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Power Science

Nanotubes May Improve Solar Energy Harvesting 93

Posted by Zonk
from the just-put-in-a-direct-nuclear-tap dept.
eldavojohn writes "Scientists are hoping that the 'coaxial cable' style nanotube they developed will resolve energy issues that come with converting sunlight to energy. The plants currently have us beat in this department but research is discovering new ways to eliminate inefficiencies in transferring photons to energy. Traditional methods involve exciting electrons to the point of jumping to a higher state which leaves 'holes.' Unfortunately, these electrons and holes remain in the same regions and therefore tend to recombine. The new nanotubes hope to route these excited electrons off in the same way a coaxial cable allows a return route for electrons. End result is fewer electrons settling back into their holes once they are elevated out of them yielding a higher return in energy."
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Nanotubes May Improve Solar Energy Harvesting

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  • by pzs (857406) on Tuesday April 24, 2007 @12:10PM (#18856425)
    If you believe these guys:

    http://www.trec-uk.org.uk/index.shtml [trec-uk.org.uk]

    All we need is to concentrate the power we already have. Apparently, less than 1% of the world's desert would be enough for all the world's power.

    I'm not sure whether I believe this, but I certainly think we should be filling those otherwise useless deserts that cover a large portion of the globe with energy harvesting technology. Maybe the Arab countries, fairly replete with this kind of energy rich terrain, could convert from oil economy to exporting something better for the planet?

    Peter
    • Re: (Score:2, Insightful)

      by Rukie (930506)
      Nanotubes have been around for some time now, but these look like they are structured differently and with different materials. Although, I do believe the problem isn't so much as "efficiency" as it is "price." Once solar energy becomes competitive/better than fossil fuels, I think we will see a huge increase in hydrogen storage (for batteries) and solar energy, along with wind mills for n ighttime power and cloudy days.

      In fact, they even have clear glass windows that college solar energy as well (might hav
      • by Pxtl (151020) on Tuesday April 24, 2007 @12:29PM (#18856775) Homepage
        That was my reaction too. Energy-innefficient solar collectors aren't really a huge concern so much as the dollar-per-watt efficiency. I mean really, the reason people aren't solar-panelling their rooftops isn't that they don't have enough roof, but that they don't have enough coin.
        • This depends (Score:5, Insightful)

          by mdsolar (1045926) on Tuesday April 24, 2007 @12:53PM (#18857191) Homepage Journal
          At the 15% efficiency of silicon, quite a lot of roofs have enough area to cover what a building uses. Orientiation comes into this as well as the height of the building. Taller buildings have less roof per unit floor space which tends to track electicity use. At 7% efficiency, the number of roofs that can cover 100% of the building's use goes down a lot because we're at the edge of feasability at 15%. So, cheaper, lower efficiency solar panels, can turn out to work better where surface area is not at a cost premium. This tends to be in rural areas rather than where most houses are.

          Commercial buildings can often benefit from lower cost, low efficiency panels because they are gaining from using space that they otherwise would not and they are more bottom line driven and can't cover they're full electic use under either senario.
          --
          Go Solar for what you already pay anyway: http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html [blogspot.com]
          • by div_2n (525075)
            With a few exceptions, it's economics--period.

            If [value of expected energy output over lifetime of panels] > [cost of panels] * [interest rate on lease/loan] then people/companies are more likely to buy.

            The closer the number of years it takes to recover the cost of the investment gets to one year, the greater the likelihood of a buy goes up.

            If the government would make the cost of buying solar cells a 100% tax credit with no limit, I bet you would see a huge increase in installations.
            • by mdsolar (1045926)
              There is some wiggle room on the fringe but I think you are mainly right. People will pay extra soemtimes fro green tags; in Texas this has turned out to be cheaper than regular power recently. And, there is more to your calculation than just the interest on the loan, you also want to look at what you might make from investing elsewhere if you were not paying on a loan.

