‘We’ve all been taught that this doesn’t happen’
From the University of Michigan
A dramatic and surprising magnetic effect of light discovered by University of Michigan researchers could lead to solar power without traditional semiconductor-based solar cells.
The researchers found a way to make an “optical battery,” said Stephen Rand, a professor in the departments of Electrical Engineering and Computer Science, Physics and Applied Physics.
In the process, they overturned a century-old tenet of physics.
“You could stare at the equations of motion all day and you will not see this possibility. We’ve all been taught that this doesn’t happen,” said Rand, an author of a paper on the work published in the Journal of Applied Physics. “It’s a very odd interaction. That’s why it’s been overlooked for more than 100 years.”
Light has electric and magnetic components. Until now, scientists thought the effects of the magnetic field were so weak that they could be ignored. Rand and his colleagues found that at the right intensity, when light is traveling through a material that does not conduct electricity, the light field can generate magnetic effects that are 100 million times stronger than previously expected. Under these circumstances, the magnetic effects develop strength equivalent to a strong electric effect.
“This could lead to a new kind of solar cell without semiconductors and without absorption to produce charge separation,” Rand said. “In solar cells, the light goes into a material, gets absorbed and creates heat. Here, we expect to have a very low heat load. Instead of the light being absorbed, energy is stored in the magnetic moment. Intense magnetization can be induced by intense light and then it is ultimately capable of providing a capacitive power source.”
What makes this possible is a previously undetected brand of “optical rectification,” says William Fisher, a doctoral student in applied physics. In traditional optical rectification, light’s electric field causes a charge separation, or a pulling apart of the positive and negative charges in a material. This sets up a voltage, similar to that in a battery. This electric effect had previously been detected only in crystalline materials that possessed a certain symmetry.
Rand and Fisher found that under the right circumstances and in other types of materials, the light’s magnetic field can also create optical rectification.
“It turns out that the magnetic field starts curving the electrons into a C-shape and they move forward a little each time,” Fisher said. “That C-shape of charge motion generates both an electric dipole and a magnetic dipole. If we can set up many of these in a row in a long fiber, we can make a huge voltage and by extracting that voltage, we can use it as a power source.”
The light must be shone through a material that does not conduct electricity, such as glass. And it must be focused to an intensity of 10 million watts per square centimeter. Sunlight isn’t this intense on its own, but new materials are being sought that would work at lower intensities, Fisher said.
“In our most recent paper, we show that incoherent light like sunlight is theoretically almost as effective in producing charge separation as laser light is,” Fisher said.
This new technique could make solar power cheaper, the researchers say. They predict that with improved materials they could achieve 10 percent efficiency in converting solar power to useable energy. That’s equivalent to today’s commercial-grade solar cells.
“To manufacture modern solar cells, you have to do extensive semiconductor processing,” Fisher said. “All we would need are lenses to focus the light and a fiber to guide it. Glass works for both. It’s already made in bulk, and it doesn’t require as much processing. Transparent ceramics might be even better.”
In experiments this summer, the researchers will work on harnessing this power with laser light, and then with sunlight.
The paper is titled “Optically-induced charge separation and terahertz emission in unbiased dielectrics.” The university is pursuing patent protection for the intellectual property.
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Obviously, this is still in the theory/conceptual stages. I wouldn’t get too excited just yet. A practical application of this concept is still years, if not decades off. But, if it could work, it would be a boon for solar power.
This can’t be correct! We have a consensus of 2,742 physicists! Obviously funded by Exxon-Mobil and the tobacco companies. Its worse than we thought. These people aren’t climate scientists. Deniers all.
Input 10 million watts per square centimeter. Output?
If you’ve got 10 megawatts/cm^2 (100 gigawatt per square meter), why would you play around with this at 10% efficiency when you could use that intensity to superheat just about any substance and run a conventional heat engine in a combined-cycle at 50% efficiency or more?
“10 million watts per square centimeter” of focused sun light for an output of?
Sounds like a optical version of a Stirling engine.
The first thing I thought of was Maxwell’s Demon. http://en.wikipedia.org/wiki/Maxwell%27s_demon
10 MW/cm^2 Hmm… That’s about 100 billion w/m^2 or 100 million x natural light.
Big lens. Or really tiny fibre. All for how much output?
Mostly for another research grant, I suspect.
Sunlight power density is about 1.4 kW/m^2. To get 10 megaW/cm^2 looks to be about 15 million times the power density. I guess you could get some of that with focusing lenses but do you end up melting the glass fiber?
If it works, very interesting indeed.
Yeah, I see theory all the time, the main theme of this is isn’t it interesting that something that was not thought possible is in fact occurring. I need to understand this a little more from a conceptual standpoint as to the mechanics involved though, I cannot seem to wrap my head around exactly what is occurring here.
I do not think anyone is against solar power, just its current cost, which admittedly has gotten considerably better in the last decade. It just has to drop a bit more.
Simplifying the solar radiation on Earth to 1kw/m^2, we obtain 0.1w/cm^2.
(10 million w/cm^2) / (0.1 w/cm^2) = 100 million suns of focusing power.
I think that “sunlight is not this intense on its own” is a vast understatement.
10 Megawatts per sq. Centimeter?
And, the reflector is how large?
I smell another cold fusion story coming.
A very appropriate topic for ‘Watts up with that?’ !
I wonder how this will modify those “equations of motion”.
Actually this is huge, if only because electro-magnetism is thought to be so well understood and wasn’t. A fresh look a fundamental force may prove interesting.
So thinking outside the box for a moment – something I’m prone to do anyway – one uses this technology to build self-powered space elevators, use them to raise more geostationary collectors to the desired altitude, bring up more fibers, energize them, collect the excess power at ground level, and then sell weekend vacations at outposts along the elevator. It needs a motto – “Higher, ever higher!”
But wait – there’s more!
With all these lifting stations we could haul some light weight plumbing up to the generating stations and force feed CO2 up the pipe and out the far end where the solar wind carries it to the dead sea bottoms of Barsoom and beyond.
Surely there’s a flaw somewhere in my scheme. This is all too simple.
/sarc
I`m no Electric Universe proponent, but how does this sit with their “theories” ?
I wonder if it is reversible. That would also be very interesting.
Scientifically, this is probably extremely interesting. Although it wasn’t published as a Physical Review Letter so it’s not super interesting. They seem to be implying that they can get a 2nd order response out of a material that has inversion symmetry. But that’s not clear.
Getting the same response with an orders of magnitude lower intensity, don’t hold your breath.
Nifty, but I’ll wait to get excited until I see a prototype that works in regular sunlight on a day that isn’t perfectly clear.
so they may someday be able to create a cheap solar cell that has 10% efficiency … I don’t care if its free … won’t amount to a hill of beans for usable energy except for remote locations … just like solar cells today …
dp says: “…Surely there’s a flaw somewhere in my scheme.”
Don’t call me Surely.
“10 million watts per square centimeter”
Right.
Reminds me of the formula for time travel –
“First you start with a small black hole …”
Andrew30’s question about reversibility probably hits the spot. This sounds to me like a piece of weapons research, carefully couched in non-lethal terms for patents and such.
Let’s hold off on shutting down Grand Coulee.
Future death-ray perhaps? .. hehehe
The picture documents that William Fisher isn’t wearing laser safety goggles while he’s operating the laser and is in fact standing over it in operation. He’s in serious breach of very standard safety precautions, and I’d guess in violation of U. Mich. safety regs. He’s also risking permanent eye injury.
Best of luck to them and their work. It sounds very promising. But someone ought to collar Mr. Fisher.
