In the study of the feasibility of solar tracking systems for crystalline silicon photovoltaic (PV) panels in hot and cold regions, it is argued recently that a tracking system is not necessary for sunbelt countries owing to the overheating that results from excessive exposure to solar irradiance. This conclusion has been formulated based on a mathematical model, which in turn is based on the assumption that the PV module temperature can be calculated using an empirical relation of this temperature to ambient temperature, available solar irradiance, and nominal operation cell temperature (NOCT). To support this conclusion, it is claimed that the mathematical model is validated experimentally. However, this assumption is vague and widely used in the literature. The objective of the present work is to reevaluate the above-mentioned assumption and to discuss the results deriving from it. It is shown experimentally in the present work that the above-mentioned assumption overestimates the PV module temperature. At a solar irradiance of 900 W/m 2 , ambient temperature of 25 ℃, and wind speed of 5 m/s, the measured PV module temperature is lower than the value calculated based on the mentioned assumption by 29.26%.
• ' The outhors are working on a project sponsored by the supreme council of. Universities to deal with the subject of duplex powder preform forgings. As a part of its relevant program,the effect on hardness and tensile strength of liquid phase sintering was investigated. For such a study,specimens in circular and rectangular cross sections were produced from EMP 4607 steel powders with the additions of some different brazing alloy powders with an amount of 3.5%. Similar specimens were also prepared from DT 4607 steel powder only. Brinell hardness values were measured for cylindrical specimens. Tensile tests were performed by making use of the specimens with rectangular cross sections.The effect on mechanical properties of both sintering time and liquid phase sintering was observed.The results obtained at this stage were discussed with the aid of micro-structures examination.
To develop the EPR material quality, electrical and structural charact erizations were executed by EBIC, LBIC, TEM, ECP and X diffraction. Two interface types were observed; some interfaces parallel and constitued by Σ3 and Σ9 twins, show low electrical activity; other are curved with no defined index and higher electrical activity. Some orientations such as (111),(220),(331) appear more frequently.
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