CONTENTS
CONTENTS ....................................................................................................................... i
LIST OF SYMBOLS ......................................................................................................iv
LIST OF ABBREVIATIONS .......................................................................................vi
LIST OF FIGURE ....................................................................................................... viii
LIST OF TABLES .........................................................................................................xii
INTRODUCTION ........................................................................................................... 1
CHAPTER 1. LITERATURE REVIEW .................................................................... 4
1.1. Overview of renewable energy use in the World ---------------------------- 4
1.2. Overview of solar cell use in the Angola ------------------------------------- 6
1.3. The photovoltaic effect ---------------------------------------------------------- 9
1.4. Physics of Solar Cells ----------------------------------------------------------11
1.5. Overview of Silicon Solar Cell Technologies -------------------------------17
How does PERC technology improve performance? ------------------------20
1.6. Influence of tropical climate in the performance of PV panels ----------21
1.6.1. Spectrum -------------------------------------------------------------------22
1.6.2. Irradiance ------------------------------------------------------------------22
1.6.3. Module temperature ------------------------------------------------------23
1.6.4. Wind speed ----------------------------------------------------------------23
1.6.5. Incident angle--------------------------------------------------------------23
1.6.6. Effect of humidity on the solar panels ---------------------------------24
1.6.7. Effect of dust on the solar panels ---------------------------------------25
CHAPTER 2. THE INFLUENCE OF ANGOLA TROPICAL CLIMATIC
CONDITION ON THE PV SYSTEM PERFORMANCE ....................................27
2.1. Experimental introduction -----------------------------------------------------27
2.2. Influence of Solar radiation ----------------------------------------------------29
2.3. Influence of Temperature ------------------------------------------------------32
2.4. Influence of humidity ----------------------------------------------------------37
2.5. Effect of radiation on PV characteristics ------------------------------------40
2.6. Effect of an inverter ------------------------------------------------------------42
2.7. Effect of wind actions on PV panels -----------------------------------------42
2.7.1. General ---------------------------------------------------------------------42
i
2.7.2. Computational Fluid Dynamics (CFD) Procedure -------------------47
2.7.3. Effect of wind actions on solar panels ---------------------------------51
Chapter summary --------------------------------------------------------------------67
CHAPTER 3. STUDY ON TITANIUM DIOXIDE APPLICATION AS
SOLAR CELL SELF-CLEANING LAYER ...........................................................68
3.1. Settlement overview of dust on a solar panels glass cover ----------------68
3.2. Thin film TiO2 using as self cleaning material of solar panels------------69
3.2.1. The self-cleaning properties ---------------------------------------------69
3.2.2. Theoretical basis of self-cleaning ---------------------------------------69
3.2.2. 1.Young’s equation -------------------------------------------------------70
3.2.2.2. Cassie model ------------------------------------------------------------70
3.2.2.3. Wenzel model -----------------------------------------------------------71
3.2.2.4. Cassie and Baxter’s Equation -----------------------------------------71
3.2.3. Thin film TiO2 using as self-cleaning material -----------------------72
3.3. Nanocrystalline TiO2 thin film deposited by spray pyrolysis technique
and sol gel –hydrothermal method ----------------------------------------------------73
3.3.1. Experiment details --------------------------------------------------------74
3.3.2. Characterizing of TiO2pure and doped iron or tungsten thin film --77
3.3.2.2. Characterizing of Fe-dopedTiO2 thin film---------------------------81
3.3.2.3. Characterizing of W-dopedTiO2 thin films--------------------------84
3.3.3. Self-cleaning properties of TiO2pure and doped iron or tungsten thin
film ----------------------------------------------------------------------------------------88
Chapter conclusion -------------------------------------------------------------------93
CHAPTER 4. GROWTH AND CHARACTERIZATION OF Al2O3 ULTRATHIN FILM AS A PASSIVATION LAYER FOR SILICON SOLAR CELLS
............................................................................................................................................95
4.1. The need for silicon solar cells passivation layer Al2O3 -------------------95
4.2. Carrier Recombination in Crystalline Silicon -------------------------------96
4.3 Surface passivation --------------------------------------------------------------98
4.4. Surface passivation materials------------------------------------------------ 100
4.4.1. Silicon dioxide SiO2 ---------------------------------------------------- 101
4.4.2. Hydrogenated amorphous silicon nitride a-SiNx:H ---------------- 101
4.4.3. Hydrogenated amorphous silicon a-Si:H ---------------------------- 101
4.4.4. Aluminum oxide Al2O3 ------------------------------------------------ 102
ii
4.5. Growth Al2O3 ultra-thin film by Atomic Layer Deposition ------------- 102
4.5.1. Introduction ALD technique------------------------------------------- 102
4.5.2. Growth process of thin film aluminum oxide by ALD ------------ 104
4.5.3. Process for p-type Si solar cells(PERC) fabricated ----------------- 105
4.5.4. The investigated method ----------------------------------------------- 107
CONCLUSION ----------------------------------------------------------------------- 118
The scientific and practical significance of the thesis ------------------------- 119
Recommendations for Future Studies ------------------------------------------- 120
REFERENCES ................................................................ Error! Bookmark not defined.
