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Keywords— Dust deposition effect, Photovoltaic, Air pollution,
Temperature, Humidity, Air velocity.
Abstract—Due to the energy crisis and growing demand for
energy as the conventional energy sources have approached depleting
and can’t meet the world demand of energy. Fossil fuels have created
plentiful environmental problems, such as global warming, acid rain,
smog, water pollution... etc. Solar energy has the positive conditions
as it is free from environmental pollutions, sustainable and requiring
low maintenance. Solar energy can be collected to produce electricity
by a variety of methods. Among these methods, photovoltaic PV
systems have shown great success due to many reasons. Photovoltaic
energy is preferred because it is clean, and secure. Therefore, a
photovoltaic energy system will be one of the considerable sources of
alternative energy for the current and future. PV systems performance
depends on many factors, like geographical factors (latitude,
longitude, and solar intensity), environmental ones (temperature,
wind, humidity, pollution, dust, rain, etc.) and the type of PV used.
Studies proved that dust has significant influences the
performance of the PV system. The dust accumulation on the surface
of solar module causes decreasing in its performance. Dust particles
differ in phase, sort, chemical and physical properties depending on
many environmental conditions. Air temperature and humidity in
addition to wind speed play a significant role in defining dispersed
dust and how it will accumulates on the cell. As a result one can
determine cleaning procedure. The important of this study came due
to the transfer of large scale PV technology to the desert area in Arab
countries. This area is hot and dusty most of the time and dust
represent the main barrier to PV utilization. This paper revises the
research in studying the impact of dust on PV system performance.
I. INTRODUCTION
HE increasing concerns about rising fossil fuel prices and
climate change highlights the interest in renewable energy
which can play an important role in producing local, clean,
and unlimited energy. Renewable energy includes any energy
source that is replenished at least as fast as it is used. As
Zeki Ahmed Darwish is with the University Kebangsaan Malaysia, Bangi
43600, Selangor, Malaysia; e-mail: z_ahmed91@ yahoo.com).
Hussein A Kazem, is with Sohar University, Sohar, PO Box 44, PCI 311
Oman. (e-mail: h.kazem@soharuni.edu.om).
K Sopian. is with the University Kebangsaan Malaysia, Bangi 43600,
Selangor, Malaysia; (e-mail: ksopian@eng.ukm.my).
M.A.Alghoul is with the University Kebangsaan Malaysia, Bangi 43600,
Selangor, Malaysia; e-mail: dr.alghoul@ gmail.com).
Miqdam T Chaichan. is with the University of Technology, Baghdad, Iraq;
(e-mail: miqdam1959@yahoo.com).
examples of these renewable energies are ocean and tides
energies, geothermal energy; biomass energy; hydroelectric
power; wind power and sunlight energy [1].
The sun is humanity’s oldest energy source that occupies
scientists and engineers for hundreds of years to harness the
power of sunlight for a wide range of applications as heating,
lighting, and industrial tasks. Sunlight is an excellent energy
source with consistent supply and inexhaustible. Solar energy
also has several challenges, namely that it is only available
during the day; it varies throughout the day and year, and is
less energy dense than fossil fuels [2].
PV solar energy or more simply PV is one way to achieve
solar energy usage. PV is a method of generating electrical
power by converting solar radiation into direct current
electricity using semiconductors that exhibit the photovoltaic
effect. The photovoltaic effect was first noted by a French
physicist, Edmund Bequerel, in 1839, who found that certain
materials would produce small amounts of electric current
when exposed to light [3].
Many publications cover silicon photovoltaic panels in
several aspects. Solar cells are made of the same kinds of
semiconductor materials used in the computer industry –
typically silicon. Semiconductors can be used to transform
sunlight into electricity because of their atomic structure. In
typical PV installations, PV arrays are formed by connecting
multiple PV modules in various configurations (i.e., series,
parallel, series–parallel, etc.) [4].
Solar energy can be generated in large centralized plants
covering hundreds of acres, such as the 14 MW installations at
Nellis Air Force Base (AFB) in Nevada, or in smaller
distributed applications of several kW, such as those on
individual home roofs [5].