Sounds like MRI – something well known already.
“Hey, Doc, we only need 1.21 gigawatts to power the flux capacitor!”
Ok, it sounds interesting, but as an useful power source…? not so sure…
polistra says: April 14, 2011 at 8:29 pm
“sounds to me like a piece of weapons research…”
Sorry, I think I did not indicate my idea clearly.
I do not expect that it is physically probable to create or to focus natural light to the required level onto a optical fiber without a space based magnifying glass and a glass fiber made from unobtainium.
I though that if the physical action is reversible it should be easily demonstrable.
The ability to create an intense light source using only a piece of glass and some wire (no pump tube, no mirrors, no gasses, no filament and no semi-conductors) would be a real breakthrough. A permanent (in human terms) light bulb.
On the light as a weapon side; the United States already has a ship based laser that they publicly demonstrated last week (in the Pacific off the California coast) to smoke another boat (moving, bobbing etc.) at a great distance; also on the same day they demonstrated a land based high power free electron laser to destroy something else. Word is there FEL can get through 12 feet of steel in about 1 second and the ship based system is good to a distance of ‘miles not feet’.
I don’t think that this student’s work is any kind of “weapons research”, if it were you would not be hearing about it, yet. Remember how long it took before the laser gyroscope became ‘public’, that was “weapons research”
Interesting post. But if, in fact, there were materials that would be more sensitive to sunlight (being far more diffuse than 10 million watts per square centimeter) so as to create this magnetic effect, wouldn’t we see electricity flowing in those materials already? I don’t think that such materials really exist. But who knows, we may find some.
I think working with lasers makes you crazy, anyway. Just kidding.
This just goes to show that the more convoluted and complicated these solar schemes are the more expensive and unreliable they become. So in that spirit I’ll see your magnetic glass fiber and raise you one Trombe wall. As always, with solar, low tech wins every single time.
tom gannett says:
April 14, 2011 at 7:01 pm
> I smell another cold fusion story coming.
Glad to oblige.
Last week the Swedish Skeptical Society (sorta like the US version, but without the record of denying climate skeptics respect) validated a Rossi E-cat device, see
http://www.nyteknik.se/nyheter/energi_miljo/energi/article3144827.ece which says, in part:
Perhaps readers are forgetting the large advances made between the discovery that radio waves can be transmitted over a distance, and the development of today’s cell phones. The work is closer to Marconi and Tesla than Vodafone.
Give the guys a break! It was embarassing to read some of the above. Have you ever worked out the W/m^2 of a well made small laser? And that for a material not even slightly optimised? Ask a HAM radio operator to show you the size, power and efficiency of an early radio transmitter.
What’s the point of having a website for new and interesting technologies (for skeptics, no less) if all you think about is diminishing new ideas! These are hardly the first people to demonstrate that there are fundamental misunderstandings about life, the universe and everything held high. Perhaps read Lee Smolin’s book on problems with physics. There is a lot of room for improvement and this would be a good one.
There are evidently more minds than before accepting that there is some sort of ether, which obviously does not have the properties of a gas as was thought in Victorian times. One has to be very careful not to offend the mullahs of science so it is given various names that often include the word ‘continuum’.
Tesla had a very different understanding of what fills space. He was right on a couple of other things as people may recall, but he did not demonstrate anything I would accept to support his understanding of it. Maybe he was wrong, but there is no shortage of ideas. So we should stand on middle ground when looking at breakthrough understandings.
Light, gravity and electricity are probably waves through some etherial field or material of indeterminate, perhaps directly undetectable ‘continuum’. This is hardly a new idea and appeared in books over a century ago. As electricity and magnetism are directly linked they can be viewed as ‘one’. To find that light interacts with selected materials creating both electrical and magnetic effects is surely not a surprise.
Congratulations to Rand and Fisher. May they overturn the dogma that clutters the minds of so many, and establish sound principles in its place. The principles do not have to be narrow and exclusive or in the possession of an elite, particularly and most dangerously, a self-appointed one.
Is the energy density mentioned available near the sun? What is the falsefiable statement in this case?
Well said Crispin in Johannesburg.
Come on, the allusion to solar power is the standard PhD student pick-up line at a bar. If you are forced to describe your work to a vaguely attractive girl are you going to say
“I am working on optically induced magnetism in solids”
to which she replies
“goodbye”
Or do you say
“I am working on improving solar energy for the benefit of all humanity”
at which point she might not walk away. Which for most PhD physics students is a win. Anyone who has been a PhD physics student has either (a) done this or (b) seen their friends do it. No matter how tenuous or far-off the link to something a chick might dig, you play it up. Back in the department conferences no one gives a stuff, because they think it is cool, just because it is.
on April 14, 2011 at 6:43 pm
Jonathan said:
“Simplifying the solar radiation on Earth to 1kw/m^2, we obtain 0.1w/cm^2.
(10 million w/cm^2) / (0.1 w/cm^2) = 100 million suns of focusing power.
I think that “sunlight is not this intense on its own” is a vast understatement.”
No, the sunlight can do that indeed. Just put their 1cm^2 fiber into the focus of one lens or parabolic mirror which focuses a 1000m^2 area (sarc).
The real problem is: what’s the outgoing energy we could get from that so wide device?
“The paper is titled Optically-induced charge separation and terahertz emission in unbiased dielectrics.
That reminds me of the lab engineer who needed a mirror in his lab.
But there was no way he could get it into the budget. So he changed it to “Optical reflector device” and there was no problem.
Aliens figured this stuff out a long time ago.
The energy density is not a problem .
Take 1 kw/m² (just the usual sunny day) and concentrate all the rays on a surface of 1 mm² .
You’ll still get “only” 1 kw in total but the energy density on this 1 mm² became 1 kw/mm² what gives in other units 1000 MW/m² or 0.1 MW/cm² .
To get their 10 MW/cm² , they need a factor 100 over the above focusing power so they need to focus 1m² on a square of 0.1 mm x 0.1 mm .
This is hard but not unfeasible .
What I suspect is that producing a lens (or a curved reflector surface) with such an accuracy would cost far more than the value of a power generating capacity of 1 kw .
Of course creating a lens or surface 1000 times bigger with the same accuracy would cost more than 1000 times the price of a 1 m² module so there would be no economies of scale .
So if this theory is true , it would just be a more expensive alternative to the traditional photovoltaic cell .
And as we know that photovoltaic cells are already 10 times more expensive than coal or gas alternatives , this “new” technology would become economically interesting the day we run out of sand .
I don’t expect it happening in the next few millions of years .
10,000,000 watts per cm2 is a crazy amount of concentration.
Until and unless this drops by many orders of magnitude, it will be no more significant to actually doing anything than those ftl quantum effect demonstrations have been until now.
“Intense magnetization can be induced by intense light and then it is ultimately capable of providing a capacitive power source.”
I find that statement odd. Capacitors work based on an electric field. They have two (or more plates) in close proximity, separated by an insulator (dielectric). Differences in electron density between the two plates result in energy stored in the electric field.
Inductors are the magnetic equivalent of capacitors and they store energy in the form of a current flow induced by the magnetic field.
Surely to capture this magnetic energy, an inductor will be required to generate a current flow in order to charge the capacitance although I would have thought it would be easier to simply deliver the current derived from the magnetic field straight into a battery.
Anyway as others have pointed out, the light density required is so extreme that this is unlikely to ever become practical, even if it is an interesting discovery in the field of physics.
