Energies, Volume 16, Issue 17 (September-1 2023) – 310 articles

Water cut is a vital monitoring and surveillance parameter with great significance in oil production operations and processing. Water-cut measurements are also challenging due to the significant variations and the harsh measurement environment. The objective of this article is to review the current water-cut measurement techniques and suggest future areas that are expanding to overcome existing measurement challenges. Commercially available online methods such as capacitance-based sensors, tomography techniques, gamma densitometry, ultrasonic meters and infrared meters, and the traditional laboratory offline methods, are discussed, along with their principle of operation, detection range, and sensing resolution. Also, the discussed techniques are summarized, highlighting their main advantages and limitations. Furthermore, future trends and research areas, such as Artificial Intelligence (AI), soft computing, Metamaterials, and Nuclear Magnetic Resonance (NMR), which are integrated with water-cut measurements, are briefly mentioned. The current research hotspots are directed toward integrating full-range measurements with multi-parameter detection, high sensitivity, and reliability. Full article

Solid-state energy conversion has been established as one of the most promising solutions to address the issues related to conventional energy generation. Thermoelectric materials allow direct energy conversion without moving parts and being deprived of greenhouse gases emission, employing lightweight and quiet devices. Current applications, main thermoelectric material classes, and manufacturing methods are the topics of this work; the discussion revolves around the crucial need for highly performing materials in the mid-temperature range, and around the development of more scalable fabrication technologies. The different manufacturing methods for thermoelectric bulk materials and films are also discussed. Small-scale technologies are generating increasing interest in research; the high potential of aerosol jet printing is highlighted, stressing the many advantages of this technology. A promising approach to scale the production of miniaturized thermoelectric devices that combines high energy ball milling and aerosol jet printing is proposed in the conclusion. Full article

Considering the negative effect of anthropological activities on climate in recent decades, all countries entailed a universal commitment to fight against climate change by boosting innovation and introducing new technologies. In this context, our paper aimed to investigate the impact of innovation input in terms of research and development (R&D) costs and technology expressed as technical equipment and machinery (TEM) on the reported greenhouse gas (GHG) emissions in chemical industry companies in five Central and Eastern European countries. This study employed a panel regression model with fixed effects and covered data from 2015 to 2020. The empirical results emphasize a negative relationship between R&D costs and GHG emissions, indicating the companies’ commitment to developing innovative solutions that contribute to lower destructive emissions. Additionally, the findings related to the influence of TEM on GHG emissions reveal a positive impact, highlighting the need to improve manufacturing technologies. The practical implications of our findings can be meaningful for both policymakers and businesses operating in the chemical industry in developing countries. Policymakers should offer financial incentives to support research and investments in clean technologies, while businesses should prioritise such investments to mitigate GHG emissions. Full article

Recently, there has been growing recognition of the significance of energy and environmental challenges. Utilization of lithium-ion batteries in electric vehicles has shown considerable potential and benefits for tackling these issues. The effective management of battery temperature has become a crucial factor in the advancement and widespread adoption of lithium-ion batteries in electric vehicles. In this study, a thermo-coupled pseudo-two-dimensional (P2D) electrochemical model is employed to simulate the heat generation of the NCM811-21700 cylindrical battery cell at various discharge rates at an ambient temperature of 25 °C, and is validated by experimental data. The validation results demonstrate that the thermo-coupled P2D model can effectively predict the battery voltage curve during the discharge process with less than 4% errors. Although there is a slightly larger error in the temperature prediction during the battery 2C and 3C discharge processes, the maximum error approaches 10%, which is still generally within an acceptable range. In addition, the battery’s electrochemical and thermal characteristics during discharge are presented. The suggested thermo-coupled electrochemical model can be used for applications in the thermal management system of the NCM811-21700 battery. Full article

