Solar Towers are a magnificent alternative to solar cells.

March 24, 2009 4:39 PM

A solar updraft tower generates electricity with nothing more than a greenhouse and a tall chimney. A 195 meter tall prototype in Spain cheaply operated at 50 kW for years. Now there are plans to build others, including a 40 MW tower, 750 meters tall (near twice as tall as the current tallest structure in the EU). Two others, a 200 MW tower in Australia (previously discussed) or a 400 MW tower in Namibia could become the tallest structure of any kind if built: 1km and 1.5km tall, respectively. Yet even those are dwarfed by the theoretical super chimney which could stand 5km tall and 1km wide. Such a tower would use the Earth's atmosphere itself as the greenhouse, could cause rain, reduce global warming and generate over 300,000 MW of "green" electricity.

EnviroMission has a fantastic video demonstration of their Solar Tower.

posted by brenton (61 comments total)

Umm. What material can you use to build a 5km tall tower?
posted by leotrotsky at 4:49 PM on March 24, 2009

I'll take two!
posted by IndigoJones at 4:52 PM on March 24, 2009

also, Isn't this basically what a Supercell Thunderstorm does? Rain is great, but hail & tornadoes are not.
posted by ArgentCorvid at 4:54 PM on March 24, 2009

Umm. What material can you use to build a 5km tall tower?

carbon fibre nanotubes of course, for the price of a couple of space elevators the genesis towers will shoot you into the celestial sphere when the rapture is complete.
posted by doobiedoo at 4:56 PM on March 24, 2009 [3 favorites]

Reading this solar tower advocacy page while listening to the Obama news conference is a little bit weird.
posted by box at 5:03 PM on March 24, 2009

Now why on earth would we be wanting to invest in this technology when we are sitting on mountains of cheap brown coal that generates healthy profits.

I mean, wheres the profit in mining, shipping and infrastructure- not to mention the truly exciting geo-sequestration that will come on line within the next 50 years or so. (seriously)
posted by mattoxic at 5:06 PM on March 24, 2009 [1 favorite]

If we could somehow combine all the herculean, linear infrastructure projects that have been touched on on Metafilter; gravity trains, space elevators and solar towers I....really don't know where I was going with that, it'd just be very cool, like compressing the entire filmography of Michael Bay into every commute between Harrow and Saturn VI.
posted by doobiedoo at 5:11 PM on March 24, 2009 [2 favorites]

What material can you use to build a 5km tall tower?

I'll be happy to solve that problem, if you write the environmental impact statement.

If that thing really is sucking 300 gigawatts out of the weather system, it's going to change weather patterns on a continental level.
posted by Chocolate Pickle at 5:25 PM on March 24, 2009

Does anybody know if this will downscale to a residential/farmstead size? I've been involved with renewable energy for a decade and this is new to me. The wiki article says a tall chimney is needed for adequate pressure to turn a turbine, which leads me to wonder if it would work at smaller sizes. 50mW is ten times more than needed by a household...
posted by werkzeuger at 5:26 PM on March 24, 2009

Oops, that was supposed to be 50 kW.
posted by werkzeuger at 5:27 PM on March 24, 2009

This would have been the ideal thing to build at NYC's "ground zero" for a number of reasons.
posted by ZenMasterThis at 5:44 PM on March 24, 2009 [3 favorites]

It's not that the prototype was 195m tall; it's that the greenhouse collection took up 11 acres! That's a hell of a greenhouse.
posted by GuyZero at 5:47 PM on March 24, 2009

Does anybody know if this will downscale to a residential/farmstead size?

Pretty much no. For one thing, the efficiency scales a lot faster than the size. For another thing, like all solar power it doesn't work at night and how well it works in day is a function of the weather.
posted by Chocolate Pickle at 5:50 PM on March 24, 2009

Another way to do this without building a tower is to create a tower out of a tornado.

As for the tower: why not take a percentage of the money coming in for the power to add solar panels along one side of the tower? You could increase your power output capability year by year.
posted by eye of newt at 5:58 PM on March 24, 2009

Chocolate Pickle: ..it doesn't work at night..

