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This study examined the influence of biohydrogen fermentation under the high bicarbonate alkalinity (BA) and pH to optimize these critical parameters. When sucrose was used as a substrate, hydrogen was produced over a wide range of pH values (5–9) under no BA supplementation, however, BA affected hydrogen yield significantly under different initial pHs (5–10). The actual effect of high BA using raw piggery waste (pH 8.7 and BA 8.9 g CaCO3/L) showed no biogas production or propionate/acetate accumulation. The maximum hydrogen production rate (0.32 L H2/g volatile suspended solids (VSS)-d) was observed at pH 8.95 and 3.18 g CaCO3/L. BA greater than 4 g CaCO3/L also triggered lactate-type fermentation, leading to propionate accumulation, butyrate reduction and homoacetogenesis, potentially halting the hydrogen production rate. These results highlight that the substrate with high BA need to amend adequately to maximize hydrogen production.

In this paper a solid oxide fuel cell (SOFC) system for cogeneration of heat and power integrated with a stratified heat storage tank is studied. The use of a storage tank with thermal stratification allows one to increase the annual operating hours of CHP: heat can be produced when the request is low (for instance during the night), taking advantage of thermal stratification to increases the heat recovery performance. A model of the SOFC system is presented to estimate the energy required to meet the average electric energy demand of the residence. Two fuels are considered, namely syngas produced by gasification and natural gas. The tank model considers the temperature gradients over the tank height. The results of the numerical simulation are used to size the SOFC system and storage heat tank to provide energy for a small household using two different fuels. In particular it was shown that in the case of syngas, due to larger system heat output, a larger tank volume was required in order to accumulate unused heat over the night. The detailed description of the tank model will be useful to energy system modelers when sizing hot water tanks. Problem formulation is reported also using a Matlab script.

In the research field of multilevel converters, three-level NPC (neutral-point-clamped) converters, which unfortunately may cause the deviation of the neutral-point voltage of DC-link capacitors, are widely discussed. Theoretically, virtual space vector modulation (VSVM) could guarantee the balance control of the neutral-point voltage. However, there still exist some uncontrollable space vector regions. Based on VSVM, this paper proposes a varied virtual space vector modulation (VVSVM) method for three-level NPC converters. Under complete modulation conditions, this method can control the balance of the neutral-point voltage of DC-link capacitors by adjusting the duty cycle of small vectors and regulating the current generated by virtual medium vectors. Compared with commonly used VSVM methods and mixed modulation strategies, this method is simpler and more practical. The effectiveness and validity of this method are verified by simulations and experiments.

Based on the benchmark solid oxide fuel cell (SOFC) dynamic model for power system studies and the analysis of the SOFC operating conditions, the nonlinear programming (NLP) optimization method was used to determine the maximum electrical efficiency of the grid-connected SOFC subject to the constraints of fuel utilization factor, stack temperature and output active power. The optimal operating conditions of the grid-connected SOFC were obtained by solving the NLP problem considering the power consumed by the air compressor. With the optimal operating conditions of the SOFC for the maximum efficiency operation obtained at different active power output levels, a hierarchical load tracking control scheme for the grid-connected SOFC was proposed to realize the maximum electrical efficiency operation with the stack temperature bounded. The hierarchical control scheme consists of a fast active power control and a slower stack temperature control. The active power control was developed by using a decentralized control method. The efficiency of the proposed hierarchical control scheme was demonstrated by case studies using the benchmark SOFC dynamic model.

This paper explores real power generation planning, considering distributed generation resources and energy storage in a small standalone power system. On account of the Kyoto Protocol and Copenhagen Accord, wind and photovoltaic (PV) powers are considered as clean and renewable energies. In this study, a genetic algorithm (GA) was used to determine the optimal capacities of wind-turbine-generators, PV, diesel generators and energy storage in a small standalone power system. The investment costs (installation, unit and maintenance costs) of the distributed generation resources and energy storage and the cost of fuel for the diesel generators were minimized while the reliability requirement and CO 2 emission limit were fulfilled. The renewable sources and loads were modeled by random variables because of their uncertainties. The equality and inequality constraints in the genetic algorithms were treated by cumulant effects and cumulative probability of random variables, respectively. The IEEE reliability data for an 8760 h load profile with a 150 kW peak load were used to demonstrate the applicability of the proposed method.

