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POLYCRYSTALLINE SILICON SOLAR CELLS: CHEAP AND EFFECTIVE
Brian McDonald (bpm35@pitt.edu)
USING POLYCRYSTALLINE SILICON
SOLAR CELLS TO POWER OUR
EVERYDAY LIVES
time in batteries. The most common batteries are lead-acid
batteries and nickel-cadmium batteries.
Unfortunately photons often reflect off the surface of the
solar cell or impact too far from the electric field and go
unused. The location of impact cannot be changed in any
way but the number of photons that reflect off the surface
can be greatly reduced. An antireflective coating can be
administered to the cell to increase the number of photons
that are absorbed. The cell can also be covered with a piece
of glass to achieve the same effect.
When photons’ wavelengths lie outside the spectrum of
visible light they sometimes simply do not have enough
energy to release an electron in the solar cell. The required
energy of a photon in a crystalline silicon cell is about 1.1
electron volts which is difficult for some photons to match
[5].
Another issue is silicon’s property of being a
semiconductor which means that it has a very high internal
resistance and much of the energy absorbed from the
photons is lost. Through all these problems, however, these
solar cells still manage to output a large amount of energy.
In the recent attempts to solve the problem of our
reliance on fossil fuels, solar energy has become one of the
most promising solutions. Unfortunately, the most efficient
solar cells are also the most expensive. The lowest costing
solar cell that is readily available today is the polycrystalline
silicon solar cell. Continuing research and development of
these specific solar cells is very important because it is the
most likely type to become common in the lives of average
middle class people.
Furthering the development of
polycrystalline silicon solar cells will not only cut down our
reliance on fossil fuels but will be much more cost efficient
than them as well.
OVERVIEW OF POLYCRYSTALLINE
SILICON SOLAR CELLS
Monocrystalline vs. Polycrystalline Silicon Formations
From a general standpoint, solar cells, or photovoltaic
cells, convert photons to electrons that can be used to store
the energy [1]. This is only possible because of the silicon
used in the solar cell. Silicon is a semiconductor which
allows the cell to convert the photons to electrons. This
happens because the structure of silicon’s electrons allows
the atoms to bond and form a single silicon crystal. A single
silicon crystal can become unstable and decompose if it
becomes too large [5]. A solution to this issue is to use
multiple smaller silicon crystals rather than a single large
silicon crystal. The presence of multiple crystals in one
module is where the name polycrystalline silicon comes
from. Polycrystalline silicon solar cells are much easier to
produce than monocrystalline silicon solar cells due to their
stability.
A POLYCRYSTALLINE SILICON SOLAR
CELL IN EVERY HOME
Impact on Reliance on Fossil Fuels
We currently rely on fossil fuels for a large percentage of
our energy. The depletion of fossil fuels is a big issue in the
world today and solar energy is a popular replacement for
that lost energy. Solar cells can be attached to everything
from vehicles to buildings and homes to absorb and store
energy. The fuel efficiency of vehicles can be increased by
utilizing power from solar cells which would reduce the use
of fossil fuels in vehicles all over the world. Even more
solar cells can fit onto the roof of a house or industrial
building. The amount of energy produced from this many
cells is enough to power the building and possibly even have
excess power left over to store for future use. Especially
during cold seasons the energy can be used to replace the use
of fossil fuels in providing heat to home and other buildings.
How Solar Cells Work
The structure of a silicon crystal allows the electrons to
flow freely throughout the crystal. This flow of electrons
creates an electric field [5]. If a photon were to strike the
solar cell it would create a small hole in the field of
electrons. Electrons from the electric field will flow to fill
this hole. “The electron flow provides the current, and the
cell's electric field causes a voltage” [5]. With current and
voltage comes power which can be channeled and used to
power items requiring electricity, or stored for use at a later
Economic Benefits
An average family or home owner would never be able
to buy the most cutting edge solar cells, which means that it
is unrealistic to expect a real impact on the average person’s
life. For example, a higher end device could use lenses and
University of Pittsburgh, Swanson School of Engineering
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Brian McDonald
mirrors to focus the photons and would be much more
efficient. Polycrystalline silicon solar cells, however, are
very affordable and are ideal for the average family or
homeowner. Because monocrystalline silicon solar cells are
more difficult to make they are much more expensive and
not practical for the majority of people who could find use
for solar panels. The price of polycrystalline silicon solar
cells is projected to decrease in coming years due to the
market for solar cells growing 25%-45%/year [3].
