Solar Cells

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Arizona to become 'Persian Gulf' of solar energy (CNN). • Abengoa Solar will operate .... sun light intensities. P. Hsu's Lecture Notes: “electrical power 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: • •

2.

Converting the wind energy into electricity Wind, Propeller, Electric Generator, Current Flow

Solar Cells •

Converting the Sun’s (light) energy directly into electricity • • •

3.

Intensity of the sunlight Wavelength of the sunlight Type and surface area of the solar cell

Fuel Cells •

Producing electricity by combining Hydrogen and Oxygen to produce H2O 2

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-) 1. • • • • 2.

on the outer valence cell)

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 • 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

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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) 9

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 .

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 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 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) 16

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 = ? 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 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 ƒLight intensity (type of light) ƒLight wavelength (color of light) ƒAngle of incident light ƒSurface condition of solar cells (cleanness) ƒTemperature 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 24

Review Question 2 A P-type semiconductor is a ___?_____ carrier? A. B. C. D. E.

Photon Electron Hole Ion None of the above 25

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 26

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