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Renewable Energy Sources.

Solar Cells

SJSU-E10

S-2008John Athanasiou

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Renewable Energy SourcesRenewable:

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

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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:

• Nucleus- Center of the atom:

 1. Protons (P+)-- positively charged. -- equal to the number of electrons.

2 Neutrons -- no charge.

3. Electrons (e-) -- negatively charged.

-- orbit the nucleus.

The outermost electrons of an atom

determine its chemical and electrical properties www.cfo.doe.gov/

Protons (P+)

Neutrons

(e-)

Democritus   c.300 BC

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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 (-)

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Silicon Si14, Boron B5, Phosphorus P15

e-e-

e-e-e-

e-e-

e-

e-

N

e-

Si

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

e-e-

B

e-

e

e

e

e

e

e

e-

e

P

e

e

e

e

e

e

e

e

e

e e

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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

• 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.

www.altensol.comph/solal-photovoltaic

Hole is the “empty space” left behind as a result of the movement of the free electron. Holes have + charge.

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Solar Cell Schematic. .

Protective Cover-Glass

Electrical ContactAntireflective Layer

N

P-N Junction

P

Electrical Contact

Load

current

Not to scale

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. 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.

www.altensol.com.ph/solar_photovoltaic_philip

The Process

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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.

R. Chang: Solar Cell Technology F07

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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

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Q - What is a Series circuit?A – One where electricity travels on one path.

V = V1 + V2 I = Constant

V1

V2

V1=1.5

V2=1.5

I=1.7 A

P = (V1 +V2) (I)= (1.5+1.5) (1.7)

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Series Connection: Solar Cells and Eq. Batteries

www.makeitsolar.com

I2I1

(I)

I=I1+I2

I2

(I2 = I – I1)

V = Constant

I1 = 1.7 AI2 = 1.7 AI = 1.7 + 1.7 = 3.4 A.V1 = V2 = 1.5 V Power = ?

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Qb. Given the values and the set up bellow, what is the total Power generated?

I1 = 1.0 AI2 = 1.0 AV = 3.0 V

a. P = 3.0 Wb. P = 4.0 Wc. P= 5.0 Wd. P= 6.0 W

V = 3.0I1

I2

I

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Factors affecting Solar Cell Performance

Light intensity (type of light)Light wavelength (color of light)Angle of incident lightSurface 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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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.

POT + V _

I

P. Hsu’s Lecture Notes: “electrical power sources”

Measurements

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Setup in the lab

cell #1

cell #2

cell #3

cell #4

cell #5

cell #6

POT

Power meter

V I W

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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. Sunlight

B. White light

C. Incandescent light

D. Halogen light

E. All of the above

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Review Question 2

A P-type semiconductor is a ___?_____ carrier?

A. Photon

B. Electron

C. Hole

D. Ion

E. None of the above

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Review Question 3

Which of the following will impair a solar cell’s performance?

A. Thickness of the cellB. A water stainC. Shape of the cellD. All of the aboveE. None of the above

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