I believe the book by Lee Smolin is “Three Roads to Quantum Gravity” which discusses space itself as having a Planck size. The theory is called Loop quantum gravity and has interesting implications. I recommend the book for anyone with interests along this line. It also discusses some of the problems with string theory.
The book is about 10 years old but I have not found any follow up. Maybe someone here has followed this more closely.
A factor of great importance in laser work is the focus. During my foray of research into it, we had (a) an inquiry from a wheat farmer who wanted to cut his stubble to the ground by sweeping a laser beam through it from a central point (b) a maker of coconut ice candy whose cutting knives would clog up, better to use a laser and slice with high heat – workable (c) a major maker of cardboard boxed, whose knives also used to clog up – workable, but expensive … and many others. The point in common was a confusion of energy density in the tiny voulme of a fine focus, with the false thought that such power and cutting ability could be applied over large distances.
Weapons reserach has seen lasers in large aircraft, but the limit is the weight of the power supply and (presumably) slabs, plus the refrigeration system. Maybe that’s why they are concentrating on ships. Not so familiar with the free electron laser, but a 12 foot sheet of steel seems highly improbable for practicality. One would have to keep the focus in exactly the same spot, which is hard to imagine on bobbing ships.
The lead article is quite unclear. I can’t envisage energy capture using capacitance principles, but we need a better description. Don’t write it off until there is one. That’s anti-science.
Or Steve Martin’s bit about “How to be a Millionaire, and never pay taxes”
First… get a million dollars.
Right.
Reminds me of the formula for time travel –
“First you start with a small black hole …”
The Sun’s surface puts out 63,200,000 watts/m2 or 6,320 watts/cm2 (per second).
So the energy levels quoted in the article are 1,500 times more powerful than the surface of the Sun.
Very Interesting…. How does this fit with the Plasma Universe theory/idea. Where electo magnetic interactions have more effect on the motions of Galaxies than does gravity?
…… This is quite astounding.
****
TomVonk says:
April 15, 2011 at 4:22 am
The energy density is not a problem.
****
No, it certainly still is. You can’t get past the fact that to capture a reasonable amount of low-density solar energy (compared to fossil or nuclear), you’ll need a comparatively enormous area & amount of hardware to do so.
You can’t cheat simple physical realities of low-power-density sunlight, and in addition to that, cloudy days or nighttime.
Sounds like “anal rectification” instead of “optical rectification” to me and another grasp for grants.
See: (It’s an hour long. Watch all of it.)
http://www.youtube.com/watch?v=V7jKL2-B0QA&feature=player_embedded
Photonic energy induces charge separation in water – this is a much more prominent
effect than heating the water by photons.
Another thought:
“Gravity lenses”.
“Astronomers assigned the phenomena to gravity only because they were already in search of such “proofs.” They needed the bending to be caused by gravity, so they ignored the more likely explanations. As in so many other instances, they let the theory determine the data. Instead of having data, and then developing a theory to contain it, they had a theory, and then went in search of data to support it. ”
http://milesmathis.com/lens.html
see also
http://tallbloke.wordpress.com/2011/02/09/ed-dowdye-light-bending-proposal/
DirkH says:
April 15, 2011 at 6:38 am
“Photonic energy induces charge separation in water – this is a much more prominent
effect than heating the water by photons. ”
Well, i wrote it that way because that’s how Dr. Gerald Pollack explained it in the video but maybe it’s not simply the photonic energy but the electromagnetic effect of light that is suggested by Stephen Rand.
Well DirkH to be fair you should have some reason to be proposing hypotheses (data if you will) and then test a set of possible hypotheses to see which best survives the data that is then collected to invalidate them.
Developing a hypothesis solely from data observations is the inductivist trap. On the other hand, searching for data to support a hypothesis is the cherry-picking trap.
DMC says:
April 15, 2011 at 7:36 am
“Well DirkH to be fair you should have some reason to be proposing hypotheses (data if you will) and then test a set of possible hypotheses to see which best survives the data that is then collected to invalidate them.
Developing a hypothesis solely from data observations is the inductivist trap. On the other hand, searching for data to support a hypothesis is the cherry-picking trap.”
I didn’t develop a hypothesis; it was pure conjecture; and i don’t urge anyone to pay me billions for it to save the planet.
I see the possibility of a connection between what Rand and Fischer report and what Dr. Pollack says. YMMV.
Hmm… still it’s energy conversion so the energy must be coming from somewhere. If there was no measureable loss of energy in the light beam in the experiment, the conversion efficiency must be ridiculously low. Where is the energy coming from? Is the light exiting at a lower wavelength or what? You are not getting free energy out of this. It has to come from somewhere.
Well the sun provides at the earth surface, about 1000 W/m^2 or 100 mWatts per squ cm.
So to get to 10 MWatts/m^2, they need a concentration ratio of 10^8.
The sun is a near point source; but it has an apparent source size of half a degree. To scrunch all the solar energy from some area (A) to some smaller area (a) that is 10^8 times smaller or 10^4 times smaller diameter (0.01% of the diameter), that light cone angle has to increase by about that same 10^4 ratio; well strictly speaking the sin of the angle does.
So a 0.5 degree cone has a half angle of 0.25 degree and sin of that is 0.004. So 10^4 times that is 40.
So the concentrated light beam has a cone half angle whose sin is 40.
That is simply wonderful U of Michigan. Are you aware that the Etendue is an invariant under all Optical transformations; so it is simply impossible to concentrate a half degree cone of light by 100 million times.
Come back to me, when you have calculated Arcsin(40); and I’ll give you some more grant money.
Why do I have to go through this ?
Pure psychobabble. Are you sure this wasn’t released on April 1st Anthony?
“”””” TomVonk says:
April 15, 2011 at 4:22 am
The energy density is not a problem .
Take 1 kw/m² (just the usual sunny day) and concentrate all the rays on a surface of 1 mm² .
You’ll still get “only” 1 kw in total but the energy density on this 1 mm² became 1 kw/mm² what gives in other units 1000 MW/m² or 0.1 MW/cm² . “””””
Well Tom, I agree with the accuracy of your arithmatic.
The problem lies here:- “”””” Take 1 kw/m² (just the usual sunny day) and concentrate all the rays on a surface of 1 mm² . “””””
Assuming the source is the sun with a source divergence cone angle of 0.25 degree; then that is an impossible task. Calculate the Etendu of your solar source, and then try concentrating that 10^8 times. And your method only concentrates it a million times; well that is if you can calculate Arcsine (4.36)
Theoretically it’s interesting to know that Lazing energy from negligible particles can generate magnetic effects that are 100 million times stronger than previously expected, tho there is the obvious flaw of converting massive amounts of energy to produce tiny amounts of energy, and the other flaw of needing technology that has yet to be invented, developed and tested.
This is not new, theoretically, as many theories indicate that the rules of physics change at very high energy levels. This just may be one of those situations. See Steven Hawking and Joao Magueijo, among others theorize that rules may change at extremely high energy levels. The interesting question is not if one can efficiently use this finding at this time but did these guys actually prove it happens?
The “optical invariant” nhu, to use the notation of Conrady; where (n) is the refractive index of the medium, and (h) is the ray height (from the optical axis), and (u) is the angle of elevation of the ray from the optical axis; is a paraxial form of the more general NHsin(U). That two dimensional formula translates to NH^2.Sin^2(U) in three dimensions, or NA.sin^2(U) where A is the source area, and U is the maximum divergence angle of the marginal rays.
