Flexible nanoantenna arrays capture abundant solar energy
August 11th, 2008Researchers have devised an inexpensive way to produce plastic sheets containing billions of nanoantennas that collect heat energy generated by the sun and other sources. The technology, developed at the U.S. Department of Energy's Idaho National Laboratory, is the first step toward a solar energy collector that could be mass-produced on flexible materials.
While methods to convert the energy into usable electricity still need to be developed, the sheets could one day be manufactured as lightweight "skins" that power everything from hybrid cars to iPods with higher efficiency than traditional solar cells, say the researchers, who report their findings Aug. 13 at the American Society of Mechanical Engineers 2008 2nd International Conference on Energy Sustainability in Jacksonville, Fla. The nanoantennas also have the potential to act as cooling devices that draw waste heat from buildings or electronics without using electricity.
The nanoantennas target mid-infrared rays, which the Earth continuously radiates as heat after absorbing energy from the sun during the day. In contrast, traditional solar cells can only use visible light, rendering them idle after dark. Infrared radiation is an especially rich energy source because it also is generated by industrial processes such as coal-fired plants.
"Every process in our industrial world creates waste heat," says INL physicist Steven Novack. "It's energy that we just throw away." Novack led the research team, which included INL engineer Dale Kotter, W. Dennis Slafer of MicroContinuum, Inc. (Cambridge, Mass.) and Patrick Pinhero, now at the University of Missouri.
The nanoantennas are tiny gold squares or spirals set in a specially treated form of polyethylene, a material used in plastic bags. While others have successfully invented antennas that collect energy from lower-frequency regions of the electromagnetic spectrum, such as microwaves, infrared rays have proven more elusive. Part of the reason is that materials' properties change drastically at high-frequency wavelengths, Kotter says.
The researchers studied the behavior of various materials -- including gold, manganese and copper -- under infrared rays and used the resulting data to build computer models of nanoantennas. They found that with the right materials, shape and size, the simulated nanoantennas could harvest up to 92 percent of the energy at infrared wavelengths.
The team then created real-life prototypes to test their computer models. First, they used conventional production methods to etch a silicon wafer with the nanoantenna pattern. The silicon-based nanoantennas matched the computer simulations, absorbing more than 80 percent of the energy over the intended wavelength range. Next, they used a stamp-and-repeat process to emboss the nanoantennas on thin sheets of plastic. While the plastic prototype is still being tested, initial experiments suggest that it also captures energy at the expected infrared wavelengths.
The nanoantennas' ability to absorb infrared radiation makes them promising cooling devices. Since objects give off heat as infrared rays, the nanoantennas could collect those rays and re-emit the energy at harmless wavelengths. Such a system could cool down buildings and computers without the external power source required by air-conditioners and fans.
But more technological advances are needed before the nanoantennas can funnel their energy into usable electricity. The infrared rays create alternating currents in the nanoantennas that oscillate trillions of times per second, requiring a component called a rectifier to convert the alternating current to direct current. Today's rectifiers can't handle such high frequencies. "We need to design nanorectifiers that go with our nanoantennas," says Kotter, noting that a nanoscale rectifier would need to be about 1,000 times smaller than current commercial devices and will require new manufacturing methods. Another possibility is to develop electrical circuitry that might slow down the current to usable frequencies.
If these technical hurdles can be overcome, nanoantennas have the potential to be a cheaper, more efficient alternative to solar cells. Traditional solar cells rely on a chemical reaction that only works for up to 20 percent of the visible light they collect. Scientists have developed more complex solar cells with higher efficiency, but these models are too expensive for widespread use.
Nanoantennas, on the other hand, can be tweaked to pick up specific wavelengths depending on their shape and size. This flexibility would make it possible to create double-sided nanoantenna sheets that harvest energy from different parts of the sun's spectrum, Novack says. The team's stamp-and-repeat process could also be extended to large-scale roll-to-roll manufacturing techniques that could print the arrays at a rate of several yards per minute. The sheets could potentially cover building roofs or form the "skin" of consumer gadgets like cell phones and iPods, providing a continuous and inexpensive source of renewable energy.
Source: Idaho National Laboratory
Aug 30, 2005 |
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well if the thermoelectric generators that GM is working on pans out, that would be the solution right there. it should increase the overall efficiency of solar
So you will be able to bolt your notebook to your esky and have cold drinks non-stop while playing your favourite computer game.
Portable coolers with batteries attached that get charged up while cooling down your picnic lunch then when your picnic is over you pull out the batteries and plug them into your geo-compass to find your way home.
