Solar Tower
January 6, 2003 10:55 AM   Subscribe

A kilometre-high solar tower, to be built in the Australian outback by EnviroMission Ltd, will become the world's tallest structure when completed in 2006. Designed by Jorg Schlaich of Schlaich Bergermann und Partner, the solar tower (or solar chimney) operates like a hydroelectric power plant, but uses hot air instead of water, and it could provide enough electricity for 200,000 homes. Time calls it one of the best inventions of 2002, and I think it's one of the most ingenious ideas I've ever heard. Another solar chimney project was planned in Rajasthan, India, but I haven't found any information on its current status.
posted by homunculus (52 comments total) 2 users marked this as a favorite
I don't know if I'm more impressed with a kilometer high or a glass roof that spans 4.3 miles. Well, I would probably say a kilometer tall building. How'd you like to be the guy that gets to put the little blinking light at the top of that tower?
posted by Ron at 11:36 AM on January 6, 2003

Wow. Sci-fi. This is truly great news, although the tower can't be used all around the globe. They should invent something which could make electricity out of ice and snow.

Maybe these power stations could be used to make electricity for hydrogen plants. Are we going to see a transformation of "oil countries" into "hydrogen countries"?

In which way are these towers better than ordinary solar cells?
posted by hoskala at 11:39 AM on January 6, 2003

For the record, a LexisNexis search on the proposed Indian project finds no mention of it in the last two years. Alas.

An article in Melbourne's The Age, however, did have this hopeful bit of info about EnviroMission's part-owner, Energen:

Energen aims to build similar solar power stations in Arizona, Nevada, Texas, Mexico and eastern California. It also has the rights to develop the technology in Jordan, Vietnam, Pakistan, India, China and Egypt.
posted by gompa at 11:42 AM on January 6, 2003

How ironic... solving the greenhouse effect by building a massive greenhouse.

Would this only be feasable in a hot climate, or could it work in a cold climate with a lot of sunshine (like much of Canada)?

I like the fact that the massive greenhouse can also be used to grow food, so you don't just get an industrial wasteland but you're actually making more of the world fertile.
posted by Emanuel at 11:46 AM on January 6, 2003

What about the blast of superheated air this thing will spew out into the stratosphere? That can't be good for the climate, birds, cloud formation, etc.
posted by Mid at 11:51 AM on January 6, 2003

i'm amazed this thing can be built and would love to see more specifics on the actual construction (materials, sizes, etc), i fear to think what the loads must be like at the bottom or what this thing will do in the wind. I wonder if they're hiring...
posted by NGnerd at 11:58 AM on January 6, 2003

Very nice. Finally a giant step towards ending dependancy on non replenishable resources. Let's build them everywhere we can, in whatever form a particular area can support. Did I mention I'm for it? :)
posted by LouReedsSon at 12:02 PM on January 6, 2003

Mid, were you being sarcastic? I couldn't tell. But if you are serious, then I think, and I'm just guesstimating here, that the reason they made it a kilometer high is that after this superheated air gets up that high, it will have cooled down to near ambient temperature. Mabye that's why they didn't make it 2 kilometers high. Cold air doesn't want to rise so their isn't enough juice to turn the turbines. Again, I'm just guessing.
posted by Ron at 12:07 PM on January 6, 2003

Is this the same sort of generator that's at the heart of the big tower at the beginning of Ken MacLeod's The Cassini Division?
posted by ROU_Xenophobe at 12:21 PM on January 6, 2003

What about the blast of superheated air this thing will spew out into the stratosphere? That can't be good for the climate, birds, cloud formation, etc.

I wondered the same thing, but I think Ron might be right about the air having cooled down quite a bit by the time it reaches the top. Still...imagine a significant % of the land area in a region covered by these things, essentially turning all the sun energy that normally hits the land there into electricity...that's got to have some effects on the climate. Still...sounds like a second order effect that could probably be figured out.

Here is a quote from the sbp site: "Solar chimneys are large-scale power plants with an output of 5 to 200 MW each. For that the glass roof has to be several kilometers in diameter and the tube has to be as high as possible to achieve a large annual output." I wonder why the tube has to be "as high as posisble?"