That quantity is invariant under optical transformations (refraction and reflection). It applies to ANY optical system; and that includes IMAGING optical system, such as lenses or mirrors, as well as NON-IMAGING optical systems such as Compound Parabolic Concentrators, of the types developed by Roland Winston, et al at the University of Chicago Department of Physics, and the Enrico Fermi Institute. It is a constraint that derives from the second law of thermodynamics, and was thus derived by Rudolph Clausius.
Winston et al have shown that non-imaging concentrator systems, outperform imaging systems, certainly at optical frequencies; and they actually made a source brighter than the sun, by using a solid crystal Compound Parabolic Concentrator made from a high refractive index material; as I recall some sort of YAG, but the focussed energy was inside the crystal.
Conrady and others have shown that for imaging systems, only “Aplanatic” systems can reach the theoretical concentration limit; that is sytems corrected for both Spherical aberration, and coma. No (imaging) optical system can form a brighter image than an Aplanatic system.
And parabolic mirrors aren’t even close to being aplanatic since they have totally astronomical amounts of coma.
Any demonstration of the above described phenomenon, could only be done using some sort of laser source, that is a far betetr approximation to a point source than is the sun. Unfortunately, lasers are not independent energy sources.
You are still stuck with the sun as the only practical optical source of large amounts of energy.
I located a ppt presentation on this paper, which provided a lot more detail. This is an interesting physical phenomenon. Solar farms soon? Not so much.
In traditional optical rectification, the Electric field of an incident optical beam induces motion of an electron, resulting in emission of radiation. Some of this will be at harmonic frequencies and/or a DC charge, depending on how the electron motion is confined by other E fields created by the material’s atomic structure. The effect is very small and has no practical use for generating low frequency/DC signals or generating power, especially once p/n junctions were perfected. It is used with some success for generating THz radiation in noncentrosymmetric solids.
These guys have argued that (at least from what I could extract from the presentation), while the electron moves in response to the E field, it is moving through the B field also present in an optical beam. The electron moving in the B field results in an additional orthogonal force that distorts the electron motion into a (slight) C shape.
This effect is really small, or it would have been observed in the 1960’s, when optical rectification was first observed. There is a resonance that can occur, resulting in much larger effects (much more distorted C shape). In their experiment, a femtosecond pulsed laser was focused into a sample and they observed scattered light that was consistent with the predicted process.
For power conversion, one example given uses an F/1 lens to focus 1 kW/m^2 of sunlight onto the end of a 141 micron diameter, 10 meter long optical fiber containing a special material. Electrodes are located at the ends of the fiber. The predicted power conversion efficiency is 25% with some other assumptions.
Now for the bad news.
The sunlight focused by an F/1 lens provides about 10^8 Watts/m^2 at the fiber core, assuming lossless two-axis tracking of the lens/fiber assembly with the sun. This concentrating ratio of 100,000:1 is more than 200 times higher than what is considered practical by developers of solar concentrator PV.
The currently investigated simple materials (liquids like the familiar carcinogens Benzene and Carbon tetrachloride) require more than 10^12 Watts/m^2, about 10,000 times higher than what can be achieved under best-case solar concentrator conditions.
A material with a much lower intensity requirement is needed.
I predict that a quantum well material system, perhaps grown on the inside surface of a hollow optical fiber preform, using vacuum deposition techniques, could conceivably allow engineering of a designer nano-composite that could provide the needed magnitude of effect.
Now, does that sound simpler or less expensive than a stationary, lens-free, large-surface-area p/n junction?
“”””” For power conversion, one example given uses an F/1 lens to focus 1 kW/m^2 of sunlight onto the end of a 141 micron diameter, 10 meter long optical fiber containing a special material. Electrodes are located at the ends of the fiber. The predicted power conversion efficiency is 25% with some other assumptions.
Now for the bad news. “””””
Well the bad news is that with an f/1 lens you can’t get sunlight concentration of that order. No f/1 lens exists that can do that across the spectral range from say 0.25 micron to 4 microns which contains 98% of the solar spectrum energy.
People need to understand that lasers produce essentially point sources of near monochromatic coherent EM radiation, and such a source can be focussed to extremely high energy densities.
Sunlight is incoherent, polychromatic, and of a 15 minute of arc half cone angle of beam divergence. Such an energy source cannot be concentrated 10^8 times by any Physical means; known or unknown. The laser beam maybe !
So if you can’t make a sunlight powered laser, with some non- negligible conversion efficiency from broad spectrum incoherent sunlight to coherent monochromatic laser energy, you can kiss this one off.
If they can make it into a portable laser pistol weighing less ‘an 40 pounds I’ll consider donating, otherwise put an A.C.M.E stamp on it because then, at the very least, one customer named Wile E. will buy one, and that’s actual one sale which mean they can sell 100% the first year.
George E. Smith-
Agreed that the 100,000 concentration factor is not possible with imaging optics. I was reporting what was presented by the researchers in their presentation. The closest I have read for achieving 100,000 concentration factor was with a Winston non-imaging concentrator, with the claim of a 56,000 concentration of terrestrial sunlight (not sure if the spectrum was limited). Of course, the output of this type of concentrator does not couple efficiently into an optical fiber.
http://www.nature.com/nature/journal/v339/n6221/abs/339198a0.html
Wow, 10 MW/sqcm. Sooo…. not going to power my laptop any time soon?
Interesting research. Keep up the good work.
I does read like Tesla’s ideas.
“”””” chris y says:
April 15, 2011 at 12:14 pm
George E. Smith-
Agreed that the 100,000 concentration factor is not possible with imaging optics. I was reporting what was presented by the researchers in their presentation. The closest I have read for achieving 100,000 concentration factor was with a Winston non-imaging concentrator, with the claim of a 56,000 concentration of terrestrial sunlight (not sure if the spectrum was limited). Of course, the output of this type of concentrator does not couple efficiently into an optical fiber. “””””
I’m VERY familiar with the “Ideal” non-imaging concentrators of Roland Winston; and if you read what I wrote above you will see I already mentioned his achievement of a 56,000 concentration of sunlight, and I also mentioned that was done with a solid CPC , which took advantage of the (N) factor in the optical invariant, by using a high refractive index YAG crystal to make the CPC.
That concentration factor (56,000) is only available INSIDE the crystal; you can’t get it outof there; and in particular you can’t couple it all into ANY Optical fibre, since the 56,000 concentrated “beam” has an angular extent of 2pi steradians; or a cone angle of 90 degrees; so that is far in excess of the propagation NA of ANY known Optical fibre.
But 56,000 concentration is chicken feed compared to the 10^8 concentration required by these researchers; which is why I said it is not available from sunlight by any physical means.
Roland Winston first got involved in Non imaging concentrators and devised the CPC and other novel structures while working at Argonne National Laboratories. His interest was in efficiently gathering and concentrating the light flashes from multi-thousands of tons of cleaning fluid and other liquids deep underground in order to detect neutrinos, and other rare events. The scintillation flashes were to be detected by a large array of (very) large Photomultiplier tubes around the huge tank of liquid. His effective concentrators (along With Ari Rabi) reduced the number of photomultipliers from near infinity to only about a half infinity.
After he moved to U of Chi, he turned his attention to ideal non imaging concentrators for solar energy collectors.
I’m very familiar with the work of Winston et al, as I have one of the very few non-imaging concentrator patents, for one of the few configurations that Winston did not discover. It is used in some form today, in efficient light extraction from LED lamps.
The basic geometry covered by my patent covers a circular arc and two different parabolic arcs, that form one continuous, and slope continuous surface to extract virtually all of the light that exits from a block shaped LED die, and directs that into an output beam, all of which emerges from a larger surface area, but over a more restricted (and slectable) viewing angle. Virtually NO flux emerges outside that designed beam angle.