The output of PV is rated by manufacturers under Standard
Test Conditions (STC), temperature = 25 oC; solar irradiance
(intensity) = 1000 W/m2, and solar spectrum as filtered by
passing through 1.5 thickness of atmosphere. These conditions
are easily recreated in a factory but the situation is different for
outdoor. With the increasing use of PV systems it is vital to
know what effect active meteorological parameters such as
humidity, dust, temperature, wind speed; etc has on its
efficiency. This paper investigates the effect of dust on PV
system performance. Monto and Rohit have revised the effect
of dust on PV performance based on two time periods: from
1940-1990 and 1990-2010 [6]. These studies revised the effect
of dust based on the two periods while our paper discussed the
Impact of Some Environmental Variables with
Dust on Solar Photovoltaic (PV) Performance:
Review and Research Status
Zeki Ahmed Darwish, Hussein A Kazem, K. Sopian, M.A.Alghoul and Miqdam T Chaichan
T
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effect based on three main points: effect of dust properties,
effect of PV system parameters and effects of environmental
parameters. So investigation of the direct effect of dust and the
other parameters added to the dust to produce compound effect
is the aim of this paper.
II. EFFECT OF DUST PROPARTIES
Solar energy has the favorable circumstances of being
free from environmental pollutions, sustainable and requiring
low maintenance. How-ever a solar photovoltaic (PV) and any
solar energy systems depend strongly on geographical location
and weather conditions. The operation of the PV system under
real climatic conditions must be known [7].
The atmospheric condition in which substances are present
at concentration higher than their normal ambient levels is
called air pollution. Air pollution produces a harmful effect on
man, animals, vegetations or materials [8]. These substances
can be natural such as dust, or manmade. These chemical
elements or compounds are capable of being airborne and can
exist in the atmosphere as gases, liquids, or solid particles.
Much attention has been shifted toward particles of size (both
PM10 and PM2.5) recently. It is known that particulate matter
that is composed of various materials is mainly responsible for
air pollution and stronger associations with health [9].
Particles which are smaller than 10μm can penetrate as far as
the terminal bronchiole and alveoli, thereby adversely
affecting the lungs function. These particles have many
resources most of it are manmade. Millions and millions of
tons of these particulates are emitted in to the air by
automotives, trucks, power plants and…etc [10].
The PV application all over the world is facing many
problems. One of the most important problems is the
accumulation of atmospheric dust on the solar panels surface
which causes decreasing its performance sharply [11]. This
atmospheric dust have several effects on the use of
photovoltaic power systems, including decreasing of the
amount of sunlight reaching the surface and this leads to the
decrease of the performance efficiency[12]. Al-Sudany in
(2009) studied the effect of natural deposition of dust on solar
panels under Baghdad environment, it was noted that the
transmittance during one month, as an average decreased to,
approximately, 50%. This result refers to the accumulation
period as a strong effective parameter that causes a large
decreasing in transmittance. This is due to the increasing of
accumulated dust thickness with time [13].
Then the first point to be investigated is the effect of dust
properties on the PV performance. This section separated into
two main points: dust accumulation, and dust pollutant.
A. Dust Accumulation
Haeberlin et al in 1998 studied the accumulation of pollution
by iron dust and other components at the edges of framed solar
cell modules in Burgdorf. This accumulation caused a gradual
reduction of output power of PV up to 8-10%. When the
material of dust was analyzed the conclusion was that the dust
in Burgdorf environment composed from iron oxide, silicon
and some of organic materials [14].
Mazumder et al analyzed the dust deposition mechanisms on
a solar module, the conclusions they deduced that the
reduction in solar modules performance depends on the
particle size, shape, distribution, deposition mechanisms and
orientation of dust deposits on the module [15].
The relevant properties of lunar dust in USA were studied
by Timothy et al in 2007, they specified three main problems
which are dust adhesion, surface electric fields and dust
transport. They conclude that mechanical adhesion resulted
from the barbed shapes of the dust grains, and dust adhered to
space suits both mechanically and electrostatically [16].