              I'm thinking in terms of silicon being at grid parity (as it already is in Hawaii) and some other technology being below grid parity but
              • by QuickFox (311231)

                if coal, oil, gas and nuclear susbidies were ended,
                What? Are those things subsidized in the US? Amazing! No wonder your CO2 emissions per capita are through the roof! [grida.no]

                Here in Sweden it's the other way round, renewable energy is subsidized (as a temporary measure to help the industry get started) and gasoline is taxed.
                • by mdsolar (1045926)
                  I think nuclear power is subsidized in Sweden and Sweden is relying on it to meet Kyoto. Though we're losing our touch I think, if you want to send some of that gas tax to us to cover our defense spending, we might not act so stuck up this time: http://en.wikipedia.org/wiki/Swedish_response_to_H urricane_Katrina [wikipedia.org]. Glad you were so quick to offer help back then.
                  • Re:This depends (Score:4, Insightful)

                    by QuickFox (311231) on Tuesday April 24, 2007 @04:01PM (#18860481)

                    Glad you were so quick to offer help back then.
                    I appreciate that you noticed.

                    if you want to send some of that gas tax to us to cover our defense spending,
                    Sorry, that's impossible, because Sweden disagrees with your methods. I don't know how Sweden's official motivation is worded, but among the general public the mainstream opinion is that the Iraq war is fueling terrorism rather than curbing it, and we don't want to fuel terrorism. This is not some after-the-fact observation, it has been the firm mainstream opinion since well before the Iraq war started.

                    OTOH we have Swedish troops in Afghanistan.

                    Speaking of our relationship, I do feel that we and the US, in fact the entire Europe and the US, need to be much stronger allies than we are, in spite of the differences that we have. We need to make every effort co-operate in those areas where we agree. We have lots of common goals, and there are lots of areas where we agree.

                    In fact, even when we disagree we could often co-operate. For instance, we might play good-cop/bad-cop roles when dealing with recalcitrant nations. That's far more constructive than building rivalries.

                    I think we could achieve lots of great things together if we could just co-operate better.
                    • by mdsolar (1045926)
                      I think that you are correct that cooperation on a broader scale would be good. I mentioned the gas tax because much of or defense spending supports "lower" oil prices. I've been wondering how soon we'll be asking for a fixed exchange rate with the euro in exchange for more controled spending on our part.
                    • by QuickFox (311231)

                      I mentioned the gas tax because much of or defense spending supports "lower" oil prices.

                      I'm not sure if I understand you correctly. No, we don't want lower gas prices, on the contrary. The gas tax is there to keep the gas prices artificially high. That's so people are discouraged from spewing more carbon dioxide than necessary.

                      This is why I'm astonished by gas subsidies, paying people to pollute more.

                      If a Swedish politician advocated war for the sake of some economic advantage, like keeping some prices low, there would be an extreme uproar and he would be totally fried. In future elections he

                    • by mdsolar (1045926)
                      Yours is a refreshing view point. The way we say it is that the free flow of oil is in the nation's strategic interest. So, we spend a lot on making sure that it flows freely.

                      Ultimately we need the price of oil to fall below the cost of extraction but this will only come about by reducing demand to well below supply. Your method of taxing to reduce demand can be a part of this but I fear that doing this at the level that would cause productive wells to be shut down would be impoverishing. I suspect tha
                    • by QuickFox (311231)

                      The way we say it is that the free flow of oil is in the nation's strategic interest. So, we spend a lot on making sure that it flows freely.

                      [...]

                      From my experience, however, from the inside, people feel that they are doing a very good thing protecting our country so that the coruption is easily overlooked. I don't know when spreading peace will become a priority again.

                      Very interesting. Several US behaviors that have seemed incomprehensible become more understandable when considering the parts I quoted.

                      Been nice talking to you.

                    • by mdsolar (1045926)
                      Same here. You might want to look at http://stepitup2007.org/ [stepitup2007.org] to see how our conception of stratigic interest might be changing in a way that is more aligned with your way of thinking.
            • My friend's solar install was $25K. A tax credit? I hope you mean tax deduction, because most people don't even pay $25K in taxes a year.

              But yes, I do think that some tax break should exist. California has a large subsidy [californiaconnected.org] but it isn't unlimited (first come, first serve).

        • by Urza9814 (883915)
          From what I hear it pays for itself in 8 years and you can usually (in the US at least) get a government grant to cover half of that. Only problem is it's not normal yet. It takes a long time for people to start doing things differently.
        • by drix (4602)
          There are 300 million Americans, and probably 80% of them live in single family dwellings. Figure 3 persons/household. That's 80 million roofs. It costs about $20,000 for a residential PV installation. So $1.6 trillion.

