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Öğe Evaluation of residential stand alone photovoltaic systems in mega cities of the world(Taylor & Francis Inc, 2024) Akgayev, Berkeli; Unsur, VeyselGrowing concerns about the climate change accompanied with energy crisis due to the unrest in the world have pushed the energy market to utilize sustainable and secure alternatives such as solar photovoltaics (PV). However, for residential consumers, the primary concerns are the reliability of the supply and the cost of PV-generated electricity. This study reports on the economic feasibility and technical analysis of PV systems in megacities worldwide. Nine mega cities, Beijing, Berlin, Istanbul, London, New Delhi, New York, Paris, Seoul, and Tokyo, have been selected based on their significant population sizes and the pronounced demand for electricity independence among residents. The annual production, load matching, and PV-electricity and battery dispatch are discussed, with Lazard's levelized cost of electricity (LCOE) and net present value (NPV) employed as economic indicators. While calculated LCOEs ranged from $0.084/kWh to $0.27/kWh across different cities, the NPVs were predominantly negative, varying approximately between -$2,000 and -$20,000, with Berlin as an exception. Finally, a sensitivity analysis was conducted, revealing that the LCOE is more sensitive to financial parameters than to module efficiency and irradiation.Öğe Screen printable fire through nickel contacts for silicon solar cells(Elsevier, 2023) Akgayev, Berkeli; Sezgin, Aysegul; Yilmaz, Mucahit; Unsur, VeyselMetallization of crystalline silicon (Si) solar cells is indispensable for reducing the cost while increasing the overall efficiency. Developing alternative materials to the most commonly used screen printed silver (Ag) contacts is a critical factor. Here, in this study, a nickel (Ni) metal paste consisting of Ni metal particles, glass frit and an organic vehicle is fabricated for screen printed Ni contacts. To prevent possible Schottky barrier formation, a graphene layer is placed on the front surface of the Si solar cell between Ni and Si forming a metal-2Dsemiconductor structure ensuring the ohmic (or ohmic-like) contacts. It is demonstrated here that the graphene is transferred successfully onto the textured front surface of the cells and G/2D peaks are observed clearly, indicating the good quality of the graphene layer. Constituents of Ni metal paste, glass frit and organic vehicle, are fabricated in concordance with nickel metal powder and mixed to achieve optimal electrical output parameters. The findings suggest that the transition temperature of the glass frit is between 270 degrees C and 300 degrees C resulting in around 475 degrees C softening temperature, which gives excellent etching behavior to the paste. The average contact resistance of the screen printed Ni contacts governed by etching process is measured around 6.9 m & omega; cm2. The SEM images of the contacts show a uniform distribution and sintering behavior similar to that of silver counterparts. The light current-voltage measurements read the open circuit voltage of 660 mV, the short circuit density of 39.11 mA/cm2 and the fill factor of 81.4% resulting in around 21% efficiency.