The type of occupant activities is a significantly important factor to determine indoor thermal comfort; thus, an accurate method to estimate occupant activity needs to be developed. The purpose of this study was to develop a deep neural network (DNN) model for estimating the joint location of diverse human activities, which will be used to provide a comfortable thermal environment. The DNN model was trained with images to estimate 14 joints of a person performing 10 common indoor activities. The DNN contained numerous shortcut connections for efficient training and had two stages of sequential and parallel layers for accurate joint localization. Estimation accuracy was quantified using the mean squared error (MSE) for the estimated joints and the percentage of correct parts (PCP) for the body parts. The results show that the joint MSEs for the head and neck were lowest, and the PCP was highest for the torso. The PCP for individual activities ranged from 0.71 to 0.92, while typing and... [more]

Fundamental shifts in the structure and generation profile of electrical grids are occurring amidst increased demand for resilience. These two simultaneous trends create the need for new planning and operational practices for modern grids that account for the compounding uncertainties inherent in both resilience assessment and increasing contribution of variable inverter-based renewable energy sources. This work reviews the research work addressing the changing generation profile, state-of-the-art practices to address resilience, and research works at the intersection of these two topics in regards to electrical grids. The contribution of this work is to highlight the ongoing research in power system resilience and integration of variable inverter-based renewable energy sources in electrical grids, and to identify areas of current and further study at this intersection. Areas of research identified at this intersection include cyber-physical analysis of solar, wind, and distributed ene... [more]

In this work, an investigation into the influence of prescribed motion on a body caudal fin aquatic unmanned vehicle (AUV) energy harvester is carried out. The undulatory−oscillation locomotion inspired by fishes actuates a composite beam representative of a spinal column with a piezoelectric patch. Two patch configurations—one at the head and tail—are considered for the AUV energy harvester, with a length that would not activate a harmonic in the system. An electromechanical model which accounts for the strain of the prescribed motion and the induced relative strain is developed. Discretizing the relative strain using Galerkin’s method requires a convergence study in which the impacts of the prescribed motion, dependent on the undulation and envelope of the motion, are investigated. The combination of prescribed motion and structural terms leads to a coupling that requires multiple investigations. The removal of the undulation of the system produces a more consistent response. The per... [more]

The organosolv-fractionation process can act as a biorefinery process because it can separate the main components of biomass, such as lignin and hemicellulose, with high purity. The ethanol-based organosolv-fractionation process was applied to separate carbohydrates and lignin from rice husks, and the extraction behavior was observed according to various reaction variables. Various reaction conditions such as different temperatures (150 °C, 170 °C, and 190 °C), reaction times (30 min, 60 min, and 120 min), and ethanol concentrations (40%, 60%, and 80%) were tested while maintaining the solid:liquid ratio (1:10) and sulfuric acid concentration (0.25 wt.%). Two optimal reaction conditions for the target components were chosen: for sugar recovery, 150 °C, 60 min, and 40% ethanol were used as condition 1, and for lignin recovery, 170 °C, 120 min, and 80% ethanol were used as condition 2. Under condition 1, 91.5% of the glucan was preserved in the residual solid, and 75.0% of the xylan was... [more]

Ammonia is a toxic exhaust component emitted from internal combustion engines. Both pure ammonia and the products of its reaction with nitrogen and sulfur compounds, being the source of particulate matter (PM) emissions, are dangerous for human health and life. The aim of the article was to demonstrate that NH3 can be produced in exhaust gas after-treatment systems of spark-ignition (SI) engines used in light-duty vehicles. In some cases, NH3 occurs in high enough concentrations that can be harmful and dangerous. It would be reasonable to collect research data regarding this problem and consider the advisability of limiting these pollutant emissions in future regulations. The article presents the results of the spark-ignition engine testing on an engine test bench and discusses the impact of the air−fuel ratio regulation and some engine operating parameters on the concentration of NH3. It has been proven that in certain engine operating conditions and a combination of circumstances lik... [more]

This study identifies unstable and soluble layers in commercial photovoltaic modules during 1.5 year long-term leaching. Our experiments cover modules from all major photovoltaic technologies containing solar cells from crystalline silicon (c-Si), amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS). These technologies cover more than 99.9% of the world market. We cut out module pieces of 5 × 5 cm2 in size from these modules and leached them in water-based solutions with pH 4, pH 7, and pH 11, in order to simulate different environmental conditions. Unstable layers open penetration paths for water-based solutions; finally, the leaching results in delamination. In CdTe containing module pieces, the CdTe itself and the back contact are unstable and highly soluble. In CIGS containing module pieces, all of the module layers are more or less soluble. In the case of c-Si module pieces, the cells’ aluminum back contact is unstable. Module pieces from... [more]

