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Carbon Nanotube Towers Could Increase Solar Power

Posted by Zonk on Tue Mar 01, 2005 06:19 PM
from the tiny-towers-of-power dept.
Science Technology
Vict0r writes "Researchers at the Georgia Tech Research Institute have recently demonstrated a way to grow carbon nanotubes in towers. The article also discusses applications for solar cells." From the article: "Reflections off the Gothamesque towers would provide more opportunity for each photon of sunlight to interact with the p/n junction of the cell. That would increase the power output from PV cells of a given size, or allow cells to be made smaller while producing the same amount of power."
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  • Even better (Score:5, Funny)

    by nizo (81281) * on Tuesday March 01 2005, @06:21PM (#11817921) Homepage Journal
    Reflections off the Gothamesque towers would provide more opportunity for each photon of sunlight to interact with the p/n junction of the cell.

    We need mirrored solar cells. Just set them up so they reflect the light back and forth between all the cells for a neverending unlimited source of energy!

    • That would be cool if only that pesky photo din't get absorbed ;)
    • "In this house, we obey the laws of thermodynamics!" - Homer S.
    • Obviously, you'd have some energy loss.... but mostly, why wouldn't this work? I'm not scientist or electrical engineer, but I would think you could point a light beam from the sun using mirrors into a chamber full of mirrors and that also had solar panels in it.........

      • Re:Even better (Score:4, Informative)

        by Umbral Blot (737704) on Tuesday March 01 2005, @06:26PM (#11817989) Homepage
        Because solar panels take energy from the light to produce electricity. You can only extract so much energy from a given photon.

      • Re:Even better (Score:5, Informative)

        by Issue9mm (97360) on Tuesday March 01 2005, @06:28PM (#11818004) Homepage
        Because, as is the point, the solar panels ABSORB the light, not reflect it back. I don't have any hard numbers, but as PV cells are designed specifically to absorb sunlight, let's assume they do this pretty well. While some (let's say 20%) of a ray of sunlight is reflected back into the chamber, it would surely be caught by the next PV cell and absorbed wholly (unless, possibly, that PV cell is already working at maximum absorption, which, if is the case, negates the point of bothering to reflect in the first place.)

        -9mm-
      • Because evil gnomes will sneak in when you're not looking and hold their hands between the mirrors to block the light and foil your plans, obviously.
        • Mirrors have a cost, to use a mirror to reflect the nominal light reflected off of a solar cell back into the solar cell would never be as cost effective as using the same mirror to reflect the much higher energy of direct sunlight onto the cell.

          At some point the additional cost of higher effeciency isn't the best use of materials.

          30% effeciency is a workable number - and the cost of energy isn't affected as much by doubling this number as it is by other concerns, such as tracking the sun, storing the ene

    • Make solar cells like leaves not like guts ! (Score:5, Interesting)

      by mishmash (585101) on Tuesday March 01 2005, @07:02PM (#11818337) Homepage
      No. If surface area mattered then leaves (nature's way of capturing solar energy) would have folds and protrusions like the gut does to increase surface area. What leaves do is make sure that some of the light gets through to the next layer. This happens both in an individual leaf - light is not caught just at the top surface but all the way through the leaf. Also a leaves don't trap all the available light, some is left for leaves below - it's totally dark walking through a forest. Make the solar cells more transparant - thats the way to get the effect of increased surface area the article referes to.

  • Small problem (Score:5, Funny)

    by winstonmeister (863683) on Tuesday March 01 2005, @06:23PM (#11817944)
    "Reflections off the
    Gothamesque towers would provide more opportunity for each photon of sunlight to interact with the p/n junction of the cell.
    Unfortunately, Batman tends to work at night, so solar cells won't be of too much help.
    • Maybe they could convert the batmobile to hydrogen, and use the solar for disassociation of water. Personally, I'd like to see this made into a portable nitrous oxide manufacturing machine. It could at least provide the power, and everything you need is present in air if you can figure out a way to separate out nitrogen, too. :)

  • But what could you do... (Score:5, Funny)

    by Fitzghon (578350) on Tuesday March 01 2005, @06:24PM (#11817958)
    ... with a Beowulf cluster of these things?

    Fitzghon

  • Carbon Nanotubes....in towers? (Score:4, Interesting)

    by eddiegee (236525) on Tuesday March 01 2005, @06:24PM (#11817962)
    So where's my Space Elevator?
    • I was wondering whether or not you could use this technology to grow cables for a space elevator. If you could get a spiral form going, it might be able to spew out cable (okay, it would probably be too slow to be called "spew") pre-formed.

