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Physics 100
Lecture 20
Solar Photovoltaic Energy
April 11, 2018
4
Written Quiz – Chapters 8-9
Timer applet
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The Electromagnetic Spectrum
Electromagnetic waves carry energy
Waves are characterized by wavelength,
frequency, and speed
Speed c is constant, so higher frequency
f corresponds to lower wavelength l
f cl
6
The
Electromagnetic
Spectrum
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Photons
Electromagnetic waves come in little bundles
of energy called photons.
The higher the frequency (bluer the light) the
greater the energy.
The photons that are sufficiently energetic are
absorbed by solar cells to create electricity.
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photon constant frequencyE
Rank the energies of visible, radio, and
ultraviolet photons, from least to greatest.
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A. radio < visible < ultraviolet
B. visible < radio < ultraviolet
C. ultraviolet < visible < radio
D. radio < ultraviolet < visible
About Semiconductors
Semiconductors are often doped with impurities
P-type has too few bonding electrons
N-type has too many bonding electrons
A p-n junction forms the core of a working
photovoltaic cell. It gives the charges energy.
A photon striking the junction forms an
electron-hole pair, but the electron and hole are
forced in different directions, creating an
electrical current.
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A semiconductor
lattice
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n-typep-type
The
Photovoltaic
Effect
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Photovoltaic cells
Three kinds:
• Single-crystal
• Polycrystalline
• Amorphous
More info: http://www.eere.energy.gov/basics/renewable_energy/pv_cell_materials.html
Photo credits: http://www.eepe.murdoch.edu.au/resources/info/Tech/pv/index.html
Durable, reliable
Energy is intermittent
Expensive – 3 to 4 year
payback
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Solar Photovoltaic
Facts
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SEIA Solar Industry Data
The U.S. in 2015 has over
22,700 MW of installed solar
PV capacity, enough to
power more than 4.6 million
average American
households
Since the beginning of 2010,
the average cost of a PV
system has dropped by more
than 45 percent, and by an
even greater amount for
utility-scale projects.
15
Right here at UWSP
There is a large solar
photovoltaic panel at the
Noel Center for the Fine
Arts. The energy it
produces is used to light
a section of the inner
courtyard area.
More information about campus
energy production and usage can
be found at the UWSP Office of
Sustainability.
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What does it mean to say the efficiency
of a solar cell is 15%?
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A. 15% of the incident voltage becomes
current
B. 15% of the cell’s electrons become
holes
C. 15% of the incident light energy
becomes electrical energy
D. 15% of the input energy becomes light
energy
Storing solar energy
Intermittent solar and wind energies must
be stored for round-the-clock use.
Besides charging a battery (pp. 382-384, 397),
electrical energy can be stored by
pumping water (pp.386, 398), compressing
air, or converting it to the kinetic energy of
a rotating flywheel by means of a motor
(p. 398). Let’s explore the latter idea…
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A flywheel’s energy in J is given by
0.15[ω(rpm)]2. What power is needed
to spin rotor to 6000 rpm in 2.0 min?
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A. 450 W
B. 7.5 W
C. 3.0 kW
D. 45 kW
A flywheel’s energy in J is given by
0.15[ω(rpm)]2. What power is needed
to spin rotor to 6000 rpm in 2.0 min?
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A. 450 W
B. 7.5 W
C. 3.0 kW
D. 45 kW
2
2
0.15
0.15 6000 rpm J45,000 J/s
2.0 min 60 s/min
45 kW
WP
t t
P
Suppose the motor/flywheel system
is 88% efficient. What electrical
solar power must be supplied?
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A. 51 kW
B. 40 kW
C. 8.8 kW
D. 197 kW
Suppose the motor/flywheel system
is 88% efficient. What electrical
solar power must be supplied?
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A. 51 kW
B. 40 kW
C. 8.8 kW
D. 197 kW
out
solar
outsolar
45 kW 51 kW
0.88
Pe
P
PP
e
If a solar array is 24% efficient and
the insolation is 700 W/m2, what
array area is required?
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A. 0.0175 m2
B. 304 m2
C. 29.1 m2
D. 168 m2
If a solar array is 24% efficient and
the insolation is 700 W/m2, what
array area is required?
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A. 0.0175 m2
B. 304 m2
C. 29.1 m2
D. 168 m2
solar
solar
2
2
51,136 W
0.24 700 W/m
304 m or about 57 ft 57 ft
P IA
PA
I
Photovoltaic power plants
Solar Star California (579 MW, world’s largest in 2015)
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Photo credit: SunPower
Photo credit: Clean Technica and photo link
List of largest photovoltaic power stations
Photovoltaic power plants
Cestas Solar Farm France (300 MW, largest in Europe)
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Photo credit: PV magazine
Photo credit: PVTech
Photovoltaic power plants
Sarnia Solar Project, Canada (80 MW)
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Right here in Wisconsin
A 2.0-MW solar field built for Dairyland Power Cooperative in Medford, WI.
(Photo: Courtesy of Renew Wisconsin) USA Today article
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Right here in Wisconsin:
A 100-MW solar photovoltaic project is
planned (to open in 2021)
The Point Beach Solar Energy Center in Two Rivers, WI will be modeled
after the North Star Solar Project in North Branch, MN, the largest in the
Midwest. (Photo: Courtesy of D. E. Shaw Renewable Investments) Web site
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