ENGR0011 Section: Schaub 4:00 PM
Group #L16
THERMOELECTRICS: THE FUTURE OF ENERGY CONSERVATION
Dan Gruber (dgg12@pitt.edu)
WHAT ARE THERMOELECTRICS?
Very recently, thermoelectrics have come to light as a
viable solution to the problem of energy conservation.
Thermoelectrics can be used for cooling a system, such as
cooling a heated computer processor, or converting thermal
energy within the byproduct of heat in a system into
electrical energy. My focus is on the applications of
thermoelectrics as a solution to energy loss in a system as
heat. A fair percentage of energy escapes in any given
system as heat. In fact, “for many systems, more energy is
lost as heat than is used” [1]. Scientists have been working
for years to develop a material capable of recycling lost heat
as electricity, “but so far the conversion efficiency of
thermoelectric materials has been way too low to yield a
commercially viable device” [2]. Within the past few weeks,
however, Northwestern University researchers have
developed a thermoelectric material that maintains
significantly higher conversion efficiency than any other
previous materials [3]. In other words, this revolutionary
material is consistently more efficient in converting heat to
raw electric power. This new breakthrough has given
scientists hope for even greater achievements in the field of
thermoelectrics. Scientists and engineers look forward to the
practical application of thermoelectrics to energy
conservation within systems. As a rule, based on the codes
of ethics of individual and general fields of engineering
study and research, researchers and engineers look to
develop systems with higher sustainability; that is, engineers
look to find systems that can use and reuse as much of its
own energy without relying on outside sources of power.
Thermoelectrics, as a venue to assist systems in reusing
thermal energy that might otherwise be lost to factors
outside a system, provide researchers and engineers with a
unique opportunity to expand on the prospect of
sustainability. In my opinion, more should be invested into
this presently growing technology to enable even greater
developments in energy conservation. This will allow for
greater energy efficiency and sustainability almost
everywhere, from the field of heavy industry to fields of
environmentally friendly energy systems to commercial
fields, such as the automobile industry. With greater
development in thermoelectrics we can make better use of
all the thermal energy lost every day to work toward a more
sustainable future that will ultimately lessen the negative
impact on our planet and its resources.
ENGINEERING THERMOELECTRICS
University of Pittsburgh, Swanson School of Engineering 1
10/30/12
The technology behind thermoelectrics lies in its
materials. The materials must be adjusted to gather the
highest ZT value. ZT, the figure of merit for thermoelectrics,
represents the ratio of electrical conductivity to thermal
conductivity [4]. Ideally, one would want a material that is
highly electrically conductive and highly thermally resistant.
This would allow for free electron movement in the material,
while also preventing the phonons, the vibrations that carry
thermal energy, from migrating [5]. The interaction between
the phonons and the material, insofar as there is a proper
segregation of phonons from the rest of the thermoelectric
system, provides the electrical output. This ideal material
should have a relatively high ZT value. What, then, would a
high ZT value look like? The standard for many decades
would reach, but not surpass, a ZT value of 1 for the most
efficient thermoelectric materials. Recent improvements at
Northwestern University have raised the ZT value of
efficient thermoelectrics from 1 to 1.8 and then again from
1.8 to 2.2 [2]. In the future, scientists will continue to make
improvements to existing materials to further increase the
ZT value. Mercouri G. Kanatzidis, who led the research at
Northwestern University, optimistically says, “Improving
the ZT never stops -- the higher the ZT, the better” [4]. As
long as the material can be improved, researchers and
engineers have yet to put a completely definite cap on what a
good ZT should be.
SETBACKS IN DEVELOPING EFFICIENT
THERMOELECTRICS
The general idea behind thermoelectrics has existed since
the 19th century, but only since the first space trips have we
been searching for an efficient way to convert heat to
electricity. One of the largest setbacks we have found in
searching for efficient thermoelectrics is finding the most
efficient material. It is important to refer back to the figure
of merit, the ZT. Efficiency in thermoelectrics is guided by
its ZT. A higher ZT will be more efficient than a lower ZT.
