Nghiên cứu ảnh hưởng của môi trường nhiệt đới angola tới hoạt động và một số giải pháp công nghệ nâng cao hiệu suất của pin mặt trời silic

24
(iii) The equivalent stress is found maximum at vertical bar of
support of solar panel. The maximum value is about 7.46 ×
104 Pa. This value is lower than the limit stress of aluminum
alloy (7.1 × 109 Pa).
3. Fe doped- TiO2 thin film deposited by USPD:
(i) Fe-doped TiO2 thin film formed anatase phase and tetragonal
structure. Crystal size is about 15 ÷ 25 nm; Eg = 3.32 ÷ 3.43
eV.
(ii) With 1.5% Fe-doped TiO2 sample have the best activity
Photocatalytic in UV with value kapp = 0.016 min-1.
4. W-doped TiO2 thin film deposited by sol-gel mix hydrothermal
method:
(i) W-doped TiO2 thin film formed anatase phase and tetragonal
structure. Wolfram formed with structure WO3.
(ii) W-doped TiO2 thin films have thickness about 1.30 ÷ 1.50 µm.
Crystal size is about 15 ÷ 25 nm. High transmittance and
optical band gap are about Eg = 3.6 ÷ 3.5 eV.
(iii) With 2% W-doped TiO2 sample have the best activity
Photocatalytic in Vis with value kapp = 0.14 min-1.
5. The Al2O3 ultra-thin films have been grown by ALD technique
Trimethyl Aluminum (TMA), and water have been used as the
metal and oxygen precursors:
(i) The estimated deposition growth rate was 1.0 Å/cycle at
deposition temperature of about 200oC. The Al2O3ultra-thin
films have refractive index n = 1.6 ÷ 1.75 in visible light.
(ii) The best valuable is about eff ~ 700 µs with thickness is
about 11nm. If used post-deposition annealing (PDA), the
carrier lifetime is eff ~ 770 µs after PDA with thickness is
about 11 nm. the efficiency is the best about 20.55% when
the Al2O3 film thickness is about 11 nm.

1
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 receive 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 photovoltaics (PV) are currently poised to be used to harness
solar energy. Photovoltaics, commonly known as solar cells, convert
sunlight directly to electricity via p-n junction [1, 2].
Angola is in the Western region of southern Africa, occupying an
area of approximately 1.246.700 km2 area, that makes Angola the
sixth largest country of Africa. Luanda is the largest city in Angola
and is also its capital. The population of Luanda is about 2.8 million
people. Luanda is also urbanizing at approximately 4% annually.
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 “Studying the influence of Angola’s tropical
climatic conditions on the operational efficiency of Silicon
photovoltaic solar cells and finding technological solutions to
enhance their performance”.
Object and scope of research of the thesis:

The aim of this Thesis is to review photovoltaic module
technologies for increased performance in tropical climate. This
research seeks to review the cell, technologies utilised in PV module
manufacture.
This section reviews the major environmental factors that affect
the performance of solar PV system.
Ambient conditions such as the intensity of solar radiation,
temperature, wind speed, humidity and dust significantly influence
the performance of PV panels.


2
The impact of solar systems on rural livelihoods and experiment
influence of tropical climate in the operation of solar cells in Angola.
The simulation of the interaction between wind and the solar
panels in Angola by computational fluid dynamics.
Study and investigate the effect of technological parameters on
TiO2 thin film deposition on the anti-reflective glass layer for
cleaning in PV system.
Study and investigate the influence of atom layer deposited (ALD)
technology parameters on the formation of Al2O3 thin films applied as
passive layer of c-Si solar cell.
Research Methods:
In this study, we used the experimental method in combination
with theoretical guess and simulation method as computational fluid
dynamics. All samples in the thesis are samples that we built
ourselves on the systems we built and developed (except the ALD).
The deposition methods include the Ultrasonic spray pyrolysis
deposited (USPD) method, hydrothermal hydrolysis method and
ALD method.

Sample quality was investigated by X-ray diffraction (XRD),
Raman scattering spectroscopy, scanning electron microscope
(SEM), atomic force microscope (AFM), …
The scientific and practical significance of the thesis
Scientific significance:
Survey and study the effect of real environmental conditions on
the characteristics of c-Si solar cells in Angola. Simulate the effect of
wind on c-Si solar cells in real conditions in Angola.
Study and investigate the effect of technological parameters on
TiO2 thin film deposition on the anti-reflective glass layer for
cleaning in PV system.
Study and investigate the effect of ALD technology parameters on
the formation of Al2O3 thin films applied as passive layer of c-Si
solar cell: Study the conditions necessary for low temperature
depossition of Al2O3 thin films by the ALD technique and examines
properties of the resulting films.
The practical meaning of the thesis:
The first time investigated the effect of real conditions on the
activity of c-Si solar cells in Angola.
The first-time study examines the effect of wind on off-grid solar

