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Power Earth

Hairy Solar Cells Could Mean Higher Efficiency 203

kitzilla writes "Two research groups working independently have come up with what they say are cheap processes for growing nanowires to be used with solar cells. The 'hairy' cells provide a direct path for electrons collected at the panel face to reach an electrode, something which has the potential to dramatically improve system efficiency."
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Hairy Solar Cells Could Mean Higher Efficiency

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  • Anonymous Coward (Score:2, Informative)

    by Anonymous Coward on Monday May 19, 2008 @04:47PM (#23467804)
    solar cells are pn junctions and DO NOT Collect electrons. i am to lazy to get into solid state theory right now. so go figure how exactly pv cells work.
  • by Hankapobe ( 1290722 ) on Monday May 19, 2008 @04:52PM (#23467854)
    but what is really needed is a photovoltaic that will release two electrons for every photon. If any of you material guys out there do that, you'll be a gazillionaire! That will really make photovoltaics productive enough to really complete with other alternative energy source - assuming fossils fuels don't go up much higher than they are now. Photovoltaics need to get down below $0.15 kwh on the roof (the heat from a typical roof reduces photovoltaic's efficiency by at least 10%).
  • Re:Let me guess... (Score:4, Informative)

    by frying_fish ( 804277 ) on Monday May 19, 2008 @04:56PM (#23467894)
    Slight problem at the moment is band gap, and tuning a semiconductor to have the appropriate bandgap that will cover the visible spectrum. Currently there is no single device that is sensitive to the whole visible spectrum, but there is research into this. This is one of the major reasons for the low efficiency in solar cells.
  • Re:Let me guess... (Score:4, Informative)

    by chuckymonkey ( 1059244 ) <charles.d.burton@gmai l . com> on Monday May 19, 2008 @04:57PM (#23467900) Journal
    Personally I love solar voltaic panels with a little of that canned cheese on them. On a more serious note, why do people not focus on the tech that we have now? For instance if you want solar the solar thermal systems are pretty cheap to build and have decent efficiency. I just don't get why everyone is so stuck on solar voltaic which is as someone else said in a perpetual early adoption stage when a good chunk of baseline power could be provided by solar thermal.
  • by BlueParrot ( 965239 ) on Monday May 19, 2008 @04:58PM (#23467904)
    If I am not completely mistaken "classical" semi conductor cells can reach efficiencies of 40%, meaning that even with perfect 100% efficiency you would get at best a factor 2.5 improvement. Of course, 100% efficiency is an impossibility and thus I think we can safely assume that these cells will never reach more than 80%-90% efficiency, which would be an improvement of a factor of 2 over current technology. Now last estimate I saw was that in Europe solar cells work out to be about 4 times as expensive as wind power (which is itself rather pricey ), so even assuming the 100% efficiency, efficiency gains alone cannot make solar economical.

    Add in to this that a large part of the cost of solar is the energy needed to produce the cells, which means that if you get that energy from a more expensive power source, the price of the cells will increase. I.e, if one started to replace relatively cheap generation capacity with more expensive solar cells, then the cost of energy, and hence the cost of the cells, would increase.

    It would therefore appear to me that for solar to have a chance to become competitive what is needed is focus on lowering the cost of producing the cells, because the gains from improving their efficiency cannot offset their presently large price, and it appears unlikely that pushing for higher and higher efficiencies will be possible without making the cells more expensive.
  • Re:Anonymous Coward (Score:5, Informative)

    by QuasiEvil ( 74356 ) on Monday May 19, 2008 @05:00PM (#23467922)
    AC's got it right. For those who are TLTRTFM (Too Lazy To ...), what the poster should have said is that they help channel charge carriers away from the junction so that they don't immediately recombine. *That* is one of the holy grails of PV design, and one of the reasons that current production cells are incredibly inefficient.
  • by clonan ( 64380 ) on Monday May 19, 2008 @05:07PM (#23467982)
    Currently availible non-specialty cells (the cells used for space etc are not used for general power) are typically between 5 and 15%.

    Therefore getting to the 80-90% range would result in a 5-18X improvment.

    Since solar is currently 4X, that means it will drop to .2-.8X of CURRENT power costs.

