1 Renewable Energy Sources. Solar Cells SJSU-E10 S-2008 John Athanasiou

2 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 H 2 O

3 Energy Usage

4 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

5 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.

6 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. 2Neutrons -- no charge. 3.Electrons (e-) -- negatively charged. -- orbit the nucleus. The outermost electrons of an atom determine its chemical and electrical properties Protons (P + ) Neutrons (e - ) Democritus c.300 BC

7 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 (Si 14 ) Addition of “impurities” like Phosphorus (P 15 ) and Boron (B 5 ) can increase their conductivity. Current: the steady flow of electrons which carry electric charge (-)

8 Silicon Si 14, Boron B 5, Phosphorus P 15 e -e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- N e-e- 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-e- B e-e- e e e e e e e-e- e P e e e e e e e e e e e

9 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 (P 2,8,5 ) dopant : n-type (extra valence electrons are added) Silicon (Si) with Boron (B 2,3 ) dopant = p-type (missing fourth valence electron, holes)

10 Qa. Adding Impurities Adding impurities to silicon in order to generate “holes” we are building __?__ material. A.N- type B.P-Type

11 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.

12 Solar Cell Schematic.. Protective Cover-Glass Electrical Contact Antireflective Layer N P-N Junction P Electrical Contact Load current Not to scale

13. 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. The Process

14 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

15 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

16 Q - What is a Series circuit? A – One where electricity travels on one path. V = V1 + V2 I = Constant V1V1 V2V2 V 1 =1.5 V 2 =1.5 I=1.7 A P = (V 1 +V 2 ) (I)= ( ) (1.7)

17 Series Connection: Solar Cells and Eq. Batteries I2I2 I1I1 (I) I=I 1 +I 2 I2I2 (I 2 = I – I 1 ) V = Constant I 1 = 1.7 A I 2 = 1.7 A I = = 3.4 A. V 1 = V 2 = 1.5 V Power = ?

18 Qb. Given the values and the set up bellow, what is the total Power generated? I 1 = 1.0 A I 2 = 1.0 A V = 3.0 V a.P = 3.0 W b.P = 4.0 W c.P= 5.0 W d.P= 6.0 W V = 3.0 I1I1 I2I2 I

19 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

20 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”

21 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” Measurements

22 Setup in the lab V IW

23 VoltageCurrentPowerLoading 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

24 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

25 Review Question 2 A P-type semiconductor is a ___?_____ carrier? A. Photon B. Electron C. Hole D. Ion E. None of the above

26 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

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