Researchers discover source for generating 'green' electricity

June 22, 2011, University of Minnesota

University of Minnesota engineering researchers in the College of Science and Engineering have recently discovered a new alloy material that converts heat directly into electricity. This revolutionary energy conversion method is in the early stages of development, but it could have wide-sweeping impact on creating environmentally friendly electricity from waste heat sources.

Researchers say the material could potentially be used to capture waste heat from a car's exhaust that would heat the material and produce electricity for charging the battery in a hybrid car. Other possible future uses include capturing rejected heat from industrial and or temperature differences in the ocean to create electricity. The research team is looking into possible commercialization of the technology.

"This research is very promising because it presents an entirely new method for energy conversion that's never been done before," said University of Minnesota aerospace engineering and mechanics professor Richard James, who led the research team."It's also the ultimate 'green' way to create electricity because it uses waste heat to create electricity with no ."

To create the material, the research team combined elements at the to create a new multiferroic alloy, Ni45Co5Mn40Sn10. Multiferroic materials combine unusual elastic, magnetic and electric properties. The alloy Ni45Co5Mn40Sn10 achieves multiferroism by undergoing a highly reversible phase transformation where one solid turns into another solid. During this phase transformation the alloy undergoes changes in its that are exploited in the device.

During a small-scale demonstration in a University of Minnesota lab, the new material created by the researchers begins as a non-magnetic material, then suddenly becomes strongly magnetic when the temperature is raised a small amount. When this happens, the material absorbs heat and spontaneously produces electricity in a surrounding coil. Some of this heat energy is lost in a process called hysteresis. A critical discovery of the team is a systematic way to minimize hysteresis in phase transformations. The team's research was recently published in the first issue of the new scientific journal Advanced Energy Materials.

Watch a short research video of the new material suddenly become magnetic when heated.

In addition to Professor James, other members of the research team include University of Minnesota aerospace engineering and mechanics post-doctoral researchers Vijay Srivastava and Kanwal Bhatti, and Ph.D. student Yintao Song. The team is also working with University of Minnesota chemical engineering and materials science professor Christopher Leighton to create a thin film of the material that could be used, for example, to convert some of the from computers into electricity.

"This research crosses all boundaries of science and engineering," James said. "It includes engineering, physics, , chemistry, mathematics and more. It has required all of us within the university's College of Science and Engineering to work together to think in new ways."

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1.2 / 5 (9) Jun 22, 2011
Doesn't this pose a problem with entropy. If waste heat can be converted into electricity without energy input aren't they creating a perpetual motion machine? Or is this hysteresis, a term I'm not familiar with, create more entropy than is lost from converting heat into electricity? If so, would the universe end in hysteresis death and not heat death.
4.5 / 5 (4) Jun 22, 2011
No, because you still need to create the heat somehow and the electricity generated will not be enough to continue the heating process since heat (and, in this case, hysteresis) cause the system to be less than 100% efficient

If it were 100% efficient then, yes, it would be a perpetual motion machine but then we wouldn't be able to extract any work from it, thereby making it fairly useless
4.7 / 5 (6) Jun 22, 2011

No, this is not a perpetual motion machine, it's a method of capturing heat that would otherwise be lost to the environment and transforming it back into a usable form.

So, if you have an 50% efficient engine that is taking in 10 watts worth of fuel and outputting 5 watts of usable energy, it is then losing 5 watts of energy as heat. If you wrapped your engine in this material and its efficiency was 50% then you would be able to capture 2.5 watts of that lost heat and use it as electricity. You still have 10 watts in and 10 watts out, you've just changed how efficient your system is.

Hysteresis means that the system's output is dependent on its internal states in addition to its inputs. The article is unclear on the details, but basically by minimizing the impact that hysteresis on the system they are able to increase its efficiency. Think of hysteresis in this case as internal drag. If you minimize it, you get more power out of the system.

not rated yet Jun 22, 2011
By absorbing heat and converting it to electricity could you make a refrigerator that produces energy for the house while keeping its content cold as it removes heat from the system?
4.5 / 5 (2) Jun 22, 2011
By absorbing heat and converting it to electricity could you make a refrigerator that produces energy for the house while keeping its content cold as it removes heat from the system?

