• Energy Research

Graphitic carbon Nitride (g-C3N4) is one of the most utilized graphitic materials in hydrogen (H2) production via photocatalytic water splitting. Thus, a detailed critical overview, updated with the most recent works, has been performed on the synthesis methods, modification techniques, characterization, and mechanisms of g-C3N4 and g-C3N4-based composite materials, with the aim of clarifying the optimum course towards highly efficient hydrogen-producing photocatalysts based on this promising material. First, the synthesis methods for different morphologies of pure g-C3N4 (bulk, nanosheets, nanotubes and nanodots) are critically analyzed in detail for every step and parameter involved, with special mention regarding the modification methods of g-C3N4 (doping and composite formation). Next, the most common results of g-C3N4 characterization, regarding structural, morphological, optical, and electrical properties, are presented and analyzed. Then, a detailed critical survey of the mechanisms, using g-C3N4 and g-C3N4-based composites during photocatalytic activity, is performed with a focus on their effect on their hydrogen production capabilities via water splitting. This review aims to provide a clear image of all aspects regarding the use of g-C3N4 for photocatalysis, as well as a comprehensive guide for research targeted towards this promising graphitic material.

Nowadays, water pumping systems based on photovoltaics as a source of electricity have widely increased. System cost and efficiency still require enhancement in order to spread their application. Perovskite solar cells (PSCs) are the most hopeful third-generation photovoltaic for replacing the silicon-based photovoltaic thanks to their high power conversion efficiency, reaching 25.8%; tunable band-gap; long diffusion length; low fabrication temperature; and low cost. In this work, for the first time, we proposed a high-power-density hybrid perovskite solar cell thermoelectric generator (TEG) array for feeding a synchronous reluctance motor (SynRM) driving a water pump for use in an irrigation system. A control technique was used to achieve two functions. The first function was driving the motor to obtain the maximum torque/ampere. The second was harvesting the maximum perovskite solar cell array output power on the basis of the maximum power point tracking (MPPT) algorithm using the perturbation and observation approach. Thus, the proposed hybrid perovskite solar cell–thermoelectric generator feeds the motor via an inverter without DC–DC converters or batteries. Accordingly, the short life problems and the high replacement cost are avoided. The proposed complete system was simulated via the MATLAB package. Moreover, a complete laboratory infrastructure was constructed for testing the proposed high-power-density hybrid perovskite solar cell–TEG array for the water pumping system. The results revealed that using the high-power-density hybrid perovskite solar cell–TEG array, both the motor’s output power and the pump’s flow rate were improved by 11% and 14%, respectively, compared to only using the perovskite solar cell array. Finally, both the simulation and experimental results proved the high-performance efficiency of the system in addition to showing its system complexity and cost reduction.

In the present study, energy and exergy analyses of a simple supercritical, a split supercritical and a cascade supercritical CO2 cycle are conducted. The bottoming cycles are coupled with the main two-stroke diesel engine of a 6800 TEU container ship. An economic analysis is carried out to calculate the total capital cost of these installations. The functional parameters of these cycles are optimized to minimize the electricity production cost (EPC) using a genetic algorithm. Exergo-economic and exergo-environmental analyses are conducted to calculate the cost of the exergetic streams and various exergo-environmental parameters. A parametric analysis is performed for the optimum bottoming cycle to investigate the impact of ambient conditions on the energetic, exergetic, exergo-economic and exergo-environmental key performance indicators. The theoretical results of the integrated analysis showed that the installation and operation of a waste heat recovery optimized split supercritical CO2 cycle in a 6800 TEU container ship can generate almost 2 MW of additional electric power with a thermal efficiency of 14%, leading to high fuel and CO2 emission savings from auxiliary diesel generators and contributing to economically viable shipping decarbonization.

In this article, the construction and experimental behavior of an Internet of Things (IoT)-compatible steel health monitoring system are examined. Falling under the general category of nondestructive testing, this new sensor is combined with an energy harvester to produce an autonomous automated device that can measure, store, and transmit measuring data without any need for human intervention. Based on common principles like the Hall effect, the monitoring system is put to use, and its results are presented.