iii
LIST OF SYMBOLS
Number
Symbol
Name
1
A
Quality factor
2
C
The specific heat capacity (J/K.kg)
3
CF
The force coefficient
4
Cp
The pressure coefficient
5
D
Average crystallite size
6
E
Energy
7
e
Electron
8
EA
Ionization energy
9
EC
Conduction band energy
10
EF
Fermi energy
11
Eg
Optical band gap energy
12
EV
Valence band energy
13
F
The force applied on the surface
14
ff
fill factor
15
h
Hole
16
J
Current density
17
Jmax
Current density at maximum power output
18
JSC
Short circuit current density
19
m
Mass (kg) of the material
20
Pmean
21
Q
Quantity of heat (Joules)
22
R0
Initial resistance (Ω)
23
R
Resistance between the contacts
24
RS
Serial resistance
25
Rsh
Shunt resistance
26
Rsheet
Sheet resistance
27
t
Time
28
T
Transmittance
29
TA
Absolute temperature
30
TC
Calcined temperature
The mean pressure
iv
31
Te
Environmental temperature
32
TS
Substrate temperature
33
V
Voltage
34
Vmax
Voltage at maximum power output
35
VOC
Open circuit voltage
36
Absorption coefficient
37
Thickness
38
Conversion efficiency of the solar cell
39
λ
Wavelength
40
λex
Excitation wavelength
41
e
Electron mobility
42
p
Hole mobility
43
ρ0
Initial resistivity (Ωm)
44
Resistivity
45
eff
Effective lifetime
46
rad
Carrier lifetime due to radioactive recombination
47
Auger
Carrier lifetime due to band to band i.e. Auger recombination
48
SRH
Carrier lifetime due to defects i.e. SRH recombination
49
Surf
Carrier lifetime due to surface recombination
v
LIST OF ABBREVIATIONS
Number
Symbol
Name
1
AFM
Atomic Force Microscope
2
ALD
Atom layer deposited
3
APE
Average photon energy
4
CFD
Computational fluid dynamics
5
CVD
Chemical vapour deposition
6
DRE
Department of Renewable Energy
7
ECCP
Energy Pool of Central Africa-
8
EDX
Energy Dispersive X-ray
9
ETA
Extremely thin absorber
10
FESEM
11
FTO
12
FWHM
Full width at half maximum
13
IEA
International Energy Agency
14
LED
Light Emitting Diode
15
MB
Methylene blue
16
MINEA
Ministry of Energy and Water
17
MPPT
maximum power point tracking
18
PV
Photovoltaic
19
PCE
power conversion efficiency
20
PDA
Post deposition annealing
21
PECVD
22
PERC
Passivized emitter and rear cell
23
PERL
Passivized emitter and rear locally diffused cells
24
PMT
Solar cells
25
PO
Field Emission Scanning Electron Microscope
Tin oxide doped Fluorine
Plasmaenhanced chemical vapor deposition
Power output
vi
26
SHS
Solar home system
27
SAPP
Southern African Power Pool
28
SEM
Scanning Electron Microscope
29
SPD
Spray Pyolysis Deposition
30
STC
Standard test conditions
31
TCO
Transparent conducting oxide
32
TMA
Trimethyl Aluminum
33
TTIP
Titanium tetraisopropoxide
34
USPD
Ultrasonic Spray Pyolysis Deposition
35
UV-VIS
36
VASE
37
XPS
X-ray photoemission spectroscopy
38
XRD
X-ray diffraction
UV-VIS Spectrophotometer
Variable-angle spectroscopic ellipsometer
vii
LIST OF FIGURE
Figure 1.1. Price comparison of energy sources [5]. .................................................................. 4
Figure 1. 2. PV module price over time [14]. ............................................................................. 5
Figure 1.3. Graph illustration absorption of a photon in a semiconductor with an Eg band gap [16]. 10
Figure 1.4. Component parts of a typical PV cell. ................................................................... 11
Figure 1.5. Graph illustration structure of a 1D p-n homogeneous solar cell....................................... 12
Figure 1.6. Ideal short-circuit current density of p-n junction solar cell as a function of Eg [22]. ..... 14
Figure 1.7. J- V curves of a solar cell in the dark and under illuminated condition [17]. ........ 15
Figure 1.8. Graph illustration equivalent circuit of a real solar cell [17]. ................................ 15
Figure 1.9.Graph of p–n junction solar cell factor as a function of band gap .......................... 16
Figure 1.10. Market share of PV cells (%) [26]. ...................................................................... 17
Figure 1.11. Scheme of a modern crystalline silicon cell [29]. ................................................ 18
Figure 1.12. Imaging of Poly‐crystalline Si cell (a), and Mono-crystalline Si cell (b) [19]. ... 20
Figure 1.13. The structure of a conventional cell (a) and the structure of a cell with PERC
technology (b) [17] ................................................................................................................... 20
Figure 1.14. A cell with PERC technology will generate more current due to the reflection of
light at the backside of the cell ................................................................................................. 21
Figure 2. 1. Average monthly insolation levels in Luanda. ...................................................... 27
Figure 2. 2. Diagram of collecting and monitoring data of operating solar panels. ................. 28
Figure 2. 3. Kipp & Zonen’s Pyranometer Model CMP6, ISSO 9060 / WMO First Class
Standard: (a) Solarimeters measurement system; (b) The anemometer. .................................. 28
Figure 2. 4. The software for collect data. ................................................................................ 29
Figure 2. 5. The solar irradiance intensity through the experimental day in day. .................... 29
Figure 2. 6. Maximum output power versus solar radiation. .................................................... 30
Figure 2. 7. The PCE versus solar radiation. ............................................................................ 30
Figure 2. 8. The open circuit voltage Voc(a) and the short circuit current Isc (b) with varying
solar radiation. .......................................................................................................................... 31
Figure 2.9. The ambient temperature and modules temperature on time in day. ..................... 33
