No abstract

Proper installation, especially the tilt angle, directly affects the system’s output. Determination of the optimal tilt angle of a solar cell module depends on the solar radiation characteristics, season, and reflectivity in the local area. One of the important parameters that affect the performance of a solar collector is its tilt angle with the horizon. This is because of the variation of tilt angle changes the amount of solar radiation reaching the collector surface. A mathematical model is presented for determining the optimum tilt angle at different orientations (surface azimuth angle) for the solar collector, on a daily basis, as well as for a specific period such as monthly, seasonally and yearly basis. The optimum angle was computed by searching for the values for which the extraterrestrial solar radiation on the collector surface is a maximum for a particular day or a specific period. The results reveal that changing the tilt angle 12 times in a year (i.e. using the monthly optimum tilt angle) or even 4 times/year (i.e. using the seasonally optimum tilt angle) maintains approximately the total amount of solar radiation near the maximum value that is found by changing the tilt angle daily to its optimum value. This achieves a yearly gain in solar radiation of 5.5% at 0o latitude to 78% at 60o latitude more than the case of a solar collector fixed on a horizontal surface.

: One of the important parameters that affect the performance of a solar collector is its tilt angle with the horizon. This is because of the variation of tilt angle changes the amount of solar radiation reaching the collector surface. Meanwhile, is the rule of thumb, which says that solar collector Equator facing position is the best, is valid for tropical region? Thus, it is required to determine the optimum tilt as for Equator facing and for Pole oriented collectors. In addition, the question that may arise: how many times is reasonable for adjusting collector tilt angle for a definite value of surface azimuth angle? A mathematical model was used for estimating the solar radiation on a tilted surface, and to determine the optimum tilt angle and orientation (surface azimuth angle) for the solar collector at any latitude. This model was applied for determining optimum tilt angle and orientation in the tropical zones, on a daily basis, as well as for a specific period. The optimum angle was computed by searching for the values for which the radiation on the collector surface is a maximum for a particular day or a specific period. The results reveal that changing the tilt angle 12 times in a year (i.e. using the monthly optimum tilt angle) maintains approximately the total amount of solar radiation near the maximum value that is found by changing the tilt angle daily to its optimum value. This achieves a yearly gain in solar radiation of 11% to 18% more than the case of a solar collector fixed on a horizontal surface.

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 possible energy gain in the case of two axes tracking as well as a fixed system with Equator facing tilted solar PV module with latitude angle and daily optimum slope is calculated basing on Hottel clear sky radiation model (HM) and ex-terrestrial solar radiation model (ESRM). The calculated results are compared with the data obtained from a PV system with 252 Wpeak power module installed on a two axes solar tracker which was designed and constructed locally. The main components of the tracker are introduced. It was found that, the maximum possible energy gain calculated basing on HM and ESRM are practically identic. For example, on 25 August from 8 O’clock to solar noon, the hourly energy gain values of HM are 1.672, 1.336, 1.170, 1.098 and 1.097 while they are 1.677, 1.337, 1.170, 1.098 and 1.098 in the case of ESRM. The corresponding measured values on the same day are 1.746, 1.36, 1.16, 1.043 and 1.027. Thus, the theoretical data are consistent with the measured ones. Moreover, it was found that the tracked system is more economic feasible than latitude tilted similar one with a relative solar energy gain of 0.32%.