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March 20, 2008

Thermoelectric 40% improvement in a cheap material

Researchers at Boston College and MIT have used nanotechnology to achieve a major increase in thermoelectric efficiency, a milestone that paves the way for a new generation of products - from semiconductors and air conditioners to car exhaust systems and solar power technology - that run cleaner.

UPDATE:Info from the Technology Review on how this process is easily and cheaply scaled to tons of material.

"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.

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.


UPDATE: VC's Kleiner Perkins have funded these researchers in a company called GMZ Energy.

GMZ’s breakthrough, actually a technology licensed from the Massachusetts Institute of Technology, is the discovery of materials that can be cheaply manufactured and easily integrated into existing designs, and are also more efficient than other thermoelectric materials. That could both expand the existing thermoelectrics market, and put GMZ in a leading position within it. It’s in the late stages of testing by manufacturers, and the company is gearing up to manufacture about 7 tons of it per year, enough for a few million devices.

One of the many factors holding down the fuel efficiency of today’s vehicles is the amount of energy they dump off as waste heat. A few clever placements of thermoelectric material can capture back up to about a fifth of that heat as electricity and cycle it back into the power system — a perfect application for hybrid vehicles.


High-Thermoelectric Performance of Nanostructured Bismuth Antimony Telluride Bulk Alloys

The dimensionless thermoelectric figure-of-merit (ZT) in bulk bismuth antimony telluride alloys has remained around 1 for more than 50 years. Here we show that a peak ZT of 1.4 at 100 °C can be achieved in p-type nanocrystalline bismuth antimony telluride bulk alloy. ZT is about 1.2 at room temperature and 0.8 at 250°C, which makes these materials useful for cooling and power generation. Cooling devices that use these materials have produced high temperature differences of 86°, 106 °, and 119°C with hot-side temperatures set at 50°, 100°, and 150°C, respectively. This discovery sets the stage for use of a new nanocomposite approach in developing high performance low-cost bulk thermoelectric materials.



The ZT figure of 0.8 to 1.4 means about 8-15% recapture of energy from heat. Get ZT up to 10 and things get really interesting. But capture 8-15% cheaply and that can be very good too.



A cross-section of nano-crystalline bismuth antimony telluride grains, as viewed through transmission electron microscope. Colors highlight the features of each grain of the semiconductor alloy in bulk form. A team of researchers from Boston College and MIT produced a major increase in thermoelectric efficiency after using nanotechnology to structure the material, which is commonly used in industry and research. Image / Boston College, MIT, and GMZ Inc.


The team’s low-cost approach, details of which are published today in the online version of the journal Science, involves building tiny alloy nanostructures that can serve as micro-coolers and power generators. The researchers said that in addition to being inexpensive, their method will likely result in practical, near-term enhancements to make products consume less energy or capture energy that would otherwise be wasted. Using nanotechnology, the researchers at BC and MIT produced a big increase in the thermoelectric efficiency of bismuth antimony telluride — a semiconductor alloy that has been commonly used in commercial devices since the 1950s — in bulk form. Specifically, the team realized a 40 percent increase in the alloy’s figure of merit, a term scientists use to measure a material’s relative performance.


FURTHER READING
I have provided extensive and in depth coverage on the impact that better thermoelectrics will have.

ThermoCeramix makes materials with a much higher “emissivity”, meaning they’re more efficient at heating up. These materials have some obvious uses in everyday household appliances like those I just mentioned, as well as commercial processes.

So imagine, instead of having a centralized water heater in your house, having a bit of ThermoCeramix material wrapped around the pipe in your faucet. When you turn on the hot water tap, it heats up instantaneously.


Being more efficient at converting heat into usable work is hugely important, especially if it can be done for large power plants and vehicles.

In 2005, world primary energy consumption was 462.798 quadrillion Btus. Thus, daily world energy consumption was 1.27 x 10^15 Btus. One barrel of oil contains 5.8 x 10^6 Btus. Therefore, in 2005, the daily energy consumption was 219 million barrels of oil equivalent.

If we divide the world daily primary energy consumption of 1.27 x 10^15 Btus by the daily Btu production from one average nuclear plant (240 x 10^9), we find the world consumed the equivalent amount of energy from about 5,300 nuclear plants each day in 2005.

A typical car engine is only 20% efficient and a typical steam power plant (used primarily by coal and nuclear plants) is only 33% efficient. This means that only a fraction of the heat created is turned into usable energy.


If thermoelectrics can increase those efficiencies by 10-50% that would clearly be huge.

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