For the interconnected power system with large-scale wind power, the problem of the small signal stability has become the bottleneck of restricting the sending-out of wind power as well as the security and stability of the whole power system. Around this issue, this paper establishes a small signal stability region boundary model of the interconnected power system with large-scale wind power based on catastrophe theory, providing a new method for analyzing the small signal stability. Firstly, we analyzed the typical characteristics and the mathematic model of the interconnected power system with wind power and pointed out that conventional methods can’t directly identify the topological properties of small signal stability region boundaries. For this problem, adopting catastrophe theory, we established a small signal stability region boundary model of the interconnected power system with large-scale wind power in two-dimensional power injection space and extended it to multiple dimensions to obtain the boundary model in multidimensional power injection space. Thirdly, we analyzed qualitatively the topological property’s changes of the small signal stability region boundary caused by large-scale wind power integration. Finally, we built simulation models by DIgSILENT/PowerFactory software and the final simulation results verified the correctness and effectiveness of the proposed model.

This paper proposes three probability models to assess the impact of communication delays and bit errors on differential protection. First, the mechanism of relay protection malfunction caused by communication delays and bit errors is introduced. In general, a channel’s consistent delay or bit error results in refuse-operations, while a channel’s inconsistent delay normally causes false trips. Based on the analysis of the probability distributions of communication delays and bit errors, probabilistic models of false trips and refuse-operations are proposed. Simulation results, using typical parameters, are implemented to investigate the effects of communications on the malfunction probability of differential protection.

Buildings do not usually perform during operation as well as predicted during the design stage. Disagreement between simulated and metered energy consumption represents a common issue in building simulation. For this reason, the calibration of building simulation models is of growing interest. Sensitivity and uncertainty analyses play an important role in building model accuracy. They can be used to identify the building model parameters most influent on the energy consumption. Given this, these analyses should be integrated within calibration methodologies and applications for tuning the parameters. This paper aims at providing a picture of the state of the art of calibration methodologies in the domain of building energy performance assessment. First, the most common methodologies for calibration are presented, emphasizing criticalities and gaps that can be faced. In particular the main issues to be addressed, when carrying out calibrated simulation, are discussed. The standard statistical criteria for considering the building models calibrated and for evaluating their goodness-of-fit are also presented. Second, the commonly used techniques for investigating uncertainties in building models are reviewed. Third, a review of the latest main studies in the calibrated simulation domain is presented. Criticalities and recommendations for new studies are finally provided.

In this work, the effects of the electric fields on the flame propagation and combustion characteristics of lean premixed methane–air mixtures were experimentally investigated in a constant volume chamber. Results show that the flame front is remarkably stretched by the applied electric field, the stretched flame propagation velocity and the average flame propagation velocity are all accelerated significantly as the input voltage increases. This indicates that the applied electric field can augment the stretch in flame, and the result is more obvious for leaner mixture. According to the analyses of the combustion pressure variation and the heat release rate, the peak combustion pressure P max increases and its appearance time t p is advanced with the increase of the input voltage. For the mixture of λ = 1.6 at the input voltage of −12 kV, P max increases by almost 12.3%, and t p is advanced by almost 31.4%, compared to the case of without electric fields. In addition, the normalized mass burning rate and the accumulated mass fraction burned are all enhanced substantially, and the flame development duration and the rapid burning duration are remarkably reduced with the increase of the input voltage, and again, the influence of electric field is more profound for leaner mixtures. The results can be explained by the electric field-induced stretch effects on lean burn methane-air mixture.