Sand and dust particles deposition on PV surface in dry
region are presented with numerical and analytical models by
Neil [17] and supported by a laboratory investigation of sand
particles accumulation on a glass surface. The accumulation of
sand particles on horizontal glass surface is found to
exponentially reduce the available area for transmission of
incident photons. A grain threshold algorithm in the software
Gwyddion was used to determine the fractional area of glass
covered by particles. Figure 1 shows that the available free
area on the glass slide decreases with increasing amounts of
sand both before and after a gentle disturbance caused the sand
structures to settle. The rearrangement effect becomes more
pronounced with increasing sand accumulation, as a result of
clustering and the formation of upper layers of particles.
Fig. 1 reduction in the free fractional area of a glass slide with
increasing quantities of sand [17].
Filled circles in figure 1 show the ash-deposited coverage
while open circles show coverage after application of gentle
disturbance to the glass slide. The solid and dotted lines are
exponential and linear fits to the data respectively.
Initially all sand particles are distant from each other and
subsequent particles landing on them cannot be supported and
fall onto the glass. In this regime the free surface area
decreases linearly with sand mass. As more particles arrive on
the surface, clusters are gradually formed and there is an
increasing probability that subsequent particles will land on a
cluster rather than on the glass. This causes the evolution of
the free surface area to deviate from the linear behaviour
described by Al-Hasan [18]. The model which is describe this
process, consider adding particles of an arbitrary shape to a
slide. The total area of particles deposited as a fraction of the
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total area of the slide is
N
, and is directly proportional to
their mass.
The free fractional area
A
is not simply
N−1
because
particles overlap. This behaviour can be represented
mathematically taking into account the probability that small
particles lands on free surface area is
A−1
, such that
N
eAA
dN
dA −
−=⇒−= 11
(1)
There are important differences however between this
simple model and reality. In particular, it is clear that there is a
limit to how closely grains can pack together and that some,
but not all sand grains can support a second grain. Recalling
that the close packing factor must be used to connect particle
area
N
and filling fractions
1
F
and
2
F
, the evolution of the
layers (i) is described by
)(1
1
1
Fc
dN
dF −=
α
(2)
)](1)[( 21
2FcFc
dN
dF −=
α
(3)
where
α
represent random close packing fraction ~ 0.8 and
the fractional filling level of a given layer
)(i
, (
i
F
) a layer
can contribute to obscuring the surface is
i
F
α
,
)(
i
Fc
is the
cluster function describe the fraction of sand grains that sit
within a cluster. The total area is given by
21 )1(1 FFA
αα
−−−=
(4)
This model has been used to investigate dust accumulation
in dry regions which are in quantitative agreement with
laboratory investigation on particle accumulation on a glass
slide.
Al-Sudany studied dust accumulation on PV system in Iraqi
weathers and concluded that the dust accumulation on the
surface of solar module causes decreasing in the performance
about (35-65) % for one month accumulated time. In the dry
weather the adhesive force between the dust atoms and the
glass cover of solar module is the only reason for dust
deposition, while, there are many layers of dust arise on the
solar module surface in weather with high humidity [13].
B. Dust Pollutants
The air pollution is degradation of PV performance as a
result to accumulation of solid particles varying in type,
composition and shape. Kaldellis and Fragos [19] conducted
an experimental study to compare the energy performance of
two identical pairs of PV-panels; the first being clean and the
second being artificially polluted with ash, i.e. a by-product of
incomplete hydrocarbons’ combustion mainly originating from
thermal power stations and vehicular exhausts.
Figure 2 shows the impact of different mass deposition of
ash on PV's energy performance which is decrease between the
clean and polluted panels varying between 2.3% and 27% as it
has recorded with time period of 1h.
Fig. 2 Energy difference between clean and the polluted pair panel
for various mass deposition in cases of naturally and artificially
polluted PV [19].
