Liquid fuels obtained in refining crude oil are one of the most important energies in economic activity. The domestic wholesale market for liquid fuels is of decisive importance for price formation in the national economy. The noncompetitive behavior of the market players at this level of the distribution chain can significantly affect all downstream price levels and the producer−consumer surplus balance. Therefore, the competitiveness of this market should be screened and assessed regularly, especially when significant external factors change. This article attempts to evaluate the impact of structural changes on the global market of crude oil and energy products after the outbreak of the COVID-19 pandemic on the competitiveness of the wholesale fuel market in Poland. Using asymmetry of the reaction of product prices to changes in the prices of inputs as a marker of noncompetitive behavior and the NARDL model as a test specification, the price paths of market players before and after t... [more]

Turbulent combustion modelling in internal combustion engines (ICEs) is a challenging task. It is commonly synthetized by incorporating the interaction between chemical reactions and turbulent eddies into a unique term, namely turbulent flame speed sT. The task is very complex considering the variety of turbulent and chemical scales resulting from engine load/speed variations. In this scenario, advanced turbulent combustion models are asked to predict accurate burn rates under a wide range of turbulence−flame interaction regimes. The framework is further complicated by the difficulty in unambiguously evaluating in-cylinder turbulence and by the poor coherence of turbulent flame speed (sT) measurements in the literature. Finally, the simulated sT from combustion models is found to be rarely assessed in a rigorous manner. A methodology is presented to objectively measure the simulated sT by a generic combustion model over a range of engine-relevant combustion regimes, from Da = 0.5 to Da... [more]

The main goal of setting energy efficiency priorities is to find ways to reduce energy consumption without harming consumers and the environment. The renovation of buildings can be considered one of the main aspects of energy efficiency in the European Union (EU). In the EU, only 5% of the renovation projects have been able to yield energy-saving at the deep renovation level. No other study has thus far ranked the EU member states according to achieved results in terms of increased usage in renewable sources, a decrease in energy usage and import, and reduction in harmful gas emissions due to energy usage. The main purpose of this article is to perform a comparative analysis of EU economies according to selected indicators related to the usage of renewable resources, energy efficiency, and emissions of harmful gasses as a result of energy usage. The methodological contribution of our study is related to developing a complex and robust research method for investment efficiency assessmen... [more]

An improved high step-down DC-DC converter for charging the batteries in an electric vehicle application is proposed in this paper. It adopts the topology of the conventional full-bridge converter, which has a coupled inductor current-doubler rectifier as the secondary side of the transformer. In addition, four power switches are driven using a phase-shifting technique. The proposed converter can achieve a high step-down voltage with low-voltage stress on the rectifier diodes. In addition, the coupled inductor current-doubler rectifier of the secondary side can reduce the ripple current and losses of the secondary side to achieve high efficiency. Furthermore, the proposed converter can overcome the drawbacks of the conventional full-bridge converter, such as switching loss caused by high switching frequency, duty-cycle loss, voltage stress, and numerous components, and can increase the efficiency with the soft-switching technique. A 600 W laboratory prototype of the proposed converter... [more]

Community renewable energy (CRE) has recently been proposed as one of the effective policy tools to make a community sustainable and to strengthen this association. CRE is, however, not widespread yet in Thailand, and evidence-based research on CRE in the country is rather scarce. This paper aims to investigate the characteristics of CRE in Thailand to identify the key factors affecting its implementation. Data were collected through semi-structured interviews and document analysis for 26 active CRE projects in Thailand. Results show that the characteristics of CRE in Thailand are rooted in the geographical location of a community. A legal structure was created from a pre-existing group to implement a CRE project. The primary motivation for implementing CRE is sustainable development of a community. We examined essential factors separated into two groups—internal and external factors—in reference to CRE in developed nations. We highlight several issues concerning the further developmen... [more]

Based on threshold regression models, this paper analyzes the effect of economic growth on energy intensity by using panel data from 21 developed countries from 1996 to 2015. Results show that a 1% increase in GDP per capita can lead to a 0.62−0.78% reduction in energy intensity, implying economic growth can significantly reduce energy intensity. The extent of the reduction in energy intensity varies depending on the economic development stages represented by key influencing factors including energy mix in consumption, urbanization, industrial structure, and technological progress. Specifically, the reduction in energy intensity due to economic growth can be enhanced with relatively more renewable energy consumption and more urban population until a threshold point, where the enhancement disappears. On the other hand, the extent of the energy intensity reduction due to economic growth can be weakened with relatively more tertiary industry activities and more research and development (R... [more]

