Raghed Melhem
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Raghed Melhem has a total of 7 co-authors. Here are the top co-authors by number of shared publications:
Ahmed G. Abokhalil
Department of Sustainable and Renewable Energy Engineering, University of Sharjah, Sharjah, P.O. Box 27272, United Arab Emirates
2 shared publications- Anis Allagui
University of Sharjah
2 shared publications - Yomna Shaker
University of Science and Technology of Fujairah
2 shared publications - Ahmed S. Elwakil
University of Sharjah
1 shared publication - Ali Abou-Elnour
Engineering Department, University of Fujairah (UOF), Fujairah P.O. Box 2202, United Arab Emirates
1 shared publication - Fatma Mazen Ali Mazen
Fayoum University
1 shared publication
Latest Publications
- Open Access
Investigation of the Optimum Solar Insolation for PV Systems Considering the Effect of Tilt Angle and Ambient Temperature
As interest in PV installation has spiked in recent years, the need for optimizing several factors of PV performance has become crucial. These are tilt angle and solar cell temperature (taking into account ambient temperature) and their effect on solar insolation for solar photovoltaic (PV) systems. The objective of this study is to achieve the optimal tilt angle and cell temperature accordingly by developing a MATLAB program to reach the target of maximizing the received solar insolation. To achieve this, additional solar angles such as the azimuth, hour, latitude angle, declination angle, hour angle, and azimuth angle need to be calculated. By computing the solar insolation for specific regions of interest, specifically the Gulf Cooperation Council (GCC) countries, the desired results can be obtained. Additionally, the study aims to assess the influence of PV cell temperature on the I–V curves of commercially available PV modules, which will provide insights into the impact of temperature on the performance characteristics of PV cells. By employing a developed model, the study examined the combined collective influences of solar received radiation, tilt angle, and ambient temperature on the output power of PV systems in five different cities. The annual optimal tilt angles were found to be as follows: Mecca (21.4° N)—21.48°, Fujairah (25.13° N)—25.21°, Kuwait (29.3° N)—29.38°, Baghdad (33.3° N)—33.38°, and Mostaganem (35.9° N)—2535.98°. Notably, the estimated yearly optimal tilt angles closely corresponded to the latitudes of the respective cities. Additionally, the study explored the impact of ambient temperature on PV module performance. It was observed that an increase in ambient temperature resulted in a corresponding rise in the temperature of the PV cells, indicating the significant influence of environmental temperature on PV module efficiency. Overall, the findings demonstrate that adjusting the tilt angle of PV modules on a monthly basis led to higher solar power output compared to yearly adjustments. These results underscore the importance of considering both solar radiation and ambient temperature when optimizing PV power generation.
Open AccessInvestigation of the Optimum Solar Insolation for PV Systems Considering the Effect of Tilt Angle and Ambient Temperature
As interest in PV installation has spiked in recent years, the need for optimizing several factors of PV performance has become crucial. These are tilt angle and solar cell temperature (taking into account ambient temperature) and their effect on solar insolation for solar photovoltaic (PV) systems. The objective of this study is to achieve the optimal tilt angle and cell temperature accordingly by developing a MATLAB program to reach the target of maximizing the received solar insolation. To achieve this, additional solar angles such as the azimuth, hour, latitude angle, declination angle, hour angle, and azimuth angle need to be calculated. By computing the solar insolation for specific regions of interest, specifically the Gulf Cooperation Council (GCC) countries, the desired results can be obtained. Additionally, the study aims to assess the influence of PV cell temperature on the I–V curves of commercially available PV modules, which will provide insights into the impact of temperature on the performance characteristics of PV cells. By employing a developed model, the study examined the combined collective influences of solar received radiation, tilt angle, and ambient temperature on the output power of PV systems in five different cities. The annual optimal tilt angles were found to be as follows: Mecca (21.4° N)—21.48°, Fujairah (25.13° N)—25.21°, Kuwait (29.3° N)—29.38°, Baghdad (33.3° N)—33.38°, and Mostaganem (35.9° N)—2535.98°. Notably, the estimated yearly optimal tilt angles closely corresponded to the latitudes of the respective cities. Additionally, the study explored the impact of ambient temperature on PV module performance. It was observed that an increase in ambient temperature resulted in a corresponding rise in the temperature of the PV cells, indicating the significant influence of environmental temperature on PV module efficiency. Overall, the findings demonstrate that adjusting the tilt angle of PV modules on a monthly basis led to higher solar power output compared to yearly adjustments. These results underscore the importance of considering both solar radiation and ambient temperature when optimizing PV power generation.
