in Ethiopia, which hosts one of the worlds biggest "canyons" with a geographical depression with steep slopes. Algeria and Sudan also have these ridges.)
-- django, Jun 17 2004


So you want a taller inflatable wind tower and you think it would be hard, why not inflate it with Helium? At the very least you could have the top helium.
-- sartep, Jun 17 2004


sartep, yes, that would be a very good idea. The problem is, that in these open deserts, windspeeds can get seriously high.

Concrete withstands this, an inflated tower may withstand this too, but it would shake and wave, making the updraft of the hot air from the greenhouse less continuous and predictable.
-- django, Jun 18 2004


Running it up the side of the mountain would make an awful lot of land conveniently close to add reflectors alongside the tube, to increase insolation and generate even more power.
-- elhigh, Jun 13 2005



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