Environmental dust particles repelling from a hydrophobic surface under the electrostatic influence are considered and the dynamics of the dust particles are analyzed incorporating the high speed camera. The velocity of the repelled dust particles are formulated using the force balance incorporating the forces associated with the electrostatic repulsion, particle adhesion, particle drag, and the inflight particles interaction under the charge influence. The functionalized silica particles are deposited on the glass surface towards achieving a hydrophobic wetting state on the surface. An electronic circuitry is designed and built while generating the electrostatic effect, in the pulse form, on the dust particles located on the surface of the hydrophobic plate. Findings revealed that functionalized silica particles deposited surface results in hydrophobic wetting state with contact angle in the order of 158° ± 2° and contact angle hysteresis of 2° ± 1°. The electrostatic impulsive force generated on the plate surface enables to repel most of the sizes of the dust particles; however, some of the small dust particles remain as the residues on the surface after the electrostatic influence. The dust particle velocity predicted from the analytical formulation agrees with that obtained from the high speed camera data. The pinning force of the small size particles (0.6 µm≤), due to adhesion on the surface, is found to be larger than the average size particles (∼1.2 µm), which in turn, suppresses these particles repelling from the surface under the electrostatic influence. The residues of the dust particles on the as received glass surface after dust repelling are more than those residues on the hydrophobic surface. This behavior is associated with the dust particles adhesion on the surface. Consequently, hydrophobic wetting state on the plate surface improves the dust particle repelling from the surface.

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Environmental Dust Particles Repelling from A Hydrophobic Surface under Electrostatic Influence.

Soiling, the accumulation of dust, is a detrimental influencing factor for solar energy generation in desert climates, as it blocks the sun light and therefore reduces the energy yield of photovoltaic (PV) modules. Accordingly, soiling requires mitigation by frequent cleaning. However, regular cleaning of PV modules can damage glass surfaces and commonly used anti-reflective coatings (ARCs), which typically enable 2–3% or even higher increases in the power output. Within this study, the damage potential of dry manual cleaning on uncoated solar glass and two different commercial ARCs is examined. For this, a cleaning test apparatus and methodology applicable to full size PV modules were developed. The changes in the optical behavior of coated and uncoated glass samples were investigated both theoretically and experimentally, including the analysis of spectroscopic reflectance and microstructural damage patterns. It is found that dry brushing on dusty surfaces causes only minor damage to uncoated glass surfaces with no changes in hemispherical reflectance, even at high numbers of brush cycles. In contrast, both the tested coatings indicate significant reductions of the AR performance, already after 100 brush cycles with increasing reflectance up to 2.3% at 600 nm. Furthermore, the coatings indicated different stabilities during extended abrasion testing, but still retained the AR properties after 500 cycles of testing, reflecting harsh and bi-weekly cleaning over 20 years of operation. Localized coating removal and—to a less extent—coating thinning were identified as ARC degradation mechanisms, which were supported by spectroscopy experimental and simulation results for microstructural analysis of the samples.

Resilience of industrial PV module glass coatings to cleaning processes

Enhancing the efficiency of rooftop solar photovoltaic panel with simple cleaning mechanism

Two dust samples were collected from the same solar panels on June, 2017 in Dakar. The first was sent to Ithemba Labs (South Africa) and the second to Lincon Nebraska University (USA) for structural and physical properties study. This work aims to evaluate the dust impact on PV efficiency. The study shows that these particles have a non-spherical shape with sizes between 0 and 50 μm. However, most of them have a size about 2 μm. Elemental composition based on Energy Dispersive X-ray microanalysis indicates that dust is dominated by elements such as O, Na, Mg, Al, Si, Cl, K, Ca, Ti, Mn and Fe. Some elements such as P, S, Zn, Sr, Zr and Cr are minority or in traces form. The analysis shows that this African dust is a mixture of different chemical compounds with a predominant phase consisting of SiO2 type quartz about 73.8% of the total and the second phase is certainly calcite(CaCO3) representing 13.6% of the collected particles. The rest (12.6%) is presumably a mixture of Iron Oxide Chloride (FeOCl), Mantienneite (Al2FeH33K0.5Mg3O34P4Ti) and Kaersutite (Al2Ca2Mg6NaO24Si6). Finally, the diffuse reflectance spectroscopy (DRS) shows that these particles reflect more than 70% of the irradiation reaching the PV panels surface.

Structural and physicochemical properties of dust collected on PV panels surfaces and their potential influence on these solar modules efficiency in Dakar, Senegal, West Africa

This study was carried out at the International Center for Training and Research in Solar Energy (CIFRES) and its main purpose was to study the performance of a solar module cleaning system. To handle this work, a measuring platform consisting of two polycrystalline (pc-Si) PV modules was designed. The modules were connected to a waterless cleaning system on the surface of the solar panels. The platform also contained a temperature sensor on the surface of the module, a pyranometer, shunt resistors (for current measurement), and an acquisition unit. This platform was exposed under real conditions and measurements of the parameters were taken in increments of ten seconds. Only one of the two modules was cleaned daily, and an evaluation of the degradation rate of the short-circuit current (Isc) of the dust module with respect to the cleaned module was carried out. After one month of exposure, the analysis of the results showed a degradation rate of 17.13% of the short circuit current (Isc) of the dirty module compared to the clean module. Compared to the initial conditions under the standard test conditions, a degradation of 10.16 and 24.09%, respectively for the clean module and the dirty module was obtained. This work also showed that a polynomial relation exists between the degradation rate and the dust deposition density with a coefficient of determination of 0.9933.

	Key words: Photovoltaic modules, dust, short-circuit current, impact, automatic cleaning without water, degradation.

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Mamadou Sylla

Papers

Study of the performance of a system for dry cleaning dust deposited on the surface of solar photovoltaic panels