• Energy Research

Abstract The production and storage of thermal energy are important processes that contribute to the satisfaction of daily needs. They are effective ways of managing the thermal energy available from various solar applications. The most efficient storage technique is the use of phase change materials (PCMs) because these components can keep large amounts of thermal energy in stock. The problem is that this approach continues to be confronted with difficulties despite significant progress in research, design and modelling. Nevertheless, these difficulties can be resolved through numerical simulations that enable the identification of powerful tools for optimising thermal system design and predicting thermal behaviour. Correspondingly, in this work, thermo-mechanical modelling was conducted to describe the different methods of heat transfer that can optimise thermal energy storage via PCMs. This study also established a numeric resolution and the spatio-temporal discretisation of the basic equations accompanying the numerical model. The proposed numerical solution improves the prediction of thermal behaviour and can be used as a guide in designing new systems capable of producing and storing solar energy.

Solar energy is a natural source that provides clean and renewable energy, which supplies two types of energy: thermal energy and photovoltaic energy. Whereas, the most effective way to exploit this energy is photovoltaic cells. However, for all the incident solar radiation, the solar panels can absorb a limited quantity of energy. While, the rest of radiation energy gets lost as heat, that increases the temperature of the photovoltaic cells, this is the reason why the productivity of electricity is decreased. Therefore, to exceed this issue and benefit from the two sources of sun radiation, a hybrid thermo-electrical system is proposed. The system is a solar panel surrounded by the phase change material that can absorb the temperature to increase the efficiency of solar system and use this energy to produce a hot water.

Solar trackers increase energy production by adjusting the collector to the optimum angle relative to the sun. Nevertheless, these devices are still fronting several challenges that limit their performance, which affects their use, such as the bad atmosphere impact, the components multiplicity, the complexity of programming and repairing. The provision of integrated solar trackers that completes the system, self-driven to face the sun, ensures stability against bad weather and easeful use that can be a step forward, which increases their use and improves the production of green energy. In this study, an integrated solar tracker has been proposed that based on the shape memory alloys (SMA). These materials can act as a thermo-mechanical actuator that memorizes two shape, one at high temperature the second at low temperature. The exposure of solar radiation raises the actuator temperature. According to degree of temperature, the actuator controls the angle of inclination with which the collector moves to face the sun. Then, a mathematical modelling has been carried out to optimally adapt the proposed actuator with the solar system. In order to validate the numerical study, a comparative study has been conducted to compare the concordance of the simulation results with literature. The proposed solar system that integrated the thermo-mechanical tracker shows an increase of energy production about 39% compared to a fixed system.

The phase change materials (PCM) are materials that can improve thermal energy storage and production in buildings. This technique has sparked a lot of interest due to the large amount of energy that can be produced by integrating PCM into the collector or that can be stored by integrating the PCM into the tank. Despite considerable progress in research and design, PCM technologies still face diverse challenges. Indeed, other variables that have a significant impact on this phenomenon have been overlooked such as engineering and heat transfer modes especially heat radiation. Besides, the selected temperature of phase change has a direct impact on PCM efficiency. Since the higher the phase change temperature, the more heat is produced. Hence, combining two different types of PCM that have different properties will improve thermal energy efficiency.This research aims to establish a new PCM system that combines two complementary kinds of PCMs have different melting temperatures. The system seeks to improve storage and production by optimizing engineering and adapting the phase change point as needed, according to weather conditions and seasons. Therefore, the thermo-mechanical modelling studies the different heat transfers for the triangular geometry for both types of PCM in order to adapt the proposed geometry with the PCM system. The results showed that the proposed system could absorb thermal energy in most cases due to the selected low phase change point. Then, PCM system continues to store thermal energy until the system reaches the second phase change. Therefore, the numerical study showed significant improvement in predicting the thermal behavior in solar systems as well the average storage time has been reduced by 10%. In contrast, the proposed study can be used to optimize energy consumption in air conditioning and improve production in photovoltaic systems.

The performance of solar systems is influenced by external environmental as weather, climates and irradiation, while for internal factors as conductivity, interfaces homogeneous and material, it can be improved by configuring the optimal characteristics of the solar system. Accurately, the thermal interfacial resistance in the different components of solar system influences significantly the transformation of solar energy into electricity and heat for the reason that heat transfer dropping between phase change material (PCM) and photovoltaic system. In this study, a novel engineering of a hybrid solar system that purposes to increase electrical energy in the photovoltaic (PV) system by absorbing heat has been proposed. The proposed system integrates two types of PCM in order to increase the thermal stability time, reduce the temperature variation and optimize the efficiency of thermal production. Moreover, the interface of contact has been improved and homogenized in order to optimize the heat exchange between the components of the systems which is increasing the evacuation of heat for the PCM that optimized the production of electricity and heat. Consequently, a systematic study evaluates the efficiency of the PV/PCM system in terms of electrical and thermal production has been proposed. Hence, the numerical study showed that there is a similarity between the results obtained and the previous results, and there is an obvious improvement after adding two types of PCM with different melting point compared to PV system with one type of PCM or without PCM. Electrical power output has been improved significantly that reaches 54.5% in the beginning of the day compared to PV without PCM and the electrical efficiency grows by about 34% compared to PV without PCM and can achieve 42.5% with two PCM. The absorbed heat can increase the production of thermal energy after optimizing the interface of contact that can be achieved about 52% compared to a system PV without PCM and the productivity can reach 63% with proposed system PV with two PCM.