Protection against the electromagnetic fields around high-voltage transmission lines is an issue of great importance, especially in the case of buildings near power lines. Indeed, the developed fields can be harmful for the habitants and electrical/electronic devices, so the implementation of appropriate measures to address the above electromagnetic interference issue is necessary in order to ensure the safety of both human beings and equipment. Several practices have been proposed to reduce the electric and the magnetic fields around overhead and underground transmission lines (minimum distance, shielded cables, anechoic chamber etc.). In this context, the scope of the current paper is the use of highly permeable magnetic sheets for shielding purposes, along with the development of an appropriate procedure, based on finite element analysis (FEA) for the efficient design of passive shielding. The simulation results are compared with laboratory measurements in order to confirm the adequacy of the proposed methodology. The good agreement between the FEA outcomes and the experimental results confirms that the developed FEA tool can be trustfully used for the design of the shielding means in the case of overhead or underground power lines.

Abstract Solar energy has been considered for many years one of the most reliable and predictable renewable energy resources for the production of both electricity and heat. At the moment, renewable energy market is mainly focused on photovoltaics and solar thermal systems. Quite recently, the implementation of thermoelectric generators in solar energy conversion systems, as an alternative method for exploiting the potential of this huge resource, has attracted increasing attention. In this paper, the performance of a thermoelectric-based solar conversion unit is investigated computationally, using ANSYS Workbench v. 14.0 CAE Software. The electrical output of the system under consideration has been evaluated and performance prediction has been conducted under various operating conditions, demonstrating maximum power output of 33.7 W. Moreover, different techniques are discussed in order to enhance power output and optimize system operation according to the incoming solar irradiation levels, which can differ significantly throughout the year.

Abstract Although photovoltaics have been established as the dominant technology considering the field of solar energy conversion systems, issues regarding their relatively low efficiency still remain practically unsolved. Very recently, the possibility of combining photovoltaic (PV) cells and thermoelectric generators (TEGs) in hybrid systems, as a means of improving the overall conversion efficiency, has attracted particular attention. In this paper, the performance of a tandem PV–TEG hybrid, employing poly-Si as well as dye-sensitized solar cells, has been examined experimentally. Thermoelectric devices of different thermoelement geometry have been tested in order to identify the corresponding performance effect. In addition, the outcomes of the experimental process have been exploited in order to evaluate the performance of the system under real operating conditions. The analysis conducted indicates that the utilization of TEGs with shorter thermoelements results in enhanced power output levels, when conditions of actual operation are considered. Moreover, although improved power output is obtained by the setup employing the polycrystalline cell, dye-sensitized technology could become particularly attractive when the incorporation of solar cells in PV–TEG hybrids operating under conditions of elevated temperature is examined.

In this paper, after illustrating the current state of the art, we present our own technology in manufacturing super-paramagnetic nanoparticles (SPAN). The method is based on chemical coprecipitation by using single ion precursors, like chloride or/and nitrate salts. Apart from synthetic route description, a demonstration ofthe methods used for structural analysis and electric-magnetic properties determination is done followed by the comments and remarks on the recorded results. Finally, the role of doping in magnetic and optical properties of the prepared nanomagnetic materials is illustrated and the potential utilization of these materials in various technological applications is presented.

Abstract During the last decade thermoelectrics have emerged as a promising alternative amongst other green power production technologies due to the unique advantages they present. In this respect, performance prediction of thermoelectric devices is critical both for evaluating the potential application of new materials and defining the crucial design parameters of thermoelectric generators and systems. This paper investigates, computationally as well as experimentally, the performance of a commercially available Seebeck module under steady-state operating conditions. Computational results, retrieved using ANSYS Workbench (v. 14.0), were compared to performance data available by the manufacturer. Additionally to that, in order to further verify the integrity of the modelling procedure, experimental evaluation using the same commercial module was conducted in laboratory environment. Although a relatively large deviation between computational and manufacturer data was observed when the mean operating temperature of the generator was taken into account, a very good agreement was established in terms of generator efficiency, providing also a rational explanation to the resulting divergence of the first case. Furthermore, the outcomes of the experimental analysis validated the accuracy of the finite element modelling process.