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1.1 Introduction Solar Energy

Chapter one

1.1 Introduction Solar Energy


The sun is beaming light and heat. All wind, fossil fuel, hydro and biomass energy have their origins in sunlight, it is the first energy in the earth and using widely rang  application technology such as  solar heating ,solar photovoltaic’s, solar thermal electricity, solar architecture and artificial photosynthesis.[1] [2]

About half the incoming solar energy reaches the Earth’s surface
There are two important facets about the solar energy
1.  the earth receives 174 petawatts (PW)  (1 petawatt = 1015watt) of incoming solar beaming and insulation Approximately 30%  at the  upper atmosphere reflected back to the space, absorbed by cloud , ocean , and land masses
2. The sun emitted radiation widely spectrum, the spectrum received the earth 49% of the spectrum as the heat, 46% anther the radiation received the light but not all the visible. .[3]

1.2. Why researchers are interested in solar energy?
Physical and chemical researchers are becoming more interested in solar power to avoid pollution from carbon emissions increased. The following are examples of the many
2.1 advantage
1. Energy clean and available
2. Financial saving
3. Better for the environmental however solar collectors and other equipment manufactured in factories causes little pollution
4. Free energy comes from the sun
5. Can used in remote area
6. It can be used in many devices in life such as calculators and other low power.
2.2 disadvantage
1. Can only use when Sunday.
2. Solar collectors, panels and solar power stations built very expensive. Conventional power stations. Saving power in battery is large and heavy to carry place to anther and can used in night it is needed replace time to time.
3. Large areas of land are required to collector solar energy and same country poor solar energy such as UK because unreliable climate. [4.5]
1.3. General semiconductor
A semiconductor is a material with properties between metal and insulator with a degree of electronic conductivity. Many modern devices are based on semiconductor for example quantum dots, solar cells, light-emitting diodes (LEDs) and transistors.
A semiconductor has many properties:
1. Variable conductivity
2. Depletion
3. Energetic electrons travel far
4. Light emission
5. Thermal energy conversion
Commonly, these elements are found in Group XIV of the periodic table. found Groups III and V such as gallium arsenide GaAs, gallium phosphide GaP and indium phosphide InP, Ⅱ-Ⅵ compound cadmium sulfide and cadmium selenide, Organic semiconductors, made of organic compounds such as PPV (poly (phenylene vinylene ).
1.4. Photovoltaic (PV)
PV is the system convert irradiation sunlight into direct current electricity (DC) to generate electrical power by semiconductors which have photovoltaic effect; it has been employed solar panel because containing photovoltaic materials (e.g.  Monocrystalline silicon, amorphous silicon, copper indium gallium selenide and cadmium sulfide).
1.5. Photoelectrochemical (PEC).
PEC cell are based semiconductor materials in solar energy conversion onto electrical power. Instead of the solid state p-n junction, PEC is used in the Photovoltaic solar cells; a semiconductor electrolyte junction is used in potoelectrochemical cells.
When a semiconductor is immersed in contact with a suitable electrolyte solution, before thermodynamic equilibrium takes please at the holes. The result space charge layer (SCL) Fermi level of semiconductor will be bent upward and downward in cases of n-type and p-type respectively.

A schematic showing a – intrinsic. B- n-type semiconductor. C- p-type semiconductor.