This is basically a large-scale version of the solar closet idea that Nick Pine talks about (Good article here). Basically capturing and storing the sun's energy as heat, cheaply and efficiently, and then doing useful work with it, either heating a house, or in this case generating electricity.
posted by jacobsee at 12:23 PM on January 6, 2003

surely a large proportion of the cost of building this thing is the central tower. If so, why not have the chimney horizontal, out the side of the building?

Or is the 'hot-air-rises' thing a large part of the equation?

I just don't see the australian government funding such a loopy idea.

Also, - it's a fricken 1km high tower! Put a ladder up the side, which 'X-TREME sporter' isn't going to climb up with a parachute or hang-glider on their back?

And how does it produce energy 24 hours a day? Does the air get sucked back in the top when the air cools down? I can't work out if the sides of the building at the perimeter are closed or open for more air to come in.
posted by balinx at 12:31 PM on January 6, 2003

it will be interesting to see what this giant disc shaped mirror will look like from space. A very good idea, and god knows we need innovation concerning the world's energy supply. I've been reading about this on various web sites and newspapers for the past month... no article offers more information than the last, and from what i've culled it's still very much in the theoretical stages. I hope it becomes a reality..
posted by shadow45 at 12:44 PM on January 6, 2003

balinx, it does need to be vertical. It works off the whole warm air rises idea. I would imagine that as you go up, the diameter of the chimney gets smaller so the air is forced to speed up. But as the air gets higher it cools down so I'm thinking that as the diameter gets smaller, the air gets cooler so you might have an almost constant velocity all the way up the chimney until the air cools to ambient. And as for producing energy 24 hours a day, I, again I'm guessing, would think that that is the reason the roof is 4.3 miles long. When the sun goes down there is 4.3 miles, I'm assuming this is a radius so that would be, uh, 58 square miles that heated air is trapped under at the end of the day. That might be enough to keep the effect going all night long, just like the Lionel Richie song. It is a really interesting idea. Too bad it takes up so much space.
posted by Ron at 12:47 PM on January 6, 2003

NGnerd - if you follow the "but it uses hot air instead of water" link given by homunculus, you can get to this page, which describes the structure of the tower: a 130m (426ft) diameter reinforced concrete tube with 25cm (10in) thick walls and some sort of steel spoke-like bracing inside.
posted by pitchblende at 12:51 PM on January 6, 2003

Ron- well, the air does cool off before it reaches the top, but only by making the air immediately around the tower warmer... So you're just letting the heat out more gradually, really. Don't know if that makes a difference ecologically/weather-pattern-wise. Perhaps, to increase the heat in this greenhouse, we can tint the windows?
posted by kahboom at 12:52 PM on January 6, 2003

To answer some of the questions.
1) It's not a loopy idea. Quote "Solar Tower technology has been tested and proven with a successful pilot plant constructed in Manzanares Spain. The plant operated for seven years between 1982 and 1989, and consistently generated 50kW output of green energy."
The state government is supporting the project.

2) Yes the chimney has to be vertical, 'hot air rises' is how it works. It's different from solar cells because electricity is produced by rotating the turbine (and therefore a magnet) inside a coil of wire. Solar cells produce electricity directly from the photons shining on the cell. (Consult your local high school science teacher). I'm pretty sure the air loses energy (and so temperature) as it rises.

3) It produces power 24 hours a day presumably by a 'heat bank'. Think big stones heated by the sun retaining their heat for several hours after the sun goes down. It's the temperature difference between ground level and high altitude that matters. It produces peak power in the heat of the day, which is when power is most needed and valuable.

4) I wouldn't worry about the impact on the local climate / area. Australia is a BIG place (size of the 48 contiguous US states), and this thing (if you don't fly into it) probably has less impact than a couple of shopping mall car parks.
posted by ozjohn at 12:55 PM on January 6, 2003

Let's build them everywhere we can

not on my sky line thank you, sutro tower is bad enough.
posted by badstone at 1:42 PM on January 6, 2003

Build them on the Equator, and you could have them double as the bases for space elevators.
posted by SealWyf at 2:03 PM on January 6, 2003

Tower does not narrow.

Air is heated by day, stored heat is released by night.