This paper provides a theoretical framework to explore how the support policies for renewable energies can promote rent-seeking incentives in private firms. We develop a political economy of rent-seeking that considers the link between the regulatory decisions of political agents and the potential scope of socially wasteful pursuits. We argue that systematic public support schemes bring rent-seeking as a perception shared by entrepreneurs that influencing political allocations of resources is an essential and potentially preferable source of private profit than other for-profit economic avenues. As evidence of our claims, the framework is applied to the case of Spain to illustrate the economic effects of support policies on the production and distribution of renewable energy. We find rent-seeking behavior in Spain’s renewable energy industry, and precisely that: (i) political regulations have induced market concentration and rent-seeking in renewable energy firms, (ii) these firms have... [more]

In this study, carbon nanotubes (CNTs) were used as cathodes for lithium−oxygen (Li−O2) batteries to confirm the effect of oxygen functional groups present on the CNT surface on Li−O2 battery performance. A coating technology using atomic layer deposition was introduced to remove the oxygen functional groups present on the CNT surface, and ZnO without catalytic properties was adopted as a coating material to exclude the effect of catalytic reaction. An acid treatment process (H2SO4:HNO3 = 3:1) was conducted to increase the oxygen functional groups of the existing CNTs. Therefore, it was confirmed that ZnO@CNT with reduced oxygen functional groups lowered the charging overpotential by approximately 230 mV and increased the yield of Li2O2, a discharge product, by approximately 13%. Hence, we can conclude that the ZnO@CNT is suitable as a cathode material for Li−O2 batteries.

Methanolysis of vegetable oils in the presence of homogeneous catalysts remains the most important process for producing biodiesel. However, there is still a lack of accurate description of the reaction kinetics. This is in part due to the complexity of the reacting system in which a large number of interconnected reactions take place simultaneously. In this work, attention is focused on the biphasic character of the reaction medium, formed by two immiscible liquid phases. The behavior of the phases is investigated regarding their physicochemical properties, mainly density and mutual solubility of the components, as well as composition. In addition, two kinetic models with different level of complexity regarding the biphasic character of the reaction medium have been developed. It has been found that a heterogeneous model considering the presence of the two phases and the distribution of the several compounds between them is indispensable to get a good description of the process in ter... [more]

In response to the uncertainty of extreme climate change, energy consumption structure has been actively adjusted globally. Based on panel data of 101 countries or regions from 2006 to 2019, a panel data model with fixed effects is used to analyze the heterogeneous impacts of extreme climate risks on global consumption transition. The results show that extreme climate change has promoted the transition of the energy structure, reduced the consumption of fossil energy, and increased the consumption of renewable energy. Meanwhile, there are heterogeneous impacts of extreme climate change risks on the energy transition when different countries suffering from extreme weather conditions. Areas with high levels of economic development and coastal countries are more inclined to respond to climate change through energy transition. It is further confirmed that, under the impact of business cycle and oil price fluctuations, economic recession and falling oil prices will strengthen the correlatio... [more]

To ensure optimum working conditions for lithium-ion batteries, a numerical study is carried out for three-dimensional temperature distribution of a battery liquid cooling system in this work. The effect of channel size and inlet boundary conditions are evaluated on the temperature field of the battery modules. Based on the thermal behavior of discharging battery obtained experimental measurements, two temperature control strategies are proposed and studied. The results show that the channel width of the cooling plates has a great influence on the maximum temperature in the battery module. It is also revealed that increasing inlet water flow rate can significantly improve the heat transfer capacity of the battery thermal management system, while the relationship between them is not proportional. Lowering the inlet temperature can reduce the maximum temperature predicted in the battery module significantly. However, this will also lead to additional energy consumed by the cooling system... [more]

For energy supply in the Arctic regions, hybrid systems should be designed and equipped to ensure a high level of renewable energy penetration. Energy systems located in remote Arctic areas may experience many peculiar challenges, for example, due to the limited transport options throughout the year and the lack of qualified on-site maintenance specialists. Reliable operation of such systems in harsh climatic conditions requires not only a standard control system but also an advanced system based on predictions concerning weather, wind, and ice accretion on the blades. To satisfy these requirements, the current work presents an advanced intelligent automatic control system. In the developed control system, the transformation, control, and distribution of energy are based on dynamic power redistribution, dynamic control of dump loads, and a bi-directional current transducer. The article shows the architecture of the advanced control system, presents the results of field studies under th... [more]

Stable power supply has become a crucial thing in the current era of technology and automation. Although the power system has multiple stability issues and causes, frequency fluctuation plays a vital role in normal operation, whereby a system with significant frequency deviation can lead to the needless blackouts of the whole power system. With the rapid growth in power electronic converter (PEC)-based technologies and the huge penetration of nonsynchronous generators, the modern power system is becoming more complex by the day. This paper provides a comprehensive study on the stability issues that occur in modern power systems, mainly due to PEC-based technology integration. The in-depth reasons and the impacts of unstable power systems, along with their controlling techniques, are discussed to generate a clear understanding. Furthermore, the importance of frequency stability in a power system is discussed with respect to some important events that occurred in the past. This paper als... [more]