Over the last years, the pretreatment of biomass as a source of energy has become one of the most important steps of biomass conversion. In this work the effect of a mild subcritical hydrothermal carbonization of a tropical woody biomass was studied. Results indicate considerable change in carbon content from 52.78% to 65.1%, reduction of oxygen content from 41.14% to 28.72% and ash slagging and fouling potential. Even though decarboxylation, decarbonylation and dehydration reactions take place, dehydration is the one that prevails. The mass and energy balance was affected by the treatment conditions than the severity of the treatment.

To improve knowledge of the wind loads on photovoltaic structures mounted on flat roofs at the high angles required in high latitudes, and to study starting flow on low aspect ratio wind turbine blades, a series of wind tunnel tests were undertaken. Thin flat plates of aspect ratios between 0.4 and 9.0 were mounted on a sensitive three-component instantaneous force and moment sensor. The Reynolds numbers varied from 6 × 10 4 to 2 × 10 5 . Measurements were made for angles of attack between 0° and 90° both in the free stream and in wall proximity with increased turbulence and mean shear. The ratio of drag to lift closely follows the inverse tangent of the angle of incidence for virtually all measurements. This implies that the forces of interest are due largely to the instantaneous pressure distribution around the plate and are not significantly influenced by shear stresses. The instantaneous forces appear most complex for the smaller aspect ratios but the intensity of the normal force fluctuations is between 10% and 20% in the free-steam but can exceed 30% near the wall. As the wind tunnel floor is approached, the lift and drag reduce with increasing aspect ratio, and there is a reduction in the high frequency components of the forces. It is shown that the centre of pressure is closer to the centre of the plates than the quarter-chord position for nearly all cases.

In this work, an LCL-type resonant dc/dc converter with a capacitive output filter is modeled in two stages. In the first high-frequency ac stage, all ac signals are decomposed into two orthogonal vectors in a synchronous rotating d–q frame using multi-frequency modeling. In the dc stage, all dc quantities are represented by their average values with average state-space modeling. A nonlinear two-stage model is then created by means of a non-linear link. By aligning the transformer voltage on the d -axis, the nonlinear link can be eliminated, and the whole converter can be modeled by a single set of linear state-space equations. Furthermore, a feedback control scheme can be formed according to the steady-state solutions. Simulation and experimental results have proven that the resulted model is good for fast simulation and state variable estimation.

While ever-growing bio-ethanol production poses considerable challenges to the bioenergy supply chain, the risk of refinery operation disruptions further compromises the efficiency and reliability of the energy supply system. This paper applies discrete and continuous reliable facility location models to the design of reliable bio-ethanol supply chains so that the system can hedge against potential operational disruptions. The discrete model is shown to be suitable for obtaining the exact optimality for small or moderate instances, while the continuous model has superior computational tractability for large-scale applications. The impacts of both site-independent and dependent disruptions ( i.e. , due to flooding) are analyzed in empirical case study for the State of Illinois (one of the main biomass supply states in the U.S.). The reliable solution is compared with a deterministic solution under the same setting. It is found that refinery disruptions, especially those site-dependent ones, affect both optimal refinery deployment and the supply chain cost. Sensitivity analysis is also conducted to show how refinery failure probability and fixed cost (for building biorefineries) affect optimal supply chain configuration and the total expected system cost.

For establishing hydrate-based technologies for natural-gas storage/transport, CO 2 capture from industrial flue gases, etc. , we need appropriate guidelines for the scale-up of hydrate production/processing equipment from laboratory scales to industrial scales. This paper aims to provide technical remarks on the scale-up of hydrate-forming reactors, the central components of hydrate production/processing equipment, particularly focusing on such a reactor design that hydrate-forming gas is dispersed in an aqueous phase which is either stirred in a tank or forced to flow through a tube. Based on the principles of classical fluid mechanics and heat-transfer analysis, the paper derives semi-empirical formulas that show how the capacity for heat discharge from each reactor and the power for operating the reactor are required to change with an increase in its size. Consequently, it is concluded that the stirred-tank design is unfavorable for significant scale-up and that the scale-up of tubular reactors should be made without significantly increasing the in-tube flow velocity.