With the goal of achieving “carbon peak in 2030 and carbon neutrality in 2060”, as clearly proposed by China, the transportation sector will face long–term pressure on carbon emissions, and the application of hydrogen fuel cell vehicles will usher in a rapid growth period. However, true “zero carbon” emissions cannot be separated from “green hydrogen”. Therefore, it is of practical significance to explore the feasibility of renewable energy hydrogen production in the context of hydrogen refueling stations, especially photovoltaic hydrogen production, which is applied to hydrogen refueling stations (hereinafter referred to “photovoltaic hydrogen refueling stations”). This paper takes a hydrogen refueling station in Shanghai with a supply capacity of 500 kg/day as the research object. Based on a characteristic analysis of the hydrogen demand of the hydrogen refueling station throughout the day, this paper studies and analyzes the system configuration, operation strategy, environmental effects, and economics of the photovoltaic hydrogen refueling station. It is estimated that when the hydrogen price is no less than 6.23 USD, the photovoltaic hydrogen refueling station has good economic benefits. Additionally, compared with the conventional hydrogen refueling station, it can reduce carbon emissions by approximately 1237.28 tons per year, with good environmental benefits. Full article

The purpose of this experimental work was to investigate the role of the leading-edge wavy shape technique on the performance of small-scale HAWT fixed-pitch rotor blades operating under off-design conditions. Geometric parameters such as amplitude and wavelength were considered design variables to generate five different wavy shape blade models in order to increase the aerodynamic performance of the rotor with a diameter of 280 mm. A dedicated airfoil type S822 for small wind turbine application from the NREL Airfoil Family was chosen to fulfil both the aerodynamic and structural aspects of the blades. Rotor models were tested in a wind tunnel for different wind speeds while maintaining constant rotational speed to provide the blade-tip chord Reynolds number of 4.7 × 10⁴. The corrected tunnel data, in terms of power coefficients and tip-speed ratios, were compared first with the literature to validate the experimental approach, and then among themselves. It was observed that for minimal sizes of tubercles, the performance of the rotor increases by about 40% compared to the RB1 baseline rotor model for a low tip-speed ratio. Conversely, for the maximum size of the tubercles, there is a marked decrease of about 51% of the rotor performance for a moderate tip-speed ratio compared to the RB1 rotor model. Among these models, specifically, the RB2 rotor model with the smallest values of amplitude and wavelength provides a 2.8% higher peak power coefficient compared to the RB1 rotor model, and at the same time preserves higher performance values for a broad range of tip-speed ratios. Full article

Solid oxide fuel cells (SOFCs)’ main advantage in fuel flexibility appears to be an interesting subject for further exploration. From the literature survey, direct utilisation of hydrocarbon as fuel for SOFCs has garnered attention with promising results reported. Various approaches, showcasing potential for using methane (CH₄) and heavier hydrocarbons in SOFCs, have been described. The direct use of hydrocarbons can occur through either direct internal reforming or gradual internal reforming, with requisite precautionary measures to mitigate carbon formation. While the internal reforming process could proceed via steam reforming, dry reforming or partial oxidation, an exciting development in the direct use of pure hydrocarbons, seems to progress well. Further exploration aims to refine strategies, enhance efficiency and ensure the long-term stability and performance of hydrocarbon-fuelled SOFC systems. This review delves into the progress in this field, primarily over the past two decades, offering comprehensive insights. Regardless of fuel type, studies have largely concentrated on catalyst compositions, modifications and reaction conditions to achieve better conversion and selectivity. Finding suitable anode materials exhibiting excellent performance and robustness under demanding operating conditions, remains a hurdle. Alternatively, ongoing efforts are directed towards lowering working temperatures, enabling consideration of a wider range of materials with improved electrochemical performance. Full article

This study focuses on the optimization of an electric heater design for molten salt pre-heating in a supercritical CO₂–molten-salt loop. The scope of the investigation is to analyze typical designs of similar components for identifying possible malfunctions and defining proper modifications in the geometry and operating conditions to address such technical issues and optimize the attained thermal efficiency. By performing computational fluid dynamics simulations for reference designs of such components, two particularities pertinent to the temperature distribution are identified as the most likely ones: the development of hot spots and thermal stratification. As a further step, new designs and operating conditions are proposed and their effects on eliminating the hot spots and stratification development phenomena are evaluated. It is shown that the homogeneous distribution of heat flux density across the heating elements is the most favorable option for avoiding the development of hot spots, while the mitigation of thermal stratification is possible through the development of turbulent flow. The proposed design and operating conditions are expected to facilitate the optimization of molten-salt electric heater operation and promote the development of next-generation molten-salt–supercritical-CO₂ concentrating solar power plants. Full article

