Turning heat to electricity... efficiently

[DeltaV]

http://www.physorg.com/news177761180.html

"Hagelstein says that with present systems it’s possible to efficiently convert heat into electricity, but with very little power. It’s also possible to get plenty of electrical power — what is known as high-throughput power — from a less efficient, and therefore larger and more expensive system. “It’s a tradeoff. You either get high efficiency or high throughput,” says Hagelstein. But the team found that using their new system, it would be possible to get both at once, he says."

[Aero]

That is interesting. One application of thermoelectric devices that has been studied for several years is that of converting the waste heat from over-the-road trucks to electricity. The idea is to layer the device onto the hot exhaust manifold, allowing the removal of the belt driven generator. The result is a significant improvement in fuel efficiency both on the road and while parked with the engine idling. I don't know whether or not such systems have been reduced to practice.

[TallDave]

If they can get to 90% of the Carnot limit... wow. That could be a big market. There is obviously a HUGE amount of waste heat out there.

[DeltaV]

Prior research from MTPV Corp:
http://www.mtpvcorp.com/MTPV2/Publicfil ... e%2042.pdf

[nextbigfuture]

Carnot vs best practice at diff temp gaps
Overall waste heat available in the US 7 quad from industrial

http://nextbigfuture.com/2009/11/four-t ... iency.html

http://nextbigfuture.com/2009/01/micron ... taics.html

The better heat transfer with smaller gaps
http://nextbigfuture.com/2009/07/heat-t ... eater.html

brian Wang

[Betruger]

If they can get to 90% of the Carnot limit... wow. That could be a big market. There is obviously a HUGE amount of waste heat out there.

Reads like they mean 90%, in practice, of 40% theoretical.

[nextbigfuture]

http://nextbigfuture.com/2009/11/quantu ... cient.html
highlights of the 242 page thesis

Quantum dot coupling is to restrict number of states and increase efficiency. Columb coupling is to avoid the blackbody limit.

10 Watts per square centimeter and higher for some designs. Has a couple of quantum dot / dieelectric designs.

the thesis
http://dspace.mit.edu/bitstream/handle/ ... sequence=1

[crj11]

There is another heat to electricity method based on proton exchange membranes similar to those used in fuel cells. It also seeks to eventually reach 85% of Carnot efficiency. Current efficiency is about 40% of Carnot. One useful feature of this device is that it can be used "in reverse" as a solid state heat pump. And the best feature of all is that it was created by the inventor of the super soaker! He has used the profits from the super soaker to self-finance much of his R&D.

Assuming both ideas come to fruition, the question is which will be cheaper to manufacture. The Solar Thermal cells look fairly complicated. A proton exchange membrane could be less costly.

http://spectrum.ieee.org/semiconductors ... -generator

[Giorgio]

I remember reading about him almost a couple of years ago, but, apart from the initial promises and working diagrams, no more news was released on the project.
Also the website dedicated to the project apparently is not loading anymore:
http://www.johnsonems.com

[crj11]

I checked and also can not access the web site. This is strange, since it loaded fine yesterday. The most recent information on the device is from a very informative lecture at Xerox PARC which can be found at http://www.parc.com/event/713/high-effi ... ngine.html .

Since his research is self financed and he seems pretty motivated and sure that the idea will work, he'll probably keep at it until he either succeeds or decides that it is impractical to reach the required level of efficiency.

In his talk he mentions that about 57% of the energy currently used generates waste heat, so there's a lot of incentive to make something to use that heat.

[Aero]

Is it correct to add the efficiencies of an IC engine and the waste heat recovery system?

For example, if an IC engine powered hybrid car or truck achieves 30% efficiency, fuel to the road, and a thermoelectric (or similar) device achieves 10% waste heat recovery efficiency charging the battery, does that mean that the vehicle is achieving 40% efficiency?

I think its more complicated than that but this simple example points the way, showing significant fuel savings available from even low efficiency thermoelectric devices. Which electric car configuration would be most suitable for using such a system? Plug-in hybrids (New Toyota Pruis)? Extended range electrics (Chevy Volt)? Or the inline electric configurations like Mercedes or BMW are developing?