Similar study by same authors [20], systematic experimental
study of the pollution deposition was conducted to investigates
the performance of two identical pairs of PV panels, the first
panel being clean and the second being artificially polluted
with three different type of air pollutants namely red soil,
limestone and carbonaceous fly-ash particles. The
experimental study was carried out under same environmental
conditions as (ambient temperature, solar radiation, humidity
etc,). According to the results obtained, it was found that the
decreasing magnitude depending on the type of pollutant (i.e.
composition, colour, diameter etc.). Based on the results, red
soil deposition on PVs’ surfaces causes the most considerable
impact on PVs’ performance and thus the highest generated
energy reduction, followed first by the limestone and secondly
by the carbon-based ash. Specifically, an amount of 0.35 g/m2
of red soil deposition on PV-panels’ surfaces may reduce the
generated energy by almost 7.5% (compared with the
respective of the clean one) while approximately the same
deposition density for limestone 0.33 g/m2 causes almost 4%
energy reduction. On the other hand, even if almost doubling
the pollutant mass for ash 0.63 g/m2 the generated energy is
decreased by only 2.3%. This may be explained due to the
colour, composition and used diameter range of red soil
causing the PV-panel to operate with lower performance.
Fig. 3 Energy yield reduction of the polluted pair panel due to the
different pollutants mass deposition in (g/m2) [20]
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Figure 3 shows the resulting energy yield reduction
percentage between the clean "Ec" and the polluted "Ep" pair
panel (adjusted in same tilt angle) as a function of different
mass densities of red soil, limestone and carbon-based ash.
In Fig 3 there is a strong indication that red soil deposition
on PV-panels leads to rather worse results compared with
other two pollutants. It seems that the generated energy
strongly reduces with the red soil deposition on PVs' surfaces
while the effect is slightly smaller for limestone and
considerably smaller for carbon-based ash.
Kazem et al [21] have investigated experimental the effect
of three types of dust pollutants (red soil, ash and sand) on the
performance of PV panels (mono-c, multi-c and a-Si
technologies investigated). The authors claimed that ash have
the highest effect in comparison with other pollutants. Also, it
is found that a-Si is performing better than mono-c and multi-c
in dusty environment as shown in Fig. 4.
Kaldellis and Kapsali [22] have developed a theoretical
model in order to be used an analytical tool for obtaining
reliable result concerning the expected effect of regional air
pollution on PVs' performance. Air pollution represented by
red soil, limestone and carbon-based ash related to previous
study. In addition to, experimental concerning the dust effect
on PVs' energy yield in a more polluted from air pollution
urban environment is used to validate the proposed theoretical
model.
Conversion efficiency "
η
" is defined as the ratio between
the produced power '' Pout'' and the incident solar power ''Psolar''
available in collector's surface ''Ac'' . Thus
TcTc
out
solar
out
GA IU
GA
P
P
P..
.===
η
(5)
Fig. 4 Reduction in PV voltage due to the three pollutants [21]
where ''GT'' being the corresponding total solar radiation. ''I''
current and ''U'' the output voltage normally comprising a
function of time ''t'' in order to calculate the generated power
of installation.
The dust deposition ''
M∆
''is expressed in g/m2 ,via the PV
collector area ''AC'' , as;
c
m
MA
∆
∆=
(6)
where
m∆
is the total mass of dust layer on the surface of the
polluted pair of PV- panels.
Capacity factor ''CF'' (or energy yield) is defined as the ratio
between the actual and rated output over a period time ''
t∆
'' as
tP
E
CF
P
t
∆
=∆
.
(7)
where
P
P
is the peak power.
Energy yield reduction percentages between the clean
''
0
CF
'' and the polluted ''
CF
'' pair panel as a function of
different mass deposition densities for red soil, limestone and
carbon-based ash for each examine case is expressed as:
E
E
EE
CFCFCF
CF
cl
polcl ∆=×
−
=
×
−
=∆
100
100)(
0
0
(8)
Deposition of dust particles on the PV panels lead to an
extra amount their energy performance, the rate of which
depends strongly on the type of pollutant.
At this point, an attempt is made to simulate the PV-panels’
energy yield (or capacity factor) drop on the basis of the air
pollutant type (i.e. red soil, limestone and flying ash) and the
corresponding specific mass deposition''
M∆
''. In order to
develop a reliable and practical relation an exponential
function of the general form:
jj
MA
j
eCFCF
∆−
=
.
.
(9)
where ''
j
A
'' is the coefficient of standard deviation of mass
measurements as in table 1 and the ranges between 0.06 and
0.24 depending on the type of pollutant ''j'', while ''
j
CF
'' is the
capacity factor of polluted pair of panels for specific pollutant
mass deposition ''
j
M∆
'' (in g/m2).