If I'm not mistaken, the larger versions generate so much energy in the massive greenhouse that it continues to generate power 24 hours a day.
posted by Adam_S at 6:02 PM on March 24, 2009

oddly enough, i've known about a very similar project for years (i read about it in the now-defunct science spectra magazine) that works in the exact OPPOSITE way. these towers i read about use sprayers along the top perimeter to spray a fine mist across the top. the weight of the water drags air into the chimney and pulls it toward the ground. as the air falls, the surface of the droplets both cleans and cools the air, and at the bottom the water is collected in a pool (where the dirt in it settles out and is later collected), and escaping air along the bottom perimeter drives turbines to power the pumps...as well as generating excess energy from the temperature differential. these were planned with areas like los angeles in mind...hot, and with a lot of air pollution...air conditioners for the outside, if you will.
posted by sexyrobot at 6:04 PM on March 24, 2009

A solar updraft tower generates electricity with nothing more than a greenhouse and a tall chimney

... and turbines. The turbines are important.
posted by electroboy at 6:04 PM on March 24, 2009 [6 favorites]

Grow pot in there, then when they've reach maximum height set the whole thing on fire. Presto, Nevada gets a monster bong hit!
posted by CynicalKnight at 6:13 PM on March 24, 2009 [1 favorite]

Instead of building a tower, you could probably find a sunny spot with a relatively steep mountain adjacent. Then you could either build a tube up the side of the mountain, or dig a vertical shaft through the center - instant weather volcano!
posted by AndrewStephens at 6:14 PM on March 24, 2009

Anybody know how much the Australian tower would be expected to cost? I went through the EnviroMission website (not thoroughly), but couldn't find any estimates of cost. Nor was there any indication of how much backing they have.

The closest I found was this:

The Australian Solar Tower project has of six distinct phases:

* Project optimization (completed)
* Pre-Feasibility Commercialisation (completed)
* Final Feasibility (underway)
* Final Design and Construction
* Construction
* Commercial Operation

Surely we're looking at many billions of dollars. Colour me skeptical, but I can't see the cost-benefit analysis turning out too well.
posted by kisch mokusch at 6:19 PM on March 24, 2009 [1 favorite]

..like all solar power it doesn't work at night and how well it works in day is a function of the weather.

Updraft towers actually have this advantage over conventional solar technology in that they still operate amazingly well at night, on overcast days, and in the winnter.
posted by brenton at 6:29 PM on March 24, 2009

300 jiggawatts? Great Scott!
posted by adamrice at 6:41 PM on March 24, 2009

I don't understand the rain part of the mega super chimney. If it's in a desert, where's all that water coming from?
posted by Dr. Send at 6:43 PM on March 24, 2009

the theoretical super chimney which could stand 5km tall

Does anybody know if this will downscale

Just give the project to Ian Faith and it'll come back only 5m tall. . .



but it will go to 11.
-
posted by Herodios at 6:52 PM on March 24, 2009

1. 300Mw is not much energy, in the big picture - about 1/3 or less the size of a nuclear power plant, 1/6th the size of some of the larger coal fired plants.

2. Considering how hard it is to build even wind power due to environmental and other concerns, imagine how difficult it would be to find a spot for a 5km tall tower - that's about 15,000 feet or the height of some the highest Rocky Mountains, it's visibility would cover 1000s of square miles around. Potentially impacting 10s of thousands of people.

It would work in places where:

A. There is nobody around. Australia

-or-

B. The project isn't constrained by anti-tragedy of the commons (ie. Saudi Arabia, Russia, China).
posted by stbalbach at 6:53 PM on March 24, 2009

I'm not sure how this scales, presumably linearly with area, but it seems like you could power a home or two with a one-acre structure.
posted by adipocere at 7:01 PM on March 24, 2009

It's 300,000Mw for the super-chimney, not 300Mw. As in about 2% of global energy usage.
posted by kafziel at 7:02 PM on March 24, 2009

If that thing really is sucking 300 gigawatts out of the weather system, it's going to change weather patterns on a continental level.

Perhaps as global weather becomes more intense, we're going to want to.
posted by Durn Bronzefist at 7:41 PM on March 24, 2009

Anybody know how much the Australian tower would be expected to cost?

This History Channel clip, linked to from the Enviromission site, estimates the cost of the 200MW Australian tower at $700 million (US, I assume).
posted by stargell at 7:44 PM on March 24, 2009

It sure would bite to get your Frisbee stuck on the roof of one of those.
posted by turgid dahlia at 7:44 PM on March 24, 2009 [1 favorite]

You can buy shares in EnviroMission - if you really really want. Me personally, I think that while this is great in principle, building the first tower at that scale is going to be such a massive challenge that nobody in the private sector is ever going to risk it.
posted by wilful at 7:48 PM on March 24, 2009

Thanks stargell, I missed that (obviously).
posted by kisch mokusch at 7:57 PM on March 24, 2009

here's the oceanic version :P

cheers!
posted by kliuless at 8:48 PM on March 24, 2009

Extremely limited siting, enormous capital cost ($4000/kW for the Australian project, or double the cost of a nuclear reactor), and relatively low power output? D.O.A.
I hope they build a few though, because they're undeniably cool.
posted by Popular Ethics at 10:01 PM on March 24, 2009

I don't understand the rain part of the mega super chimney. If it's in a desert, where's all that water coming from?

