Solar energy is a long-established technology, which has zero CO2 emissions, and provides low-cost energy for a given area of land. The concentrator photovoltaic (CPV) has been given preference over the photovoltaic due to its high efficiency. In a CPV system, most of the solar cell area has been replaced with an optical concentrator. Various parabolic trough based CPV systems have been presented where a concentration of <300 is achieved. In the current research, a design is presented to achieve a high concentration of 622×. The design consists of two stages of concentration including parabolic trough as a main concentrator and nonimaging reflective grooves as a secondary concentrator. The trough reflects the incident light towards the secondary reflector where the light is redirected over the solar cell. Design of the two-stage concentrator, ray-tracing simulation, and results are presented. The system achieved an optical efficiency of 79%. The system would also be highly acceptabl... [more]

This study examines the cointegration and short- and long-run causal relationships between economic growth and CO2 emissions, fuel consumption and the amount of freight transported by road transport in the Visegrad Group countries between 1990 and 2019. The autoregressive distributed lag (ARDL) bound testing methodology was used to develop the results for each tested dependent variable. The results confirmed a long-run cointegration between economic growth and fuel consumption by road transport in the Czech Republic and Slovakia. In addition, a long-run relationship between economic growth and freight volume and CO2 emissions by transport was demonstrated for Slovakia. For Poland, there was only a long-run relationship between energy consumption by road freight transport and CO2 emissions. In the short run, relationships were shown between the volume of freight transported by the road freight transport sector and CO2 emissions for Hungary and Poland. Short-run relationships between eco... [more]

Microgrids have arisen as an alternate solution to the problem of power generation in distributed energy. Compared to ac microgrids, dc microgrids (DC MGs) are superior in terms of system efficiency, power quality, affordability, and ease of control. For the integration of renewable energy generation into microgrids, power electronic converters are required. When power electronics converters are tightly regulated, they behave as a constant power load (CPL) which exhibits a negative incremental impedance characteristic. As a result, oscillations occur in voltage response at a DC bus. To suppress the voltage oscillations in DC MGs, various damping stabilization techniques are proposed by researchers. This paper provides a comprehensive review on active damping stabilization techniques. To improve the system’s stability, active damping can be implemented in three distinct zones: source-side, load side or CPL side, and intermediate level. After analyzing each zone, their merits and drawbac... [more]

Greenhouses extend growing seasons in upper latitudes to provide fresh, healthy food. Costs associated with carbon-emission-intensive natural gas heating, however, limit greenhouse applications and scaling. One approach to reducing greenhouse heating costs is electrification by using waste heat from cryptocurrency miners. To probe this potential, a new quasi-steady state thermal model is developed to simulate the thermal interaction between a greenhouse and the environment, thereby estimating the heating and cooling demands of the greenhouse. A cryptocurrency mining system was experimentally evaluated for heating potential. Using these experimental values, the new thermal model was applied to the waste heat of the three cryptocurrency mining systems (1, 50, and 408 miners) for optimally sized greenhouses in six locations in Canada and the U.S.: Alberta, Ontario, Quebec, California, Texas, and New York. A comprehensive parametric study was then used to analyze the effect of various para... [more]

Real-time energy management of battery storage in grid-connected microgrids can be very challenging due to the intermittent nature of renewable energy sources (RES), load variations, and variable grid tariffs. Two reinforcement learning (RL)−based energy management systems have been previously used, namely, offline and online methods. In offline RL, the agent learns the optimum policy using forecasted generation and load data. Once the convergence is achieved, battery commands are dispatched in real time. The performance of this strategy highly depends on the accuracy of the forecasted data. An agent in online RL learns the best policy by interacting with the system in real time using real data. Online RL deals better with the forecasted error but can take a longer time to converge. This paper proposes a novel dual layer Q-learning strategy to address this challenge. The first (upper) layer is conducted offline to produce directive commands for the battery system for a 24 h horizon. It... [more]

Electrical energy conversion and storage in DC systems, with increasing importance in industry, requires DC−DC power electronic converters with performances adapted to today’s requirements. In recent years, the applications of DC−DC converters have expanded, including energy storage management strategies, due to the use of supercapacitors for energy storage instead of—or together with—rechargeable batteries, in order to improve overall performance. This article presents a non-isolated, common-ground, bidirectional hybrid switched-capacitor DC−DC converter, which can be efficiently used for supercapacitor charging/discharging, due to its high voltage conversion ratio. The hybrid converter was obtained from the conventional bidirectional buck topology, inserting an “active” switched-capacitor cell. In addition to the high voltage conversion ratio, the switched-capacitor cell brings another important advantage: decreasing the values of all passive components without interrupting the input... [more]

