Solar Energy PES/ENSC 1600 Test 4 Review
last updateas of : Friday, 13-Dec-2019 15:01
still updating...
you may use the following on test 4 "Hades edition plus"
a real calculator (i.e no iPhones, Droids, R2's, iPads, etc...)
two "real" (3 x 5 inch) notecards
may be double sided,
handwritten only (i.e. actual ink/pencil on paper, do not photocopy diagrams, pictures, maps, etc...)do NOT combine the total area of two doublesided notecards into one sheet of paper (otherwise you will not be allowed to use it.)
original document (i.e. not photocopied, not printed from digital device, not virtual on iPad or iPhone or other electronic device...)
Potential Problems, Equations, Exercises, etc...
anti-reflective coatings
Total Internal Reflection (TIR)
Polarizers, & Analyzers
n of air (n = index of refraction)
n of water
E & M (wavelenths, colours, & frequencies)
in-class Scantron Form Multiple Choice Usual Suspects... Review Questions
Silicon in the form of silicon dioxide ( Si O2 ) otherwise known as Quartz sand is common and found on the Earth’s crust.
Monocrystalline crystalline silicon solar cells are the most efficient in type.
Made from very thin slices, or wafer, of a large single crystal.
Polycrystalline type of cell produced from molten silicon using a casting process and having a random crystal structure.
A type of optical loss is reflection from the back of the cell, without subsequent absorption. It may be reduced by using an uneven back surface by total internal reflection. Such technique is referred to as light trapping.
If the temperature coefficient is negative on a PV cell during a hot summer day it means that the voltage decreases
as the temperature rises.Photovoltaic energy conversion efficiency is dependent on the wavelength of the impinging light.
PV stands for Photo voltaic.
Crystal pulling is the least expensive way to grow large amounts of pure crystal.
Boron (B) is a trivalent impurity.
Phosphorus (P) is a pentavalent impurity.
Because “n-type” materials have more conduction-band electrons than holes in the covalent bond, the electrons are called: majority carriers.
Holes are called: minority carriers.
Holes are caused by thermal energy excitation of electrons.
Semiconductors are atoms that contain: 4 valence electrons, and thus, are neither good conductors nor good insulators.
Si is used more commonly than Ge in the production of solid-state components because it is more tolerant of heat.
There is an energy band above the valence shell (or valence band) called the: conduction band.
When an electron absorbs enough energy, it jumps from the: valence to the: conduction band.
The energy given up by an electron is in the form of light or heat.
Covalent bonding is the method by which some atoms complete their valence shells by: “sharing valence electrons" with other atoms.
When silicon atoms form covalent bonds, the resulting material is a: Si crystal.
When a valence electron jumps to the conduction band, a gap often referred as hole is left in the covalent bond.
For every conduction band electron, there must exist a: “valence band-hole”. Such combination is referred to as (a) electron-hole pair.
Intrinsic “Si: is a poor conductor.
Doping is the process of adding impurity atoms to pure: Si.
A trivalent element is one that has: 3 valence electrons.
Although atoms are built of oppositely charged particles, their overall “ Q ” (charge) is neutral because they contain an equal number of: protons & -e.
The most important parts of a PV cell are the: semiconductor layers because this is where -e are freed and electric: “ I ” is created.
Doping implies impregnation of silicon by positive and negative agents, such as phosphor and boron.
Phosphor: creates a: free electron that produces the so-called: n-type material.
Boron: creates a: “hole” or a shortage of an: electron, which produces the so-called: p-type material.
Textbook Reading & Study Materials for Chapter 9
Chapter 9: Photovolatic Systems
9.1 Semiconductors
Atom consists of the nucleus and electrons that orbit the nucleus.
In quantum mechanics -e of an isolated atom can have only specific discrete or quantized energy levels.
When atoms are brought close together, the electronic energy of individual atoms is altered and the energy levels are grouped in energy bands.
Electrons in the outermost shell are the only ones that interact with other atoms.
Electrons in the valence band are loosely attached to the nucleus of the atom and, therefore, may attach more easily to a neighboring atom, giving them a negative charge and leaving the original atom as a positive charged ion.