Figure 2.10. Average panel temperature versus ambient temperature. .................................... 34
Figure 2.11. Open circuit voltage (a) and Short circuit current (b) versus ambient temperatures...... 35
Figure 2.12. The conversion efficiency versus ambient temperature. ...................................... 37
Figure 2.13. Maximum power output versus wind speed. ....................................................... 37
Figure 2.14. The relationship between open circuit voltage and relative humidity. ................ 38
Figure 2. 15. The relationship between short circuit current and relative humidity................. 38
Figure 2.16. The relationship between relative humidity and ambient temperature. ............... 39
Figure 2. 17. The relationship between relative humidity and PV efficiency. ......................... 39
viii
Figure 2. 18. Equivalent circuit for amorphous solar cell. The current sink Irec stands for
recombination losses in i-layer. ................................................................................................ 40
Figure 2.19. Current-Voltage characteristics of PV cells before and after projecting by
neutrons with different illumination dose :1-=0; 2- =6*108; 3-=1.2*109; 4-=1.8*109;
and 5-=2.4*109. ..................................................................................................................... 41
Figure 2.20. Comparison of power converted by inverter (Pac) and power produced by PV system
(Pmax). ...................................................................................................................................... 42
Figure 2. 21. Location of the application point of the global wind force acting on monopitch
canopies (SR EN 1991-1-4/2006)............................................................................................. 44
Figure 2. 22. Scheme of a free standing panel in the air flow (a, c [81]); (b) the resulting
movement due to flow separation [82] ..................................................................................... 44
Figure 2. 23. Illustration of lift and draft forces ....................................................................... 45
Figure 2.24. Wind speed (km/h) in Luanda shows days per month ......................................... 46
Figure 2. 25. Solar panels placed at ground level ..................................................................... 47
Figure 2.26. Generated model of solar panels(a) Support and (b) Support with solar panels .. 48
Figure 2.27. Computational domain ......................................................................................... 49
Figure 2.28. Mesh of computational domain ............................................................................ 49
Figure 2.29. Mesh of computational domain ............................................................................ 50
Figure 2. 30. Distribution of pressure and streamline of fluid flow around solar panels at
centered XY plan – Wind velocity 3m/s & Attack angle 0o ..................................................... 51
Figure 2. 31. Distribution of pressure and streamline of fluid flow around solar panels at
centered YZ plan – Wind velocity 3m/s & Attack angle 0o ..................................................... 52
Figure 2.32. Distribution of pressure and streamline of fluid flow around solar panels at
centered XZ plan – Wind velocity 3m/s & Attack angle 0o ..................................................... 53
Figure 2.33. Distribution of pressure on solar panels – Wind velocity 3m/s & Attack angle 0o........ 54
Figure 2.34. Effect of inclined angle of PV to aerodynamic characteristics - Wind velocity
3m/s & Attack angle 0o: a) Coefficient of lift and drag force and b) Aerodynamic quality .... 55
Figure 2. 35. Distribution of pressure and streamline of fluid flow around solar panels at
centered XY plan – Inclined angle 30o& Attack angle 0o ........................................................ 56
Figure 2. 36. Distribution of pressure and streamline of fluid flow around solar panels at
centered YZ plan – Inclined angle 30o& Attack angle 0o......................................................... 57
Figure 2. 37. Distribution of pressure and streamline of fluid flow around solar panels at
centered XZ plan – Inclined angle 30o& Attack angle 0o......................................................... 58
Figure 2. 38. Distribution of pressure on solar panels – Inclined angle 30o& Attack angle 0o 59
Figure 2. 39. Effect of inclined angle of PV to aerodynamic characteristics - Inclined angle
30o, Attack angle 0o: a) Coefficient of lift and drag force and b) Aerodynamic quality .......... 60
Figure 2. 40. Distribution of pressure and streamline of fluid flow around solar panels at
centered XY plan – Wind velocity 9m/s & Inclined angle 30o ................................................ 61
Figure 2 41. Distribution of pressure and streamline of fluid flow around solar panels at
centered YZ plan – Wind velocity 9m/s & Inclined angle 30o ................................................. 62
Figure 2.42. Distribution of pressure and streamline of fluid flow around solar panels at
centered XZ plan – Wind velocity 9m/s & Inclined angle 30o ................................................. 63
ix
. Figure 2.43. Distribution of pressure on solar panels – Wind velocity 9m/s & Inclined angle 30o 64
Figure 2.44. Effect of inclined angle of PV to aerodynamic characteristics - Wind velocity
9m/inclined angle 30o: a) Coefficient of lift and drag force and b) Aerodynamic quality ....... 65
Figure 2.45. Mesh of strength analysis problem: a) Without solar panels and b) With solar panels . 66
Figure 2.46. Total deformation - Wind velocity 9m/s; Attack angle 0o& Inclined angle 30: .. 66