I have in my desk, a solid (Polycarbonate) array of CPCs each with a 8mm x 8mm exit aperture, and the whole of that surface lights up as bright as the emitting surface of the LED die (which is much smaller). It was initially developed for a high mount stop light for the 1996 Ford Thunderbird. They eventually abandoned using it, since it required too many LEDs to make the 8 square inches of CHMSL light required by the SAE spec, and because of its design it was hundreds of times too bright to put on the tail of an automobile. The whole 8 square inches, requiring about 200 LED die (10 x 10 mils), would have been as bright as the surface of the LED, over the SAE required viewing angle and drop to zero outside of that.
Eventually, a lamp based on the principle of my patent, went into the actual tail light of the 1996 Thunderbird, and I still see them on the roads all the time.
And today’s LED tail lights are mostly dark empty space, with only a few actual lighted areas, visible in any viewing direction. The SAE Eventually realized their spec was impractical; so they revised it and abandoned the requirement for a full uniformly illuminateed 8 square inches.
So there isn’t much about ideal concentrators that I don’t know; either imaging, or non-imaging.
No Discussion of non-imaging optics would be complete without mentioning Winston’s collaborator; the late W.T Welford of the Optics Section, Department of Physics, Imperial College of Science and Technology, at the University of London.
Their book on non-imaging concentrators is the bible of that dicipline.
Come on guys, give them a chance. The header to this interesting piece does state that “a
dramatic and surprising magnetic effect of light discovered by University of Michigan researchers could lead to solar power without traditional semiconductor-based solar cells.”
Now, I don’t know much about physics, being as I am, a retired former railway engineer (no, not that one!). However, I have a son who is well into the last lap of a chemistry PhD and, whilst a lot of what he’s doing is way above my head, I know full well from what he’s told me that there is a huge amount of effort and study that needs to be put into bridging the gap between an interesting discovery and any possibility of putting such a discovery into practice.
Sometimes, interesting discoveries pay off hugely. Sometimes they don’t. I believe it’s called research. That seems like a pretty good thing for a university to be doing.
“Of what use is a new-born baby?”
Wow… I’m a long-time reader of WUWT, but for lack of scientific background I rarely comment. Reader comments are frequently as interesting and educational to me as the articles themselves, but I think a lot of you folks are getting way too critical of a very preliminary finding. My opening line is, of course, attributed to Ben Franklin in response to critics of the first hot air balloon in 1783. I hope you see the analogy here.
I grasp enough of your calculations to see that this optical effect is wildly inefficient and impractical with U of M’s current setup. So….? Let them tease the materials and the setup and come back with a progress report. Then if the data looks bogus, the WUWT brain trust will probably spot it and call foul. But in the meantime, these guys need to get creative with their materials and processes, and yes probably with grant money… but again I say “So…” Most things cost money. If this previously unknown effect is actually measurable, it may be possible to develop it into something much bigger. Were superconductors practical at first? Did Bernoulli tubes look like the answer to heavier than air flight?
So please, folks, let’s not get into a “herd mentality” with our skepticism.
Interesting!
Also of interest is that chlorophyll generates an electrical (ionic) charge from absorption of certain light spectra. Seems like Mother Nature already has it figured out.
I agree with Jerry, when anything is unexpected to the order of magnitude of 100 million times, I find it of interest. Hopefully something of use will come out of this in the years to come.
For a few months now I have been at HP in the thermal inkjet division. A
favorite discussion by the brass here is the power density in the thermal
inkjet heads. In order to get the ink to jet, the power in the ink well switches
from off to 30x the energy density on the surface of the sun.
Very high power densities are in billions of HP inkjet heads all over the earth.
Cheap, high power density is readily available. Cheap, higher power density is
on the way. (No, I cannot provide any more details.)
Now, could much be done with this? Hard to say, but I am thinking about
quantum dots. What is the maximum power density of quantum dots? I
see some possibilities with multiple excitation QD and crystal lenses.
Like others have said, do not discard this new bit of science.
“”””” Frank Perdicaro says:
April 15, 2011 at 4:22 pm
For a few months now I have been at HP in the thermal inkjet division. A
favorite discussion by the brass here is the power density in the thermal
inkjet heads. In order to get the ink to jet, the power in the ink well switches
from off to 30x the energy density on the surface of the sun. “””””
So from now on, I guess I should be saving my empty HP inkjet heads, and start building myself a solar energy concentrator out of them. And speaking of “empty”, the most remarkable thing about HP inkjet heads, is how quickly they become empty. But that is not so surprising, since it seems that the vast majority of them are shipped from the factory already half empty.
I understand perfectly, how the ink jet “jets” can wear, so that the whole head needs occasional replacement; so HP advises against “refilling” their heads,
So since you engineers know how long the heads last; why don’t you design the cartridge capacity, so the ink runs out at about the same time as the jets wear out.
We have some sort of ersatz coffee/espresso/latte machine at work, and it has a bin at the top, that the service lady periodically fills with coffee beans. It also has a tank at the bottom, into which the discarded ground coffee grounds, are ejected.
Now being an old product design engineer, I would think that the rational thing to do, would be to design the waste grounds container, so that it can hold ALL of the ground coffee beans, that the upper bin can hold. That way the service lady, can fill the hopper, with fresh beans, and empty the discarded grounds bin at the same time.
Well no such luck; you play Russian roulette with this machine, if you ask it for a cup of coffee, while you can see coffee beans in the hopper. Every now and then you will get a message to empty the discard bin.
If I was the head of the manufacturer of that machine, I’d fire the ass of every engineer, and every marketting person who was ever involved in the design of that machine or its specifications.
There’s a certain silicon valley computer manufacturer, that builds LCD computer displays, that make much better mirrors, than they do computer screens. There’s no possible place you can put any lighting in your office, and not have it reflect into your eyes of that LCD mirror. And for good measure, they surround the screen, with a rounded profile polished black frame, so that even if a screen reflection doesn’t get in your eye, the frame reflection certainly will.
So you can unplug the power cord from those monitors, and they will fail the contrast specification for that product; unless you have them in a darkened room. I’d clean house of that department, as far as engineers, and marketting decision makers goes, If I was in charge.
Do you have any idea how hard it is to make a display that is immune to reflected light corruption. When I used to work for that particular company (I actually did that), we used to jump through hoops, and pull all sorts of optical tricks to increase display contrast in high ambient light.
Well you only have to walk around in Fry’s store to see which manufacturers don’t understand contrast.
Not directly related to power density; but if you multiply the typical reflectance (maybe 5%) of typical sheet glass, by the roughly 200 foot candles of illumination typically demanded at desk level in Office environments, and then you compare that to the typical LCD display white level, you quickly realize that 50,000 :1 contrast ratios are simply mythology.
So is getting from nowhere near point source illumination from a sun source to a near diffraction limited spot with astronomical energy density.
It’s not a technology problem it’s freshman year Physics; maybe High School level.
Their laser source experiments might be very interesting physics; in fact I’m sure it is. But it is total BS to imagine you can do the same thing with a solar energy source; well at least not from where earth is in space.
And for those, who for lack of understanding, think we should all cheer at this University of Michigan work. It is not the research and the Physics behind it that is being promoted here; that much sounds quite interesting. It is the BS promotion of this concept as a possible substitute for “solar cells”, which last time I checked are used for converting incoming solar energy (at around 1 KW/m^2), into useful electricity.