There's still moisture in the air even in the desert, and colder air can't hold as much water as warmer air, so as the air exits the chimney and cools down, the water vapour condenses (or possibly freezes in the case of the superchimney) and forms clouds.
posted by benign at 10:05 PM on March 24, 2009

oddly enough, i've known about a very similar project for years (i read about it in the now-defunct science spectra magazine) that works in the exact OPPOSITE way. these towers i read about use sprayers along the top perimeter to spray a fine mist across the top. the weight of the water drags air into the chimney and pulls it toward the ground. as the air falls, the surface of the droplets both cleans and cools the air, and at the bottom the water is collected in a pool (where the dirt in it settles out and is later collected), and escaping air along the bottom perimeter drives turbines to power the pumps...as well as generating excess energy

So someone's come up with an invention that will produce not only enough energy to power itself, but also create excess energy we can tap into? Pardon me if this sends up a few red flags.

As for the greenhouse idea...
If that thing really is sucking 300 gigawatts out of the weather system, it's going to change weather patterns on a continental level.

Would that make a dent? Weather systems are huge. Is there a reliable way to measure the total energy contained within? (Pardon my ignorance if this is obvious, I don't study weather.)
posted by Avelwood at 10:06 PM on March 24, 2009

Instead of building a tower, you could probably find a sunny spot with a relatively steep mountain adjacent. Then you could either build a tube up the side of the mountain, or dig a vertical shaft through the center - instant weather volcano!

You know, that would work really well outside Palm Springs. There's already a tram that takes you from the desert floor up to about 8000 feet.
posted by fshgrl at 10:15 PM on March 24, 2009

I haven't clicked on all of the links, so apologies if this is a stupid question.

Cn things be grown in the greenhouse? Would the wind current be too strong, and the buildings would basically be a reservoir, or would they be usable in the normal way in adition to the tower aspect?
posted by paisley henosis at 10:25 PM on March 24, 2009

Umm. What material can you use to build a 5km tall tower?

* Waves hands

Details!
posted by Bonzai at 10:49 PM on March 24, 2009 [1 favorite]

paisley, my understanding from spending a fair amount of time on the enviromission website previously, is that it's a gentle breeze until you get close to and into the actual chimney. Lots of potential for growing stuff.
posted by wilful at 10:51 PM on March 24, 2009

300GW is the maximum power output of the superchimney. Lets assume it hits 85% of that on average, or 255,000 MW. For 12 hours per day (assuming it doesn't run at night, again worst case), thats 3,060,000 MWh per day, or 1,116,900,000 MWh per year. In 2007, the US generated 4,157,000,000 MWh.

Summer peak demand was around 790,000 MW, so three of these could just about power the US if you can get them to run 24/7 (assuming they match the loads well enough). Then maybe one more needed to handle switching over from gasoline to PHEVs (10kWh/day * 150,000,000M cars = 1.5M MWh per night).
posted by SirOmega at 10:53 PM on March 24, 2009 [1 favorite]

Having absorbed an apocalyptic view of Haiti from Jared Diamond's Collapse, I've often wondered if it would be possible to build a solar chimney there. (Essentially, Haiti still relies on burning wood for much of its energy needs, leading to deforestation and environmental disaster.) Certainly the location is ideal for a solar energy application (and neighboring Dominican Republic plans a traditional solar farm). Anyway, am I correct that solar chimneys are more efficient in land use? Also, what would be the potential cost of a system large enough to be worthwhile for Haiti's needs? There's hardly a more deserving country in the Western Hemisphere.
posted by dhartung at 11:30 PM on March 24, 2009

EnviroMission was also planning on building solar towers in the U.S.
posted by homunculus at 11:57 PM on March 24, 2009

They're still planning on it. Check their site, stuff is happening (albeit slowly).

