Ancient effect harnessed to produce electricity from waste heat

Ancient effect harnessed to produce electricity from waste heat

A phenomenon first observed by an ancient Greek philosopher 2,300 years ago has become the basis for a new device designed to harvest the enormous amounts of energy wasted as heat each year to produce electricity. The first-of-its-kind "pyroelectric nanogenerator" is the topic of a report in ACS' journal Nano Letters.

Zhong Lin Wang and colleagues at Georgia Tech explain that more than 50 percent of the energy generated in the U.S. each year goes to waste, much of it as heat released to the environment by everything from computers to cars to long-distance electric transmission lines. Heat can be converted to electricity using something called the pyroelectric effect, first described by the Greek philosopher Theophrastus in 314 B.C., when he noticed the gemstone tourmaline produced and attracted bits of straw when heated. Heating and cooling rearrange the molecular structure of certain materials, including tourmaline, and create an imbalance of electrons that generates an electric current. Wang's group wanted to apply the ancient principle to make a nanogenerator (NG) that could take advantage of heat changes in the modern world, which uses a time-dependent temperature change to generate electricity.

To do that, the researchers made nanowires out of , a compound added to paints, plastics, electronics and even food. Using an array of short lengths of nanowire standing on end, they demonstrated a device that produces electricity when heated or cooled. They suggest the nanogenerators could even produce power as temperatures fluctuate from day to night. "This new type of NG can be the basis for self-powered nanotechnology that harvests thermal energy from the time-dependent in our environment for applications such as wireless sensors, temperature imaging, medical diagnostics and personal microelectronics," the authors said.


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First practical nanogenerator produces electricity with pinch of the fingers

More information: “Pyroelectric Nanogenerators for Harvesting Thermoelectric Energy” Nano Lett., 2012, 12 (6), pp 2833–2838. DOI: 10.1021/nl3003039

Abstract
Harvesting thermoelectric energy mainly relies on the Seebeck effect that utilizes a temperature difference between two ends of the device for driving the diffusion of charge carriers. However, in an environment that the temperature is spatially uniform without a gradient, the pyroelectric effect has to be the choice, which is based on the spontaneous polarization in certain anisotropic solids due to a time-dependent temperature variation. Using this effect, we experimentally demonstrate the first application of pyroelectric ZnO nanowire arrays for converting heat energy into electricity. The coupling of the pyroelectric and semiconducting properties in ZnO creates a polarization electric field and charge separation along the ZnO nanowire as a result of the time-dependent change in temperature. The fabricated nanogenerator has a good stability, and the characteristic coefficient of heat flow conversion into electricity is estimated to be 0.05–0.08 Vm2/W. Our study has the potential of using pyroelectric nanowires to convert wasted energy into electricity for powering nanodevices.

Journal information: Nano Letters

Citation: Ancient effect harnessed to produce electricity from waste heat (2012, June 13) retrieved 21 September 2019 from https://phys.org/news/2012-06-ancient-effect-harnessed-electricity.html
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Jun 13, 2012
"Heat to power nano devices" I guess its a start. Hopefully it can be scaled up.

Jun 13, 2012
bed of nails, . . . . why that? 'Pantheon' on top? . . .

Jun 13, 2012
Aren't all effects ancient?

Jun 13, 2012
How does this hyped claim:

"a new device designed to harvest the enormous amounts of energy wasted as heat each year to produce electricity"

relate to the possible use in self-powered NANOtechnology?

Jun 13, 2012
Impressive nanoconstruction.

Jun 14, 2012
Its good to hear of an effective Thermoelectric system, why cant we combine this technology with solar cells, so we can capture more energy from sunlight. Also the solar cells will be self cooling and last longer.

Jun 14, 2012
If an effect was noticed since antiquity, can you call it ancient for this reason?
-.

Jun 14, 2012
"Heat to power nano devices" I guess its a start.

It's heat differential to power. The problem is that most devices - after being powered up, will settle at a certain temperature level. As long as the temperature remains constant this technique produces no power.

Thermoelectric system, why cant we combine this technology with solar cells

For the above mentioned reason. It makes no sense (and the power density is way too low). It's similar to generating energy from the strain on railway rails due to heating in summer. You can see them deform, so there is a lot of energy there. However the power (Energy per time unit) is very low.

As the authors note: This may be useful in nanodevices.
I'm thinking mediacl devices in bloodstreams or other turbulent media where temperature gradients happen a lot.

Jun 14, 2012
I don't understand, why the ZnO layer must be distributed into nanopillars, as the compact layer would work in the same way (providing we could achieve the uniform crystal orientation).

Jun 14, 2012
cars have decent temperature gradients.

Jun 14, 2012
the characteristic coefficient of heat flow conversion into electricity is estimated to be 0.050.08 Vm2/W
IMO the common thermoelectric cells would be way more effective - the pyroelectric effect appears only when the material is heated and after then its electricity disappears (it's essentially the piezoelectricity induced with dilatation of material during heating instead of mechanical stress). These cells would generate sustainable power only when the temperature of surface would cycle fast in certain range (as the formula dT/dTo at the above picture implies).

Jun 14, 2012
I don't understand, why the ZnO layer must be distributed into nanopillars, as the compact layer would work in the same way (providing we could achieve the uniform crystal orientation).

I suppose it is in order to reduce thermal conductivity between the plates.

Jun 14, 2012
I don't understand, why the ZnO layer must be distributed into nanopillars, as the compact layer would work in the same way (providing we could achieve the uniform crystal orientation).

ZnO is piezoelectric (a property closely related to pyroelectricity). That means that deformations (e.g. due to heat differentials changing on both ends) cause an electric voltage accross the structure. A flat plane would, under thermal change) hardly move, and so the induced voltage would be minimal. Nanopillars give you a lot of 'stress' over the entire device and therefore a much greater resulting number or elctron/holes created.

cars have decent temperature gradients.

That would be enough for thermoelectricity. but we're talking pyroelectricity here (which needs a CHANGING gradient - i.e. a second derivative other than zero). Car engines do not provide this most of the time. Only during startup or other, major, load changes.

Jun 14, 2012
ZnO is piezoelectric (a property closely related to pyroelectricity). That means that deformations (e.g. due to heat differentials changing on both ends) cause an electric voltage accross the structure.
This implies, it's the thermal expansion of the upper silver plate, which generates the deforms of ZnO nanopillars and the voltage at their end. This is not true - the voltage is generated in ZnO directly and the silver plate is just current collector for it.

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