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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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Compare to normal TEC's?
By joe4324 on 1/20/2011 12:16:02 AM , Rating: 2
So I have used TEC's (Peltiers, Thermocouples?) for years. And they are hell-a in-effective as power producers but they do work. Those cute wood-stove TEC fans push a lot of air if the fire is hot enough. (

I might be pulling this number out of my rear but I feel as if normal TEC's at peak Delta are 5-7% efficient? If that is true more than double would be fantastic! But if its rare-earth metals then.... well... poop...

I've wanted to build all matter of devices to make power with TEC's but I could never get the math to work in my favor vs just buying a solar panel or whatever else I want to make power just not enough efficiency...

RE: Compare to normal TEC's?
By joe4324 on 1/20/2011 12:34:46 AM , Rating: 2
On a second note, If I could spend 200-300$ plus some DIY fabrication and experimenting and figure out how to pull a few amps of continuous 12v+ DC power so long as the wood stove was loosing heat out of the flue well then I would be on board to give it a shot!

Just for fun! Lets assume that:

My wood stove looses 40% of the BTU's of the wood out the flue (I'm sure mine is worse than this actually!)

So, 40% waste heat. At 7,000 BTU's per pound of seasoned firewood (this is a low'ish number) I'm loosing 2800 BTU's out the roof.

So, if I could somehow harness 50% of that energy to run through this new device (say a section of Aluminum flue pipe with a plate built in to bolt this TEC to it then heatsink it etc) That gives me 1400 BTU's per lb of wood.

1400x.14% = 196 BTU's, eh, thats not much... a little more conversions...

196 BTU = 0.0574419298 kilowatt hours, or 57 Watts.

Hey thats not so bad actually!

I burned 65Lbs of wood three nights ago when it was -16F.

65x67 = 3.7 Kwh power production for the day?

That sounds too good to be true...

Lets cut it in half just to assume everything works half as good as this stupidly ideal senario...

65lbs of wood burned @ 40% heat loss = 3.7KwH x.50% = 1.85KwH.

That still sounds too good to be true... Even if I got half that again it would be worth investigating. I will burn 6000-8000lbs of wood this winter (and this is a very small amount compared to most!)

dreams of KwH....

RE: Compare to normal TEC's?
By superPC on 1/20/2011 6:05:29 AM , Rating: 2
57 watts? 3.7 kWh a day? that's bad. 57 watts is not even enough to light my entire house. not enough for most laptop (maybe enough for netbook). 3.7 kWh would cost only around 37 cent a day. a month it cost 11.10 $.

RE: Compare to normal TEC's?
By joe4324 on 1/20/2011 5:09:36 PM , Rating: 2
It really is subjective, I live on less than 3.7Kwh for a whole day right now. I am averaging betwee 1.5-2.5 KwH per day for my home. Its off-grid and right now while I am at work my inverter is turned off so I'm using zero energy. I also turn it off when I am sleeping, so my home only 'consumes' energy from around 6pm to 2-3am everyday. This will change with the addition of a few more people. But its totally doable. And this includes me playing Bad Company 2 on my desktop for a few hours every now and then!

It realy is subjective :) I could live the rest of my life on a trickle of 57Wh indefinately :) Provided I could bank it up.

RE: Compare to normal TEC's?
By superPC on 1/20/2011 6:12:47 AM , Rating: 2
sorry, i missed that part where you said the calculation is for per pound of wood. 3.7 kWh per day per pound of wood is great. if you burn 8000 pounds of wood each winter that that would generate nearly 30000 kWh. that would save you 3000 $ for the whole winter electric bill! awesome. that makes me want to use this thermoelectric generator all around my house.

RE: Compare to normal TEC's?
By Strunf on 1/20/2011 7:54:33 AM , Rating: 2
The problem is that this 14% are connected to the delta in the temperature, if you put your TEG inside your flue at some point your delta will be close to 0 and then your production would be none. If you put your TEG on the flue part that is on the roof then the energy you could harness there is much lower.

What I see and seems much more effective (in terms of energy) is to put pipes filled with water around your flue and connect them to a central heating, then you just have to make this water circulate and you heat your all house with it.

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