[MSimon]

Is it correct to add the efficiencies of an IC engine and the waste heat recovery system?

For example, if an IC engine powered hybrid car or truck achieves 30% efficiency, fuel to the road, and a thermoelectric (or similar) device achieves 10% waste heat recovery efficiency charging the battery, does that mean that the vehicle is achieving 40% efficiency?

I think its more complicated than that but this simple example points the way, showing significant fuel savings available from even low efficiency thermoelectric devices. Which electric car configuration would be most suitable for using such a system? Plug-in hybrids (New Toyota Pruis)? Extended range electrics (Chevy Volt)? Or the inline electric configurations like Mercedes or BMW are developing?

I believe for an IC engine 1/3 of the energy is power out. 1/3 goes into the cooling water. 1/3 out the exhaust. Roughly.

The odds of being able to capture 1/3 the exhaust energy and turn it into electricity are small. 1/6th to 1/10th are better bets. That means going from about 33% to about 40%. If it is cheap enough. And it will need to be able to produce 1KW for about $100 mfg cost. Maybe it can be done.

[clonan]

I believe for an IC engine 1/3 of the energy is power out. 1/3 goes into the cooling water. 1/3 out the exhaust. Roughly.

But isn't the "cooling water" third there just to remove excess heat from the engine? Why cant we use these systems as a way to extract heat directly from the engine or at the very least run the coolant over the thermoelectric device. This will reduce the wear on the radiator (maybe even permitting a smaller radiator system) and generate extra juice.

So really we are going from 33% to 47%.

The real trick is...will the weight be worth it?

[Aero]

Is it correct to add the efficiencies of an IC engine and the waste heat recovery system?

I believe for an IC engine 1/3 of the energy is power out. 1/3 goes into the cooling water. 1/3 out the exhaust. Roughly.

The odds of being able to capture 1/3 the exhaust energy and turn it into electricity are small. 1/6th to 1/10th are better bets. That means going from about 33% to about 40%. If it is cheap enough. And it will need to be able to produce 1KW for about $100 mfg cost. Maybe it can be done.

That's still a very nice improvement in fuel economy, over 20% improvement for the properly configured vehicle. Have IC engines been designed to minimize waste heat to the cooling water? I expect overall engine efficiency drives the temperature of the cooling water hence it can't be tinkered with for the benefit an add on subsystem. Still, a small amount of electricity could be generated using the approximately 100 degree F radiator to ambient temperature differential. The exhaust manifold to ambient temperature differential is much more usable, like 500 degrees or more. Of course the add on device would likely need cooling.

Mfg cost is another question. The high efficiency devices discussed in this thread will be expensive and are not available yet. Conventional thermoelectric devices are easy by comparison, just thin bi-metallic layers of rather common materials. Early devices were simply thin sheets of material sandwiched together in a pressure frame. (Pressure is for good heat conduction.) My contacts (5 years ago) tell me that they can be manufactured by electroplating. I think it should be feasible to electroplate a thermoelectric device to an existing exhaust manifold.

It seems harder, but maybe someone should look into screen printing them. A good project for EEStor to fall back on.

[Aero]

Big Oops.

http://en.wikipedia.org/wiki/Thermoelectric_effect

The very last section, Uses, reads as follows:

Germany automakers Volkswagen and BMW have developed thermoelectric generators (TEG) that recover waste heat from a combustion engine.

According to a report by Prof. Rowe of the University of Wales in the International Thermoelectric Society, Volkswagen claims 600W output from the TEG under highway driving condition. The TEG-produced electricity meets around 30% of the car’s electrical requirements, resulting in a reduced mechanical load (alternator) and a reduction in fuel consumption of more than 5%.

BMW and DLR (German Aerospace) have also developed an exhaust powered thermoelectric generator that achieves 200 W maximum and has been used successfully for more than 12,000-km road use.

Space probes to the outer solar system make use of the effect in radioisotope thermoelectric generators for electrical power.