Maybe microbes living there have constructed photosynthesis for these frequencies?
http://www.biolog...131.html
I've been expecting carbon nanotubes and manipulation of graphene to resolve the problems "any year now" for a while.
http://www.nrel.g...3263.pdf
Perhaps if infrared black body radiation was low entropy coherent radiation like radio or microwave transmissions the system might work. Otherwise, one cannot defy the 2nd law of thermodynamics.
We are talking about electrons - they 'live' on scaffoldings made of molecules, but their energy doesn't correspond straightforwardly.
Such diode - Maxwell's demon for electrons is one of many examples showing that classical thermodynamics is only an approximation - something like mean field which forgets about internal structure.
Other is for example spontaneous crystallization in which entropy goes in 'forbidden' direction...
Everything above near absolute zero emits some IR. If such a device could work one could use it to absorb energy from one body and use the electrical energy to heat another body even if both bodies started at the same temperature and were both in an insulated box. This can not happen in our universe.
I hate to see money wasted on a project that has no chance to work.
http://www.physor...616.html
Thermodynamics for example assume that every state of the same energy has the same probability, the problem is that some of them are difficult to access - small local minimals.
It forgets about creating macroscopic structures ...
If You will have some concrete arguments, please join discussion
http://www.thesci...890t.php
The Idaho National Lab news release implies that their antenna device will "gather" ambient (high entropy) IR and spontaneously convert it into low entropy electrical energy. Its the same as if you put two chunks of metal that were at the same temperature in contact with each other in an insulated box. You would not expect one to get hot and the other cool. If they did it would not violate the 1st law but would the 2nd. How much more concrete can one get?
For example it require that we have only short interactions (at most r^-{dimension of space}), but we have much further interactions thanks of electron movement...
Resonator doesn't need heat flows to create sound wave and than electricity. It uses straightforward kinetic energy of gas molecules - heat.
If the antenna system worked why not tune it to the background radiation left over from the big bang that permeates all space? Free energy must come at a cost of increased entropy. We have to live with the fact that the universe is running down.
To make it have stochastic behaviour (spectrum is real and falling to 0), we have to introduce some parameters which corresponds to averaged values.
Considered models like quantum Ising are muuuch simpler than the reality - we shouldn't reason from them that there exists completely universal always increasing entropy...
About sound way - I have to admit that I read it in a different place. In the article I've linked there is written that it uses temperature differences - it's not an argument.
But about these nanoantenas - they would use that behaviour of molecules and electrons are completely different. Temperature says only the average energy of molecules.
There are some bacterias that can feed with thermal infrared, but it comes from place with higher temperatures.
http://www.physor...677.html
Our question is if this temperature difference can drop to 0.
ps. I can think of 'laws' that are not contradictable, but still doesn't have to correspond to realty... like some from parapsychology :)
Place hot gas between the separators. It's isolated thermally, but it produce thermal photons. The only way photon can escape is through the second end of the tube, so it would work as jet engine - because photons have momentum in one side, the tube has to get momentum into the second. And we have stream of photons we can use to create work somewhere else.
Above example uses that despite that kinetic energy of molecules behave randomly, each one has specific movement/oscillation, which energy can be changed into ordered one - electromagnetic oscillation of photon.
You will say that the problem is with perfect mirrors, but they are just a perfect isolator for thermodynamics of photons.
In above example we've ordered this chaotic energy into ordered: momentum of the tube and stream of photons.
One of basic assumption for thermodynamics is that particles interact to finally equilibrate their energies ... photons don't ... and interaction between molecules and their electrons are much more complicated.
I've simplified about the mirrors - to conserve momentum they have to absorb some momentum/energy, but it doesn't change anything.
2nd law is excellent approximation for stochastic behavior, but we have to remember that it is still a simplification.
There are some natural processes which favor ordering.
http://arxiv.org/...1048.pdf
Your photon flashlight would only work as long as there is a greater density of photons inside the tube (lower entropy) than outside (higher entropy). As a result of using your flashlight you are increasing the entropy of the universe. Photons are spreading out into space and therefore are less ordered. That is why the sky is dark at night. If you point your flashlight to the sky the molecules will cool down when its battery goes dead.
Somehow, you are hung up on the idea that thermodynamics applies only to things with mass. Thermodynamics applies to changes in any form of energy.
Maybe at the quantum level you can have time reversal and local ordering but in the world we experience time goes in one direction and overall entropy increases. There is no free lunch and gathering ambient IR to make electrical power would require more power than it would produce.