    Now remember that hydro is essentially 100% tapped. Wind has a much more limited range and is already approaching the likley maximum efficiency. Nuclear is great but will take some time to spin up. Oil/natural gas prices are climbing rapidly and coal is becoming more expensive to mine and or clean.

    Solar PV provides a great load matching power source that will help reduce an individuals demand on the system even if it doesn't complely remove the need for other power sources as well.
  • by Anonymous Coward on Monday May 19, 2008 @05:31PM (#23468200)
    Photovoltaics can't supply base load now, but that doesn't that you can't get a solar plant to supply base load. The trick is to instead, use thermal energy. We can store the excess thermal energy overnight to continue generating power in the dark, until the sun shines again. Check it out []
  • by Anonymous Coward on Monday May 19, 2008 @05:45PM (#23468358)
    Thermal solar is the lowest costs of all AE except for hydro. At this time, it is the same costs as a recent coal plant i.e. a plant that is cleaner than average. Of course, the solar thermal is clean all the way around.
    In addition, it is fairly easy to store the heat in salts and generate during the night. Spain, Arizona, New Mexico, Northern Africa, etc. are all headed in GW size of solar thermal. Spain expects to sell power back to its northern neighbors at a tidy profits. Arizona has a 1/4 GW install going in. In addition, another group is close to building a 1/2-3/4 GW in NM or southern CO (possible to take advantage of 3 different power companies and 5 states incentives).

    All in all, the only joke is a fool like you.
  • by BlueParrot ( 965239 ) on Monday May 19, 2008 @05:48PM (#23468382)

    Currently availible non-specialty cells (the cells used for space etc are not used for general power) are typically between 5 and 15%.

    Therefore getting to the 80-90% range would result in a 5-18X improvment.

    Since solar is currently 4X, that means it will drop to .2-.8X of CURRENT power costs..

    I said 4X WIND POWER costs. Not current power costs. Britain's Royal Academy of Engineering estimates the cost of wind power at roughly 3 times that of nuclear, so even if you achieve 90% efficiency that would put you at roughly twice the cost of nuclear generation ( assuming 15% efficiency for present cells ). Now, to give an idea of how hard 90% efficiency would be to reach, the Sun's average surface temperature is 5778K , meaning a solar cell at 300K could at best reach 95% efficiency without violating the laws of thermodynamics.

    That is, ignoring ANY other problems you are closing in on the theoretical limits allowed by the laws of physics if you are to get such efficiencies, and you have to do this without increasing the costs of your cells. Any dust on the cells and you can forget it. Protective glass coating is a no-no since it would absorb in the UV range. Heck, simply finding a material that is reasonably transparent at all the relevant wavelengths could be tricky. Add in to this that you cannot use any expensive/toxic/rare elements, that the cells should have to last for a long time, that they should survive a wide range of temperatures and be able to handle a reasonable level of abuse, and it becomes far from certain that it is even possible to reach 80% efficiency, let alone to do so in the foreseeable future.

  • by NeutronCowboy ( 896098 ) on Monday May 19, 2008 @06:04PM (#23468530)
    Now it's been a while since I dealt with Physics and all that, but... release 2 electrons for one photon? How would that work? Photons knock electrons out of their bonds by imparting enough energy into the electron so that it moves into the conduction band. However, photons are either absorbed or not - this is not billiards.
  • by timmarhy ( 659436 ) on Monday May 19, 2008 @07:50PM (#23469454)
    nonsense. the largest thermo solar power plant is just 64 mega watt - enough for 15,000 homes. compared to coal fired stations that can supply 700,000 homes, yes it's a JOKE.
  • by aliloln ( 973288 ) on Monday May 19, 2008 @08:52PM (#23469950)
    No, they are talking about 300W halogen floor lamps (single halogen bulb fixtures). There are even 500w halogen bulbs. Google Halogen 300w and you'll find the bulbs.
  • by Anonymous Coward on Monday May 19, 2008 @09:49PM (#23470364)
    What you're looking for is a multiexciton creating material. There is a decent amount of research going into it right now. Generally, a high energy photon which is more than twice the bandgap creates a high energy exciton, and somehow (competing theories right now) the relaxation process generates low energy excitons.
  • by jelle ( 14827 ) on Monday May 19, 2008 @11:19PM (#23470946) Homepage
    The first coal plants couldn't even supply one modern home with power... They have plans to build 'em much bigger, such as 553MW for Mojave Solar Park: []
  • Re:Let me guess... (Score:3, Informative)

    by Ihlosi ( 895663 ) on Tuesday May 20, 2008 @03:04AM (#23472296)
    PV is about 15-20% efficient.