Dynamic thermal insulation systems (DTISs) can adapt to external environment conditions and help to reduce energy consumption and increase occupants’ thermal comfort, contributing towards the mitigation of overheating. DTISs adjust their configuration to optimize heat transfer through the façade. In this study, the performance of a DTIS was assessed through laboratory tests and numerical simulation. The DTIS is based on the ventilation of an air gap that facilitates the heat exchanges between the exterior and the interior. To extend the results of the experimental campaign, a set of scenarios was assessed based on numerical simulation. The results of the laboratory tests showed that the R-value obtained when the mechanical ventilation of the air gap is off (insulation state) is 3.89 m².°C/W. In comparison, when it is on (conductive state), the R-value is 1.56 m².°C/W, which corresponds to a reduction of approximately 60%. The results of the simulations showed that, when the shading system was on, the higher U-value was useful more than 50% of the time with discomfort, increasing to 75% when the shading system was off. Full article

Global energy consumption has led to concerns about potential supply problems, energy consumption and growing environmental impacts. This paper comprehensively provides a detailed assessment of current studies on the subject of building integrated photovoltaic (BIPV) technology in net-zero energy buildings (NZEBs). The review is validated through various case studies, which highlight the significance of factors such as building surface area to volume ratio (A/V), window-wall ratio (WWR), glass solar heating gain coefficient (SHGC), and others in achieving the NZEBs standards. In addition, this review article draws the following conclusions: (1) NZEBs use renewable energy to achieve energy efficiency and carbon neutrality. (2) NZEBs implementation, however, has some limitations, including the negligence of indoor conditions in the analysis, household thermal comfort, and the absence of an energy supply and demand monitoring system. (3) Most researchers advise supplementing facade and window BIPV as solely roofing BIPV will not be able to meet the building’s electricity usage. (4) Combining BIPV with building integrated solar thermal (BIST), considering esthetics and geometry, enhances outcomes and helps meet NZEB criteria. (5) BIPV designs should follow standards and learn from successful cases. However, to ascertain the long-term reliability and structural integrity of BIPV systems, a comprehensive study of their potential degradation mechanisms over extended periods is imperative. The review paper aims to examine BIPV applications in-depth, underscoring its pivotal role in attaining a net-zero energy benchmark. Full article

This study employs a life cycle assessment (LCA) approach to investigate the environmental burden of photovoltaic power generation systems that use multi-crystalline silicon (multi-Si) modules in Pakistan. This study evaluates the energy payback time (EPBT) of this class of systems, and considers various environmental impacts, including climate change, acidification, and eutrophication. The assessment accounts for upstream, midstream, and downstream processes, including cell as well as module production. The critical stages in the production cycle were identified, including the metallic silicon transformation into solar silicon and the assembly of the panels, which involve energy-intensive materials such as aluminum frames and glass roofing. Despite using the most efficient conversion technology, the former stage consumes a significant amount of electricity. This study reveals that multi-Si PV systems in Pakistan have an EPBT that is considerably less than their lifespan, ranging from 2.5 to 3.5 years. These findings suggest that the development of PV systems in Pakistan is a very interesting option for energy production. Additionally, this study compares solar PV and wind power generation systems in various regions of Pakistan. The study outcomes can facilitate evidence-based decision-making processes in the renewable energy sector and contribute significantly to Pakistan’s endeavor to transition toward a sustainable energy system. Full article