          Current estimates say we will have spent $1 trillion invading Iraq when it's all said and done. We spend an additional $500 billion every year on off^H^H^Hdefense. I'm not some hippy saying we should abolish the military, but it definitely makes you think. We really could afford to do somethi
        • The price is unconscionable, even with California's partial subsidy. My friend paid like $25K for his system (before subsidy). Why haven't solar cell prices dropped like other technology has? If a DVD player can go from $1K to $100 in a few years, why isn't solar getting cheaper?

          I'd adopt solar in a second and put a panel everywhere if I didn't have to pay my left nut for a kilowatt. Hopefully this new tech will be cheap some day.

    • Re: (Score:3, Interesting)

      by TheMeuge (645043)
      The costs of this endeavor would be enormous, in terms of the need to obtain the various materials needed for this, assemble them, then manufacture and set up both the finished equipment, as well as the infrastructure for distributing this energy. Couple that with the fact that transmitting electricity is a very lossy process over distance, and you wind up with a very difficult task indeed.

      Rather than try to concentrate solar energy production, I think we're much better off distributing it. If every roof in
      • in terms of the need to obtain the various materials needed for this

        Yeah, because carbon, oxygen and argon are rare, whereas you can find copper and gallium pretty much anywhere you look.

        assemble them, then manufacture

        The difference is enormous!

        set up ... the infrastructure for distributing this energy

        Indeed, because we don't already have a framework for transmitting electricity. If only solar didn't make a different kind of electricity...

        Couple that with the fact that transmitting electricity is a very lo

    • The infrastructure required to transfer electricity from centralized facilities, and the losses suffered along the way, don't make this very appealing.

      A panel on your roof may not be as efficient, but it's yours. In an sunny place, you may be able to sell power to the local grid during the daytime peak hours. (You might buy it back at night, but the rates are lower then.)

      There will always be a need for a grid, and some big power plants, but making as much new capacity decentralized and as local as possible
      • by Rei (128717) on Tuesday April 24, 2007 @12:49PM (#18857117) Homepage
        The problem is that insolation varies greatly around the world. I would very much love to get solar panels for my house, but up here in Iowa, we get half as much sun as the desert southwest. Yet, we're positively awash in solar energy compared to, say, Washington and Alaska, which have half what we get here.

        Halving the amount of energy doesn't just double payback time when you consider cost amortization. It increases it many more times, often making it so that it will never pay back.

        Now, up here, self-generated wind power is an economically viable alternative to grid power... *if you don't live in a city*. I've crunched the numbers. Inside city limits, your towers are more expensive (you can't use guyed towers -- not enough space) and your heights are limited too close to the ground. On the other hand, it's perfectly reasonable for farms (and power companies) to invest in. One great thing about the big tower wind turbines is that you lose almost no ground area; you can farm nearly up to their base.
        • by misleb (129952)
          Just FYI, Washington isn't that much farther north than Iowa and eastern Washington gets plenty of sunshine.

          • by Rei (128717)
            It's not just how far north you are; weather patterns play as much of a role as latitude. Looking at an insolation map, where I am in Iowa shows up as ~3.5 kWh/m^2/day. The Seattle area shows up as 2 kWh/m^2.day. No part of Washington shows up as better than ~2.8 or so. Meanwhile, the desert southwest approaches 6 kWh/m^2/day.

            To get an idea of how important weather patterns are to insolation, the Congo gets significantly less than near the southern tip of Africa. Here in Iowa, we get almost as much as
            • by Rei (128717)
              Sorry -- seattle is "less than" 2 kWh/m^2, not equal to 2. Looking at another map, it looks ot be something like 1.6, 1.7, something like that. this is for flat plate, fixed. For heliostat, I found a table of cities. Some numbers:

              Chicago: 3.14(!)
              Seattle: 3.57
              Fairbanks: 3.99
              Phoenix: 6.53
              Inyokem (CA): 7.66

              However, the lows matter more in terms of unit selection:

              Chicago: 1.47(!)
              Seattle: 1.60
              Fairbanks: 2.12
              Phoenix: 5.78
              Inyokem (CA): 6.87

              Notice the difference.
            • by misleb (129952)

              It's not just how far north you are; weather patterns play as much of a role as latitude. Looking at an insolation map, where I am in Iowa shows up as ~3.5 kWh/m^2/day. The Seattle area shows up as 2 kWh/m^2.day. No part of Washington shows up as better than ~2.8 or so. Meanwhile, the desert southwest approaches 6 kWh/m^2/day.

              That is suprising because eastern/central Washington is more or less a desert.. high desert. It's certainly nothing at all like the Seattle area. I wonder what causes the insolation.

