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Professor Mercouri Kanatzidis holds up his device that can harvest 14 percent of waste heat as usable electricity.  (Source: Northwestern University)
New lead-based compound could see a variety of scenarios -- including helping power the machines in the absence of sunlight

A new material from researchers at Northwestern University could offer a way to capture and recycle waste heat better than ever before [press release].  The material can convert a record 14 percent of the waste heat passing through it to usable electric energy.

When manmade devices perform work, be it a computer or a car, they produce heat.  That heat is ultimately lost, reducing the energy efficiency of our devices.  Some have cleverly exploited this fact, using waste heat to offer desirable comfort heating.  But ultimately, the only good solution is to try to somehow recapture that heat in a usable form.  To do that, the right material was necessary.

Semiconductors have long been considered a promising candidate, as they can produce electricity when heated.  Lead telluride (composed of lead and tellurium ions on a lattice) was considered one of the most promising candidates, as it was relatively efficient in accomplishing the heat to electricity transformation.  

But attempts to improve that efficiency via various techniques, such as nano-inclusions resulted in an undesirable side effect -- increased scattering of electrons, reducing overall conductivity.  Obviously, if you're converting heat to electricity, you have to funnel it out of the device, so this was unacceptable.

The NU team, lead by Chemistry professor Mercouri Kanatzidis discovered that by using a special type of nano-inclusion, the scattering could actually be reduced.  The trick was to use special crystals of rock salt (SrTe).  Professor Kanatzidis sums up, "It has been known for 100 years that semiconductors have this property that can harness electricity. To make this an efficient process, all you need is the right material, and we have found a recipe or system to make this material."

Materials Science professor Vinayak Dravid also assisted in the study.  He describes the results, stating, "We can put this material inside of an inexpensive device with a few electrical wires and attach it to something like a light bulb. The device can make the light bulb more efficient by taking the heat it generates and converting part of the heat, 10 to 15 percent, into a more useful energy like electricity."

The study on the promising material earned a place [abstract] in the prestigious peer-reviewed journal Nature Chemistry.

So the material seems great, but what about its commercialization prospects?

Well, lead telluride is relatively rare , but occurs naturally in mountain deposits as the mineral Altaite.  Significant deposits have been found in the Altai mountains of northeast Asia;  Zyrianovsk, Kazakhstan; the Ritchie Creek Deposit in Price County, Wisconsin; the Koch-Bulak gold deposit in Kazakhstan; Moctezuma, Mexico; and Coquimbo, Chile.

Given that air or liquid bearing waste heat can be channeled through a relatively small area, a little telluride (say in a heatpipe on a computer component) could go a long ways, recycling almost a sixth of the wasted energy.

Strontium is very abundant, so coming up with sufficient quantities of the nano-inclusion material shouldn't be as big an issue.

Aside from making existing devices more efficient, the material could be used to make new low voltage electronic devices, powered by waste heat from the human body.

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RE: Passive airconditioner in the summer?
By ddopson on 1/20/2011 12:03:24 AM , Rating: 2
No. The device produces electricity when heat naturally flows "downhill" from a more hot side (burner of some sort) to the less hot side (surrounding environment).

The problem with air-conditioning in the summer is that you want to do the reverse, convince heat to flow from the less hot side (your room) to the more hot side (outdoors). That fundamentally takes energy.

I have a friend who was looking into a startup that wanted to take devices like this that generate ~11 watts, bundle them with a cellphone charger and an LED based lamp and sell them in various parts of Africa for $100 - $200. For people with unreliable access to electricity, having a mechanism to read by at night can be a big leg up economically.

By ddopson on 1/20/2011 12:05:58 AM , Rating: 2
In case it isn't clear, the use case for the 11-watt device is to slap it on the side of a wood-burning stove. Such stoves are much more common than many of us city-people realize. My girlfriend's parents in New Zealand have one. They are in the country and don't have access to piped natural gas. On the other hand, they have lots and lots of free trees.