23

Figure 4. 2. Morphology of Al2O3 thin films before PDA and after PDA

4.7. Chapter summary
CONCLUSION
1. Experimented on the effects of climatic conditions in the Luanda,
Angola on PV modules for a year was investigated. The weather
parameters were studied as the intensity of sunlight, ambient

temperature, humidity and wind speed in outdoor conditions. The
investigation results show that:
(i) When the ambient temperature rises by about 1o, the
temperature of the c-Si solar cell system increases by nearly
10o.
(ii) When the relative humidity of the environment increases from
60% to 85%, the efficiency of the PV decreases by 2.4%.
2. The simulated results shown that:
(i) The inclined angle of solar panels β = 30o within velocity of
wind 9m/s and horizontal wind direction (attack angle α
equal zero degree) is the best choice of system.
(ii) The lower left corner in the direction of the wind is the largest
distortion of about 0.685 mm.


22

3

Al2O3 in the films. The Al2p binding energy of 74.1 ± 0.2 eV is
within the range of values reported in references [186-188]. The
major peak at the binding energy of 531.3 eV can be assigned to
oxygen bonded to aluminum in Al2O3.
Table 4. 1. XPS binding energy (eV) and atomic ratio of Al-2p and
O-1s core level for Al2O3

systems in Angola.
The structure of the thesis
In addition to the "Introduction", "Conclusion", "List of symbols
and abbreviations", "List of tables", "List of images and drawings",

and " references ", the thesis is presented in four chapters as follows:
Chapter 1: Overview
Chapter 2: Survey and study the effect of real environmental
conditions on the characteristics of c-Si solar cells in Angola. Simulate
the effect of wind on c-Si solar cells in real conditions in Angola.
Chapter 3: Study and investigate the effect of technological
parameters on TiO2 thin film deposition on the anti-reflective glass
layer for cleaning in PV system.
Chapter 4: Study and investigate the influence of ALD
technology parameters on the formation of Al2O3 thin films applied
as passive layer of c-Si solar cell.

Film
Al2O3

Binding energy
Al2p (eV)
74.1

Binding energy
O1s( eV)
531.4

Atomic ratio
O/Al
1.79

The implied Voc increases dramatically from 652.6 mV to about
656.9 mV at 4nm of thickness. This result clearly showed the
improved passivation performance of the ultrathin ALD-Al2O3 films.

For 11nm of thickness, the maximum implied Voc, 659.1 mV, was
obtained after PDA.
Fig. 4.15 shows the effective minority carrier lifetime of p-type cSi wafers passivated by 5, 10, 15 and 20 nm Al2O3. For original c-Si
wafer, the eff was measured to be  6 ms. After depositing a 20 nmthick Al2O3 layers, a higher eff of  900 ms is obtained. The results
show that the effective minority carrier lifetime is improved when the
Al2O3 thin films is deposited on c-Si surface. To study the full
potential and the thermal stability of the surface passivation
performances of Al2O3layers, the lifetime samples were exposed to
PDA at temperature (Ta) ranging from 530 to 670 oC with PDA time
of 5 min in nitrogen enviromental. The effective minority carrier
lifetime increasing with increasing PDA of Al2O3 films and begin
reduction at PDA about 600oC. The effective minority carrier lifetime
is maximium value about 288.3µs at PDA about 600oC and 20nm of
thickness Al2O3. The different thickness of Al2O3 thin films, effective
minority carrier lifetime was effected. The blisters gas can be have
before PDA,due to make reduction of effective minority carrier
lifetime.Morphology of Al2O3 thin films before PDA and after PDA
illutration in figure 4.16.

CHAPTER 1. LITTERATURE REVIEW
1.1. Overview of renewable energy use in the World
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. 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 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 determines the choice of

energy for the individual, company, community or nation.
To achieve a full competitiveness of PV energy worldwide
(especially in those location where sun irradiation is lower) 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.
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.


4

21

Nowadays, photovoltaics 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.
1.2. Overview of solar cells 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 costs of PV modules in Angola are still too high
for most rural farmers or potential solar home system (SHS) users.
Consequently, the climate of Angola is characterized by two
seasons: the rainy season, from October to April and dry, known for

Cacimbo, from May to August, drier, as the name implies, and at
lower temperatures. Moreover, while the coast has high rates of
rainfall, which will decrease from north to south and 800 mm for 50
mm, this area has annual temperature above 23 ° C.
A wide range of benefits can be obtained from PV technology and
solar systems, apart from light, for instance, operation of radio and
TV sets, communication equipment, water pumps, fans, etc. Almost
50% of the households stated that the children benefited most from
the PV System. Half of the respondents stated that having light was
the best thing with a PV, and almost as many (43%) mentioned new
possibilities for entertainment. The possibility to read and study at
night was the greatest benefit by about a third of the respondents.
1.3. The photovoltaic effect
1.4. Physics of Solar Cells
1.5. Overview of Solar Cell Technologies
1.6. Influence of tropical climate in the performance of PV panels
This section reviews the major environmental factors that affect
the performance of solar PV system.
Ambient conditions such as the intensity of solar radiation,
temperature, wind speed, humidity and dust significantly influence
the performance of PV panels. This Thesis focuses on the tropical
climate like in Vietnam and Angola. These zones are characterised by
high-temperature and humidity, heavy cloud cover and high rates of
precipitation. The ambient temperatures range from 15 to 45 °C and
it can provide the PV modules temperature to rise to 80 °C or higher.

