Heat and mass transfer, widely involved in various energy systems, has great impacts on the safety, efficiency, as well as performance of these systems [...]

Reducing energy costs in Europe is more challenging than before due to extreme price increases. The use of local renewable energy sources is one way to contribute to this effort. In the case of spa resorts, the use of heat from hot springs for therapeutic baths is an option. It is necessary to cool down this thermal mineral water to a temperature acceptable to the human body. However, due to the high mineral content of this water, heavy fouling can be a problem for conventional heat exchangers. The purpose of this study is to identify the suitable cooling technology in terms of required cooling capacity and waste heat recovery capability. The cooling technology was selected on the basis of a literature search. A pilot cooling unit consisting of vacuum cooler and plate heat exchanger was designed and tested in a real spa resort for six months. Both selected technologies have demonstrated the ability to cool thermal mineral water in long-term operation, as well as the possibility to util... [more]

Most coal and gas outbursts occur in the coal thickness variation zone. However, it is difficult to illustrate the mechanism of outbursts in coal thickening areas by physical simulation experiments. In this study, a coupled multi-field model, established by considering the stress−strain field, gas transport field and damage field, was used to investigate the evolution of stress, gas pressure and plastic failure zones under different variation gradients and amplitudes of coal thickness. The simulation results show that the stress peak at the coal thickening transition zone caused by mining is higher than that at the constant thickness coal seam. The stress peak at the coal thickening transition zone decreases from 18.8 MPa to 16.9 MPa with the increase in the transition zone from 0 m to 10 m under the constant coal thickness variation from 3 m to 7 m; while it increases from 16.2 MPa to 19.3 MPa with the increase in the transition zone from 2 m to 10 m under the constant coal thickness... [more]

The performance of photovoltaic solar cells is usually analyzed using continuous models, for instance, 1M5P. I-V and P-V curves are fitted by a mathematical expression from the electrical model. In the case of 1M5P, characteristics are fitted using five parameters that are obtained using a small number of I-V points from a wider set of data, keeping the curve shape given by the mathematical expression from the model. A novel model was recently proposed to overcome this issue. The d1MxP model is based on the discretization of the electrical behavior of the diodes in models such as 1M5P. The d1MxP methodology is equivalent to an analytical incremental calculation and since it connects the given points, the model error should be lower than the one obtained using models as 1M5P. It is based on the connection of adjacent points (with small voltage differences) instead of having the entire voltage range represented by some parameters (as the continuous models do, for instance, 1M5P). In this... [more]

Based on the decision of representatives from the West African region and feedback from locals in Togo, an advanced continuous-feed, forced-draft, biomass cookstove named “Apeli” was developed. The stove was tested in modified ISO measurements based on the ISO 19867-1:2018 standard. This included a long shutdown operation using wood pellets and short shutdown operations using wood pellets, bamboo pellets, wheat straw pellets and palm kernel shells. Due to the fast shutdown capability, the short shutdown was chosen for more realistic results using this stove type. For cold start and long shutdown operation using wood pellets, the thermal efficiency is determined as 44.1% at a 1116 W power output by emitting 0.272 g CO and 17.2 mg PM 2.5 per MJd at high load. At low load, the efficiency is 38.0% at a 526 W power output by emitting 1.1 g CO and 45.1 mg PM 2.5 per MJd. Due to a misinterpretation of the standard, the burnout duration of the tests with long shutdown is approx. 1.5 min shorte... [more]

Citizen energy in general and renewable energy communities (RECs) in particular are becoming key vehicles for decentralisation, but also for the democratisation of the energy system. These initiatives are now more diverse than ever and are likely to continue to act as incubators for significant projects in the transition to a renewable energy system. Beside the legal, regulatory, and financial challenges, there are several socio-economic and regulatory barriers that hinder the implementation of community energy projects. For this reason, policy learning and the dissemination of good/best practices that are transferable also to other contexts are important. This is an aspect that has not yet attracted much investigation, and only a few studies have explored the importance of transfer activities for the implementation of REC initiatives and their motives. This article aimed to address this knowledge gap by focussing on the transfer processes of best practices initiated in a particular re... [more]