Current full production solar panels for at least two of the leading manufacturers, can honestly claim to have about 20% air mass one solar conversion efficiency. That is very laudable, and perhaps 30-40% is reachable with newer materials, and known science. And in solar conversion what is being converted is WATTS PER SQUARE METRE, so the ONLY thing that matters about such panels is the conversion efficiency, since available space (SQUARE METRES) is rather limited; and the sun isn’t going to increase the supply rate any time soon.
So talk about cheap production and other such nonsense is simply that; nonsense. Land isn’t cheap and as somebody wiser than me once observed, “they ain’t gonna make any more of it.”
Matthew says:
April 14, 2011 at 7:49 pm
Nifty, but I’ll wait to get excited until I see a prototype that works in regular sunlight on a day that isn’t perfectly clear.
————————————————-
Did you hear about Dye sensitized solar cell? works even in moon light….
I guess its not clear to me, but if you are getting 2W/msqd from the sun, it seems there is no way to get more than this except by collecting in a capacitor device and accumulating it – still you can’t get more energy/time. If the point is that it might convert 10% of 2W/… directly to electfricity cheaply, I believe the apparatus needed will not beat silicon in cost. Stiill, the phenom is interesting and may have other practical applications. Hand it over to engineers – physics researchers tend to do something interesting and then speculate in fantasyland.
What does this new found effect have upon the validity of the AGW theory? Isn’t some of this newly discovered energy heating up the atmosphere? Have they included it in their models?
The Michigan discovery suggests a new salient in particle physics- the hunt for the teleon, the elusive triad of faith, hope, and charity quarks particle researchers at the Swiss supercolluding ultraclimber collider are seeking along with its eleemosynary resonance, the templeton.
Purse string theory suggests that , just as photons with energies in excess of 1 GEV create electron-positron pairs, templetons accelerated to Nielsen energies > 10.5 megabucks (IU ~ 8.7 x107 CHF) will cause the Hicks Boxon, AKA the “Gaga particle” to emerge from the intellectual vacuum along with eschatons, atheons, and telethons starring Fritjof Capra.
These yield high-spin reports of quantized teleology that NPR theory , and to observe their contrast with the microwave background, we seek a matching grant from the Discovery Institute to measure the evanescent cash flow of teleons orbiting amplitude modulated talk radio circuits before decaying into the null set of teleologists worth televising. To detect the resulting telluric currents, Texas A&M physicists will retune its marching band’s tubas into an array of superconducting ear trumpets to detect angelic choral radiation left over from the Big Band event leading metaphysicians date to November 23, 4004 BC.
Phil’s Dad says:
April 14, 2011 at 5:59 pm
“Input 10 million watts per square centimeter. Output?”
According to the researchers they believe they can attain 10% efficiency so the answer would be 1 million watts.
The key is that the input is sunlight and the output is electricity. Sunlight, at least for now, is still free.
The attractive part is a material getting the same efficiency as a PV cell but at a much lower cost.
I wonder about the needed materials though. 10mw/cm^2 at which the effect manifests itself is a lot of energy for a conductor to carry and no conductor is lossless so even a small fraction converted to heat will melt (if not vaporize) most materials. Fer instance say you took a fresnel lens 10 meters on a side in full sun cloudless sky at the equator and put a piece of glass where the focus is 1 square centimeter. That would give you about 10 million watts/cm if the math done in my head is correct. It seems to me that wouldn’t just melt the glass but would vaporize it or just about anything else. Maybe not diamond but I don’t think diamond fibers are going to be cost-effective.
I’d love to know what material the lab setup is using to pipe light of that intensity.
One thing’s for sure though you’d have no problem turning sand into glass with a fresnel lens that big…
This is just a knee-jerk reaction and I could be wrong.
I dropped a decimal point in that fresnel lens size. To get 10 million watts per square centimeter you’d need 100 million square centimeter fresnel at 1/10th watt per square centimeter in full sun, cloudless sky, at a low latitude which works out to a square fresnel lense 100 meters square or about 2 American football fields.
Anyone have one of those laying about? I seem to have misplaced mine. Out of that you get a megawatt of electricity (best case) which sells for about $100/hour in the U.S. right now. In an ideal environment (no clouds at all) it could operate for about 2,000 hours per year. Let’s say it has a service life of 25 years so we get roughly 50,000 hours of operation or $5 million in revenue.
I can’t believe you could even cover the initial construction cost to build the sucker with $5 million. Worse, invested at 5% APR that 5 million will turn into 20 million in 25 years using the rule of 72. So you’d have to build it for about a million bucks and then not pay a penny more in operating expenses for the next 25 years to just break even. And that’s not counting what it costs to deliver the juice from point of production to point of consumption (you need to build a grid or use someone else’s) as the $100 per megawatt is the average delivered-to-your-front door price of electricity.
I didn’t even begin to address the actual physical requirements of concentrating sunlight by a factor of 100 million. Whether a mirror or a lense it has to track the sun which introduces far more cost & complexity. This is so far from practical it’s breathakingly stupid. Far easier to concentrate sunlight by a factor of a 1000 with mirrors or lenses and using that to generate heat for a heat engine/generator which might get 50% efficiency and thus require 5 times less sunlight to collect in the first place. Even in that situation there are a large number of experimental solar electric installations in the world and none of them can come close to competing with coal on a level playing field.
It’s worse than I thought.
Solar electricity By T. Markvart page 237
I can’t copy the text but you can read it. It appears there’s a theoretical limit to the energy density you can get from sunlight. You can’t get higher than the energy density of the surface of the sun which is 62 kilowatts per square centimeter for an approximate blackbody at a temperature of 5700K. Practically speaking they need a material where this effect occurs at more like 100 w/cm which is a 1000x concentration of the solar maximum at the earth’s surface of 0.1w/cm. Currently they say it only occurs at 10 million w/cm.
To be fair they did say they needed a material with lower energy density requirements. They just neglected to say that “lower” is about 100,000 times lower.
Yes, Dave, there you have it. ANY dispersed low-density energy source, however “free”, requires 2 things: lotsa real estate and lotsa capital-hungry equipment. Which then needs to be maintained, upgraded, replaced, etc. Whether its solar or tidal or wind or wave, all these diffuse energy sources are also plagued with uncontrollable variability, and cannot be forced to track demand.
Every one is a money pit, and a dead end. Only in isolated areas with no access to a grid are they economic, and then only on small scales.
Dave Springer says: April 16, 2011 at 10:09 am
“Sunlight, at least for now, is still free. ”
That gave me a pause. In the UK you have to pay for a license to convert an energy signal that is passing through the air (TV License). If they were to tweek the legislation, just a bit, expand the frequency band, then there could be a charge for operating a device that used the Suns energy signal. No new law would be needed but the license title would become more generic.
License to operate a through-the-air radiated energy conversion device.
With the nuclear crisis in Japan still raging, it seems there is renewed interest in Solar energy once again. Granted, solar may not provide all energy needs, but it certainly goes someway to help those who so desire become energy neutral.
Maybe this is garbled by the journalist, but the explanation makes zero sense to me–gobbletygook. We do not extract voltage in anything.
Brian H says:
April 16, 2011 at 5:54 pm
“Yes, Dave, there you have it. ANY dispersed low-density energy source, however “free”, requires 2 things: lotsa real estate and lotsa capital-hungry equipment.”
Sunlight isn’t quite so dispersed as one might think. Every square kilometer receives about 200 megawatts daily on average. A square kilometer of arable land is a hobby farm in Texas and a square kilometer of non-arable land if you’re lucky will support two dozen head of cattle. There’s more solar energy recieved by the Texas panhandle each year than is consumed by the entire western world.