- 1 October 2025
- Published by The Electrochemical Society in Journal of the Electrochemical Society
- Vol. 172 (10) , 100527
Transient Heat Diffusion in a Semi-Infinite Resistor-Capacitor Transmission Line in Response to a Voltage Step
Temperature change in electrochemical energy devices is a very important effect that takes place in the bulk ion-conducting electrolyte, electron-conducting electrodes, and at the interface in between. However, not enough theoretical studies are done on this problem. In this work, we assume a porous electrode/electrolyte system modeled as a typical one-dimensional, distributed RC transmission line (TL), where the resistors are used to represent the resistance of the bulk electrolyte, and the capacitors are used to represent the electric double-layer capacitance at the electrode/electrolyte interface. In response to a step voltage excitation, we derive first the resulting expression for the heat source term as a result of the interaction of current with the electric field. From there we solve analytically the unsteady heat conduction equation with the distributed source term using the Laplace and Fourier cosine integral transforms. The numerical simulations reveal the dependence of the electrical variables (voltage, current and power) on the electrical diffusion time, whereas, the temperature distribution shows a co-dependence on both the electrical and thermal diffusion times. These results can be used to optimize thermal management and prevent overheating in supercapacitors and batteries.
- 1 October 2025
- Published by The Electrochemical Society in Journal of the Electrochemical Society
- Vol. 172 (10) , 100527
Transient Heat Diffusion in a Semi-Infinite Resistor-Capacitor Transmission Line in Response to a Voltage Step
Temperature change in electrochemical energy devices is a very important effect that takes place in the bulk ion-conducting electrolyte, electron-conducting electrodes, and at the interface in between. However, not enough theoretical studies are done on this problem. In this work, we assume a porous electrode/electrolyte system modeled as a typical one-dimensional, distributed RC transmission line (TL), where the resistors are used to represent the resistance of the bulk electrolyte, and the capacitors are used to represent the electric double-layer capacitance at the electrode/electrolyte interface. In response to a step voltage excitation, we derive first the resulting expression for the heat source term as a result of the interaction of current with the electric field. From there we solve analytically the unsteady heat conduction equation with the distributed source term using the Laplace and Fourier cosine integral transforms. The numerical simulations reveal the dependence of the electrical variables (voltage, current and power) on the electrical diffusion time, whereas, the temperature distribution shows a co-dependence on both the electrical and thermal diffusion times. These results can be used to optimize thermal management and prevent overheating in supercapacitors and batteries.
- 14 July 2025
- Published by The Electrochemical Society in Journal of the Electrochemical Society
- Vol. 172 (7)
Analysis of a Network of Non-Identical Parallel-Connected Supercapacitors
Supercapacitors are widely used in various applications ranging from wind turbine pitch control systems to regenerative braking in electric and hybrid vehicles. This is due to their unique properties including high power density, scalability, high reversibility, and long operational lifetime. Although it is well-known that associating non-identical supercapacitors in parallel increases the equivalent capacitance of the network at a constant voltage, their dynamic behavior in the time domain remains underexplored. However, this cannot be simply done using the models of ideal capacitors, because supercapacitors exhibit a combined resistive-capacitor, dispersive nature. In this work, we analyze the behavior of supercapacitors connected in parallel (two or more different devices) in both the time and frequency domains using the constant phase element (CPE) as the building model. The CPE has a fractional impedance of the form $z(s)=(C_{\alpha} s^{\alpha})^{-1}$ with $C_{\alpha}$ a positive constant representing a pseudocapacitance, and $\alpha$ a dispersion coefficient that takes values between zero and one. From our theoretical analysis we obtain explicit expressions for the power-law-like voltage response of the supercapacitor network under constant current excitation in terms of the generalized Mittag-Leffler function. The derived forml{\ae} are validated by experimental time and frequency-domain data of real commercially-available devices.- 14 July 2025
- Published by The Electrochemical Society in Journal of the Electrochemical Society
- Vol. 172 (7)
Analysis of a Network of Non-Identical Parallel-Connected Supercapacitors