Singapore has committed to achieving net zero emissions by 2050, which requires the pursuit of multiple decarbonization pathways. ${\mathrm{CO}}_2$ utilization methods such as fuel production may provide a fast interim solution for carbon abatement. This paper evaluates the feasibility of green hydrogen-based synthetic fuel (synfuel) production as a method for utilizing captured ${\mathrm{CO}}_2$. We consider several scenarios: a baseline scenario with no changes, local production of synfuel with hydrogen imports, and overseas production of synfuel with ${\mathrm{CO}}_2$ exports. This paper aims to determine a ${\mathrm{CO}}_2$ price for synfuel production, evaluate the economic viability of local versus overseas production, and investigate the effect of different cost parameters on economic viability. Using the current literature, we estimate the associated production and transport costs under each scenario. We introduce a ${\mathrm{CO}}_2$ utilization price (CUP) that estimates the price of utilizing captured ${\mathrm{CO}}_2$ to produce synfuel, and an adjusted ${\mathrm{CO}}_2$ utilization price (CCUP) that takes into account the avoided emissions from crude oil-based fuel production. We find that overseas production is more economically viable compared to local production, with the best case CCUP bounds giving a range of 142–148 $/t${\mathrm{CO}}_2$ in 2050 if ${\mathrm{CO}}_2$ transport and fuel shipping costs are low. This is primarily due to the high cost of hydrogen feedstock, especially the transport cost, which can offset the combined costs of ${\mathrm{CO}}_2$ transport and fuel shipping. In general, we find that any increase in the hydrogen feedstock cost can significantly affect the CCUP for local production. Sensitivity analysis reveals that hydrogen transport cost has a significant impact on the viability of local production and if this cost is reduced significantly, local production can be cheaper than overseas production. The same is true if the economies of scale for local production is significantly better than overseas production. A significantly lower carbon capture cost can also the reduce the CCUP significantly. Full article

Renewable penetration, particularly the increasing deployment of PV by residential customers, organizations, and utilities, is leading to the rapid evolution of the power grid. However, the power system’s architectural changes affect the quality of supply and give rise to power quality issues such as harmonics, fluctuations, disturbances, etc., at the point of common coupling (PCC). Therefore, in this work, a power network was modeled to study the impact of PV systems on PCC. At first, a detailed review is presented for on-grid PV systems with different inverter topologies, control techniques, sources of harmonic generation, and their mitigation strategies. After that, several use cases considering various sources of harmonics in a network with on-grid PV are modeled and simulated using MATLAB/Simulink. In-depth research was performed in this work to examine the many variables that affect harmonics, such as solar radiation levels, controller tuning, and load changes. Results with a real-time simulation platform (OPAL-RT) are presented in this paper for several use cases. Lastly, comprehensive discussions are presented from the acquired offline and real-time simulation results. Full article

Dust accumulation on a PV panel surface can considerably lead to photovoltaic energy degradation. A particle-based dust accumulation model was proposed to estimate the surface dust coverage fraction on a PV panel. The model determines the effect of the surface dust coverage fraction on the performance of the PV panel. Gravity, wind, and particle-surface interaction forces were resolved to their components, and force balance was established to determine surface-parallel (slipping force) and surface-orthogonal (adhering force) component forces. The proposed model was validated through a schedule of lab and field experiments and by comparing the predicted values with the results of a validated model developed by Lu and Hajimirza. The relationship between a solar panel’s output power and the surface dust coverage fraction under the wind effect was established for three types of dust (graphene, silica, and natural dust) using Response Surface Methodology (RSM). Statistical analysis was applied to determine the most and least influencing variables on the output power of three types of solar panels (mono-crystalline, polycrystalline, and thin-film PV panels) exposed to dust accumulation. The obtained results show that dust particle size, wind velocity, and PV panel tilt angle play important roles in enhancing or degrading PV performance. Lower values of the tilt angle resulted in maximum output power, while high values of the tilt angle reduced the incident sunlight on the surface of the PV panel, resulting in lower output power. However, higher values of the tilt angle led to a lower dust coverage area of the PV panel and consequently decreased the power losses of the PV panel. The results also show that wind velocity has a considerable impact on the dust scraping of fine particles from a PV surface. The enhancement percentages of PV performance due to wind influence are 4.85%, 5.85%, and 10.9% for graphene, silica, and natural dust, respectively. Full article

The European Union (EU) has agreed to gradually include shipping in the EU emissions trading scheme (EU ETS), which makes shipping companies vulnerable to carbon price fluctuations. The aim of this paper is to investigate the effectiveness of carbon and petroleum futures contracts in managing carbon and bunker risks. We examine the effectiveness of alternative hedging methods, including both static and dynamic approaches, to estimate optimal hedge ratios under single and composite cross-hedge settings. Our results show that carbon future contracts are important for hedging the carbon emission allowances price risk, and Brent oil futures are the most effective instrument for out-of-sample hedging of bunker prices. In addition, the hedging effectiveness indicates that conventional methods outperform the sophisticated models in terms of variance reduction. Our study offers new insights into how the carbon and bunker markets relate to a combination hedging in reducing the joint price risk, which can be used to promote risk management in the market. Full article