Fossil additives are a primary energy source and their contribution is around 80% in the world. Therefore, bioadditives that reduce their impact are each very important. This article discusses the chemical transformation of glycerol to carbonate, ethers, esters, ketals, and acetals, compounds with high technological applications, especially in the fuel sector as bioadditives. Mainly, heterogeneous catalysts are important in the production of more than 80% of chemicals in the word. The focus is on demonstrating how the Keggin heteropolyacids (HPAs) are efficient catalysts in the reactions of syntheses of glycerol-derived bioadditives, either in homogeneous or heterogeneous phases. Although solid, HPAs have a low surface area and are soluble in polar solvents, hampering their use as heterogeneous catalysts. Alternatively, they have been successfully used supported on solid matrixes with a high surface area. Another option is converting the Keggin HPAs to insoluble salts simply by exchang... [more]

This study investigates the effects of crude oil and natural gas future returns on energy stock portfolios. We consider returns of portfolios of energy companies approximated by energy ETFs and returns of Brent crude oil and natural gas contracts listed on the US market from January 2015 to September 2022. To study the relationship between Brent crude oil, natural gas, and ETFs, we apply Granger causality in mean and variance, Dynamic Conditional Correlation and the tail dependence-focused copula approach. The research hypothesis regarding the dependence between energy ETFs and the underlying energy risk factors—crude oil and natural gas, and therefore, the existence of hedging or diversification opportunities, was verified. Our empirical findings indicate that crude oil has a medium effect on energy ETFs, and for natural gas it is even lower in the analyzed period, so hedging opportunities are weak, but opportunities for diversification arise.

The widespread introduction of functionally-smart inverters will be an indispensable factor for the large-scale penetration of distributed energy resources (DERs) via the power system. On the other hand, further smartization based on the data-centric operation of smart inverters (S-INVs) is required to cost-effectively achieve the same level of power system operational performance as before under circumstances where the spatio-temporal behavior of power flow is becoming significantly complex due to the penetration of DERs. This review provides an overview of current ambitious efforts toward smartization of operational management of DER inverters, clarifies the expected contribution of machine learning technology to the smart operation of DER inverters, and attempts to identify the issues currently open and areas where research is expected to be promoted in the future.

This paper presents an overview of various sensorless control methods, with a focus on dual three-phase permanent magnet synchronous machines (DTP-PMSM). Owing to the important role that DTP-PMSMs play in motion-control applications in industry, most academic researchers and industry activists seek to reduce costs and size while increasing the capability and efficiency of motion applications. This has led to an increase in the number of publications about multiphase machines in recent years. The purpose of this article is to review the most important sensorless control techniques, which are divided into two main categories, namely saliency-based control method for low-speed range and model-based control method for high-speed range. Both methods are subdivided into other categories, with a focus on DTP-PMSMs. The methods are compared with each other for the purpose of selecting the most suitable control technique for implementation in applications such as ship propulsion, wind turbines,... [more]

Hybrid Renewable Energy Systems (HRESs) have proven to be viable solutions for rural electrification. They not only electrify rural locations but also provide environmentally sustainable, secure, and affordable energy if optimized. These systems can best be described as generators of electricity from multiple energy sources that complement each other. Optimized HRESs often generate affordable electricity by minimizing the levelized cost of electricity (LCOE) and carbon emissions. The investigation of social benefit factors within energy poverty is a relatively new discussion in the study of modeling off-grid energy systems. In this perspective article, we examine the importance of computational tools for the energy transition of rural and remote communities. We show that classical and heuristic models possess the capability of optimizing hybrid renewable energy systems considering social parameters including health, education, and income. This is followed by a discussion about the pote... [more]

The replacement of hydrocarbon fuels by ammonia in industrial systems is challenging due to its low burning velocity, its narrow flammability range, and a large production of nitric oxide and nitrogen dioxide when burned close to stoichiometric conditions. Cracking a fraction of ammonia into hydrogen and nitrogen prior to injection in the combustion chamber is considered a promising strategy to overcome these issues. This paper focuses on evaluating how different levels of ammonia cracking affect the overall burning velocity, the lean blow-off limit, the concentration of nitric oxide and nitrogen dioxide, and the flame response to acoustic perturbations. Swirl stabilized premixed flames of pure ammonia−air and ammonia−hydrogen−nitrogen−air mixtures mimicking 10%, 20%, and 28% of cracking are experimentally investigated. The results show that even though ammonia cracking is beneficial for enhancing the lean blow-off limit and the overall burning velocity, its impact on pollutant emissio... [more]