Figure 2.47. Equivalent Stress - Wind velocity 9m/s; Attack angle 0o& Inclined angle 30o: .. 66
Figure 3 1.Contact angle platform ............................................................................................ 70
Figure 3.2. Wetting on flat and rough surfaces: (a) flat, (b) rough, Wenzel case; (c) Cassie and
Baxter case. ............................................................................................................................... 71
Figure 3.3. Type two self-cleaning mechanism exists of TiO2 thin films ................................ 72
Figure 3.4.The pyrolysis system at SEP, HUST....................................................................... 75
Figure 3.5. Raman spectra of the TiO2 films deposited at substrate temperatures ................... 78
Figure 3. 6.FESEM images of TiO2 films deposited at: a) 4000C; b) 4500C. .......................... 78
Figure 3.7. AFM image of TiO 2 films deposited at substrate temperatures: a) 400; b) 450
and c)5000C ............................................................................................................... 79
Figure 3. 8.The optical transmission spectra of TiO2 films deposited at substrate temperatures. ...... 80
Figure 3.9. The plots of (αh)2 versus h for optical band gap the calculation of TiO2 films
deposited at substrate temperatures .......................................................................................... 80
Figure 3.10.XRD patterns of the F0, F15, F35, F55 and F75 samples ..................................... 82
Figure 3.11. FESEM images of the Fe doped TiO2 thin films: (a) F15; (b) F35; (c) F55 (d) F75. ... 83
Figure 3.12. Transmittance spectra of Fe doped TiO2 thin films: (a) F0; (b) F15; (c) F35; (d)
F55 (e) F75. .............................................................................................................................. 83
Figure 3.13. Plot of the band-gap and Fe3+ concentration of the doped samples ..................... 84
Figure 3. 14.XRD patterns of the W doped TiO2 thin films: (a) W0; (b) W1; (b) W2 and(d) W5.... 85
Figure 3.15. Raman spectra of W doped TiO2 thin films: (a) W0; (b) W1; (b) W2 and(d) W5. ....... 85
Figure 3.16. SEM image of a) TiO2 thin film and b) its cross sectional .................................. 86
Figure 3.17. SEM images of W doped TiO2 thin films (a) W0; (b) W1; (b) W2 and(d) W5... 86
Figure 3.18. Transmittance spectra of W doped TiO2 thin films: (a) W0; (b) W450; (c) W1;
(d) W2 (e) W5........................................................................................................................... 87
Figure 3.19. The plot of (h)2 vs. hfor the W doped TiO2 thin films: (a) W0; (b) W450; (c)
W1; (d) W2 (e) W5................................................................................................................... 87
Figure 3.20. Photocatalytic degradation rate of MB in the presence of samples. .................... 88
Figure 3.21. Linear transform ln(C0/C) = f(t) of the kinetic curves of MB degradation of TiO2 ...... 90
Figure 3.22. Photocatalytic degradation rate of MB in the presence of TiO2 .......................... 91
Figure 3.23 Linear transform ln(C0/C) = f(t) of the kinetic curves of MB degradation of W doped
TiO2 thin films: (a) W0; (b) W1; (b) W2and (d) W5 under visible light irradiation. ......................... 92
Figure 3. 24. Images observed superhydrophilic ability of samples. ....................................... 93
Figure 3.25. Images observed superhydrophilic ability of samples under visible light irradiation.... 93
x
Figure 4. 1. Schematic of recombination mechanism. ............................................................. 97
Figure 4. 2. Schematic drawing for ALD process in one cycle .............................................. 104
Figure 4. 3. The flow diagram for p-type Si solar cells(PERC) fabricated ............................ 107
Figure 4. 4. (a) Schematic of the inductively coupled photoconductance apparatus used for
measuring the effective lifetime. (b) The Xenon photo flash lamp WCT-120 here used for
QSSPC, fabricated by Sinton Consulting ............................................................................... 109
Figure 4. 5. Spectroscopic ellipsometry measurements for the sample deposited at 200 cycles: (left)
amplitude ratio Psi (in percentage) with WVASE32 parameter fitting, (right) phase shift delta (in
degree) with WVASE32 parameter fitting. The measurements were carried out with different
incident angles........................................................................................................................................... 110
Figure 4. 6. Al2O3 film thickness as a function of the number of ALD cycles (Tdep ≈ 2000C). ....... 111
Figure 4. 7. Refractive index (n) and extinction coefficient (k) as functions of wavelength of
the 200-cycle Al2O3 sample. .................................................................................................. 111
Figure 4. 8. SEM image of 30nm ALD Al2O3 on Si .............................................................. 112
Figure 4. 9. XPS survey spectrum of Al2O3 film deposited at 200 cycles. ............................ 112
Figure 4. 10. High resolution XPS spectra of Al2p and O1s for Al2O3 film deposited at 200 cycles......113
Figure 4. 11. Affection of substrate temperature on Al2O3 film growth by ALD technique. 114
Figure 4. 12. The plots effective carrier lifetime as a function of Al2O3 film thickness ........ 114
Figure 4. 13. The plots effective Voc as a function of Al2O3 film thickness ......................... 115
Figure 4. 14. The plots effective efficiency as a function of Al2O3 film thickness ................ 115
Figure 4. 15. The plots effective Effective minority lifetime as a function of annealing temperature.....116
