voltage. The threshold voltage was 9.8 kVp-p for the 10-mm-pitch
device and 8.4 kVp-p for the 7-mm-pitch device.
The maximum cleaning efficiency was approximately 80% and
was achieved at a low frequency (less than 20 Hz). The cleaning
performance decreased at higher frequencies because particle
motion cannot follow the high-speed change of polarity
[21,33,35,36]. However, low-frequency operation is not an issue
because high-speed cleaning is not necessary for this system.
Improved device
The cleaning performance of the system was further improved
by adopting a V-shaped configuration for the wire electrodes, as
shown in Fig. 8. An angle of 0 corresponds to the horizontal
(original) configuration and an angle of 90 corresponds to the
vertical configuration. It is clear that a V-shaped configuration
(with angles between 45 and 75) for the electrodes improved the
cleaning performance of the system. Careful observation of particle
motion made using the high-speed microscope camera and numerical
calculations suggest that when the V-shaped configuration
is used, some particles on the panel are repelled not only downward
but also toward the lateral sides of the panel, and this phenomenon
increases the cleaning efficiency.
Effect of surface loading of sand
El-Shobokshy et al. [37] reported a mean deposition rate of sand
on solar panels of 0.387 g/m2/day and a cumulative dust deposition
in one month of approximately 10 g/m2 in Riyadh, Saudi Arabia
(latitude 24.9). A much higher level of cumulative sand deposition,
more than 400 g/m2 in one month, has been recorded at Kuwait
international airport [38]. Because the amount of sand deposition
on the panel depends on the geographic and meteorological condition
of the location where the solar panels are installed, the