hat tip to constant reader wilfred for this item
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Solar Towers are making the news again thanks to a deal in Australia that just might see the first major one get built.* But what is a Solar Tower, you ask? A Green energy generating system (see this image) that works off the fact that heat rises.
If built, it will be nearly double the height of the world’s tallest structure, the CN Tower in Canada.
The Solar Tower is hollow in the middle like a chimney. At its base is a solar collector — a 25,000-acre, transparent circular skirt. The air under the collector is heated by the sun and funneled up the chimney by convection — hot air rises. As it rises, the air accelerates to 35 mph, driving 32 wind turbines inside the tower, which generate electricity much like conventional wind farms.
But the Solar Tower has a major advantage over wind farms and solar generators: It can operate with no wind, and 24 hours a day. Thanks to banks of solar cells, the tower stores heat during the day, allowing it to produce electricity continuously.
The standing argument against building Solar Towers essentially has been the costs. But the costs are beginning to look more attractive all the time. As TocqueDeville (on Kos) states:
It will cost about 500 million bucks. Standard coal powered plants that generate 200MW cost around 750 million and that doesn’t include the cost of mining, processing, and transporting coal.
Alternative Energy Blog, however, suggests the cost will be more, but only initially:
EnviroMission and SBP estimate the cost of their first 200-megawatt solar thermal tower at $670m, and say the cost of subsequent towers would fall. An engineering infrastructure, materials manufacturing plants and trained workforce would be in place and the design and construction would have been refined.
And it’s still estimated that investors will wait 10 years to see a return on their investment, but as the Wired article points out:
The same was true for nuclear power — a much more complex and dangerous technology. However, the U.S. government invested enormous sums of money to create a new source of energy from the atom. But it wasn’t a particularly wise investment, according to Sherif.
"Energy from nuclear power plants remains very expensive and there is the huge waste problem," he said.
And while there’s renewed interest in nuclear power, the world’s supply of uranium is limited, while the sun’s energy is not, he said.
China is reportedly very interested in this technology and if they apply their relentless "get the costs down" approach to building the Towers, they may just become affordable for nations all over the world. It’d be a shame for US energy companies to lose some of their political power because they missed the boat on this one.
*"A 650-foot solar tower was built in Manzanares, Spain, in 1981 by German structural engineers Schlaich Bergermann and Partner. Producing 50 kilowatts, it operated for seven years. But with oil prices at $15 a barrel in the mid-1980s, there was little interest in building a larger one, Sherif said." Those prices aren’t coming back any time soon.
good news indeed. but 25,000 acres? dang if that doesn’t sound like a big skirt. Also, for reference sake, how big a city does a 200MW generation facility support?
Edward,
thats a great image. hopefully we can see it in our lifetime.
“but 25,000 acres? dang if that doesn’t sound like a big skirt.”
Sure is. At 640 acres = 1 square mile, this is nearly 40 square miles, or a square over 6 miles per side.
Heat doesn’t rise. One could say hot air rises, but that’s not strictly true either. The same hot air that strain mightily skyward here on a cool day (like today) in Orlando might sink like a rock at noon in the Sahara. Picky, I know, but it’s all I’ve got today.
Dunno about the “produce[s] energy continuously” bit, though. Depends on how it’s done. At some point the 30-odd square kilometers that will be rendered lifeless will start to become a factor.
I believe it supports 200,000 homes. 1,000 plants would supposedly cover all US homes, and 3,000 would cover all US consumption.
So 3,000 x 25,000 acres = 75,000,000 acres. For reference, all of Death Valley is only 3.3 million acres, so space is definitely an issue here and Solar Towers will not replace all other energy sources. Still, because they’re totally renewable and remarkably clean, (and because the technology can be expected to improve once they’re in use and their size can arguably get smaller), they represent a good investment, IMO.
Man, the thermal efficiency of that installation will suck. What about steam-generation solar towers? And compared to a Natural-Gas Combined Cycle plant (~$500/kW), $3,200/kW is just a crippling difference in capital costs. You’ve much more promise in bringing down photoelectric solar costs than this technology, especially given the substantial acreage that would be used.
Murat…I hope so too.
Heat doesn’t rise. One could say hot air rises, but that’s not strictly true either.
I almost corrected that, but then the phone rang.
But why is it not strictly true that hot air rises?
Well, USA, one upside to this sort of thing is it’s basically only got a few moving parts (turbines and generators), which puts is going to put maintenance costs of the moving-parts equipment about as low as it can get. Also, no emissions.
BTW anyone besides me notice that the drawings of the installation are inconsistent with the area given? A 3.5km radius collector is going to occupy about 9.5k square kilometers, not 25k.