Figure 4. 16. Morphology of Al2O3 thin films before PDA and after PDA ........................... 116
xi
LIST OF TABLES
Table 1. 1. Solar Village Program .............................................................................................. 8
Table 2. 1. The influence of irradiation on Isc and Voc of experimental PV samples. .............. 41
Table 2. 2. Terrain roughness, power-law exponent and boundary layer thickness values
corresponding to different exposure categories [80] ................................................................ 43
Table 2. 3. Characteristics of solar panels ................................................................................ 48
Table 2.4. Boundary conditions................................................................................................ 50
Table 3.1. The table of chemicals ............................................................................................. 74
Table 3.2. The factor investigation and samples. ..................................................................... 76
Table 3.3. The table of samples. ............................................................................................... 76
Table 3. 4. Band gap and roughness of samples at substrate temperatures .............................. 81
Table 3. 5. Crystallite sizes, band-gap energies Eg and absorption wavelengths of the
undoped and Fe3+doped samples. ............................................................................................. 84
Table 4. 1. List of materials grown by ALD [139]–[143]. ..................................................... 103
Table 4. 2. Available reactant groups for specific elements [140]–[144] . ............................ 103
Table 4. 3. XPS main-peak parameters, atomic concentration, and O/Al atomic ratio of the
200-cycle sample. ................................................................................................................... 112
Table 4. 4. XPS binding energy (eV) and atomic ratio of Al-2p and O-1s core level for Al2O3. .... 113
xii
INTRODUCTION
Alternative energy sources have been promoted due to the diminishing resources, rising
costs and sustainability concerns faced by carbon-based fossil fuels. Wind and solar energy
are the most promising renewable energy sources that received significant amount of research
and development. These energy sources are safe and much less harmful to the environment.
Solar energy is beginning to grow and is currently on the rise, even though the price is still
much more expensive than traditional energy sources [1].
The photovoltaic (PV) are currently poised to be used to harness solar energy.
Photovoltaic, commonly known as solar cells, convert sunlight directly to electricity via p-n
junction [2].
Angola is in the Western region of southern Africa, occupying an area of approximately
1.246.700 km2, which makes Angola be the sixth largest country of Africa. The extent of Angolan
coastline is of more than 1.600 kilometers, bordering the Atlantic Ocean. Angola has land borders
to the North with the Republic of Congo and the Democratic Republic of the Congo, to the East
with the Democratic Republic of Congo and Republic of Zambia, and to the South with the
Republic of Namibia, with an extension of more than 1.400 km [3].
The current population of Angola in 2018 is estimated at 29.25 million, up from 2014's
estimated 25.6 million. As one of the least densely populated countries in the world, Angola
has a density of 14.8 people per square kilometer. Luanda is capital in Angola. The population of
Luanda is about 6.5 million people. Luanda is also urbanizing at approximately 4% annually.
Although Angola is a member of the Power Pool of South Africa (Southern African Power
Pool, SAPP) and the Power Pool of Central Africa (Energy Pool of Central Africa-ECCP), the
country has no current links with its neighbors, with exception of several isolated lines that
supply several towns on the south with Namibia. Today, more than 13 million Angolans, or
about 26 percent of the population, have no access to electricity, according to the International
Energy Agency (IEA). Rural areas, especially those in the rural south of the country, have no
access to a grid.
Angola is a Southern African nation whose varied terrain encompasses tropical Atlantic
beaches, a labyrinthine system of rivers and Sub-Saharan desert that extends across the border
into Namibia. This fact benefits the existence of insulin throughout almost every year. The global
solar radiation is in the annual horizontal plane, between 1.370 and 2.100 kWh/m2 and year. Due
to the exceptionally sunny climate, solar energy holds huge potential for Angola, especially in
rural areas. The Rural Electrification Program issued mid 2012 aims to benefit 8 million
people in 2016. Solar generation systems play a large part in the second and third round of
this program, which focuses on building mini systems and distribution of electricity. This goal
is part of the Angeles 2025 goal to increase capacity by four times and to achieve
an electrification rate of 50-60%. The World Energy Outlook 2011 of the IEA states that 13.7
million Angolans (26.2%) have no structural access to electricity, especially in the rural south
of Angola. Because of the high irradiation levels (6.3 kWh/m2day in Angola), Solar PV has
huge potential for providing a solution to Angola’s energy difficulties.
The Ministry of Energy and Water (MINEA) is now in a phase of concluding the
National Strategy for Renewable Energies. Solar PV will be essential in short, medium and
long term. MINEA announced the installation of 142 solar PV systems worth of 534.6
1
kilowatts. These installations will be distributed among medical centers, schools,
administrative buildings and streetlights.
