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Thursday, March 20, 2008 Cheap, Efficient ThermoelectricsNanomaterials could be used for lower-emission cars and solar panels.
Thermoelectric materials promise everything from clean power for cars to clean power from the sun, but making these materials widely useful has been a challenge. Now researchers at MIT and Boston College have developed an inexpensive, simple technique for achieving a 40 percent increase in the efficiency of a common thermoelectric material. Thermoelectric materials, which can convert heat into electricity and electricity into heat, hold promise for turning waste heat into power. But thermoelectric materials have not been efficient enough to move beyond niche applications. The new jump in efficiency, achieved with a relatively inexpensive material, may finally make possible such applications as solar panels that turn the sun's heat into electricity, and car exhaust pipes that use waste heat to power the radio and air conditioner. The researchers started with bismuth antimony telluride, a thermoelectric material used in niche products such as picnic coolers and cooling car seats. Then Gang Chen, a professor of mechanical engineering at MIT; Institute Professor Mildred Dresselhaus; and Boston College physics professor Zhifeng Ren crushed it into a powder with a grain size averaging about 20 nanometers, and pressed it into discs and bars at high heat. The resulting material has a much finer crystalline lattice structure than the original material, which is made up of millimeter-scale grains. Chen and Ren's nanocomposite formulation of the material is 40 percent more efficient than the conventional form of the material at 100 °C, and it works at temperatures ranging from room temperature to 250 °C. "Power-generation applications [for thermoelectrics] are not big now because the materials aren't good enough," says Chen. He believes that his group's more efficient version of the material will finally make such applications commercially viable. Thermoelectric materials must be able to maintain a heat gradient, which means that they must be good conductors of electrons and good thermal insulators. When one end of a bar of thermoelectric material is heated, electrons move from the hot side to the cold, creating an electrical current. If a material conducts heat well, this current-generating temperature gradient will dissipate. Unfortunately, in most bulk materials, electrical conductivity and thermal conductivity "go hand in hand," says John Fairbanks, who heads thermoelectrics efforts in the Department of Energy's Vehicle Technologies Program. One approach to making better thermoelectric materials has been to build nanostructured materials from the bottom up. Interfaces in these materials reflect the flow of heat without impeding electrical current. Researchers who have grown arrays of silicon nanowires, pressed silicon and germanium nanowires into millimeter-scale bars, and tested single organic molecules have had success on a small scale, but making such materials in bulk is a major hurdle. The researchers' nanocomposite technique creates many interfaces in the material that reflect thermal vibrations, says Chen. Peidong Yang, a professor of chemistry at the University of California, Berkeley, says that the work is "a great example of how defect engineering can significantly impact on the [vibration] transfer in solids." Ren says that it's easy to make large amounts of the nanocomposite material: "We're not talking grams; we're not talking kilograms. We can make metric tons." Because bismuth antimony telluride is already used in commercial products, Ren and Chen predict that their technique will be integrated into commercial manufacturing in several months. |
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Heating Plug-in Hybrids
04/14/2008
Comments
TragicComic on 03/20/2008 at 3:41 PM
2
daveorbit2 on 03/20/2008 at 4:15 PM
2
Katherine Bourzac on 03/21/2008 at 10:04 AM
Associate Editor
7
MakeSense on 03/21/2008 at 5:43 PM
61
nekote on 03/21/2008 at 6:52 AM
109
Both heating and cooling?
250 degrees C likely the final upper limit?
Lining the inside or outside of exhaust tailpipes of ICE (Internal Combustion Engines) with it?
Make it into a "bandage" / "tape" that can be wrapped around hot pipes?
Longevity / life span / robustness / durability?
"Wears like iron" / Tough? Fragile / brittle?
Toxic?
Metal flues / chimneys?
Including industrial / electric power plants?
What sort of Voltage, Amperage, Wattage / power is under consideration?
DC, of course?
10W? 100W? 500W?
What other materials are under consideration for this nano particle "composite" technique?
Katherine Bourzac on 03/21/2008 at 10:09 AM
Associate Editor
7
Siphon on 03/21/2008 at 9:23 AM
65
These offer more perspective than PV because storing heat is comparatively simple and cheap. Hot water, ionic liquids and higher temparature molten salts, and solid media are very promising developments.
It may be possible to replace the power block of thermal plants (nuclear, solar thermal, geothermal) with a block of layered nano antennas to radically improve thermal to electric conversion (and thus, electrical output).
For this application, higher temperature would be beneficial as the radiative emissivity (which is actually what we want for this application as the radiation is in the infrared bandgap) goes up to the fourth power of the absolute temperature difference.
There are some problems to be solved with regards to converting the electrical power to useful qualities for grid applications, but the advantages of possible low cost and very high efficiency plus the path to inexpensive dispatchability make it worth a serious try.
Katherine Bourzac on 03/21/2008 at 10:06 AM
Associate Editor
7
Siphon on 03/22/2008 at 11:51 AM
65
Clearly, progress is being made, but I'm not sure if it's enough to really mean something for solving energy problems.
Reptile on 03/22/2008 at 4:22 PM
4
Could also increase efficiencies of the units that focus sunlight on a medium that boils and drives turbines--forget what they're called. Both the bottom/reverse of the collectors and especially the condenser systems are possibilities. But price?
Perhaps too much to expect in these short articles, but an indication of of absolute price guesstimates and current efficiencies with current devices would be helpful, as others have commented.
And is it true that the current devices have, in truth, a one percent energy conversion efficiency? Or is it that the conversion UNIT of existing systems is regarded as a unity but that the current efficiency percentage is different--higher or lower? The way I read an above comment is that these new devices at this point may have a 2 percent thermal efficiency. Again, apply this system to the bottom of a silicon (or other) PV device and it would appear to increase power output per unit area by at least 10 percent. If so, and again, price is all.
bkf11 on 03/22/2008 at 12:26 AM
5
zig158 on 03/22/2008 at 3:34 AM
42
I think it will be carbon that makes all the difference. Carbon can be hard and a very good electric insulator, or very soft and a good electric conductor depending on how the atoms are arranged. When we gain the ability to design and build custom carbon structures, every thing will be different.
zippo on 03/22/2008 at 2:11 PM
24
hachi on 03/22/2008 at 10:19 PM
16
ctasser on 03/29/2008 at 2:50 PM
1
Considering, that Cassini is still traveling in outer space powered by nuclear power/thermo-electrics.
In Germany I have heared about a new TEG module design.
We should finally see some interesting developments in this sector, after 40 years...
kavli on 03/30/2008 at 11:49 AM
1