Oh, I see what happened. People are using the land area that was acquired to built the facility as the area occupied by the collector itself. Incorrectamundo!
So, Slarti, are u saying you could concievably get two towers on that same property (if the land was suitably flat)? Can someone who isn’t mathamatically challenged figure out if 3,000 Towers can supply the entire US with electricity, how much land that would take?
Look at my example, Edward. Hot air won’t rise if it’s in the presence of even hotter air.
And of course that’s all wrong too. Hot[ter] air only rises because it’s less dense than the surrounding air. One could release some very hot (but dense) gas in cooler environs, and it still might not rise. Think Archimedes, and buoyancy.
As for your last question…that was supposed to be 9.5k acres, not square kilometers. So just multiply by 3000.
Sure is. At 640 acres = 1 square mile, this is nearly 40 square miles, or a square over 6 miles per side.
For comparison purposes, the rough square defining the boundaries of Washington, DC is about 8 miles on a side. (67 sq. mi., to be exact)
It’s worth noting that a lot more of Australia, proportionally, is composed of empty space where nobody lives than the United States is. Something like 80% of Australia’s population lives within the rough arc from Sydney around down to Adelaide. U.S. population is a bit more spread out, and the places where there is a lot of empty space for something like this don’t tend to be real close to the places where there’s the most energy demand, so when considering something like this here, the cost and environmental impact of transmission become a significant factor.
That said, more power to ’em. (No pun intended.) We’d have a lot more enthusiasm for projects like this if renewables weren’t so often opposed by the GINOs who don’t want wind turbines blocking their view and whatnot.
As tempting as it may be to obliterate all life in the DC area by building one or two of these there…
“And while there’s renewed interest in nuclear power, the world’s supply of uranium is limited, while the sun’s energy is not, he said.”
I may be wrong, but I’m unaware that there’s much danger of the earth running out of uranium in the forseeable future; am I wrong, Edward?
And, of course, the sun’s energy is limited. If one allows for enough time. What, that’s a ridiculously far off time? Granted. How far off is the time when uranium shortages loom on earth due to any possible use of nuclear power plants (taking into account the most ambititious possible expansion of their number)?
I’m not putting this forth as an argument against these solar towers; I’m simply questioning the sense of this specific assertion I quote. The pros and cons of nuclear power would seem to be a separate question.
I believe it supports 200,000 homes. 1,000 plants would supposedly cover all US homes, and 3,000 would cover all US consumption.
I’m not sure about that, but someone will have to check my math. The last number I recall seeing (meaning someone better at math than me translated quadrillions of Btus into joules and then to watts) was US consumption of 3.29 Terawatts of power (for 2000, this report* doesn’t show too much of a gain since then so this number is probably OK). Isn’t that 3,290,000 megawatts? That’d require 16,450 of these right?
Not that we’ll ever depend solely on one source though. I’m interested to hear about any expected weather effects of drastically heating up 14sqmiles of surface per tower.
*Interestingly, this report shows that per capita usage has not increased at all since 1970, but that use per dollar of GDP has halved. So, we’re actually getting more efficient GDP-wise.
Man, the thermal efficiency of that installation will suck.
Let’s go to the back of the envelope. 25K acres, at 40K ft^2/A and 1m^2/10ft^2 gives us 10^8 m^2. The sun puts out 1300 w/m^2 onto the earth, but only 1000 makes it through the atmosphere. And that’s for area perpendicular to the sun. Multiply by 25%* to account for nighttime and getting rays on the slant. That’s 2.5 x 10^10 watts going in. And 2 x 10^8 watts coming out.
Call it 1% efficiency. Photovoltaics can do 15-20%, IIRC.
* This is a global average. The earth (assuming it a sphere) presents a cross-sectional area to the sun of 25% of its total surface area. On the equator, the number would be higher. At the poles, smaller. Australia is in the mid-latitudes, so the global average is close enough.
(All numbers from memory. I welcome corrections.)
It’s not 25K acres though, Amos. It’s 9.5, as Slarti noted. What’s the math on that?
Well, if we’re looking for very large open spaces to put our solar power collectors in, we might want to eventually look up again.
Gotta get that lb-to-$ cost to orbit down, though.
“about any expected weather effects of drastically heating up 14sqmiles of surface per tower.”
They would be significant. Trust me. I would volunteer to have a dozen built somewhere west of my home-town of Dallas, to counter-act our concrete heat effects and prevent the rainstorms from circling around us.
[blush]
Divides the energy input by a factor of about 2.5: 10^10 watts going in, 2×10^8 coming out. 2%.
(You mean I’m supposed to read the thread first? That’s too much like work!)