Great flash demo in the Project Section under Technology.
posted by linux at 2:07 PM on January 6, 2003

Regarding environmental issues: If this thing were not built, the sun would shine, the ground warms up, surrounding air warms up, warm air rises. This contraption just moves all the warm air from over a large area to one spot, 1 km up. But then it dissipates. In the big scheme of things, no big deal. Burning fossil fuels adds heat to the atmosphere, but here there is no additional heat in the picture, versus the 'do nothing' scenario. If anything, the overall effect is temporarily cooling, because some of the heat energy is transformed into electrical energy. After running motors, lights, etc., that electricity eventually turns back into heat.

In any case, an environmental impact statement is supposed to be ready in March, it says here.
posted by beagle at 2:33 PM on January 6, 2003

posted by troutfishing at 2:46 PM on January 6, 2003

Okay, enough of this armchair quarter-backing. I'm breaking out the math and thermodynamics:
If no extra heat were being generated, there would be no extra energy to be converted to electricity.
A fair bit of incoming radiation is ordinarily reflected back into space, and doesn't heat up anything unless it is absorbed by the atmosphere. Sand and other desert-like areas typically reflect 30-40% of incident energy according to the introductory heat transfer textbook I have lying around the office. This project will try to reduce that number to 0, and to convert that extra heat into electricity. Peak (noon) solar insolation is around 1000 W/square meter, giving an rms insolation value for daylight hours of around 700W/m^2.
A 7km diameter circle has an area of about 38.5 km^2, or 38 500 000 m^2.
So... 30%x700W/m^2x38.5x10^6m^2 = 8 000 MW of extra heat captured during daylight hours, of which they say 200 MW, or 2.5%, is converted to electricity.
posted by cardboard at 3:10 PM on January 6, 2003

Shouldn't we build the giant greenhouses directly over every shopping mall parking lot in the US? We would activate a lot of underused space and general ugliness. Also, if we put them over "dirty spaces" like parking lots or brownfields, could we somehow kill two birds with one rock and filter pollution from the process somehow? Or at least contain contamination.

Very exciting.
posted by DenOfSizer at 3:14 PM on January 6, 2003

"In which way are these towers better than ordinary solar cells?"

They don't need direct sunlight. You could probably even build them here in Seattle.
posted by muppetboy at 3:18 PM on January 6, 2003

cardboard, I believe the area would be about 154 km^2. I think 2*pi*r is the circumference.
posted by Ron at 3:21 PM on January 6, 2003

"What about the blast of superheated air this thing will spew out into the stratosphere? That can't be good for the climate, birds, cloud formation, etc."

Possibly a problem, but I don't think this would affect climate at all. Remember pretty much all that heat was going to end up there anyway through reradiation. If you think about it from a physics perspective, since the net effect of this thing is to *extract* energy, something has to be getting *cooler*, not warmer...
posted by muppetboy at 3:21 PM on January 6, 2003

"it will be interesting to see what this giant disc shaped mirror will look like from space"

it's not a mirror.
posted by muppetboy at 3:23 PM on January 6, 2003

so here's my question:

"could this be done on a small scale? what about on the rooftop of a building? could it be done with a featherweight material like mylar (the chimney would be held up by the rising air and thus blow around some)?"
posted by muppetboy at 3:27 PM on January 6, 2003

So what happens when a terrorist detonates a bomb at the base of the tower that shatters all the glass for a few hundred meters? Won't this knock out power for everyone drawing electricity from it? Wouldn't it take a long time to repair?

If this thing is as truly revolutionary as we all are saying, wouldn't the oil interests have an interest in seeing it fail? I'm looking at you, Saudi Arabia.
posted by Hammerikaner at 3:30 PM on January 6, 2003

I just don't see the australian government funding such a loopy idea.

The Australian federal government is backing this in a big way, as is the New South Wales (state) government.

Too bad it takes up so much space.

You're kidding, right? Australia is basically the same land area as the mainland US, with only 16 million people living in it, almost all of whom live on the coast. You could put a hundred of these things here and 90% of the population would never even notice them.