Electricity providing companies are also offering deals to
customers who use solar cells in their homes. Customers of
electric companies can have the option to sell their excess
power back to the company that provides to them. With this
new option customers have the possibility of making back
the money they spent on their solar cells. Some solar cell
producing companies offer other deals to convince people to
buy their products. For example “Enfinity, a photovoltaic
(PV) solar energy development company, provides
customized solar solutions, including the design, installation,
funding, monitoring and maintaining of the systems. As part
of the power purchase agreement, customers only pay for the
energy produced by the facility, not for equipment or
installation” [4]. Deals like this give people economic breaks
they almost cannot turn away.
A somewhat more controversial discussion arises when
the Code of Ethics for Engineers states that “Engineers are
encouraged to adhere to the principles of sustainable
development in order to protect the environment for future
generations” and explains that “’Sustainable development’ is
the challenge of meeting human needs for natural resources,
industrial products, energy, food, transportation, shelter, and
effective waste management while conserving and
protecting environmental quality and the natural resource
base essential for future development” [6]. It is common
knowledge that the Earth’s supply of fossil fuels is being
depleted. This is why the search for new energy sources is
becoming such a big deal. At quick glance solar cells seems
like a legitimate replacement for fossil fuels; however, when
you take a closer look at how solar cells are made, it
becomes apparent that fossil fuels are used in the production
of all solar cells. This brings about an ethical dilemma about
whether or not the energy that will be generated by the solar
cell is worth sacrificing the energy contained in the fossil
fuels used to make it. The most important step the
engineering community can take is to make the solar cells
worth the losses in fossil fuels.
Efficiency
Education is the foundation of engineering and bringing
new members into the engineering community. Those
already in the engineering community are obligated by the
Code of Ethics for Engineers to continue in their education.
The code states “Engineers shall continue their professional
development throughout their careers and should keep
current in their specialty fields by engaging in professional
practice, participating in continuing education courses,
reading in the technical literature, and attending professional
meetings and seminars” [6]. The most important item
mentioned in this portion of the code is that engineers shall
participate in continuing education courses.
As for those who are in the process of studying to enter
the field of engineering, the education is much different.
Some are trying to reevaluate engineering education and
make changes to the way it is done. Patricia Campbell, a
leader of an education-consulting firm in Groton, Mass., is
working to reform engineering education through three
major ways. The first is that students would take classes in
“clusters” rather than taking individual classes, the second is
to work to improve students’ spatial-visualization skills, and
the third is to improve student-faculty interactions [7]. This
is just one example of how engineering education is being
reformed and refined in the world today.
As a first semester freshman studying engineering at the
University of Pittsburgh, I begin to wonder whether or not I
am qualified to speak knowledgeably on these topics of
engineering controversy and education. I believe that with
my very brief background in engineering that began only
two months ago, I am not very well qualified to write about
what engineers should and should not put more research and
EDUCATION IN ENGINEERING
The efficiency of polycrystalline silicon solar cells falls
below that of monocrystalline silicon solar cells. While
Mitsubishi Electric Corp of Japan has announced that they
have developed a polycrystalline silicon solar cell with an
18% efficiency, there are monocrystalline silicon solar cells
with efficiencies that range from 25%-30% [2]. This
difference in efficiency is due to the increased number of
crystals in the polycrystalline cell. Efficiency is also
affected by the angle at which the solar cells are oriented.
The angle which gives the maximum efficiency is related to
the hemisphere where the solar cells are located, and the
current time of year.
ETHICAL CONCERNS REGARDING
DEVELOPMENT OF SOLAR CELLS
The NSPE Code of Ethics for Engineers states that
“Engineers shall at all times strive to serve the public
interest” [6]. Furthering development and research in the
area of solar cells is in accordance with this statement made
in the code of ethics. Finding new sources of energy to
replace fossil fuels is very important to the majority of the
public. With growing interest in expansion of energy
sources, solar cells are becoming more and more popular
and common in the lives of those in this majority.