The 'only' problem is that it's placed randomly. 2nd law says that summarized randomness - entropy can only grow.
I agree that generally it's true, but there are some special cases where order is favored.
One of them You've almost mentioned is the big bang, which created world with relatively small entropy, so it can mainly grow.
We rather believe that CPT is conserved, so reversing time arrow should also make that entropy still grows ... but if You play a movie in reverse direction, thanks of unbelievable coincidences - entropy shrinks...
The low entropy of big bang have chosen the time arrow!
Photons from the flashlight don't have to spread - they don't interact with each other!
We could for example place them between two mirrors - they would bounce between, each time giving part of own momentum ... and just vanish asymptotically transferring all it's energy into momentum of the mirrors - into ordered work.
Photon is always faster than the mirror, so because of momentum conservation each time it transfer some of its momentum - part of its energy is changed into kinetic energy of the mirror.
Ok - simpler example: everything is in vacuum, without gravity.
Take this tube with interior covered with mirror. Fix two transparent separators inside and place hot gas between them.
Now place two mirrors which can freely move inside the tube.
Some of photons will be bounced by a mirror - giving part of own momentum.
The heat of the gas will be slowly converted into momentum of the mirror, which can be converted into work.
This example doesn't even need perfect mirrors.
So if we place something which need high energy electron nearer one side of antenna, it's more likely that electron jump through this threshold.
So the whole electricity generator should look like:
-conductor-threshold-antenna-conductor-threshold-
and electrons will more likely go left.
If the antennas are printed, above threshold could be just narrowing.
2nd law says only that we cannot order energy stored in chaotic movement, but there are natural processes that favor order.
Ok - if we (like prof. Novack and I) are wright, there would be other counterintuitive consequences like that computations may cost no energy...
I was thinking about crystallization...
During this process we get higher ordering (lower entropy), but the cost is energy difference between free and bind molecule - this energy is usually just dispersed around, increasing general temperature.
But what if we wouldn't allow this energy to run away randomly ... for example storing it in chemical energy of some molecule, like ATP ...
That lead me to mechanisms that could allow organisms to feed directly with heat (not using thermal infrared):
Let say that we have two molecules(A,B) which has larger total energy separated(E1) than when they are bind (E2
Let say that we have two molecules(A,B) which has larger total energy separated(E1) than when they are bind (E2, smaller than E1).
Additionally there is energy barrier between these states.
Now when they are bind in solution, their thermal energy statistically sometimes exceed the barrier, and they split (reducing temperature!).
But to bind them back, they not only have to reach the barrier, but they have also to find each other in the solution - it's not very likely, so statistically concentration of AB is relatively small comparing to concentration of separated molecules.
Now we will need a catalyst which reduce the barrier, but then use the energy difference for example to bind ADP and phosphate.
For example it catches all required molecules and uses energy stored in own structure to take A and B closer, to make them reach the top of the barrier, then use energy they produce to bind ADP P and restore own energy.
I know - this enzyme would work in both directions, but concentration of AB should be small, such that the wanted direction should dominate.
Consider a solution of purified microtubules. Under the correct ionic strength and pH one can show that at 0 degree C the tubulin protein is more or less monomeric. If you raise the temperature to 20 degrees C the tubulin spontaneously polymerizes into microtubules and the solution appears cloudy. This is reversible with temperature. So, the process happens therefore delta G must be negative, one is adding heat therefore delta H is positive, but one seems to be creating order so how can delta S be negative (How can two positives add to a negative)? In this case it turns out that the monomeric form of the protein is highly hydrated and the associated water is in an ice-like state so the reaction is being driven by the entropy from the "melting" of this water.
It was this sort of discovery that led to the the concept of hydrophobic bonds which play such an important role in molecular biology.
All other examples of crystallization have also been shown to obey the 2nd law if one looks at the whole system. One must pay for order by creating more disorder.
Think about crystallization - joining new molecule increase ordering, but puts into environment difference of energies of these both states.
Why do You think that it's impossible instead of wasting this energy, put it in chemical energy of some molecule?
It would require extremely sophisticated mechanism, but microscopic physics shouldn't forbid it... ?
There is no way around the 2nd law period. End of discussion.
You still haven't told why You think it's impossible?
2nd law is mathematical property of statistic - if it's universally true, it should be proved.
I've looked at a few of them - approximations, simplifications... as a mathematician I call something like that not a proof, but argument.
Do You know any real proof?
I was thinking a lot about entropy in
information theory. That for example has lead me to new entropy coder
http://www.c10n.i...ives/720
When I'm thinking about static pictures, I feel intuitively that entropy should generally increase.