This paper presents a new selective and non-directional protection method to detect ground faults in neutral isolated power systems. The new proposed method is based on the comparison of the rms value of the residual current of all the lines connected to a bus, and it is able to determine the line with ground defect. Additionally, this method can be used for the protection of secondary substation. This protection method avoids the unwanted trips produced by wrong settings or wiring errors, which sometimes occur in the existing directional ground fault protections. This new method has been validated through computer simulations and experimental laboratory tests.

Pressure drop is an important consideration in Total Site Heat Integration (TSHI). This is due to the typically large distances between the different plants and the flow across plant elevations and equipment, including heat exchangers. Failure to consider pressure drop during utility targeting and heat exchanger network (HEN) synthesis may, at best, lead to optimistic energy targets, and at worst, an inoperable system if the pumps or compressors cannot overcome the actual pressure drop. Most studies have addressed the pressure drop factor in terms of pumping cost, forbidden matches or allowable pressure drop constraints in the optimisation of HEN. This study looks at the implication of pressure drop in the context of a Total Site. The graphical Pinch-based TSHI methodology is extended to consider the pressure drop factor during the minimum energy requirement (MER) targeting stage. The improved methodology provides a more realistic estimation of the MER targets and valuable insights for the implementation of the TSHI design. In the case study, when pressure drop in the steam distribution networks is considered, the heating and cooling duties increase by 14.5% and 4.5%.

In this paper, a reflex charger with zero-voltage-switching (ZVS) and non-dissipative cells for photovoltaic (PV) energy conversion is presented. The proposed reflex charger has the following advantages: (1) A ZVS cell is incorporated to reduce the switching losses of the main and auxiliary switches. Therefore, the conversion efficiency of the proposed reflex charger can be improved significantly, (2) A non-dissipative charging/discharging reflex cell is used to increase charging efficiency and extend lifecycle of battery. Finally, a prototype reflex charger with ZVS and non-dissipative cells is built and implemented. Experimental results are presented to verify the performance and the feasibility of the proposed reflex charger for PV energy conversion.

Unbalanced voltage will inevitably cause power and DC voltage fluctuations in a three-phase PV system. The deterioration of power quality will do great harm to the PV panels and the loads, so it is necessary to suppress the power fluctuations. This paper further explores the coefficients control strategy of PV converters under unbalanced voltage conditions, aiming to suppress power fluctuations by controlling the injection of some specific orders of current harmonics into the grid. In order to achieve this, the current reference of the PV inverter has been changed by bringing in two control coefficients, and the expression of each order of the current harmonics has been deduced. Based on the standards of PV systems, the regions from which the coefficients can be selected are determined. Then, by tuning these coefficients in the feasible regions, the output parameters (power fluctuation, current THD and odd harmonics) can be controlled precisely. The model of this method is built and simulated in PSCAD/EMTDC, and as a result, it is shown that the power fluctuations can be restricted according to different power quality requirements.

It is of great importance and urgency for Taiwan to develop offshore wind power. However, relevant data on offshore wind energy resources are limited. This study imported wind speeds measured by a tidal station and a buoy into the software WAsP to estimate the high-altitude wind speeds in the two areas. A light detection and ranging (Lidar) system was set up near the tidal station and buoy. High-altitude wind speeds measured by the Lidar system were compared with the WAsP-estimated values, and it was discovered that the two data sets were consistent. Then, long-term wind speed data observed by buoys and tidal stations at various locations were imported into WAsP to forecast wind speeds at heights of 55–200 m on the west coast of Taiwan. The software WAsP Engineering was used to analyze the extreme wind speeds in the same areas. The results show that wind speeds at 100 m are approximately 9.32–11.24 m/s, which means that the coastal areas of west Taiwan are rich in wind energy resources. When a long-term 10-min average wind speed is used, the extreme wind speed on the west coast is estimated to be between 36.4 and 55.3 m/s.