This study investigates the development trend of smart-green cities, focusing on seven megacities in China. It addresses three issues that are common in urban green development, including the relationship between “smart” and “green”, the scenario analysis of green development, and the uniqueness of megacities in green development. System dynamics modeling is applied. The simulation results reveal an “S”-shaped development curve for both aspects, indicating a gradual and accelerating growth pattern. Notably, the curve representing energy consumption lags behind the curve for smart city development by approximately three years. After 2030, when the smart city construction is expected to be completed, the proportion of the tertiary industry and investment in science and technology will play a significant role in limiting energy consumption. This study concludes by providing policy suggestions, including the need for long-term plans with phased targets, considering the specificity of megacities, and addressing external influences. Full article

In recent years, the increasing environmental problems, especially the issue of global warming, have motivated demand for a cleaner, more sustainable, and economically viable energy source. In this context, wind energy plays a significant role due to the small negative impact it has on the environment, which makes it among the most widespread potential sustainable renewable fuel nowadays. However, wind turbine control systems are important factors in determining the efficiency and cost-effectiveness of a wind turbine (WT) system for wind applications. As wind turbines become more flexible and larger, it is difficult to develop a control algorithm that guarantees both efficiency and reliability as these are conflicting objectives. This paper reviews various control strategies for the three main control systems of WT, which are pitch, torque, and yaw control, in different operational regions considering multi-objective control techniques. The different control algorithms are generally categorized as classical, modern (soft computing) and artificial intelligence (AI) for each WT control system. Modern and soft computing techniques have been showing remarkable improvement in system performance with minimal cost and faster response. For pitch and yaw systems, soft computing control algorithms like fuzzy logic control (FLC), sliding mode control (SMC), and maximum power point tracking (MPPT) showed superior performance and enhanced the WT power performance by up to 5% for small-scale WTs and up to 2% for multi-megawatt WTs. For torque control systems, direct torque control (DTC) and MPPT AI-based techniques were suitable for reducing generator torque fluctuations and estimating the torque coefficient for different wind speed regions. Classical control techniques such as PI/PID resulted in poor dynamic response for large-scale WTs. However, to improve classical control techniques, AI algorithms could be used to tune the controller’s parameters to enhance its response, as a WT is a highly non-linear system. A graphical abstract is presented at the end of the paper showing the pros/cons of each control system category regarding each WT control system. Full article

This study investigated the impact of dual-fuel operation using ethanol-blended diesel fuel enriched with hydroxy gas on CRDI engine performance, combustion, and emission characteristics. Neat diesel fuel was used to run the engine, along with a 20% volume fraction of an ethanol-diesel mixture that had been enhanced with three distinct streams of hydroxy gas, namely 1, 1.5, and 2 LPM. Hydroxy gas was generated by an electrolysis technique using a plate-type dry cell electrolyser (316 L stainless steel) in the presence of a NaOH catalyst. Compared to E20 (Ethanol 20%) fuel, HHO gas enrichment with lower proportions of ethanol blend E20 + 2LPM had a 2.74% increase of BTE and a 5.89% decrease of BSEC at a 5.02 bar BMEP condition. Similarly, HC, CO, and smoke emissions decreased by 4.61%, 5.19%, and 3.1%, while NOx emissions and EGT increased by 3.22% and 3.06% compared to E20. With the addition of HHO gas, combustion characteristics such as HRR, CP, and ignition delay improve while the combustion duration increases. At maximum BMEP, cylinder pressure and heat release rate increase by 3.18% and 6.58% for E20 + 2LPM HHO, respectively. It was found that the 20% volume of the ethanol-diesel blend, with 2 LPM of hydroxy gas, positively affects engine characteristics. Full article