      • Re:Carbon Nanotubes....in towers? (Score:5, Interesting)

        by Rei (128717) on Tuesday March 01 2005, @06:51PM (#11818194) Homepage
        No. The problem with tubes this small is that there is insufficient van der waals force holding them together; the tubes are strong, but the force keeping them as a single bundle isn't. And probably won't be unless we can produce quite large tubes. One alternative is that, under high pressures, nanotubes interlink and trade their strong sp2 bonds (graphite) for weaker, but still quite strong sp3 bonds (diamond) between tubes. In theory, these interlinked ropes (not really nanotubes, but a new material) should be quite producable once regular vdw-bonded nanotube ropes without any sort of binder in them become producable and affordable.

        There's another problem with space elevators, though: not only would interlinked tubes prove somewhat weaker than non-interlinked tubes in all likelyhood, but non-interlinked SWNTs proved rather weak in direct tensile strength tests. One test that I read about had a maximum strength of just over 60GPa, instead of the >100 typically called for to produce a reasonable space elevator on Earth. Now there are many different types of SWNTs depending on how the graphite is rolled up, so they could vary, but signs don't look good.
          • Unfortunately, that won't work - these will be denser. The two critical factors for keeping the distance-to-width-doubling low for a space elevator: material density and tensile strength. Lets say that these are twice as dense. If the tensile strength is the same but the density is doubled, the distance between width-doublings of the cable is halved, which means that the cable has to double in width twice as many times, which is generally a completely unacceptable situation.

            Still, they're interesting :)
          • And let me tell you, those bundles are pretty tough to exfoliate, at least from a chemical standpoing

            Unfortunately, not from a tensile strength standpoint. The strongest nanotube rope strengths I've read about simply used nanotubes in a binder, and were about as strong as kevlar. Pure nanotube ropes tended to be under 1GPa, if I'm remembering the articles I've read correctly.

  • Slightly OT (Score:4, Interesting)

    by frankthechicken (607647) on Tuesday March 01 2005, @06:24PM (#11817963) Journal
    For soldiers operating in the field, especially in desert areas that receive lots of sunlight, the new "solar tube" cells could provide an alternate power source for the growing number of electronic devices they use

    Given the amount of energy this "growing number of electronic devices" probably puts out, doesn't it make the slodiers easier to spot due to the energy signatures they are putting out? If so, doesn't it slightly impact on the actual usefulness of the electronic devices?

    I'm guessing this is factored in, but how much shielding is possible, and how far would the new "solar tube" be able to be shield it's energy signature from the enemy?

    • Re:Slightly OT (Score:5, Interesting)

      by Rei (128717) on Tuesday March 01 2005, @07:00PM (#11818300) Homepage
      I'd actually been thinking about that. For example, picture the speaker on a communications device. Speakers give off a lot of EMF (they're effectively a big fluctuating electromagnet pulling on a diaphragm) - even shielded ones are generally pretty easy to detect and tell what sound was coming from the speaker. CRT monitors (not that common on portables) pump out lots of EMF, too (run "Tempest for Eliza" some time - you don't even need a sensitive directional antenna to listen in). I've read about keyboards have been tempested from over 50 feet away.

      What good is an encrypted signal when the people that you're hunting in a city have a good parabolic antenna pointed at you through a wall that they're hiding behind and are listening to the signal from your radio? Heck, they don't even need to know what you're saying, just that you're there.

      Of course, pretty much everything about warfare would be a heck of a lot harder if the US actually fought a *real* enemy instead of collapsing third-world nations armed with reject Soviet equipment from the 1950s and 1960s.
    • For soldiers operating in the field, especially in desert areas that receive lots of sunlight, the new "solar tube" cells could provide an alternate power source for the growing number of electronic devices they use

      Woah, let's back it up a bit here - if we have a more efficient form of generating electricity, we will reduce the cost of producing hydrogen which will make it cheaper and more viable to move to a hydrogen economy so we won't need all these soldiers in desert countries protecting the oil^h^h^h
    • I'm guessing it's factored in, but honestly, soldiers put out kilocalories of EM in the infrared range already; it's called BODY HEAT. The few additional watts from electronic devices are probably not going to make that big of a difference, unless you're a pathfinder or something...

