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World’s most efficient thermoelectric material developed

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September 20, 2012

Thermoelectrics can be used to convert energy currently lost as heat wasted from industry ...

Thermoelectrics can be used to convert energy currently lost as heat wasted from industry and vehicle tailpipes into electricity (Photo: Shutterstock)

Approximately 90 percent of the world’s electricity is generated by heat energy. Unfortunately, electricity generation systems operate at around 30 to 40 percent efficiency, meaning around two thirds of the energy input is lost as waste heat. Despite this, the inefficiency of current thermoelectric materials that can convert waste heat to electricity has meant their commercial use has been limited. Now researchers have developed a thermoelectric material they claim is the best in the world at converting waste heat into electricity, potentially providing a practical way to capture some of the energy that is currently lost.

The new material, which is based on the common semiconductor telluride, is environmentally stable and is expected to convert from 15 to 20 percent of waste heat to electricity. The research team, made up of chemists, material scientists and mechanical engineers from Northwestern University and Michigan State University, say the material exhibits a thermoelectric figure of merit (or “ZT”) of 2.2, which they claim is the highest reported to date.

The higher a material’s ZT, the more efficient it is at converting heat to electricity. While there’s no theoretical upper limit to ZT, no known materials exhibit a ZT higher than 3. The researchers believe with a ZT of 2.2, the new material is efficient enough to be used in practical applications and could usher in more widespread adoption of thermoelectrics by industry.

"Our system is the top-performing thermoelectric system at any temperature," said Mercouri G. Kanatzidis, who led the research. "The material can convert heat to electricity at the highest possible efficiency. At this level, there are realistic prospects for recovering high-temperature waste heat and turning it into useful energy."

With the huge potential for thermoelectrics to recover some of the heat energy that is currently lost, they have been the focus of much research that has seen them improve significantly in recent years. So much so that the Mars rover Curiosity features lead telluride thermoelectrics, although its system only has a ZT of 1. BMW is also testing systems to harvest the heat from the exhaust systems and combustion engines of its cars.

Aside from capturing some of the wasted heat energy emitted through a vehicle’s tailpipe, the new material could be used in heavy manufacturing industries, including glass and brick making, refineries, and coal- and gas-fired power plants, and on large ships and tankers, where large combustion engines operate continuously. Such applications are seen as ideal as the waste heat temperatures in these areas can range from 400 to 600 degrees Celsius (750 to 1,100 degrees Fahrenheit),which is the sweet spot for thermoelectrics use.

The team’s paper describing the development of the new material is published in the journal Nature.

Source: Northwestern University

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
10 Comments

Please check my math and estimate;

assuming a 100 hp car engine and 35% efficiency in that engine, 15% lost to drive train, leaving 50% heat loss.

If a unit was built to capture as much heat as possible - say 50% of that;

then:

.5 * 100 hp * .5 * 640 watts/hp * 15% efficiency of thermoelectric material / 13.2 volts = 181 amps available for: battery charging and running all the electric items in the car: lights, radio, etc.

ought to work!

notarichman
20th September, 2012 @ 10:05 am PDT

I heard that ICEs operated roughly in 1/3s: 1/3 of the energy goes out the tailpipe, 1/3 goes out the radiator or lets say convection, and 1/3 goes out the driveshaft.

Thermoelectric would work to capture some of the energy going out the tailpipe - and hopefully even some of the convection heat. Yes, thermoelectric should eliminate the alternator, and ideally would be another energy input into a hybrid system.

You could conceive of a "limp" mode in which you've run out of gas, but you found some other kind of fuel, and you could operate off the thermoelectric and slowly work your way into a gas station. That may be pie-in-the-sky - but I remember KITT (the Knight Industries Two Thousand) could work off any combustible fuel - even blood!

Grunchy
20th September, 2012 @ 11:04 am PDT

Are telluride thermocouples more or less expensive than the alternatives?

If more expensive over its service life will the extra electricity pay for the difference in price?

If the waste heat is residue after the engine has extracted the energy that it can from it (exhaust gas) or from the engines cooling system a sterling cycle engine stands to give greater efficiency. If the engine is heating the room it is in a tall chimney and small wind turbine might give greater efficiency.

Slowburn
20th September, 2012 @ 11:31 am PDT

The article and your comments fail to note one feature of thermoelectric generation, unlike solar or I.C.E. the waste heat out of the first generator still has enough latent energy to be feed stock for another thermoelectric generator, therefore any one cycle does not need to be hyper-efficient if you use a compound or multi-stage conversion.

Robin McCabe
20th September, 2012 @ 02:54 pm PDT

But what about going the other way? How efficient is this material at cooling?

Standard Peltier junction cooling "chips" aren't very efficient, they produce much more heat on the hot side than they move away from the cold side. They're great for cooling small things quickly or larger spaces like coolers less quickly but there has to be a good method of moving the heat away.

'Course those devices are optimized for heat transfer and are horrible at converting temperature differentials into electricity.

They can be stacked and connected in series one manufacturer's specification can be run to around 200C 392F and the minimum temperature is -150C -238F.

The best location for such devices would be on the exhaust from heating systems in the Arctic and Antarctic. Stick the cold end outside and you have free electricity. (Free aside from the cost of the Peltier stacks.)

Gregg Eshelman
20th September, 2012 @ 06:32 pm PDT

Can this be used only for just the waste heat or can perhaps be used to replace the turbines in nuclear generators and, if so,

what is the efficiency?

Raja479
30th December, 2012 @ 05:17 pm PST

Would it have killed you to include a temperature difference/efficiency graph? It takes a particularly inefficient heat engine to get this up to the design point.

Bob Stuart
14th January, 2013 @ 07:41 am PST

the recent 2 stroke gasoline deisel could benefit from a little nitro-methane I'd think to get the combustion efficiency up. With a way to utilize the waste heat I'd think think a 100mpg vehicle would be do-able. Peltier affect(effect?) was being used in the coil on plug sensors to read the exhaust gas temperatures only a decade or so ago- wasn't there prior.

what will they come up with next?

Since electric heat is 100% efficent- I'd wonder when the flip side would be true.

Kwazai
14th January, 2013 @ 09:56 am PST

If it works so well why not put it on roofs? Seems to me those black shingles absorb quite a bit of heat. If it would work simply feed the power into the homes electrical system.

Mivoyses
21st March, 2013 @ 05:23 am PDT

Thermoelectric methods require cold as well. In the winter months this application has some promise, however in the summer months it would be very unreliable. The best application is in flight where your gift is both hot from engine combustion and cold atmospheric temperatures.

We have considered the viability of this application.

donwine
4th December, 2013 @ 12:54 pm PST
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