Speaking of slowly, the h-dogg posted about this in 2003.
posted by Wolof at 12:02 AM on March 25, 2009

I don't understand why you have to build a chimney at all/why the chimney has to be vertical? Why not have a big greenhouse and a large pipe that runs up the side of a mountain? Sure, it might not be quite as efficient as a vertical chimney, but it'd be a a lot cheaper and you wouldn't have to worry about how you go about building something that's 5km tall.

You could even grow tomatoes and stuff in the greenhouses (well, sort of, might be a bit windy).
posted by BigCalm at 3:10 AM on March 25, 2009 [2 favorites]

can't we just stick to parabolic troughs and tower systems? PV is nice, but always takes relatively scarce materials and a lot of complicated processing. central tower recievers and parabolic trough systems can be built using abundant materials, get decent efficiency, and can run 24hrs with a proper heat storage system. dish receivers with sterling engines are nice and get even better efficiencies, but there's not heat storage system you can use so far as i know. so central receiver tower and parabolic trough it is. there's plenty of space to build this shit and satisfy our energy demands.
posted by molecicco at 3:26 AM on March 25, 2009

Someone stop my brain melting... Does it matter if the turbine is at the top of the bottom of the chimney?

I was trying to work it out with a hydro plant as an analogous system, where you traditionally put the turbine near the outlet, so it has a large head of water above it, but in hydro you don't tend to draw from the top of the lake.

With air, does it make any difference if you have the entire chimney of air rushing upwards to the turbine, or if you have the chimney sucking air away from the turbine...?
posted by twine42 at 4:00 AM on March 25, 2009

Ever since they spammed me in 2003, I've been suspicious of Enviromission, and my previous comments about them here stand. I wish them luck, but I don't see them being a significant energy producer any time soon.
posted by scruss at 4:06 AM on March 25, 2009

I don't understand why you have to build a chimney at all/why the chimney has to be vertical? Why not have a big greenhouse and a large pipe that runs up the side of a mountain? Sure, it might not be quite as efficient as a vertical chimney,

The chimney is so you get a chimney effect, which is driven by pressure differential. So no, it doesn't have to be vertical, but the point is that it has to be high up. In order to reach the same height building at an angle, you need a lot longer tower (divide by cos(θ) to find out how much longer) which means more materials. A cost analysis will tell you which is actually better in the long run.

It's not that the prototype was 195m tall; it's that the greenhouse collection took up 11 acres!

I'm actually wondering how I size one for my back yard. I don't have 11 acres, but then I also don't need 50 kW. Thinking out loud: Wind power rises with the square of the velocity, IIRC, whereas air volume and therefore heating rate in this case would rise linearly with the area. So if I wanted just 5 kW, I could get by with just an acre, but it would still have to be 195m tall. Alternatively, if I had 11 acres I could build a tower 195/sqrt(2) = 140 meters tall and get 5 kW.

So....I guess that's not happening.
posted by DU at 6:28 AM on March 25, 2009 [2 favorites]

twine42: Someone stop my brain melting... Does it matter if the turbine is at the top of the bottom of the chimney?

Bottom would be better, but it would work either way. The air would cool off as it travels up the pipe, losing heat out the pipe walls. This would slow the flow rate at the top slightly. Also who wants to repair a turbine 5km in the air?

The hydro analogue doesn't apply here because the fluids are being driven by entirely different means. In a dam it's the pressure due to the weight of the water above. Here the air is being driven by a temperature difference between the inside of the tower and the atmosphere around the top. (small nit, hydro dams do draw from the top of the lake, but they pipe it down to the bottom level immediately)

I think the reason no one has proposed running a pipe up a mountain side is that it would end up being 40% longer, with attendant thermal and friction losses. Plus the "supertower" concept calls for a 1km diameter tower, which is ridiculous on its own, and would be even more difficult to build one on its side.
posted by Popular Ethics at 6:29 AM on March 25, 2009

Wikipedia has a better description of the vortex tornado engine.
posted by eye of newt at 8:41 AM on March 25, 2009

three of these could just about power the US if you can get them to run 24/7

Sounds great on many levels, but I'd worry about the risk of putting a nation's entire energy production in just a few towers. That's effectively reducing a heterogeneous, redundant system (albeit inefficient, dirty, & sprawling) to a few points of failure. There had better be some good technical support to keep those suckers running, not to mention a bullet-proof military defense.

At least that's what I'd be thinking if I were playing Starcraft.
posted by LordSludge at 10:39 AM on March 25, 2009

So someone's come up with an invention that will produce not only enough energy to power itself, but also create excess energy we can tap into? Pardon me if this sends up a few red flags.


you can put the flags down...it's not a closed system. the excess energy comes from the temperature/pressure differential between the top of the tower and the bottom (thats why the taller the tower, the more energy...) a temp. differential is also ultimately what makes a combustion engine work. if the outside air were as hot as that in the pistons in your car, there would be no reason for the hot compressed air in the piston to go anywhere.