Gas consumption is subject to large seasonal fluctuations between the summer season (period with lower request) and the winter season (time with increased consumer demand). Underground gas storage applications (UGS) help to ensure a steady and reliable supply of natural gas, even during periods of peak demand, smoothing price fluctuations and providing a means of balancing the supply and demand of natural gas on a daily, weekly, or seasonal basis. However, UGS activities can induce vertical ground displacement, which is usually strictly associated with the injection and withdrawal of gas into/from the reservoir. It is necessary to carefully monitor and manage the potential impact of UGS activities on the subsurface and surface to ensure the stability and safety of the local environment. The Interferometric Synthetic Aperture Radar (InSAR) technique can provide a wide range of high-precision information on seasonal surface deformation associated with UGS activities useful for increasing the amount of information on ground deformation monitoring. This study introduces a unique and replicable approach to investigating freely available ground movement data for a fractured aquifer reservoir located in the Madrid Basin (Guadalajara, Spain), which is currently employed for seasonal underground gas storage applications. Notably, this study gives a comprehensive comparison of InSAR results of UGS activity in a deep aquifer, leveraging data that are entirely open-source and easily accessible. The Yela UGS project exploits a carbonate reservoir (dolomite) managed, since 2012, by Enagás, the Spanish main Transmission System Operator (TSO). InSAR data from 2015 to 2021 provided a full and coherent ground deformation pattern of the area. Based on this data, a fully integrated volumetric variation model was developed, elucidating the effects of gas storage activity. A significant correlation between the periodic injection/withdrawal rates of natural gas and InSAR ground deformation over time was identified. Full article

A new combined boost-Cuk-forward (CBCF) converter with ripple-free input current and low switch voltage stress is proposed for high step-up applications. Two coupled inductors are applied to achieve low switch voltage stress as well as balanced dc-link voltages, wherein the former is placed in series with the boost diode, and the latter is formed as a forward converter. Because these inductors are coupled with the output Cuk inductor, a ripple-free input current is also attained. The proposed converter is run at discontinuous conduction mode (DCM) by applying a low output-side Cuk inductance to reduce the switching loss by providing a ZCS turn-on of MOSFET and removing the diode reverse recovery current. In addition, the proposed converter does not have a problem with ground leakage current. The practical results verify the performance and effectiveness of the proposed CBCF high step-up converter. Full article

In a high percentage of new energy-islanded microgrids, the overall inertia of the system gradually decreases, and the transient stability requirements of the microgrid frequency and voltage become more and more demanding under low-inertia conditions. To improve the transient stability of low-inertia islanded microgrid frequencies and voltages, this paper proposes a transient stability enhancement strategy for islanded microgrids based on energy storage system (ESS)–virtual synchronous generator (VSG) control. Model predictive control (MPC) is added within the active control loop of the VSG to achieve dynamic correction of the active power reference value of the VSG; PI control link is added within the reactive control loop to achieve a fast dynamic response of the reactive power command value. The ESS achieves fast and accurate regulation of frequency and voltage according to the power reference value of the VSG active control loop and the power command value of the reactive control loop simultaneously. Considering the need to ensure the ability of VSG to operate stably during transients, a comprehensive current-limiting technique combining virtual impedance and phase limiting is used to limit the fault current of VSG and maintain its synchronization and stability. Finally, the simulation results verify the strategy’s effectiveness and the superiority of the transient stability enhancement effect. Full article

The main purpose of this paper is the techno-economic analysis of hydrogen production from biogas via steam reforming in a pilot plant. Process flow modeling based on mass and energy balance is used to estimate the total equipment purchase and operating costs of hydrogen production. The pilot plant installation produced 250.67 kg/h hydrogen from 1260 kg/h biomethane obtained after purification of 4208 m³/h biogas using a heat and mass integration process. Despite the high investment cost, the plant shows a great potential for biomethane reduction and conversion to hydrogen, an attractive economic path with ecological possibilities. The conversion of waste into hydrogen is a possibility of increasing importance in the global energy economy. In the future, such a plant will be expanded with a CO₂ reduction module to increase economic efficiency and further reduce greenhouse gases in an economically viable manner. Full article

In an era of increasing environmental challenges, the transition to a low-carbon economy is an essential step for the manufacturing and industrial sectors. The quality of business processes plays a key role in the transition to a zero-carbon economy. The objective of the paper was, thus, to analyze the break-even point in core and supporting business processes using the proposed linear model based on regression analysis. The aim was to identify the impact of qualitative processes in the pre-production, production, and post-production phases on reaching the break-even point and how these processes affect profits in engineering companies operating in low-carbon sectors. The results suggest that supporting quality processes would generate the highest profit. Investing in improving the quality of core and supporting business processes has a twofold impact, as it improves the bottom line of enterprises through enhancing their reputation as socially responsible businesses. Corporate reputation based on corporate social responsibility in a low-carbon economy represents a valuable intangible asset that helps industrial companies to develop a sustainable and thriving low-carbon business ecosystem. Full article