  • But not word... (Score:5, Interesting)

    by davecrusoe (861547) on Tuesday March 01 2005, @06:27PM (#11817996) Homepage
    "For soldiers operating in the field, especially in desert areas that receive lots of sunlight, the new "solar tube" cells could provide an alternate power source for the growing number of electronic devices they use. Without the need for trucking in fuel, compact PV cells could directly power certain applications or be used to recharge batteries in soldiers' equipment..." But, no word about innovative residential or consumer uses for the material? What about powering mobile computing systems for rural schools in India, or for use in purifying water in Africa? Sigh.
    • The three-dimensional cells could also be useful in space applications, where power is in constant demand and launch weight is critical. Ultimately, they also could be used in developing nations where low-cost electrical power is vital to expanding economies.

      Missed this paragraph, did you?
    • What about powering mobile computing systems for rural schools in India, or for use in purifying water in Africa?

      Until India and Africa come up with the money to drive this technology, they'll have to wait for those that are actually paying for it to develop it.

      Sigh.
    • Powering mobile computing systems for rural schools in India isn't mentioned because the rural school system of India isn't paying for the research - the DoD is.
    • Remember that a lot of technologies start in military applications long before they move out to civilian use.

      Why is this?

      Firstly, because military problems attract money. Privates bitch to Sergeants, Sergeants bitch to Captains, Captains bitch to Colonels, Colonels bitch to Generals, Generals bitch to Congress, who has the people's money. If a private is too hot, too cold, too vulnerable, lacking ammo, too slow, too visible, etc, it becomes a problem that the Generals will address in order that the so

      • That's because the military contractors have control of hundreds of billions in unaccountable budgets. So we have to wait while their braindrain sucks up the innovators, then maybe kills a lot of people so they can't keep it secret anymore, then we can get started on consumer apps. That's pretty wasteful.
        • If we maintain the mindset that military applications drive innovation, then that's all we'll receive.
          The military is just the ultimate "early adopter" of technology. The underlying research and science is driven by educational institutions.
          One of the reasons the military is such a driving force in innovation is because, like the space program, they are constantly trying to solve problems at the "extremes". Questions like "what if half the country was nuked" was one of the main reasons for the decentra
          • One of the reasons the military is such a driving force in innovation is because, like the space program, they are constantly trying to solve problems at the "extremes".

            Another is that they have lots of money. I imagine if we funded the department of education the way we funded the military, we might have all sorts of research grants for building new education tools.
            • I imagine if we funded the department of education the way we funded the military, we might have all sorts of research grants for building new education tools.
              I doubt it, while the problems for military applications are complicated, they are easy to identify. While I agree schools are under funded, what exactly innovative would you get with $40 billion more in education? Building more schools and hiring more teachers is not innovative. If you're thinking giving more money to universities to do research

  • 20 um vertical structures?!? (Score:4, Interesting)

    by Sebastopol (189276) on Tuesday March 01 2005, @06:47PM (#11818159) Homepage

    preface: my nanotech is limited to semiconductor process only.

    looking at the image, the towers appear to be 20um cubes, and the tubes look incredibly uniform. That is some impressive feat to build such a tall structure!

    this makes me think of 3D model creation tools that use a laser and a tank of epoxy-like goop to 'draw' a 3D prototype of a design.

    can this accomplishment be extended to this technique to "render" nanodevices (er, microdevice machines), out of tubes?

  • a lot of solar news lately (Score:5, Informative)

    by grqb (410789) on Tuesday March 01 2005, @06:48PM (#11818172) Homepage Journal
    So far this week we've had quite a bit of solar news...solar power airplane to fly around the world [thewatt.com], another breakthrough in solar power that brings the price of solar from $8/watt to about $1/watt [thewatt.com] and now this...hmmm I should get into this business it seems!


    Carbon nanotubes are also all over the map these days so why not nanotubes and solar? I guess we'll have to wait a while until this becomes commercial though because I don't think carbon nanotubes can be scaled up very easily.

    • Yeah. (Score:3, Interesting)

      by Grendel Drago (41496)
      And I'm sure we'll have solar as a major component of distributed power generation right after that commercial fusion plant gets built.

      --grendel drago
      • One irony,

        Effecient solar energy is dangerous.

        Any solar collector in the hands of a moron could evaporate a target. You think ants have it bad - wait until your average home solar dish blows a gear and the focal point drifts into something else.

