Amir Abdallah

Structural and physical properties of the dust particles in Qatar and their influence on the PV panel performance

Recently, extensive R&D has been conducted, both by industry and academia, to significantly raise the conversion efficiency of commercial photovoltaic (PV) modules. The installation of PV systems aimed at optimizing solar energy yield is primarily dictated by its geographic location and installation design to maximize solar exposure. However, even when these characteristics have been addressed appropriately, there are other factors that adversely affect the performance of PV systems, namely the temperature-induced voltage decrease leading to a PV power loss, and the dust accumulation (soiling). The latter is the lesser acknowledged factor that significantly influences the performance of PV installations especially in the Middle East region. In this paper we report on the investigation of the structural and physical properties of the desert-dust particles in the State of Qatar. The dust particles were collected directly from the PV panels installed in desert environment and characterized by different techniques, including scanning electron, optical and atomic force microscopies, X-ray diffraction, energy-dispersive, UV-Vis, micro-Raman and Fourier transform infrared spectroscopy. The vibrating sample magnetometry analyses were also conducted to study the magnetic properties of the dust particles. The influence of the dust accumulation on the PV panel performance was also presented and discussed.

The impact of silicon solar cell architecture and cell interconnection on energy yield in hot & sunny climates

Extensive knowledge of the dependence of solar cell and module performance on temperature and irradiance is essential for their optimal application in the field. Here we study such dependencies in the most common high-efficiency silicon solar cell architectures, including so-called Aluminum back-surface-field (BSF), passivated emitter and rear cell (PERC), passivated emitter rear totally diffused (PERT), and silicon heterojunction (SHJ) solar cells. We compare measured temperature coefficients (TC) of the different electrical parameters with values collected from commercial module data sheets. While similar TC values of the open-circuit voltage and the short circuit current density are obtained for cells and modules of a given technology, we systematically find that the TC under maximum power-point (MPP) conditions is lower in the modules. We attribute this discrepancy to additional series resistance in the modules from solar cell interconnections. This detrimental effect can be reduced by using a cell design that exhibits a high characteristic load resistance (defined by its voltage-over-current ratio at MPP), such as the SHJ architecture. We calculate the energy yield for moderate and hot climate conditions for each cell architecture, taking into account ohmic cell-to-module losses caused by cell interconnections. Our calculations allow us to conclude that maximizing energy production in hot and sunny environments requires not only a high open-circuit voltage, but also a minimal series-to-load-resistance ratio.

Improved Self-cleaning Properties of an Efficient and Easy to Scale up TiO 2 Thin Films Prepared by Adsorptive Self-Assembly

Transparent titania coatings have self-cleaning and anti-reflection properties (AR) that are of great importance to minimize soiling effect on photovoltaic modules. In this work, TiO2 nanocolloids prepared by polyol reduction method were successfully used as coating thin films onto borosilicate glass substrates via adsorptive self-assembly process. The nanocolloids were characterized by transmission electron microscopy and x-ray diffraction. The average particle size was around 2.6u2009nm. The films which have an average thickness of 76.2u2009nm and refractive index of 1.51 showed distinctive anti soiling properties under desert environment. The film surface topography, uniformity, wettability, thickness and refractive index were characterized using x-ray diffraction, atomic force microscopy, scanning electron microscopy, water contact angle measurements and ellipsometry. The self-cleaning properties were investigated by optical microscopy and UV-Vis spectroscopy. The optical images show 56% reduction of dust deposition rate over the coated surfaces compared with bare glass substrates after 7 days of soiling. The transmission optical spectra of these films collected at normal incidence angle show high anti-reflection properties with the coated substrates having transmission loss of less than 6% compared to bare clean glass.

Emerging frontiers of N-Type silicon material for photovoltaic applications: The impurity-defect interactions

Solar photovoltaic (PV) energy is one of the main renewable energy sources, and crystalline silicon presently dominates completely this field. To date, the positively doped (p-type) crystalline silicon (c-Si) wafers have occupied most of the solar PV market. However, cells made with n-type crystalline silicon wafers are actually more efficient. This is because the material properties offered by n-type crystalline silicon substrates are suitable for higher efficiencies. Properties such as the absence of boron-oxygen related defects and a greater tolerance to key metal impurities by n-type crystalline silicon substrates are major factors that allow these better efficiencies. This yields a better bulk minority carrier lifetime, therefore, the performance of commercial photovoltaic n-type Si devices is strongly controlled by the surface and contact quality. A well-designed solar cell processing sequence can mitigate their effects to yield high efficiency devices. We propose here a review of the properties of defects, impurities, and impurity-defect interactions that can occur during crystal growth and device processing, as well as the high-efficiency fabrication process flow allowed by the use of n-type c-Si.