Quantification and Mitigation of the PV-Soiling in Bifacial Modules Configuration

Bifacial PV modules technology is emerging as a reliable solution to enhance the output power energy compared to traditional monofacial modules since both sides of the PV module absorb solar radiation. In addition, bifacial PV modules reduce the LCOE and might be a natural soiling mitigation approach, with small or no soiling in the rear side of the module. In this work, dust accumulation was measured for bifacial configuration based on uncoated and silica-coated glass coupons. The outdoor testing was carried out in the harsh desert conditions of the state of Qatar. Samples were characterized every two months to assess the soiling-rate and the silica coating degradation. Silica films were deposited by a reactive RF magnetron sputtering of a SiO2 target under different oxygen to argon flow ratios [r(O2) = O2/Ar, ranging from 0 to 25%]. The refractive index (n), extinction coefficient, total transmission and reflectance were systematically investigated, and three-dimensional average roughness data construction was carried out to probe the surface morphology. Contact angle measurements were performed to assess the wettability of these silica coatings as a function of r(O2). The dust accumulation (soiling) was expressed in terms of the surface coverage (SC) by the dust particles and then correlated to the r(O2) and the tilt angle (θ)of these samples. Both front and rear sides of these coupons were considered and empirical equations representing the SC were deduced for each r(O2) as a function θ. The degradation of these silica coatings was assessed through the micro hardness (H) analysis and has shown that after 24 months of outdoor exposure, the films hardness decreased by only 5 %. Finally, a computational analysis based on the measured experimental optical properties were performed to simulate the photovoltaic (PV) device performance and a clear improvement in the photoconversion efficiency was observed with respect to r(O2). Several optimizations and simulations are currently ongoing to see the effects of soiling rate, albedo, rain, cleaning costs and frequency on the bifacial PV system.