Solar Cells That Emit Light Break Efficiency Record 139
benfrog writes "Researchers at the University of California-Berkeley say they have come up with a counter-intuitive way of making solar cells more efficient — making them emit light. In a press release the scientists claim to be the first to demonstrate that the better solar cells are at emitting photons (the more LED-like they are), the more efficient they are at generating electricity. However, 'unlike an LED, the electrons in a solar cell are absorbing photons from an exterior source as well as emitting their own.'"
Idea (Score:5, Funny)
This would be great for space colonies and sea-floor dwellings.
Re:Idea (Score:5, Funny)
In this seafloor habitat dwelling we obey the laws of thermal dynamics!
Re:Idea (Score:4, Funny)
And that's why we can't have nice things.
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In this seafloor habitat dwelling we obey the laws of thermal dynamics!
As opposed to the laws of *athermal* dynamics?
Note to the woosh-impaired: "thermodynamics"
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Yea, I noticed after I posted. Nothing I could do about it then :P
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Re:Idea (Score:4, Insightful)
Why don't they just funnel the emitted light back to the solar panels and thus make them independent of an external light source?
This would be great for space colonies and sea-floor dwellings.
Thermodynamics and all that. But you could probably sit a couple of these facing each other and recapture some of that light. Also, I'd expect space colonies to have relatively easy access to an external light source.
Re:Idea (Score:5, Informative)
Because the light will be of lower energy (and therefore of a different wavelength) than that which the solar cells absorbed.
Basically, instead of heating up, these cells emit the energy in a controlled manner, in semi-directed infrared (probably) radiation. No laws of thermodynamics are being bent: The waste product is just closer to the type of the input than in other solar cells.
You could similarly say that a water turbine is more efficient if it lets water flow out: It is. The water will just have less flow strength than it did when it went in. The difference is what the turbine is collecting as energy. In this case, instead of letting the light 'back up' in the solar cells (as heat), it's released.
Re:Idea (Score:5, Insightful)
This is so cool. Every day brings us closer to glowy alien crystal energy technology.
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But it uses gravity! /sarcasm
(just in case)
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LIght emission is negative absorption [Re:Idea] (Score:3)
Light emission is the converse of light absorption, so any solar cell that absorbs light must, by the same mechanism, emit light, unless other loss mechanisms prevent it. Obviously light emission is a loss mechanism-- light emitted is clearly not turned into electricity. However, all other loss mechanisms can be eliminated by sufficiently clever design, but light emission is a loss required by the laws of thermodynamics. Thus, a solar cell is optimized when there is no other loss mechanism other than lig
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Actually, I suspect that's why it works so well. The emitted light is being reabsorbed by the panel, increasing overall efficiency. Kinda calls to mind how a reflux still works.
Stands to reason (Score:2)
Just like a good reflector of thermal energy also makes an excellent insulator, a good design for converting voltage to photons can be referenced to do the opposite.
Re:Stands to reason (Score:4, Informative)
Just like how a speaker can be used as a microphone. It make noise when you run signal-carrying voltage through it, but also makes electricity when you scream into it.
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Yep, you can use larger speakers to make really good low frequency mics. Hell, in a pinch you could use your ear buds as a mic for your PC, if that sort of thing ever came up.
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I'd think that some sort of thermal conversion would be more in order. After all, Congress generates a LOT of hot air ...
Regards,
dj
What's counter-intuitive about it? (Score:5, Informative)
Re:What's counter-intuitive about it? (Score:5, Insightful)
Um, if someone needs the relevant college-level courses to understand this, then by definition it is NOT intuitive.
What do you think "intuitive" means exactly?
Re:What's counter-intuitive about it? (Score:5, Funny)
What do you think "intuitive" means exactly?
Intuitive (adj.) - Anything I already know.
Re:What's counter-intuitive about it? (Score:5, Insightful)
plus, isn't sophomore college physics, like, a facebook app or something by now?
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as a slashdotter, the rest of us slashdotters presume that you're a more-than-competent physicist, chemist, biologist, astronomer, economist, engineer, gamer, proofreader, and Dr. Who/BSG/Star Trek/Star Wars/Matrix/LOTR archivist. if you're not, someone who is will pull your card.
What, no B5 or Firefly? Please turn in your geek card. ;-)
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The intuition of a person that has taken (and paid attention to) college-level courses is *of course* more efficient at comprehending things that are the topics of the courses.
