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Nanotubes May Improve Solar Energy Harvesting

Posted by Zonk on 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."

10 of 93 comments (clear)

  1. Concentrating existing power also important by pzs · · Score: 3, Interesting

    If you believe these guys:

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

    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

    1. Re:Concentrating existing power also important by TheMeuge · · Score: 2, Interesting

      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 the U.S. was covered with solar panels, we'd have a large part of the solution already figured out. Plus, we'd be largely immune to isolated grid problems, resulting in less power outages.

  2. Re:Wrong headline by grungebox · · Score: 4, Interesting

    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.

  3. nanotube antenna design by G4from128k · · Score: 3, Interesting

    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.

    --
    Two wrongs don't make a right, but three lefts do.
  4. Times have changed by solar_blitz · · Score: 2, Interesting

    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 old potato and light bulb science project kids do.

  5. shitty solar panels by jcgf · · Score: 2, Interesting

    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...

  6. What do you do with the incoming 500THz signal by G4from128k · · Score: 2, Interesting

    1. Rectify it for power
    2. Phase shift it to create a beam-former
    3. The compare it to a local or global reference signal to extract phase information

    --
    Two wrongs don't make a right, but three lefts do.
  7. A different problem with photovoltaics by necro81 · · Score: 2, Interesting

    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 top out at about 21%. One can create multiple junction cells to capture different segments of the spectrum at higher efficiency. Consider this chart of maximum efficiency under lab conditions.

    1. Re:A different problem with photovoltaics by pmosh · · Score: 2, Interesting
      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 high energy or kick up another electron across the bandgap through Auger recombination. This has been demonstrated a few times for nanometer-sized semiconductor particles called quantum dots and is called "hot electron capture" or "multiple exciton generation" in the scientific literature.


      What I'm trying to say is that nanorod structures have the potential of increasing the maximum efficiency because they might be able to collect those higher energy photons and pull out more electricity than a conventional photovoltaic cell.

      Hopefully this will be practical someday...the multijunction cells are just way too expensive how they are currently made.

  8. Heating by BlueParrot · · Score: 1, Interesting

    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, more expensive, and less durable, is not going to be competitive. EVER. The ONLY way solar energy can become competitive is for the price of other forms of energy generation to sky-rocket. Whereas this may be true for fossil fuels, nuclear, wind, hydro, geothermal and biomass are not set to become more expensive any time soon. On the contrary, developments in reactor technology is set to make nuclear costs comparable to gas ( and that includes waste disposal and decommissioning ). Wind power is seeing improvements as we speak. Geothermal is not set to get any more expensive, and biomass is already competitive with fossil fuels. Solar simply doesn't stand a chance. Even if solar cell's were as cost efficient as solar heat collectors, they would still lose out compared to the alternatives. Solar cells are good for remote applications where you can't stick a power plant, like in an orbiting satellite. For pretty much everything else they are rubbish.