Carbon emissions reduction is crucial to global climate governance and sustainable development. By 2060, China envisioned being carbon-neutral, and it has adopted a series of policies and measures for environmental management, especially in the main stream of Yangtze River basin, where China’s carbon emissions are centered. The spatial distribution characteristics and agglomeration effects of carbon dioxide (CO2) emissions in the main stream of Yangtze River basin are analyzed from 2010 to 2019 based on the perspective of local (city and state) administrative regions, and uses the spatial Durbin model to examine the influencing factors and spatial spillover effects of carbon emissions. The findings discovered from the extensive research are as follows: First, carbon emissions in the main stream of Yangtze River basin present a fluctuating upward trend, and CO2 emissions in the lower reaches are significantly higher than those in the middle and upper reaches, which are closely related t... [more]

This paper presents a critical review, from a wind farm control perspective, of different methodologies in the open literature that enable wind farms to participate in ancillary service provision. Firstly, it considers the services currently provided in power systems with high levels of wind generation (specifically, Denmark, Ireland, and Great Britain), reviewing current regulatory frameworks and recommendations. Secondly, it reviews the ancillary service markets that wind farms do not currently participate in, considering the barriers to entry and discussing potential solutions using a proper control-enabled framework. Thirdly, it also considers the future perspective for wind farm participation in ancillary service provision, including a review of the body of published academic research on wind farm participation in ancillary service provision. Finally, this review concludes by suggesting where the gaps are in the academic literature, and subsequently suggests future work. Two examp... [more]

Approximately 40% of the overall energy consumption of society is consumed by buildings. Most building energy usage is due to poor envelope performance. In regions with cold winters, the corners of structures typically have the lowest interior surface temperature. In corners, condensation, frost, and mold are common. This has a substantial effect on building energy usage and residents’ comfort. In this study, the heat loss of corner envelopes is evaluated, and a suitable insulation construction of wall corners is constructed to increase the surface temperature of the envelope interior. Computational Fluid Dynamics simulation has been used to examine the heat transmission in a corner of an ultra-low energy building in this study. By comparing the indoor surface temperature to the soil temperature beneath the building, the insulation construction of wall corners has been tuned. The study results indicate that the planned insulation construction of wall corners can enhance the internal su... [more]

In this work, the novel design of a sliding mode TriboElectric Nano Generator (TENG)—which can utilize vibration amplitude of a few hundred microns to generate useful electric power—is proposed for the first time. Innovative design features include motion modification to amplify relative displacement of the TENG electrodes and use of biological material-based micron-sized powder at one of the electrodes to increase power output. The sliding mode TENG is designed and fabricated with use of polyurethane foam charged with the biological material micropowder and PolyTetraFluoroEthylene (PTFE) strips as the electrodes. Experimentations on the prototype within frequency range of 0.5−6 Hz ensured peak power density of 0.262 mW/m2, corresponding to the TENG electrode size. Further numerical simulation is performed with the theoretical model to investigate the influence of various design parameters on the electric power generated by the TENG. Lastly, application of the proposed TENG is demonstr... [more]

The objective of this work is to analyze the possibility of compliance with the objectives committed to by the Canary Islands authorities, which aim to reach a completely decarbonized economy by 2040, meaning ten years earlier than the entire EU. Since historically, energy planning in the Canary Islands did not achieve its objectives by far, we will first identify the historical obstacles which had prevented the achievement of this planification, to later highlight the main differences between the energy transition foreseen by the current planning instruments of the government of the Canary Islands and the expected evolution of the energy transition of the archipelago. Beyond this point, and, within the frame of energy governance, we will understand how the root of this failure lies in planning instruments developed hierarchically, without including the view of the different stakeholders involved in the process. The final goal, after identifying the main barriers faced by the energy tr... [more]

In this paper, a numerical model of a capillary tube is developed. The considered expansion device is placed against the suction line at the inlet of the compressor. Wrapping the capillary tube around the suction line allows heat to be recovered by superheating the refrigerant leaving the evaporator. This increases the degree to which the fluid is superheated, preventing liquid droplets from entering the compressor and causing damage. The open-source software PYTHON is used for modelling the non adiabatic capillary tube, and the results are validated by comparing them with experimental tests. This study demonstrates that an accurate contact of the capillary tube with the suction line affects the superheating of the compressor inlet fluid by increasing its temperature by up to 5 degrees and produces an increase in COP of 3−4%. On the other hand, the length of the capillary tube affects the flow rate of the refrigerant circulating in the cycle; in particular, it is noted that a 300% incr... [more]

The building sector is crucial in all of the possible net zero scenarios suggested for the European Union. In this area, the Italian situation is exemplary. Italy suffers from an aging and low-performance building stock and needs to increase its annual rate of energy retrofits in order to achieve its 2030 and 2050 targets. Even though since at least 2007, several different incentives schemes intended to stimulate energy-efficiency interventions have been in place, Italy has not been sufficiently able to promote deep retrofits. In 2020, in order to help the economy recover after the lockdowns that were introduced to face the first phase of the COVID-19 pandemic, the existing incentives were increased to up to 110% of investments for interventions that improved the energy class by at least two grades. This so-called “Superbonus” was also extended to the public social housing sector thanks to a credit assignment scheme. Given the results of this provisional phase, a possible policy roadma... [more]

