Bigjahan 1
`
Bavrina Bigjahan
Writ 340 – Professor Townsend
Illumin Article
May 7, 2013
Solar Panels: a Stream of Energy
Abstract
Solar power has been used by humanity for thousands of years. In today's world, there are
many forms of harnessing solar power to create electricity. One of the most common forms of
electric generation is through photovoltaic cells. Surprisingly, this process of electric generation
is similar to electric generation from a water wheel, where atoms move through a mini turbine to
create electricity. Currently, photovoltaic cells are constrained by space limitations and the
efficiency of the materials used, mainly silicon, by which atoms can move. The future of
photovoltaic electric generation is limited only by our imagination, as space around is used more
efficiently incorporating photovoltaic cells, and the materials used are changed from silicon to
organic photovoltaic cells.
I
Introduction
Humanity’s use of solar energy extends back through thousands of years. The earliest
documented use of solar energy is where magnifying glasses were used in Ancient Greece to
burn ants in the 7th century BC. Solar energy was also used for ceremonial purposes where
multiple reflective mirrors would focus the sun’s energy on a singular object (like a torch) to set
fire.1 Perhaps the best known example of solar energy in the ancient world was the myth that
Archimedes used giant mirrors as a weapon when he reflected sunlight towards attacking Roman
ships around 212 BC and set them on fire.2
In today’s world, one of the most common forms of electric generation is through
photovoltaic cells.3 Surprisingly, this process of electric generation is similar to electric
Bigjahan 2
`
generation from a water wheel, where atoms move through a mini turbine to create electricity.
Electric generation from photovoltaic cells is constrained by the materials used in its
construction, and space requirements. However, the future of solar energy and photovoltaic cells
is looking sunny with the use of new materials, and innovative ways of effectively placing solar
panels.
II
Photovoltaic Cells – Borrowed Technology from Water Wheels
The electricity generated from photovoltaic cells is very similar to electric generation
from a water-wheel. In a water-wheel, water pushes against the paddles, and rotates the wheel in
the opposite direction of the water current. This creates a turbine, which creates electricity.
Figure 1: Water wheels and solar cells generate energy in a similar fashion 4
Harnessing electricity from solar energy works in much the same way as a water wheel.
The process of converting solar power into solar energy is as follows: the sun’s rays hit
photovoltaic cells; an electric current is created as more of the sun’s rays hit the photovoltaic
cells; the electric current is transferred to the charge controller; the charge controller converts the
electric current to Alternating Current (AC) power or Direct Current (DC) power.5 The
difference between AC power or DC power is based on the energy flow where DC power flows
one way, and AC power can flow both ways.6
Bigjahan 3
`
Figure 2: Process of sun rays converting to electric power
The similarity of the water wheel example occurs when the sun’s rays hit the photovoltaic
cells. Obviously, a photovoltaic cell’s components are different than a water wheel.
Photovoltaic cells are electrical devices that convert solar power to electricity. As will be
discussed in greater detail below, photovoltaic cells are primarily made up of silicon.
Photovoltaic cells consist of two layers, a Positive layer (P-layer) and a Negative layer (NLayer). The P-layer is positively charged, which means that the atoms have fewer electrons. The
N-layer is negatively charged and has extra electrons. Separating the P and N- Layer is the P-N
junction. The P-N junction is a barrier with a neutral charge.7
Figure 3: Three major parts of a solar are: N-Layer, Junction, and P-Layer8
Sunlight carries small energy particles called photons. When sunlight hits a photovoltaic
cell, each photon breaks an electron away from the P-layer and causes it to go the N-layer, and
another photon causes a positive atom from the N-layer, to go to the P-layer.9
Bigjahan 4
`
Figure 4: Process of breaking a photon to an electron inside a solar cell8
The importance of the P-N junction is that it acts as a barrier. Freed electrons that go to
the N-layer cannot go back to the P-Layer. The extra electrons look for an exit. An outlet, which
is device that allows electrons to exit, is provided. The extra electrons go through the outlet, then
through a load, and then go to the P-Layer. Movement through the load creates electric current.7
This concept is analogous to the water wheel discussed above.
Figure 5: Flow of electrons in a solar cell is similar to the flow of water around a water wheel8
Like a water-wheel, the more electrons that flow through the load, the more electricity is
created. And the more photovoltaic cells that are connected together, the more electricity is
generated.