This project was reported some time ago on the ABC and more recently in The Bulletin
posted by dg at 3:45 PM on January 6, 2003

also, wouldn't it be a lot cheaper to build this thing on the side of a very steep south facing hill? you'd get rid of half of the materials requirements!
posted by muppetboy at 3:45 PM on January 6, 2003

"You could put a hundred of these things here and 90% of the population would never even notice them."

that's a huge understatement. in the middle of the outback, you could put 100,000 of these things up and 99.9% of people would never know.
posted by muppetboy at 3:47 PM on January 6, 2003

Maybe these power stations could be used to make electricity for hydrogen plants. Are we going to see a transformation of "oil countries" into "hydrogen countries"?

in the middle of the outback, you could put 100,000 of these things up and 99.9% of people would never know.

So with enough solar towers, it sounds like Australia really could follow Iceland's example and switch completely from fossil feuls to hydrogen. Go for it Australia!
posted by homunculus at 4:15 PM on January 6, 2003

These things are also known as solar chimneys. The thermodynamics are right. It's building the thing a whole km high (0.6miles to non-metric Americans and Libyans) that is a bit tricky. (Sears Tower is only 0.44 km high.) Thanks to Google I found a discussion on building solar chimneys next to tall structures like a nearby hill.

Pity is Australia is so flat. :-(
posted by ozjohn at 4:23 PM on January 6, 2003

cardboard, I believe the area would be about 154 km^2. I think 2*pi*r is the circumference.

Cardboard got the number right. A=pi*r^2, not pi*d^2.

Cardboard's efficiency calculation only considers daytime operation of the turbines, and the BBC article mentions that they will operate 24 hours. If the peak solar incidence at 12:00 solar time is 1000W/m and there is 12 hours of daylight, the available solar resource will amount 27.5 MJ/m^2/day. The text I have mentions that a well-designed solar collector can absorb ~70% of that, giving 22 MJ/m^2/day. Multiply that resource by the collector area (38.5e06 m^2) and the collected solar energy is determined to be 847 061 GJ. Assuming the turbines operate at 200 MW 24 hours a day, they'll produce 17 280, giving an overall efficiency of ~2%. If you use cardboard's estimate of the absorbed solar energy (30%), you get an efficiency of about 5.5%.

By comparison, a pv array can produce electricity at a an average efficiency of 10-14%. A pv array on the same land area could produce 118 588 GJ/day, (corresponding to an average instantaneous output of 1372 MW) without a 1 km high monolith. That said, the constant 200 MW output of this monstrosity would be a whole lot easier to integrate into a utility's production strategy than seven times that amount available in a sinusoidal pattern.

"could this be done on a small scale? what about on the rooftop of a building? could it be done with a featherweight material like mylar (the chimney would be held up by the rising air and thus blow around some)?"

A similar principle, called stack effect can be used instead of fans and blowers to cool and ventilate buildings (1, 2, 3).
posted by astirling at 4:39 PM on January 6, 2003

After a steady decline over the last month, the stock price for the code EVM on the ASX exchange jumped over 6% overnight.

Is it possible that this could be related the amount of exposure it just received through metafilter?
posted by balinx at 5:53 PM on January 6, 2003

sorry to post yet again but i find this interesting.

i've been doing some research on comparing the cost of this to regular wind power installations.

here is a site detailing information on a cluster of 100 wind turbines, each rated at 1.5MW. 150MW total, which is 3/4 of the projected output of the kilometre high tower. The cost of the project? 160million. The tower? 800million..

The cluster is a proven technology, in operation NOW.

I realise however, that general wind patterns are not reliable. The sun coming up is a lot more reliable.

But, you also get the benefit of HUGE redundancy in a 100 turbine cluster.

Then again, on the plus side for the tower, it'd probably be a huge tourist boon for being so unique...

Still, you could get close to 400 of the 1.5MW turbines going for 800million. Possible more, considering economies of scale.
posted by balinx at 6:33 PM on January 6, 2003

holy freaken bejeus that a big blade. (1.5MW model).
posted by balinx at 6:41 PM on January 6, 2003

True, balinx, but you miss one major advantage with the tower - it can be located in areas which are not major population centres, where the wind turbines generally need to share space (such as coastlines) with humans. The outback in Australia is really really empty and really really hot, making it perfect for a solar chimney. Not so good for wind turbines, though. Horses for courses.