Some electrons in the valence band may possess a lot of energy, which enables them to jump into a higher band. These -e are responsible for the conduction of electricity and heat, and this band is called the conduction band.
The difference in the energy gap of an electron in the valence band and the innermost shell of the conduction band is called the band gap.
Materials whose valence gap is full and whose conduction band is empty have very high band gaps and are called insulators because no current can be carried by -e in the filled band and the energy gap is so large that, under ordinary circumstances, a valence -e cannot accept energy, since the empty states in the conduction band are inaccessible to it. The band gap in these materials is greater than 3 eV.
Materials that have a relatively empty valence bands and may have some -e in the conduction band are called conductors. In this case, the valence and the conduction bands overlap.
Valence -e are able to accept energy from an external field and move to an unoccupied allowed state at slightly higher energy levels within the same band. Metals fall in this category.
Valence -e in a metal can be easily emitted outside the atomic structure and become free to conduct electricity.
Materials with valence gaps partly filled have intermediate band gaps and are called semiconductors. The band gap in these materials is smaller than 3 eV. They have the same band structure as the insulators but their energy gap is much narrower.
The two types of s.c. are the pure ones: intrinsic s.c., and those doped with small amounts of impurities: extrinsic s.c.
Intrinsic s.c.: the valence -e are excited by thermal or optical means and jump the narrow energy gap into the conduction band, where the -e have no atomic bonding and therefore are able to move freely through the crystal.
9.1.1 p-n Junction
Si belongs to group 4 of the periodic table of elements.
In s.c., if the material that is doped has fewer -e in the valence gap than the s.c., the doped material is: p-type s.c.
The p-type s.c.is electronically neutral but it has positive holes (missing -e) in its structure, which can accommodate excess -e.
P-type material is obtained when Si atoms are replaced with periodic table group 3 elements, like gallium (Ga) or indium (In), and thereby form positive particles, called holes, that can move around the crystal through diffusion or drift.
For Si, the energy needed to get and -e across a p-n junction is: 1.11 eV (1 eV = 1.6 x 10^-19 J)
In the n-type s.c., because the doped impurity donates additional -e for the conduction current, it is called the donor and its energy level is called the donor level.
In the p-type s.c., the doped impurity accepts additional electrons; therefore, it is called the acceptor and its energy level is called the acceptor level, and is located in the forbidden band.
9.1.2 Photovoltaic effect
When photon enters a photovoltaic material, it can be reflected, absorbed, or transmitted through.
When a photon is absorbed by a valence -e of an atom, the energy of the -e is increased by the amount of energy of the photon.
If energy of the photon is greater than the band gap of the s.c., the -e which has excess energy, will jump into the conduction band, where it can move freely.
When a photon is absorbed, an -e is knocked loose from the atom.
If the photon energy is smaller than that of the band gap, the -e will not have sufficient energy to jump into the conduction band, and the excess energy is converted into kinetic energy of the -e, which leads to increased temperature.
Irrespective of the intensity of the photon energy relative to the band gap energy, only one -e can be freed. This is the reason for the low efficiency of the PV cells.
Free -e are generated in the n-layer by the action of the photons.
When photons of sunlight strike the surface of a solar cell and are absorbed by the s.c., some of them create pairs of -e and holes.
9.2.2 Types of PV technology (pg 498-500)
a. crystalline Si (80% PV market)
Crystalline modules are more efficient (i.e., give greater power output per unit area of module) moderate climates, and space-constrained projects.
b. thin films (~20% market share)
Thin-film modules higher yield (i.e. greater energy production for a given power rating) in high temperatures. Suitable for hot climates and abundant space.
c. triple-junction cells (concentrating PV)
Monocrystalline silicon cells
Multicrystalline silicon cells
Amorphous silicon
Cadmium Telluride (CdTe)
Copper Indium Gallium Selenide (CIGS)
Thermophotovoltaics
Properties of Glass: Physical properties:
Density
Properties of Glass: Optical Properties:
Transparency
Opacity
Colour
Photosensitivity
Refraction of light
Reflection of light
Glass Treating: Strengthening:
Thermal tempering
Ion exchange
Lamination
Tempered glass
E Glass
Commerical Glasses
Agents for colouring glass