You may have heard the legend of how in 212 BC, Archimedes defended the port city of Syracuse against the invading Romans by setting their ships afire with the help of mirrors that concentrated the sun’s light. It sounds a bit implausible…
However, maybe you’ve heard of Comte Buffon — the guy who figured out how to compute the number pi by dropping needles on the floor. According to Michael Lahans, Buffon also did an experiment to see if Archmedes’ idea was practical. He got a lot of mirrors, each 8 × 10 inches in size, adjusted to focus their light at a distance of 150 feet. And according to Lahans:
The array turned out to be a formidable weapon. At 66 feet 40 mirrors ignited a creosoted plank and at 150 feet, 128 mirrors ignited a pine plank instantly. In another experiment 45 mirrors melted six pounds of tin at 20 feet.
Should we believe this? I don’t know. Some calculations could probably settle it. Or you could try the experiment yourself. If you do, tell us how it goes.
But there are also non-military uses of concentrated solar power. For example, the new power plant named after Archimedes, located in Sicily, fairly near Syracuse:
• Archimede website.
• Archimede solar power plant, Wikipedia.
It started operations on July 14th of this year. It produces 5 megawatts of electricity, enough for 4,500 families. That’s not much compared to the 1 gigawatt from a typical coal- or gas-powered plant. But it’s an interesting experiment.
It consists of about 50 parabolic trough mirrors, each 100 meters long, with a total area of around 30,000 square meters. They concentrate sunlight onto 5,400 metres of pipe. This pipe carries molten salts — potassium nitrate and sodium nitrate — at a temperature of up to 550 °C. This goes on to produce steam, which powers an electrical generator.
The news is the use of molten salt instead of oil to carry the heat. Molten salt works at higher temperatures than oils, which only go up to about 390° C. So, the system is more efficient. The higher temperature also lets you use steam turbines of the sort already common in gas-fired power plants. That could make it easier to replace conventional power plants with solar ones.
The project is being run by Enel, Europe’s third-largest energy provider. It was developed with the help of ENEA, an Italian agency that deals with new technologies, energy and sustainable economic development. At the Guardian, Carlo Ombello writes:
So why hasn’t this technology come before? There are both political and technical issues behind this. Let’s start with politics. The concept dates back to 2001, when Italian nuclear physicist and Nobel prize winner Carlo Rubbia, ENEA’s President at the time, first started Research & Development on molten salt technology in Italy. Rubbia has been a preminent CSP [concentrated solar power] advocate for a long time, and was forced to leave ENEA in 2005 after strong disagreements with the Italian Government and its lack of convincing R&D policies. He then moved to CIEMAT, the Spanish equivalent of ENEA. Under his guidance, Spain has now become world leader in the CSP industry. Luckily for the Italian industry, the Archimede project was not abandoned and ENEA continued its development till completion.
There are also various technical reasons that have prevented an earlier development of this new technology. Salts tend to solidify at temperatures around 220°C, which is a serious issue for the continuous operation of a plant. ENEA and Archimede Solar Energy, a private company focusing on receiver pipes, developed several patents in order to improve the pipes’ ability to absorbe heat, and the parabolic mirrors’ reflectivity, therefore maximising the heat transfer to the fluid carrier. The result of these and several other technological improvements is a top-notch world’s first power plant with a price tag of around 60 million euros. It’s a hefty price for a 5 MW power plant, even compared to other CSP plants, but there is overwhelming scope for a massive roll-out of this new technology at utility scale in sunny regions like Northern Africa, the Middle East, Australia, the US.
The last sentence is probably a reference to DESERTEC. We’ll have to talk about that sometime, too.
If you know anything about Archimede, or DESERTEC, or concentrated solar power, or you have any questions, let us know!
Azimuth 
For some reason this post appears in the “Latest Posts” box in the upper right corner, but (at least in my browser) the text doesn’t appear on the main Azimuth page: the Solèr’s Theorem post is still on top.
I’m not having that problem. Is anyone else having that problem?