But when I think about evolution of a state ... something spoils the picture ... the physics is just too complicated for such universal
laws ... it's not just randomness, but sometimes order is favored!
Next example - look at anti-reflective coating. It uses destructive interference - kind of effect which can be easily lost while approximations...
This effect happens only from anti-reflective side. From the other reflectiveness would be much larger.
Wouldn't it work as Maxwell's demon - spontaneously create gradient of density in photon containment? Reduce entropy and allow us to create work from heat...
Let us say that it is highly improbable instead of impossible. Consider two equal sized cubes of metal both at 20 degrees C. If we put the two cubes in contact what is the chance that heat will flow from one to the other so that one reaches 40 degrees C. and the other goes to 0 degrees C? Theoretically there is a chance that this could happen but would you put money on it?
But what if there are some very ineffective processes which can make some order - reduce entropy.
In most of experiments these effects would be just shadowed by general entropy growth, explained as imprecision...
How can You exclude this scenario?
Maybe such rare processes could be used in conscious way - by us or highly determined organism...
2nd law is not a dogma but mathematical property of assumed physics.
If it would be really perfect - there should be found real proof a long time ago...
The problem with nanoantennas is with the rectifier, isn't it?
You would probably say that the rectifier for such high frequencies, would have to be in low temperature, so there would be heat flow?
Now place everything in lower temperature - dominant thermal infrared frequency will be smaller - easier to rectify ... so at some point we will be able to rectify without temperature difference?
Even if you had such a rectifier the antennas would not work with incoherent black body radiation.
Also, if you had such a rectifier you would not need antennas. Thermal energy would push the electrons through such magic rectifiers. Just put a bunch in series to get whatever voltage you want and convert thermal energy directly into electrical energy. I am sure there are mechanistic reasons why such rectifiers are not possible but that is a little too far from my field to present a proof.
Antenna makes that electrons are excited in specific place - the further from antenna, the lower energy electron has (equilibrated with environment), the smaller probability it will go through energy barrier.
So if we have two equal barriers and one is nearer to the antenna - it's more probable the electron will go through it.
Do You have any more arguments than it always grows because it usually grows?
The entropy reducing mechanisms would have to be sophisticated and probably has to have very small efficiency - because of general entropy increase, it would be extremely difficult to observe them by accident - the argument that they were not observed yet is far from being a proof.
Such processes should be usually just shadowed by general entropy growth - experiments made by people full of faith in this law doesn't prove it.
This law is not fundamental rule of our physics, but mathematical resultant of it.
And it looks so simple that should be already proved if it would be possible...
Look at anti-reflective coating - thick layer of higher refractive index material and thin of lower.
http://en.wikiped..._coating
The destructive interference in thin layer happen practically only from antireflective side (thin layer) - it should reflect a bit less amount of photons than the second side - be Maxwells demon for photons?
But ask Yourself, where this faith is from?
There is no real mathematical proof, only some simple experiments, arguments ... I agree that they say that it's great approximation, but not that it's perfect.
Remember that some time ago every experiment confirmed Newton's physics ...
If anti-reflective coating works, maybe similar effect could be used for electrons, to convert directly heat into electricity...?
http://www.advanc...p?t=9670
About anti-reflective coating
http://en.wikiped..._coating
take thick layer of higher refractive index material and thin of lower. When going to material with higher index, there is partial internal reflection.
Choose thickness of the thin layer so that dominant wavelength of thermal infrared would interfere destructively with own reflection.
From the second side we doesn't have such effect - photon is more likely to be reflected.
Now for example use it to divide gas containment - it should spontaneously create temperature gradient - the temperature at anti-reflective side should be a bit lower.
Perpetual motion You mention, orders energy stored in chaotic thermal fluctuations - is forbidden if and only if 2nd law is true ... so I'll better not comment Your first argument.
About anti-reflective coating - look at wiki article, Fresnel's equations and answer Yourself if it's anti-reflective from the second side...
Look at animation on the top of
http://en.wikiped...quations
if time would be reversed, to reverse the process two photons with precise energy would have to meet - it's highly unlikely - the situation is opposite to usually met.
From the second side large amount of photons will be reflected while meeting the thick layer...
But generally 2nd law is mathematical property of statistics of assumed model of physics. Let's assume that there is a valid proof. Used by us models of physics conserves CPT symmetry, so this proof should still work with reversed time - contradiction.
So it's only a matter of time until we will find some tricks to bend this rule...