    36% in concentrator cells, but they'll be stuck in the lab for quite a while, and will probably be infeasible for large installations.

    Thermal is currently 40% in some units, and a prototype achieved 60%.

    That's the efficiency of the turbine itself. The plant will have some additional losses (not all of the sunlight hitting the area of the plant will actually be collected, etc).

  • by locofungus ( 179280 ) on Tuesday May 20, 2008 @03:21AM (#23472410) []

    There are, of course, disadvantages as well. In particular, HVDC doesn't really work well for a grid, only for point to point links. So if you want to move power from one AC grid to another then HVDC makes sense (8GW link under the English Channel for example - note that England and France use the same frequency but different phase - and the angle (presumably) isn't constant - so you'd probably have to use a DC link although that could be just a few metres but once you've got both DC and AC it's cheaper to move power using DC than AC)

  • Re:Let me guess... (Score:1, Informative)

    by Anonymous Coward on Wednesday May 21, 2008 @01:14AM (#23488650)

    *groan* so now Nuclear shills are AC's, how pathetic. Did you post as A.C so you could mod your own post as Interesting, how very creative of you.

    Resorting to baseless accusations and the ad hom fallacy is hardly conducive to the discussion.

    actinides are highly radioactive with half lives of around 600 years.

    The actinides produced are either fissionable or can be bred into fissionable elements, and then used as fuel. They aren't "waste."

    first of all while our current level of material sciences and technology cannot produce a safe nuclear reactor, perhaps one day we can (or use it in space craft) which is why I said "long term isotope storage". Plutonium, whilst deadly is also extremely valuable.

    You're missing the point. I bring up plutonium because people complain that constructing breeders will produce it, but I make the two points that breeders can be configured to produce non-weapons grade plutonium and that we already have weapons grade plutonium we have to dispose. Plutonium can be used as nuclear fuel and by eliminating it we reduce the proliferation risk, but only if we build suitable reactors.

    No problem, don't mine uranium in the first place

    Did you even read what I wrote? I said plutonium from decommissioned bombs. It has already been mined. It's weapons grade plutonium. You can't just bury it in a hole in the ground and hope nobody ever finds it. You can put it in a reactor and use it as fuel. If you don't want to do that then what do you propose to do with it?

    And I'm more concerned with radioactive products created by exposure to plutonium finding their way into the water table.

    Take a drive through New Jersey and look at the chemical plants sometime. They process toxic materials all day long on the industrial scale and yet I can still drink the water, because there are regulations in place to ensure containment. The regulations in place on the nuclear industry are even more stringent despite the fact that the toxicity of nuclear materials is no greater than less stringently regulated chemical toxins. You can also throw in the fact that "radioactive" and "dangerous" are not synonyms. A bag of coffee beans, a bottle of vegetable oil and a smoke detector are all radioactive but you'll hardly get cancer from having them around your house.

    Show me a link to a proposed breeder reactor planned for construction for commercial power generation.

    You mean like this []?

    Except the difference is that CO2 and other greenhouse gas production for nuclear is an ongoing consequence of making fissionable reactor fuel, whereas they are one time inputs for solar/wind/wave.

    Nonsense logic. All construction has a finite lifetime after which it must be upgraded or replaced. Solar and wind have ongoing CO2 costs because plant and equipment must be replaced as it ages and fails. And you're still making the assumption that the energy used for processing has to come from fossil sources while, again, the entire point of this exercise is to replace them.

    You expect me to believe that USEC phased out CFC 114 use when they have access to a valid military exemption under the authority of the DOE, and that the last available data in 1999 revealed that over 800000 pounds of CFC 114 was released into the atmosphere. Since subsequent data is not available AND prototype designs of the new centrifuge were only finalised in 2007 it's not to much of a stretch to conclude that CFC 114 is still very much in use in the enrichment facilities.

    Now you're arguing against the implementation rather than the concept. You already know what the solution is: Revoke the exemption and retrofit any existing facilities so that they no longer use CFCs. It isn't that it can't be done, it's that it wasn't being done. Congratulations, you've successfully convinced

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