Table 1 Coefficient ''A'' and standard deviation
pollutant
Aj
Ash
0.06±0.024
Limestone
0.10±0.034
Red soil
0.24±0.085
In same context, the efficiency difference ''
η
∆
'' between
the polluted and the clean pair of PV-panels is defined as:
CT
P
CT
j
CT
j
CT
j
CT
j
AG PCF
AG
CFCF
tAG
EE
AG
P
AGP
..
.
)(
....
0
0
0
0
=
−
=
∆
−
=−=∆
η
(10)
or equal (11)
)1.(
.
0
jj
MA
j
e
∆−
−=∆
ηη
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In order to calculate the total capacity factor reduction
percentage ''
)(CF∆
'' as a result to accumulation dust
particles on the PV-panels surface one may combine Eqs. 9
and 8 into the following approach
(12)
with ''
M∆
'' in (g/m2) being the total mass of dust
accumulated on PV-panel's surface and coefficient ''
eq
A
''
depending on the mass content of dust for each pollutant
''
j
M∆
'', i.e:
∑
=jjeq AwA .
(13)
M
M
w
j
j
∆
∆
=
(14)
and
0.1=
∑j
w
(15)
III. EFFECTS OF PV SYSTEM PARAMETERS
A. Effect of Tilt Angle
A tilt angle is one of the important factors that determine the
performance of PV panels. In an experiment carried out in
Roorkee by Grag [23] discovered that gather dust on a glass
plate decrease transmittance by average of 8% after an
exposure period of 10 days. Hegazy [24] studied dust
deposition on glass plate with different tilt angles as well as
measured the transmittance of the plate under different weather
conditions. It was found that degradation in solar transmittance
depend on the tilt angle. Also, the work by Sayigh et al [25] of
dust deposition on a tilted glass plate located in Kuwait city
were found to reduce the transmittance of the plate from 64%
to 17% for tilt angles ranging from 00 to 600 respectively after
38 days of exposure to the environment.
New test methods and analytical procedures were provided
by David in 1997 to characterize the performance of solar cell
modules and arrays. The outdoor measurements of
performance parameters under standard conditions and for all
operating conditions were used. For the first time, the
influences of irradiance, temperature, and tilt angle were
studied. The empirical relationships obtained from the
measurements can be used to improve the methods used for
system design [26 &27].
B. Effect of PV Technology
PV module is classified into two categories which are silicon
crystalline and thin film. Each category of PV modules (solar
cells) contain of different types. The types of silicon crystalline
are monocrystalline, polycrystalline; hybrid silicon, emitter
wrap through cell and silicon crystalline investment while
amorphous silicon, cadmium sulphide or telluride and copper
indium disellenide or copper gallium are the types of thin film.
The investigations found that a-Si performs best in dusty
environment [28].
In 2006 Krauter et al provided a simulation program to
examine the optical transmission of any solar cell modules
under real-world conditions. The target was to compare
various types of antireflection material and glazing of solar
cell systems. They concluded that replacing the material of
anti-reflection coating which has other refractive index causes
an increase in solar module performance about 27% at
incidence angle 80° [29].
C. Effect of Cleaning
Dust is probable to stick on to the array by Van der Waals
adhesive forces. These forces are very strong at the dust
particle sizes expected. Cleaning method must be
overcome these forces. There are four ways classified to
remove dust the surface of solar panel namely natural,
mechanical, electro-mechanical and electrostatic. More
investigation and ideas are important to reduce the effect of
dust.
The simplest removal methods are the natural dust removal.
The natural dust removal methods are rainfall and wind
clearing. They can be made possible by simply choosing an
array orientation other than horizontal [30].
The electrostatic dust removal is another method of dust
removal. When the array surface is charged, the array will
attract particles of opposite charge, and repel particles of the
same charge [31].