At the office I had the same problem, now that I’m home everything is okay.
FWIW, I had a very weird experience. The RSS reader said the new post was there so I came to read the whole thing and it wasn’t there (but Nathan’s comment was as a way to get at it). A while later I refreshed the main page and it appeared on the main page. Later on I refreshed and it disappeared. Finally it seems to be there permanently.
Nine units of SEGS (Solar Electricity Generating) plants built mid eighties through early nineties, in the Southern California deserts having been quietly and reliably generating a total of ~350 MW for a long time. With the recent permitting of other large scale CSP power plants also in California, more upgraded parabolic mirrors collector arrays will be used with a projected optical efficiency of 83%. See for example Blythe solar power project recently approved by California Energy Commission that will consist of four identical units of 250 MW power plants. Blythe Plant will be the largest solar power plant ever to be built at a single location though First Solar Agua Caliente PV power plant, with 290 MW AC rating continues to be the single largest solar generating plant in the world when completed and as things stand. The annual average solar to electric efficiency of these power plants is still lower than the conventional power plants but as technology improves, this efficiency figure may also change.
Thanks, Ali! I spent the morning learning about solar power. I added your information to
• Concentrated solar power, Azimuth.
and also a long-needed new page:
• Photovoltaic solar power, Azimuth.
Here’s what I wrote:
Greg Gbur has a nice summary of investigations into the Archimedes death ray, here.
Hi, I’m curious if any of you would concur with my calculation of the size of a 19% efficiency PV array with 7500 Wh/sq meter radiation, to generate the average amount of energy to deliver $1 of GDP?
What I get is 1300sf for a day on average. So for your $6 glass of wine as average spending you’d need the equivalent of 7800sf of PV array?, and for your $50k income, the use of a 180,000sf array every day.
http://www.synapse9.com/design/dollarshadow.htm
I find it a bit tough to follow these calculations. Let me try to redo some of them, sticking to metric as much as possible.
The earth receives about 150 watts/m2 of solar radiation, averaging over location and time of day (including night!).
You use a different figure…
But following you, I’ll multiply by figure by 0.19 since solar cells aren’t perfectly efficient, and by 0.5 assuming only half the ground gets covered, and by 5/6 assuming an energy return on energy invested of 6.
This brings it down to about 12 watts/m2.
Then you do a conversion from energy to GDP, which people might argue about: you say that in 2008, the world GDP was about 64 trillion dollars, and the world energy consumption was about 512,000 quadrillion BTU. I like metric, so I’ll convert that to 5.4 × 1023 joules.
Hmm, Wikipedia says the world used 4.7 × 1020 joules in 2008. That’s 3 orders of magnitude off!
Where are you getting your figure of 512285 quadrillion BTU? Your table 3 doesn’t go up to 2008, but it seems to say that in 2007 the total energy use was about 477 quadrillion BTU. Again, that’s about 3 orders of magnitude off.
Did you perhaps mean 512.285 quadrillion BTU? If I use that figure I get about 8000 BTU per dollar of GDP, which matches your figure.
Okay, so you left out the decimal point in your table but it didn’t really affect the next step in your calculation.
Let me redo it my way. Wikipedia gives a world GDP of $57 trillion in 2009, which is at least roughly consistent with your $64 trillion in 2008. (Did it go down due to the financial crisis?)
So, I’ll use your figure of $64 trillion GDP and the Wikipedia figure of 4.7 × 1020 joules in 2008, and get 7.3 million joules per dollar GDP.
Before I proceed, I have to ask, what does this figure of “7.3 million joules per dollar GDP” really mean? Surely it doesn’t take this much energy for me to produce a dollar of goods or services!
But I guess you’re claiming it does?
Anyway, to finish off the calculation, if one dollar GDP equals 7.3 million joules in some mysterious sense, and solar power brings in 12 watts/m2, then in some mysterious sense solar power brings in “one dollar per second per 6 million square meters.”
But surely people building solar power plants earn a lot more than that from the power they sell!