Perhaps you were thinking of common sense?
The vast majority of people have *crappy* intuitions.
Re:What's counter-intuitive about it? (Score:5, Insightful)
The vast majority of people also have crappy common sense. Saying something is intuitive without stating what background is required for it to be intuitive is just a dick move trying to make everyone else look stupid for not knowing everything you know. I learned a long time ago that things I think are obvious are frequently not to other people.
Of course, some of those things include not posing for photos on railroad tracks and making your kids ride with their seat belts buckled. The "bowling ball and a feather falling in a vacuum" question decidedly takes the back seat compared to the lack of intuition some people exhibit.
Re:What's counter-intuitive about it? (Score:4, Informative)
Nice circular definition? "Something is intuitive if it's intuitive to me"?
Intuition is direct, a priori, instinctive comprehension of a concept, NOT relying on experience, and "without inference or the use of reason".
It is counter-intuitive that a solar cell "throwing away" light will result in higher energy output.
If you have facts/knowledge/education on your side that counter this "layman's expectation", you're no longer relying on intuition.
Claiming you develop a better "personal intuition" as a result of education/experience/whatever is simply an incorrect use of the word.
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in.tu.i.tion/,int(y)oo'iSHun/
Noun:
(1) The ability to understand something immediately, without the need for conscious reasoning.
(2) A thing that one knows or considers likely from instinctive feeling rather than conscious reasoning.
Synonyms: insight - instinct
Note there is nothing in the definition about laypersons, or a priori comprehension. Intuition is defined by the absence of conscious reasoning, not by the absence of all reasoning. A large portion of our processing is unconscious, below the surface cognition we normally consider "thinking". The brain is massively parallel and is constantly processing a vast amount of data. Some of this we are aware of, the conscious portion. Other portions only come to the surface in the form of dreams. But most of it we n
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http://en.wikipedia.org/wiki/Intuition_(philosophy) [wikipedia.org]
Very first sentence of article:
"Intuition is a priori knowledge or experiential belief characterized by its immediacy."
OK, so let's agree that both a priori and experience play a part. But the whole point is the meaning of the term "counter-intuitive" for the title of this article! That is why I said "layman's expectation".
In short, if you insist on defining "intuition" by experience, the term "counter-intuitive" is meaningless.
It's like protesting that 6
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I did read the article, and I did acknowledge that there are two schools of thought: "both a priori and experience play a part"... that would be the two schools of thought the article describes? In other words, I conceded your point that subconscious reasoning (ie, informed by experience) can play a part.
So seriously, piss off with your "you're not even reading or responding to
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Good grief.
Summary of discussion:
1) This is an incorrect usage of 'counter-intuitive' ... ...), but I concede your point about experience & subconscious reasoning. However, "counter-intuitive" STILL is perfectly fine here. Here's why: ...
2) No it's not, because this is what "intuitive" means:
3) No, "intuitive" can include experience.
4) OK, I still think "a priori" is a valid school of thought (here's why:
5) YOU'RE CHANGING THE GOAL POSTS!1!
The "goal post" is, and always has been, defending "counter-intu
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Well, it should be obvious to even the most dim-witted individual who holds an advanced degree in hyperbolic topology, ng-bwui, that Homer Simpson has stumbled into....the third dimension.
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You don't need college courses.
Newton's third law of motion, which anyone should have learned in MIDDLE SCHOOL, is enough to understand this. For any action, there is an equal, and opposite reaction. Light absorbed, light emitted. Dead fucking simple.
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You need to stop moderating if you can't read and think critically. There is nothing wrong with what I've stated. This is entirely a classical issue we're discussing, sonny.
It's Older and More General Than That (Score:2, Interesting)
Thermodynamics teaches us that the most efficient cyclical process is one that can be run in reverse the same way it is run forward. The more irreversible the process, the more it strays from equilibrium, the more it runs uncontrolled (all synonyms) the farther it is from being maximally efficient.
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This is so wrong, it isn't even funny. For instance, Red Dye #40 is a great absorber of light, but has a quantum yield of emission of near zero (unless you think your red Kool Aid is fluorescent). Also, plants do a great job of absorbing light, but they aren't very good emitters, either.
This is the sort of thing that happens when someone sees one equation written in a textbook and then assumes that it actually describes the real world.