“all these diffuse energy sources are also plagued with uncontrollable variability”
The sun has been reliably shining on the earth for billions of years so I’m not buying that argument either. The variability is purely a matter of clouds and over a course of a year there’s very little variability from year to year. You can bank on annual insolation being relatively invariant.
The first and foremost problem with solar is that electricity isn’t what we need. We need liquid fuels that can be stored cheaply, indefinitely, and without loss. If you have liquid fuel you can make it into electricity on demand. All the solar “alternatives” you mention generate electricity. I agree none of those look promising for a variety of reasons the largest of which is that we need liquid fuel.
There is one solar technology that stands out from the rest. Biosynthetic production of liquid fuel. Every square kilometer can easily produce 10 million gallons of diesel, kerosene, or ethanol each year quite reliably if you can custom design bacteria to turn air, sunlight, and brackish water into hydrocarbon fuels. This can be done cheaply and easily once genetic engineering advances to the point where we can plug in the genes for a custom effluent pump into a bacterium that produces a significant fraction of its total weight in hydrocarbons. You simply give the critter an effluent pump for some chemical that’s a sterilant to wild species, treat the water with it, and you can have open ponds where nothing grows except what you want to grow. Harvesting is as simple as straining them out of the water and crushing them like so many grapes.
The US consumes somewhere south of a billion gallons per day of fuel. A thousand square kilometers of biosynthetic fuel farms can supply the entire nation’s liquid fuel appetite at an equivalent price of about $5/bbl oil. Generating plants just need something that burns to heat their boilers. Liquid hydrocarbon fuel works as well as coal or natural gas for this purpose so add another thousand square kilometers and our cup will overfloweth with cheap electricity.
The day this becomes reality is quickly approaching. There are pilot plants being built right now using custom designed patented cyanobacteria that can produce 2 million gallons of diesel per year per square kilometer at a cost equivalent to $30/bbl oil. These plants are just the first baby steps. Synthetic biology advances are coming along at a pace that reminds me of Moore’s Law for semi-conductors. These pilot plants are like the first transisters with doublings in efficiency every 18 months until theoretical limits are approached. The theoretical limit appears to be only in how much sunlight hits the ground which is on the order of hundreds of megawatts per square kilometer on average night and day 365 days per year.
The Texas panhandle alone (a mere tenth of the state) is 70,000 square kilometers and isn’t used for much of anything right now except wind farms, oil wells, and cattle grazing. No one would even notice 2,000 square kilometers of it covered in shallow pools of brackish oily water soaking up the sun except from a satellite view where it would appear like a few dark freckles.
Andrew30 says:
April 16, 2011 at 11:01 pm
>>Dave Springer says: April 16, 2011 at 10:09 am
>>“Sunlight, at least for now, is still free. ”
“That gave me a pause.”
Well then the following is really going to blow your mind.
I predict that within 20 years you’ll have to pay to take carbon dioxide OUT of the atmosphere. Carbon is the basic construction material used by biosynthetic bacteria to build stuff for us. When we get to the point (rapidly approaching) where bacteria can produce perfectly dried dimensional lumber with zero flaws reproducing any natural woods you care to name for next to zero cost people will be sucking CO2 out of the atmosphere for that purpose faster than we can replace it burning fossil fuels. Much faster. Producing hydrocarbon fuels in the same manner is carbon neutral because the carbon is just a temporary energy storage medium where upon combustion it goes back into the atmosphere. When we have a self-reproducing microscopic robotic slave labor force (which is essentionally what genetically engineered bacteria are) building durable goods for us out of carbon then it is no longer temporary removal. Removal for durable goods is semi-permanent in nature – wood lasts for centuries at least.
A 180 degree turnaround from carbon dioxide the pollutant into carbon dioxide the valuable commodity. That which the greens want to make us pay to emit into the atmosphere they will want us to pay to extract from the atmosphere tomorrow. Mark my words… 20 years or less and this will be the new state of affairs.
Dave;
I wasn’t implying that we’d run out of real estate, merely that you have to “lay on” your collectors over a large area; that implies lots of “stuff” (panels, windmills, whatever) that have to be made, installed, maintained, tapped, replaced, etc. This is non-trivial. In fact, it is a major distinction from concentrated sources, and often is very poorly costed and carried out. Part of the real estate requirement is transmission, not generally properly accounted for. The sites where diffuse energy can be gathered are not typically close to demand, and long corridors need to be dedicated and wired up.
And so it goes.
As for the biofuel options, they have been unmitigated disasters or hoaxes, so far. Whether ponds can be fed with enough “waste” at low enough transport and acquisition cost to contribute is yet to be demonstrated. As has the collection and refinement technology and costing.
Dave;
About charging to pull CO2 out of the air, that should be the situation now. The planet is in a CO2 famine, induced by the flora themselves. We fauna should be doing all we can to keep up our side of the cycle/bargain by maxing out on emissions!
“”””” Dave Springer says:
April 16, 2011 at 2:26 pm
It’s worse than I thought.
Solar electricity By T. Markvart page 237
I can’t copy the text but you can read it. It appears there’s a theoretical limit to the energy density you can get from sunlight.
The sun is a nearly colimated radiation souce with a divergence cone half angle of about 15 minutes of arc or 0.25 degrees.
The theoretical maximum concentration ratio for the output “beam” in air or vacuum is 1/sin^2(0.25deg) = 52,525
That of course is areal concentration. The linear concentration is about 229.
If you produce the final concentrated beam in a medium of refractive index (n) then you can increase the concentration by n^2.
I don’t know how many times I have to post this; obviously I’m just wasting my time here talking into an empty hole.
Concentration of sunlight by a factor of 10^8 is impossible; NO MATTER WHAT as Dr William Schockley would say.
The same problem works in reverse. You cannot take an arbitrarily small source of radiation and “passively” spread it over an arbitrarily large area so that it visible over some finite viewing angle.
A single modern LED die that is say a 10 mil (250 micron) cube is capable of emitting all of the photons required to meet the SAE spec for a CHMSL; Center High Mounted Stop Light; which requires eight square inches of illuminated area that is visible over some vertical and horizontal viewing angles at a certain “brightness” level. It is impossible; using passive optical means; reflection-refraction-diffraction etc to so redistribute all those photons from the LED into the beam required by the SAE spec.
The basic reason is that using passive means, any element of the output “light source” within its restricted viewing angle must be as “bright” as the original surface of the LED die, is over its much greater viewing angle (180 degrees, or 90 degree cone half angle). Of course the output can’t be brighter, but it can’t be less bright either, except for losses due to innefficiency; and the LED die surface is hundreds of times brighter than is the SAE spec requirement.
The significance of the “passive” resrtiction, is that the desired result can be achieved through “active means”, which is in effect time division multiplexing.
You can illuminate a smaller area or a smaller viewing angle but it will be much brighter than the spec, and then you can rapidly scan that source over either the area or the soilid angle, or both, to give the illusion of constant illumination, but it now will have a duty cycle reduced brightness.
The same effect can be met in principle without moving parts by simply running the beam through a scattering medium; which amounts to a time division multiplexing. The photons travel according to a statistical probability, so that on average, only a few of them go to a particular location while travelling in a given direction. The problem with diffuse scattering, is that there is always backscattering, and scattering into undesirable directions; so it is an extremely lossy process requiring even more photons from the LED.
In practice it isn’t possible, which is why NO automobile LED CHMSL is anything like a uniformly illuminated 8 square inches over the restricted solid viewing angle required by the SSAE spec; they are mostly dark empty space, with just an array of lit dots viewable.