III
Construction and Types of Solar Panels
Solar energy is green. Unlike other forms of electric generation, solar panels do not
produce hazardous waste materials. Each solar panel works for decades. For example, early
Bigjahan 5
`
commercialized solar panels made in the 1970s still work at approximately 80% of their original
efficiency.10 However, the electricity produced from photovoltaic cells is limited by the materials
used, and the space required for solar panels.
a) What Materials Make Up Current Photovoltaic Cells and the Limitations That
Exist With Those Materials
The movement of electrons depends on what materials are used in a photovoltaic cell. In
2011, 90% of solar panels were silicon based10 because of the stability of silicon’s atomic
structure. If there was too much electron movement within the materials used, it would cause the
photovoltaic cells to melt.11
There are four major types of solar panels: monocrystalline silicon solar cells,
polycrystalline silicon solar cells, film solar cells, and vaporware solar panels. Silicon is the
major element used in the production of the first two examples listed. The main difference
between these four groups is conversion efficiency, which is a measurement of calculating how
much electricity is produced with a given amount of sunlight.
Monocrystalline silicon solar cells are the most efficient solar cells, where they generate
the optimum amount of electricity. As such, monocrystalline solar panels are ideal for regions
where space for installing solar panels is limited. This way, the solar panel will generate the
maximum amount of electricity compared to its competitor types. The problem with
monocrystalline solar panels is that they are the most expensive because the main element in the
production of this type is a single and very pure crystal of silicon.12
Bigjahan 6
`
Figure 7: Monocrystalline Silicon Solar Cells13
Polycrystalline silicon solar cells are slightly less efficient compared to monocrystalline
solar panels, but they are much cheaper. The reason behind its lower price is that polycrystalline
silicon solar cells have a lower level of silicon purity, resulting in an easier form of
manufacturing.
Figure 8: Polycrystalline Silicon Solar Cells14
One way to tell the difference between monocrystalline and polycrystalline solar panels is
to observe whether the solar panels look rectangular or are filleted at the edge. In the production
of monocrystaline solar panels, the Czochralski process is used (a specific method of crystal
growth used to obtain single crystals of semiconductors) during which monocrystalline solar
cells are made out of silicon ingots which have a cylindrical shape. In order to maximize the
performance, the four corners of the solar cell are cut out of the cylindrical ingots to make silicon
wafers. Therefore, a monocrystalline solar panel looks like it is made of small octagons. On the
Bigjahan 7
`
other hand, polycrystalline solar cells are rectangular; thus, it has less material waste during its
production. 16
Thin film solar cells (TFSC) are the least efficient silicon based solar cell, require the
most amount of area to generate the same amount of energy when compared to monocrystalline
and polycrystalline solar panels. The manufacturing process for TFSCs is simplest and result in a
lower cost. TFSC panels come with a shorter warranty since its life expectancy is the lower
compared to monocrystalline and polycrystalline solar panels.
Figure 9: Thin Film Solar Cells (TFSC)16
The fourth type of solar panels is called Vaporware solar panels, which is the least
expensive choice in terms of generating power. Vaporware solar panels are still being
researched, and there is not mass production. Vaporware solar panels work by spraying plastic
over the solar cells. This type is claimed to be the future of solar energy since it is very efficient
in terms of generating electricty,17 and it will cost very low, around 5 cents a watt18.
Currently, the percentage of energy from the sun turning into electricity can range
anywhere from 5% to 44%. Provided below is an efficiency graph that has been maintained by
L.L. Kazmerski at the National Renewable Energy Laboratory since 1984. This chart documents
all variations of the types of solar panels listed above.
Bigjahan 8
`
Figure 10: Efficiency graph of various types of solar cells’(discussed in this paper): The efficiency of photovoltaic
cells has continued to rise for decades.19
b) Space Limitations of Solar Power
The disadvantages with solar panels are that they need to be outside with lots of space in
order to capture sunlight, they need to be constantly cleaned and maintained, and they have a
high initial cost that takes years to make up.