Well, kind of (Score:5, Informative)
Ideally, you would want all of your electron-hole pairs to never recombine (which would keep them from emitting photons). Since that's obviously not possible, this would be the best possible outcome of internal recombination.
The bigger problem (Score:5, Interesting)
Sure, it would be nice to have much more efficient solar cells, but there's another issue keeping costs up.
It's the home infrastructure.
Right now, it costs more to install the solar cells on a roof than it does to make them, and once you add in the cabling and battery/storage system for balancing the load or for nighttime use, the actual power generating part of the system is much less than half of the whole system cost. Increasing efficiency is great, and will let you cut the overall size of the system for a similar capacity, but the big issue is making a solar system that's easy to install, with cheap storage, for a lot less.
Cheap batteries and inexpensive support systems are the things we need now...
Re:The bigger problem (Score:5, Insightful)
Make the solar cells part of modular homes where the roof and panel are built as one in a mass-production factory.
Re:The bigger problem (Score:4, Informative)
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No you don't.
I've got plenty of 12V native devices. Stereos, monitors, rack servers, guitar amps, and much, much more.
I would only need a battery bank and perhaps some power-smoothing circuitry.
And FYI, these devices have existed for almost longer than my three decades of life.
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Even with the "Damn you Tesla!" hint that it was a lighthearted joke you managed a major league WHOOOOSH
I don't know of any electronic device that isn't DC based. Most, however, are designed to accommodate the AC delivery system we've used for the last century.
BTW...Is your house wired for DC or would you need to run all new outlets for the 12V native devices? If, I suspect, it's the latter which is easier, converting DC to AC and running through the existing wiring in the house or running a sep
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Wires are wires are wires if you're pushing enough power through them. 12V @ roughly 200A is not going to lose too much over a few dozen feet. You just drop the circuit breaker onto a DC storage supply, and hook charging panels + charge controller to the power supply.
I did it with warehouses in Memphis (822 Rozelle) houses are much simpler of a matter.
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It has a resistance of 13 mOhm/m. A few dozen feet is about 10 meters, so the resistance is 13*10*2 (two wires) = 260mOhm. At a current of 200 A the voltage drop = 52V. This means you couldn't push those 200 A into the cable with a 12V supply if you'd short circu
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My above-mentioned warehouse in Memphis used AWG12, which you'll commonly find in many homes here in the USA. It was also built in the 1930s.
Handles 12V just fine up to 400A.
Also, you can use PWM to bypass some of the resistive and capacitive losses, giving the power signal an AC-like effect, which is what we do in our LED lighting for horticulture, down long (4-10 meters) of NFT channel.
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Same calc, with 5.211 mOhm/m gives me a bit over 0.1 Ohms and thus about 20V of drop @ 200A. It's closer, but it's still impossible to push 200A through 2x10 meters of AWG12 cable with 12V of supply.
You could get 12V at the end by pushing 32V in at the beginning, but the cables will get hot. With 4KW of dissipation you'd be burning the house down. Standard insulation will melt.
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My co-responder Neil here laid out the technical reasons why it's a Bad Idea (tm). To summarize his explanation: the wire will get hot. Very hot. It will melt its insulation and catch your framework on fire before the copper melts itself.
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Most electric motors are AC based.
Yes...they are. So are incandescent bulbs as well as a host of other home staples. Which is why you would need dual wiring for Khyber's utopia. Unless you are going to go out and swap out the breaker anytime your family decides they want to plug in a lamp where the laptop currently is. Or just replace all your bulbs with LED's and all your electric motors with Stepper motors. [wikipedia.org]
Electric != electronic
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incandescent bulbs don't care if it is AC or DC, both will work. The motor comment however is correct.
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You only need cheap batteries if you are trying to be off grid (or your utility doesn't do net metering). Otherwise, let the grid be your battery.
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I just spoke to the Grid and he says, "Fuck you, pay me. I'm in the business of charging you for electricity, not storing your excess. What are you, some kind of German commie?"
Re:The bigger problem (Score:4, Interesting)
I disagree. The grid is in the business of transferring electricity around. The grid doesn't care if it's electricity generated at a plant and sent to your home, or generated at your home and transferred to your neighbors home. And of course you'll pay to be attached to the grid, but that could take many forms, almost any manner of which would be cheaper than buying a bank of batteries.