      • by mdsolar (1045926)
        It's not just the power lines, transportation infrastructure takes less of a hit with solar as well. The amount of mass that has to be transported is about 200 times less for solar than for coal. http://mdsolar.blogspot.com/2007/01/saving-not-bor rowing.html#comment-4164085150001376667 [blogspot.com].
    • In ideal conditions, it seems reasonable that a little bit of desert would yield an enormous amount of power. But conditions are rarely ideal. Your power arrays out there in the desert need to be maintained by someone - do you also build desert communities? You have to pipe the power from the desert out to where it's going to be used. Efficient? A 3% loss over a thousand kilometers means that sending power from Albuquerque, NM to Washington, DC would result in nearly 10% energy loss - assuming an absolutely

      • by mdsolar (1045926)
        I agree with you about the maintenance issue and I'd also be concerned about grit blown in the wind, but I'm not so sure you are correct about the issues with power transmission over long distances. The Pacific Intertie does pretty well bringing cheap hydro to LA, and I think that if we took a longer view, we might invest in lower resistance lines (by making them thicker). Here is a senario where you'd do that anyway: http://mdsolar.blogspot.com/2007/03/coast-to-coas t .html [blogspot.com]. While you're reading, checkou
        • The high-voltage DC systems may be different, but at least with AC, making the conductors thicker doesn't really help that much past a certain point.

          I think it's actually a surface-area dependency rather than a cross-section one; that's why you see big high-tension power lines with multiple sets of small conductors rather than one really big one. Multiple small conductors give you more surface area and less weight (and cost in copper). This is due to the skin effect.

          However you can't just pack multiple cond
          • by mdsolar (1045926)
            I suspect your right that conductor geometery is pretty key. The cross-sectional area formula is a pretty gross approximation. Some HVDC underground cable seems to look a little like co-ax, perhaps because capacitance with the ground is an issue. I do think that going to higher voltage is possible with a (perhaps hollow) fatter conductor since the corona discharge is really about a gradient.
    • by PSU '11 (1092933)
      at first it may seem logical to use the vast amount of land available to harvest the suns energy. However the problem is that these areas are not close to the major areas around the world that use the most energy. Also efficiency becomes a problem. Getting energy from a desert in the middle of nowhere creates the problem of transporting the energy to the places that need it. Not all of the energy would be transported from point A to point B because no system is 100% efficient. It also would make it necessar
  • by rumblin'rabbit (711865) on Tuesday April 24, 2007 @12:11PM (#18856437) Journal
    The proper headline should be "global warming solved for 3rd time this week".
    • Re:Wrong headline (Score:5, Interesting)

      by grungebox (578982) on Tuesday April 24, 2007 @12:17PM (#18856549) Homepage
      Actually, the headling IS wrong, rumblin'rabbit. The use of the term "nanotubes" is incorrect. These are nanowires (that's what the field, and the article itself, call them). These aren't "tubes" in that they aren't hollow; the difference is not at all trivial.
      • Re: (Score:3, Funny)

        by PPH (736903)
        So does this mean that the Internet might actually be a bunch of wires as well, instead of a bunch of tubes?


        Please say it ain't so!

      • by zotz (3951)
        Man! And here I was hoping to build out a nano-internet in a bread box!

        all the best,

        drew
    • Re:Wrong headline (Score:5, Insightful)

      by Rei (128717) on Tuesday April 24, 2007 @12:22PM (#18856651) Homepage
      Unfortunately, "works in a lab" and "mass producable at a commercially viable price in the remotely near future" are two very different things. The former only rarely becomes the latter in fields like solar power. Thankfully, there are so many advancements that a few always tend to make it and push the industry forward.
      • by Alsee (515537)
        "works in a lab" and "mass producable at a commercially viable price in the remotely near future" are two very different things.

        More like theoretical computer simulation, "works in a lab", and "mass producable at a commercially viable price in the remotely near future" are three very different things. Unless I'm mistaken, the article sounds like a pure theoretical computer analysis of a neat mutilayer nanostructure they haven't been able to built yet at all, not even in a lab.

