ArticlePDF Available

Abstract and Figures

The accumulation of dust on the surface of a photovoltaic module decreases the radiation reaching the solar cell and produces losses in the generated power. Dust not only reduces the radiation on the solar cell, but also changes the dependence on the angle of incidence of such radiation. This work presents the results of a study carried out at the University of Malaga to quantify losses caused by the accumulation of dust on the surface of photovoltaic modules. Our results show that the mean of the daily energy loss along a year caused by dust deposited on the surface of the PV module is around 4.4%. In long periods without rain, daily energy losses can be higher than 20%. In addition, the irradiance losses are not constant throughout the day and are strongly dependent on the sunlight incident angle and the ratio between diffuse and direct radiations. When studied as a function of solar time, the irradiance losses are symmetric with respect noon, where they reach the minimum value. We also propose a simple theoretical model that, taking into account the percentage of dirty surface and the diffuse/direct radiation ratio, accounts for the qualitative behavior of the irradiance losses during the day.
Content may be subject to copyright.
Analysis of dust losses in photovoltaic modules
J. Zorrilla-Casanova*1, M. Piliougine1, J. Carretero1, P. Bernaola1, P. Carpena1,
L. Mora-López2, M. Sidrach-de-Cardona1
1 Dpto. de Física Aplicada II, Universidad de Málaga, 29071 Málaga, Spain
2 Dpto. de Lenguajes y Ciencias de la Computación, Universidad of Málaga, 29071 Málaga, Spain
* Tel: 34- 95-213-2772 , Fax: 34-95-213-1355, Email: ppz@ctima.uma.es
Abstract: The accumulation of dust on the surface of a photovoltaic module decreases the radiation reaching the
solar cell and produces losses in the generated power. Dust not only reduces the radiation on the solar cell, but
also changes the dependence on the angle of incidence of such radiation. This work presents the results of a
study carried out at the University of Malaga to quantify losses caused by the accumulation of dust on the
surface of photovoltaic modules. Our results show that the mean of the daily energy loss along a year caused by
dust deposited on the surface of the PV module is around 4.4%. In long periods without rain, daily energy losses
can be higher than 20%. In addition, the irradiance losses are not constant throughout the day and are strongly
dependent on the sunlight incident angle and the ratio between diffuse and direct radiations. When studied as a
function of solar time, the irradiance losses are symmetric with respect noon, where they reach the minimum
value. We also propose a simple theoretical model that, taking into account the percentage of dirty surface and
the diffuse/direct radiation ratio, accounts for the qualitative behavior of the irradiance losses during the day.
Keywords: optical losses, dust effects, energy losses
1. Introduction
The accumulation of dust on the surface of the photovoltaic modules decreases the incoming
irradiance to the cell and produces power losses (see [1] and references therein). Previous
studies [2] show that in dry areas, these losses could reach 15%. In these cases the only
solution is to clean the modules with water. In large-scale photovoltaic plants this task is often
expensive, especially in those areas with water shortage.
Some approaches to analyze and quantify the effect of dust on photovoltaic modules have
been proposed in the literature. The early studies about the relationship between dust and
transmittance date back to a few decades ago, all of them in the context of solar thermal
collectors. For example, in [3], the effect of dust on the irradiance received by various
inclined surfaces of flat-plate collectors have been studied. The performances of one
photovoltaic and two thermal panels during several months of outdoor exposure in Saudi
Arabia have been measured in [4]. For the photovoltaic panel, the average degradation rate of
the efficiency was 7% per month. The authors of [5] made an experimental study of the effect
of accumulation of dust on the surface of photovoltaic cells. Several kinds of dust having
different physical properties were used. Experiments were performed using a solar simulator.
They concluded that the results depend on many factors like the principal dust material, the
size of dust particles and dust deposition density. We can see in [6] a computerized
microscope system that has been developed for studying the physics of dust particles, which
adhere to the surface of solar collectors and photovoltaic modules. The device enables
investigators to calculate the particle size distribution of dust and the fraction of surface area
covered by dust. Some examples are given for the use of such a measuring system for the
study of photovoltaic and solar-thermal collector surfaces. Wind tunnel experiments were
described in [7] to study the effect of wind velocity and air dust concentration on the drop of
photovoltaic cell performance caused by dust accumulation on such cells. I-V characteristics
were determined for various intensities of cell pollution. The evolutions of the Isc, Voc, Pmax,
and FF were examined.
This work presents measurements of radiation losses produced by the accumulation of dust.
The experiment has been carried out at the roof of the Photovoltaic Laboratory of the
University of Málaga (latitude 36.7 N, longitude 4.5 W, altitude 50 m) in the south of Spain.