According to Bloomberg Report of Solar PV in 2012, Angola revealed its plans to invest in
about 130 solar projects 32, although there was no information regarding the size or
technology. There is also a CDM project in the feasibility stage, providing a total of 0.730
MW from 70 solar PV villages (grid connected). Furthermore, a capacity building program
conducted by Econ Pöyry emphasizes a large potential for solar PV in the south of the
country, where hydropower resources are more limited. The study includes a 3 MW solar
plant in Tombua, with potentially further solar plants being installed in Namibia and
Benguela. However, this is just the beginning. The Angolan government has stated that it still
needs a lot of knowledge and experience to successfully implement more renewable energy
installations.
Due to the Angola’s climate and location, solar energy seems to be the primary choice for
investigation. This following analysis the effects of solar radiation, ambient temperature, the
surface temperature of the PV panels, meteorological data, and relative humidity on the
performance of a c-Si solar cells, grid-tied system. The importance of this study is in the
analysis of a PV system in the first year of operation, to understand the initial performance
and losses occurring in the beginning of the lifetime of the system, and to rank the factors that
affect its performance. The study will focus on the technology available to harness it. Details
on the PV technology and setup used in this research are discussed in the following sections.
In short, one of the issues that attracted tremendous attention in the world and especially in
Angola, is to study the applicability of solar cells to one of the most environmentally friendly
renewable energy sources in remote areas and to reduce the cost of solar cells. This is a real
and urgent issue to solve the problem of energy security. This is also the basis for us to select
the contents of this thesis. Thesis title “Study an influence of Angola’s tropical climatic
conditions on operating efficiency of Silicon photovoltaic solar cells and technological
solutions to enhance their performance’’
Object and scope of research of the thesis:
The aim of this thesis is to study an influence of Angola’s tropical climatic conditions on
operating efficiency of Silicon photovoltaic and technological solutions to enhance their
performance.
This research seeks to review:
-
-
-
The major Angola’s tropical environmental factors such as the intensity of solar
radiation, temperature, and wind speed, humidity and dust that affect the performance
of PV system.
The simulation of the interaction between wind and the silicon photovoltaic panels by
computational fluid dynamics.
Titanium dioxide thin films deposited by ultrasonic spray pyrolysis deposition (USPD)
and sol gel mix hydrothermal dip coating application as self-cleaning layer in thin film
solar cell.
Ultra-thin film Aluminum oxide deposited by atom layer deposition (ALD)
application as passivation layer in thin film solar cell.
2
Research Methods:
We have experimented on the effects of climate conditions in the Luanda, Angola on PV
modules. The weather parameters we studied as the intensity of sunlight, ambient
temperature, humidity and wind speed in outdoor conditions.
The flow of wind over the model of a photovoltaic structure exposed to wind flowing over
an open terrain has been investigated using ANSYS Fluent software
The deposition methods include the USPD method, sol gel mix hydrothermal method and
ALD method.
Sample quality was investigated by X-ray diffraction, Raman scattering spectroscopy,
scanning electron microscope, atomic force microscope, UV-VIS spectra, variable-angle
spectroscopic ellipsometry and X-ray photoemission spectroscopy.
The scientific and practical significance of the thesis
We are analyzing the influence of Angolan tropical climate on performance of siliconbased photovoltaic system located in Luanda, Angola. By analyzing the effects of different
variables that affected the performance of silicon PV system located in an African tropical
environment, it was observed that solar irradiance had the greatest impact on performance.
This implies that the unexpected factor such as dust accumulation will probably have a
significant impact on the performance of the system by reducing the amount of sunlight that
the PV panels are exposed to.
The calculated results using ANSYS Fluent software show that, inclination of panels has
the largest effect on the wind loads acting on solar panels. Small changes in panel inclination
are observed to result in significant changes in wind loads.
We have deposited transparent TiO2 thin films using TiAcAc precursor by employing a
simple and inexpensive spray pyrolysis and sol-gel-hydrothermal techniques. Fe, W-doped
TiO2 films are essential for application as a self-cleaning surface in solar panels.
Study and investigate the effect of ALD technology parameters on the formation of Al2O3
ultra-thin films applied as passive layer of c-Si solar cell. The Al2O3 ultra-thin films can be
used as a passivation layer to improve performance of silicon based solar cells.
The structure of the thesis
In addition to the "Introduction", "Conclusion", "List of symbols and abbreviations", "List
of tables", "List of images and graphs", and " References ", the thesis is presented in four
chapters as follows:
Chapter 1: Literature review
Chapter 2: The influence of tropical climatic condition on the PV system performance in Angola.
Chapter 3: Experimental study on titanium dioxide application as solar cell self-cleaning layer.
Chapter 4: Growth and characterization of aluminum oxide ultra-thin film as a passivation
layer for silicon solar cells
3
CHAPTER 1. LITERATURE REVIEW
1.1. Overview of renewable energy use in the World
There are many options for reducing greenhouse gas emissions from energy systems while
still meeting the global energy needs. One of the options could be renewable energy, which is
huge potential to mitigate climate change, can also provide people with utilities when using
them. Renewable energy can, if properly implemented, contribute to socio-economic
development, access to energy as a safe source of energy, and reduction of negative impacts
on the environment and health.
In the most demanding conditions, increasing the share of renewable energy in the energy
mix will require policies to stimulate changes in the energy system. The deployment of
renewable energy technologies has increased rapidly in recent years. Additional policies are
needed to attract the necessary increase in technology and infrastructure investment.