There has been a huge amount of resistance to the installation of wind turbines in different areas of the world, perhaps dooming them to small-scale installations. Unfortunately, the wind is most reliable in the same places that people like to live.
posted by dg at 6:45 PM on January 6, 2003

The engineering company already build one such power plant in Manzanares (Spain): big picture here, excellent PDF document here and stunning view (kingsize) from the turbine+chimney here. More pictures here. This one was already impressive, the one in oz will be awesome.
posted by ugly_n_sticky at 7:59 PM on January 6, 2003

Why aren't these going up in the deserts of the American Southwest? They could supply California with all the power it needs!
posted by ParisParamus at 8:10 PM on January 6, 2003

About solar chimneys vs. solar cells: solar cells may be more efficient, but they also are (I believe) pretty nasty to manufacture environmentally. They're also probably more complicated to operate. Once you work out how to build the big freaking tower, the power station itself is a dead-simple air turbine. And finally, the solar chimney has the rather neat side-effect of creating a large area of potentially farmable land underneath it, rather than a giant patch of shade.

I heard about these a few months ago, and of all the alternative-energy technologies, they seem like one of the best compromises for efficiency, feasability, and simplicity. Now if we can just get hydrogen cell technology figured out, they can build a few major farms of solar chimneys in uninhabited areas and ship that clean power up here to dark and snowy Maine. :-)
posted by rusty at 8:25 PM on January 6, 2003

ugly_n_sticky , thanks for the pictures!

I'm surprised that the chimney is so tall when there appears to be only one generator right at the base.

is the chimney tall for the reason
1) to get the hot air away from the site? (doesn't make immediate sense to me, atleast not to this scale)
2) to provide room for multuple turbines...?

maybe they were planning on installing more turbines but didn't get to that stage... ?
posted by balinx at 8:31 PM on January 6, 2003

The tower is tall both to allow the use of multiple turbines, and to generate more hot air (hot air rises, and the longer a glass chimney, the hotter the air can become).

(Or at least that's what someone who got a 92 on the physics Regents in high school thinks)
posted by ParisParamus at 9:09 PM on January 6, 2003

Seeing projects like this gives me some small hope for humanity.
posted by moonbiter at 9:14 PM on January 6, 2003

the chimney is not glass. its 1 metre thick concrete at the bottom, tapered to a width of 25cm at an altitude of 500m, and remains at 25cm width till the top.

i guess while the air remains trapped inside the chimney, it is always lighter than the air around it, and therefor is in effect producing an upword force on any air underneath it. as soon as the chimney ends this pressue is dispersed.

so, i solved my own question i guess. sorry for thinking aloud.
posted by balinx at 9:24 PM on January 6, 2003

Well, glass would work better. Or transparent alluminum.
posted by ParisParamus at 9:35 PM on January 6, 2003

astirling, I was assuming it was a 4.3 mile radius but it looks like that is the diamter then. 4.3 mile radius, man, that's huge.
posted by Ron at 10:14 PM on January 6, 2003

I don't understand the elements of this thing. It's a chimney the width of a soccer field a top a 4.3 mile glass roof? Huh?
posted by ParisParamus at 5:24 AM on January 7, 2003

The chimney is tall because it operates by exploiting the temperature differential between the base of the tower and the top. The higher you go, the colder it gets (up to a point; temperature v. altitude describes a pretty funky curve, but only at altitudes you're not likely to be building to in this century)-- and therefore the higher you build, the more efficient the chimney gets.

This is how the chimney operates at night. The differential between ground level and chimney top is relatively constant between day and night. Ideally, the greenhouse base isn't even needed. The chimney would operate without it, but at much reduced output.

The greenhouse and the idea of using solar heat banks are just passive optimizations of the whole system, and act only to exaggerate the temperature differential.
posted by Cerebus at 7:38 AM on January 7, 2003

Another thing that may be worth considering when trying to decide where these could be deployed is that it might have to be a seismically quiet area. i would imagine that a serious quake could very much disrupt that amount of glass.

On the other hand, i know that they can to some pretty spectacular things with quake-proofing, it's just that i normally see that technology applied to vertical structures, not horizontal. (though here you have both).
posted by quin at 1:26 PM on January 7, 2003

also proposed as a way of removing smog from inner-city los angeles.
maybe a worthy contender for the replacement structure for the World Trade Organisation buildings in new york?
fairly comprehensive new scientist article, 'electric dreams'.
posted by asok at 8:48 AM on January 8, 2003

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