Why all the focus on centralized energy sources? Every building has a roof. I say we work toward moving buildings off the power grid, or at least maintain the grid only as a supplemental source of energy to pick up the slack when sunlight is in short supply. Every house and office building has a roof, and most are pretty large in proportion to the volume of the building beneath. That’s a lot of unused surface area, absorbing heat from the sun that our AC systems work overtime to get rid of. In fact, it could actually turn out that home and business owners could sell power back to the grid for, say, high-rises and industry to buy up.
Anyway, if folks were no longer dependent on the grid and were generating their own power, you could say good buy to energy crises and blackouts. I know technology and cost are the hurdles here, but is this any less true of these centralized schemes?
It ought to be noted, too, that these things are dependend on latitude, seasons, and weather. What might generate 200 Megawatts in full sun would generate substantially less than that under cloud cover. And if 200 MW is peak output at midday, what’s the output at 4PM?
The same questions apply to PVs, pretty much, because it’s the same energy input.
Why all the focus on centralized energy sources?
I think because it allows folks to be mobile, and the costs are diffuse. Part of the difficulty in deciding to solarize a house is the ROI. It can be many years. Chances are, you’ll move by then and if your buyers aren’t as concsious as you, well, you lose.
Now if everyone that was living outside of a multi-unit building were forced to install a solar solution (and building owners were forced to do the same), like we’re forced to buy cars with catalytic converters, that’d be a different story. The problem there is that Seattlites might feel ripped off due to the lack of sun they receive in comparison to Albuquirkies.
The difficulty is noone wants to mandate that type of thing, much like noone wants to simply ration gas.
Looking at the design, I don’t see any reason why you couldn’t put photovoltaic cells under the glass portion and have a dual use for that space. Assuming the price fot the photovoltaics justified their use.
There’s no one solution that’s going to free us from fossil fuels, so calculating how many of these things we’d have to build to supply all the power the US requires seems sorta silly. I expect that a half dozen of these would probably take some the pressure off of the power grid in the southwest.
There’s no one solution that’s going to free us from fossil fuels, so calculating how many of these things we’d have to build to supply all the power the US requires seems sorta silly.
Amory Lovins (head of RMI) has been doing a lot of whole-system analysis of energy usage and how to get off of fossil fuels in the next few decades, and just published a book on his latest study. It’s freely downloadable here.
The fact that peak power generation comes at times of peak solar thermal load might make these very useful in warmer climates, for taking A/C peak loads.
I think because it allows folks to be mobile, and the costs are diffuse. Part of the difficulty in deciding to solarize a house is the ROI. It can be many years. Chances are, you’ll move by then and if your buyers aren’t as concsious as you, well, you lose.
But isn’t this a bit like car manufacturers a couple of years ago saying there was little market for hybrid cars when the dealers literally couldn’t keep them on the lots? Is there really no market for this sort of thing, or are entrenched interests keeping such a market from developing?
And even if some governmental intervention is necessary, you don’t need to require solarization. Just fund serious R&D, and offer tax incentives to early adopters. Or maybe institute a pollution credit trading system for citizens and industry, bring the hidden costs of energy consumption up front and then let the market work it out in a way that it isn’t allowed to right now. Easier said than done, yes, but worth looking into, I would think.
“Well, USA, one upside to this sort of thing is it’s basically only got a few moving parts (turbines and generators), which puts is going to put maintenance costs of the moving-parts equipment about as low as it can get. Also, no emissions.”
So? Why not use a steam generator (still not a lot of moving parts) in a Rankine cycle with a turbine to increase your delta-T and raise your efficiency up from the miserable ~2% that Amos calculated (after corrections).
“Amory Lovins (head of RMI) has been doing a lot of whole-system analysis of energy usage and how to get off of fossil fuels in the next few decades”
I’ll note that whether Lovins is a prophet, genius, nutjob or charlatan or a mix of all four is still indeterminate. He’s the Buckminister Fuller of our time.
or are entrenched interests keeping such a market from developing?
Entrenched self-interest. Solar costs some coin to install. Here in SF, the BP site puts the cost of a medium sized system at $51,000!
Oops, that’s the retail price. After tax credits ($2K) and rebates ($14K), the price is still $35K. With a yearly savings of $1,800 you get an ROI of nearly 20 years. No thanks.
However, the site also states that:
Per year, this system will eliminate the production of
10,455 lbs of CO2
3.1 lbs of NOX
0.3 lbs of SO4
This is equivalent to planting 2 acres of trees
I’m not defending this as an efficient design. It’s simple and pretty bulletproof, which has advantages. Getting the collected heat to do work in another way requires a slightly different approach, no? Feel free to come up with something that’s many times more efficient and doesn’t require the 1 km tower, and you’ll be a hero.
what an interesting tecknology! can i find the cost analysis?