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The grid is in the business of whatever the corporate entity that owns it says it is. And if you should come up with a way to generate energy without it, you will find out just how fast the Grid can be weaponized.
The grid today is foolish (Score:2)
Public roads, on public land are the essential infrastructure on which our society functions, it dates back long ago. It is done by the people (aka the government.) Everybody puts money in and everybody benefits.
The electrical grid gets heavy subsidizes and often leverages its monopoly power to corrupt government. The grid should be another public network just like the roads it usually runs next to. City water and sewage is also an old solution we continue. Electricity is now essential and while it is no
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As I said "you only need cheap batteries if you are trying to be off grid".
As far as whether batteries are necessary for spurring a broader solar market, it is a small minority of people who would be buying solar panels to avoid power outages. If solar panel costs were finally low enough that you could install a (battery-free) system that would provide signficant net savings over its life, you wouldn't hear a lot of people saying "but if I still lose power when the grid is out, why should I bother".
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And most people do not consider the fact that a saved dollar is tax free while an earned dollar is taxed at 14 to 28%.
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Obviously this includes government rebates, but while talking about personal out-of-pocket costs I saw a vendor in Austin, TX selling a 6kW system, installed, for $19.5k. After city of Austin $14,475 rebates (paid directly to the vendor; never out of your pocket), and $1508 federal tax credit (out of your pocket unless you pay quarterly or adjust your W4), the cost for the system was just $3,517. $3,517 is crazy good for a 6kW system, which in Texas supposedly generates about 8400 kW-h of electricity a ye
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THanks. Sums it up nicely. Keep in mind though that Austin Energy is rapidly building green energy sources (and other energy sources, too) to meet a growing demand.
It costs Austin $14k to subsidize 6kW of summertime peak energy generation on my roof, which I'll provide to the grid at baseline rates (or reduce my own demand at peak rates). Suppose it costs Austin more than $14k to build, transport, and maintain 6kW of summertime peak energy generation in a field in west Texas. If so, then this isn't real
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Assuming that it operates 25 years without a glitch, that it's never damaged in a storm, that it never requires an electrician, that no kids find it fun to throw rocks at your roof or whatever. Sounds like you're more than breaking even but I'd budget something for maintenance, nothing ever seems to be quite as zero maintenance as promised.
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Once it's on your home, your insurance covers it in the event of damage. The anecdotal reports I've seen indicate that solar panels are more durable than asphalt shingles when it comes to hail, so it's possible that installing a solar system will reduce your home insurance claims as well. Hence, you may not be paying for the cost of this coverage in the form of higher rates.
The inverter needs to be replaced every 10 years or so if you buy a whole-house one, but new DC panels have an inverter on the back o
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Because the grid never goes down.
Around here, at least, that is more or less true. We get maybe one power outage a year, and it usually lasts for about two seconds until a backup kicks in somewhere.
When the power goes out, so does your grid-tied system.
That's true, but it's not really a problem for most people. Grid-tied systems aren't meant to improve reliability, they are meant to reduce costs and/or emissions.
On the other hand, if reliability is your concern and you're willing to pay extra, buy some batteries for backup.
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Well, cost of the support system is something that ends up getting cheaper with scale and technology improvements
And maybe you don't need a battery, or need only a small one.
The key here is efficiency, or better summed up by "bang for the buck".
Energy during the night is cheap, so it makes sense to use from the grid.
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My solar installation doesn't have any batteries. I use micro-inverters instead of a bulk inverter and am still connected to the grid. So, during the day (when the ACs or dryer aren't running) I push power back and help run my neighbors' houses, at night, I pull from the grid to run the house. This way I don't have to replace batteries every 5-7 years and if some panels get shaded/have a problem, they don't pull down the entire array.
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I recently heard of an idea to put a small inverter circuit in (under) each individual PV cell. This was a side point in a lecture on a different topic, so they didn't explain the details, but the idea was that this would simplify the equipment needs downstream from the array. Also, they claimed that this made each panel more resilient because damage to one cell would not affect the entire panel. Sorry I can't recall the citation, I've been watching a bunch of this stuff on YouTube lately and don't remember
Logan's Run (Score:3, Interesting)
Who else immediately thought of the solar powered car in the Logan's Run TV series? I could never understand why the solar collector glowed... now I know!