Energy Recovery Battery Testing Systems (ERBTS) plays an important role in battery manufacture. The conventional ERBTS configuration contains a fundamental transformer, and a bidirectional Direct Current (DC)–DC and Alternating Current (AC)–DC converter. All ERBTS are connected in parallel, thus constituting a special and complicated AC micro-grid system. Aiming at addressing their low energy recovery efficiency, complex grid-connected control algorithm issues for islanded detection, and complicated power circuit topology issues, a hierarchical DC-link voltage hybrid AC–DC micro-grid that contains composite energy storing devices is proposed. Moreover, an energy management optimal scheme for the proposed scheme is put forward. The system configuration of the proposed scheme is described in detail. Compared to the conventional scheme, the proposed scheme has the merits of simplified power circuit topology, no need for phase synchronous control, and much higher energy recovery efficiency and reliability. The validity and effectiveness of the proposed technique is verified through numerous experimental results.

Hot water extraction of aspen woodchips was treated at about 160 °C for 2 h with a liquor-to-solid ratio of 4.76:1 in a 1.84 m3 batch reactor with external liquor circulation. Both five-carbon and six-carbon sugars are obtained in the extraction liquor. Xylose and xylooligomers are the main five-carbon sugar in the hot water extract, which reached a maximum concentration of 0.016 mol/L, and 0.018 mol/L, respectively. Minor monosaccharides including galactose, mannose, rhamnose, glucose, and arabinose are also obtained during the hot water extraction. Rhamnose is the main six-carbon sugar in the extraction liquor, which has a maximum concentration of 0.0042 mol/L. The variations of acetyl groups and formic acid are investigated due to their catalytic effect on the extraction reactions. Zeroth-order kinetics models are found to be adequate in describing the dissolved solids, acids, xylose, and xylooligomers.

Italy promoted one of the most generous renewable support schemes worldwide which resulted in a high increase of solar power generation. We analyze the Italian day-ahead wholesale electricity market, finding empirical evidence of the merit-order effect. Over the period 2005–2013 an increase of 1 GWh in the hourly average of daily production from solar and wind sources has, on average, reduced wholesale electricity prices by respectively 2.3€/MWh and 4.2€/MWh and has amplified their volatility. The impact on prices has decreased over time in correspondence with the increase in solar and wind electricity production. We estimate that, over the period 2009–2013, solar production has generated higher monetary savings than wind production, mainly because the former is more prominent than the latter. However, in the solar case, monetary savings are not sufficient to compensate the cost of the related supporting schemes which are entirely internalized within end-user tariffs, causing a reduction of the consumer surplus, while the opposite occurs in the case of wind.

The paper presents selected isotropic and anisotropic mathematical models to calculate the distribution of solar radiation on the photovoltaic module plane with any spatial orientation. A comparison of solar radiation models for Poland is based on measured data and received from the Institute of Meteorology and Water Management. Power density of solar radiation for different angular positions, especially for representative days of each month, was calculated. Based on the statistical analysis of the percentage root-mean-square error (RMSE%), mean-bias error (MBE%) and the Pearson correlation coefficient of an individual mathematical model, our own correction factor for diffuse radiation was proposed. A modified Liu-Jordan model was compared with six common mathematical models showing better agreement of measured and calculated values of solar radiation density. The presented analysis explains which mathematical model is the most suitable for central Poland (Poznań, 52°25’ N, 16°56’ E) and shows the validity of applying the modified model to improve the accuracy of determination of the radiation power density for a given elevation and azimuth angle using values for a horizontal plane.

We present a novel design of a single-cylinder free piston engine linear generator (FPELG) incorporating a linear motor as a rebound device. A systematic simulation model of this FPELG system was built containing a kinematic and dynamic model of the piston and mover, a magneto-electric model of the linear generator, a thermodynamic model of the single-cylinder engine, and a friction model between the piston ring and cylinder liner. Simulations were performed to understand the relationships between pre-set motor parameters and the running performance of the FPELG. From the simulation results, it was found that a motor rebound force with a parabolic profile had clear advantages over a force with a triangular profile, such as a higher running frequency and peak cylinder pressure, faster piston motion, etc. The rebound position and the amplitude of rebound force were also determined by simulations. The energy conversion characteristics of the generator were obtained from our FPELG test rig. The parameters of intake pressure, motor frequency, and load resistance were varied over certain ranges, and relationships among these three parameters were obtained. The electricity-generating characteristic parameters include output power and system efficiency, which can measure the quality of matching the controllable parameters. The output power can reach 25.9 W and the system efficiency can reach 13.7%. The results in terms of matching parameters and electricity-generating characteristics should be useful to future research in adapting these engines to various operating modes.