Attaining sustainable development and cleaner production is a major challenge both for developed and developing economies; income, institutional regulations, institutional quality and international trade are the key determinants of environmental externalities. The current work attempts to study the role of environmental taxes and regulations on renewable energy generation for developed economies. For that, the authors have used the annual dataset for the period 1994 to 2018. More specifically, the study investigates the impacts of environmental taxes, environment-related technologies and the environmental policy stringency index on renewable electricity generation in 29 developed countries. Given the short available data of these countries, the authors have developed panel cointegration and panel regressions models (fully modified ordinary least square (FMOLS), quantile regressions). The heterogeneous panel empirics stated that environmental regulations and income level support renewab... [more]

As a result of global energy demand increase, concerns over global warming, and rapid exhaustion of fossil fuels, there is a growing interest in energy system dependence on clean and sustainable energy resources. Attractive power technologies include photovoltaic panels, wind turbines, and biomass power. Fuel cells are also clean energy units that substitute power generators based on fossil fuels. They are employed in various applications, including transportation, stationary power, and small portable power. Fuel cell connections to utility grids require that the power conditioning units, interfacing the fuel cells and the grids, operate accordingly (by complying with the grid requirements). This study aims to model a centralised, single-stage grid-tied three-level diode clamped inverter interfacing a multi-stack fuel cell system. The inverter is expected to produce harmonic distortions of less than 0.5% and achieve an efficiency of 85%. Besides the grid, the system consists of a 1.54... [more]

Partial discharge (PD), where high field strengths on power cables cause charge build up and discharge within a dielectric at sites of imperfections or inhomogeneities, can lead to noise issues and potential failure of the dielectric. This paper presents the first stage of a research activity that aims to develop a transmission-line matrix (TLM)-based simulation “workbench” useful to investigate PD events in a transmission line. The proposed approach allows the predicting of the electromagnetic disturbances generated by the PD event, and the analysis of external field coupling, such as from intentional electromagnetic interference or lightning, which can add to the field stresses. The paper is focused on defining the right modeling method to simulate PD phenomena in a transmission line context. The best approach to integrate the PD model with the model of the transmission line, useful to describe the propagation of the conducted and radiated emissions produced by PD, is analyzed. A fir... [more]

The aggregation of operational active and reactive power flexibilities as the feasible operation region (FOR) is a main component of a hierarchical multi-voltage-level grid control as well as the cooperation of transmission and distribution system operators at vertical system interconnections. This article presents a new optimization-based aggregation approach, based on a modified particle swarm optimization (PSO) and compares it to non-linear and linear programming. The approach is to combine the advantages of stochastic and optimization-based methods to achieve an appropriate aggregation of flexibilities while obtaining additional meta information during the iterative solution process. The general principles for sampling an FOR are introduced in a survey of aggregation methods from the literature and the adaptation of the classic optimal power flow problem. The investigations are based on simulations of the Cigré medium voltage test system and are divided into three parts. The improv... [more]

Appropriate management of energy sources is one of the basic undertakings in the energy sector. Climate policy changes and the development of technologies enabling the acquisition of energy in a way to reduce the negative impact on the natural environment lead to diversity in the structure of the energy sources being used. Therefore, it is important to assess the impact of these changes on the development of energy sectors by particular countries. The article contains the analysis of various energy sources utilization by European Union (EU) countries and the assessment of the energy production sector potential, and the development of this potential in relation to changes in the energy sources structure. For this purpose, a multidimensional comparative analysis was used. The data for the analysis are derived from the Eurostat database for the years 2017 and 2019 for 28 EU countries and they concern the use of energy sources such as combustible fuels, coal and manufactured gases, natural... [more]

Non-intrusive load monitoring (NILM) is an important research direction and development goal on the distribution side of smart grid, which can significantly improve the timeliness of demand side response and users’ awareness of load. Due to rapid development, deep learning becomes an effective way to optimize NILM. In this paper, we propose a novel load identification method based on long short term memory (LSTM) on deep learning. Sequence-to-point (seq2point) learning is introduced into LSTM. The innovative combination of the LSTM and the seq2point brings their respective advantages together, so that the proposed model can accurately identify the load in process of time series data. In this paper, we proved the feature of reducing identification error in the experimental data, from three datasets, UK-DALE dataset, REDD dataset, and REFIT dataset. In terms of mean absolute error (MAE), the three datasets have increased by 15%, 14%, and 18% respectively; in terms of normalized signal ag... [more]

SiC MOSFETs have an excellent characteristic of high switching speed, which can improve the efficiency and power density of converters significantly. However, the fast switching processes of SiC MOSFETs cause serious crosstalk problems in bridge-arm configurations, which restricts the devices’ performances. This paper presents a detailed and accurate improved crosstalk analytical model, which takes into account the nonlinear capacitances, the parasitic inductances, the reverse recovery characteristics of the anti-parallel diodes, and the nonlinear voltage switching and damping oscillation process. The novelty of the proposed model lies in the fact that under the condition of comprehensively considering all these non-ideal factors of the bridge-arm, the effects of multi-parasitic elements and multi-variables coupling to the crosstalk are hierarchically divided. The parasitic elements and their correlations are described in detail and the direct and indirect variables’ impacts are clearl... [more]