The campus is located between a residential and an industrial area surrounded by open fields
with shrubs, weeds and some olive trees. Several roads with heavy traffic flow are very close
to the building. At the time of the measurements, some excavations have been conducted in
the vicinity of the building, which has increased the amount of inorganic dust particles present
in atmospheric air.
2. Methodology
The objective of this work is to quantify losses caused by the accumulation of dust on the
surface of photovoltaic modules. With this aim, irradiance values measured by two mSi cells
have been recorded every ten minutes during a year. These cells have been previously
calibrated against a reference pyranometer Kipp and Zonen CMP21. One of the reference
cells has been cleaned daily, while the other has not been cleaned throughout the experiment
(one year). Other parameters, such as rainfall and wind speed have been also measured.
Each reference cell has a low value shunt resistor between its terminals, and then the voltage
drop across the shunt must be proportional to the short-circuit current and so it is further
proportional to solar irradiance on the cell. The determination of the calibration constant for
each cell is based on a comparison with a reference pyranometer under natural sun along a
clear-sky day (only values of irradiance greater than 200 Wm-2 have been taken into account).
Both sensors (the reference cells and the pyranometer) are connected to an A/D module
(cFP-AI-112) installed in Compact FieldPoint cFP-2120 data acquisition system that have
been programmed to store a measure of all sensors at one-minute intervals. The manufacturer
of the pyranometer provides a sensitivity constant that must be used to determine the actual
irradiance value from the voltage its voltage output. Finally, a linear regression (setting offset
to zero) between voltage values across each shunt and irradiance value have been performed
to determine each constant.
Once the calibration procedure has been performed both cells remained installed and
connected to the acquisition data system and measures of both of them have been recorded
every three minutes along one year. The output value of each cell has been multiplied by the
constant obtained by the calibration procedure in order to get the irradiance. Whereas one of
them has been cleaned manually every day, the other cell has only been cleaned by rain. As
well as registering irradiance values, the irradiation value along each day has been computed
using trapezoidal integration too.
By comparing recorded irradiance values sensed by the two reference cells, dust influence on
the received radiation can be quantified, and as consequence its effects on the solar energy
received in the cell. Daily irradiation losses caused by dust are calculated comparing
irradiation values sensed by the clean and the dirty cells. The two calibrated cells and the
pyranometer are placed on a plane whose tilt angle is 30º (see Fig. 1). The period of
measurements comprises from 12/15/08 to 12/14/09. Along that period, summer was dry
without any rain, and winter and spring had rainfall more frequent than usual for this period.
An autumn with low rainfall completes the meteorological period. The availability of data for
the studied period has been 96.4%.
Fig. 1. The experimental setup used in the measurements.
3. Results
3.1. Irradiation daily losses
The evolution of the irradiation daily losses along the year of measurements is shown in
Fig. 2. These losses (HL) represent the fraction of daily energy that a PV module will not
receive as consequence of dust deposited on their surface, and are calculated as
(%) 100 CC DC
CC
HH
HL H




(1)
where HCC is the daily irradiation measured by the clean reference solar cell (W h m-2) and
HDC is the daily irradiation measured by the dirty cell (W h m-2). As can be seen in Fig. 2, the
losses produced by the presence of dust are strongly dependent on the rainfall. In rainfall
periods, a good cleaning of the dirty cell is produced and it recovers its initial performance;
even a light rain, below 1 mm, is enough to clean the cover glass, reducing daily losses HL
below 5%. However, in long periods without rain, like summer, the accumulation of dust can
cause daily losses exceeding 20%.
Fig. 2. HL values for all days of measurements along a whole year (left axis). We also plot daily
values of rainfall (right axis).
The mean of the daily energy losses along a year caused by dust is 4.4%. Monthly averages of
daily energy losses are lower than 2% except in summer months, when the lack of rain favors
the accumulation of dust and causes the increase of losses above 15%. Note that the energy
production reaches its maximum in these summer months, and therefore the possible adverse
effect of dust is very relevant.
3.2 Evolution of the dust losses along the day
As seen in the last section, accumulations of dust on the surface of a photovoltaic module
reduce strongly the energy received. We have not observed any influence of the wind speed or
direction on the losses, probably because the high relative humidity contributes to the
adherence of the dust particles on the module surface. As shown in previous studies [7-10],
these losses should not be constant during the day, but have to be dependent on the incidence
angle of beam radiation. In order to study this dependency, irradiation values sensed by the
clean and the dirty cells throughout the day are compared. In this case, relative irradiance
losses are calculated as:
(%) 100 CC DC
CC
GG
GL G




(2)
where GCC is the irradiance value measured by the clean reference solar cell (W m-2) and GDC
is the irradiance value measured by the dirty reference solar cell (W m-2). It should be pointed
out that losses caused by the dependence of the transmission coefficient of the glass cover on
the angle of incidence does not affect in the calculation of GL since it is identical in both cells.
