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Solar Cells That Emit Light Break Efficiency Record

Posted by samzenpus on from the shine-on dept.

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.'"

42 of 139 comments (clear)

  1. Idea by busyqth · · Score: 5, Funny

    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.

    1. Re:Idea by X0563511 · · Score: 5, Funny

      In this seafloor habitat dwelling we obey the laws of thermal dynamics!

      --
      For large sets, this will be our guide even unto death, for the LORD will work for each type of data it is applied to...
    2. Re:Idea by mooingyak · · Score: 3, 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.

      --
      William of Ockham had no beard. The most likely explanation is that it was chewed off by squirrels every morning.
    3. Re:Idea by Daniel_Staal · · 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.

      --
      'Sensible' is a curse word.
    4. Re:Idea by CaptainLugnuts · · Score: 2

      Once this gets worked out tailoring the waste output into the IR could be quite useful.

    5. Re:Idea by Intrepid+imaginaut · · Score: 4, Insightful

      This is so cool. Every day brings us closer to glowy alien crystal energy technology.

    6. Re:Idea by geekoid · · Score: 3, Funny

      And that's why we can't have nice things.

      --
      The Kruger Dunning explains most post on /. http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect
  2. What's counter-intuitive about it? by SirGarlon · · Score: 5, Informative

    If you've taken sophomore college physics, it's not counter-intuitive at all that an efficient absorber is also an efficient emitter.

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    1. Re:What's counter-intuitive about it? by Wraithlyn · · Score: 4, 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?

      --
      "Mind, as manifested by the capacity to make choices, is to some extent present in every electron." -Freeman Dyson
    2. Re:What's counter-intuitive about it? by gman003 · · Score: 5, Funny

      What do you think "intuitive" means exactly?

      Intuitive (adj.) - Anything I already know.

    3. Re:What's counter-intuitive about it? by Eponymous+Hero · · Score: 5, Insightful

      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.

      plus, isn't sophomore college physics, like, a facebook app or something by now?

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    4. Re:What's counter-intuitive about it? by robot256 · · Score: 4, 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.

    5. Re:What's counter-intuitive about it? by Wraithlyn · · Score: 3, 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.

      --
      "Mind, as manifested by the capacity to make choices, is to some extent present in every electron." -Freeman Dyson
    6. Re:What's counter-intuitive about it? by voidphoenix · · Score: 3, Insightful

      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 never really see.

      Your education and experience are part of this processing, and the more "education/experience/whatever" you have on a particular subject matter, the better your intuition is on that subject matter. This is not voodoo, it simply means the processing has been integrated into the deeper regions and we no longer have to actively or consciously think about it. To the conscious mind, it's like we "just know it".

      As an example, a beginning driver, especially on a stick shift, will be thinking about details like gas pedal, brake pedal and clutch pedal timing, which gear to shift to, when to shift to neutral, and on top of all that, steering and navigating. An experienced driver doesn't need to consciously plot the gas off, clutch down, shift, etc... steps, they basically happen automatically. Some will argue it's muscle memory, but it's more than just the movements. The timing of all that, of what to do and when to do it, requires being able to integrate multiple data streams.

      Another example, diagnosing computer problems. I've been fiddling around with computers for decades, and basically, family and friends come to me when their computers "don't work". Many times, they'll be describing (in non-tech terms) the problem and I'll "just know" what's wrong when they're barely done with the second sentence. I don't think "a priori" is correct, at all. If I I didn't have the education/experience/whatever, I simply would not be able to figure that stuff out. But because I do, I can, often intuitively, meaning, I don't have to consciously think about it. The character Dr. Gregory House, from the House, MD TV series, also displays this. His expertise is broad and deep, and so he can intuitively figure out obscure medical problems.

      The brain is a constantly self-adjusting neural network, sort of like an FPGA, and although they aren't exact analogies, one can think of education as data/software. Early on, you're thinking about it and solving problems in software. But given time and practice, the software in the brain migrates into the hardware, kind of like programming an FPGA. Once it's coded in the FPGA, it can mostly avoid using the stack and registers (your conscious mind) and you "just know" the answers/solutions/whatever. And yes, intuition is very personal. What is intuitive to me will not necessarily be intuitive to you, and vice versa. We have differently-programmed FPGAs.

