Enhance the performance of photovoltaic solar panels by a self-cleaning and hydrophobic nanocoating
Nanocoating characterization
Scanning electron microscopy (SEM)
The surface morphology of the nanocoating was observed with a Quanta FEG250 scanning electron microscope. Representative images of the sample with low (8000×) and high (30,000×) magnification are Fig. 5. The SEM images show the surface roughness of the nano-coating, which is an important factor for the hydrophobicity and thus the contact angle. The nanocoating has increased the surface roughness at the nano and micro scale, and this increases the hydrophobicity and contact angle according to the Wenzel and Cassie models17.
SEM images of PDMS/SiO2 nanocoating.
Energy dispersive X-ray (EDX)
Figure 6 shows the EDX spectrum for nanocoating. The presence of Si and O, which suggests the proper dispersion of silica nanoparticles throughout the coating18, is undeniably supported by EDX data, and the presence of C, along with O, accounts for the functionalizing chemicals used. The weight percent of O, Si, and C was 41.99, 40.66, and 17.35%, respectively.
Energy dispersive spectroscopy (EDS) for nanocoating.
Transmission electron microscopy (TEM)
Transmission Electron Microscopy (TEM) is a crucial technique for determining the NP’s structure, size, and distribution pattern19. The metal oxide nanoparticles are well dispersed in the PDMS polymer. The average nanoparticle size was 11 nm as shown in (Fig. 7). Through the hydrophobic chain of PDMS, PDMS-SiO2 nanoparticles cross-link with one another, which further leads to the formation of clusters of different sizes and then the micro-nanostructure. as shown in Fig. 7. The average cluster size was 80 nm. All TEM images magnifications were 100 nm.
TEM images of the PDMS-SiO2 nano coating.
Ultraviolet–visible spectrophotometer (UV–Vis):
The Uv–Vis spectroscopy curve in illustrates that the nanocoating had a high transmittance in the visible light range (Fig. 8). The average transmittance for the prepared nano coating was 91% in the visible light range (400–800 nm) and the nanocoating was resistant to UV (200–390 nm) radiation.
The UV–Vis spectroscopy of the PDMS/SiO2 nanocoating.
Fourier transform infrared spectroscopy (FT-IR)
Fourier transform infrared spectroscopy (FTIR) is a technique for identifying distinctive functional groups from spectral bands, allowing us to determine the conjugation between the nanomaterial and the adsorbed biomolecule20. The analysis is determined by measuring a sample’s absorbance to an incident infrared spectrum between 400 and 4000 cm−1 (Fig. 9). The major spectral bands and the characteristic functional groups of the spectral bands are shown in Table 5.
Fourier Transform Infrared Spectroscopy for PDMS/SiO2 nanocoating.
Surface wettability of nanocoating (WCA)
The contact angle, which varies from 0° to 180°, can be used to qualitatively identify whether a surface is hydrophilic or hydrophobic. The contact angle is a measurement of the relative magnitudes of adhesive (liquid to solid) and cohesive (liquid to liquid) forces acting on a liquid. Contact angle measurement is probably the method used the most frequently to determine solid surface tension. The three most widely used methods for measuring contact angles are the sessile drop, captive bubble, and Wilhelm plate methods. In the used sessile drop experiment, a droplet of a completely purified liquid is administered to a solid surface using a syringe or a micropipette. A goniometer placed in the eyepiece of a low-magnification microscope is typically used to view the droplet and calculate the resulting contact angle21. The contact angle was measured through the manipulation of water drop shapes on the samples using the OCA 15EC Contact angle model produced by the company of Data Physics Instrument Gmbh. The water contact angle for the prepared nano coating was 123 degrees, which means that the PDMS/SiO2 nanocoating is hydrophobic (Fig. 10).
Water contact angle of PDMS/SiO2 nanocoating on glass substrate.
Current–voltage curves for clean panels (I–V curves)
The I-V curves for a clean reference panel (RP), a commercial-nanocoated panel (CNP), and a prepared-nanocoated panel (PNP) are shown in Fig. 11 and the important points in Table 6. The short circuit current Isc was 5.69, 5.7, and 5.82 A, respectively, and the open circuit voltage Voc was 20.3, 20.5, and 20.7 V, respectively, at solar radiation of 960 ± 7 W/m2 and a PV panel surface area of 0.6 m2. The characteristics and efficiency of the prepared nano-coated panel were higher than those of the reference and commercial nano-coated panels. This is due to the roughness and nano-micro scale pyramidal shapes that are widely spread on the surface of the nano-coating, which reduces the reflectivity of light on the surface of the panels22.
The I–V curve for RP, CNP, and PNP.
Power-voltage curves for clean panels (P–V curves)
The maximum power Pmax for clean reference panel (RP), commercial-nanocoated panel (CNP), and prepared-nanocoated panel (PNP), was 78.5, 81.4, and 84.4 W, respectively, as shown in Fig. 12.
The P–V curves for RP, CNP, and PNP.
Fill factor for clean panels (FF)
The fill factors for clean reference panel (RP), commercial-nanocoated panel (CNP), and prepared-nanocoated panel (PNP), were 0.68, 0.69, and 0.7, respectively. The main parameters are illustrated in Table 7. Because the nanocoated panel produces the highest Imp and Vmp, it is the panel with the highest fill factor. This indicates the high efficiency compared to other panels23.
