Nanotubes May Improve Solar Energy Harvesting

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."

Comments

Concentrating existing power also important

[pzs]

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

Re:Concentrating existing power also important

[Rukie]

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 have been on slashdot?) We definitely have the ability, were just willing to spend the resources.

Re:Concentrating existing power also important

[TheMeuge]

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.

Re:Concentrating existing power also important

[Pxtl]

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.

Wrong headline

[rumblin'rabbit]

The proper headline should be "global warming solved for 3rd time this week".

Re:Wrong headline

[grungebox]

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:Wrong headline

[Rei]

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.

Re:Wrong headline

[PPH]

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!

Centralization is the wrong way to go

[StefanJ]

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 means addressing political, social, and security externalities that have been ignored thus far.

Re:Centralization is the wrong way to go

[Rei]

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.

Only 5 Years Away

[Nom du Keyboard]

And I'm sure this is only 5 years away from commercial use, just like every other such announcement.

nanotube antenna design

[G4from128k]

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.

Hmm

[tttonyyy]

"Hope", "may" and "unfortunately" all in one article.

It's like reading about Duke Nukem Forever.

Just the small matter of tdynamics and economics..

[Ancient_Hacker]

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.

OK, I have the middle steps

[gmcraff]

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

In other news

[Timesprout]

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

[solar_blitz]

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.

Plants have us beat?

[mdsolar]

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. 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

shitty solar panels

[jcgf]

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...

Re:shitty solar panels

[mdsolar]

Definitely not a jump start! That takes the highest current draw of all. These things are good if you leave a vehicle parked for a long time. They keep the battery topped off.

What do you do with the incoming 500THz signal

[G4from128k]

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

This depends

[mdsolar]

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

Re:This depends

[QuickFox]

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.

Nanowires (not nanotubes)

[pmosh]

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 grow nanowires/nanorods just by flowing gas over a material and a substrate in a tube furnace, so cost may turn out to be fairly low. Patterning these by photolithography (how computer chips are made) would definitely be too expensive, along with molecular beam epitaxy or atomic layer deposition. My hope is that a simple inexpensive thermal process would work to grow these or other photovoltaic nanorods. The reason that so many stories are posted about solar energy is that it's our one scaleable renewable energy that could eventually displace a significant fraction of the fossil fuel energy that we currently use and spew CO2 into the air. For a really interesting lecture about world energy and alternatives check out Dr. Nate Lewis' presentation at http://nsl.caltech.edu/energy.html (the video is probably the best). Who knows, one of these breakthroughs if it works well could change a lot for us.

A different problem with photovoltaics

[necro81]

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.

Re:A different problem with photovoltaics

[pmosh]

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.