      --
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    7. Re:What's counter-intuitive about it? by The+Grim+Reefer · · Score: 2

      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. ;-)

  3. Well, kind of by Anonymous Coward · · 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.

  4. Re:Ehh by uigrad_2000 · · Score: 3, Informative

    Well, Physicists from MIT beat 100% efficiency a month ago. (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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  5. The bigger problem by cirby · · 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...

    1. Re:The bigger problem by cpu6502 · · Score: 4, Insightful

      Make the solar cells part of modular homes where the roof and panel are built as one in a mass-production factory.

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    2. Re:The bigger problem by Chuckstar · · Score: 2

      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.

    3. Re:The bigger problem by Chuckstar · · Score: 3, 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.

    4. Re:The bigger problem by ArhcAngel · · Score: 3, Informative

      You still have to convert the energy from DC to AC so your DC appliances with AC2DC converters can plug into the wall. Damn you Tesla!

      --
      "A person is smart. People are dumb, panicky dangerous animals and you know it." - K
    5. Re:The bigger problem by Khyber · · Score: 2

      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.

      --
      Still waiting on Serviscope_minor to wake up to fucking reality and realize that Jessica Price isn't going to fuck him.
    6. Re:The bigger problem by Maxo-Texas · · Score: 2

      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%.

      --
      She was like chocolate when she drank... semi-sweet at first and then increasingly bitter.
    7. Re:The bigger problem by SydShamino · · Score: 2

      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 year. At 10.5 cents per kW-h (a low rate than I pay now), that nets $882 in savings each year.

      That's breakeven in less than four years. The remaining 21 years or so of system life are profit.

      --
      It doesn't hurt to be nice.
  6. Logan's Run by eggfoolr · · 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!

    1. Re:Logan's Run by cpu6502 · · Score: 4, Funny

      There was a car?
      I was too busy watching Jenny Agutter: http://i2.listal.com/image/343660/600full-jenny-agutter.jpg I ought to download and read the Logan's Run book sometime.

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    2. Re:Logan's Run by kimvette · · Score: 3, Informative

      She was not in the TV series.

      --
      The Christian Right is Neither (Christian nor right). See: Matthew 23, Matthew 25, Ezekiel 16:48-50
    3. Re:Logan's Run by R3d+M3rcury · · Score: 2

      In the TV Series, Jessica was played by Heather Menzies. Nice to look at also, in a 1970s kind of way.

  7. Re:Stands to reason by KlomDark · · Score: 3, 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.

  8. Re:Stands to reason by squidflakes · · Score: 2

    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.

  9. Hmph... by PopeRatzo · · 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?

    --
    You are welcome on my lawn.
  10. No joke by Memophage · · Score: 5, Funny

    Guess I can't tell that joke about a solar-powered flashlight anymore.

    1. Re:No joke by silentcoder · · Score: 3, 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.
      Frankly compared to things like LED based airport runway signal lights a solar powered flashlight isn't even all that impressive :D

      --
      Unicode killed the ASCII-art *
  11. Re:Stands to reason by Eponymous+Hero · · Score: 3, Funny

    sure, rage quit a game, throw the mic across the room and realize the plug didn't come with it, and pretty soon you're wearing headphones around the side of your head over your mouth.

    --
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  12. LIght emission is negative absorption [Re:Idea] by Geoffrey.landis · · Score: 2

    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 light emission, which is to say, when the light emission is maximized.

    (In fact, it is optimized when the light emission back toward the source is maximized; all emission that isn't back toward the source could in principle be retroreflected and reabsorbed. This would be known as "light trapping".)

    --
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  13. Re:Stands to reason by RenderSeven · · Score: 2

    Which is why we should have installed speakers in Congress years ago. Screaming politicians could generate scads of Green Energy!

  14. Re:Stands to reason by djlowe · · Score: 3, Funny

    Which is why we should have installed speakers in Congress years ago. Screaming politicians could generate scads of Green Energy!

    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

  15. Re:Ehh by Khyber · · Score: 3, 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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  16. Re:Photosynthesis by Khyber · · Score: 3, 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.

    --
    Still waiting on Serviscope_minor to wake up to fucking reality and realize that Jessica Price isn't going to fuck him.
  17. It's Older and More General Than That by Anonymous Coward · · 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.

  18. 2 more ways to make better solar cells by Taco+Cowboy · · Score: 2

    http://www.gizmag.com/nanocrystalline-silicon-nanoshell-photovoltaics/21391/

    http://www.technologyreview.com/energy/39887/

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