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7/23/2019 Pouls, Jazz (Solar Cells)
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Solar Cells
Jazz Pouls
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Why solar cells?
Global Warming Rising Oceans/Melting Ice
Fossil Fuel Dependency
Rising price of gas
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What is a solar cell?
A device that absorbs light from the sun and
produces electrical current
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History of the Solar Cell
Edmond Becquerel 1839
o Discovers photovoltaic effect
Russell Ohl 1946
o
Patents the modern p-n junction solar cell
Bell Laboratories 1954
o First practical solar cell: 6%
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How does a solar cell work?
Photovoltaic Effect
o Photons knock electrons out of atom
o Electrons move upwards throughsemiconductor, then to an external
circuit, thus creating current
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n-type dopate: 5 valence electrons
in the Si crystal, free electron
p-type dopate: three valence electrons
in the Si crystal, positively charged “hole”
How does a solar cell work?
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p-n junction: where the two doped silicons
meet
depletion zone: creates an electric field
within the cell
How does a solar cell work?
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A solar cell in action
When hit with a photon of sufficient energy, electrons
jump from the valence band to the conduction band. The energy necessary to make this jump in energy is
called the band gap. Semiconductors are perfect for solar cells
because they only conduct when theirelectrons absorb photons from the sun
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A solar cell in action
Electrons in the conduction band leave
behind positively charged “holes” in thecrystal.
Electrons could “recombine” but...
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A solar cell in action
The electric field created by depletion zone
only allows electrons to go upwards.
This creates a diode, due to the p-n
junction.
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A solar cell in action
17:54
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A solar cell in action
front surface contacts
substrate
external circuit
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Solar Cell Efficiency
Power of incident light is calculated by:
o Irradiance x Surface Area
Power of incident light
Power of electric current produced
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Shockley-Queisser Limit
Major Assumptions: 1 junction, 1 material, unconcentrated sunlight
1.34 eV
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Why the limit?
Energy is lost because:
o the sun’s energy is converted to heat
o recombination occurs
o photons pass through the cell
Not to mention: reflection
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How to beat the system!
Concentrate the light
Multijunction cells
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But unfortunately...
Commercial solar cell/panel efficiencies
range from 10% to 20%
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Applications
Solar panels first relevant in space
Power output to Weight ratio is high
Space programs willingly to pay a premium
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Applications
Solar panels have become increasingly
attractive for home and business owners as
efficiencies have gone up and prices have
gone down. Solar energy is a low-maintenance
investment for many.
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Applications
Although solar cars are not going to be
practical anytime soon, solar energy could
be used to create hydrogen for fuel cell
vehicles.
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Applications
Large scale:
o Huge arrays with lots of surface area
o Preferably in flat deserts with little cloud cover
o Sun-tracking devices
o Concentrators/Reflectors
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Further Technologies
Thin-Film Solar Cells
Common materials:
o a-Si:H, CdTe, Cu(In,Ga)Se2
Proso Easier to manufacture
o Lower cost
o Less material used
o Often flexible
Cons:
o Lower efficienc
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Further Technologies
Thin-Film Solar Cells
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Further Technologies
Transparent Solar Cells
UCLA
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Further Technologies
Transparent Solar Cells
Only absorb photons that are invisible tohumans, letting visible light through
MIT
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Further Technologies
Transparent Solar Cells
Applications
o Windows
o Cellphones
o Computers
Only 2% efficiencies so far
Lots of room for improvement
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Joseph-Louis Lagrange
Lived 1736-1813
(kinda) French mathematician,
astronomer and physicist
Given Legion of Honor byNapoleon
Involved in both the Prussian
and French Academy of
Sciences
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Joseph-Louis Lagrange
Tautochrone curve
Lagrangian points
Lagrangian Mechanicso energy and momentum
o not forces
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Joseph-Louis Lagrange
Number Theory
Algebra
Calculuso Helped create calculus of variations
o Euler-Lagrange equation
o Lagrange error bound
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William Rowan Hamilton
Lived 1805-1865
Irish physicist, astronomer and
mathematician
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Reformulated classical and
Lagrangian mechanics
Resulted in Hamiltonian Mechanics
o
Hamilton’s principle function Served as base for quantum
mechanics
Optics
o Wave Theory of Light
Quaternions
William Rowan Hamilton where
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References
Anthony, Sebastian. "MIT Startup Makes Transparent Solar Panel." ExtremeTech. N.p., 25 Feb. 2013. Web. 18 July 2013.
Hamakawa, Yoshihiro. Thin-film Solar Cells: Next Generation Photovoltaics and Its Applications. Berlin: Springer, 2004. Print.
Hurley, Tracy, and Jane Alba. "Solar Panels." Animation. Sumanas, Inc., 2008. Web. 20 July 2013.
Jha, A. R. Solar Cell Technology and Applications. Boca Raton: Taylor & Francis, 2010. Print.
"MIT Startup Makes Transparent Solar Panel." ExtremeTech. N.p., 25 Feb. 2013. Web. 18 July 2013.
Nelson, Jenny. The Physics of Solar Cells. London: Imperial College, 2003. Print.
Reddy, P. Jayarama. Science & Technology of Photovoltaics. Leiden: CRC Taylor and Francis Group Balkema, 2010. Print.
"Solar Efficiency Limits." Solar Efficiency Limits. Four Peaks Technologies, 2011. Web. 22 July 2013.
Wrenn, Eddie. "Scientists Create Transparent Solar Panels." Mail Online. Daily Mail, 24 July 2012. Web. 18 July 2013.
Würfel, Peter. Physics of Solar Cells: From Basic Principles to Advanced Concepts. Weinheim: Wiley-VCH, 2009. Print.