        BAM

        AIK
  • Can someone tell details about how they do it ? The sighted news articles doesn't give any details. Can they grow individual carbon nanotubes vertically ? There had been earlier work on controlled alignment of carbon nanofibers [aip.org] from ORNL folks. Their technique could grow the nanotubes in different directions using electric field. There is also an option of controlling the direction of growth using polarized light.

    If precise formation as well as placement can be achieved, it will get over the biggest hurdle in getting into the electronics. There are still other issues (eg. contacts, surface adsorbtion etc) to be addressed though.

  • Hmm.... (Score:3, Insightful)

    by Squirmy McPhee (856939) on Tuesday March 01 2005, @08:17PM (#11819172)
    The nanometer-scale scale towers, which would be coated by the special p-type and n-type semiconductor (p/n) junction materials used to generate electrical current, would increase the surface area available to produce electricity.

    Generally, increasing surface area on solar cells is detrimental to producing electricity, particularly if the semiconductor material is very thin. (Yes, I am well aware that it is more than counteracted by the additional light coupled into the cell, but the writer makes it sound as though increasing surface area is a magical formula for making more power. And the increase in surface area, by itself, is still detrimental.) I would very much like to know what are the "special" semiconductor materials they plan to coat the towers with.

    I don't think this is so much a breakthrough as it is just another in a long line of textured substrates for thin-film solar cells that don't even work yet and won't be hitting the market for another 10 years.

    Because their cells will be more efficient, Ready believes they can use older and more mature p/n-type material technologies and less costly silicon wafers to hold down costs and rapidly advance the project into products that can be used in the field.

    If he is going to use silicon wafers as simple substrates then his cells had better be substantially more efficient than standard crystalline silicon solar cells -- otherwise, he is guaranteed to be priced out of the market. Silicon wafers make up half the cost of a solar module, and the module materials and assembly make up another 30-35%. Assuming he can actually deposit these nanotowers and their semiconductor coatings at a cost similar to that of converting a silicon wafer to a silicon solar cell, it doesn't give him much choice but to leverage efficiency to get a lower cost per watt.

    • How hot do solar cells get? Would it be worth it to be a combined PV/water heating solar setup? I wonder if you could get useful efficiency out of the panel if it were under an inch of water and a sheet of greenhouse plastic. Barring that, I guess you could attach it to a water block, but that sounds more expensive.
      • Nah ... the algae growing in the tank would cut down solar efficiency too much.
      • No, all the heat energy in the PV should be going into accelerating electrons to the cathode instead. Any heat is waste, inefficiency, and powering a cooler just consumes more energy from the net. Besides, silicon solar cells get more efficient per incident watt as they heat up - a catch-22 that should be broken by making cells with a different nanoarchitecture which captures more of the incident power.
      • Actually, you sometimes do see solar cells mounted on heatsinks, so your idea isn't as outlandish as some would think. Generally, these cells are mounted this way only when used with an active sun tracking system and a lens concentrator in front of them (generally a fresnel) to collect more light and focus it on the cell. Since you are concentrating the light, heat becomes a real problem (think burning ants), so it needs to be dumped somehow, and this is typically accomplished via alluminum heatsinks. They
    • Oh yeah. Solar cell should work in the infrared! Why hasn't anyone ever thought of that?

      Oh wait.. they have. And it simply can't be done with the solid-state solar cell technology of today. You can't have a bandgap that small and get a current.

      And yes, of course there is a lot of research going on in this.

      So, what is the point of your comment? Do you mean to say that you have a solution noone knows about, or are you bitching about the state of solar cells today because you think you know something noone
      • Solar cells are shiny and hot. They'll be more efficient when they're black and cold. What's so wrong about mentioning that in a discussion of breakthrus in solar cell material science? In fact, what's wrong with you just answering "current tech doesn't allow bandgaps in infrared, so they waste heat"? Do you have a shiny, hot solar cell stuck up your ass or something? BTW, smartass, they're not shiny because of anything infrared, unless your species has bugeyes in addition to rectally consuming silicon.
    • Actually if you think about it, it is no less than a tower

      A typical carbon nanotube is ~1-5 nm in diameter. A 2 micrometer long nanotube means an aspect ratio (length/height to diameter) of almost 1000. Even the tallest skyscraper don't go beyond 7:1. WTC had height to width ratios of 6.49 to 1. Bank of American plaza has the highest with 7.24 to 1.

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