However, the presence of dust modifies the angular dependence of the irradiance, which is
different for the clean and the dirty cell, and precisely this effect is measured with GL.
These losses represent the fraction of irradiance that the cell will not receive, and in the case
of PV modules, power losses. When cells are clean, losses are approximately constant during
the day. As dirt is deposited on the dirty cell, the behavior of the losses is not constant
throughout the day in clear sky days, becoming dependent on the angle of incidence. Daily
evolution of dust losses on the 08/06/09 is shown in Fig. 3. This is a clear sky summer day,
almost two months after the last rains; as consequence, dust level deposited on the dirty cell
surface is high, causing daily losses of 14.8%.
Fig. 3. Relative irradiance losses (GL) along a day.
The typical behavior of GL as a function of the incident angle () is shown in Fig. 4. In this
figure, we plot GL curves obtained in several days with different HL values (i.e. with different
amounts of dust). As expected, losses are strongly dependent of the incident angle of
radiation. Minimum transmittance losses occur at noon (12.4%) when the incident angle is
minimum. As incidence angle increases, losses increases slowly, but the growth rate increases
as the angle. Nevertheless, from an angle of about 60º, losses remain almost constant for a
window of about 10º and then, after a maximum of about 21%, they decrease. This occurs at
first and last hours of the day, when incidence angle is between 60-80º and irradiance value is
about 200 Wm-2. (Note that morning maximum is slightly lower than afternoon maximum; the
cause is that calibrated cells are no exactly in the same plane an there are a little bench
between them). Dependence of dust losses with the angle is shown in Fig. 4.
0
5
10
15
20
25
30
35
0 20406080100
(degrees)
GL (%)
4% 8.8% 13.7% 18.4% 21.6%
Fig. 4. Dependence of GL with the angle of incidence (θ) for several days with different HL values.
This behavior is related with the proportion of diffuse irradiance on global irradiance in the
early morning and evening, when its value increases. In section 4, a theoretical model justifies
this behavior. On cloudy days, when the global irradiance is mainly diffuse irradiance, losses
remain almost constant throughout the day. Diffuse irradiance has not specific direction and
hence losses are not dependent on the incidence angle.
Table I summarizes HL, θ and GL at solar noon and the maximum value of GL for each day
shown in Fig. 4. Values of HL are between 4.0% for the first day and 21.6% for the last day.
It can be noticed that all the shape of the curves is generic and it is not dependent on the HL
value.
Table I. Measured parameters of Fig. 4
Date HL (%) θ at solar noon
(degrees)
GL at solar
noon (%)
GL maximum
(%)
27/06/2009 4.0 17.0 3.5 5.9
13/07/2009 8.8 15.1 7.5 12.5
30/07/2009 13.7 11.7 11.7 18.9
23/08/2009 18.4 4.4 16.0 25.0
04/09/2009 21.6 0.2 18.4 30.4
4. Modeling the losses produced by the dirt
We have developed a simple model to justify the shape of the typical behaviour of the relative
transmittance losses due to the presence of dust in the solar cell (see Fig. 3). The model is
based on the following assumptions:
a) Dust grains are modelled as spheres homogeneously distributed on the surface of the
panel.
b) Each sphere has a reflection coefficient R, which accounts for both specular and
diffused reflection.
c) Total incoming radiation from the Sun (IT) is composed of direct radiation (I0) and
diffuse radiation (ID). We consider that this latter radiation comes homogeneously
from any direction and it is kept constant along the day. Note that the total irradiance
received by a clean solar cell is given by:
0cosθ
CC D
GI I (3)
where θ is the angle of incidence of direct radiation on the panel. The albedo radiation
has been neglected.
d) In the dirty solar cell, any sphere of dust shadows the panel thus reducing the light
reaching it. However not all radiation reaching the spheres is lost because part of if is
reflected (a factor R) and can be partially recovered by the panel. Both effects, the
shadowing and the recovery of light, depend on the angle of incidence of the direct
radiation and thus vary along the day. On the other hand, there is no such dependence
in the diffuse radiation since we assume that ID is constant along the day.
To quantify the irradiance losses GL due to the presence of dust in the solar cell we use
Eq. (2). In order to understand the effect of the dust on the losses we have to analyse
separately the direct and diffuse radiations.
