Turning heat to electricity... efficiently

Nov 18, 2009 by David L. Chandler

(PhysOrg.com) -- In everything from computer processor chips to car engines to electric powerplants, the need to get rid of excess heat creates a major source of inefficiency. But new research points the way to a technology that might make it possible to harvest much of that wasted heat and turn it into usable electricity.

That kind of waste-energy harvesting might, for example, lead to cellphones with double the talk time, laptop computers that can operate twice as long before needing to be plugged in, or power plants that put out more electricity for a given amount of fuel, says Peter Hagelstein, co-author of a paper on the new concept appearing this month in the .

Hagelstein, an associate professor of electrical engineering at MIT, says existing solid-state devices to convert heat into electricity are not very efficient. The new research, carried out with graduate student Dennis Wu as part of his doctoral thesis, aimed to find how close realistic technology could come to achieving the theoretical limits for the efficiency of such conversion.

Theory says that such can never exceed a specific value called the Carnot Limit, based on a 19th-century formula for determining the maximum efficiency that any device can achieve in converting heat into work. But current commercial thermoelectric devices only achieve about one-tenth of that limit, Hagelstein says. In experiments involving a different new technology, thermal diodes, Hagelstein worked with Yan Kucherov, now a consultant for the Naval Research Laboratory, and coworkers to demonstrate efficiency as high as 40 percent of the Carnot Limit. Moreover, the calculations show that this new kind of system could ultimately reach as much as 90 percent of that ceiling.

Hagelstein, Wu and others started from scratch rather than trying to improve the performance of existing devices. They carried out their analysis using a very simple system in which power was generated by a single quantum-dot device — a type of semiconductor in which the electrons and holes, which carry the electrical charges in the device, are very tightly confined in all three dimensions. By controlling all aspects of the device, they hoped to better understand how to design the ideal thermal-to-electric converter.

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.

A key to the improved throughput was reducing the separation between the hot surface and the conversion device. A recent paper by MIT professor Gang Chen reported on an analysis showing that heat transfer could take place between very closely spaced surfaces at a rate that is orders of magnitude higher than predicted by theory. The new report takes that finding a step further, showing how the heat can not only be transferred, but converted into electricity so that it can be harnessed.

A company called MTPV Corp. (for Micron-gap Thermal Photo-Voltaics), founded by Robert DiMatteo SM ’96, MBA ‘06, is already working on the development of “a new technology closely related to the work described in this paper,” Hagelstein says.

DiMatteo says he hopes eventually to commercialize Hagelstein’s new idea. In the meantime, he says the technology now being developed by his company, which he expects to have on the market next year, could produce a tenfold improvement in throughput power over existing photovoltaic devices, while the further advance described in this new paper could make an additional tenfold or greater improvement possible. The work described in this paper “is potentially a major finding,” he says.

DiMatteo says that worldwide, about 60 percent of all the energy produced by burning fuels or generated in powerplants is wasted, mostly as excess heat, and that this technology could “make it possible to reclaim a significant fraction of that wasted energy.”

When this work began around 2002, Hagelstein says, such devices “clearly could not be built. We started this as purely a theoretical exercise.” But developments since then have brought it much closer to reality.

While it may take a few years for the necessary technology for building affordable quantum-dot devices to reach commercialization, Hagelstein says, “there’s no reason, in principle, you couldn’t get another order of magnitude or more” improvement in throughput power, as well as an improvement in efficiency.

“There’s a gold mine in waste heat, if you could convert it,” he says. The first applications are likely to be in high-value systems such as computer chips, he says, but ultimately it could be useful in a wide variety of applications, including cars, planes and boats. “A lot of is generated to go places, and a lot is lost. If you could recover that, your transportation technology is going to work better.”

More information: "Quantum-coupled single-electron thermal to electric conversion scheme" by D. M. Wu, P. L. Hagelstein, P. Chen, K. P. Sinha,3 and A. Meulenberg, in Journal of Applied Physics, published online Nov. 13, 2009, link.aip.org/link/?JAPIAU/106/094315/1

Provided by Massachusetts Institute of Technology (news : web)

Explore further: High-intensity sound waves may aid regenerative medicine

add to favorites email to friend print save as pdf

Related Stories

Discovery Captures, Converts Heat

Apr 06, 2005

Your car's engine loses 70 percent of its energy as waste heat-but Australian and Oregon scientists may have figured out an efficient way not only to recover that lost energy, but to at long last capture the power-producing ...

Thermoelectric materials are 1 key to energy savings

Nov 20, 2007

Breathing new life into an old idea, MIT Institute Professor Mildred S. Dresselhaus and co-workers are developing innovative materials for controlling temperatures that could lead to substantial energy savings by allowing ...

Promising new material that could improve gas mileage

Oct 09, 2008

With gasoline at high prices, it's disheartening to know that up to three-quarters of the potential energy you are paying for is wasted. A good deal of it goes right out the tailpipe instead of powering your car.

Breakthrough made in energy efficiency, use of waste heat

Apr 01, 2009

Engineers at Oregon State University have made a major new advance in taking waste heat and using it to run a cooling system - a technology that can improve the energy efficiency of diesel engines, and perhaps some day will ...

Material may help autos turn heat into electricity

Jul 24, 2008

Researchers have invented a new material that will make cars even more efficient, by converting heat wasted through engine exhaust into electricity. In the current issue of the journal Science, they describe a material with t ...

Recommended for you

Universe may face a darker future

3 hours ago

New research offers a novel insight into the nature of dark matter and dark energy and what the future of our Universe might be.

High-intensity sound waves may aid regenerative medicine

21 hours ago

Researchers at the University of Washington have developed a way to use sound to create cellular scaffolding for tissue engineering, a unique approach that could help overcome one of regenerative medicine's ...

Formula could shed light on global climate change

Oct 30, 2014

Wright State University researchers have discovered a formula that accurately predicts the rate at which soil develops from the surface to the underlying rock, a breakthrough that could answer questions about ...

User comments : 9

Adjust slider to filter visible comments by rank

Display comments: newest first

fixer
4 / 5 (3) Nov 18, 2009
Now this is a very useful piece of info, if it can be combined with solar cell technology it has the potential to provide free electricity and start reversing global warming.
Alexa
5 / 5 (2) Nov 18, 2009
Whole thesis can be downloaded from there:

http://dspace.mit...quence=1
Going
not rated yet Nov 19, 2009
The Carnot Limit may be based on a 19th-century theory but its a fundamental property of heat so don't disparage it as ancient.
retrosurf
not rated yet Nov 19, 2009
It sounds like tunneling-based thermionic conversion.
Very clever.
jonnyboy
Nov 19, 2009
This comment has been removed by a moderator.
jamesrm
not rated yet Nov 22, 2009
It may lead to implantable electronics powered by body heat

Regards
James
fixer
not rated yet Nov 22, 2009
James,
As I understand it you need a temperature difference to cause energy to flow, you don't get that in the body.
I assume you are thinking of built in phones, and this has already been done using the blood supply to generate energy.
see http://www.physor...670.html
jamesrm
not rated yet Nov 23, 2009
I was thinking more like this
www.patentstorm.u...ion.html
thales
not rated yet Nov 23, 2009
Very exciting. I imagine this would make nuclear power plants significantly more efficient.
fixer
not rated yet Nov 23, 2009
James,
I see the device requires a reliable 2 degree difference to work, not good when you live in a hot climate.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.