The European Union created a European Green Deal Program (EGDP). This program aims at a sustainable economy through the transformation of the challenges related to climate and the environment. The main goal of EGDP is climate neutrality by 2050. The increase of alternative biomass residues utilization from various food processing industries and cooperation in the energy and waste management sector is required to meet these expectations. Nut shells are one of the lesser-known, yet promising, materials that can be used as an alternative fuel or a pre-treated product to further applications. However, from a thermal conversion point of view, it is important to know the energy properties and kinetic parameters of the considered biowaste. In this study, the energy and kinetic parameters of walnut, hazelnut, peanut, and pistachio shells were investigated. The results showed that raw nut shells are characterized by useful properties such as higher heating value (HHV) at 17.8−19.7 MJ∙kg−1 and m... [more]

The general consensus among academics is that the spatio-temporal humidity distribution is more or less uniform in an indoor space. This has, for the large part, not yet been proven by an academic study; subsequently, this paper aims to demonstrate that this is not always true. The paper makes use of a validated transient CFD model, which uses the Low Reynolds Number k-ϵ turbulence model. The model simulates people in a room at a constant skin temperature and emitting a constant source of humidity using source terms in the species equation. The model is eventually used to predict the implications of having a high source of humidity, in the form of occupancy, on the micro-climate’s spatio-temporal humidity distribution. The results for the high-occupancy case show that different locations experience various amounts of humid air, with a 31% difference between the lowest and highest locations. The amount of water vapor in each person’s proximity is deemed to be highly dependent on the flo... [more]

Non-Newtonian fluids may cause nonlinear seepage even for a single-phase flow. Through digital rock technologies, the upscaling of this non-Darcy flow can be studied; however, the requirements for scanning resolution and sample size need to be clarified very carefully. This work focuses on Bingham fluid flow in tight porous media by a pore-scale simulation on CT-scanned microstructures of tight sandstones. A bi-viscous model is used to depict the Bingham fluid. The results show that when the Bingham fluid flows through a rock sample, the flowrate increases at a parabolic rate when the pressure gradient is small and then increases linearly with the pressure gradient. As a result, an effective permeability and a start-up pressure gradient can be used to characterize this flow behavior. By conducting flow simulations at varying sample sizes, we obtain the representative element volume (REV) for effective permeability and start-up pressure gradient. It is found that the REV size for the ef... [more]

Decarbonisation and efficiency goals set as a response to global warming issue require appropriate decision-making strategies to promote an effective and timely change in energy systems. Conceptualization of change is a relevant part of energy transitions research today, which aims at enabling radical shifts compatible with societal functions and market mechanisms. In this framework, construction sector can play a relevant role because of its energy and environmental impact. There is, however, the need to move from general instances to specific actions. Open data and open science, digitalization and building data interoperability, together with innovative business models could represent enabling factors to accelerate the process of change. For this reason, built environment research has to address the co-evolution of technologies and human behaviour and the analytical methods used for this purpose should be empirically grounded, transparent, scalable and consistent across different tem... [more]

Recent technological developments in modular multilevel converter-based high-voltage direct current (MMC-HVDC) transmission systems have shown significant advantages over the traditional HVDC and two-level voltage source converter (VSC) transmission systems. However, there are a lack of studies on the protection methods for MMC-HVDC overhead lines where the protection method should be able to provide a fast and accurate response and be able to identify lightning strikes. In this paper, a wavelet entropy-based protection method is proposed. Due to the capability of revealing time−frequency distribution features, the proposed protection method combines wavelet and entropy to identify the time−frequency characteristics of different faults. Simulation results show that the proposed method can accurately and quickly determine the types of faults or disturbances with appropriate noise tolerance. In addition, the impact of the ground resistor and fault distance on the performance of the propo... [more]

In the context of the increasing popularity of self-sufficient communities around the globe, this study aims to compare the economic performance of energy management in two distinct situations: whether it is conducted individually or collectively within a community. After setting the context and completing a literature review, a research gap concerning the influence of regulatory frameworks in the economic results is identified. Therefore, this work presents this comparison under several frameworks employed to promote renewable energy, in order to provide a more realistic point of view and deliver insights in policy making. To this end, a mixed integer linear program (MILP) is developed, and the formulation of three key regulatory schemes is embedded into it: feed-in tariff, net metering, and self-consumption schemes. A what-if analysis is performed in order to take into account different combinations of rewarding parameters for each regulatory framework, as well as different profiles... [more]