The amount of cattle manure generated accounts for over 40% of the livestock manure in South Korea. Most livestock manure is utilized as a fertilizer and a soil amendment. However, the soil nutrients have exceeded saturation in South Korea. Accordingly, cattle manure, including lignocellulosic biomass, was applied for solid fuel production in this study. The three different types of carbonization process, namely, hydrothermal carbonization, torrefaction, and carbonization (slow pyrolysis), were estimated for a comparison of the hydrochar, torrefied char, and biochar characteristics derived from cattle manure. The processes were performed at temperatures ranging from 190 to 450 °C. The evaluation of the hydrochar, torrefied char, and biochar produced by three processes was conducted by the proximate, ultimate, calorific value, fuel ratio, and energy yield, which were used for the analysis of fuel quality. Additionally, the ash properties, including silicon dioxide, chlorine, and base-to... [more]

Heat transfer is present in all modern engineering applications and plays a fundamental role in improving the efficiency of energy conversion systems [...]

Electric vehicles (EVs) are becoming increasingly popular due to their low emissions, energy efficiency, and reduced reliance on fossil fuels. One of the most critical components in an EV is the energy storage and management system, which requires compactness, lightweight, high efficiency, and superior build quality. Active cell equalization circuits such as those used in battery management systems (BMS) have been developed to balance the voltage and state of charge (SoC) of individual cells, ensuring the safety and reliability of the energy storage system. The use of these types of equalization circuits offers several benefits including improved battery performance, extended battery life, and enhanced safety, which are essential for the successful adoption of EVs. This paper provides a comprehensive overview of the research works related to active cell equalization circuits. This review highlights the important aspects, advantages and disadvantages, and specifications.

Due to the need for highly efficient and compact power electronic converters to operate at higher frequencies, traditional wire-wound magnetics are not suitable. This paper provides a comprehensive review of planar magnetic technologies, discussing their advantages as well as associated disadvantages. An extensive review of the research literature is presented with the aim of suggesting models for planar magnetics. Several strategies are proposed to overcome the limitations of planar magnetics, including winding conduction loss, leakage inductance, and winding capacitance. The goal of this study is to provide engineers and researchers with a clear roadmap for designing planar magnetic devices.

The complexity of biodiesel aging has shown that the mechanism needs further research. The rate of aging product formation and associated interactions can help improve fuel quality. Since biodiesel is a multicomponent system and constant changes occur in the chemical environment, which interactions yield which products must be shown in more detail. Particularly under observation was the correlation between peroxides and epoxides. In addition, it is critical that the influence and interactions of new drop-in fuel candidates be investigated. In this work, the kinetics of the formation of aging products of methyl oleate (C18:1) are studied. The aim was to reduce the complexity in order to be able to make more precise and detailed statements about the mechanism. Ketones, acids, peroxide, and epoxide values were recorded. A distinction is made between pure methyl oleate and mixtures with 3 wt% isopropylidene glycerine (solketal). After solketal decomposed in the blends, the aging process sh... [more]

Computational methods play a significant role in reducing energy consumption in cities. Many different sensor networks (e.g., traffic intensity sensors, intelligent cameras, air quality monitoring systems) generate data that can be useful for both efficient management (including planning) and reducing energy usage. Street lighting is one of the most significant contributors to urban power consumption. This paper presents a summary of recent attempts to use computational methods to reduce energy usage by lighting systems, with special focus on graph-based methods. Such algorithms require all the necessary data to be integrated, in order to function properly: this task is not trivial, and is very time-consuming; therefore, the second part of the paper proposes a novel approach to integrating urban datasets and automating the optimisation process. In two practical examples, we show how spatially triggered graph transformations (STGT) can be used to build a model based on the road network... [more]

The integrated injection-production string is the core tool used in thermal recovery wells for heavy oil, the mechanical behavior of which is complex due to the coupling effect of downhole temperature and pressure and the load induced by steam huff and puff operations. In this paper, an analysis model that calculates the temperature and pressure field during steam huff and puff operations has been established based on the basic principles of energy conservation and heat transfer. Then, the force distribution and strength check of the integrated injection-production string were analyzed. The fatigue damage of the string was evaluated by considering dynamic loads during the injection process. The corrosion life of the string was predicted. Finally, the failure mechanism of the integrated injection-production string in thermal recovery wells for heavy oil was illustrated. The results showed that the strength of the string and vibration fatigue are not the main causes of failure, but corro... [more]