For example, with respect to the space required to make solar cells worthwhile, a recent
study Arkansas shows that in order to generate 1800 Megawatts of energy (1800 Megawatts is
enough electricity to power approximately 1.8 million average Arkansas homes) using nuclear
reactors, only 1100 acres of land is needed. But to generate the same amount of energy using
photovoltaic panels 13320 acres is needed. This is more than 12 times the space needed to build
a nuclear reactor.20
In addition to cost, solar cells need to be cheaper in order to be accessible to the general
population. It currently takes about 15 years to 25 years to payback the costs of installing solar
panels at a residential unit.21 Maintenance and cleaning of solar panels also creates additional
costs that are easily forgotten sometimes.
Bigjahan 9
`
IV
Future of Photovoltaic Cells
The earth receives more energy from the sun in one hour than what the world needs in a
full year.22 The future of photovoltaic cells will come from two forms: space allocation; and new
materials that will have higher efficiency in converting the sun’s power into electricity.
With regards to adequate space allocation, new ways will be used to make efficient use of
solar panels. For instance, we as society can start adding solar panels to existing infrastructure,
like walls or buildings. Besides just the structural importance of a wall, it will now have new
functions such as energy collection. For example, 16,000 solar panels on top of two miles of a
man-made tunnel in Belgium.23 The tunnel now acts as a tunnel, and generates electricity.
Photovoltaic cells will also begin to use other materials. For example, organic
photovoltaic cells will be used. What this means is that the same process above will happen,
except with different materials on a molecule base rather than an atom based “water-wheel”
process. As discussed above, current photovoltaic cells primarily use silicon because of the
stability of its atomic structure. Electricity created is because of movement created by instability
at the atomic level. The difference between organic photovoltaic cells and the current silicon
photovoltaic cells is that rather than photons interacting with atoms, photons will interact with
chemical compounds in organic photovoltaic cells. Larger chemical compounds will replace the
smaller atomic particles such as electrons and atoms.24 The advantages of organic photovoltaic
cells is that they are much more low-cost than silicon, and their materials are much more
abundant.25
Therefore, the future of photovoltaic electric generation is limited only by our
imagination, as space around is used more efficiently incorporating photovoltaic cells, and the
materials used are changed from silicon to organic photovoltaic cells.
Bigjahan 10
`
Bavrina Bigjahan
Bavrina Bigjahan is a senior majoring in Civil Engineering at University of Southern
California. Bavrina can be found playing tennis and cooking in her free time.
Bigjahan 11
`
Citation:
[1] "The History of Solar," U. S. Department of Energy - Energy Efficiency and Renewable
Energy, [online] http://www1.eere.energy.gov/solar/pdfs/solar_timeline.pdf (Accessed:
14 Mar. 2013).
[2] Grier, Peter, "Obama on 'Mythbusters': What Happened with His 'death Ray'?" The Christian
Science Monitor, [online] 09 Dec. 2010 http://www.csmonitor.com/USA/Politics/TheVote/2010/1209/Obama-on-Mythbusters-What-happened-with-his-death-ray (Accessed:
19 Mar. 2013).
[3] "Concentrating Solar Power." U. S. Department of Energy - Energy Efficiency and
Renewable Energy, [online]
http://www.eere.energy.gov/basics/renewable_energy/csp.html (Accessed: 14 Mar.
2013).
[4] "Waterwheel Design." For Hydro Electric Power. Alternative Energy Tutorials, [online]
http://www.alternative-energy-tutorials.com/hydro-energy/waterwheel-design.html
(Accessed: 2 Apr. 2013).
[5] "Solar Energy | Smart Energy Today | Energy Conservation ExpertsSmart Energy Today |
Energy Conservation Experts." Smart Energy Today, [online]
http://www.smartenergytoday.net/industryknowledge/solar-energy/ (Accessed: 20 Mar.
2013).
[6] "AC/DC: What's the Difference?" PBS, [online]
http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html (Accessed: 19 Mar. 2013)
[7] Delorme, Dan. "Lesson and Lab Activity with Photovoltaic Cells." Cornell University,
[online] June 2004
http://www.ccmr.cornell.edu/ret/modules/documents/PhotovoltaicCells.pdf (Accessed: 19
Mar. 2013).
[8] "How Photovoltaic Cells Work." SolarEnergynet News. [online]
http://www.solarenergy.net/Articles/how-photovoltaic-cells-work.aspx (Accessed: 1 Apr.
2013). (Original Image Source)
[9] Watson, Margaret. "The Photovoltaic Effect." Sustainable Energy Systemz RSS. [online] 3
Jan. 2012 http://sustainableenergysystemz.com/the-photovoltaic-effect/172/ (Accessed: 3
Apr. 2013).