CHAPTER IV- GROWTH AND CHARACTERIZATION OF
AL2O3 ULTRA-THIN FILM AS A PASSIVATION LAYER FOR
SILICON SOLAR CELLS
4.1. The need for silicon solar cells passivation layer AL2O3

4.2. Carrier Recombination in Crystalline Silicon
4.3 Surface passivation
4.4. Surface passivation materials
4.5. Growth Al2O3 ultra-thin film by Atomic Layer Deposition
4.6. Results and discussion
From fitting results, the thickness of the 200-cycle film was
estimated of 19.95  0.01 nm. VASE measurements and fitting were
also done for other samples deposited at 50, 100 and 150 cycles,
resulting thicknesses of 4.94 ± 0.01, 10.03 ± 0.01, 15.16 ± 0.01,
respectively.
The recorded binding energy profiles are shown in figure 4.6. The
survey spectrum shows the peaks corresponding to the binding
energies of Al, O and C. The presence of the C1s peak is
advantageous as contaminant carbon can compensate the surface
charging effect. The peaks observed at binding energies of 74.1 ± 0.2 eV
and 531.4 ± 0.2 eV can be
attributed to Al2p and O1s,
respectively. These binding
energies are in good agreement
with the binding energies of
Al2 O3
films
reported
in
literature [183-185].
The atomic concentration is
calculated by using the following
equation
Figure 4. 1. XPS survey spectrum
of Al2O3 film deposited at 200

(4.12)
cycles.
with Ai the peak area off a
photoelectron peak and Si the relative sensitivity factor of the peak
(SO=0.711, and SAl=0.234).
It can be found that the Al2p peak could be fitted with only one
peak, suggesting that aluminum may be present only in the form of


20

5

particles (W0; W1; W2 and W5) exhibit.
The value of kapp can be calculated by the slope of linear plot. We
can obtain that the kapp value of 2 wt% WO3/TiO2 is 0.14 min-1, 1
wt% WO3/TiO2 and 5 wt% WO3/TiO2 is about 0.11min-1 being
approximately four times for pure TiO2 (0.004 min-1), respectively.
Therefore, it dares say that coupling with an effective metal oxide is a
promising selection to significantly enhance the photocatalytic
activity of TiO2 under visible light illumination.
3.3.2.3. Superhydrophilic properties
Superhydrolysis properties of samples were observed under UV
irradiation. Images observed superhydrophilic ability of samples:
F15, F35, F55 and F75 shown in figure 3.23. As we can see, in part
glass substrate had not coated TiO2, the blue ink droplet was still
shrink and almost no spread. In part of coated doped Fe, the blue ink
droplet was spreader and formed thin film. In all four cases Fe
doping, the survey results are almost same.
Combining with the above result on UV-Vis spectra, the better

hydrophilicity for Fe doped TiO2 thin film can be attributed to the
doped TiO2 thin film with a narrower band gap. Hence, the narrower
the band gap of the film is, the more the film accepts photon energy,
and the greater the film creates superhydrophilicity.

The relative humidity is in the range of 45 ÷ 95% with wind speeds
of 0.2 m/s and higher. Consequently, PV modules operating in the
tropical climatic conditions seem to be possessed higher failure rates
than those in other climates.
The next Sections discuss the major environmental factors that
affect the performance of solar PV system.
Chapter Sumary
CHAPTER II - THE INFLUENCE OF TROPICAL CLIMATIC
CONDITION ON THE SOLAR PV PERFORMANCE IN ANGOLA

F15
F35
F55
F75
Figure 3.34. Images observed superhydrophilic ability of samples
3.3.3. Chapter conclution

2.1. Experimental introduction
In this Chapter, we are analyzing the influence of Angolan
tropical climate on performance of small scale, grid connected,
silicon-based photovoltaic system located in Luanda, Angola from
September 2011 to September 2012. The outputs of PV system under
real working conditions are influenced by some environmental
factors as solar radiation, ambient temperature, the surface
temperature of the PV panels, meteorological data, and relative

humidity. 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. A PV
system is in Ya Hoji Henda Central, Luanda, Angola, and the average
daily irradiance in this region in Luanda is around 4.5 kW h/m2/day,
and changes slightly from season to season.
To test the performance of the system, the data recorded every
second. The recordings of these data were collected several times a
week at different time intervals throughout the day.
2.2. Influence of Solar radiation
One of the main factors affecting the performance of PV systems
is the amount of radiation to which cells are exposed. The irradiation
solar on time in day in month in Angola are corresponding to the
measurement. The amount of incoming solar irradiance is much
higher in duration 11 a.m. until 4 p.m. which can be determined as
the peak sun during the day. The irradiance intensity incident on a
PV module in the field is not constant and may only reach 1100
W/m2 around solar noon.
The maximum power output of the system with solar irradiance


6

19

was measurement. The data points fit a linear relationship seems to
be the only solar irradiation variable which significantly determines
the output of the system. It is shown that the output of the system is
directly related to the amount of radiation reaching the PV panels.