This paper presents bioenergy value chain modelling to estimate the biomass and bioenergy cost of production and biomass netback in combined heat and power (CHP) systems. Modelling compares biomass cost and netback to analyse the feasibility of CHP systems, as well as the internal rate of return (IRR) and payback period (PBP). Models are implemented into the IMP Bio2Energy® software (Instituto Mexicano del Petróleo, Mexico City, Mexico) for practical application and demonstrated for bioenergy generation in the agroindustrial processes of tequila production, coffee and orange processing using as biomass the agave bagasse, coffee pulp and orange peels coproducts, respectively. Results show that the CHP systems are economically feasible, i.e., biomass cost of production is lower than netback, PBP between 3 and 4 years and IRR > 20%. The cost of bioenergy is lower than the cost of fuel oil and grid electricity being replaced. The sensitivity analysis for boiler steam pressure showed that t... [more]

Several building energy simulation programs have been developed to evaluate the indoor conditions and energy performance of buildings. As a fundamental component of heating, ventilating, and air conditioning loads, each building energy modeling tool calculates the heat and moisture exchange among the outdoor environment, building envelope, and indoor environments. This paper presents a simplified heat and moisture transfer model of the building envelope, and case studies for building performance obtained by different heat and moisture transfer models are conducted to investigate the contribution of the proposed steady-state moisture flux (SSMF) method. For the analysis, three representative humid locations in the United States are considered: Miami, Atlanta, and Chicago. The results show that the SSMF model effectively complements the latent heat transfer calculation in conduction transfer function (CTF) and effective moisture penetration depth (EMPD) models during the cooling season.... [more]

The transfer functions G(s) for different types of heat exchangers obtained from their partial differential equations usually contain some irrational components which reflect quite well their spatio-temporal dynamic properties. However, such a relatively complex mathematical representation is often not suitable for various practical applications, and some kind of approximation of the original model would be more preferable. In this paper we discuss approximate rational transfer functions G^(s) for a typical thick-walled double-pipe heat exchanger operating in the counter-flow mode. Using the semi-analytical method of lines, we transform the original partial differential equations into a set of ordinary differential equations representing N spatial sections of the exchanger, where each nth section can be described by a simple rational transfer function matrix Gn(s), n=1,2,…,N. Their proper interconnection results in the overall approximation model expressed by a rational transfer functi... [more]

We use a dataset for the group of G7 countries and China to study the out-of-sample predictive value of uncertainty and its international spillovers for the realized variance of crude oil (West Texas Intermediate and Brent) over the sample period from 1996Q1 to 2020Q4. Using the Lasso estimator, we found evidence that uncertainty and international spillovers had predictive value for the realized variance at intermediate (two quarters) and long (one year) forecasting horizons in several of the forecasting models that we studied. This result holds also for upside (good) and downside (bad) variance, and irrespective of whether we used a recursive or a rolling estimation window. Our results have important implications for investors and policymakers.

Solar energy transformation technologies are increasingly being used worldwide in the district heating sector. In the Baltic states, only one district heating company has implemented a large-scale solar collector field into its thermal energy production system, which is analyzed within this research. In this study, we analyzed the first year operation of the solar field, solar collector efficiency, and several influencing factors, i.e., ambient air temperature, heat carrier flow, and the temperature difference between the supply and return heat carrier temperatures. The study includes collecting and compilation of the data, analyzing influencing factors, and data analysis using the statistical analysis method. In addition, the research presents a simplified multi-regression model based on the actual performance of a large-scale solar field, which allows for forecasting the efficiency of solar collectors by taking into account the main operational parameters of the DH system. The result... [more]

The article compares the climate conditions in an excavation with thermally insulated roof and sidewalls to the conditions when such insulation is absent. The analysis of the temperatures presented in the article consisted of limiting the heat transfer from the rock mass to the heading in one of the Polish coal mines. It is widely believed that the thermal insulation of heading sidewalls, through which fresh air is supplied, can substantially improve climate conditions. The article’s objective is to evaluate the impact of thermal insulation on the surface of the roof and sidewalls on the reduction in heat transfer from the strata with a high virgin temperature to mine air. Preventing the existing climate hazard involves higher costs of coal extraction, whereas the consequences of inadequate prevention threaten the health or life of the miners.