1.6. Energy band gab
Distance between valance bands ( VB ) and conductive bands ( CB ) in atom, different value for insulators, semiconductor and conductor, in insulators, high energy band gab because large distance between valence band ( VB ) and conductive band ( CB ) , but in conductive no energy band gap because overlap between valence band ( VB ) and conductive band ( CB
A schematic showing energy band gab
1.7. Solar Panel
Solar cells are connected to gather to generate electricity from sunlight. Produced electricity can be used to support commercial and residential applications.  Each cell is rated by its direct current (DC) output power under standard test conditions (STC).
1.7.1 Efficiencies
Efficiencies for cell photovoltaic depend on constructions to can generator electricity from range frequencies of sunlight 300nm – 800nm special  ultraviolet, infrared and UV-visible.
1.7.2Type of solar Cell
There are two types of solar cells inorganic and organic.
1.7.2. a An inorganic solar cell .
Using Inorganic semiconductor to make solar cell include crystalline, multicrystalline, amorphous, and microcrystalline Si, the III A compounds and alloys, CdTe, and the chalcopyrite compound, copper indium gallium diselenide (CIGS) , found Groups III and V such as gallium arsenide .
Some applications were developed in the last century.
a. Supplying power in remote location such as electronic communications.
b. Supplying power for consumer products such as calculators.
c. Supplying power for applications in space such as for satellites.[6]
7.2. B organic solar cell.
Using organic electronic to conductive polymer organic or small molecular to absorption frequencies of sunlight to produce electricity by organic photovoltaic [7], some organic photovoltaic material uses such as PPV (poly (phenylene vinylene ),  CN – PPV ,polyacetylene and many other material .

1.8. Cadmium Sulfide (CdS)
Cadmium Sulfide is yellow or orange solid depend in size when growth crystal convert from yellow to orange and it is occur  in nature with two different crystal structures as the rare minerals greenockite ( hexagonal system ) and hawleyite ( sample cubic ) , it’s have many commercial application such as  pigment and  thin film solar cell

Hawleyite-3D-balls                                Greenockite-3D-balls

1.8.1 Cadmium sulfide properties
Show some basic properties of cadmium sulfide.
Molecular formula
Molar mass
144.48 g mol−1
Appearance    Yellow-orange to brown solid.
Exited absorbance 392nm.
4.826 g/cm3, solid.
Melting point /Boiling point
1,750 °C at (10 MPa) /980 °C.
Solubility in water
soluble in acid e.g 1M HCl.

1.8.2 Different methods of preparation of CdS such as
1. Sol gel techniques. [8]
2. Sputtering. [9]
3. Chemical bath deposition. [10]
4. Spraying with precursor cadmium salt, sulfur compound and dopant.[11]
5. Screen printing using a slurry containing dispersed CdS.[12]
6. Chemical bath deposition.
7. or compensation by Chemical bath deposition and Chemical bath deposition.
Chooses from this method Chemical Bath Deposition ( CBD) is one method cheapest other method to deposition thin film and not needed expensive equipment , can uses  batch processing deposition or continuous processing deposition  because have many  benefits or advantage  such as
1.    Needed only one solution in container.
2.    Cheapest.
3.    Yield stable.
4.    Good reproducibility by relative same condition.
1.9. Recycling
Mostly, solar panels are manufactured from frames aluminum, iron and semiconductor.
Recycling possibilities depend on:
1.  Silicon based modules: aluminum and plastic frames are broken up manually at the beginning of the process. The module is then crushed in a mill and the different fractions are separated in to its components. [13] More than 80% of the incoming weight is possible to recover.
2. Non-silicon based modules: they require particular recycling method such as the use of chemical baths deposition in order to separate the different semiconductor materials. [15] For cadmium telluride, the regeneration process begins by crushing the cell and subsequently separating the different parts. Up to 90% and 95% of the glass, the semiconductor materials respectively are contained recycling process is designed to recover. [16]
1.10. Thin film
Thin film modern technology heavily was used to produce thin layer of semiconductor material by deposition onto substrata (e.g FTO and ITO), Many semiconductor can be used as thin film electrode in solar cells such as ZnO, CdS, CdSe, CuS ,CdTe and other .
1.11. CdS Thin Film
Which is one some important semiconductors for application in solar cells and electronic device , CdS is interested developed thin film because has suitable energy bond gap ~ 2.3 eV, important optical properties , highly absorption coefficients and can was prepared many different methods and starter material.
1.12. Objectives of this work
The main goal of this work is two fold:
1) Examine the recycled cell efficiency in light-to-electricity conversion (short circuit current density Jsc, open–circuit photo potential Voc).
2) Stabilize the recycled solar cell in a manner similar to methods used by other researchers.
1.13. Hypothesis
We assume the following:
Recycling CdS solar cells will be valuable, because:
1) The Cd2+ ions will not be allowed to contaminate water and environment.
2) The newly recycled CdS solar cells will have comparable efficiencies like freshly prepared CdS The process will have environmental and economic value in the future and will give new pathways to recycle other types of solar cells.
1.14. Novelty
1.    To our knowledge, complete recycling of CdS based solar cells has not been reported. Therefore, this work will be conducted here for the first time.
2.    Other types of solar cells, such as those of Si, need not be recycled since Si yields non-hazardous SiO2 after disposal, and do not need to be recycled. Solar cells with hazardous species, such as CdS, must be recycled. This reflects novelty and relevance of this proposed work.

