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Science Technology

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.'"
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Solar Cells That Emit Light Break Efficiency Record

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  • Idea (Score:5, Funny)

    by busyqth ( 2566075 ) on Wednesday April 25, 2012 @04:50PM (#39799825)
    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.
    • Re:Idea (Score:5, Funny)

      by X0563511 ( 793323 ) on Wednesday April 25, 2012 @04:52PM (#39799853) Homepage Journal

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

    • "Independent" is a bit strong of a term, given that even if they were perfectly efficient they would need an external source to actual *generate* electricity instead of just maintain their energy. That said, I would assume they would funnel the light back unless (1) it interfered with letting the external light in or (2) it was of a wavelength that was poorly absorbed by the panels anyways.
    • Re:Idea (Score:4, Insightful)

      by mooingyak ( 720677 ) on Wednesday April 25, 2012 @04:57PM (#39799907)

      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)

      by Daniel_Staal ( 609844 ) <> on Wednesday April 25, 2012 @05:04PM (#39799967)

      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.

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

    • 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.

  • 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)

      by KlomDark ( 6370 ) on Wednesday April 25, 2012 @05:29PM (#39800179) Homepage Journal

      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.

      • 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.

        • Re: (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.
      • Which is why we should have installed speakers in Congress years ago. Screaming politicians could generate scads of Green Energy!
        • Re: (Score:3, Funny)

          by djlowe ( 41723 ) *

          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 ...



  • by SirGarlon ( 845873 ) on Wednesday April 25, 2012 @05:01PM (#39799949)
    If you've taken sophomore college physics, it's not counter-intuitive at all [] that an efficient absorber is also an efficient emitter.
    • by Wraithlyn ( 133796 ) on Wednesday April 25, 2012 @05:40PM (#39800341)

      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?

      • by gman003 ( 1693318 ) on Wednesday April 25, 2012 @05:51PM (#39800483)

        What do you think "intuitive" means exactly?

        Intuitive (adj.) - Anything I already know.

      • by Eponymous Hero ( 2090636 ) on Wednesday April 25, 2012 @06:19PM (#39800885)
        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?
        • 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. ;-)

      • Readily apparent to one's intuition.

        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.

        • by robot256 ( 1635039 ) on Wednesday April 25, 2012 @06:58PM (#39801281)

          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.

        • by Wraithlyn ( 133796 ) on Wednesday April 25, 2012 @07:09PM (#39801371)

          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.

          • Re: (Score:3, Insightful)

            by voidphoenix ( 710468 )

            (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

            • []

              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

      • by geekoid ( 135745 )

        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.

      • by Khyber ( 864651 )

        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.

    • by Anonymous Coward

      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.

    • 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)

    by Anonymous Coward on Wednesday April 25, 2012 @05:02PM (#39799959)

    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)

    by cirby ( 2599 ) on Wednesday April 25, 2012 @05:20PM (#39800079)

    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...

    • by cpu6502 ( 1960974 ) on Wednesday April 25, 2012 @05:27PM (#39800151)

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

      • by ArhcAngel ( 247594 ) on Wednesday April 25, 2012 @06:14PM (#39800807)
        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! []
        • by Khyber ( 864651 )

          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.

          • WOW!

            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
            • by Khyber ( 864651 )

              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.

              • Pushing 200A through default 2,5mm^2 wires would pose a firehazard (2,5 mm^2 is default in the Netherlands. This is about AWG 16) these wires are rated for 16A over long periods of time. Pushing more than 10 times that power through is a bad idea.
                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
                • by Khyber ( 864651 )

                  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.

                  • AWG 12 is less than our 4mm^2. 4mm^2 is rated for 32A where I am from. The voltage doesn't matter, the current screws you over.
                    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.
                  • Boys and girls, please don't drive 400 amps through twelve gauge wire in your homes - at least not if you value your homes (or your lives)...

                    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.
                    • You know what... I take this back. What was I thinking. If you're using a 12v source you might not burn down your house. You won't have much power to work with on the far end of your line (a few amps, 4 or 5 perhaps) which might give you enough power to run your laptop. Of course, you could get 200 amps through a 10 meter 12 gauge wire by grounding it on the far side... but then you would burn your house down.
            • Most electric motors are AC based.
              • 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. []

                Electric != electronic

                • incandescent bulbs don't care if it is AC or DC, both will work. The motor comment however is correct.

    • 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.

      • 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.

        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?"

        • by Chuckstar ( 799005 ) on Wednesday April 25, 2012 @05:58PM (#39800561)

          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.

          • The grid is in the business of transferring electricity around.

            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.

          • 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

      • Because the grid never goes down. When the power goes out, so does your grid-tied system.
        • 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".

          • I looked into this recently, and it is actually pretty close to the break-even point in my area. The cost to install a grid-tie system would be totally paid off by about 15 years of energy savings, assuming the rates don't up drastically, and the panels would have another 5-10 years of life left. It isn't dramatic enough that people are going out and getting solar panels to make a quick buck, but it's enough that people who want to do the right thing aren't penalized in the long run.
            • 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%.

            • 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

              • Sounds like communism to me: Your neighbor's tax money used to pay for your solar panels. How can this even exist in Texas?
                • Your neighbor is also paying for your roads, your sewers, your national defense, your medical care, your social security, your fire department... and on and on and on. I'm not saying I agree with the subsidies (I'm actually quite against them) but have a bit of perspective here.
                  • 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

                • When you install solar panels on your home, that reduces the peak load on the grid, which in turn reduces the chance that your neighbor will experience brown-outs, black-outs or rate hikes to add capacity. So it's not entirely crazy for them to subsidize your solar panels. Communism generally sounds terrible until you realize that we don't all live on individual planets.
              • by Kjella ( 173770 )

                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.

                • Some of the leasing companies cover all the installation and maintenance costs and then charge you either monthly or per kilowatt-hour, and the rates guarantee some (albeit smaller) guaranteed savings over utility costs.
                • 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

        • by Jeremi ( 14640 )

          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.

    • by JamesP ( 688957 )

      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.

    • by Epi-man ( 59145 )

      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.

    • 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)

    by eggfoolr ( 999317 ) on Wednesday April 25, 2012 @05:24PM (#39800117)

    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!

  • Hmph... (Score:3, Funny)

    by PopeRatzo ( 965947 ) on Wednesday April 25, 2012 @05:39PM (#39800333) Journal

    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?

  • No joke (Score:5, Funny)

    by Memophage ( 88273 ) on Wednesday April 25, 2012 @05:46PM (#39800413)

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

    • Re:No joke (Score:4, Insightful)

      by silentcoder ( 1241496 ) on Wednesday April 25, 2012 @06:31PM (#39801049)

      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

  • some rolling roads, a life detector, and a massive fundamentalist revolution and we should be all set...

I THINK MAN INVENTED THE CAR by instinct. -- Jack Handley, The New Mexican, 1988.