Nanotubes May Improve Solar Energy Harvesting 93
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."
Concentrating existing power also important (Score:3, Interesting)
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:Concentrating existing power also important (Score:3, Interesting)
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.
Re:Wrong headline (Score:5, Interesting)
nanotube antenna design (Score:4, Interesting)
Times have changed (Score:2, Interesting)
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.
shitty solar panels (Score:3, Interesting)
What do you do with the incoming 500THz signal (Score:3, Interesting)
2. Phase shift it to create a beam-former
3. The compare it to a local or global reference signal to extract phase information
A different problem with photovoltaics (Score:3, Interesting)
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.
Heating (Score:1, Interesting)
Re:A different problem with photovoltaics (Score:2, Interesting)
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.