Again, this value is determined by a ratio of electrical
conductivity to thermal conductivity. Vinayak P. Dravid,
one of the researchers for the Northwestern team, says, “it is
hard to increase one without compromising the other,”
remarking on the difficulties in finding an efficient
thermoelectric material [4]. Finding a naturally occurring
material that can provide a sufficient ZT value has proven a
difficult, if not impossible, task. Many different insulators,
conductors, and semiconductors were tested in the search for
the ideal material. There were drawbacks for each type of
naturally occurring material attempted. Insulators, which
Dan Gruber
have both a low electrical and thermal conductivity, and
conductors, which have a high electrical and thermal
conductivity, proved to be too weak of thermoelectrics for
any legitimate use. In either of these materials, according to
the ratio of electrical to thermal conductivity, the ZT would
be too low to be efficient enough for use. Any naturally
occurring semiconductor also failed to meet sufficient
efficiency standards. However, modifying a semiconductor
at the atomic level allowed for a relatively high ZT of 1,
considering that unmodified materials could not reach this
value prior [2]. This seemed to be the best ZT number. After
decades, though, this number stalled at 1 for lack of better
material. However, more recent advances have managed to
bring that number up significantly. We now know that a ZT
of 1 was only just the beginning.
lattices, researchers discovered a far more efficient material
that can be used to allow the free flow of electrons while
holding back the flow of phonons.
Originally, thermoelectric materials could only regain
about 5-7 percent of lost thermal energy [5]. With these
more recent breakthroughs, researchers predict 15-20
percent efficiency [1]. More remarkable than these numbers,
this method of manipulating the scattering of phonons in the
material used, lead telluride, can be used by any other
thermoelectric material. This means that the method used by
these researchers and engineers to create this efficient
material can be replicated on virtually any compatible semiconductive material. These researchers have done more than
simply create a monopoly for lead telluride to work as the
only thermoelectric material. They’ve created a system
whereby any like material can be manipulated in a similar
manner. A cheaper material, for instance, of similar
properties to lead telluride, could be implemented to create a
sufficiently efficient thermoelectric material that would cost
less for the public. This versatility of materials, along with a
general development of the technology over time, will allow
for even greater values of efficiency or make thermoelectrics
more economically viable to the public [1]. “‘I am sure that
the authors’ findings will trigger exponential progress in the
performance of thermoelectric materials,’ writes [Tom
Nilges, a chemistry professor at the Technische Universität
München in Garching, Germany]” [2]. Researchers are now
confident that they can reach ZTs of 2.5 or 3, which means
the efficiency of thermoelectric materials is predicted rise as
well.
ADVANCES IN DEVELOPING
THERMOELECTRIC MATERIALS
Within the past decade, scientists and researchers
managed to develop materials that would provide a higher
ZT number than 1. Scientists had already known how to
modify the thermal conductivity of the material at an atomic
scale, by replacing certain atoms along the thermoelectric
material’s crystal lattice, to find a ZT of about 1 or 1.1 [2].
In doing this, scientists disrupted only the phonons, the
thermal vibrations, of a short wavelength. In 2004,
researchers and engineers at Northwestern University found
that by adjusting the material at the nanometer-scale, by
rearranging the crystal lattices, they could create a ZT of up
to about 1.7 in the test materials [2]. Their method, which
was really a combination of methods, disrupted the phonons
of short and medium wavelength. Very recently, however,
scientists and researchers at Northwestern University have
managed to obtain a ZT of 2.2. The method used
compounded the previous methods of material configuration
at smaller scales with another layer of configuration at the
mesoscale, at about the scale of 1 micrometer. (See figure
below [2]) “In particular, the researchers improved the longwavelength
scattering
of
phonons
by
controlling and
tailoring
the
mesoscale
architecture of
the
nanostructured
thermoelectric
materials”
[3].
By rearranging
the
larger
structure
of
WHY ARE THERMOELECTRICS
IMPORTANT?