4.1. Direct radiation
For the direct radiation the shadowing increases with the angle of incidence, reaching the
maximum for θ = 90º. At the same time, the fraction of the light specularly reflected reaching
the panel increases with up to a maximum value and finally decreases for very large . On
the other hand, the fraction of light diffusely reflected reaching the panel is constant because
the direction of the reflected rays is independent of the angle of incidence. The sum of all
these contributions is not evident and therefore we simulate the phenomenon using a ray
tracer [11]: For each angle of incidence we trace 106 rays reaching a square cell of unit area
with a single sphere on its center. We impose periodic boundary conditions. The reflection
coefficient of the spheres is set to R = 65 % (19.5 % specular and 45.5 % diffuse), and the
radius of the sphere is set to r = 0.315 units, which is equivalent to a coverage of 31.17 % of
the surface of the cell. In Fig. 5 we show GL as a function of the angle of incidence for this
simulation (dashed line). The values of the parameters are physically acceptable and have
been chosen in order to fit the experimental results (also shown in Fig. 5) for small angles of
incidence. As can be observed, the model does not reproduce at all the behaviour of GL for
large angles of incidence. In particular it gives a monotonously increasing GL while the
experimental one reaches a maximum and decreases for very large angles of incidence.
4.2. Diffuse radiation
As we see, the contribution of direct radiation alone does not suffice to explain the
experimental results. Therefore we incorporate the diffuse radiation to the model. Again we
generate and trace 106 rays with directions uniformly distributed. The total amount of energy
carried by these rays is equivalent to 23 % of the total radiation that would reach the cell
under normal incidence. When these rays are included in the simulation (solid line in Fig. 5)
the result obtained for GL agrees fairly well with the experimental results and in particular, it
reproduces the reduction of the losses observed at large angles of incidence.
Fig.5. Relative irradiance losses of a dirty solar cell as a function of the angle of incidence of solar
direct radiation. Hollow triangles (circles) correspond to real data measured in morning (afternoon)
hours on the 4th of September, 2009 (Malaga, Spain). Dashed line corresponds to the results obtained
with a simulation (see text for details) in which diffuse radiation is not considered whereas the solid
one has been obtained by taking into account this radiation.
4. Conclusions
In this work we have studied in general the energy losses due to accumulated dust on the
surface of photovoltaic modules. First, we present results about daily irradiation losses and we
show that the mean value of this quantity along a whole year is about 4.4%. In rainfall
periods, the rain water cleans the dirty cell and it recovers its normal performance: even a
light rain, below 1 mm, is enough to clean the cover glass, reducing daily losses HL clearly
below the average value of 4.4%. However, in long periods without rain, like summer, the
accumulation of dust can cause daily losses exceeding 20%.
Second, we present results of the dust-caused irradiance losses GL and its dependence on the
angle of incidence θ. The curve that describes the dependence of these losses on the angle of
incidence has a very specific shape: GL has a minimum at solar noon, then increases with θ
up to a maximum value found when θ 75º, and then decreases for larger values of θ. This
behavior can be explained by the influence of the diffuse radiation.
In addition, we have presented a simple model, simulated with the ray-tracing technique, to
explain the behavior of losses in solar modules due to the presence of dust. With this model
we have shown the relevance of diffuse radiation in order to understand the full behavior of
losses as a function of the angle of incidence. Indeed, when only direct radiation is considered
the modeldoes not provide results comparable to experimental measures. On the other hand,
when diffuse radiation is also taken into account, the model reproduces quite well the shape of
the experimental data for reasonable values of the input parameters.
We conclude that the estimation of energy losses produced by the presence of dust have to be
calculated in a different way for photovoltaic systems with fixed modules or with solar-
tracking. In addition, the proportion of the diffuse component in the global radiation must be
taken into account when estimating the energy losses produced by the dust on the system
energy performance.
Finally, it is very important to quantify energy losses produced by dust in dry areas where
such losses could reach large values and so producing a substantial decrease in the efficiency
of photovoltaic systems. In these cases a regular cleaning of the modules would be necessary
thus increasing maintenance costs.
Acknowledgements
We acknowledge the Spanish “Ministerio de Ciencia e Innovación” (grant No. ENE07-67248)
and “Junta de Andalucía” (grant No. P07-RNM-02504) for financial support.
References
[1] M. Mani, R. Pillai. Impact of dust on solar photovoltaic (PV) performance: Research
status, challenges and recommendations, Renewable and Sustainable Energy Reviews 14,
2010, pp. 3124-3131.
[2] M. Piliougine, J. Carretero, M. Sidrach-de-Cardona, D. Montiel, P. Sánchez-Friera.
Comparative analysis of the dust losses in photovoltaic modules with different cover
glasses. Proceedings of 23rd European Solar Energy Conference, 2008, pp. 2698-2700.
[3] H.P. Garg, Effect of dirt on transparent covers in flat-plate solar energy collectors, Solar
Energy 15 (4), 1974, pp. 299-302.
[4] S.A.M. Said, Effects of dust accumulation on performances of thermal and photovoltaic
flat-plate collectors, Applied Energy 37 (1), 1990, pp. 73-84.
[5] M.S. El-Shobokshy, F.M. Hussein, Effect of dust with different physical properties on the
performance of photovoltaic cells, Solar Energy 51 (6), 1993, pp. 505-511.
