Carbon Nanotube Towers Could Increase Solar Power

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."

Comments

Even better

[nizo]

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!

Re:Even better

[Game_Ender]

That would be cool if only that pesky photo din't get absorbed ;)

Re:Even better

[PitaBred]

"In this house, we obey the laws of thermodynamics!" - Homer S.

Re:Even better

[Umbral Blot]

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

[Issue9mm]

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-

Re:Even better

[Anonymous Coward]

Like your 'n' got absorbed?

Small problem

[winstonmeister]

"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.

But what could you do...

[Fitzghon]

... with a Beowulf cluster of these things?

Fitzghon

Carbon Nanotubes....in towers?

[eddiegee]

So where's my Space Elevator?

Re:Carbon Nanotubes....in towers?

[Rei]

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.

Slightly OT

[frankthechicken]

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

[Rei]

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.

But not word...

[davecrusoe]

"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.

Re:But not word...

[Adeax]

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.

Re:But not word...

[gmcraff]

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 solution will be a military advantage.

Secondly, because the military will accept a sub-optimal solution if it addresses the primary problem really well, or if it addresses a previously unaddressed problem. Consider the WWII company radio. It was expensive, heavy, bulky, the range wasn't very good, the transmission quality was horrible and it was fairly fragile. There was probably a very high failure rate in the manyfacturing process. It required a dedicated soldier to bear and operate it, to the exclusion of food and ammo, which reduced his combat effectiveness and survivability. It was recognizable from a distance, which made him target number one for snipers.

All that being true, a company with a radio was part of an army. A company without a radio was a isolated group of men without support or supply that would surely only last a single firefight, if that. As technology developed, the radio got lighter, cheaper, more reliable, and encrypted. Soon it was affordable to equip a platoon with a radio, then individual squads. At a certain point along this progression, the technology really took off to the civilian market once it was cheap, reliable and small enough for, say, an important business person to have a brick-size device. With the new influx of money from a consumer market, the radios became smaller and cheaper until just about every one of us has a personal radio: the cell phone.

So, while you beat your breast and cry out to the cosmos, "Why does all the technology has to have military purposes first," remember that the military purposes will wring bugs out of the technology, establish an industrial base from which to launch into the civilian market, and provides a "reference" that business can rely on. If you try to jump straight into the civilian market with a buggy technology, no problems-solved stories and no industrial base, you'll be out of business like a dot-COM unless you have VERY deep pockets, or very stupid/very far-sighted (HA!) venture capitalists.

20 um vertical structures?!?

[Sebastopol]

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

[grqb]

So far this week we've had quite a bit of solar news...solar power airplane to fly around the world, another breakthrough in solar power that brings the price of solar from $8/watt to about $1/watt 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.

Make solar cells like leaves not like guts !

[mishmash]

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.

Controlled growth of Carbon nanotubes

[karvind]

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 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.

Re:Controlled growth of Carbon nanotubes

[phoenixTMW]

No one has been able to grow vertical carbon nanotubes individually without support. Problem is, when the tubes get too long, they flop over. In these columns, the tubes help support each other.

Re:Why are solar cells shiny?

[Doc Ruby]

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.

Yeah.

[Grendel Drago]

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

Re:Why are solar cells shiny?

[k98sven]

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 else does?

Hmm....

[Squirmy McPhee]

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.