The process of pelleting miscanthus biomass often encounters issues related to the low durability of the obtained pellets and high energy inputs. To solve these issues, the use of copra meal as a supplement is proposed. This paper presents the results of research on energy parameters of miscanthus biomass pellets supplemented with copra meal in terms of energy consumption in the pressure agglomeration process. As part of this research, the energy parameters of miscanthus biomass, copra meal biomass, and their blends were characterized. Next, the raw materials were used for the production of pellets in the pressure agglomeration process. The investigations included proximate and ultimate analysis and estimation of heating values. Moreover, the total fat content, mechanical durability, kinetic strength, and bulk density were determined, and the energy consumption in the pelleting process was assessed. The results indicate that the energy consumption in the miscanthus biomass pelleting pr... [more]

The European Union, in accordance with its decarbonization objectives, has enacted the Directive (EU) 2018/2001 and subsequently the Directive (EU) 2019/944 that legally recognizes and regulates the formation of citizen energy communities. These are believed to be key enablers for reducing buildings’ carbon footprint by allowing for a wider diffusion of on-site renewable energy generation and by maximizing renewable energy self-consumption. In this study, the benefits of the energy community are assessed through simulations of average Italian buildings of various sizes, different energy efficiency levels, equipped with a photovoltaic system and a heat pump-driven heating system, and located in heating-dominated climates. The work focuses on energy communities both at the apartment scale—i.e., in a multi-family building—and at the building scale—i.e., in a neighborhood. The net energy consumption, the self-consumption, and the self-sufficiency of all the possible energy communities obta... [more]

This study investigates the dependence between extreme returns of West Texas Intermediate (WTI) crude oil prices and the Crude Oil Volatility Index (OVX) changes as well as the predictive power of OVX to generate accurate Value at Risk (VaR) forecasts for crude oil. We focus on the COVID-19 pandemic period as the most violate in the history of the oil market. The static and dynamic conditional copula methodology is used to measure the tail dependence coefficient (TDC) between the variables. We found a strong relationship in the tail dependence between negative returns on crude oil and OVX changes and the tail independence for positive returns. The time-varying copula discloses the strongest tail dependence of negative oil price shocks and the index changes during the COVID-19 health crisis. The findings indicate the ability of the OVX index to be a fear gauge with respect to the oil market. However, we cannot confirm the ability of OVX to improve one day-ahead forecasts of the Value at... [more]

The objective of this paper is to provide new data about the possibility of using ammonia as a carbon-free fuel in a spark-ignition engine. A current GDI PSA engine (Compression Ratio 10.5:1) was chosen in order to update the results available in the literature mainly obtained in the CFR engine. Particular attention was paid to determine the lowest possible load limit when the engine is supplied with pure ammonia or a small amount of H2, depending on engine speed, in order to highlight the limitation during cold start conditions. It can be concluded that this engine can run stably in most of these operating conditions with less than 10% H2 (of the total fuel volume) added to NH3. Measurements of exhaust pollutants, and in particular NOx, have made it possible to evaluate the possibility of diluting the intake gases and its limitation during combustion with pure H2 under slightly supercharged conditions. In conclusion, the 10% dilution limit allows a reduction of up to 40% in NOx while... [more]

In this study, a resonance avoidance control algorithm was designed to address the tower resonance problem of a semi-submersible floating offshore wind turbine (FOWT) and the dynamic performance of the wind turbine, floater platform, and mooring lines at two exclusion zone ranges were evaluated. The simulations were performed using Bladed, a commercial software for wind turbine analysis. The length of simulation for the analysis of the dynamic response of the six degrees of freedom (DoF) motion of the floater platform under a specific load case was 3600 s. The simulation results are presented in terms of the time domain, frequency domain, and using statistical analysis. As a result of applying the resonance avoidance control algorithm, when the exclusion zone range was ±0.5 rpm from the resonance rpm, the overall performance of the wind turbine was negatively affected, and when the range was sufficiently wide at ±1 rpm, the mean power was reduced by 0.04%, and the damage equivalent loa... [more]

Many studies have proposed a peer-to-peer energy market where the prosumers’ actions, including energy consumption, charge and discharge schedule of energy storage systems, and transactions in local energy markets, are controlled by a central operator. In this paper, prosumers’ actions are not controlled by an operator, and the prosumers freely participate in the local energy market to trade energy with other prosumers. We designed and modeled a local energy market with a management algorithm that uses community energy storage for prosumers who competitively participate in trade in the real-time energy market. We propose an energy-trade management algorithm that manages the trades of prosumers in two phases based on bids and offers submitted by prosumers. The first phase is to manage the trade of prosumers who have submitted fair prices to trade with other prosumers in the real-time energy market. The second phase is managing the trade of prosumers that could not trade in the first pha... [more]