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Renewable Energy Sources
.
Solar Cells
SJSU-E10
S-2008
John Athanasiou
1
Renewable Energy Sources
Renewable:
They can last indefinitely
1. Wind Turbine:
• Converting the wind energy into electricity
• Wind, Propeller, Electric Generator, Current Flow
2. Solar Cells
• Converting the Sun’s (light) energy directly into electricity
• Intensity of the sunlight
• Wavelength of the sunlight
• Type and surface area of the solar cell
3. Fuel Cells
• Producing electricity by combining Hydrogen and Oxygen
to produce H2O
2
Energy Usage
3
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
4
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.
5
Democritus
Atoms c.300 BC
An atom is composed of three different particles:
Protons (P+)
• Nucleus- Center of the atom:
1. Protons (P+)-- positively charged. Neutrons
-- equal to the number of
electrons.
2 Neutrons -- no charge.
3. Electrons (e-) -- negatively charged.
(e-)
-- orbit the nucleus.
The outermost electrons of an atom
determine its chemical and electrical
properties
www.cfo.doe.gov/
6
Material Classification
(based on the No of electrons (e-) on the outer valence cell)
1. 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
2. Insulators
• Many (e-)
• “Lazy”, do not like to move, even with a “kick”.
• Rubber, plastic , glass, wood
3. 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 (-)
7
Silicon Si14, Boron B5, Phosphorus P15
e e-
- e e-
e-
e- e- e-
B
e e-e-
N
Si e-
e-
e
e - e- e-
e-e e- e- -
e
e e - e-
e -
e e e - e-
e
e-
e e e
e P e
e
e -
e
e e
8
e
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)
9
Qa. Adding Impurities
• Adding impurities to silicon in order to generate
“holes” we are building __?__ material.
A. N- type
B. P-Type
10
Photon Hits the Atom of a “Semi” Material
.
Hole is the “empty space” left behind as a result of the movement of the
free electron. Holes have + charge.
11
www.altensol.comph/solal-photovoltaic
Solar Cell Schematic
. .
Protective Cover-Glass
Antireflective Layer current
Electrical Contact
N
Load
P-N Junction
P
Electrical Contact
Not to scale
12
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.
13
www.altensol.com.ph/solar_photovoltaic_philip
So, How does it work?
• 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.
14
R. Chang: Solar Cell Technology F07
Qc.
• Name the junction that is created by doping
adjacent regions of a semiconductor
A n-type
B p-type
C Valence junction
D p-n junction
E Silicon
15
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 P = (V1 +V2) (I)= (1.5+1.5) (1.7)
I = Constant
16
Series Connection: Solar Cells and Eq. Batteries
(I2 = I – I1)
(I)
I1 I2
I=I1+I2
I2 I1 = 1.7 A
I2 = 1.7 A
I = 1.7 + 1.7 = 3.4 A.
V = Constant V1 = V2 = 1.5 V
Power = ?
17
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 a. P = 3.0 W
V = 3.0 V b. P = 4.0 W
c. P= 5.0 W
I2 d. P= 6.0 W
I
I1
V = 3.0
18
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 19
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” 20
Measurements
I
+ POT
V
_
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.
21
P. Hsu’s Lecture Notes: “electrical power sources”
Setup in the lab
V I W
cell cell cell
#1 #3 #5
cell cell cell
#2 #4 #6 Power meter
POT
22
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
23
Review Question 1
A solar cell is designated to capture
energy from:
A. Sunlight
B. White light
C. Incandescent light
D. Halogen light
E. All of the above
24
Review Question 2
A P-type semiconductor is a ___?_____
carrier?
A. Photon
B. Electron
C. Hole
D. Ion
E. None of the above
25
Review Question 3
Which of the following will impair a solar
cell’s performance?
A. Thickness of the cell
B. A water stain
C. Shape of the cell
D. All of the above
E. None of the above
26
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