Among the important renewable energy sources (hydropower, biomass, wind and solar),
photovoltaic (PV) is the fastest growing sector with an average annual growth rate of about 60
% in the year 2012 [4].
Figure1.1. presents a plot of cost and price comparison of different energy sources in USD
($). It can be seen in the graph that the cost of 1kwh energy from PV is highest.
0.20
0.18
0.16
Cost, $/kwh
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
solar
wind
coal
natural gas
Energy sources
Figure 1.1. Price comparison of energy sources [5].
The performance of a PV system can be characterized by its power output (PO), power
conversion efficiency (PCE) and reliability [6]. The PO measures the capacity of the module
and the amount of electricity (in watts) it can generate. On the other hand, the PCE quantifies
the percentage of power generated by the module in comparison with the total solar energy
available to the system. Generally, solar module reliability measures the probability that it
will perform the intended function over a specified interval understated conditions. Cost has
been identified as an important factor in the choice of energy sources especially in the
developing countries like Vietnam or Angola. To increase the adoption of the PV module in
4
the developing countries, the cost has to be as low as possible. We can identify that PV
module’s cost plays an important role to determine the choice of energy for the individual,
company, community or nation.
According to REN21 [7], depending on system size, local solar radiation conditions and
other factors, solar cell prices range from 9-13 cents/kWh for large scale installations. The
price of solar cells is about 22-44 cents/kWh in European countries. In the United States,
the installation price on the roof is 20-37 cents/kWh. In long-term calculations, the cost of
solar power will fall below 10 cents/kWh. IEA ETP (2012) [8], in their calculation, shows
that PV cost in 2030 will be around 7-11 cents/kWh for large scale projects and 8-14
cents/kWh for installation of PV panels on the roof. Martín-González in their study [9], [10],
has announced that solar electricity costs will be 5 to 10 cents/kWh by 2030-2040, depending
on the region.
In recent years, solar PV becomes the power supply in a wide variety of locations, this
happened mainly due to the huge drop in the production costs, which greatly reduced the retail
price of panels (from an average cost in 2006 of 4.5 $/Wp to less than 1 $/Wp in 2013) [2].
Several factors have contributed to lowering the cost of solar energy such as the ability to
deposit thin films over large areas, the ability to automate the technology, increase the
photovoltaic efficiency, etc. The trend of the achieved cost reduction of PV modules is
depicted in Figure1.2 [11]. To progress this trend, it is proposed that improvement of the
performance and reliability of PV module in the World difference climatic zones would
engineer its adoption and usage, especially in African country as Angola. PV technology is
poised to meet the energy needs of these regions owing to its decentralized, sustainable and
renewable nature [2], [12], [13].
6
PV module price per watt, $
5
4
3
2
1
0
1990
1995
2000
2005
2010
2015
Year
Figure 1. 2. PV module price over time [14].
To achieve a full competitiveness of PV energy worldwide (especially in those locations
and to further reduce the price of electricity generated by PV modules, research is required to
improve their conversion efficiency and reduce the material utilization, reducing in this way
part of the production costs.
5
In short, solar energy has become an increasingly important source of clean energy in the
world. With significant advances in technology, solar cells can increase efficiency and
promise to bring significant growth to this "green energy" industry in the future. Nowadays,
photovoltaic research will continue intense interest in new materials, cell designs, and novel
approaches to solar material and product development. The price of photovoltaic power will
be competitive with traditional sources of electricity.
Our study, however, aims to review available PV cell technologies commercially available
as will be thoroughly discussed in this section.
1.2. Overview of solar cell use in the Angola
In recent years, the Angolan government has been doing several efforts to popularize solar
photovoltaic (PV) technology to supply energy services to people without access to an electric
grid connection. Although the price for solar PV panels has decreased over the years, the cost
of PV modules in Angola are still too high for most rural farmers or potential solar home
system (SHS) users.
In June of 2003, the Angola PV LUATA project was started. It is implemented by the
Department of Renewable Energy (DRE), National Energy Directorate of the Ministry of
Energy and Waters, Government of Republic of Angola. It is supported financially by the
British Petroleum Company (BP), as advisors to the DRE. It is a pilot project with the aim to
investigate whether the PV LUATA approach is appropriate and can be integrated in the rural
electrification strategy Angola.
The project has supported the formation and operation of three LUATA in the district of
Piranhas Province of Bengo. In all cases, the BP business is a subsidiary to an existing
company with business activities in other fields: farm implements, waste management and a
farmer’s cooperative.
Specifications of the systems were based on experiences from other solar power projects,
consideration of usefulness and affordability, and surveys of energy use and affordability in
the Bengo Province. The base system is composed of 28 modules with an output of 24V
200Wp. Each grouped in 7 parallel of 4 modules connected in series to provide an up voltage
96V and intensity 112A, a total power 10.8 kWp; A charge controller battery of 112A. 48
batteries of 2V, 900Ah wired in series to a voltage up to 96V. An inverter is at
96Vc.c/220Vac and 12.000W ÷ 14.000W power.