Power line communication (PLC) is a technology that exploits existing electrical transmission and distribution networks as guiding structures for electromagnetic signal propagation. This facilitates low-rate data transmission for signaling and control operations. As the demand in terms of data rate has greatly increased in the last years, the attention paid to broadband PLC (BPLC) has also greatly increased. This concept also extended to railways as broadband traction power line communication (BTPLC), aiming to offer railway operators an alternative data network in areas where other technologies are lacking. However, BTPLC implementation faces challenges due to varying operating scenarios like urban, rural, and galleries. Hence, ensuring coverage and service continuity demands the suitable characterization of the communication channel. In this regard, the scientific literature, which is an indicator of the body of knowledge related to BTPLC systems, is definitely poor if compared to that addressed to BPLC systems installed on the electrical transmission and distribution network. The relative papers dealing with BTPLC systems and focusing on the characterization of the communication channel show some theoretical approaches and, rarely, measurements guidelines and experimental results. In addition, to the best of the author’s knowledge, there are no surveys that comprehensively address these aspects. To compensate for this lack of information, a survey of the state of the art concerning BTPLC systems and the measurement methods that assist their installation, assessment, and maintenance is presented. The primary goal is to provide the interested readers with a thorough understanding of the matter and identify the current research gaps, in order to drive future research towards the most significant issues. Full article

This paper focuses on the possible roles of aggregators in the European electricity markets and the challenges and opportunities they face in participating in different market segments. Demand response (DR) is becoming increasingly important with the growth of renewable energy, and aggregators can play a critical role in balancing supply and demand in real time. This paper provides an overview of prices in electricity markets in which DR aggregators can participate and provides recommendations for aggregators regarding which markets to focus on. However, the regulatory framework for aggregators is still evolving in Europe, creating challenges for them to navigate different market designs, regulatory frameworks, and pricing mechanisms. Through a combination of literature review and data analysis, this paper aims to provide insights for aggregators on how to maximize profits and minimize risks in the European electricity market. The article achieves this by conducting an extensive analysis of various markets, comparing their essential attributes relevant to the functioning of aggregators. Full article

Direct Air Capture (DAC) is a promising technology to fight climate change by capturing carbon dioxide (CO₂) from the air. For DAC to be a negative emissions technology, the captured CO₂ must be removed permanently, but can also be used as a net-zero technology to produce sustainable chemicals, fuels or other materials. This review presents a comprehensive survey of recent advancements, challenges, and potential applications of DAC technology, with an emphasis on the recent rapid increase in the number of DAC developers, the majority of them being founded in the past 4 years. Through pilot projects and recent commercial deployments, several DAC companies have made significant advances and demonstrated their scalability. Cost and energy efficiency remain significant impediments to the wide deployment of DAC. Integration with emission-free energy sources and utilization of waste heat are being researched to boost the total energy efficiency of DAC systems. Further research of electrochemical technologies for regeneration or direct capture are needed, as well as the development of new, modified, or hybrid adsorbents for improved capture efficiencies. Moreover, favorable regulations and financial incentives are crucial for enhancing the viability of DAC projects and will need to substantially increase if Paris Agreement goals are to be achieved. Full article

The replacement of fossil-based products with renewable alternatives is today a major research topic. Biofuels, such as second-generation ethanol, offer a promising way to overcome dependence on fossil fuels. However, second-generation biorefineries still face bottlenecks that hinder their economic sustainability. These include challenges in pretreatment (formation of inhibitors and high costs of chemicals) and hydrolysis (high enzyme costs and low solid content) and maximizing the utilization of biomass components. To achieve economic sustainability, biorefineries can adopt approaches such as integrating first and second generation (1G and 2G) technologies, using different production alternatives, or diversifying the product portfolio. This last alternative could include the simultaneous production of biomaterials, building blocks, and others from all fractions of the materials, favoring biorefinery profitability. Techno-economic assessment plays a crucial role in assessing the economic feasibility of these approaches and provides important information about the process. This article discusses how product diversification in cellulosic biorefineries enhances their economic sustainability, based on simulation techniques and techno-economic analysis, with a comprehensive and critical review of current possibilities and future trends. The information discussed can inform stakeholders about investing in 2G ethanol biorefineries, including strategies, associated risks, and profitability, allowing better planning of different options of future ventures. Full article