As much as 40 percent of petrol energy is lost to heat
waste. Two thirds of coal energy is lost to the escape of
thermal energy [5]. So much energy is continuously lost
from these systems. Systems with lower energy efficiency
and sustainability must rely more heavily on outside sources
of power. Such reliance on other power sources puts undue
amounts of strain on the environment around them. As an
engineer, I must seek the path that creates sustainable
systems that lessen the dependence and burden on the
environment around me. The National Society of
Professional Engineers’ (NSPF) code of ethics has
something to say about the protection of the environment for
the uses of the future. The NSPF says, “engineers are
encouraged to adhere to the principles of sustainable
development in order to protect the environment for future
generations” [6]. Engineers have a duty not only to
themselves but to the environment around them. The
American Institute of Chemical Engineers (AIChE) and the
Institute of Electrical and Electronics Engineers (IEEE) both
have a similar directive in their codes. The AIChE code of
ethics states that its engineers should strive to “protect the
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environment in performance of their professional duties” [7];
The code of ethics for the IEEE advises its engineers to
watch and warn for harmful environmental effects [8].
Engineers hold the well-being and protection of the
environment to a high degree. Thermoelectrics are important
because they give scientists and engineers the opportunity to
explore sustainable energy systems that will help protect the
environment for many years.
In general, there are two ways to overcome the loss of
energy and the increased strain on the environment: create
better systems where heat is not a significant by-product or
has less opportunity to escape or find a way to regain energy
lost as heat escapes. Although both solutions would assist an
engineer’s goal to create a more energy sustainable world,
given the more recent advancements and breakthroughs in
thermoelectric materials, the more viable solution now is the
latter, to find a way to regain most of the thermal energy
released as a part of the system. The most efficient
thermoelectric materials can convert up to 20 percent of
surrounding thermal energy into electrical energy. Applied
to the automobile industry, thermoelectrics can increase the
efficiency of the energy use and consumption of cars up to 8
percent. Higher energy efficiency would lighten the car’s
dependence on gas and could create more fuel efficient
vehicles because of that. Thermoelectrics applied to cars
would have clear benefits, as you would see in the gas
mileage increasing. Given how successful scientists and
researchers have been so far, and how confident they are that
they will continue to make progress, it is really only a matter
of time before thermoelectrics become commercially
available and commercially viable. These thermoelectric
materials can also be used to retrieve the waste heat energy
lost from coal energy. In that case, where two thirds of the
energy is lost, thermoelectrics could be even more helpful in
retrieving and converting larger quantifications of energy.
Thermoelectrics could have a large impact on the world
of already sustainable energy solutions. Solar panels, as of
now, “only metabolise the photons from the high-frequency
part of the electromagnetic spectrum, meaning most of the
sun's rays are lost as waste heat” [5]. The addition of
thermoelectric materials to the general make and
composition of solar panels would grant these eco-friendly
devices the ability to absorb a much larger spectrum of the
Sun’s energy. “Use thermoelectric materials to harness the
entire spectrum and your solar panel will get whopping good
efficiencies” [5]. Thermoelectrics would have the benefit of
being able to absorb some of the energy it previously could
not receive. The commercial benefit would be that the
energy necessary to power a house or other commercial
items would be provided now in a larger part by the
thermoelectrically supported solar panel. There would be a
slightly reduced energy bill if solar panels were applied to a
house as well.
Thermoelectrics are important and interesting to me for
these and a few other reasons. I wish to be an electrical
engineer. I see thermoelectrics as a fantastic opportunity to
work toward a more complete sustainable system of energy
conservation. I would be more than overjoyed if I were to
see such a feat progress in my lifetime. More than that, if I
could have a hand in its development, it would be a very
personal thing for me to work with. We have before us a key
opportunity to decrease our environmental footprint, and I
think it’s really unique to be knowledgeable about it or be a
part of it. Thermoelectrics are not new, but I am glad to look
upon thermoelectrics as we discover new ways to utilize it
for better and more efficient energy. I think there is value as
well in discussing the prospect of thermoelectrics within a
paper format such as this one. This assignment has allowed
me to have some experience now with a real, current
engineering issue. It has given me the opportunity to find a
subject that I can be interested in by personalizing it for me.