[6] S. Biryukov, D. Faiman, A. Goldfeld, An optical system for the quantitative study of
particulate contamination on solar collector surfaces, Solar Energy 66 (5), 1999, pp.
371-378.
[7] D. Goossens, E. Van Kerschaever, Aeolian dust deposition on photovoltaic solar cells:
the effects of wind velocity and airborne dust concentration on cell performance, Solar
Energy 66 (4), 1999, pp. 277-289.
[8] N. Martin, J.M. Ruiz, Calculation of the PV modules angular losses under field
conditions by means of an analytical model, Solar Energy Materials & Solar Cells 70,
2001, pp. 25-38.
[9] M. García, L. Marroyo, E. Lorenzo, M. Pérez, Soiling and other optical losses in
solar-tracking PV plants in Navarra, Progress in Photovoltaics: Research and
Applications, DOI: 10.1002/pip.1004.
[10] N. Martin, J.M. Ruiz, Annual angular reflection losses in PV modules. Progress in
Photovoltaics: Research and Applications 13, 2005, pp. 75-84.
[11] A.S. Glassner (Ed), An introduction to ray tracing, Academic Press, 1993.
... These measurements showed a reduction of output efficiency by up to 26% as dust deposition increased from 0 g/m 2 to 22 g/m 2 [8]. Zorrilla-Casanova et al. [9] attempted to quantify the performance loss due to dust accumulation under natural conditions in Spain, by investigating the mean reduction of system output over a period of twelve months. During this period, the amount of power generated decreased by 4.4% and their analysis suggested severe losses of more than 20% in long, dry seasons without rain were probable [9]. ...
... Zorrilla-Casanova et al. [9] attempted to quantify the performance loss due to dust accumulation under natural conditions in Spain, by investigating the mean reduction of system output over a period of twelve months. During this period, the amount of power generated decreased by 4.4% and their analysis suggested severe losses of more than 20% in long, dry seasons without rain were probable [9]. Pavan et al. [10] addressed the effect of various soiling type on system performance of two 1MWp PV plants in Italy. ...
... Therefore, the modified k-ε turbulence model with TSWF and with aid of unique discretization technique can accurately predict the phenomena next to regions where high gradients exists. The modified k-ε turbulence model with damping functions is obtained from equations (1) to (9) while the TSWF was calculated using equations (10) to (14) [33]. ...
Article
Despite the global acceptance and rapid market penetration of PV power plants and recent advancements in increasing panels electrical efficiency, soiling is still one of the most critical challenges that deteriorate the performance. This study proposes a unique method for PV panel self-cleaning based on dew formation on panel’s active surface and with aid of Single Axis Tracking (SAT) mechanism. Both experimental study and numerical simulations were performed in this research to highlight the effectiveness of self-cleaning method. Such approach is based on rotation of panels toward ground during night in an inclined position for simultaneous dew formation and cleaning of panels via water droplets runoff and prevention of dust accumulation. Experimental results exhibit a maximum loss of 5.9% in panel efficiency during a 94 days testing period while for the fixed PV and SAT without night position losses were measured to be 33.2% and 11.9% respectively. Using a validated CFD model, a new PV glazing geometry was proposed to increase dew formation for more effective self-cleaning. CFD numerical results demonstrate that the amount of collected dew mass formed on the panel can be increased by about 86 % while dew film thickness increased by about 67% compared to conventional flat glaze configuration. Overall, the proposed system outperforms its counterparts based on a continuous self-cleaning strategy on a nightly basis which does not require any additional capital and labor costs, energy consumption and water resources.
... Zorrilla-Casanova claimed in their studies [36] that the most effective technique for cleaning PV modules is the use of water. Even a light rain of less than 1 mm is sufficient to clean the covered panel. ...
Thesis
Full-text available
Solar power is a significant contributor in renewable energy considering the solar energy potential of Turkey. A vast amount of investment has been made during the last decade on photovoltaic solar plants, with the deployed power having reached 6.2 GW in July 2020 and still growing. A global trend in solar power is the deployment of solar panels on water such as lakes and dam reservoirs with advantages given as reduction of land use, reduction of evaporation and provision of cooling for the solar panels. Some applications have been established globally, and a typical example has been deployed in Buyukcekmece Lake, Istanbul, Turkey. This study, differing from the actual works, aims to design an offshore deployment, which may be useful for the southern shores of Turkey and competitive with the proposed offshore wind farms in terms of cost and renewable energy production. For this purpose, seven locations along the Aegean and Mediterranean coasts of Turkey have been selected. The study presents the evaluated outputs for solar power production and compares them with the offshore wind alternative for the proposed study locations. A simple cost estimation for a fixed offshore photovoltaic power plant has also been worked out. It has been found out that offshore photovoltaic energy may be competitive with wind energy and even more feasible for some sites with a low wind energy potential, which may be the sole feasible solution regarding site-based potential of various renewable energy forms.