Re:Logan's Run (Score:5, Funny)
There was a car?
I was too busy watching Jenny Agutter: http://i2.listal.com/image/343660/600full-jenny-agutter.jpg [listal.com] I ought to download and read the Logan's Run book sometime.
Re:Logan's Run (Score:4, Informative)
She was not in the TV series.
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That doesn't mean he wasn't busy looking at her.
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That is understandable. XFD
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In the TV Series, Jessica was played by Heather Menzies [imdb.com]. Nice to look at also, in a 1970s kind of way.
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It's funny with the *vast* number of science fiction movies and TV shows that show alien/futuristic technology with strange lights to think that they might have had it right all along.
Hmph... (Score:3, Funny)
Why are these scientists wasting their time with so-called "solar cells"? Everyone knows solar energy can't possibly work. There's just not enough energy in the sun for it to be useful to us.
Fossil fuels are the result of plant life after millions of years, so they're the real "green" technology. And the sun had absolutely nothing to do with them.
These scientists, who are probably mostly foreign, want to strip us of our birthright: a personal vehicle that weight 6000 lbs. Hell, my wife, Lovey, has a couple of Escalades and she recycles all the plastic wrap that our food comes in. So who's really the "green" one?
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All the good stuff comes in cans, well except for dinners. They come in a little tray you can stick in the microwave.
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Look up desertec. Its good stuff.
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Very good stuff.
No joke (Score:5, Funny)
Guess I can't tell that joke about a solar-powered flashlight anymore.
Re:No joke (Score:4, Insightful)
That joke stopped being funny years ago - solar powered LED flashlights are on the market - I own one.
Sound useless ? It's not. It has a battery - during daytime it charges the battery from solar power, when you use it at night, the battery powers the LED lights.
It's a wonderfully useful tool on camping trips. As a bonus - since the battery isn't replaced during the lifetime of the device it has much less of a pollution (battery-acid) impact (granted this may be less of a consideration in some countries -mine has no systems in place for proper disposal/recycling of battery cells and people just toss them in the trash when they are used up).
That LEDs have become so powerful while remaining so efficient has led to us being able to do a lot of really cool things we weren't able to do even quite recently. :D
Frankly compared to things like LED based airport runway signal lights a solar powered flashlight isn't even all that impressive
heinlein was right again! (Score:2)
some rolling roads, a life detector, and a massive fundamentalist revolution and we should be all set...
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hmmm... Nehemiah Scudder == Mitt Romney? oh dear...
Re:Ehh (Score:4, Informative)
Well, Physicists from MIT beat 100% efficiency a month ago. [slashdot.org] (of sorts).
The MIT team called it a LED that functions much like a heat pump. It emitted more optical power than the electrical power it consumed. Apparently the trick is that it results in a lower entropy state, and only works on extremely small scales, so it will never lead to a practical device.
This story, however, doesn't seem to say at all that they have broken 100% efficiency. They are trying to get the total efficiency up above 30%. The amount of light given out by the cell and the electrical energy given out add up to less than 100%. The slashdot headline leads you to believe that they broke 100%, but that is not what "efficiency record" means in this case.
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Please explain how the headline to this story, "Solar Cells That Emit Light Break Efficiency Record" would "lead you to believe" that they broke 100%.
Re:Ehh (Score:4, Informative)
Go read the article, maybe? The entire LED world is abuzz right now with that news. The only issue is that it requires a HOT ENVIRONMENT, where the LED seems to utilize by converting some of that energy into visible-wavelength emissions, beating the power input/optical power output ratio of 1:1.
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I was joking.
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Beating the ELECTRICAL power input to optical power output ratio of 1:1.
Re:Photosynthesis (Score:4, Informative)
No, they fluoresce in near-UV (unless you're watching with an IR scope when using 680-700nm light.) Light conversion always works DOWN from higher energy potential to lower energy potential when there's no amplifier or booster present. We can take one blue photon and emit 7 or 8 red photons, roughly. This is why plants have this odd purple/red glow with certain near-uv wavelengths. They absorb blue, emit yellow/red photons as a result.
2 more ways to make better solar cells (Score:3)
http://www.gizmag.com/nanocrystalline-silicon-nanoshell-photovoltaics/21391/ [gizmag.com]
http://www.technologyreview.com/energy/39887/ [technologyreview.com]