We tested a wet extraction method for lipid extraction from Euglena gracilis water slurry at 0.51 MPa and 20 °C using liquefied dimethyl ether (DME). The yields, proximate analyses, elemental composition, and molecular weight distribution properties of the extracts from E. gracilis and the remaining residues obtained by DME extraction were compared with those of the extracts obtained by hexane Soxhlet extraction.

In this study, a simulation was carried out using BioWin 3.1 to test the capability of the software to predict the biogas potential for two different anaerobic systems. The two scenarios included: (1) a laboratory-scale batch reactor, and (2) an industrial-scale anaerobic continuous lagoon digester. The measured data related to the operating conditions, the reactor design parameters and the chemical properties of influent wastewater were entered into BioWin. A sensitivity analysis was carried out to identify the sensitivity of the most important default parameters in the software’s models. BioWin was then calibrated by matching the predicted data with measured data and used to simulate other parameters that were unmeasured or deemed uncertain. In addition, statistical analyses were carried out using evaluation indices, such as the coefficient of determination (R-squared), the correlation coefficient (r) and its significance (p-value), the general standard deviation (SD) and the Willmott index of agreement, to evaluate the agreement between the software prediction and the measured data. The results have shown that after calibration, BioWin can be used reliably to simulate both small-scale batch reactors and industrial-scale digesters with a mean absolute percentage error (MAPE) of less than 10% and very good values of the indexes. Furthermore, by changing the default parameters in BioWin, which is a way of calibrating the models in the software, as well, this may provide information about the performance of the digester. Furthermore, the results of this study showed there may be an over estimation for biogas generated from industrial-scale digesters. More sophisticated analytical devices may be required for reliable measurements of biogas quality and quantity.

In this article the concept, the materials and the exploitation potential of a photosynthetic microbial electrochemical cell for the production of hydrogen driven by solar power are investigated. In a photosynthetic microbial electrochemical cell, which is based on photosynthetic microorganisms confined to an anode and heterotrophic bacteria confined to a cathode, water is split by bacteria hosted in the anode bioactive film. The generated electrons are conveyed through external “bio-appendages” developed by the bacteria to transparent nano-pillars made of indium tin oxide (ITO), Fluorine-doped tin oxide (FTO) or other conducting materials, and then transferred to the cathode. On the other hand, the generated protons diffuse to the cathode via a polymer electrolyte membrane, where they are reduced by the electrons by heterotrophic bacteria growing attached to a similar pillared structure as that envisaged for the anode and supplemented with a specific low cost substrate (e.g., organic waste, anaerobic digestion outlet). The generated oxygen is released to the atmosphere or stored, while the produced pure hydrogen leaves the electrode through the porous layers. In addition, the integration of the photosynthetic microbial electrochemical cell system with dark fermentation as acidogenic step of anaerobic digester, which is able to produce additional H2, and the use of microbial fuel cell, feed with the residues of dark fermentation (mainly volatile fatty acids), to produce the necessary extra-bias for the photosynthetic microbial electrochemical cell is here analyzed to reveal the potential benefits to this novel integrated technology.

This paper deals with the power conversion system architectures to interface a stationary electrochemical storage installation with the network. Theoretical justifications about the conversion system layouts and control, used for actual Italian installations, are given. This paper aims at giving the power energy society an overview of actual possibilities of static conversion of d.c. battery sources.