Molten salt LiNO3-NaNO3-KNO3 has been investigated as heat transfer and thermal storage media for its low melting point and good thermal performance. In this paper, nanofluids were synthesized by dispersing MgO nanoparticles into LiNO3-NaNO3-KNO3, and the effects of nanoparticles on thermal properties were studied with different sizes (20−100 nm) and mass percent concentrations (0.5−2.0 wt.%). The addition of nanoparticles had little effect on melting temperature, and led to a slight increase in enthalpy of fusion by 2.0−5.5%. Compared with base salt, the density of nanofluid increased a little by 0.22−1.15%. The scanning electron microscope (SEM) test implied that nubby and punctate microstructures were responsible for larger surface area and interfacial energy, which could lead to the improvement of specific heat capacity reaching 2.6−10.6%. The heat transfer characteristics remarkably increased with the addition of nanoparticles, and the enhancement of average thermal diffusivity an... [more]

In this paper, different Pulse Width Modulation (PWM) strategies for operating with a low-switching frequency, a topology that combines Conventional Matrix Converters (CMCs), and Coupled Reactors (CRs) are presented and discussed. The principles of the proposed strategies are first discussed by a conceptual analysis and later validated by simulation. The paper shows how the combination of CMCs and CRs could be of special interest for sharing the current among these converters’ modules, being possible to scale this solution to be a modular system. Therefore, the use of coupled reactors allows one to implement phase shifters that give the solution the ability to generate a stair-case load voltage with the desired power quality even the matrix converters are operated with a low-switching frequency close to the grid frequency. The papers also address how the volume and weight of the coupled reactors decrease with the growth of the fundamental output frequency, making this solution especial... [more]

Solar chimney power plants (SCPPs) collect air heated over a large area on the ground and exhaust it through a turbine or turbines located near the base of a tall chimney to produce renewable electricity. SCPP design in practice is likely to be specific to the site and of variable size, both of which require a purpose-built turbine. If SCPP turbines cannot be mass produced, unlike wind turbines, for example, they should be as cheap as possible to manufacture as their design changes. It is argued that a radial inflow turbine with blades made from metal sheets, or similar material, is likely to achieve this objective. This turbine type has not previously been considered for SCPPs. This article presents the design of a radial turbine to be placed hypothetically at the bottom of the Manzanares SCPP, the only large prototype to be built. Three-dimensional computational fluid dynamics (CFD) simulations were used to assess the turbine’s performance when installed in the SCPP. Multiple referen... [more]

The paper presents the novel HF-GEN method for determining the characteristics of Electrical Appliance (EA) operating in the end-user environment. The method includes a measurement system that uses a pulse signal generator to improve the quality of EA identification. Its structure and the principles of operation are presented. A method for determining the characteristics of the current signals’ transients using the cross-correlation is described. Its result is the appliance signature with a set of features characterizing its state of operation. The quality of the obtained signature is evaluated in the standard classification task with the aim of identifying the particular appliance’s state based on the analysis of features by three independent algorithms. Experimental results for 15 EAs categories show the usefulness of the proposed approach.

The aging of power transformers causes several defects and damages in the insulating system, especially in the insulating paper. The degradation of the insulating paper generates dissolved gases in the insulating oil, which are measured by gas chromatography and used as an indicator of the insulation status. The state of the insulating paper can be identified based on the degree of polymerization (DP) measurement. In some cases, when the measurement of DP is difficult, estimating DP can be accomplished through gathering information about some of the testing parameters, such as the dissolved gases (DGA), breakdown voltage (BDV), oil interfacial tension (IF), oil acidity (ACI), moisture content (MC), oil color (OC), dielectric loss (Tan δ), and furans concentration specifically (2-furfuraldhyde (FA)). The statistical tools (correlation and multiple linear regression), based on 131 transformer samples, can be used to build a relation linking DP and one or more of the previous parameters t... [more]

A local thermal non-equilibrium analysis of heat and fluid flow in a channel fully filled with aluminum foam is performed for three cases: (a) pore density of 5 PPI (pore per inch), (b) pore density of 40 PPI, and (c) two different layers of 5 and 40 PPI. The dimensionless forms of fully developed heat and fluid flow equations for the fluid phase and heat conduction equation for the solid phase are solved analytically. The effects of interfacial heat transfer coefficient and thermal dispersion conductivity are considered. Analytical expressions for temperature profile of solid and fluid phases, and also the channel Nusselt number (NuH) are obtained. The obtained results are discussed in terms of the channel-based Reynolds number (ReH) changing from 10 to 2000, and thickness ratio between the channel height and sublayers. The Nusselt number of the channel with 40 PPI is always greater than that of the 5 PPI channel. It is also greater than the channel with two-layer aluminum foams until... [more]