Thereby, it can be considered the site location has a big potential
in installing the PV system. The highest amount of solar irradiance
was found at 13.41 p.m (28.2.2012) with 1200 W/m2 where the
minimum was 125.50 W/m2 at 9.49 a.m (04.1.2012). The low solar
irradiance intensity might be due to a very short and a sudden
blockage of the Sun disk with too heavy clouds.
It can be noted from the results that irradiation solar is about
100W/m2 ÷1000 W/m2 in time in day. The irradiation solar are not
more different between month in year. Addition, irradiation solar in
horizontal and vertical is different. So, the irradiation solar is about
100W/m2 ÷1000 W/m2 respectively has been observed.

values up to 88 %. The optical band gaps of 3.6 to 3.51 eV were
estimated for as-deposited and annealed films respectively. As it can
be seen, in both cases, the gap energies obtained by this method are
bigger than the value in stoichiomteric bulk TiO2 (3.20 eV for
anatase phase and 3.11 eV for rutile) which is probably due to the
polycrystalline nature and to the reduced grain size of the films.
3.3.2.2. Photocatalysis properties
The photocatalytic activities of samples were determined by
measuring the degradation of MB under visible light irradiation.
The photocatalytic activities of pure TiO2 and Fe doped TiO2 as a
function of reaction time. Among five tested, only the F15 (Fe doped
1.5%) showed the highest photocatalytic activity and as the
concentration of Fe increased in TiO2, the photocatalytic efficiency
was gradually decreased.
Figure 3.21 shows the related kinetics data over the catalysts
under visible light irradiation.
3.0
The regression curve of natural

2.5
logarithm of normalized MB
concentration versus reaction
2.0
time
approximates
linear,
1.5
indicating that the kinetics of
MB degradation over the
1.0
photocatalysts follows first0.5
order reaction kinetics:
0.0
ln (C/C0) = kappt
0
20
40
60
80 100 120 140 160 180 200
Irradiation time, min
where C is the concentration
of solute remaining in the Figure 3.2. Linear transform
solution at irradiation time of t ln(C0/C) = f(t) of the kinetic
and C0 is the initial concentration curves of MB degradation of
at t = 0. kapp denotes the TiO : F0;F15;F35;F55 and F75
2
degradation rate constant which
enable to determine the photocatalytic activity. The correlation
coefficients R2 are 0.96, 0.97, 0.78, 0.69 and 0.95 for F0, F15, F35,

F55 and F75, respectively, at testing that the straight lines fit
experimental data well. The value of kapp can be calculated by the
slope of linear plot. From Fig.3.20, we can obtain that the kapp value
of 1.5 wt% Fe doped/TiO2 is 0.016 min-1 respectively.
The photocatalytic activities of pure TiO2 và WO3/TiO2 nano

16

Experiment
fit

14

14

10

8

12

10

8

6

4
100

F0
F15
F35
F55
F75

y = 5.740+0.011x
R2= 0.941

6

200

300

400

500

600

700

Solar radiation (W/m2)

800

900

4

100

ln(C/Co )

Efficiency (%)

Pmax (W)

12

200

300

400

500

600

700

800

900

2

Solar irradiation(W/m )

Figure 2.1, 2.7 Maximum output power and PCE versus solar radiation
Figure displays the effect of solar irradiance on output power of
PV panel at PV panel temperature about 45 °C. The highest output
power of PV panel will be produced by a high solar irradiance. As
illustrated in this figure, the most efficient power production by PV
panel was 15.04 % when solar irradiance was 900 Wm-2.
Unfortunately, the efficiency of PV panel was decreased when it was
exposed to lower solar irradiance. The efficiency was found in the
worst condition by 5.5 % when solar irradiance was 100 Wm-2.
Ideally, the power output of a solar panel is proportional to the
incident irradiance since the photo-current is proportional to the
irradiance. However, the irradiance intensity will affect the
conversion efficiency of a PV module due to the parasitic resistances


18

7

with the correlation coefficient r2 = 0.97. The relative error on Eg
found is only 3 % on the average.
Thin film TiO2 synthersized by sol gel hydrothermal method
The XRD patterns and Raman spectra observed band positions are
in accordance with the previous reports on the anatase phase [147].
No peaks correspond to the rutile phase was observed.
The deposited films were uniform and highly adherent.
.

and the diode quality of the solar cells [106]. The dependence of the
open circuit voltage Voc with solar radiation for the PV system is

shown in Figure 2.8. The dependence between short circuit current
and illumination intensity is linear. It can be easily to say that open
circuit voltage are increases dependent on the radiation level.
30

50.5

Short circuit current, (A)

b
)

Open circuit voltage, (V)

a
)

51.0

50.0

49.5

300

400

500

600

700

Solar radiation, (W/m2)

d
)

Figure 3.1. SEM images of W doped TiO2 thin films (a) W0; (b) W1; (b) W2
and(d) W5.