As more electrification and emission-free transportation trends receive more attention, electrical systems applied in the aircraft and automotive industries are changing from fossil fuel and hydraulic systems to electric AC machine drive systems. Three-dimensional printing technology has been contributing to a new design of machines, because it provides many opportunities without limitation compared to the conventional manufacturing system. Although 3D printing technology opened a door for increasing the efficiency and power density of AC machine drives with low conduction loss, an optimal design process for eddy current loss reduction is required, because eddy current loss is affected by the design structure of the machine. The slit structure at the stator shoe is proposed to reduce eddy current loss. With the three variables, the number of slits, the thickness of slits, and the length of ribs, a parametric analysis was conducted to find an optimal design with eddy current loss reduct... [more]

In this work, we have studied how the vertical illuminance of the human eye position, illuminance of the horizontal work surface, and the brightness of the computer screen in the office space lighting are correlated under an energy-saving environment. This investigation was conducted in a full-scale laboratory that simulates an office space with 20 adults. It was found that when the indoor ambient lighting illuminance changes, the vertical illuminance of the subject’s eye position is affected accordingly, and the two factors are strongly correlated. On the other hand, when the surrounding environment is brighter and the vertical illuminance increases, the illuminance of the horizontal working surface adjusted by the subject during the visual display terminal (VDT) operation is significantly reduced. The horizontal illuminance value can even be lower than the value frequently employed in various countries around the world, since the computer screen brightness will be adjusted accordingl... [more]

The process of looking for alternative energy sources is driven by the increasing demand for energy and environmental contamination caused by using fossil fuels. Recent investigations reported the efficiency of microalgae for biofuel production due to its low cost of production, high speed of growth, and ability to grow in harsh environments. In addition, many microalgae are photosynthetic, consuming CO2 and solar light to grow in biomass and providing a promising bioenergy source. This review presents the recent advances in the application of microalgae for biofuel production. In addition, cultivation and harvesting systems and environmental factors that affect microalgae cultivation for biofuel production have also been discussed. Moreover, lipid extraction and conversion technologies to biofuel are presented. The mixotrophic cultivation strategy is promising as it combines the advantages of heterotrophy and autotrophy. Green harvesting methods such as using bio-coagulants and floccu... [more]

This work presents a design for uninterruptible power supply inverters using Pareto front optimization for improved cost and efficiency. Three PWM modulation techniques applied to the full-bridge inverter are analyzed. As a result, the best MOSFET design solution in terms of the cost and efficiency of the inverter is evaluated based on a database with 47 power MOSFETs. Using the Pareto front, the optimal and sub-optimal solutions are compared, considering the three modulation techniques and the characteristics of MOSFETs manufactured for different voltage levels. Thermal and electrical measurements are used to validate the models.

R744 is the most competitive and ideal natural refrigerant when flammability and toxicity are strictly limited. However, there are still some problems when it is applied to a heating system. For example, the discharge pressure of the system exceeds 10 MPa, it increases the cost of the system, and the cycle efficiency is also low. To solve these problems, this paper proposes to replace R744 by mixing R744 and ethane at a ratio of (77.6/22.4) to form an azeotropic refrigerant. At present, there is little research on R744 azeotropic refrigerant. Therefore, this paper first establishes the CFD model and compiles the UDF program to focus on flow boiling heat transfer characteristics, and then, it analyzes the performance of R744 and its azeotropic refrigerant in a low-temperature heating system. The results show that the heat transfer coefficient of R744 and its azeotropic refrigerant decreases with an increase in mass flux and increases with an increase in heat flux and saturation temperat... [more]

An air-powered vehicle is a low-cost method to achieve low-pollution transportation, and compressed air engines (CAE) have become a research hotspot for their compact structure, low consumption, and wide working conditions. In this study, a pneumatic motor (PM) test bench is built and tested under different inlet pressures, operation modes, and three driving cycles. On the basis of the data obtained by sensors, power output, compressed air consumption rate, and efficiency are calculated to evaluate the pneumatic motor performances. The results show that with an increase in rotation speed, the output power and efficiency first increase and then decrease, and the compression air consumption rate decreases. With an increase in torque, the rotation speed decreases, and the power output and efficiency first increase and then decrease. With an increase in mass flow rate, the torque increases, the power output and efficiency first increase and then decrease. The pneumatic motor achieves the b... [more]