Angola’s Ministry of Energy and Water (MINEA) has announced a national strategy for
renewable energy, with solar energy an essential component in the short, medium and longterm. MINEA is targeting the installation of 142 solar photovoltaic systems providing 534.6
kilowatts, Solar Solutions West Africa says. These installations will be distributed among
medical centers, schools, administrative buildings and streetlights. The long-term goal is to
integrate renewable energy, including wind, biomass and solar, into the national grid.
Angola is set to implement rural solar energy electrification by 2025 that will benefit
several rural areas of the country. According to the Angola’s minister of Energy and Water,
João Baptista Borges, the solar energy deployment project will be keys and will add power
supply in rural areas. Solar energy projects will benefit many people, as well as schools and
other institutions. The minister said it will benefit the country’s current electrification process
6
since it was cheap, fast and effective. “Angola is a tropical country where the sun appears
during the year, so we should take more and better advantage of this natural resource”, said
the minister. Added João Baptista Borges.
The Angolan government has established a strategy whose goal is that by 2025, at least
7.5% of the electricity generated in the country will be coming from new renewable energies,
most prominent in Energy Photovoltaic that will represent about 800 MW. With this goal, it is
intended:
- Improve access to energy in rural areas (Solar Village)
-
Develop the use of new network-linked renewable technologies: Creation of plant units
to produce Photovoltaic Energy Sources;
- Promote public and private investment, aiming at the promotion of new energy sources.
In Angola, rural electrification is foreseen under three implementation models [15]:
- Rural electrification through grid extension
- Electrification through isolated systems
- Electrification through individual systems
Rural electrification through grid extension: The selected grid extension model
contemplates already numerous distribution grids outside the large urban areas, essentially to
electrify municipal townships. Those grids reach 174 locations, which represent
approximately 5% of the Angolan population. Grid extension outside large urban areas will
allow for the electrification of many municipal townships, in a total of approximately 1.7
million people. All municipal townships will be connected to the main grid, including the
border towns which will be serviced through Namibia. The electrification model proposed is
based mainly on the installation of 60kV substations, branching from existing or planned
220kV substations. These substations are generally located in municipal townships which, in
turn become points of departure to connect either other municipality townships or rural grids.
Furthermore, the connection to the main national grid reduces significantly the costs of
powering these distribution networks, thus facilitating the involvement of the private sector.
Electrification through isolated systems: The electrification by means of isolated systems
is considered for 31 localities, which represents only 1% of the population. These localities
are preferentially supplied by competitive mini-hydro, and where these are not available, by
diesel generators and PV systems. The proximity of a municipal township to a competitive
mini-hydro - for such level of consumption - reduces the gains which could be obtained from
connecting it to the national grid and changes, in various situations, the economic rationale of
interconnecting that location. The hydropower atlas has made it possible to evaluate, on a
preliminary basis, approximately 100 locations identified by the Ministry of Energy and
Water. The mini-hydro projects with lower generation costs have been resized and
reappraised to the load of the close-by municipal townships and rural grids. This appraisal has
resulted in 7 mini-hydro selection which potential to supply 9 municipal townships through
isolated systems. Additionally, a medium sized hydro project has been identified in river
Cuango, which has the potential to supply power to four municipalities with a population of
more than 300,000 people while the connection between North and East systems is not built.
7
About 21 municipal townships present high connection costs per energy unit. Therefore,
they should be electrified through isolated systems based on diesel with some solar power
support which can reduce fuel costs.
Finally, the concept of a 100% solar municipality - with photovoltaic technology and
batteries will be tested in the locality where economic rationality is the highest, considering
the high cost of transportation of diesel: The Municipality of Rivungo, in Cuando Cubango.
Should this solution be successful, it can be extended to other distant municipal townships
that have good solar resources.
Electrification through individual systems: This model comprises the creation of “solar
villages” or small local networks in communal townships and settlements with more than
3,000 inhabitants. “Solar villages” constitute an intermediate solution, which provides modern
electricity services to communal infrastructures, such as schools, health units, administration
and public lighting of main streets. Small local networks can be developed by private initiative.
The National Strategy for New Renewable Energies foresees a target of 500 solar villages by
2025. Some remote villages could benefit from solar lanterns and improved cook-stoves.
Currently, Photovoltaic Energy still accounts for less than 1% of total national energy
consumption. A program for the implementation of photovoltaic systems for the electrification of
rural areas (Solar Village Program) not covered by the transmission and distribution networks
is under way as show in table 1.1.
Table 1. 1. Solar Village Program
Number
Infrastructure
1st stage
2nd stage
3rd stage
1
Schools
10
23
33
2
Clinics
16
23
39
3
Administrative residences
10
29
39
4
Police Stations
3
7
10
5
Community centers
-
7
7
6
Public lighting
70
84
154
Total
109
173
282
Given that the manufacturing process of solar cells has been refined in recent years, this
should increase their efficiency and given that this efficiency is also intrinsically linked to
climatic conditions in which solar cells are exposed, we decided to do a study and analyze the
behavior of solar cells, exposed on the climate of Angola, which is characterized as
Subtropical Moist, whose relative humidity is as high as 60-70% in the time of year.
Angola, despite being in a tropical zone, has a climate that is not characterized for his
region, due to the confluence of three factors:
(i)
The Benguela Current, which is cold, lying along the south coast.
(ii)
The relief inside the country.
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