# Reduction of Dust on Solar Panels through Unipolar Electrostatic Traveling Wave
## 1 Introduction
Moreover, cleaning performance has been found to increase with a weak wind parallel to the direction of the plate, although high wind speed increases dust accumulation [21]. If the sum of the electrostatic force and wind force are greater than the sum of the gravitational force and the bonding force between the particles and the glass plate, dust particles will be removed from the panel [23]. The gravitational force should not be neglected as the specific gravity of the dusts and the slope of the cleaning plate are changed by the location where the SPP is located [23]. Electrostatic cleaning works by ionizing the dust on the surface of the solar panel with an electrostatic precipitator and then pushing the dirt from the panel using a set of electrodes [16]. The dust precipitator has varying efficiency for removal of dust depending on voltage and operating conditions [27]. Electrodynamic dust shields [28; 29; 30] and electric curtains for dust removal have been proposed [31]. It has also been determined that dust particles can be cleaned from the surface of panels by hydrophobic wetting under an electrostatic effect [32]. Dust particles consist of the oxide of many elements, including Si, O, Ca, K, Na, Cl, S, Fe and Mg, with various shapes and sizes [6; 32]. Other, rarer, elements are also found, including Nb, Cl, Ti, P, Fr, Au and Ba [6]. During humid weather conditions, water condensation on the dust particles creates a chemically active solution, that adheres strongly to the surface of the panels and improves the adhesion of the dust particles [32]. This can make it difficult to remove dust particles by the electrostatic method. Particle size is also important. For example, dust particles in Doha, Qatar, have an average diameter of 2.3 \(\upmu\)m [14]. Particles larger than 25 \(\upmu\)m in diameter and smaller than 300 \(\upmu\)m in diameter are efficiently cleaned by the electrostatic method [21]. This can be explained by small-sized dust particles forming clusters around large-sized particles and small-sized particles remaining in the air longer than large-sized dust particles and resettling [32]. In addition, small particles tend to stick to the surface of the glass, reducing the efficiency of the cleaning system [21; 23]. For large particles, their heavier weight prevents them from bouncing and moving [21]. Therefore, other approaches are investigated to improve cleaning performance. One way to improve electrostatic cleaning efficiency is to create a stronger electrostatic force at high voltage [23]. Cleaning efficiency is improved when the thickness of the cover glass is thin due to the reducing distance from the electrodes to the surface of the cap glass, and a high electrostatic field is formed on the cap glass surface [23]. This field pushes and removes the dust particles from the surface of the glass, regardless of whether the dust particles were initially charged [8]. One study [24] modeled the electrostatic particle removal as a thrust, sliding and rolling mechanism. Another study showed that dust can be displaced on an inclined panel using low-frequency high-voltage electricity [23]. When a single-phase square wave voltage is applied to parallel electrodes, a moving wave is not produced and, while the particles are pushed off the plate, they are not transported in any direction and are transported downwards by gravity [21]. One study applied a voltage of 1 kV p-p to parallel electrodes with diameter of 0.3 mm, length of 100 mm, and placed at an interval of 4 mm [32]. The use of a hydrophobic surface showed that dust residues can be removed by subjecting dust particles to an electrostatic force. One study [21], using a voltage of 9.8 kV for 10 mm and 8.4 kV for 7 mm at low frequency (less than 20 Hz), achieved a maximum cleaning efficiency of about 80%. At low voltages (0.7 kVp-p) the dust continues to adhere to the surface, whereas at high voltages (11.8 kVp-p) the dust is displaced by the same electrodes [28].