Kasem used a new technique to reduce the amount of
accumulated dust. Using movable platform attached to a solar
tracking system of two-axis with photovoltaic's panels on the
solar panel. The tracking system at the sunsets changed the
direction of the solar panel from west to east for the horizontal
axis (Azimuth). It also changed the tilt angle of the solar panel
to become more than 90 (about 95) for the vertical axis
(Altitude). This process was repeated daily at sunset to take
advantage of this movement. The vibration will help to
displace the deposited dust particles on solar panel surface.
The comparison of this method with fixed solar panels that
have fixed tilt angles of 30° and 45°was done. After 34 days of
accumulation period the results indicated that the maximum
losses in the output power was about 31.4% and 23.1% for
fixed solar panels at tilt angle 30° and 45° respectively. While
the losses in the output power for the solar panel with two-axis
tracking system is about 8.5% [11].
IV. EFFECTS OF ENVIRONMENTAL PARAMETERS
A. Effect of Temperature with Dust
There are many researchers who are interested in the study
of temperature effect on PV performance. In 1996 Kroposki et
al calculated temperature coefficients for maximum current Im,
maximum power Pm, short circuit current Isc, open circuit
Ee
CFCFCF
CF
MAeq ∆=×−=
×
−
=∆
∆− 100)1(
100)(
.
0
0
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voltage Voc and maximum voltage Vm for CdTe solar cell
module. They showed that for the module and array data the
current coefficients were considerably small; therefore, the
current is not affected by temperature. In the same time, the
voltage coefficients for both module and array were slightly
negative, which means that the voltage is affected highly by
temperature [32].
Increasing insulation level will made modules temperature
rises rapidly due to the increase in ambient temperature which
affects the energy dissipation of photons with energy values
higher than semiconductor s energy gap [33].
The effect of temperature and series resistance for a
crystalline silicon cell at two different light intensities was
studied also. The series resistance is greater at higher
temperatures and the temperature dependence of the low series
resistance cell is relatively stronger at low light intensity, while
the opposite is true for high series resistance cell [34].
Olchowik et al studied the effect of temperature on the
efficiency of monocrystalline solar cell modules. They
concluded that the efficiency of a monocrystalline Si solar cell
module depends on the solar irradiance reaching its surface.
Therefore, in order to increase the photo-conversion power of
Si photo module, advantageous method is to use additional
cooling systems [35].
The effect of operating temperature on the performance of
amorphous Silicon (a-Si) solar cell modules under practical
operating conditions was investigated by Astawa in 2007. The
power production drop dramatically from autumn to winter
period and the performance of solar cell modules also down
about 65% of their initial performance in the same period [36].
In 2009 Erel used thermoelectric cooler to compare between
the performance of solar cell before and after cooling. The
result indicated that the decrease in solar cell temperature
about 15 °C causes a gradual increase roughly to 0.01 volt for
each (4Cm×4Cm) solar cell [37].
The investigations found that PV output power affected by
ambient temperature. The more clean and cool PV the high
power generated and more efficiency [38]-[39].
The temperature dependence of the voltage which decrease
with increasing temperature (its temperature coefficient is
negative) is very important. The voltage decrease of a silicon
cell is about 2.3 mV per °C. The temperature variation effect
on the current or the fill factor are less pronounced and usually
neglected in the solar cell system design. Figure 5 shows the
typical performance of the solar module at different cell
temperatures. This is why only the voltage variation with
temperature is allowed for practical calculations, and for
individual module consisting of Nc cells connected in series is
set equal to [40]:
Voc=Voco–(2.3NcTc) (16)
Where Voco is the open circuit voltage under standard test
conditions (Irradiance = 1000 W/m2, air mass (AM = 1.5) and
cell temperature Tc = 25°C), Nc is the number of cells inside
the module and Tc is the cell temperature which can be
determined by using the following equation [40]:
Tc=Ta+ Ht ((TNoc–20)/0.8) (17)
Where Ta is the ambient temperature, TNoc is the normal
operating cell temperature at open circuit with conditions:
Irradiance equal to 0.8 kW/m2, AM = 1.5, ambient temperature
20 °C and wind speed > 1m/s, and Ht is the total irradiance. In
the design of the solar cell generator, the voltage will vary
more than the current with irradiance. The operation of the
module should lie as close as possible to the maximum power
point [13].