Weather systems are huge. Is there a reliable way to measure the total energy contained within?

quite easily. the main part is just figuring out how much energy is in a square mile of sunlight, and multiplying by the area of 1/2 of the earth.
posted by sexyrobot at 10:41 AM on March 25, 2009

We're pretty decent at drilling holes through rock, aren't we?

What if we took an existing, relatively enormous mountain, drilled down to sea level, and built tunnels to the drill line w/ turbines at the front?

Sure, we're not going to get a kilometer diameter drill, and there are probably volcanic implications, but it's much more realistic to carve what we need from a mountain than to build what we need from available materials.

Also, an air volcano would be kind of awesome.
posted by effugas at 10:55 AM on March 25, 2009

The system needs the greenhouse to heat the air and it relies on pressure differentials to push/pull the air upward. If it went through a mountain, I'd imagine the rock would provide way too much of a heat sink, and it wouldn't actually move the air nearly enough. That, and you'd have to do a lot of excavation to get relatively flat areas to run the greenhouses in.

The Burj Dubai is 818 m high, and it's a building that has to house people and have things like walls and elevators. I'm sure we can manage to build safe and durable towers that amount to big tubes.
posted by explosion at 1:32 PM on March 25, 2009

a series of tubes
posted by kliuless at 1:49 PM on March 25, 2009

not to mention a bullet-proof military defense

well, since you have the generators right there, just outfit the towers with Tesla's death ray. All you have to do is figure out how they work.
posted by ArgentCorvid at 3:35 PM on March 25, 2009

I'm not sure how this scales, presumably linearly with area, but it seems like you could power a home or two with a one-acre structure.

My understanding from some pop-sci article a while back is that it scales non-linearly with height - they only really start to be worthwhile when they're really really tall, and below a certain altitude differential, the losses start to accumulate so rapidly that they're pretty much pointless. So I imagine it doesn't scale for home use at all, but if you are interested in it, you should definitely look into it - don't take my vague memory as authoritative :)

But it does raise the question - if some of the world's tallest buildings have somewhat comparable height, these things should be built into the building - the greenhouse would be missing, but it should still produce a fair bit of power, relative to the building's needs.
On second thoughts, that hollow space running up the building could be filled with offices instead of a wind tunnel, and those offices would generate thousands of times more $$$ for the building owner than the wind tunnel ever could, so that idea doesn't make financial sense :(

Someone stop my brain melting... Does it matter if the turbine is at the top of the bottom of the chimney?

Yes - you can bypass the brain melt by ignoring the physics and considering the mundane - putting the weight of the turbines at the top requires a strengthening of the tower that most likely tips the design specs from "feasible" to "fanciful". Not to mention the difficulty of turbine maintenance that such an arrangement would create. :)
posted by -harlequin- at 3:50 PM on March 25, 2009

"The Burj Dubai is 818 m high, and it's a building that has to house people and have things like walls and elevators. I'm sure we can manage to build safe and durable towers that amount to big tubes."

And at one kilometre wide the height to width ratio is much more favourable than any high rise building.
posted by Mitheral at 6:54 PM on March 25, 2009

It doesn't seem to be mentioned, but wouldn't the Bernoulli effect also contribute to drive the turbines because of high winds at high altitudes? Also, wouldn't there be some kind of asymptote as the tower gets higher: as the tower gets higher, the air inside has more time and volume to cool, then the average pressure/temperature difference of the column of air to the outside atmosphere will decrease, until the cold air inside the top of the tower will decelerate and weight so much it will retard the spin of the turbines by creating weird eddy currents? Finally, what if we stuck these things over factories as well as greenhouses? They are already venting tons of heated gas into the atmosphere, why not harness that kinetic energy?
posted by headless at 12:43 AM on March 26, 2009 [2 favorites]

These large solar towers can generate power 24 hours a day due to the resident heat in the greenhouse and ground below.

This is the same as for Concentrated Solar Power (CSP) powerplants. Using CSP, less than 1% of the world's deserts could generate as much electricity as the world is now using. It has been calculated that 90% of the world's population lives within 2700 km of a desert and could be supplied with solar electricity from there.
posted by jeroen8 at 2:50 PM on April 21, 2009