PV Soiling: Quantification of Organic/Inorganic
Composition by a Plasmonic-decorated surfaces
Brahim Aïssa and Mohammad I. Hossain
Contact: baissa@hbku.edu.qa;
4. Ionic Content and TGA analysis
1. Particularity of the PV soiling issue in desert climates
▪ Power losses due to the soiling of PV modules could easily reach 1 %/day and is a
location-dependent parameter.
▪ Meteorological factors show a variation from season to season (dry vs humid periods
within the same year), and from geographical spot to another.
▪ Variation of the chemical composition of the dust particles (both in space and time).
▪ No “one-solution-fits-all” to the problem of soiling.
Dust composition is critical as different dusts affect light in different manner. Organic
dust is worst than mineral ones, and its quantification/mitigation is of a primary
importance for PV soiling issue.
Example of the geographical distribution of the
• Organic Carbon shades light  30 times higher
(d)
than Mineral Dust
• Elemental Carbon  200 times
• Ions 11 times
dominating chemical elements per geographical spot,
as measured by EDS, both on ground and on PV panels.
What is measured on the ground is not necessarily
deposited onto the PV Panel!
(a)
(e)
(b)
(c)
Figure 1: (a) Photo of the QEERI Outdoor Test Facility’s area. The inset shows PV panels after dust accumulation (Soiling). (b)
Dust caused PV energy output to decrease by 0.49%/day on average each day without cleaning. Box edges = quartiles, triangles
= means. (c) Soiling loss exhibited by PV systems under different cleaning schedules, for each day over five years.
2. Seasonal and geographical Mapping of the chemical
composition Distribution of the dust particles in Qatar
✓ Same set of dust may contain more than 11 chemical elements, with different concentrations and it varies with time (i.e., seasonally)
and with space (i.e., geographically). The same observation with compounds, including Calcite, Dolomite, Quartz, etc.
✓ Si, Mg, Ca, Na, Cl are the dominating elements. Fe, Al and Ti are also measured.
✓ Morphology (shapes, average size, particle size distribution, etc.) and structures (crystallography, cross section surface area) of the
dust particles vary from season to season, and from region to region.
✓ Organic content was also observed in the dust composition, and ionic content was also observed.
(c)
(a)
(d)
The ionic composition of the dust particle was also measured by IC.
Not all the geographical spots contain an ionic compound.
5. LSPR of Au NPs on TiO2/Glass coupons
To study in more details the mitigation of the organic part of the dust, we experienced the use of Au NPs decorating titania-coatedglass coupons that were put at outdoor conditions for dust accumulation. The expected interplayed effects are the following:
(i) The LSPR (localized Surface Plasmon Resonance) that helps to decompose the organic ligands contained into the dust particles.
(ii) This increase of the hydrophilic property of the surface (i.e., wettability).
Samples were optically measured using
ultraviolet–visible (UV–Vis) spectroscopy.
The wetting behavior was characterized
using contact angle measurements.
DektakTM 3D stylus and BrukerTM atomic
force microscopy (AFM, Fig. 6) were used to
characterize surface topology.
Calcite Distribution
JEOL 7610TM field-emission scanning
electron microscopy (FESEM) was engaged
to study the microstructure of the films.
Figure 6. AFM analysis showing a topological study of Au/TiOx systems with TiOx at three different
surface densities.
(b)
Figure 2: (a) Representative SEM micrograph showing dust particles as collected from OTF. (b) Histogram of Cl and Na
geographical distribution as collected from ground and from PV Panel. (c) TGA and derivative wt. % loss showing the
organic/inorganic composition of dust particles. (d) ARC GIS illustration of a geographical distribution of calcite
compound (CaCO3). Its concentration is both spatially and temporally dependent.
The surface tension dynamics of gold (Au) films
significantly depends on the surface kinetics of
TiOx films, which leads to the formation of Au
particles with various shapes and sizes, different
densities, and different grain distances.
As confirmed by the wetting technique using
contact angle measurement shown in Figure 7,
surface wettability has changed significantly, and
the CA has decreased from 74.2o to 42.4o with
respect to the annealing temperature. The
samples became more hydrophilic.
Figure 7. Wettability study of Au/TiOx structures
3. Daily Soiling Mapping and Particle Size Distribution
➢ For a fixed period of time: The variation of the
soiling ratio (SR%) is spatially dependent and may
go up to 300 % (e.g. SR % in Al Kharsaah vs.
Turayna, during the period of Nov. 2021).
➢ For a fixed geographical spot, the temporal
variation may go up to 300 % (e.g. SR % in Al
Kharsaah in Nov. 2021 vs. May 2021).
(d)
6. Quantification of Organic/Inorganic Composition
TiO2/Au coupons with different surface densities of Au NPs were put in outdoor conditions and dust particle were accumulated
for 2 months. Dust was removed from surface and TGA was performed systematically.
Focus was put on the region of 300-600 oC where the organic compounds decompose.
(a)
First, the formation of the Au nanostructures due to thermal treatment (in
view of the presence of plasmon resonance) is captured in the UV-Vis
absorption spectra. The usual absorption peak for Au NPs has the LSPR
absorption light band normally close to 520 nm and the broad peak with a
strong tail is an indication of the wide distribution of nanoparticle size.
Figure 8 shows the typical spectra of the plasmonic resonance peaks
ranging from 550 – 820 nm and shifting towards higher wavelength side
with an increasing bandwidth as the particle sizes changed.
(b)
A clear decrease of the quantity of organic dust is demonstrated as a
function of the Au NPs densities (Fig. 10).
➢ Tiny dust particles located mainly in the north.
➢ Larger particles mainly located in the south.
➢ Different dusts have different effects on T%:
For the same amount of dust, fine particles have a
more dramatic effect on T% because of their higher
cross-section (higher area to volume ratio).
➢ Similarly, the chemical composition of the dust
particles and their shape are critical on the light
scattering and absorption properties.
Figure 3: Typical representative examples of the ARC GIS geographical mapping of (a-b) the field measured Soiling Ratio (SR%),
and (c-d) Particle Size Distribution. ArcGIS 10.8.1 software package developed by Environmental Systems Research Institute
(ESRI) was used in this mapping for the creation of the basic GIS environment. Qatar map image was first captured from
Google Earth. A database on the GIS application to convert the image to digital format (called Digitizing process).
(d)
Figure 8: Plasmon resonance spectra of the Au/TiOx systems
(b)
Figure 9: Weight loss of the dust particles vs.
temperature. Focus is put on the region of 300-600 oC
where the organic compounds decompose
Wt.% at 300oC-600oC region
(a)
(c)
Structural characterization of the grown
films was carried out using x-ray
photoelectron spectroscopy (XPS) and
BrukerTM X-ray diffraction (XRD).
D0
0
D1
11 NP/µm2
D2
13 NP/µm2
D3
15 NP/µm2
D4
19 NP/µm2
D5
22 NP/µm2
0.8
D6
24 NP/µm2
0.4
D7
25 NP/µm2
0.0
D8
26 NP/µm2
3.2
2.8
2.4
2.0
1.6
1.2
D0 D1 D2 D3 D4 D5 D6 D7 D8
Au NPs density (#/µm2)
Figure 10: Weight loss of the occurring at 300-600 oC vs. the surface
density of Au NPs
Acknowledgement: Authors thank the Qatar National Research Fund (QNRF, Member of Qatar Foundation) for the NPRP Grant #11S-117-180330 which is funding this research.