In the biogas industry, feedstock plans are used to estimate methane production and nutrient content in the digestate, however, these predictions do not consider the mineralized nitrogen fraction of the feedstock, which is useful when determining the quality of the digestate. In this study, the artificial fiber bag technique, which is commonly used to study feedstock degradation in ruminants, was implemented in anaerobic digestion to quantify mineralization of N and S. The artificial fiber bags were used to enclose substrates but with access to inoculum because of small pores in the bags, thereby enabling digestion. The content of the bags was analyzed before and after digestion to quantify residual mass as well as N and S concentration in the substrate. The method was validated through batch anaerobic digestion of a single substrate with and without bags, where the bags showed little influence on methane production and degradation. Semi-continuous anaerobic digestion experiments showe... [more]

High altitude airships possess tremendous potential for long-endurance spot hovering platforms for both commercial and strategic applications. The energy system, which is mainly made up of solar array and regenerative fuel cell, is the key component of a high altitude airship. The thermal effect is a major factor that affects the performance of the energy system of long endurance stratospheric vehicles. In this paper, a conceptual design method focusing on the thermal and power characteristics of an energy system for stratospheric airships is proposed. The effect of thermal behavior of solar array on the energy system is analyzed. An optimized case is obtained on the consideration of power supply, thermal behaviors of helium and solar array. Results show that the maximum temperature difference of the solar array may be reduced by about 20 K and the mass of payload can be improved by up to 5%.

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]

Drilling volumes should be increased in order to increase hydrocarbon production, but this is impossible without the usage of high-quality drilling tools made of modern structural materials. The study has to analyze the design, technological and operational methods to increase the performance of drilling tools made of various materials and has highlighted prospects of technological method applications. The scientific novelty of the study consists in the development of a new analytical model of PDC drill bit−well interaction. The developed model takes into account the drill bit manufacturing errors in the form of bit body−nipple axes misalignment on the drill bit strength. This result makes it possible to determine the permissible manufacturing errors to provide safe operation of the drill bit. It is established that there is an additional transverse force that presses the drill bit to the well wall in the rock due to manufacturing errors. It is determined that the magnitude of this cla... [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]

Air pollution caused by vehicle emissions has raised serious public health concerns. Vehicle emissions generally depend on many factors, such as the nature of the vehicle, driving style, traffic conditions, emission control technologies, and operational conditions. Concerns about the certification cycles used by various regulatory authorities are growing due to the difference in emission during certification procedure and Real Driving Emissions (RDE). Under laboratory conditions, certification tests are performed in a ‘chassis dynamometer’ for light-duty vehicles (LDVs) and an ‘engine dynamometer’ for heavy-duty vehicles (HDVs). As a result, the test drive cycles used to measure the automotive emissions do not correctly reflect the vehicle’s real-world driving pattern. Consequently, the RDE regulation is being phased in to reduce the disparity between type approval and vehicle’s real-world emissions. According to this review, different variables such as traffic signals, driving dynamic... [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.

This paper presents the overall concept of a wideband and cost-effective current sensor. The sensor consists of a paralleled Hall-based current sensor (LEM) and a wideband current transformer (CT). A significant improvement of the band range and the moderate cost of the proposed sensor enable it to be used both to measure the instantaneous value in order to precisely plot the current and to obtain signals for a closed-loop control system of high-frequency power electronic converters. The sensor should be considered as an Augmented LEM Current Sensor (ALCS), which allows it to measure low- and high-frequency current signals. Finally, it allows for the measurement of a bipolar current up to 40 A. The overall cost of the sensor, along with the previously mentioned benefits, is an important feature of the proposed sensor. The present paper presents the analytical concept of the sensor (ALCS), a theoretical approach using simulation analysis, and the experimental results, which clearly demo... [more]

Due to increasing demand for clean and green energy, a need exists for fuels with low emissions, such as synthetic gas (syngas), which exhibits excellent combustion properties and has demonstrated promise in low-emission energy production, especially at microscales. However, due to complicated flame properties in microscale systems, it is of utmost importance to describe syngas combustion and comprehend its properties with respect to its boundary and inlet conditions, and its geometric characteristics. The present work studied premixed syngas combustion in a two-dimensional channel, with a length of 20 mm and a half-width of 1 mm, using computational approaches. Specifically, a fixed temperature gradient was imposed at the upper wall, from 300 K at the inlet to 1500 K at the outlet, to preheat the mixture, accounting for the conjugate heat transfer through the walls. The detailed chemistry of the ignition process was imitated using the San Diego mechanism involving 46 species and 235 r... [more]

Vibrations are a major cause of human health disorders, circuit boards and machinery damage. Vibration dampers are considered to be the best option to counter these issues. Three-dimensional printing techniques play an increasingly important role in manufacturing small polymer parts with tailored properties. Thermoplastic elastomers (TPE) constitute a perfect material for manufacturing small-scale series absorber prototypes due to their thermoplastic nature, good elasticity and damping properties. This paper proposes a novel multi-level approach to the design and manufacturing process, e.g., the first level—selection of material; second level—decision about the geometry of a damper; third—selection of technological printing parameters; fourth—post-printing treatment. This work primarily aims to overview the design and manufacturing process levels. The impact of each step on the damping capacity of small absorbers is assessed. It was found that thermoplastic elastomers and fused deposit... [more]