B. 11BEffect of Humidity with Dust
Study the effect of humidity on PV cell, two cases must take
into account. The first case is the effect of water vapour
particles on the irradiance level of sunlight and the second case
is humidity ingression to the solar cell enclosure.
Fig. 5 temperature dependence of the I-V characteristics of a solar
module [40].
Three phenomena occur when light hits water droplets. It
may be refracted, reflected or diffracted. These effects
deteriorate the reception level of direct component of solar
radiation [41]-[42].
Kazem et al studied the effect of relative humidity on the
performance of the Photovoltaic (PV). Three types of PV
(Polycrystalline, Monocrystalline and Amorphous Silicon)
were tested in this investigation. PV system connected to
measurements humidity, current and voltage. The results
showed that the output current, voltage, and power increase
with low relative humidity. The efficiency of the PV is high
when the humidity low. Hence low relative humidity enhances
the performance of PV systems [43].
Figure 6 shows the effect of the relative humidity on the
reception of visible solar radiation. It seem that this variation
is non linear and this effect lead to little variation in
OC
V
and
vast variation in
SC
I
as in Fig 7.
The clear influence of humidity on irradiance and
SC
I
lead
to decrease in efficiency according to equation:
)( .maxmax levelirradinaceA VI
C
ocsc −−
=
η
(18)
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where AC is the effective area of the module, Isc is the short
circuit current , Voc is the open circuit voltage and
η
is the
conversion efficiency.
Fig. 6 variation of irradiance level with relative humidity [44]
Fig. 7 variation of
OC
V
and SC
I with irradiance level [44]
The trend of wind speed has a reverse effect on relative
humidity which in turn affects the received irradiance. For a
long time exposure of PV modules to humidity leads to the
ingress water into module and decrease performance [45].
In this context, delimitation with PV module is one of the
most critical failure modes during service lifetime. Module of
crystalline silicon most time fail at the cell interconnection or
due to damaged cells while the thin film fail at scribe lines
which is the dominate cause lead to modules degradation.
Accordingly, thin films are sensitive to corrosive moisture
while crystalline silicon cells are sensitive to embrillement of
the encapsulated materials. Both of these degradation
processes are increased by hot and humid weather [46]. The
effect of dust increases in humid weather because they make
together cement layer which make the cleaning process
difficult task.
C. Effect of Wind Speed and Direction with Dust
Saw and Goosens [47] has used wind tunnel to determine
the efficiency of sediment sampler designed to measure the
deposition of aeolian dust. Marble Dust Collector (MDCO)
and the inverted frisbee sampler were used in their
investigation. Efficiency was ascertained for five wind
velocities (range: 1–5
1−
ms
) and eight grain size classes
(range: 10–89
m
µ
). They were presented formulate to
determine the efficiency of an MDCO or frisbee when grain
size composition of the sediment and wind's speed and
direction are known. For the frisbee the equation:
gfueuducubuauE ++++++=
23456
(19)
where
E
= efficiency, u= wind speed (
1−
ms
), a, b, c, d, e, f,
g numerical constant this formula validate to and wind
between 0 and 7
1−
ms
.
For the MDCO the equation:
rHqHpE ++= )]4()2[cos(
(20)
where
E
= efficiency,
=H
orientation of the MDCO (rad);
qpr ,,
are coefficients should be calculated. The last equation
is validated to any speed between 1 and 7
1−
ms
.
V. CONCLUSIONS
This paper reviews the effect of some environmental
variables with dust on the PV performance. The evaluation on
the status of research has been discussed based on effect of
dust properties, effect of PV system parameters and effects of
environment parameters. Research conducted according to this
classification highlight the impact of dust on the performance
of PV. Some points are deeply investigated and some are still
need more study.
The main important points need more investigations are:
dust properties (size, geometry, electrostatic deposition
behavior), biological and electro-chemical properties of dust,
optimization study, for various geographical/climatic locations
(latitude) considering factor of optimum tilt, altitude and
orientation for solar gain, prevalent wind patterns and
minimum dust accumulation for various PV module
configurations, dust particle geometry on its deposition
behavior, electrostatic attraction on dust settlement behavior,
impact of progressive water-stains on degrading the PV
performance.
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