Transcript Renewable Energy Sources

Renewable Energy Sources
.
Solar Cells
SJSU-E10
S-2008
John Athanasiou
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Renewable Energy Sources
Renewable:
They can last indefinitely
1.
Wind Turbine:
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2.
Converting the wind energy into electricity
Wind, Propeller, Electric Generator, Current Flow
Solar Cells
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Converting the Sun’s (light) energy directly into electricity
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3.
Intensity of the sunlight
Wavelength of the sunlight
Type and surface area of the solar cell
Fuel Cells
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Producing electricity by combining Hydrogen and Oxygen
to produce H2O
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Energy Usage
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Arizona to become 'Persian Gulf' of solar energy (CNN)
• Abengoa Solar will operate the $1 billion plant
• The solar plant would be able to power 70,000 homes
• Arizona governor: No reason we can't be "Persian Gulf
of solar energy"
• Regulators requiring 15 percent of electricity from
renewable sources by 2025
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What are Solar Cells?
• Solar cells are devices which convert solar light energy
directly into electricity
• Sunlight contains packets of energy called photons that
can be converted directly into electrical energy.
• This is referred to as the photovoltaic effect.
• Photo- means light and -voltaic means electrical current;
• A solar cell provides direct current (DC) electricity, similar
to batteries.
• Batteries however use electrochemical reaction.
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Atoms
An atom is composed of three different particles:
•
3.
Nucleus- Center of the atom:
1. Protons (P+)-- positively charged.
-- equal to the number of
electrons.
2 Neutrons -- no charge.
Electrons (e-) -- negatively charged.
-- orbit the nucleus.
The outermost electrons of an atom
determine its chemical and electrical
properties
Democritus
c.300 BC
Protons (P+)
Neutrons
(e-)
www.cfo.doe.gov/
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Material Classification
(based on the No of electrons (e-) on the outer valence cell)
1.
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2.
Conductors:
Few (e-)
Free to move and join adjacent atoms.
(with a little “pressure” from an energy source /electric field).
They let electricity flow thought them easily.
Copper (Cu 2,8,18,1), aluminum, iron, steel
Insulators
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Many (e-)
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“Lazy”, do not like to move, even with a “kick”.
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Rubber, plastic , glass, wood
3.
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Semiconductors: (half & half)
Number of (e-): somewhere in the middle.
Conducting properties intermediate to those of insulators and metals.
Silicon (Si14)
Addition of “impurities” like Phosphorus (P15 ) and Boron (B5) can increase
their conductivity.
Current: the steady flow of electrons which carry electric charge (-)
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Silicon Si14, Boron B5, Phosphorus P15
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Semiconductor Doping
• How can we change the electrical properties of the pure Semiconductor
material?
• By adding foreign material to it, called dopants. (impurities)
• Boron, phosphorus, arsenic are common dopants.
• Rate of low :1 every 100,000,000 atoms
high: 1 every 10,000 atoms
Silicon (Si) with Phosphorus (P2,8,5) dopant : n-type
(extra valence electrons are added)
Silicon (Si) with Boron (B2,3) dopant = p-type
(missing fourth valence electron, holes)
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Qa. Adding Impurities
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Adding impurities to silicon in order to generate
“holes” we are building __?__ material.
A. N- type
B. P-Type
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Photon Hits the Atom of a “Semi” Material
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Hole is the “empty space” left behind as a result of the movement of the
free electron. Holes have + charge.
www.altensol.comph/solal-photovoltaic
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Solar Cell Schematic
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Protective Cover-Glass
Antireflective Layer
Electrical Contact
N
current
Load
P-N Junction
P
Electrical Contact
Not to scale
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The Process
Sunlight is made of photons, small particles of energy.
These photons are absorbed by and pass through the material of a solar cell or
solar PV panel. The photons 'agitate' the electrons found in the material of the
photovoltaic cell.
As they begin to move (or are dislodged), these are 'routed' into a current. This,
technically, is electricity - the movement of electrons along a path.
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www.altensol.com.ph/solar_photovoltaic_philip
So, How does it work?
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Light breaks silicon bonds and creates “free”
electrons and holes, “missing electrons”
Holes are positive charges
Built-in field separates electrons and holes
Step 1. Photogeneration of charge carriers,
electron (negative) and hole (positive).
Step 2. Separation of the charge carriers
through the medium.
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R. Chang: Solar Cell Technology F07
Qc.
• Name the junction that is created by doping
adjacent regions of a semiconductor
A
B
C
D
E
n-type
p-type
Valence junction
p-n junction
Silicon
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Q - What is a Series circuit?
A – One where electricity travels on one path.
I=1.7 A
V1=1.5
V1
V2=1.5
V2
V = V1 + V2
I = Constant
P = (V1 +V2) (I)= (1.5+1.5) (1.7)
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Series Connection: Solar Cells and Eq. Batteries
(I2 = I – I1)
(I)
I1
I2
I=I1+I2
I2
V = Constant
I1 = 1.7 A
I2 = 1.7 A
I = 1.7 + 1.7 = 3.4 A.
V1 = V2 = 1.5 V
Power = ?
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www.makeitsolar.com
Qb. Given the values and the set up bellow, what is the
total Power generated?
I1 = 1.0 A
I2 = 1.0 A
V = 3.0 V
I2
a. P = 3.0 W
b. P = 4.0 W
c. P= 5.0 W
d. P= 6.0 W
I
I1
V = 3.0
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Factors affecting Solar Cell Performance
Light intensity (type of light)
Light wavelength (color of light)
Angle of incident light
Surface condition of solar cells (cleanness)
Temperature on solar cells
R. Chang: Solar Cell Technology F07
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IV curve of a solar panel
• There are three set of
curves shown, for three
different sun light
intensities.
P. Hsu’s Lecture Notes: “electrical power sources”
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Measurements
I
+
V
_
POT
A variable resistor (potentiometer or POT) is used in
experimentally determining the V vs. I curve of a solar cell.
The same procedure is used in the wind turbine
experiment.
P. Hsu’s Lecture Notes: “electrical power sources”
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Setup in the lab
I
V
cell
#1
cell
#2
cell
#3
cell
#4
W
cell
#5
cell
#6
Power meter
POT
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Voltage
Current
Power
Loading condition
Vary resistance from 0 to
the full resistance of the
POT.
Take down the voltage,
current, and power
readings at a small
resistance increment
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Review Question 1
A solar cell is designated to capture
energy from:
A.
B.
C.
D.
E.
Sunlight
White light
Incandescent light
Halogen light
All of the above
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Review Question 2
A P-type semiconductor is a ___?_____
carrier?
A.
B.
C.
D.
E.
Photon
Electron
Hole
Ion
None of the above
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Review Question 3
Which of the following will impair a solar
cell’s performance?
A.
B.
C.
D.
E.
Thickness of the cell
A water stain
Shape of the cell
All of the above
None of the above
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