The influence of photovoltaic (PV) output with stochasticity and uncertainty on the grid-connected system’s voltage stability is worth further exploration. The long-term voltage stability of a 3-bus system with a large-scale PV power station considering the adjustment of an on-load tap changer (OLTC) was studied. In this typical system, two supercritical Hopf bifurcation (SHB) points are found using the bifurcation calculation. At the SHB point that appears first, a small sudden increase in reactive load power or a sudden increase in PV active power P_pv can eventually cause a voltage collapse after a long increasing oscillation. The long-term collapse phenomenon shows that SHB cannot be ignored in the PV grid-connected system. Meanwhile, the time constant of OLTC can affect the progress of long-term voltage collapse, but it has different effects under different disturbances. When P_pv drops suddenly at the SHB point, due to the adjustment of OLTC, the load bus voltage can recover to near the target value of OLTC after a long period of time. Similarly, the time constant of OLTC can affect the progress of long-term voltage recovery. To prevent the long-term voltage collapse when P_pv increases suddenly at the SHB point, a new locking-OLTC index I_lock, depending on the value of P_pv corresponding to the SHB point, and a locking OLTC method are proposed, and the voltage can be recovered to an acceptable stable value quickly. Compared with the system without OLTC, OLTC adjustment can effectively prevent long-term voltage oscillation instability and collapse, so that PV power can play a bigger role in power systems. Full article

In recent years, the share of PV (photovoltaic) panels in the generation of renewable energy has been dynamically growing. During this time, the Polish government introduced numerous programs to assist households in switching to PV panels as the primary source of energy. Therefore, the aim of the article is to indicate the PV panels that are best suited to work for individual users in households in Poland. PV panels were assessed using the PROSA multi-criteria decision analysis method, supported by a stochastic approach, based on the Monte Carlo method. This approach made it possible to choose the most balanced solutions, in terms of individual criteria, and to take into account the uncertainty and imprecision of the weights of the assessment criteria. In particular, the use of reliable weight ranges in the Monte Carlo simulations allowed the construction of a whole spectrum of evaluation and ranking models. These models indicate the PV panels that best meet the requirements and have the best balance between the individual assessment criteria. As a result of the research, it was found that the requirements of PV installations in households in Poland are best met by panels produced in China and in the Chinese–Polish cooperation. Panels of Polish production ranked further down, which means that Polish producers do not offer products that are tailored to the needs of PV installations for households in Poland. Full article

Currently, synthetic ester is gaining a bigger share in the market. This type of insulating liquid is used both in new and operated transformers filled with mineral oil. In the case of transformers in operation, the synthetic ester is used in the retrofilling procedure, drying the cellulose insulation, or as a blend with oil, the properties of which are better than those of base liquids. In all these three cases, we are dealing with a mixture of synthetic ester and mineral oil. The concentration of both of these liquids in the mixture has a significant impact on its properties; therefore, methods are necessary to determine the content of individual mixture components. The article presents a method for determining the concentration of mineral oil in a mixture with synthetic ester using near-infrared spectroscopy. Based on the conducted tests, an absorption band was determined that can be used for this purpose. This band is centered at 2126 nm. The determined dependence of the absorbance on mineral oil concentration in the mixture with synthetic ester confirmed the linear nature of this relationship. The conducted research confirmed the possibility of using the method based on near-infrared spectroscopy to determine the concentration of individual components of a mixture of mineral oil and synthetic ester. The proposed method can be used both for a mixture of new liquids and mixtures of new synthetic ester with mineral oils of different degrees of aging. The method of determining the concentration of mineral oil in a mixture with synthetic ester based on near-infrared spectroscopy is new and is characterized by a higher accuracy in relation to the methods previously described in the literature. Full article