SEM images of the WO3/TiO2 samples as well as pure TiO2 are
shown in Fig. 3.17. The surface of pure TiO2 sample is smooth with
nanoparticles size (Fig. 3.17a). An addition of WO3 affects the
morphology of the sample and their surface becomes laced with
irregularities. Also, pores and voids appear on the surface and
became more pronounced with higher WO3 loadings. This effect is
probably caused by the fast hydrolysis of the tungsten salt leaving
holes behind them that create micron-sized cavities and pores.
The films are highly transparent in the visible range of the
electromagnetic spectrum with an average transmittance reaching

20

15

10

49.0

c
)

25

800

900

5
100

200

300

400

500

600

700

800

900

Solar radiation, (W/m2)

Figure 2.2, 2.9 The open circuit voltage Voc and short circuit current
Isc with varying solar radiation.
Figure 2.9 illustrates the dependence of short circuit current Isc on
the light intensity. It has been found that short circuit current
demonstrated a small rise with increasing light intensity. The values
of Isc for light intensity about 650W/m2 was 0.26 A, respectively. The
value was slightly raised to be 0.275 A for light intensity about. It
can be noted from the results that light intensity level has a crucial
impact on current parameters of solar module rather than the voltage
parameters. Such as the solar irradiance intensity exposed to PV system
increases, the open circuit voltage and the short circuit current increase.
As a result, the performance of the PV system is also increased.
2.3. Influence of Temperature
As observed, the ambient temperature was at low temperature in
the early morning with 23.2 °C caused by the low solar irradiance
intensity of 92.50 W/m2. The ambient temperature during the
experimental day starts to be increase with the increasing solar
irradiance. The maximum ambient temperature was found at 1015
W/m2 by 31.8 °C, while the average for a day was 26.4 °C. In real
working operation, most of solar energy productions occurs when the
PV panel temperature is mostly higher than ambient temperature. The
PV panel temperature starts to increase when solar irradiance was
increased as well as the ambient temperature. There are so much
differed between these two temperatures during peaks sun duration.


8

17

The maximum PV panel temperature found at 1015 W/m2 by 50.5 °C
while the minimum was 24.6 °C at the lowest solar irradiance.
Besides, the average PV panel temperature throughout the day was
determined by 38.4 °C. The increase of PV panel temperature was
due to higher insolation heating, low wind speed with the consequent
low heat transferred from the panel to the ambient. To further
understand the behavior of PV systems in varying temperatures, a
relationship between the ambient temperature and temperature of the
solar cell is considered.
Thus, PV cells/modules operating in the tropical condition tend to
generate low magnitude of electric current which leads to low power
output and low performance.
It was found that the open circuit voltage in figure 2.12, and the
short circuit current in figure 2.13 did not decrease when the
temperature increased. It was observed that the open circuit voltage
reduce rapidly as the ambient temperature increases up to 42oC.
Figure 2.13 shows the short circuit current density for an ambient
temperature range of 30-42◦C. For semiconductors, the bandgap
decreases as the temperature increases the open circuit voltage and
the short circuit current have maximuum value in the ambient
temperature range from 30oC to 36oC.
In our experimental study, open circuit voltage Voc, and the short
circuit current Isc did not decrease when the temperature increased
were due to a difference in irradiation levels. Whilst analysing the
effect of temperature on the PV system, it was observed that both the
open circuit voltage and short circuit current slightly increases as the
temperature increases up to 34oC, and then decreases as the
temperature increases. The higher solar irradiance had a larger
influence on the performance of the modules than an increase in the
ambient temperature. The open circuit voltage and the short circuit

current have maximuum value in the ambient temperature range from
30oC to 36oC.

different from that observed on F15.
It reveals that the transmittance of TiO2 thin films has an abrupt
decrease when wavelengths are below 355 nm. This indicates a
shoulder at near 355 nm and a base which approaches near zero at
about 300 nm. The transmittance quickly decreases when below 355
nm due to the absorption light caused by the excitation electrons
from the valence band to the conduction band of TiO2. Moreover, the
wavy nature of transmittance between 355 and 900 nm is due to the
interference between the TiO2 thin films and substrate. Similar type
of behaviour observed for other samples. From these spectra it seen
that the average transmittance films increase with substrate
temperatures. Increase in transmittance with substrate temperature to
attributed to the thickness of the film, and nature of microstructure
and surface morphology.
The Eg values are about 3.32; 3.4eV and 3.43 eV with substrate
temperatures at 400; 450 and 500oC. The obtained Eg value matches with
spray pyrolysis TiO2 thin films reported by N. Mahdjoub et al [142].
Band gap and roughness of samples deposited at different
substrate temperatures shown in the following (Table 3.5).
Table 3. 4. Band gap and roughness of samples at substrate
temperatures
Substrate Temperature, Band gap, Roughness,
TT
(0C)
(eV)
(nm)
1