Chapter two
2.1 Materials
Pure CdCl2.2H2O, calculated CdS, thiourea (CS (NH2)2), NH3, NaOH, Na2S and S were purchased from Aldrich. HCl, NH4Cl were purchased from pure from frutarom. Methanol was obtained from Riedel-DeHaën in a pure form. Highly conductive fluorine tin oxide FTO/Glass samples were kindly donated by Dr.Guy Campet of ICMCB, University of Bordeaux.
2.2 Pretreatment of FTO/Glass Substrate
In order obtain good adherence and uniformity FTO/Glass for deposited CdS and recycling CdS film by chemical bath deposition (CBD) techniques, FTO/Glass was cleaned before recycling CdS film deposition process. FTO/Glass was taken after some student make solar cells such as CdS, CuS, CdSe and many others. The substrates were treated by concentrated HCl and methanol about one hour, 30miute in sonicator receptively. The substrates were treated by immersion in dilute solution of HCl (10% v/v) for 5 second, rinsing with distilled water, immersing in methanol, rinsing again with distilled water.
2.3 Preparation CdCl.nH2O
Was taken prepared CdS thin film and dissolved diluted different concentration (0.6, 0.8, 1) M, was suitable 1M HCl cleaned
2.4 Preparation of CdS Film
Preparation technique involved chemical bath deposition (CBD).
2.4.1 Chemical bath deposition (CBD) Technique
Chemical bath deposited CdS thin films in classical method, the experimental arrangement is shown in figure. The bath solution containing 25.0 mL of distilled water, 2.5 mL of 0.2 M CdS recycling, 10 ml of NH4Cl and 15.0 mL of  2.0 M NH4OH. The solution was stirred continuously, some film do not stirred and kept at 80º C during the deposition process. The held was immersed in the solution. The system was closed rubber sealing. Substrates holder was also isolated using cover plastic.

Syringe was used 2.5 mL of 0.6 M thiourea to bath solution. The final pH value of the solution became ~ 10.3. The deposition process was continued for 30, 45 minutes and one hour.

2.5 modification of CdS thin film
CdS thin film modification involved time, stirring, cooling rate control, and different annealing at 250ºC and 300ºC.
2.5.1 Annealing process
Annealing was conducted using a thermostat horizontal tube furnace, figure The CdS tin film prepared substrates were inserted in 30 cm long Pyrex cylinder. The temperature was raised to desired temperature (250ºC, 300ºC) under N2 atmosphere. The 250ºC was optimal temperature. The annealing process was continued for one hour at the constant temperature.
2.5.2 Cooling rate control
After the annealing process, the furnace was turn off and left to cool slowly to room temperature under N2 atmosphere, cooling rate was 90ºC /h on the average .
2.5.3 Time and stirring
Different CdS thin film was prepared with time, stirring and without stirring. This was taken different time 30, 45, minute receptively and one hour in order to compare between them in their PEC characteristics, using stirring processing preparations and not used.
2.6 film characterization
Which preparation recycling CdS thin films have been studied by several measurements include.
2.6.1 Electronic Absorption spectra
The optical absorption  spectra solid state the CdS thin film were studied at room temperature in the wavelength range 350-750 nm and FTO/Glass was used as a blank .CdS were using measured on Shimedzu UV-1601spectrometer.
2.6.2 Fluorescence spectrometer


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