So I guess I’ll ask you again: what does “7.3 million joules per dollar GDP” really mean?
Yea, with complicated things I can never check figures unless I start over with the concept too. I’m using IEA World indicators time series data. My copy is linked from the references noted on that page, at: http://www.synapse9.com/design/IEA-worldindicators.xlsx
The GDP difference seems due to my using PPP dollars which effectively corrects the currency fluctuations for physical productivity, and gives that nice smooth GDP curve and matching smooth Energy use curve (fig 1).
As to your question, “What does it mean… Surely it doesn’t take this much energy for me to produce a dollar of goods or services!”. I got: 8000 btu/sec = 8443528 joules/sec, so 8.4 million in 2008. So yes, that is exactly what it means, the total purchased energy the world was using in 2008, on average, to produce $1 of GDP.
I’m not sure about your last calculation, but the rest seems OK except that I’m using 7500 Watts per sq meter per month from the charts of measured solar radiation at the ground referred to. I don’t know if the world average for mid-latitudes is somewhat above or below, to that’s just a sample number.
The price energy is sold at is a quite different thing, and solar is generally subsidized to compete with oil, etc, so may be hard to gage. The $1 price the GDP value of using the 8000btu’s at the efficiency of the world economy. What I’m saying is that the value to the economy of using 8000btu or 8.4Mjoules, on average, is 1$.
What happens is when you compare these figures (shares of global energy implied) with traceable energy uses for businesses to operate, the averages are generally greater than the traceable energy uses, often a difference of 500% or more. So, some untraced energy use seem to go uncounted.
fyi – I have a long paper on the subject that’ll be in an upcoming issue of Sustainability (MDPI) fyi: http://www.synapse9.com/drafts/WindEROI_SEA.pdf There appears to be a fascinating cognitive error in the ISO standards used for designing measures business environmental impacts! Read the abstract and a couple pages and see what you think.
Phil
The competitor for Desertec is the Sahara Solar Breeder Project.
No extra-Google knowledge about the project, sorry.
As a funny aside, I’m sitting here reviewing a climate related proposal from a good PI with PhD in environmental statistics. A prior/preliminary data table has an entry for the average of outliers!
A solar breeder project! Cool! The Azimuth Project has a page on solar breeders. I’ll have to add this information there.
The idea of a ‘solar breeder’ is to make a solar power plant that makes solar power plants. The Sahara Solar Breeder Project wants to make photovoltaic panels out of Sahara sand! I’m not sure it’s a practical idea, but you gotta admit it’s got charm.
I added information about the Sahara Solar Breeder Project to our Solar breeder page. Here’s what I wrote:
Does anyone here know more?
Want to see concentrated sunshine melt rock?
I’d be more interested in seeing concentrated sunshine melt iron and steel and aluminum… Do that, especially the last one, and we’ve got something to talk about.
Here’s a patent application for a solar smelter (and a link to a database where you can search and get pdf files of patents for free): http://www.freepatentsonline.com/y2010/0078012.html
Here’s a web site, incidentally by the same guy who has the patent app above, about solar smelters. He’s apparently got a working model: http://solarcooking.wikia.com/wiki/Solar_Smelters_International
Appropriately enough, it’s on a wiki devoted to the art of solar cooking: http://solarcooking.wikia.com/wiki/The_Solar_Cooking_Archive_Wiki
Two articles in Russian by the same author on large solar smelting furnaces, behind a Springer paywall:
http://www.springerlink.com/content/kn170hg4l1650752/
“Applied Solar Energy
Volume 44, Number 1, 24-27, DOI:
10.3103/S0003701X08010088
Analysis of operating characteristics of various
smelting furnaces on a Large Solar Furnace, A. A.
Abdurakhmanov et al.”
and
http://www.springerlink.com/content/a88340r084107324/
“Applied Solar Energy
Volume 44, Number 4, 284-287, DOI:
10.3103/S0003701X08040129
Creating melting furnaces based on the large solar
furnace, A. A. Abdurakhmanov et al.”