There is increased talk about using second-life batteries in applications. In first-life applications, the batteries start from new, and a range of life cycle estimation techniques are applied. However, it is not clear how second-life batteries should be monitored compared to first life batteries. This paper investigated different algorithms from first-life applications for estimating and forecasting battery cell state of health in conjunction with capacity calculations using second life cells under long term durability testing. The paper looks at how close these models predict capacity fade based on a set of second-life batteries that have been undertaking sweat testing over six different applications. The paper concludes that there are two methods that could be suitable candidates for predicting lifespan. One of these needed to be modified from the original.

Synthesis gas (syngas) fermentation is a biological carbon fixation process through which carboxydotrophic acetogenic bacteria convert CO, CO2, and H2 into platform chemicals. To obtain an accurate overview of the syngas fermentation research and innovation from 2012 to 2022, a systematic search was performed on Web of Science and The Lens, focusing on academic publications and patents that were published or granted during this period. Overall, the research focus was centered on process optimization, the genetic manipulation of microorganisms, and bioreactor design, in order to increase the plethora of fermentation products and expand their possible applications. Most of the published research was initially funded and developed in the United States of America. However, over the years, European countries have become the major contributors to syngas fermentation research, followed by China. Syngas fermentation seems to be developing at “two-speeds”, with a small number of companies contr... [more]

Temporally and spatially resolved data on wind power generation are very useful for studying the technical and economic aspects of this variable renewable energy at local and regional levels. Due to the lack of disaggregated electricity data from onshore and offshore turbines in Germany, it is necessary to use numerical simulations to calculate the power generation for a given geographic area and time period. This study shows how such a simulation model, which uses freely available plant and weather data as input variables, can be developed with the help of basic atmospheric laws and specific power curves of wind turbines. The wind power model is then applied to ensembles of nearly 28,000 onshore and 1500 offshore turbines to simulate the wind power generation in Germany for the years 2019 and 2020. For both periods, the obtained and spatially aggregated time series are in good agreement with the measured feed-in patterns for the whole of Germany. Such disaggregated simulation results... [more]

Utilization of lignin is among the most pressing problems for biorefineries that convert lignocellulosic biomass to fuels and chemicals. Recently “lignin-first” biomass fractionation has received increasing attention. In most biorefining concepts, carbohydrate portions of the biomass are separated, and their monomeric sugar components released, while the relatively chemically stable lignin rich byproduct remains underutilized. Conversely, in lignin-first processes, a one-pot fractionation and depolymerization is performed, leading to an oil rich in phenolic compounds and a cellulosic pulp. Usually, the pulp is considered as a fermentation feedstock to produce ethanol. Herein, the results of a study where various cellulosic pulps are tested for their potential to produce valuable products via pyrolysis processes, assessed via analytical pyrolysis (py-GC), are presented. Samples of herbaceous (switchgrass) and woody biomass (oak) were subjected to both an acid-catalyzed and a supported-m... [more]

The implemented climate policy and the current geopolitical situation make us pay special attention to energy independence, both in the household and in the national dimension. One way to obtain inexpensive and environmentally friendly energy is the development of photovoltaic micro-installations. For positive changes to occur, correct state regulation and an appropriate set of administrative and economic instruments are necessary. The purpose of this article is to discuss changes in the accounting system for renewable energy prosumers and their consequences for the further development of renewable energy. The financial settlement methods favorable to prosumers were recently replaced with new solutions. According to the authors, this slows down the energy transformation.

Solar conversion devices are generally connected with energy storage systems to overcome the influence of sunlight variability. Developing an integrated solar energy conversion and storage device is an attractive approach to compensate for the energy loss of directly connecting these separate devices. In this work, a photocapacitive device is developed based on the Cu2O/CuO heterostructure, with Cu2O as a light absorber and CuO providing a platform for electron and ion storage. The coupling of Cu2O and CuO leads to a high specific capacitance of 135 mF/cm2 under bias and an open-circuit potential of 0.62 VRHE. A photo-charge and dark-discharge ability of Cu2O/CuO system under zero-bias is also discovered and explained based on the concept of Faradaic junction. This work presents an avenue for the investigation of high-performance Cu2O-based solar energy storage devices.

