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Disclaimer—This paper partially fulfills a writing requirement for first year (freshman) engineering students at the University
of Pittsburgh Swanson School of Engineering. This paper is a student, not a professional, paper. This paper is based on
publicly available information and may not provide complete analyses of all relevant data. If this paper is used for any purpose
other than these authors’ partial fulfillment of a writing requirement for first year (freshman) engineering students at the
University of Pittsburgh Swanson School of Engineering, the user does so at his or her own risk.
SOLAR ENERGY AND ME
Christopher Dern ([email protected])
INTRODUCTION: SOLAR ENERGY’S
APPEAL
power grid, the result would be energy prices three to five
times higher than they are now due to their inefficiency and
high manufacturing costs. However, improvements are being
made every day. Some test cells have exceeded 40%
efficiency [1]. While energy cells are small and utilize fairly
complex technology, power towers are large and relatively
simple. They consist of an elevated water tank, mirrors, and
salt. The water tank is placed on stilts and surrounded by
hundreds of mirrors. These mirrors sit atop individual axis
systems which allow them to follow the sun throughout the
day as well as the year. The mirrors are used to reflect the
sunlight onto the water tank. While energy cells convert
sunlight to electricity, a power tower transforms sunlight to
thermal energy, which is stored in the salt [4]. Although
advances in both the energy cells and power towers are being
made, they will be useless if the energy is unable to be stored
through the night or during a cloudy day. Some companies,
such as EIS Solar, do not even worry about a method of
storing the solar energy. If the solar panels on a building
create more power than is being used, the electricity meter
actually gets pushed backwards and the excess energy is sent
back to the power grid. This energy is then used by other
houses. In return for giving the power grid that extra boost,
the building is repaid in the form of an equal amount of
energy when its solar panels can no longer generate enough
electricity [5]. While this is a nice idea if only a few people
per grid took advantage of it, it would not work on a large
scale. The grid would receive influxes of electricity at
roughly the same times and be forced to dump most of it
since there is not a technology around that can handle storing
such a massive amount of energy. In turn, the grid would be
unable to deliver energy to the houses when they experience a
shortage as the grid possesses no form of excess energy.
When you think of how to store electricity, what is one
of the first things that come to your mind? A battery right?
So why can solar energy not be converted and stored within a
massive battery? The answer lies within the technology.
Scientists are not yet sure how to integrate large banks of
As a child some of my fondest memories stem from
the days of summer that seemed like they would never end.
My neighborhood friends and I would swim, ride bikes, play
kickball and have picnics while basking under the glorious
glow of the sun. None of us could have ever imagined that
we were playing in the light of one of the greatest sources of
power known to man. While we played freeze tag and picked
tangy blackberries from bushes, the sun was over us,
churning out immense amounts of energy. The rays of the sun
provide the equivalent of 10,000 times the power that
commercial energy produces on this planet. In just two
hours, the sun is able to saturate the earth with enough energy
to sustain current power usage for a year. Despite this
massive amount of energy being thrown at earth, the human
population is not taking advantage of it. Solar energy
accounts for less than one percent of total energy
consumption. It is environmentally friendly, abundant, and
perhaps the best part: free [1]. With fossil fuels inevitable
end looming closer every day, why has solar energy not been
put into action on a large scale all ready?
WAYS TO ATTRACT AND STORE SOLAR
ENERGY
The problem with solar energy is that there is not yet a
method for harnessing and storing such a massive amount of
energy for a relatively long period of time. Technology must
advance in the capture of the sun’s energy, the converting of
that energy into useful forms, and the storage of the energy
for when the sun’s rays no longer reach the earth’s surface.
Each of these sections of technologies has developed multiple
ways to accomplish their respective tasks. For example, both
an energy cell and a power tower can be used to capture the
suns energy. An energy cell is able to absorb sunlight and
convert it to electricity with 10-20% efficiency rate. This
number is not good. For example, if these cells were put on a
University of Pittsburgh, Swanson School of Engineering
11.01.2016
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Dern
batteries into our current power grids so they have turned to
other methods.
Inspiration can often come from nature. The grass that
I used to run around on and the plants that filled the scenery
with their magnificent beauty, for instance, provided
scientists an idea for a different way to store energy. This
technique attempts to mimic the process of photosynthesis of
plants. A photoelectrochemical cell uses solar energy to
separate water into hydrogen and oxygen which can be stored
as a fuel. To generate electricity, they are recombined in a
fuel cell. The problem with this is that advances in chemical
reaction efficiency must be made to make this idea
economically feasible. Nature’s enzymes for recombining
the two elements are far more efficient than anything an
industry has come up with yet [3]. Another technique that is
applied, especially around homes, is the usage of the ground
to store the energy. Deep, narrow holes are dug close
together with a pipe running them. A layer of insulin is then
placed over the holes. The pipe is filled with water which,
when heated by the solar energy, is able to disperse its
newfound thermal energy [2]. This method is good for
storing energy to heat a house but not much more.
by the plant. As an added benefit, when the plant comes to a
close the salt can be used as a high grade fertilizer [7].