        Not just vaporware, it's hypoth
  • by Anonymous Coward
    nanotubes - what the nanonet is made of!
  • Only 5 Years Away (Score:4, Insightful)

    by Nom du Keyboard (633989) on Tuesday April 24, 2007 @12:19PM (#18856595)
    And I'm sure this is only 5 years away from commercial use, just like every other such announcement.
    • by musakko (739094)
      If I ever get my hands on a time machine, I won't travel 100 years into the future, I'll just go 5 years. THAT'S where all the technology is!
  • by G4from128k (686170) on Tuesday April 24, 2007 @12:21PM (#18856611)
    This really has the potential for providing a third way (versus semiconductor and photochemical systems) for converting light into electricity (for power or signals). Light is just extremely high frequency radio waves. With conductive nanotubes, one could create dipole antenna arrays for submicron wavelengths.
    • This really has the potential for providing a third way (versus semiconductor and photochemical systems) for converting light into electricity (for power or signals). Light is just extremely high frequency radio waves. With conductive nanotubes, one could create dipole antenna arrays for submicron wavelengths.

      Not really - this is still just a doped semiconductor system, jsut a different architecture (nanowire vs. crystalline). Really, they're not focussing on the problem of light capture - they're focussi

  • Hmm (Score:3, Funny)

    by tttonyyy (726776) on Tuesday April 24, 2007 @12:24PM (#18856675) Homepage Journal
    "Hope", "may" and "unfortunately" all in one article.

    It's like reading about Duke Nukem Forever.
  • Ted Stevens is gearing up for a new diatribe...

    I can see it now... countries that contribute the most to global warming will have to pay more for access to the technology... Solar Net Neutrality 4Eva!
  • If you put a series of nanotubes ...

    Do you get a Nanonet ?
    • by smaddox (928261)
      You know, people keep making fun of Ted Stevens for his series of tubes comment. Given, he is completely tech-illiterate, but series of tubes isn't that far off when you consider how much of the backbone is fiber-optic cable. Fiber-optic cable pretty much is a tube - for light. It has a core through which the substance (light in this case) travels, and a shell which holds the substance in. Sounds like a tube to me.

      If you're going to make fun of Ted Stevens speech - make fun of how he called an email an "int
      • by BlueTrin (683373)
        Yeah see what you mean, I thought about it while typing and thought that it wasn't that bad of an image, but, still, he became kind of a legend with this quote : )
  • by Ancient_Hacker (751168) on Tuesday April 24, 2007 @12:29PM (#18856771)
    Expecting nanotubes to act as "maxwell's Demons" is well on the way to Polyanna-Thinking. Fine for used-car ads, political spots, and grant proposals. But a bit far-fetched for rational discussion.

    Plus on the economic issue, most nano-things cost kilobucks per square centimeter. Even if the cost came down by a factor of 10,000, it would still be uneconomical at ThunderDome prices.

  • Zeno's power cell (Score:2, Insightful)

    by jfengel (409917)
    I'm planning to tag every solar-power story "vaporware" until I see something that doesn't depend on additional breakthroughs before it comes to market. It seems like we get 50% of the way to something useful with every posting but never actually get anywhere.
  • by gmcraff (61718) <gmcraff&yahoo,com> on Tuesday April 24, 2007 @12:34PM (#18856849)
    1) Develop high efficiency, long life solar cells
    2) Figure out how to process lunar resources with robotic factories to make said cells
    3) Plate the entire far size of the moon
    4) Transmit the energy back to earth with a few lunar horizon transmitting stations with atmosphere and cloud penetrating lasers/masers/whatever
    5) PROFIT
    6) Reserve fossil fuels for high-energy-density required transportation needs, not short distance ground transport or general power production
    7) PROFIT plus ENVIRONMENTAL BENEFITS
    8) Colonize the moon with the residual infrastructure from the power grid
    9) PROFIT plus ENVIRONMENTAL BENEFITS plus OFF-PLANET HUMAN SUSTAINABILITY
    10) Use short lunar gravity well to build interplanetary transport, colonize Mars
    11) PROFIT plus ENVIRONMENTAL BENEFITS plus FULLY REDUNDANT HUMAN SUSTAINABILITY
    12) ???
    13) A fully armed and operational battlestation
     
    • by AgentSmith (69695)
      Pave the earth. Chrome the moon!
      • by Gilmoure (18428)
        Chrome the moon

        Now I'm going to have to find a dem/3d map of the moon, obtain Bryce or some such similar dumbed down 3D app and go and render a chrome moon. Damn you Teh Interweb! Damn you to hell!
  • by Timesprout (579035) on Tuesday April 24, 2007 @12:35PM (#18856857)
    The US declares war on shrubs. 'This energy theft can no longer be tolerated and we will strike back in order to bring freedom to sunlight' announced Dick Cheney standing beside a rather nervous looking President Bush.
  • Times have changed (Score:2, Interesting)

    by solar_blitz (1088029)
    It seems like two or three years ago nobody cared about research into solar energy, and now every other day an article pops onto slashdot about new ways of harnessing the sun's energy. Must be the Al Gore Effect. I'm not saying it is a bad thing, though.