... Additionally, the dust deposition on the surface of solar PV module depends on the angle onto which the panel is inclined. It has been seen that the dust piling up decreases when the inclination angle of the solar PV module changes from (0 • ) level to (90 • ) vertical, also this has been varified through experimental approach [5,9]. ...
Article
Full-text available
The constraints in the path of sustainable, cost-effective, and efficient photovoltaic power supply to the irrigation system in remote areas are addressed in this work. The intrinsic thermal losses in the PV system due to high working temperature and shading losses that are caused by dirt are mitigated through water cleaning mechanisms. Moreover, the protection against lightning strikes and surges is assimilated in the system to ensure the durability of the PV system. Lastly, cost analysis of 0.4 MW PV plant for the Area of 7444.69 m2 has been performed by the Homer Pro, and comparison is made with the same size of a Hydro power plant to estimate the economic feasibility of power generation for the purpose of irrigation through the pump house. The water-cooling mechanism resulted in the gain of one volt per panel of 260 W, which is a significant improvement with regard to collective PV plant generation. As the water cleaning mechanism for dust removal is accompanied with the cooling process, it results in the two volts rise per panel. Additionally, a cost analysis of 0.4 MW PV system provided a significant budget saving estimating USD ~2 million as compared to that of a Hydel power plant of the same size.
... Even light rains are enough to clean the panel, reducing the amount of dust accumulated. However, during long periods without rain, like summer, dust accumulation decreases the panel's performance (Zorrilla-Casanova et al. 2011). The amount of rain required for a full recovery of the module's performance in intense agriculture areas is 0.5 mm (Caron and Littmann 2012). ...
... Based on the SRatio measurements (Zorrilla-Casanova et al. 2011), the evolution of daily soiling losses (SL) for both fixed PV and PV on dual-axis tracker is presented in Fig. 9. It is deduced that SL are ranged from 2 to 7% in the case of PV with tracking and from 7 to 21% in the case of fixed solar In Fig. 10, SRatio for both fixed PV and PV on dual-axis tracker is presented for the dry period only for well identifying the difference in both trends. ...
Article
Full-text available
Soiling has a crucial importance regarding its impact mainly for countries that have high soiling levels, dust storms, water scarcity and a great solar energy potential as the case of Morocco. Soiling mitigation is therefore mostly required during spring, due to higher pollen concentration, and summer, due to the lack of heavy precipitation. In this work, systematic measurements of soiling ratio were made in Rabat, city of north-western Morocco, during almost 1 year. Soiling has been evaluated considering the effect of dual-axis tracking that was compared to photovoltaic (PV) on fixed structure. A soiling rate of about 0.22%/day has been found for static PV while only 0.1% was found for PV on tracker. An additional approach of cleaning has been proposed in this paper which aims to use dew water. Using glass samples that were exposed to real environmental conditions, similar to the exposure conditions of PV panels, the soiling ratio was determined. At sunrise time, the subsequent change of the glass sample, from the horizontal position at night into the position of 30° tilt angle during the day, is performed to promote dew flow by the force of gravity acting on the droplets of dew. It has been found that relying only on the change of tilt angle, the average soiling losses were only 3.8% compared with 11.8% for fixed PV. This approach can reduce soiling similarly to solar trackers.
... Consequently, several researchers have spent extensive time and effort to measure the amount of waste of electrical energy (Alnaser et al., 2018). The decrease in electrical energy output due to soiling varies across a large range from 4.4%-80% (El-Shobokshy and Hussein, 1993a; El-Shobokshy and Hussein, 1993b; Kalogirou et al., 2013;Mastekbayeva and Kumar, 2000;Zorrilla-Casanova et al., 2011). The wide range reduction in electrical energy is due to soiling strongly affecting the slope, orientation, and characteristics of the solar PV module such as type of coating, surface roughness, etc. ...
Article
Recent achievement and progress in solar PV play a significant role in controlling climate change. This study reviewed comprehensively electrical characteristics, life cycle of dust, optical characteristics, and different cleaning techniques related to the effect of dust on the performance of PV modules throughout different climate regions of the world. The power maximum power point (MPP) and curve of PV module under the effect of irradiance and temperature were presented. The effect of dust (shading) on the electrical efficiency of PV module was discussed based on soft, partial, and complete (soiling) shading. The physical properties of dust around the globe such as PM10 concentration, dust loading (mgm⁻²), and fine dust particles concentration were covered and discussed. Reasons behind the accumulation of dust based on, location and installation factors, dust type, and environmental factors. Environmental reasons causing dust and dust removal in accordance with the life cycle of dust was covered in detail. All the reasons that cause the generation, accumulation and removal of dust during its life cycle were explained. All forces responsible for the adhesion phase of the dust life cycle were presented. The effect of dust on PV module transmittance and electrical parameters module were discussed in detail based on physical properties of the dust at its location and installation conditions. Self-cleaning super hydrophobic surfaces based on methods such as solvents, vapor-assisted coating, powder coating, and polymerization were discussed. All cleaning technologies, including self-cleaning technologies, based on the material coating used, and the manufacturing of PV cells was compared. The future prospective for PV technologies and cleaning methods were also covered.