The negative consequences of toxic emissions from internal combustion engines, energy security, climate change, and energy costs have led to a growing demand for clean power sources in the automotive industry. The development of eco-friendly vehicle technologies, such as electric and hydrogen vehicles, has increased. This article investigates whether hydrogen vehicles will replace electric vehicles in the future. The results showed that fuel-cell cars are unlikely to compete with electric cars. This is due to the advancements in electric vehicles and charging infrastructure, which are becoming more cost-effective and efficient. Additionally, the technical progress in battery electric vehicles (BEVs) is expected to reduce the market share of fuel-cell electric vehicles (FCEVs) in passenger vehicles. However, significant investments have been made in hydrogen cars. Many ongoing investments seem to follow the sunk cost fallacy, where decision-makers continue to invest in an unprofitable p... [more]

The six Gulf monarchies—Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and United Arab Emirates (UAE)—are more politically stable than their peers in the Middle East and North Africa. Explanations for governance resilience range from repression to neopatrimonial and instrumental legitimacy, hydrocarbon-based rentierism, and permissive regional and international environments. This paper considers, in view of the proliferation and uptake of renewable energy in the Gulf, how governance resilience may be affected as a result of changes in state-society relations during the energy transition away from a fossil-fuel-based energy system. It offers a qualitative analysis of the impact of renewable energy deployment in the Gulf, supported by a rich array of secondary literature and data. It also offers a deep, if brief, dive to highlight intra-regional nuances. The authors conclude that in the short term, renewable energy deployment has a very modest impact given its limited share of power generat... [more]

The area studied covers unmined Pennsylvanian Ćwiklice and Dankowice coal deposits located in the southern part of the Upper Silesian Coal Basin, Poland. The geological structure of the area clearly affects the current distribution of methane. The content of methane is lower in coal seams lying within porous and permeable sandstones (Łaziska sandstones), whereas it is higher in seams that occur in sequences (Mudstone Series) where impermeable shales and mudstones occur. Due to the previous attempts to extract methane from boreholes, this area, characterized by a dense network of exploratory and prospecting drillings, is worth analyzing with regard to the conditions of methane occurrence in terms of extraction possibilities. Using contour maps, cross-sections and profiles, the variability of methane content and resources, as well as the moisture and ash content of coal seams, were analyzed. Methane content isolines are parallel to the boundary between the Cracow Sandstone Series and the... [more]

Utilizing heat pumps has varied benefits, including decreasing the proportion of fossil fuels in the energy mix and reducing CO2 emissions compared with other heating modes. However, this effect greatly depends on the type of external energy and the type of the applied heat pump system. In our study, two different types of heat pumps, three different modes of operation, three different types of auxiliary energy, and three different CO2 emission values from electricity generation were selected to calculate the CO2 emissions related to heating a theoretical house and calculate the CO2 emissions reduction compared with gas firing. According to the calculations, a wide range of CO2 emission reductions can be achieved, from scenarios where there is no reduction to scenarios where the reduction is 94.7% in monovalent mode. When operating in a bivalent mode, the values are less favorable, and several systems show no reduction, particularly when operating in an alternate mode at a bivalent tem... [more]

Tidal turbines generate energy from tidal currents [...]

PV-based mini-grids are identified as a feasible and, often, only economically viable option for the electrification of Kenyan remote and scattered rural areas, where connection to the national grid is challenging, and the related costs are high, if not prohibitive. This paper presents the analysis of typical Kenyan PV mini-grids by using some results of the work in the project “Reliable, Efficient and Sustainable Mini-Grids for Rural Infrastructure Development in Kenya (RESILIENT)”. After presenting average annual and seasonal daily load profiles of residential and small commercial mini-grid customers identified from the measured demands, the paper introduces the main mini-grid components and their models, including a simplified, but reasonably accurate, model of a mini-grid battery storage system based on the manufacturer’s charge−discharge curves. All mini-grid components are assembled in a scalable and easily reconfigurable simulation model of an actual Kenyan PV mini-grid, and the... [more]