Storing solar energy as thermal energy rather than electricity
seems to be the best, most cost effective way to go. As John
S. O'Donnell, executive vice president of the solar thermal
business, Ausra, once said, “a coffee thermos and a laptop
computer's battery store about the same amount of energy.
The thermos costs about $5 and the laptop battery $150” [4].
CONCLUSION: WHY SOLAR ENERGY IS
BENEFICIAL
While the world is not particularly desperate to find
alternative sources of energy, the day when fossil fuel runs
out will come. It is important that sources of renewable
energy are found, and none are more powerful than the sun. I
believe the best and fastest way to advance the use of solar
energy is through the power tower and its molten salt battery.
This design is simple and effective. Before more complex
technologies can be effectively used, the simpler ones must
be efficient. Progress is made from the base level up. When
the technology is advanced enough and the products are
affordable then the switch to solar energy can be made. This
would benefit societies by creating cleaner air and a healthier
environment to live in since solar energy produces little to no
pollutants [1]. Families could say goodbye to large electricity
bills at the expense of an initial start up fee to install the
energy system [3]. I have always been a fan of paying one
large cost instead of monthly fees. This is why the idea of
solar energy is so appealing to me. I would much rather pay
for installments once than pay an energy bill monthly. It’s
just one less thing I would have to worry about. I also like
the idea of producing clean energy that is not going to leave
behind a carbon footprint. I want my children to be able to
experience the same joy I once felt while running through the
beautiful picture nature was able to paint in my own
backyard. The advancement and use of solar energy will
create an overall healthier world by halting the production of
toxins manufactured through the use of fossil fuels. All that
is needed is a few technological improvements and a human
willingness to turn towards cleaner energy.
A MOLTEN SALT STORAGE SOLUTION
The “battery” of the power tower really intrigued me.
By using something as simple as molten salt, the thermal
energy provided by sunlight is able to be trapped. When the
thermal energy is needed later, the heat transfers from the salt
to water in the tower using a heat exchanger. The water then
turns to steam and drives a turbine [7]. I think that it is
exceptionally neat to see something similar to the table salt I
use to enrich my food be used as a type of thermal battery.
The main difference, however, is this salt is molten, while the
table salt is (thankfully) not. To improve this method of
storage experiments are being done to decrease the
temperature the salt must be kept at to remain molten while
increasing the salts stability at high temperatures. One such
research facility, Sandia National Laboratories, has found a
mixture of four nitrate salts that remained in a molten state in
temperatures as little as 100 degrees Celsius and stable when
heated to as much as 500 degrees Celsius.
Lower
temperatures call for less energy to keep the salt molten
during times when no solar energy is being absorbed while
higher temperatures allow more storage of thermal energy per
unit of molten salt [6]. Companies such as “SolarReserve”
have all ready started using this storage technique with
relatively high success. Their plants’ salt of choice is a
combination of sodium nitrate and potassium nitrate. The salt
never needs to be replaced during its over thirty year usage
ACKNOWLEDGMENT
I would like to thank my parents for assisting me with
this paper. If they had not driven me past solar farms as a
child I may have never thought of this topic to write my paper
on. It is through those efforts that I was able to write about
something I have always found interesting.
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SOURCES
[1] National Academy of Engineering. “Make Solar Energy
Economical.” NAE Grand Challenges for Engineering. 2016.
Accessed
10.30.2016
http://www.engineeringchallenges.org/challenges/solar.aspx
[2] M. Wald. “New ways to store solar energy for nighttime
and cloudy days.” New York Times. 4.15.2011. Accessed
10.30.2016
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[3] EIS Solar. “Solar Panels for Electricity in Pittsburgh.”
Energy Independent Solutions. 2016 Accessed 10.30.2016
http://www.eissolar.com/solar-panels-for-electricitypittsburgh/
[4] M. Panzer. “How can we effectively store solar energy?”
TuftsNow.
5.13.2013.
Accessed
10.30.2016
http://now.tufts.edu/articles/how-can-we-effectively-storesolar-energy
[5] Q. Xu and S. Dubljevic. “Modelling and control of solar
thermal system with borehole seasonal storage.”
Renewable Energy: an International Journal. 2016. Accessed
10.30.2016
http://web.b.ebscohost.com/ehost/detail/detail?vid=3&sid=cc
f6462c-dbc4-48c9-8f32a032a281a062%40sessionmgr106&hid=118&bdata=JnNpdG
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[6] SolarReserve. “Molten Salt Energy Storage.”
SolarReserve,
LLC.
2016.
Accessed
10.30.2016
http://www.solarreserve.com/en/technology/molten-saltenergy-storage
[7] R. Bradshaw and N. Siegel. “Molten Nitrate Salt
Development for Thermal Energy Storage in Parabolic
Trough Solar Power Systems.” ASME. 8.14.2013. Accessed
10.30.2016
http://energy.sandia.gov/wpcontent/gallery/uploads/ES2008-54174-molten-salt-fortroughs.pdf
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