Fuel cells and solar energy are promising candidates for electricity generation. It is forecast that fuel cells and solar power systems will play an important role in reducing the greenhouse gas footprint and replacing fossil fuels. Therefore, the limitations of fuel cells and solar power systems, such as low efficiency, high cost, and low reliability, must be addressed appropriately to enable their full potentials. Metal foam is a new class of material that has gained immense attention due to its excellent properties suitable for a wide range of applications. Its unique characteristics distinguish it from typical solid metals. The properties of metal foam can be modified during the fabrication stage by manipulating its physical structure. The goal of this paper is to review the application of metal foam in fuel cells and solar power systems. Besides, the performance of metal foam in fuel cells and solar systems is also discussed. Metal foam has been applied to the electrodes, gas diffusion layer and flow field of fuel cells to enhance performance, especially in regard to current density and flow distribution. Furthermore, metal foam is a heat exchanger for the solar energy harvesting system to improve its efficiency. Superior performances in experimental testing allows the possibility of commercialization of metal foam products in the renewable energy field.

Concentrated photovoltaic cell (CPV) is a solar energy harvesting device that converts solar energy into electrical energy. However, the performance and efficiency of the CPV are heavily dependent on the temperature. Besides, nonuniformity of temperature distribution on the CPV will lead to thermal aging and affects the cycle life. Hence, an effective cooling system is required to remove excess heat generated to ensure that the CPV operates at optimum operating temperature with minimum variation of temperature. Metal foam is a new class of material that possesses huge potential for thermal management. In this study, a functionally graded metal foam is proposed for the CPV thermal management system. Computational thermal fluid dynamic analysis is conducted to investigate the effect of porosity and pore density on the flow field and thermal performance of the aluminum foam heat sink. The investigation results revealed that 10 PPI functionally graded aluminum foam heat sink with two stages of porosity gradient 0.794 and 0.682 produced the lowest pressure drop and highest thermal performance. Temperature difference of 3.9 C was achieved for a solar cell with total heat generation of 900 W under water mass flow rate of 20 gs −1. K E Y W O R D S CFD model, concentrator photovoltaic, functionally graded metal foam, metal foam, thermal management system 1 | INTRODUCTION Solar energy is a type of renewable energy that exists free, abundant, and nonpolluting. 1 Development of solar energy harvesting system is necessary as it helps to reduce global warming and dependent on the fossil fuel for electricity generation. Solar harvesting system converts light energy to electrical energy for household and Nomenclature: A, cross-sectional area, m 2 ; A fs , interfacial area density between fluid and solid, m −1 ; b, constant; C, constant; d, constant; D h , hydraulic diameter, m; f, Fanning friction factor; h, enthalpy, J kg −1 ; h t , heat transfer coefficient, W m −2 K −1 ; k, turbulent kinetic energy; K, area porosity tensor; K p , permeability, m 2 ; _ m, mass flow rate, kg s −1 ; Nu, Nusselt number; p, pressure, Pa; PPI, number of pores per inch; P k , production of turbulent kinetic energy; Q, heat, W; Re k , Reynolds number based on permeability; S, entropic heat generation, J; S E , heat source on porous media, J;

Global energy demand is rising due to the rapid development and adoption of new technologies in every sector. Hence, there is a need to introduce a clean energy source that does not cause damage to the environment. Aluminium-air battery with its high theoretical specific volumetric capacity is an exciting alternative for post-lithium energy storage and has been at the forefront of energy research for years. However, the conventional aqueous electrolyte-based aluminium-air battery with bulky liquid storage, parasitic corrosion of aluminium in contact with the electrolyte, and formation of a passive oxide or hydroxide layer has precluded its widespread application. In order to achieve successful simplification and cost-effectiveness, a novel idea of a polypropylene-based aluminium-air battery is proposed. In this work, a polypropylene-based aluminium-air battery was constructed using aluminium foil as an anode, carbon fiber cloth as an air-cathode, and Polypropylene and Kimwipes as the separator. The effects of the electrolyte concentration on the aluminium-air battery were investigated and analyzed using various discharge currents. The study showed that the performance of the polypropylene separator is better than that of the Kimwipes separator. The battery capacity is negatively correlated with the concentrations of the electrolyte. At a discharge current of 30 mA, the aluminium-air battery has a specific capacity of 375 mAh g−1 when 1 M of potassium hydroxide was used as electrolyte.

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Concentrated photovoltaic cell (CPV) is a popular renewable source nowadays. It has high efficient yet cost effective energy harvesting system available in the market. The performance of the CPV depends strongly on the temperature of the solar cell. The efficiency reduces as the surface temperature of the CPV increases. It is crucial to reduce the temperature of the CPV and maintains a small temperature variation along the surface of the CPV. Metal foam is an ideal solution for a CPV thermal management system. It helps to enhance the mixing of coolant due to its porous characteristics and lead to higher heat transfer rate and reduce the overall average temperature of a CPV. The main objective of this study is to enhance the heat removal rate along of the CPV. Aluminium foam is used as a heat sink to removal the heat generated. The effects of porosities and pores density (PPI) of the aluminium foam are measured against the thermal performance. Computational thermal fluid dynamics is conducted to study the thermal performance of aluminium foam heat sink. The parameters required for the simulations are extracted from literature. The results suggested that aluminum foam is able to enhance the heat removal and maintains better temperature uniformity of the CPV. 10PPI aluminum foam with porosity 0.682 provides the most optimum results with average temperature of 55.1 ˚C and temperature different of 7.4 °C at flow rate of 40 g/s. This approach is suitable to promote the efficiency of the CPV and prolong the cycle life.