400
3.32
2.97
2
450
3.4
7.74
3
500
3.43
7.92
The calculated band-gap energies and the corresponding
wavelengths are presented in table 3.5. The values indicate that the
absorbance in the visible region of the doped samples increases with
the concentration of the Fe3+ dopant which is consistent with the
changes in the color of the samples from white to brownishbeige.
It reveals that the band-gap energy decreases steeply at low Fe3+
concentrations. At high Fe3+ concentrations Eg continues decreasing
but it changes much more slowly. In contrast to the results of earlier
studies, an intensive study of all possible combinations of Eg and
Fe3+ concentration (c) resulted with an exponential equation of the
form [147]: Eg = 2.77e−0.16c


16

30.0

27.5
52.5

Short circuit current, (A)

Open circuit voltage, (V)

55.0

50.0

47.5

25.0

22.5

20.0

17.5

45.0
30

32

34

36

38

40

15.0

42

24

26

28

30

32

34

36

38

40

42

44

o

Ambient temperature, (oC)

Ambient temperature, ( C)

Figure 2.3, 2.4. Open circuit voltage and Short circuit current
versus ambient temperature.
2.4. Influence of humidity
High temperature-humidity study was performed on c-Si PV
modules, and their performance degradations due to moisture
inception are discussed in this section. When PV cells are exposed to
humidity for long term there will be some degradation in
performance. It has been observed that the high content of water
vapour in the air causes encapsulant delamination.
49.0

26

48.5

Experiment
Fit

48.0

47.5

47.0

46.5

46.0
55

y = 50.27-0.04x
R2 = 0.978

60

65

70

75

Relative humidity, (%)

80

85

Experiment
Fit

25

Short circuit curent, (A)

Open circuit voltage, (V)

3.3.2.1. Characterzation material

Thin film TiO2 synthersized by spray pyrolysis method
Raman spectra and XRD patterns of the F0, F15, F35, F55 and
F75 thin films belong to the anatase TiO2.
In addition, no characteristic peaks of iron oxides phases appeared
for all samples. The estimated crystalline size of the F0, F15, F35,
F55 and F75 thin films was about 26 nm; 26 nm; 23,4; 21.1nm; and
18.9 nm. The error in this estimation was ± 0.3 nm. The addition of
Fe3+ could occupy regular lattice site of TiO2 and distorted crystal
structure, because the decrease in crystalline grain sizes of TiO2
(from 26 to 18.9 nm) when the Fe content increased (from 0 %
to 7.5 % atm %) it can be caused by a number of defects in
the anatase crystallites produced by the substitution of part of
the Ti4+site by Fe3+ions. The results are consistent with the R.
Meshach et al. [145].
Table 3. 3. Crystallite sizes, band-gap energies Eg and absorption
wavelengths  of the undoped and Fe3+doped samples.
Particle zise D,
Band gap
Wave length ,
Samples
nm
Eg, eV
nm
F0
26
360
3.4
F15
26
405

3.06
F35
23.4
415
3
F55
21.1
425
2.9
F75
18.9
440
2.8
3D and 2D AFM image of TiO2 films deposited under different
substrate temperatures are presented. The TiO2 films composed of
irregular grains with grain sizes of 30-60 nm. According to 3D AFM
image, the average grain size increases with the increased substrate
temperatures. In AFM analysis, rms is the most widely used value to
characterize surface roughness [146]. The rms value of the
TiO2 film is found to increase to the range of 3÷8 nm when
the films deposited at substrate temperatures 400; 450 and 5000C.
The increase in the roughness is due to the increase in the grain size.
The samples were a uniform film with nanosize and non-cracks,
consisting of nearly spherical nanoparticles of 10÷30 nm.
The particle form and size of these samples were like those of the
F15 sample. In the case of F35, F55 and F75, the morphology was

9

90

24

23

22

y = 29.76-0.082x
R2 = 0.979

21

20
55

60

65

70

75

80

85

Relative humidity, (%)

Figure 2.5, 2. 6 The relationship between open circuit voltage, short

circuit current and relative humidity
The open circuit voltage of PV module reduced with increasing
relative humidity, as figure 2.16 represents. The relative humidity has
an adverse impact on solar radiation so that the resultant negative
influence reflects on the PV cell output voltage. The open circuit
voltage was reduced by 2.1% with relative humidity increasing 60%
to 85% respectively. Relationship of open circuit voltage with
relative humidity trend of linear with R2 = 0.978. This trend of linear
relationship may be influenced by the ambient temperature and
windy velocity which had a strong inverse relationship with humidity