    As for this particular subject, it makes sense to research beings that already use this type of resource on their own. It would be interesting to see if we can even harvest chlorophyll so we could implant colonies of it onto solar cells. It'd be like the ol
    • by Rei (128717)
      It's only the first stage of plant light capture that's efficient. The entire cycle, from sunlight to sugar, is about 35% -- good, but not that incredible. However, plant cells need energy to live, so you need to look at how efficiently they store energy in a form that is useful to us. The most overall efficient plant at producing human-recoverable energy is sugarcane, at 8-11%. Most crops are a few percent efficient, while most native plants are a small fraction of one percent. Now, if we could harves
    • I've been using photo cells for decades, I'm nearly off-grid now. The reason you see more in the media is because of the economics of using coal, oil, natural gas (non-renewable), and nuclear (renewable but with hideous waste byproducts) fuels: rough economics, enough to cause wars and craziness instead of rational fuel generation plans.

      By rational, I mean the ability to prevent new housing and industry without having renewable fueling system in place and ready to fuel the needs of the new development. Wors
  • by mdsolar (1045926) on Tuesday April 24, 2007 @12:37PM (#18856905) Homepage Journal
    The link to the situation with plants shows how plants work at the quantum level but just a bit of thought shows that we are more efficient than (rooted) plants at collecting solar power. A small area, say all of the roof tops in the country, can cover all of our electric use and more using 15% efficient silicon solar panels. On the other hand, all of the arable land in the US is not enough to cover our transportation needs through biofuels. Plants may be efficient for their own purposes, but in terms of energy harvesting we do better on our own http://mdsolar.blogspot.com/2007/02/photosynthesis .html [blogspot.com]. And, as the article points out, we are on the way to doing even better.
    --
    Sprout Silicon Leaves: http://mdsolar.blogspot.com/2007/01/slashdot-users -selling-solar.html [blogspot.com]
  • shitty solar panels (Score:3, Interesting)

    by jcgf (688310) on Tuesday April 24, 2007 @12:48PM (#18857105)
    I hope this leads to better consumer solar technology. I was looking at those 12V solar panels at Canadian Tire the other day. The ones that produce about half a watt and have a cigarette lighter plug on a wire. Talk about junk. What am I going to do with that? It would not even run my 2m handheld on the low power setting let alone charge your car battery (which is what they were being advertised as doing). I suppose they didn't say how long it would take to charge it so they weren't lying exactly...
  • by pmosh (1092661)
    This could really be a fascinating technology -- although technically it's "nanowires" and not nanotubes. As an experimentalist, I really hope that when it comes to actually growing these things it is feasible; it also might be difficult to make contact to the nanowires after you've made them to collect the electricity. Nonetheless, I think that nanostructured devices (while expensive at the moment) may be the solution to making high efficiency photovoltaics possible. Sometimes it's surprisingly easy to
    • by Goldsmith (561202)
      I'm glad someone else noticed that they didn't actually "make" anything. There are lots of theoretical nanostructures out there, but only so many ways of making them, and even fewer ways of making electrical contact.
  • by necro81 (917438) on Tuesday April 24, 2007 @01:09PM (#18857501) Journal
    There is, as the article mentions, the problem of electron-hole recombination.

    Another difficulty with semiconductor photovoltaics, not addressed by this new development, is that the semiconductors make poor use of energetic photons. There are limitations, derivable from solid-state physics, that limit the maximum light-->electricity efficiency of photovoltaics. A little background:

    Depending on the chemistry, the bandgap energy of the semiconductor corresponds to a photon of a certain minimum energy. A photon with less energy (longer wavelength) than the bandgap energy will not have enough umph to create an electron-hole pair, while a photon with energy >= the bandgap energy can create an electron-hole pair. In silicon-based semiconductors, the bandgap energy corresponds to a photon in the very near infrared, almost a visible red.