[10] "How Long Do Solar Panels Last?" One Block Off the Grid: The Smart New Way to Go
Solar. [online] http://howsolarworks.1bog.org/how-long-do-solar-panels-last/ (Accessed:
18 Mar. 2013).
Bigjahan 12
`
[11] "Silicon Materials and Devices R&D." NREL: Photovoltaics Research -. National
Renewable Energy Laboratory, [online]
http://www.nrel.gov/pv/silicon_materials_devices.html (Accessed: 19 Mar. 2013).
[12] "8 Good Reasons Why Monocrystalline Solar Panels Are the Industry
Standard."Monocrystalline Solar Panels: Advantages and Disadvantages [online]
http://www.solar-facts-and-advice.com/monocrystalline.html (Accessed: 3 Mar. 2013).
[13] KSENYA. "Monocrystalline Solar Cells." Solar Tribune. [online] 9 June 2011
http://solartribune.com/monocrystalline-solar-cells/ (Accessed: 16 Mar. 2013).
[14] "Solar Panels." SunWave Solar, [online] http://sunwavesolar.net/Solar_Panels.html
(Accessed: 16 Mar. 2013).
[15] Paul, Rebecca. "GE Will Build the Largest Solar Panel Factory in the United States |
Inhabitat - Sustainable Design Innovation, Eco Architecture, Green Building." Inhabitat
Sustainable Design Innovation Eco Architecture Green Building GE Will Build the
United States Largest Solar Panel Factory Comments. Building Better Cities, [online] 7
Apr. 2011 http://inhabitat.com/ge-will-build-the-largest-solar-panel-factory-in-the-unitedstates/ (Accessed: 02 Mar. 2013).
[16] "Which Solar Panel Type Is Best?" Energy Informative. [online]
http://energyinformative.org/best-solar-panel-monocrystalline-polycrystalline-thin-film/
(Accessed: 18 Mar. 2013).
[17] Lempner, Thom. "The Four Types of Solar Electric Panels and the Benefits of Using Solar
Energy." [online] http://EzineArticles.com/6266206 (Accessed: 17 Mar. 2013).
[18] Brown, G.F., and J. Wu. "Third Generation Photovoltaics." Laser & Photonics Review 3.4
[Print] 2009: 394-405.
[19] Stevenson, Richard. "Tapping the Power of 100 Suns." [online] 31 Aug. 2012
http://spectrum.ieee.org/green-tech/solar/tapping-the-power-of-100-suns (Accessed: 02
May 2013).
[20] "-A Comparison: Land Use by Energy Source - Nuclear, Wind and Solar." Entergy, [online]
http://www.entergy-arkansas.com/content/news/docs/AR_Nuclear_One_Land_Use.pdf
(Accessed: 2 Mar. 2013).
[21] Delconte, Tom. "The Five Disadvantages of Solar Power." Home Energy Pros. [online] 4
Apr. 2013
http://homeenergypros.lbl.gov/profiles/blog/show?id=6069565:BlogPost:80025
(Accessed: 10 Mar. 2013).
Bigjahan 13
`
[22] "Will Solar Power’s Future Be Bright?" CLIMATE DECISION MAKING CENTER.
Carnegie Mellon University, [online] http://cdmc.epp.cmu.edu/docs/pub/Solar.pdf
(Accessed: Web. 23 Mar. 2013).
[23] Mauriss, Britt. "5 Fresh Innovations in Solar Technology." CleanTechnica. [online] 28 Jan.
2012. http://cleantechnica.com/2012/01/28/5-fresh-innovations-in-solar-technology/
(Accessed: 10 Apr. 2013).
[24] Jiang, Xiaomei. "Organic Semitransparent Photovoltaic Energy Converter (OSPEC) - A
Green Solution to Today's Energy Needs." Organic Semitransparent Photovoltaic Energy
Converter (OSPEC) - A Green Solution to Today's Energy Needs. [online] 08 Nov. 2012
http://www.azonano.com/article.aspx?ArticleID=2470 (Accessed: 03 May 2013).
[25] "Organic Photovoltaics Research." SunShot Initiative, [online]
http://www1.eere.energy.gov/solar/sunshot/pv_organic.html (Accessed: 2 Apr. 2013).