According to this section of the Code of Ethics for
Engineers, there are no ethical problems with the
development of solar cells.
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Brian McDonald
development into. At this point in my education I cannot do
much more than research the facts about polycrystalline
silicon solar cells and try to form an opinion based on what I
read. Perhaps later in my education I could make a better
case on these opinions with the knowledge engineering that I
will gain in that time. I believe that attempting to take a
position on an issue in engineering at this stage in my
engineering education is a bit unrealistic because to do so I
have to rely heavily on the thoughts and opinions of those
who are already knowledgeable in the various fields of
engineering relating to solar cells.
I feel the same way about reforms in engineering
education.
I cannot yet form an opinion on these
reevaluations and reforms because I am so new to
engineering education. Perhaps after the end of this
semester or the next I will be able to better compare my
education experience to those proposed in the various reform
plans.
untapped source of energy and will certainly be around
longer than our fossil fuels.
REFERENCES
[1] "Solar Energy." Britannica Concise Encyclopedia.
Chicago: Encyclopaedia Britannica, 2009. Credo Reference.
Web. 08 October 2012.
[2] "Improvements in polycrystalline Si solar cells." New
Materials Asia Sept. 2009: 6+. General OneFile. Web. 8
Oct. 2012.
[3] Bryner, Michelle, and Alex Scott. "Solar energy:
suppliers bask in white-hot market." Chemical Week 18 July
2007: 14+. Academic OneFile. Web. 8 Oct. 2012.
[4] "Solar energy." Lodging Hospitality 15 May 2009:
54. General OneFile. Web. 8 Oct. 2012.
[5] "How Solar Cells Work." HowStuffWorks. N.p., n.d.
Web. 08 Oct. 2012.
[6] "NSPE Code of Ethics for Engineers." NSPE Code of
Ethics for Engineers. N.p., n.d. Web. 30 Oct. 2012.
[7] "Re-Engineering Engineering Education to Retain
Students." - Percolator. N.p., n.d. Web. 30 Oct. 2012.
POLYCRYSTALLINE SILICON SOLAR
CELLS IN OUR FUTURE
Solar cells are simply devices we use to convert the
photons emitted from our sun into electrons which we can
use to power our devices. The flow of electrons creates an
electric current and a voltage which gives us power we can
use to power various appliances. While monocrystalline
silicon solar cells create a more effective electric field, they
are difficult to make and are therefore very expensive.
Polycrystalline silicon solar cells are easier to make but are
less efficient in collecting power. Due to the simpler
development process and lower cost, polycrystalline silicon
solar cells are ideal for the people who could benefit from
them the most.
As solar cells become more and more common, reliance
on fossil fuels will become greatly reduced. From putting
solar cells on cars to covering entire buildings fossil fuels
will no longer be as necessary as a source of power or heat.
The polycrystalline silicon solar cells are becoming more
affordable for average homeowners and they even have the
opportunity of profiting by selling their electricity back to
their respective electric companies.
Although some ethical dilemmas arise on the
development of solar cells, we can find a way to make the
rewards from solar cells worth more than the cost we pay in
fossil fuels to make them. In order to continue the
development of solar cells efficiently, we need to continue
and possibly even reform engineering education for current
and future engineers alike.
The further research and development of these
polycrystalline silicon solar cells is crucial to the future of
society. We need to reduce our reliance on fossil fuels and,
solar energy is a very credible replacement. Our fossil fuels
are running out, and we are spending more money than
necessary to use the last of them. Our sun is an excellent
ADDITIONAL SOURCES
"Solar Energy." Pakistan & Gulf Economist 1
2012. General OneFile. Web. 8 Oct. 2012.
July
ACKNOWLEDGEMENTS
I would like to thank everyone at the University of
Pittsburgh Writing Center for their helpful emails and
advice. I would also like to thank my friends and family
who inspired me to pursue Chemical Engineering, and
everyone whom I currently study Engineering with who
supports me.
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