The physical properties and the hydrogen release of NaBH 4 –Mg(BH 4 ) 2 and NaBH 4 −Ca(BH 4 ) 2 composites are investigated using in situ synchrotron radiation powder X-ray diffraction, thermal analysis and temperature programmed photographic analysis. The composite, x NaBH 4 –(1 − x )Mg(BH 4 ) 2 , x = 0.4 to 0.5, shows melting/frothing between 205 and 220 °C. However, the sample does not become a transparent molten phase. This behavior is similar to other alkali-alkaline earth metal borohydride composites. In the x NaBH 4 –(1 − x )Ca(BH 4 ) 2 system, eutectic melting is not observed. Interestingly, eutectic melting in metal borohydrides systems leads to partial thermolysis and hydrogen release at lower temperatures and the control of sample melting may open new routes for obtaining high-capacity hydrogen storage materials.

The power production of the linear generator wave energy converter developed at Uppsala University is affected by variations of mean sea level. The reason is that these variations change the distance between the point absorber located on the surface and the linear generator located on the seabed. This shifts the average position of the translator with respect to the center of the stator, thereby reducing the generator output power. A device mounted on the point absorber that compensates for tides of small range by regulating the length of the connection line between the buoy at the surface and the linear generator has been constructed and tested. This paper describes the electro-mechanical, measurement, communication and control systems installed on the buoy and shows the results obtained before its connection to the generator. The adjustment of the line was achieved through a linear actuator, which shortens the line during low tides and vice versa. The motor that drives the mechanical device was activated remotely via SMS. The measurement system that was mounted on the buoy consisted of current and voltage sensors, accelerometers, strain gauges and inductive and laser sensors. The data collected were transferred via Internet to a Dropbox server. As described within the paper, after the calibration of the sensors, the buoy was assembled and tested in the waters of Lysekil harbor, a few kilometers from the Uppsala University research site. Moreover, the performance of the sensors, the motion of the mechanical device, the power consumption, the current control strategy and the communication system are discussed.

This review paper discusses power quality considerations for direct current (DC) electric power distribution systems, particularly DC microgrids. First, four selected sample DC architectures are discussed to provide motivation for the consideration of power quality in DC systems. Second, a brief overview of power quality challenges in conventional alternating current (AC) distribution systems is given to establish the field of power quality. Finally, a survey of literature addressing power quality issues in DC systems is presented, and necessary power quality considerations in DC distribution system design and operation are discussed.

In the last decade, the importance of exploiting Chile’s Renewable Energy Sources (RESs) has increased significantly, as fossil fuel prices have risen and concerns regarding climate change issues grown, posing an important threat to its economy. However, to date, the advancement of Renewable Energy Technologies (RETs) in the country has been very limited due to various barriers. For this reason, identifying and mitigating the main barriers that hamper the advancement of RETs is necessary to allow the successful deployment of these technologies. Based on data collected from a questionnaire survey and interviews conducted among the major renewable project developers, the authors identify and rank the major barriers to the adoption of renewable energy technologies in Chile. Our findings show that the most significant barriers include “grid connection constraints and lack of grid capacity”, “longer processing times for a large number of permits”, “land and/or water lease securement” and “limited access to financing”. Furthermore, we discuss the most critical barriers in detail together with policy recommendations to overcome them.

Due to its relatively low cost, high hydrogen yield, and environmentally friendly hydrolysis byproducts, magnesium hydride (MgH 2 ) appears to be an attractive candidate for hydrogen generation. However, the hydrolysis reaction of MgH 2 is rapidly inhibited by the formation of a magnesium hydroxide passivation layer. To improve the hydrolysis properties of MgH 2 -based hydrides we investigated three different approaches: ball milling, synthesis of MgH 2 -based composites, and tuning of the solution composition. We demonstrate that the formation of a composite system, such as the MgH 2 /LaH 3 composite, through ball milling and in situ synthesis, can improve the hydrolysis properties of MgH 2 in pure water. Furthermore, the addition of Ni to the MgH 2 /LaH 3 composite resulted in the synthesis of LaH 3 /MgH 2 /Ni composites. The LaH 3 /MgH 2 /Ni composites exhibited a higher hydrolysis rate—120 mL/(g·min) of H 2 in the first 5 min—than the MgH 2 /LaH 3 composite— 95 mL/(g·min)—without the formation of the magnesium hydroxide passivation layer. Moreover, the yield rate was controlled by manipulation of the particle size via ball milling. The hydrolysis of MgH 2 was also improved by optimizing the solution. The MgH 2 produced 1711.2 mL/g of H 2 in 10 min at 298 K in the 27.1% ammonium chloride solution, and the hydrolytic conversion rate reached the value of 99.5%.