10

15

in this data set.
Figure 2.17 illustrates the effect of relative humidity on the short
circuit current produced. Increasing relative humidity reduced current
highly. Increasing relative humidity from 60 to 85% reduced the short
circuit current by 8.2%. The obtained results illustrated that at low
relative humidity conditions the open circuit voltage, and short circuit
current increase. This results egree with Kazem [109]. Addition, the
extent of this linear relationship with R2 about 0.979.
The Luanda characterized by its
medium temperatures that it ranges
from 26 to 40°C. Figure 2.18 shows
the relation between relative
humidity and air temperature for the
studied period. Relative humidity

increase causes a relative reduction
in air temperature. The recorded air
Ambient temperature, ( C)
temperatures
in
the
Luanda
summertime were suitable for the PV
Figure 2.7. The relationship
arrays operation. However, the
between relative humidity and
relative humidity seems as the
ambient temperature
dominated affecting factor in this
city that reduces the PV performance.
The relative humidity causes a reduction in the solar intensity that
reduced the resulted efficiency of a
15.2
Experiment
PV panel, as figure 2.19 reveals.
Fit
The reductions in the tested PV
14.4
panel efficiency were about 18 %
13.6
respectively.
12.8
When moisture entered the solar
cell, it provides an additional shunt
y = 21.1 - 0.1x

12.0
R = 0.984
path for the output current. This is
11.2
equivalent to the reduction of the
60
65
70
75
80
85
Ralative humidity, (%)
Rp which a significant reduction
can be. When the output is shorted
Figure 2.8. The relationship
circuited to measure the Isc, this
between relative humidity and
shunt resistance will shunt away
PV efficiency
some of the photon current Iph
generated from the photon absorption, resulting in a reduction in the

contact angle is formed (θ≤5°), as the water tends to spread
completely across the surface rather than forming droplets.
Nanostructures of these surfaces could enhance contact angle over
150°. So the raindrops, immediately after reaching the surface, would
roll on it and wash away dust particles. [130]. Titanium dioxide
nanofilms has super-hydrophobic properties for self cleaning surfaces
due to its photocatalytic activity and photo-induced superhydrophilicity. [131].
3.3. Characterization of nanocrystalline titania thin film

deposited by spray pyrolysis technique
3.3.1. Experiment
3.3.1.1. Prepare
3.3.1.2. Synthesized thin film TiO2 by spray pyrolysis method
Table 3. 1. The factor investigation and sample
TT Sample
Factor
1 T-40
[Fe] = 0
[Ti]/[AC] = 1 : 2; V = 20 ml
v = 1.0 ml/min; L = 30 cm
2 T-45
[Fe] = 0
Calcinal: TC = Ts oC, t = 20 mins;
3 T-50
[Fe] = 0
Environmental: air
4 F-15
[Fe] = 1.5 [Ti]/[AC] = 1 : 2 ; T = 450 oC
5 F-35
[Fe] = 3.5 V = 20 ml ; v = 1,0 ml/min
6 F-55
[Fe] = 5.5 L = 30 cm
Calcinal: TC = 450 oC, t = 20 min;
7 F-75
[Fe] = 7.5 Environmental: air
3.3.1.3 Synthesized thin film TiO2 by sol gel –hydrothermal method
Table 3. 2. The table of samples
Number Sample
Factor

1
W-0
[W] = 0 Sol gel, oHydrothermal
T = 140 C
2
W-1
[W] = 1
t = 24h
3
W-3
[W] = 3 Dry : T = 90oC ; t = 24h
o
4
W-5
[W] = 5 Calcined : T = 550 C ; t = 2h (for
particles)
3.3.1.4. Investigate characteration of materials
3.3.1.5. Photocatalysis
3.3.1.6. Superhydrophilic
3.3.2. Results and discussion

90

Relative humidity, (%)

80
70
60
50
40

30

20
24

26

28

30

32

34

36

38

Efficiency, (%)

o

2

40

42

44

14

11

velocity of wind increases from 3 to 6 m/s, the lift force increases but
the drag forces decreases. For wind velocity from 6 to 15m/s, lift and
drag forces vary with a very small difference as see in figure 2.39a.
The aerodynamic quality of solar panels slight with increasing of
wind velocity from 3 to 15m/s.
The variable of aerodynamic characteristics of solar panel is quite
small. So, the 9m/s of wind velocity is choosing to estimate the
simulation about direction of wind.

measured Isc as observed experimentally. The reduction will be even
more significant if Rs increases due to the corrosion of the contact
pads under the exposure of moisture. As the degradation of Voc is
small as observed experi mentally, the reduction in Isc will result in a
reduction in the Pmax. Hence, the degradation trend of Pmax is like
that of Isc.
2.5. Effect of radiation on PV characteristics
The effect of neutron radiation has been investigated in solar cells.
C-Si n+-p solar PV samples have equal surface area about 4 cm2. I-V
characteristics are measured in the dark and illuminated before and
after projecting by neutrons. All samples were irradiated at room
temperature with different time and radiation fluencies. Samples
irradiated by intensity of 103 particles per second at the dose 
(6*108; 1.2*109; 1.8*109; and 2.4*109 particles).
Table 2.1. The influence of irradiation on Isc and Voc of experimental