Solar cookers can be used to solve the problem of deforestation (as in Haiti, where all of the woodbearing plants get burned for charcoal) and indoor air pollution from wood-fueled cooking fires: http://venturebeat.com/2010/09/23/the-solsource-solar-oven-wins-500k-eu-in-the-green-challenge/
Thanks for all the info! It will be duly transcribed into the Azimuth Project.
streamfortyseven says “I’d be more interested in seeing concentrated sunshine melt iron and steel and aluminum…”
Then you’re in luck: the video does show concentrated sunshine melt steel. It also says that the hot spot reaches 3500C, and that there is no known substance on earth that can resist that. The melting point of iron is 1500C, and aluminium a mere 660.
I started a page on solar energy based on what streamfortyseven told us:
• Solar energy, Azimuth Project.
It’s just a stub so far, and I bet streamfortyseven could easily make it ten times better in half an hour. (Don’t worry about getting the formatting right; the elves will take care of that.)
I’m sure it’s obvious to all of you, but converting bauxite ore into aluminum takes a lot more energy than melting aluminum cans to recycle them. Aluminum is highly reactive. This is why the pure metal form was isolated so late — 1825. And this is why Napoleon let his guests use gold forks and knives, while reserving the more precious aluminum cutlery for himself! Little did he know how tacky this would later seem.
So, I’d like to see a solar-powered system melt rock and make aluminum!
The Syracuse experiment was done by an MIT group and Mythbusters. My recollection from the episode was that the myth was busted.
See http://web.mit.edu/2.009/www/experiments/deathray/10_Mythbusters.html
Mythbusters is going to revisit the problem on Wednesday night (December 8) at the request of President Obama who appears on the show.
I thought for sure you were trolling us, John, but apparently not!
Clearly Obama has been reading Azimuth.
what is trolling? you don’t need to post, just curious.
The current definition of trolling seems to focus on quite nasty ways that people use the internet to make other people upset.
But back when the internet was young, before the web was invented, trolling was often more benign. On so-called usenet newsgroups, people would make absurd claims with a straight face, just for the pleasure of tricking people into taking them seriously and arguing with them.
For example, I once claimed (in some usenet newsgroup where nobody knew me) that just as the Egyptians had secretly built the golden ratio into the dimensions of the pyramids (a controversial claim), the Babylonians had secretly built the number pi into their architecture: a Babylonian column had been unearthed where the ratio of the circumference to the diameter was almost equal to pi! I was roundly denounced as an idiot until somebody pointed out that I was a mathematician and must have been kidding.. That was precisely what I wanted. That’s “trolling”.
Similarly, I can imagine someone reading this blog article and posting an absurd comment claiming that Mythbusters was about to test whether Archimedes could have set those ships on fire…. at the insistence of President Obama!
So, I thought you were trolling. But it turned out you were serious.
By the way, I haven’t watched the show. What happened?
Tony wrote:
If you read Greg Gbur’s account, pointed out here by Blake Stacey, you’ll get a very interesting analysis of this question. Whether they busted the myth depends in part on what the myth was!
Yeah, as I wrote that comment I did a search to check the facts and noticed that the whole story was somewhat more complicated than I thought. Sounds like real science!
Pres.O was amusing asking them to reexamine the myth, but the Mythbusters did not choose poor approach to resolving it. Flat mirrors are almost impossible to focus to the point where they would burn cloth or wood, so where would Arch get the idea. Greek shields were concave not flat like the Roman shields, which is how a polished shield might have accidentally set something on fire, which is the mostly likely way he might have made an observation that might of lead it to try this. I was disappointed that the M people didn’t spend some time thinking like a bright high school students and tried to use a mirror might burn wood up close, and then determine if it were possible to try to accomplish the myth at a distance. Pres.O seems to be trying to hard to promote science in junior high school and higher in the USA now. By the way, he gave a very nice talk five min talk about the importance of science to the future before he handed out the National Medal of Science. You can find videos of both appearances on the white house website.