Diurnal pattern of global solar radiation in the tropics: a case study in Malaysia

Global solar radiation patterns in Bangi (2°56′7.3″N, 105°47′0.2″E), Malaysia are discussed. The frequency of occurrence of the various solar radiation patterns observed over a 5-year period is derived. These observations will provide useful information for the design of solar energy systems and equipment for installation in tropical countries having a similar global solar radiation pattern.     

The wind energy potential of Malaysia

Wind data collected at ten stations in Malaysia were analysed for wind energy potential. The data were collected over a ten-year period (1982–1991). The results were presented as a Weibull distribution and analysis indicated that the station at Mersing has the greatest potential, with a mean power density of 85.61 W/m² at 10 m above sea level.     

Thermal performance of the double-pass solar collector with and without porous media

This paper presents the thermal performance of a double-pass solar collector with and without porous media in the second or lower channel of the collector. The experimental setup has been designed to study the thermal performance over a range of design and operating conditions. Several important relationships between the design and operating conditions have been obtained. These relationships effect the thermal performance of the double-pass solar collector. The relationships include the effect of changes in upper and lower channel depth on the thermal efficiency with and without porous media. Moreover, the effects of mass flow rate, solar radiation, and temperature rises on the thermal efficiency of the double-pass solar collector have been studied. The study concluded that the presence of porous media in the second channel increases the outlet temperature, therefore increases the thermal efficiency of the systems.     

Double-Pass Photovoltaic-Thermal Solar Collector

A hybrid photovoltaic-thermal (PV/T) solar air heater system which generates both electricity and heat energy simultaneously was studied. This hybrid system consists of monocrystalline silicon cells pasted to an absorber plate with fins attached at the other side of the absorber surface. Air as heat removing fluid is made to flow through an upper channel and then under the absorber plate or lower channel of the collector. Only a small part of the absorbed solar radiation is converted to electricity, while the rest increases the temperature of the cells. Improvements to the total efficiency of the system can be achieved by the use of a double-pass collector system and fins. This paper presents the experimental and theoretical studies on a finned double-pass PV/T solar air heater suitable for low temperature applications. A steady-state closed-form solution to determine the outlet and mean photovoltaic temperature has been obtained. An experimental setup has been developed. Comparisons are made between the experimental and theoretical results and close agreement, is obtained.     

Simple indoline based donor–acceptor dye for high efficiency dye-sensitized solar cells

A simple metal-free donor–acceptor type sensitizer U01, bearing strong electron donor indoline-triphenylamine was synthesized for panchromatic sensitization of TiO₂ nanocrystalline film. Photovoltaic properties of U01 showed remarkably enhanced light harvesting due to the presence of strong electron donor and robust structure. The new U01 sensitized solar cell exhibited a photovoltaic performance: a short-circuit photocurrent density (J_sc) of 10.70 mA cm⁻², an open-circuit photovoltage (V_oc) of 0.758 V and a fill factor (FF) of 0.74, corresponding to an overall conversion efficiency of 6.01% under standard global AM 1.5 solar light condition. Our results suggest that indoline-triphenylamine based robust D–A molecular architecture is a highly promising class of panchromatic sensitizers for improvement of the performance of dye-sensitized solar cells (DSCs).     

Performance analysis of solar-assisted chemical heat-pump dryer

A solar-assisted chemical heat-pump dryer has been designed, fabricated and tested. The performance of the system has been studied under the meteorological conditions of Malaysia. The system consists of four main components: solar collector (evacuated tubes type), storage tank, solid-gas chemical heat pump unit and dryer chamber. A solid-gas chemical heat pump unit consists of reactor, condenser and evaporator. The reaction used in this study (CaCl2-NH₃). A simulation has been developed, and the predicted results are compared with those obtained from experiments. The maximum efficiency for evacuated tubes solar collector of 80% has been predicted against the maximum experiment of 74%. The maximum values of solar fraction from the simulation and experiment are 0.795 and 0.713, respectively, whereas the coefficient of performance of chemical heat pump (COP^h) maximum values 2.2 and 2 are obtained from simulation and experiments, respectively. The results show that any reduction of energy at condenser as a result of the decrease in solar radiation will decrease the coefficient of performance of chemical heat pump as well as decrease the efficiency of drying.     