Chapter
Full-text available
Abstract The giant inverse magnetocaloric effect driven by a merged magnetostructural transformations in Ni-Mn-In-Co Heusler alloys, makes them highly promising as solid state refrigerants near room temperature. Knowledge of the crystallographic behavior of these alloys at a broad temperature range is critical to the understanding of the giant magnetocaloric effect. In this study, three Ni-Mn- In-Co alloys were investigated by neutron and synchrotron diffraction techniques. The chemical compositions of the alloys, determined by the Rutherford Backscattering Spectrometry (RBS) technique, were Ni41Mn39In12Co8, Ni48Mn34 In12Co6 and Ni52Mn25In16Co7. The austenitic (A) phase of all three alloys was cubic L21 (Fm3̅m). Martensitic (M) phase of the Ni41Mn39In12Co8 alloy was a mix of 8M and 6M modulated monoclinic structures, while the other two alloys had a M composed of a mix of 7M and 5M modulated monoclinic structures. All modulated structures belong to the P 1 2/m 1 space group. Site occupancy refinements of the A phases of all three alloys, revealed that almost all the Co atoms (*97%) occupy the regular Ni (8c) sites. In the studied temperature range (50–250 K) of the M phase of the Ni41Mn39In12Co8 alloy has very low magnetization. Also, no antiferromagnetic ordring was observed in the neutron diffraction refinement of the M phase. Therefore by eliminating the possibilities of ferromagnetism and antiferromagnetism, it is concluded that the M phase of the Ni41Mn39In12Co8 alloy is spin glass.
Article
One of the concerns of using PV arrays in solar power plants is cleaning the surface of the PV array. In this paper, a suction robot called MFv01 was designed, built, and tested, which not only has a higher cleaning quality than Antonelli and Ecoppia T4 robots but also has a faster cleaning speed. Therefore MFv01 robot reduces the cleaning time of the surface of solar panels. In the MFv01 robot, two sets of brushes are used to clean the surface of the PV array that the brushes are installed in the front and back of the robot. Also, a suction system is designed that sucks the dust collected by the brushes into its garbage bag. The MFv01 operates without rails or guides and finds its spatial position by ultrasonic sensors. The movement strategy of MFv01 is such that it moves shorter paths compared to similar robots. The tests on the PV array have confirmed the simulation results and approved the effectiveness of the proposed movement strategy and suction system to improve cleaning quality.
Article
Full-text available
Photovoltaic (PV) modules in real operation present angular losses in reference to their behaviour in standard test conditions, due to the angle of incidence of the incident radiation and the surface soil. Although these losses are not always negligible, they are commonly not taken into account when correcting the electrical characteristics of the PV module or estimating the energy production of PV systems. The main reason of this approximation is the lack of easy-to-use mathematical expressions for the angular losses calculation. This paper analyses these losses on PV modules and presents an analytical model based on theoretical and experimental results. The proposed model fits monocrystalline as well as polycrystalline and amorphous silicon PV modules, and contemplates the existence of superficial dust. With it angular losses integrated over time periods of interest can be easily calculated. Monthly and annual losses have been calculated for 10 different European sites, having diverse climates and latitudes (ranging from 32° to 52°), and considering different module tilt angles.
Article
Full-text available
The objective of this work is to obtain a universal model for calculating the annual angular reflection losses (AAL) of PV modules working in real conditions, useful in the prediction or assessment of the annual performance of PV systems. Instantaneous angular losses (AL) can be calculated by using an analytical model, formerly developed by the authors, that has proved to be in good agreement with the experimental data. In this paper we have used this model to calculate AAL in an hourly basis at 79 different sites all over the world and considering ten different tilt angles, from horizontal to vertical, for south (north) oriented PV modules at north (south) hemisphere sites. From the analysis of the results, we propose an easy-to-use mathematical expression for the calculation of AAL. The model has three different versions that are to be used depending on the availability of the local radiation data. The most detailed expression of the model fits with high degree of accuracy the local AAL data, the second version consists of a global term plus a local weather-descriptive one, and the third version is a universal global model dependent only on the latitude and the PV module tilt angle. Copyright © 2004 John Wiley & Sons, Ltd.