They misspoke when saying "direct transfer of heat into energy". As usual, they still need to have temperature gradient for this to work, because they need to have heating / cooling cycle for the device to work continuously.
Here is from their abstract:
Theory predicts that under optimal conditions the performance compares favorably with the best thermoelectrics. Because of the low hysteresis of the alloy, a promising area of application of this concept appears to be energy conversion at small T, suggesting a possible route to the conversion of the vast amounts of energy stored on earth at small temperature difference.
2 / 5 (1) Jun 22, 2011
I think Mr Yevgen means 'delta T', but main idea highly practical. Waste heat shows up in engineering calc as part of what is later called 'lost work', and is highly significant when taken in macro.
1 / 5 (2) Jun 22, 2011
Wow. What has yet to be discovered?
2 / 5 (5) Jun 22, 2011
I feel this is absolutely huge in many ways. By converting waste heat back into energy you are able to immensely increase the efficiency of almost any type of heat generating device or vehicle. For example imagine incorporating this alloy into the body of an SR-71 or other high speed aircraft. As the craft heats up it will have a correspondingly higher increase in electric energy being produced and converted into it's electric engine which is transferred to a greater rate of thrust. The craft wouldn't have to store nearly the amount of propellant and thus would be much lighter and faster.
not rated yet Jun 22, 2011
Still getting my head around the whole concept but i am wondering would it be possible to create a thin sheet of this metal and paint it flat black an use it as some sort of solar energy converter?
not rated yet Jun 22, 2011
To be clear, the basic reason this works is that heat is moving from "hot" to "cold", thereby forming a heat gradient. This wouldn't be practical on any airliner since the air is actually quite warm at the contact point with the plane and we'd end up pumping heat inside, something we try to avoid by using insulators (for an extreme example, think the space shuttle entering orbit). This is also the reason it wouldn't work like you're expecting on refrigerators.

Some materials can be used as "heat pumps" and work in the opposite way: using electricity to push heat in a direction opposite to what it normally would.

This particular material is interesting for only two reasons: it is more efficient and it becomes magnetic while being used. The magnetism may be the more useful of the two...
4 / 5 (1) Jun 22, 2011
Still getting my head around the whole concept but i am wondering would it be possible to create a thin sheet of this metal and paint it flat black an use it as some sort of solar energy converter?

In theory, yes, although traditionally these "heat to energy" devices produce very little energy. Even if you paint one side black, metal tends to reach equilibrium with itself very quickly, hence the reason you don't touch the kettle while the burner is on. You'd be much better off using traditional solar energy.
not rated yet Jun 22, 2011
I know it is probably not economically feasible to build, but I've always wondered the extent of power generation by making a "thermospire", a thermoelectric tower reaching from sea level, all the way into the upper atmosphere. you could also attach PV modules on its spine; Unless it is more meaningful to have more extreme temperature differences among smaller area/volumes
not rated yet Jun 22, 2011
How much would it cost to produce this material?
not rated yet Jun 22, 2011
I've been reading these articles for the past couple of years, and whenever I see
" in the early stages of development, but it could have wide-sweeping impact on creating.."
I just shake my head, knowing we'll never see anything more than this article.
5 / 5 (1) Jun 22, 2011
It isn't clear from the article what they mean by hysteresis. It could mean that there is a time lag from the time that the critical temperature is reached to when the material actually flips to magnetic or it could mean that the temperature at which it flips to magnetic is higher than the temperature at which it flops back (to non-magnetic). I suspect they mean the latter.
not rated yet Jun 22, 2011
Sounds like they could make a pretty, if inefficient, heat-engine to rival those shelf-top 'Stirling' machines by arranging studs of this material on the rim of a wheel and placing a ferromagnetic material and modest heat-source nearby...
1 / 5 (1) Jun 22, 2011
how about packing these things in an attic...fantastic in the summer
5 / 5 (1) Jun 22, 2011
I'm not sure what sets this apart from existing thermoelectric systems. They even say so:
Theory predicts that under optimal conditions the performance compares favorably with the best thermoelectrics.

So you need 'optimal' conditions to match 'favorably' with existing thermoelectrics. Which means, efficiency is still very low and also that its use will remain limited to niche applications.
1 / 5 (1) Jun 22, 2011
how arent they sure it got its magnetism from storing it?
it looks like a copper plate what they are heating it with.
it might as well be acting like a capacitor.
not rated yet Jun 23, 2011
I wonder if it surpasses the maximum carnot efficiency.
BTW if any of you guys feel strongly about entropy, google 'fluctuation theorem'. There is always the possibility of entropy decreasing.
5 / 5 (1) Jun 23, 2011
Phase change materials usually have a life span limited by the number of cycles before failure. I wonder how many cycles this material can handle? The hysteresis issue would also limit the life cycle, slowly degrading the material. Wait and see if anything follows from this.

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