RP and PNP performance with dust accumulation
PV panels’ power within 40 days of exposure to external conditions
The power of the reference panel (RP) and prepared-nanocoated panel (PNP) degrades over time (40 days) due to an increase in dust accumulation density on the panels’ surface. The dust acts as a barrier between the sunlight and the photovoltaic cells, trapping a large portion of the sunlight and thus deteriorates the capacity of the solar panels. The power difference between RP and PNP increases with time due to the difference in dust accumulation density on each panel. The RP and PNP average power were 65.2 and 69.4 watts on the first day, 58.6 and 65.1 after 10 days, 51.9 and 62.6 after 20 days, 45.8 and 58.5 after 30 days, and 37.9 and 54.8 after 40 days, respectively, as shown in (Fig. 13). The percentage of power degradation within forty days for RP and PNP reached 42% and 21%, respectively.
The degradation in the RP and PNP power within 40 days.
The pumps’ discharge within 40 days of exposure to external conditions
The degradation in the RP and PNP power leads to the degradation in the discharge of the pumps that are connected to PV panels. The discharge difference between pumps connected to RP and PNP increases due to the increasing difference in output power of each panel with time. The RP and PNP pumps’ average discharge were 223.6 and 236.6 L/h on the first day, 206.2 and 228.6 after 10 days, 187.1 and 225.6 after 20 days, 167.2 and 213.5 after 30 days, and 137.4 and 197.7 L/h after 40 days, respectively, as shown in Fig. 14. The percentage of pumps’ discharge degradation within forty days for RP and PNP reached 39% and 16%, respectively.
The degradation of RP and PNP pumps’ discharge within 40 days.
Pv panels temperature
The continuous accumulation of dust and dirt on the PV panel surface over time, and the inhomogeneity of the dust density, lead to partial shading on the PV cells, which causes a difference in the solar cells’ productivity compared to each other. The low output cells work as a load or resistance to the high output cells. The temperature of the panels increases because of the high internal resistance. The RP and PNP average temperatures were 41.6 and 41.0 co on the first day, 42.3 and 41.4 after 10 days, 43.0 and 42.0 after 20 days, 44.2 and 43.1 after 30 days, and 45.7 and 44.5 co after 40 days, respectively, as shown in Fig. 15. The percentage of temperature increasing within forty days for RP and PNP reached 9.85% and 8.5%, respectively. Previous studies found a decrease in efficiency of 0.5%/1 °C24. The temperature difference between RP and PNP panels increased with time according to dust density, where it reached 1.2 °C, which degraded the RP panel efficiency by 0.6%.
The RP and PNP temperature within 40 days.
Dust density (g/m2) and panels’ efficiency within 40 days of exposure to external conditions
The efficiency of solar panels gradually decreases over time because of the increased density of dust accumulation on the surface of those panels. A large difference occurs between the efficiency of RP and PNP with time due to the difference in the density of dust on each panel. The RP and PNP average dust density were 0.00, 0.00 g/m2 on the first day, 2.80, 1.50 after 10 days, 4.76, 2.10 after 20 days, 7.76, 3.50 after 30 days, and 10.00, 4.30 g/m2 after 40 days, respectively. This is due to the self-cleaning property of nanocoating, which reduces the amount of dust accumulated on the PNP surface. The RP and PNP average efficiency were 13.99%, 14.85% on the first day, 12.40%, 13.79% after 10 days, 11.30%, 13.38% after 20 days, 9.59%, 12.41% after 30 days, and 8.32%, 12.01% after 40 days, respectively, as shown in Fig. 16.
The dust density (g/m2) and panels’ efficiency (%) within 40 days.
RP and PNP performance after self-cleaning:
After 40 days of exposure to weather conditions and dust, a volume of 4 L of water was sprayed onto the surface of each panel in 2 min, through orifices with a 0.5 mm diameter, to test the self-cleaning property. The dust density on RP and PNP before water spray was 10 and 4.30 g/m2, while the dust density after water spraying was 4.80 and 1.12 g/m2 respectively. As a result of hydrophobicity and consequently the low surface energy for nanocoating25, the dust was removed by water droplets by 74% in the nanocoated panel (PNP), compared to 52% for the uncoated reference panel (RP). RP and PNP had average powers of 50.03 and 65.93 W, respectively (Fig. 17).
The RP and PNP power after self-cleaning with water.
The average efficiency was 11.13% and 14.5%, respectively. The hourly average pump discharge was 181.2 and 229.0 L/h, respectively (Fig. 18). The panel’s temperatures were 43.1 and 41.2 °C, respectively. The fill factor value represents curve squareness and gives an idea of the PV panel’s quality. Normal values range from 0.7 to 0.8. For RP and PNP, the fill factors were 0.63 and 0.69, respectively (Table 8). The PNP has greater output power, greater efficiency, and the lowest temperature and dust accumulation density. Because of the hydrophobic and self-cleaning properties of the nanocoated panel, the water droplets rolled off and removed a large amount of dust from the panel surface.
The RP and PNP discharge after self-cleaning with water.