PV samples.
Before
After projecting by neutrons with
projecting
different illumination dose  (particles)
by neutrons
6*108
1.2*109 1.8*109 2.4*109

At 45o direction of wind, the lift force is negative but aerodynamic
quality of solar panels is smallest. At 135o direction of wind, both lift
force and drag force is negative. It seems that the solar panels could
not keep its fixed position.
d. Strength analysis of solar panels
The solar panels are deformed at four corners. In it, the lower left
corner in the direction of the wind is the largest distortion of about
0.685mm.
Equivalent stress is found maximum at vertical bar of support of
solar panel. The maximum value is about 7.46x104Pa. This value is
lower than the limit stress of aluminum alloy (7.1x109Pa). Thus, we
could conclude that solar panels are durable with wind velocity 9
m/s, attack angle 0o and 30o inclined angle of solar panels.
CHAPTER III- EXPERIMENTAL STUDY ON
PHOTOCATALYTIC PROPERTIES OF TITANIUM DIOXIDE
APPLICATION AS SOLAR CELL SELF CLEANING LAYER
3.1. Settlement overview of dust on a solar panels glass cover
Perhaps the most optimal method to remove dirt from surfaces is
to modify the surface to obtain self-cleaning properties.
3.2. Thin film TiO2 using as self-cleaning material of solar panels
Super-hydrophobic surfaces have the same properties as lotus

leaves. They show extremely low wetting property and greatly high
hydrophobicity. On the super-hydrophilic surface, a very small water

Isc (mA) 13.45
9.93
8.69
7.79
7.45
Voc (V) 0.475
0.455
0.44
0.43
0.41
2.6. Effect of an inverter
P m ax
P ac
Figure 2.22 displays the power
produced and converted with a
calculated average of 50%
conversion efficiency. It was too
low to what was rated by the
manufacturer. Thus, when the
efficiency of the system was
21-Au g--27-Aug -- 7-Sep --11-Sep -- 18-Sep -considered with the inverter, it
Date
dropped by almost 12%, from Figure 2. 9. Comparison of power
4.9% to 4.2%. This was twice the
converted by inverter (Pac) and
amount of reduction in efficiency
power produced by PV system

caused by a combination of
(Pmax).
factors that include, wind speed,
increasing ambient temperature, humidity, real power conversion
14
12

10

Power (W)

c. Effect of wind direction

8

6
4

2
0


12

13

efficiency of the inverter, and a general degradation of the system.
2.7. Effect of wind actions on PV panels
2.7.1. General
The two most common methods of solar panel deployment are on

the ground or on the roof of building. These systems are sensitive to
wind loading but design standards and codes of practice offer little
assistance to the designers regarding provisions for wind-induced
loading. The effect of wind on the solar panels located in the space is
as follows: i) Wind speed; ii) Wind direction; iii) Height of the
building and the presence of the parapet; iv) Angle of inclination of
the panels.
2.7.2. Computational Fluid Dynamics (CFD) Procedure
Aiming to determine the simulations of the interaction between
the wind and solar panels in this study, we use the computer program
ANSYS 18.2 fluent, which is used essentially, to calculate the
possible flows of winds and the complex pressures that act on its
surface.
The proceeds to simulate the fluids flow problem by using CFD
tool in ANSYS software include five basic steps below:

The variable of aerodynamic characteristics of solar panel is quite
small. So, we choose the solar panels installed with inclined angle of
30o. This is also accordant with sunlight conditions in Angola.

- Mesh computational domain;

2.7.3. Effect of wind actions on solar panels
a. Effect of inclined angles
According to the calculated results as shown in figure 2.34, the
wind affects a negative lift to solar panels. It means that the solar
panels adhere with ground. When the solar panels are inclined with
increased angle, the lift and drag forces vary with a little difference
but aerodynamic quality (CL/CD) increases in the absolutely value.
The wind acts on the solar panel with a minimum force, and solar

panels have less damage by wind.

CD
CL
-0.1

CL/CD

Coefficient of lift and drag force

-1.0

0.0

-1.5

-2.0

-0.2

-0.3

20

25

30

35

-2.5

40

20

25

30

35

40

Inclined angle (degree)

Inclined angle (degree)

Figure 2.10. 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
b. Effect of wind velocity
According to the calculated results as shown in figure 2.39, the
wind affects a negative lift to solar panels.
0.0

0.2

b)

a)
-0.5

0.1

Coefficient of lift and drag force

- Analyze the results.

-0.5

0.1

- Set up numerical conditions;
- Solve occurring problems;

b)

a)

0.0

-1.0

CL/CD

- Identify computational domain;

0.0

0.2

CD
CL

-0.1

-1.5

-0.2

-2.0
-0.3

-0.4

-2.5
0

3

6

9

Wind velocity (m/s)

12

15

18

0

3

6

9

12

15

18

Wind velocity (m/s)

Figure 2. 11. 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
It means that the solar panels adhere with ground. When the