I’d like a dollar for every hare brained idea I’ve ever heard, for how to either concentrate or unconcentrate light from light sources to limits that are forbidden by the second law of thermodynamics.
Two axis steerable elements do permit concentration of sunlight by factors of a few hundred to a few thousand, in practical large area systems. 10^8 concentration is neither practical nor possible.
And for those that need an auto to get around. Some DARPA funded research done at MSU. For the geeks among us there is a technical pdf linked:
http://powerandcontrol.blogspot.com/2011/04/catching-wave.html
About 60% mechanical efficiency – fuel to output shaft.
This is great to think outside the box… and it may get somewhere somehow…but,
I think we really need to focus on more OIL and GAS now – may be on properly designed nuke power-
And… maybe we could start using the sun for day lighting our buildings, and to power passive thermal chimneys for cooling, and direct gain passive heating – this stuff works and yet we still neglect it? why? Is it just too low tech to be sexy?
NotJust;
Hum, duh-duh-um. It’s like this: it works only with incredibly powerful laser light. Sunlight would have to be concentrated to a degree perhaps forbidden by the laws of optics. So we’re going to really go outside the box, here! We’ll use the sun on ordinary panels to charge up batteries, which will then be discharged at high rate through lasers, which will strike the new optic-magneto fibres, which will generate power!
Oh, wait …
The Optics of Non-Imaging Concentrators is a very interesting subject; and NI systems beat imaging Optics hands down.
The archetype of NI Concentrators is Roland Winston’s CPC, or Compound Parabolic Concentrator. In its two dimensional form, it is IDEAL in the sense of being able to practically reach the theoretical maximum concentration ratioo set by the second law of thermo-dynamics. And of course it can be used backwards, to unpack a compact source to create a larger wide area beam over a restricted viewing angle. By two dimensional, we mean a linear or trough like structure, that concentrates (or un-concentrates) in one axis only.
A practical application would be to take the light emitting from a cylindrical fluorescent tube, which radiates over 360 degrees in the plane perpendicular to the axis of the tube; and compacting ALL of that light (less reflectance losses) into an output beam, that has more illuminated area than the fluorescent tube surface, and is only visible over a limited viewing angle; say +/- 45 degrees downward from the axis of the tube. A tube say 1 3/4 inch diameter has a circumference of about 14 cm, and every point on that surface emits light over a cone half angle of 90 degrees. When you look at such a tube, you see a source that is 1 3/4 inch wide (about 4.5 cm), and it is visible over a full 360 degree, if you mount the tube vertically, or 180 degrees, if it is in the ceiling. So you can put a mirror behind it, and capture some of the backward emission. Put it in a properly designed CPC derivative reflector, and you can get a source that is visible over +/- 45 degrees, and is 14/sin (45) = 20 cm (roughly) Wide.
The key point is that the entire 20 cm times the length of the tube, within that 45 degree viewing angle range, is AS BRIGHT (less reflectance losses) as the original tube surface itself; so you went from 4.5 cm width at 360 degrees to 20 cm over a total of 90 degrees. And if you space those properly reflected tubes at the right spacing and ceiling height, then of course you can illuminate the entire office space to the required illumination level. The brain dad egg crate baffles that are put in most office ceilings, simply waste a lot of the light. With the CPC, the tube is invisible outside of that 45 degree angle off the center line.
The required reflector, is slightly more complicated than a CPC. The outer parts are a normal CPC down to about the tube axis, and then the reflector curves around the back side of the tube, spiralling in towards the tube until it touches the back of the tube down the center line, and forms a cusp normal to the tube surface. The required curly portion, is in fact the involute of the cylindrical surface. It is a perfect application of Non-Imaging Optics; and so easy to implement; yet it is not used in indoor office lighting.
When you try to take a CPC profile, and rotate it to make a three dimensional concentrator that now concentrates in two axes, so you have a sort of funnel contraption, with a circular source (or square/rectangular) in the middle; you now discover that it is no longer an IDEAL concentrator. Only the MERIDIONAL RAYS are ideally concentrated; and most of the emission consists of skew rays; which are NOT ideally concentrated. But they are quite efficiently concentrated, and it is still one of the better designs for such a source.
Notice that the two dimensional trough concentrator, that I just described, is the exact shape, that you need to collect solar energy as a “heat” source, and concentrate it on a cylindrical pipe containing a working fluid; such as water or maybe oil or what have you. In that case, you theoretically can get a concentration of 1/ sin (0.25) = 229.
So a tubular CPC collector heating a pipe can theoretically reach 229 suns; but remember that it now has to be steerable in the axis perpendicular to the tube axis, to keep the concentrated beam on the tube. In principle, it is possible to make this steering almost totally passive by using bimetallic strips that attach to the tube, and detect its heating; and rotate the reflector, to either prevent a meltdown, in the case of a loss of fluid, or regulate the Temperature.
Winston, and his associates DID develop a true IDEAL concentrator that does work in three dimensions; unlike the CPC. It is a rotationally symmetrical Hyperboloid, that looks more like a trumpet end. I suppose mathematically it would be described as a Circular Hyperboloid of One Sheet.
That can theoretically reach 229^2 concentration which is 52,525. in air, or over 210,000 in a solid form such as a YAG crystal, with a refractive index of more than 2.0. Unfortunately that concentration is only obtainable inside the high index medium; so to get access to the 200,000 suns, you would have to have your hot tube Optically immersed in the crystal. I believe the 56,000 number which Winston achieved was done with the near ideal CPC form, rather than the newer shape, which is why he couldn’t get to 200,000, since it is only ideal for the meridional rays (rays lying completely within a plane containing the optical axis of the CPC).
In a losss of fluid accident, you would have an instantaneous meltdown, at 50,000 suns or even at 200,000 suns. Forget 10^8 suns; ain’t gonna happen !
George E. Smith,
I like the Zome Works Passive solar trackers:
http://zomeworks.com/products/pv-trackers/introduction
“”””” M. Simon says:
April 19, 2011 at 1:17 pm
George E. Smith,
I like the Zome Works Passive solar trackers: “””””
Well I notice they conveniently omit the only performance spec that one would want to know; and that is the pointing accuracy. A cylindrical 229 suns concentrator, would have to be steered to better an 1/4 of a degree angle. If you made a three dimensional one to get 52,525 suns, you would have to be better than 1/4 degree in two axes simultaneously.
The problem with too high a concentration ratio, is that you have to run it at very high Temperature to benefit from the concentration.
So more practical, if you can do with boiling water Temperatures, is to reduce the concnetration ratio, by increasing the acceptance angle above 0.25 degrees, until you get to the operating Temperature range you want. Then of coursae that wider acceptance angle translates into a sloppier steering requirement.
In a practical integrated solar system; I would want a hot water system with lower concentration, and a smaller three-D system to get cooking Temperatures.
“The researchers found a way to make an “optical battery,” said Stephen Rand, a professor in the departments of Electrical Engineering and Computer Science, Physics and Applied Physics.
In the process, they overturned a century-old tenet of physics.
“You could stare at the equations of motion all day and you will not see this possibility. We’ve all been taught that this doesn’t happen,” said Rand, an author of a paper on the work published in the Journal of Applied Physics. “It’s a very odd interaction. That’s why it’s been overlooked for more than 100 years.”
And yet we are told repeatedly that the 100-year-old approximations and assumptions (er, princples) of Arrhenius (et al) ARE a valid and thoroughly sufficient “proof” of the entire theorectical basis for today’s global warming hysteria.
Yet there still remains absolutely NO proof of anything but Mann-caused global warming in the tree records, much less CAGW.