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]

Atmospheric factors, such as clouds, wind, dust, or aerosols, play an important role in the power generation of photovoltaic (PV) plants. Among these factors, soiling has been revealed as one of the most relevant causes diminishing the PV yield, mainly in arid zones or deserts. The effect of soiling on the PV performance can be analyzed by means of I−V curves measured simultaneously on two PV panels: one soiled and the other clean. To this end, two I−V tracers, or one I−V tracer along with a multiplexer, are needed. Unfortunately, these options are usually expensive, and only one I−V tracer is typically available at the site of interest. In this work, the design of a low-cost multiplexer is described. The multiplexer is controlled by a low-cost single-board microcontroller manufactured by ArduinoTM, and is capable of managing several pairs of PV panels almost simultaneously. The multiplexer can be installed outdoors, in contrast to many commercial I−V tracers or multiplexers. This adva... [more]

In recent years, wind farm layout optimization (WFLO) has been extendedly developed to address the minimization of turbine wake effects in a wind farm. Considering that increasing the degrees of freedom in the decision space can lead to more efficient solutions in an optimization problem, in this work the WFLO problem that grants total freedom to the wind farm area shape is addressed for the first time. We apply multi-objective optimization with the power output (PO) and the electricity cable length (CL) as objective functions in Horns Rev I (Denmark) via 13 different genetic algorithms: a traditionally used algorithm, a newly developed algorithm, and 11 hybridizations resulted from the two. Turbine wakes and their interactions in the wind farm are computed through the in-house Gaussian wake model. Results show that several of the new algorithms outperform NSGA-II. Length-unconstrained layouts provide up to 5.9% PO improvements against the baseline. When limited to 20 km long, the obta... [more]

In Europe, buildings are responsible for more than one third of the total final energy demands and greenhouse gas emissions. In the last twenty years, the European Union has published a succession of energy performance of building directives to define and ensure the fulfilment of a series of objectives regarding greenhouse gas emissions, energy consumption, energy efficiency and energy generation from renewable sources in buildings. For its part, Spain is adapting its legal framework, transposing these directives with the aim of achieving greater energy efficiency and sustainability for buildings. Under this context, an energy, economic and environmental assessment is performed to analyze the impact of these regulatory changes on a single-family home including a photovoltaic installation for self-consumption with surpluses and/or a solar thermal installation for domestic hot water supply, located in each one of the eight thousand one hundred thirty-one municipalities that make up Spain... [more]

This paper aims to reveal the causal relationship between energy prices and food prices and whether this relationship is similar in the food sub-groups forming the food price index used. As food prices more than doubled during the 2008 economic crisis, this relationship has received considerable attention from researchers. Many researches have been conducted to determine the causes and consequences of the 2008 food price crisis. Researches are mainly focused on crude oil and bio-energy in terms of “energy”. This research is not only differentiated by the data used but also by the methodology employed. The study attempts to add new findings to the empirical food price literature by utilizing relatively newly developed methods, namely Toda−Yamamoto causality, Fourier Toda−Yamamoto causality, and spectral BC causality tests. The spectral BC causality test clearly reveals that there is bidirectional causality between the energy price index and food price indexes (grains, other food, and oi... [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]

Geo-resources are widely exploited in our society, with huge benefits for both economy and communities. Nevertheless, with benefits come risks and impacts. Understanding how such risks and impacts are intrinsically borne in a given project is of critical importance for both industry and society. In particular, it is crucial to distinguish between the specific impacts related to exploiting a given energy resource and those shared with the exploitation of other energy resources. A variety of different approaches can be used to identify and assess such risks and impacts. In particular, Life Cycle Assessment (LCA) and risk assessments (RAs) are the most commonly adopted. Although both are widely used to support decision making in environmental management, they are rarely used in combination perhaps because they have been developed by largely different groups of specialists. By analyzing the structure and the ratio of the two tools, we have developed an approach for combining and harmonizin... [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 problem of electric network expansion has different implications concerning the definition of criteria for the comparison of different candidate projects. Transmission expansion planning usually involves a set of economic and technical influences on market framework and on network operation over defined scenario evolutions, or even combining generation and transmission planning, although the application to real-sized networks usually implies cost-benefit analysis. In this paper, a methodology for performance analysis of a set of network development projects is proposed, including zonal market framework and load flow analysis, in order to individuate possible candidate projects and their influence on active power losses, admissible load increase and admissible renewable generation increase. Those merit indicators are compared among candidate projects by means of Analytic Hierarchy Process (AHP) method, aiming at determining the most promising solution under different weights of crit... [more]

Cooking with modern energy fuels and technologies has a high potential to positively impact the users’ health and well-being, and make cooking safer and less burdensome for women and girls. To date, there have been numerous interventions targeting improved cooking solutions in displacement settings, but very few which have involved modern energy cooking, such as ethanol, biogas, LPG or electric cooking. They have been largely absent from humanitarian programming due to limited availability, affordability and lack of business models that suit those complex settings. Additionally, energy access services in displacement settings have historically relied primarily on grant-based funding. However, grants are limited to relatively short timeframes which do not align with the long-term needs of the displaced. New ways of funding energy access in displacement settings, and particularly modern energy cooking services, are urgently needed to address the scale of the challenge as the number of di... [more]