Supercapacitors are widely used in various applications ranging from wind turbine pitch control systems to regenerative braking in electric and hybrid vehicles. This is due to their unique properties including high power density, scalability, high reversibility, and long operational lifetime. Although it is well-known that associating non-identical supercapacitors in parallel increases the equivalent capacitance of the network at a constant voltage, their dynamic behavior in the time domain remains underexplored. However, this cannot be simply done using the models of ideal capacitors, because supercapacitors exhibit a combined resistive-capacitor, dispersive nature. In this work, we analyze the behavior of supercapacitors connected in parallel (two or more different devices) in both the time and frequency domains using the constant phase element (CPE) as the building model. The CPE has a fractional impedance of the form $z(s)=(C_{\alpha} s^{\alpha})^{-1}$ with $C_{\alpha}$ a positive constant representing a pseudocapacitance, and $\alpha$ a dispersion coefficient that takes values between zero and one. From our theoretical analysis we obtain explicit expressions for the power-law-like voltage response of the supercapacitor network under constant current excitation in terms of the generalized Mittag-Leffler function. The derived forml{\ae} are validated by experimental time and frequency-domain data of real commercially-available devices.- Open Access
- 9 May 2023
- Published by Wiley in International Journal of Energy Research
- Vol. 2023, 1-17
Optimum Tilt Angle and Solar Radiation of Photovoltaic Modules for Gulf Collaboration Council Countries
This article focuses on the optimization of tilt angle for solar panels in the Gulf Cooperation Council (GCC) countries. The tilt angle is a crucial factor that affects the amount of solar radiation received by the solar panel. The study uses a mathematical model to calculate the optimal tilt angle based on the latitude and longitude of the location and compares the results with the PVWatts calculator. The importance of selecting the optimal tilt angle for maximizing solar energy production is emphasized. The study finds that the mathematical model and PVWatts calculator are in good agreement, except for the negative tilt angles calculated by the model. The article also provides monthly, seasonally, and yearly irradiance values for the GCC countries calculated using the PVWatts calculator. It suggests that changing the tilt angle 12 times during the year can enhance the power output by 10.9%. The results show that the monthly automated angle has a maximum in December and a minimum in June, with Oman having the highest maximum angle of 50.5 and the lowest minimum angle of -10.58. Kuwait has the highest maximum angle of 58.33 and the lowest minimum angle of -2.75. The results are verified by the PVWatts calculator, showing a good similarity with a percentage of error around 3%. The study highlights the importance of selecting the optimal tilt angle to achieve maximum solar energy production in the GCC countries. The mathematical model and PVWatts calculator can serve as tools to calculate the optimum tilt angle for solar panels.
- 9 May 2023
- Published by Wiley in International Journal of Energy Research
- Vol. 2023, 1-17
Open AccessOptimum Tilt Angle and Solar Radiation of Photovoltaic Modules for Gulf Collaboration Council Countries
This article focuses on the optimization of tilt angle for solar panels in the Gulf Cooperation Council (GCC) countries. The tilt angle is a crucial factor that affects the amount of solar radiation received by the solar panel. The study uses a mathematical model to calculate the optimal tilt angle based on the latitude and longitude of the location and compares the results with the PVWatts calculator. The importance of selecting the optimal tilt angle for maximizing solar energy production is emphasized. The study finds that the mathematical model and PVWatts calculator are in good agreement, except for the negative tilt angles calculated by the model. The article also provides monthly, seasonally, and yearly irradiance values for the GCC countries calculated using the PVWatts calculator. It suggests that changing the tilt angle 12 times during the year can enhance the power output by 10.9%. The results show that the monthly automated angle has a maximum in December and a minimum in June, with Oman having the highest maximum angle of 50.5 and the lowest minimum angle of -10.58. Kuwait has the highest maximum angle of 58.33 and the lowest minimum angle of -2.75. The results are verified by the PVWatts calculator, showing a good similarity with a percentage of error around 3%. The study highlights the importance of selecting the optimal tilt angle to achieve maximum solar energy production in the GCC countries. The mathematical model and PVWatts calculator can serve as tools to calculate the optimum tilt angle for solar panels.