Water management in a single cell proton exchange membrane fuel cells with a serpentine flow field

Gas and water management is the key to achieving good performance from a polymer electrolyte membrane fuel cell (PEMFC) stack. Imbalance between production and evaporation rates can result in either flooding of the electrodes or membrane dehydration, both of which severely limit fuel cell performance. In the present study, a mathematical model was developed to evaluate moisture profiles of hydrogen and air flows in the flow field channels of both the anode and the cathode. For model validation, a single fuel cell was designed with an active area of 200 cm². Six humidity sensors were installed in the flow fields of both the anode and the cathode at 457 mm, 1266 mm and 2532 mm from the inlets. The experiment was performed using an Arbin Fuel Cell Test Station. The temperature was varied (25 °C, 40 °C, 50 °C and 60 °C), while hydrogen and air velocities were fixed at 3 L min⁻¹ and 6 L min⁻¹, respectively, during the operation of the single cell. The feed relative humidity at the anode was fixed at 1.0, while the feed relative humidity at the cathode was fixed at 0.005 (dry air). All humidity sensor readings were taken at steady state after 2 h of operation. Model predictions were then compared with experimental results by using the least squares algorithm. The moisture content was found to decrease along the flow field at the anode, but to increase at the cathode. The moisture content profile at the anode was shown to depend on the moisture Peclet number, which decreased with temperature. On the other hand, the moisture profile at the cathode was shown to depend on both the Peclet number and the Damkohler number. The trend of the Peclet number in the cathode followed closely that of the anode. The Damkohler number decreased with temperature, indicating increasing moisture mass transfer with temperature. The moisture profile models were successfully validated by the published data of the estimated overall mass transfer coefficient and moisture effective diffusivity of the same order of magnitude. The strategy of saturating the hydrogen feed and using dry air, as in the present work, has been shown to successfully prevent water droplet formation in the cathode, and hence prevent flooding.     

Review of the membrane and bipolar plates materials for conventional and unitized regenerative fuel cells

Fuel cell or hydrogen systems offer the potential for clean, reliable and on-site energy generation. This article review current literature with the objective of identifying the latest development in membrane and bipolar plates for the conventional fuel cell and unitized regenerative fuel cell (URFC). The result shows that the choice of both the bipolar plates and the catalysts for URFC electrodes is a delicate task, for bipolar plate the corrosion in the oxygen side will be the major problem and for the electrodes a very good candidate for fuel cell mode will not function well in the electrolyser mode and therefore it is suggested that a compromise should be considered. It is recommended that aluminum, titanium or for best results titanium with a gold-coated layer is a suitable candidate as the bipolar plate and Pt/IrO_X or Pt/Ru is suitable for an oxygen side catalyst in the URFC. For the conventional fuel cell the task is more easer because the corrosion problem is no more effective and thus the main goals for most of the studies was to concentrate on bipolar plate cost reduction, increase electrical conduction and reducing the platinum loading rate for catalyst.     

Effect of CdCl2 treatment on physical properties of CdTe films with different compositions fabricated by chemical molecular beam deposition

CdTe films with different compositions (Cd-rich, Te-rich and stoichiometric) were fabricated by revolutionary novel and low cost chemical molecular beam deposition (CMBD) method in the atmospheric pressure hydrogen flow. Cd and Te granules were used as precursors. The films were deposited on ceramic (SiO₂: Al₂O₃) substrates at 600°C. The growth rate was varied in the range of 20–30 Å/s. The composition of the samples was changed by controlling the molecular beam intensity (MBI) ratio Cd/Te. Effect of CdCl₂ treatment on morphology, photoluminescence and electrical properties of CdTe films was investigated by AFM, Raman, photoluminescence (PL) and Hall methods.