This has allowed me to self-motivate myself in this project,
so that I could get the greatest experience out of this [9]. I
have taken a personal interest in this topic that I have chosen
and I have absorbed so much of the information that I have
researched and reviewed. As a result of this assignment, too,
I have discovered and studied the different codes of ethics
for engineers. This has also been really important in this
assignment, as now I am more familiar with these codes that
all engineers should be knowledgeable of. Overall, this
assignment has opened many doors for me to peer through in
the world of engineering and that has been a tremendous
benefit.
REALIZATION OF THE POTENTIAL OF
THERMOELECTRICS
In my opinion, it is worth the effort to focus on
thermoelectrics. The study and utilization of thermoelectrics
has only just recently exited a field that had previously been
in a period of decades of stagnation. The technology is here
to look into and develop thermoelectrics more fully. There
have already been tremendous breakthroughs in this subject.
With a little more push we will certainly see even greater
strides. Certainly we can one day see thermoelectrics becom
commercially viable and helpful. Once we can apply what
we know about thermoelectrics to the world around us, with
cars and industrial factories and sustainable energy
operations, we can make everything a little bit more energy
efficient. If we become more energy efficient we can lower
our dependence on any energy, foreign or domestic. With
the right amount of focus and attention on thermoelectrics,
we are one step closer to a more energy efficient and selfsustaining world. We come one step closer, too, to a world
that is built for the prosperity of the environment for our
future generations. In developing thermoelectrics, we can
really say that we are progressing toward a healthier and
happier world that can take care of itself.
REFERENCES
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Dan Gruber
[1] J. Pitchford. (September 27, 2012). “Record Breaking
Thermoelectric Material Developed.” Overclockers Club.
(Online
Article).
http://www.overclockersclub.com/news/32755/
[2] W. Jones. (September 2012). “Waste Heat to Electricity
Breakthrough.” IEEE Spectrum. (Online article).
http://spectrum.ieee.org/semiconductors/materials/wasteheat-to-electricity-breakthrough
[3] M. Fellman. (September 19, 2012). “World Record
Holder: Thermoelectric Material is the Best at Converting
Heat Waste to Electricity.” Northwestern University. (Online
article).
http://www.northwestern.edu/newscenter/stories/2012/09/wo
rld-record-holder-.html
[4] (September 24, 2012). “Thermoelectric Material is
World’s Best.” Energy Harvesting Journal. (Online article).
http://www.energyharvestingjournal.com/articles/thermoelec
tric-material-is-worlds-best-00004751.asp?sessionid=1
[5] S. Adee. (September 26, 2012). “Thermoelectric
Efficiency Boost is Good News for Solar.” One Per Cent.
(Online blog).
http://www.newscientist.com/blogs/onepercent/2012/09/ther
moelectric-efficiency-boos.html
[6] (2012). “NSPE Code of Ethics for Engineers.” NSPE.
(Online
Website).
http://www.nspe.org/Ethics/CodeofEthics/index.html
[7] “Code of Ethics.”AIChE. (Online Website).
http://www.aiche.org/about/code-ethics
[8] (2012). “IEEE Code of Ethics.”IEEE. (Online Website).
http://www.ieee.org/about/corporate/governance/p7-8.html
[9] D. Gillet. (April 14-16, 2010). “Personal Learning
Environments in a Global Higher Engineering Education.”
IEEE Xplore. (Online Article).
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=549248
3&tag=1
ACKNOWLEDGMENTS
I would like to thank Rick Schaub for inspiring me every
Tuesday and Thursday to work hard and be the best
engineering student that I can be. I would also like to thank
Janine Carlock for providing terrific commentary and
suggestions for my second writing assignment.
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