    The electrical energy you get from the electron-hole pair comes from those charges being separated by the electrical potential at the semiconductor junction. Unfortunately, it doesn't matter if the electron-hole pair was created by a red photon, a blue photon, or ultraviolet. You'll get the same amount of electrical energy out of the solar cell from any of these photons.

    However, the red, blue, and UV photons have significantly different energies due to their different wavelengths. The UV photon, though more energetic, will produce the same electrical energy output as the less energetic red photon. If you were to shine only red light on the solar cell, it would make quite efficient use of them. Unfortunately, red is only one component of the solar spectrum. The solar cell makes poor use of the higher-energy photons in the solar spectrum, and thus has a seemingly poor light-->electricity conversion efficiency.

    If everything else went perfectly, the solid state physics at work limit the maximum efficiency for silicon solar cells to about 25%. Good cells mass-produced today [sunpowercorp.com] top out at about 21% [sunpowercorp.com]. One can create multiple junction cells to capture different segments of the spectrum at higher efficiency. Consider this chart [wikipedia.org] of maximum efficiency under lab conditions.
    • Re: (Score:2, Interesting)

      by pmosh (1092661)
      True, traditional photovoltaics get the same energy out of every color photon as long as it has enough energy to clear the bandgap. The rest of that energy is lost to vibrations in the semiconductor as heat instead of electrical energy. BUT - here's another area where nanostructured devices might help, because it takes much longer for an energetic electron to emit those vibrations in a structure on the quantum scale (i.e., nanometer scale). These energetic electrons can sometimes be collected at their hi
  • Heating (Score:1, Interesting)

    by BlueParrot (965239)
    Here we go again. Let me sum arise it. -The cheapest, most efficient AND easiest way to collect solar energy is as heat. -If this was cheap enough, people would use solar heating all over the place. -Solar heating remains of limited popularity -If solar heating is not competitive with other energy sources, despite a dramatically lower price than photovoltaics, and despite better efficiencies than are even theoretically possible with photovoltaics, then photovoltaics, which will inevitably be less efficient
    • by dbIII (701233)
      I live in Australia and I see a lot of solar panels. Navigation beacons have them. Ten year old mobile phone repeater towers have them. Electronic signs parked by the side of the road with text on them telling you about roadworks or whatever have them. Give it a few years and low end laptops will have them since all it takes is for the power requirements to drop - remember pocket calculators used to plug into the wall too. As to the other comments - yes I agree that nuclear genorated electicity that is
  • Today the Internet is built with tubes. This takes lots of land, the large tubes require lots of materials, it is difficult to pull a tube to everyone's appartment. Where the normal tubes fail in efficiency, cost, benefit and where they plainly cannot be used the Nanotubes will come to the rescue! Nanotubes don't need as much space as normal tubes, you can use existing infrastructure, for example power lines and sewage pipes to pull the nanotubes right on the surface of the wires or the pipes. Nanotubes
  • I tend to post alot about film because it's something I know. Which is why this is another humorous topic because Film has been dealing with this problem for years!

    When a photon strikes a grain of Silver Halide (AgX, where X is chloride or bromide) it knocks an electron free. This is really a poor process, so people coat the grains with sensitizing dye that increases the area available and helps to shunt the electron (http://en.wikipedia.org/wiki/Cyanine [wikipedia.org]) into the crystal structure. The fastest grains we
  • thats great once i was interested in a solar energy product but there are big hassals in a developing country to cope with but that sounds very interesting since the cells right now are converting only 11-22% of sunlight into energy

  • If the biggest problem for solar is PRICE.
    Then why are they suggesting we use nanotubes, which cost thousands of dollars per teaspoon?

    Might be great for spacecraft, but absolutely worthless for conventional use.

    The four big technologies for PV solar are:
    1. Thinfilm CIGS semiconductor panels
    2. Quantum Dots (Which allow for up to 7 electrons to be created from 1 photon)
    3. Concentrating PV Solar (Using Mirrors)
    4. Titanium Dioxide Organic Dyes
    • by qmeg (1096701)
      The four major PV technologies are in fact 1. Si 2. CdTe thin film 3. CIGS thin film 4. III-V multijunction One could do concentrating PV for 1 and 4. TiO2 dye sensitized solar cell has around 10% lab efficiency and low cost, but generally unstable, thus, not in production. One of the nanowire solar cells is a proposal to improve such solar cell by replacing dye with a semiconductor shell. Quantum Dots (Which allow for up to 7 electrons to be created from 1 photon): not even reaching 1 % efficiency so far

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