RE: Passive airconditioner in the summer?
By wordsworm on 1/20/2011 1:15:47 AM , Rating: 2
I am an admirer of the Roman method of air conditioning that I read about a number of years ago. They had a pipe leading from underground to the building, and another one that led from the ceiling to the outside. The outside part, through the ceiling to the roof, would be painted black to increase the temperature at the top, which would cause the air to exit faster, and the air cooled through the subterranean pipe to flow into the building.

In any case, it would seem to me that something that makes electricity from heat must be cooling whatever it is that's giving it the source of heat. That is to say, it must remove energy from the air to generate the electricity.

It would seem to me that there ought to be some way to use a gadget like this, if it can extract energy from, say, a room whose temperature is above 25 degrees, then that would effectively be an air conditioner. I'm not sure how exactly the invention works, but you said that there needs to be a downward effect in order for this to work. A pipe leading from the ceiling to the floor would possibly take the warmest air from the room, extract the energy, and make the cooler air heavier, thus completing the air conditioning cycle.

It just seems to me to be possible, and that an AC that can add electricity rather than subtract it would be rather... cool.

RE: Passive airconditioner in the summer?
By Prosthetic Head on 1/20/2011 5:08:25 AM , Rating: 2
Sorry, electricity generating air con is NOT possible with this or anything else. These things use a heat flow from a hot location to a colder one to generate electricity. Heat will not flow from a cold location to a hot one and heat on its own is no good for generating electricity or for that matter any form of useful work.

For more info read the wikipedia pages "Thermoelectric effect" and "Thermodynamics"

RE: Passive airconditioner in the summer?
By erple2 on 1/20/2011 10:11:35 AM , Rating: 2
That's not technically true. It's possible to generate a very small amount of electricity from this. Most AC units that I've seen have a simple "loop" in them - use some sort of gas (Freon, usually), expand it (which is very endothermic - simple expansion) to draw heat out of the surrounding area, then pump that into a compressor to re-compress the gas (which is where all of the electricity comes from - that process is pretty difficult to do). The side effect of that is that the compressed Freon is now very hot, and has to be cooled effectively, so you can again, expand it thus cooling off the surrounding area etc.

The cooling of the compressed Freon is what your outside unit is essentially for. The hot Freon gas (that's already been compressed) can be used to generate the power.

The problem, of course, is that perpetual motion machines are impossible. So the amount of electricity you can get out of the system is a small fraction of the amount of electricity required to power the A/C unit (well, according to above, about 14% in ideal circumstances). So you could theoretically have an A/C unit that uses about 14% less electricity (recirculating the electricity back into the A/C unit) than your current unit. But that's as good as your going to get.

RE: Passive airconditioner in the summer?
By Netjak on 1/20/2011 12:53:05 PM , Rating: 2
The problem, of course, is that perpetual motion machines are impossible. So the amount of electricity you can get out of the system is a small fraction of the amount of electricity required to power the A/C unit (well, according to above, about 14% in ideal circumstances). So you could theoretically have an A/C unit that uses about 14% less electricity (recirculating the electricity back into the A/C unit) than your current unit. But that's as good as your going to get

Wrong. AC doesnt produce heat or coldness. Heat is just transfered from one side to another by the AC unit and amount transfered is 3-4 times bigger than electricity used to run compressor and all other components inside. So, with your numbers, this device can provide 50% of electricity neded and theoretically one cun run AC free. But, ones need some source of heat on the inside, ie Sun, so this is not perpetum mobile.

By Chernobyl68 on 1/21/2011 12:21:49 PM , Rating: 2
An Air Conditioner is a type of heat pump. It transfers heat energy from inside your house to outside your house. Heet Energy will only flow naturally according to Entropy, that is, towards a lower state, which we measure as temperature. "Hot" or "Cold" is simply a sensation based on a temperature differential. In order to transfer heat out of the house, it uses a compressor, and in doing so increases the temperature of the gas used (via the ideal gas law, PV=nRT) which is pumped through the coils on the radiator outside the home (or on the back of the fridge, for that matter) and then uses either ambient or forced air flow over these coils to transer heat to the surrounding air. These coils are where the electrical generating substance could be placed.

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