Article
The effect of accumulation of dust and particulate matter onto the surface of photovoltaic cells has been experimentally investigated. Five kinds of dust having different physical properties were used. Three of them were limestone particulates with different classes and the other two were cement and carbon particulates. Details on the physical properties of each were obtained through size distribution analysis using an optical microscope. Well-controlled experiments were conducted using a solar simulator as a light source. The dust deposition density (g/m[sup 2]) was precisely determined in each test run. It has been concluded that fine particulates significantly deteriorate the performance of photovoltaic cells, more so than coarser particles. Cement, the main building material which may often present in the atmosphere of urban areas has shown to reduce both the short circuit current and output power when deposited onto the surface of photovoltaic cells. This is due to very small diameter of its particles. Carbon particulates, which are generated from combustion process and emitted from diesel engines among the different dusts used, have shown to result in the worst deterioration of performance of photovoltaic cells, and higher a loss in power output.
Article
The effect of dirt on the transmittance of solar radiation through various inclined glass plates and plastic films, which are used as a transparent cover for flat-plate collectors, has been studied. The dirt correction factor for glass plate inclined at an angle of 45 deg from the horizontal is 0·92, which is significantly different from the value of 0·99 given by Hottel and Woertz[1]. The correction factor is greater for plastic film than it is for glass plate for any inclination.
Article
Field data of soiling energy losses on PV plants are scarce. Furthermore, since dirt type and accumulation vary with the location characteristics (climate, surroundings, etc.), the available data on optical losses are, necessarily, site dependent. This paper presents field measurements of dirt energy losses (dust) and irradiance incidence angle losses along 2005 on a solar-tracking PV plant located south of Navarre (Spain). The paper proposes a method to calculate these losses based on the difference between irradiance measured by calibrated cells on several trackers of the PV plant and irradiance calculated from measurements by two pyranometers (one of them incorporating a shadow ring) regularly cleaned. The equivalent optical energy losses of an installation incorporating fixed horizontal modules at the same location have been calculated as well. The effect of dirt on both types of installations will accordingly be compared. Copyright © 2010 John Wiley & Sons, Ltd.
Article
The peaking of most oil reserves and impending climate change are critically driving the adoption of solar photovoltaic's (PV) as a sustainable renewable and eco-friendly alternative. Ongoing material research has yet to find a breakthrough in significantly raising the conversion efficiency of commercial PV modules. The installation of PV systems for optimum yield is primarily dictated by its geographic location (latitude and available solar insolation) and installation design (tilt, orientation and altitude) to maximize solar exposure. However, once these parameters have been addressed appropriately, there are other depending factors that arise in determining the system performance (efficiency and output). Dust is the lesser acknowledged factor that significantly influences the performance of the PV installations. This paper provides an appraisal on the current status of research in studying the impact of dust on PV system performance and identifies challenges to further pertinent research. A framework to understand the various factors that govern the settling/assimilation of dust and likely mitigation measures have been discussed in this paper.
Article
The performances of one photovoltaic and two thermal panels during several months of outdoor exposure have been measured. For the photovoltaic panel, the average degradation rate of the efficiency was 7% per month, whereas, for the thermal panels, the average degradation rate on the optical efficiency ranged from 2·8% to 7% per month for this maritime-desert-subzone type of environment.
Article
Wind tunnel experiments were conducted to investigate the effect of wind velocity and airborne dust concentration on the drop of photovoltaic (PV) cell performance caused by dust accumulation on such cells. Performance drop was investigated at four wind velocities and four dust concentrations. I–V characteristics were determined for various intensities of cell pollution. The evolutions of the short circuit current, the open circuit voltage, the maximum power, the reduction of solar intensity received by the cells, and the fill factor variation with increasing cell pollution were examined. The deposition (and accumulation) of fine aeolian dust on PV cells significantly affects the performance of such cells. Wind velocity has an important impact on cell performance drop, since the drop is larger in high winds than in low winds. However, the wind also affects the sedimentological structure of the dust coating on the cell, resulting in a higher transmittance (of light) for coatings created during high winds. The wind tunnel experiments indicate that the former effect is more important than the latter, which means that, in general, the drop in PV cell performance due to dust accumulation is larger as wind speed increases. Airborne dust concentration also affects the drop in PV cell performance, since high dust concentrations lead to a higher accumulation on the cell. Contrary to wind speed, airborne dust concentration does not seem to affect the sedimentological structure of dust coatings (with respect to light transmittance) on PV cells.
Article
We describe a computerized microscope system that has been developed for studying the physics of dust particles which adhere to various kinds of surfaces such as those of solar collectors. The device enables investigators: (1) to obtain the particle size distribution of dust on a surface; (2) to calculate the fraction of surface area covered by dust; (3) to calculate the reduction of optical efficiency (of the solar collector under study) as a function of particle size; (4) to investigate the effect of various kinds of applied force field on the adhesion of dust particles to the surface. Some examples are given for the use of such a measuring system for the study of photovoltaic and solar-thermal collector surfaces.