Basic Science and Modeling of Solar Energy by Jeremy Parra and Sandrio Elim

Topics: Science of Solar EnergyScience of Solar Energy Technology Using Solar EnergyTechnology Using Solar Energy

Science of Solar Energy Resources: Energy Flows: Chemistry and Physics background:

“The pp-chain (proton-proton chain) involves a series of nuclear reactions that are responsible for the generation of energy in the sun. The basis for the suns energy is that four hydrogen atoms fuse to form one helium atom whose mass is slightly less than the mass of the combined four hydrogen atoms. The missing mass is what was converted to energy. “In the pp-chain, two protons (moving at very fast velocities) fuse together to create deuterium. A neutrino and a positron are expelled in the process. Deuterium (one proton and one neutron) fuse with one more proton creating Helium-3. A photon is released in this process and this is what gives the sun it's energy. After Helium-3 is created, it fuses with another of its type and 2 hydrogen atoms are expelled. The result is one atom of Helium-4 and 2 atoms of Hydrogen to start the process all over again. Even though the photons are accountable for most of the sun's energy, about 5% of the energy is given off in neutrinos.” -bib. 1

Fig. 1 (copied,bib.1) Solar fusion

Hydrogen(one proton) H H electron Hydrogen

H 2 Deuterium(one proton one neutron) electron positron neutrino H Deuterium

He Helium(two protons one neutron) 3 γ photon He 3 Helium

HH He 3 Yield

Sun Light

Photon  If when a photon strikes an electron it has the amount of energy to break the electron- electron bond( band gap) a free electron will result.  This results in a positive “hole” and a negative electron.

Hole Free electron Photon

Semiconductors  A semiconductor has electrical conductivity greater that insulators but less than good conductors.  Silicon has four valence electrons.  Pure silicon is in a perfect state of valence(has no free electrons).

Si

electrons hole Free electron Silicon nucleus

Semiconductors  When phosphorous is substituted for a silicon atom, there is one electron left  The remaining electron is very loosely bound by the slightly more positive charge of the nucleus of the phosphorous atom.  This electron travels easily around the phosphorous atom.  Silicon that contains a large number of atoms with an extra valence electron is called n type silicon (n is for negative).

Si P Extra Electron N-Type

Semiconductors  If a boron atom is substituted for a silicon atom, there is one valence electron which has no partner.  This missing electron is a hole.  This yields a positive charge (the absence of an negative electron).  This is a p-type

Si B Hole P-Type Si

 The binding force of electron pairs is much stronger than the electromagnetic force between an electron and the nucleus  The extra electron moves from the n-type to the p-type  And these electrons form valence pairs with the electrons that were missing a pair  This results in a shift in charge that creates an electric field in the material.  Now the n-side(doped with phosphorus) gains a positive charge.  When the electron moved it left a proton  “Similarly, the boron atom is surrounded by one more electron than there are positive protons in the boron nucleus.”

Electric Field  The n-type side doped with Phosphorus easily lends its free electron to the positive side (doped with boron).  This leaves the n-type with one more proton than electron giving the n-type a positive charge.  And the p-type now has one more electron the proton yielding a negative charge.  This creates an electric field. With out this electric field the freed electron(freed by a photon) would just return to the same hole.  But because of the electric field the freed electron will move from the negative area to the positive area creating an electric current. And the holes will move in the other direction.

Technology Using Solar Energy Types of cells: 1.Crystalline Silicon a. Single crystal b. Multi-crystalline c. Ribbon d. Film 2.Thin films materials a. Amorphous Silicon b. Cadmium Telluride c. Copper Indium Diselenide 3.Concentrators Components: 1.PV 2.DC-AC Converter 3.Backup Power Generator 4.Stabilizer 5.Electrical Panel Source:DOE/GO FS March 1997

Types of PV Cells 1.Monocrystalline Silicon Cells 2.Multicrystalline Silicone Cells 3.Thick-film Silicon 4.Amorphous Silicon 5.Other thin films: Cadmium telluride Copper indium diselenide Gallium arsenide Tandem cells

1. Monocrystalline Silicon Most efficient PV tech Complicated process High Cost to manufacture

2. Multicrystalline Silicon Cheaper Simpler process Less efficiency Granular texture

3. Thick-film Silicon Continuous process Fine grained Bounded to aluminum frame

4. Amorphous Silicon A thin homogenous layer More effective in absorbing lights Also known as thin film PV Efficiency about 6%

5. Other Thin Films a. Cadmium telluride and Copper indium diselenide Still in research Very inexpensive process Expected efficiency quite high b. Gallium arsenide High efficiency Relatively temperature independent For special purpose only c. Tandem cells Made of two different cells Usually from silicon and gallium arsenide Better use of incoming light

Manufacturing

How It Works

Math Modeling 1.Optimal Conditions a. Equations b. Independent Variables 2.Method of Data Collection a. Software b. Units Source:DOE/GO FS March 1997

Bibliography 1) 2) 3) 4) 5) 6) 7) 8) 9)