To analyze the complex and unsteady aerodynamic flow associated with wind turbine functioning, computational fluid dynamics (CFD) is an attractive and powerful method. In this work, the influence of different numerical aspects on the accuracy of simulating a rotating wind turbine is studied. In particular, the effects of mesh size and structure, time step and rotational velocity have been taken into account for simulation of different wind turbine geometries. The applicative goal of this study is the comparison of the performance between a straight blade vertical axis wind turbine and a helical blade one. Analyses are carried out through the use of computational fluid dynamic ANSYS® Fluent® software, solving the Reynolds averaged Navier–Stokes (RANS) equations. At first, two-dimensional simulations are used in a preliminary setup of the numerical procedure and to compute approximated performance parameters, namely the torque, power, lift and drag coefficients. Then, three-dimensional simulations are carried out with the aim of an accurate determination of the differences in the complex aerodynamic flow associated with the straight and the helical blade turbines. Static and dynamic results are then reported for different values of rotational speed.

Oil/paper insulation degradation in transformers involves chemical and physical changes in the materials. Some of the chemical reactions involve very reactive intermediates called free radicals. Free radicals play a major role in a wide variety of ageing processes. The detection of these reactive species in oil may, in principle, provide useful information for monitoring oil degradation. This manuscript details a laboratory technique, which determines the relative content of free radicals in insulating oils of petroleum origin by a spectrophotometric method. Free radicals may be formed in oils under operating or test conditions. The procedure enables the determination of the relative concentration of free radicals, which can act as the precursors of decay products such as charge carriers, oxidized molecules, as well as polymerization products. The technique involves using a reactive free radical reagent, 2,2-diphenyl-1-picrylhydrazyl (DPPH), added to oil to assess free radical concentration. This method is applicable to new, reclaimed, or used oils as well as naturally or artificially oxidized oil (the cause of aging can be chemical, physical, or electrical). In this contribution, free radicals were assessed following electrical discharge application in oil.

This study calculated the provincial carbon dioxide (CO 2 ) emissions in China, analyzed the temporal and spatial variations in emissions, and determined the emission intensity from 2005 to 2015. The total emissions control was forecasted in 2015, and the reduction pressure of the 30 provinces in China was assessed based on historical emissions and the 12th five-year (2011–2015) reduction plan. Results indicate that CO 2 emissions eventually increased and gradually decreased from east to west, whereas the emission intensity ultimately decreased and gradually increased from south to north. By the end of 2015, the total control of provincial emissions will increase significantly compared to the 2010 level, whereas the emission intensity will decrease. The provinces in the North, East, and South Coast regions will maintain the highest emission levels. The provinces in the Southwest and Northwest regions will experience a rapid growth rate of emissions. However, the national emission reduction target will nearly be achieved if all provinces can implement reduction targets as planned. Pressure indices show that the South Coast and Northwest regions are confronted with a greater reduction pressure of emission intensity. Finally, policy implications are provided for CO 2 reductions in China.

Accurate estimation of model parameters and state of charge (SoC) is crucial for the lithium-ion battery management system (BMS). In this paper, the stability of the model parameters and SoC estimation under measurement uncertainty is evaluated by three different factors: (i) sampling periods of 1/0.5/0.1 s, (ii) current sensor precisions of ±5/±50/±500 mA, and (iii) voltage sensor precisions of ±1/±2.5/±5 mV. Firstly, the numerical model stability analysis and parametric sensitivity analysis for battery model parameters are conducted under sampling frequency of 1–50 Hz. The perturbation analysis is theoretically performed of current/voltage measurement uncertainty on model parameter variation. Secondly, the impact of three different factors on the model parameters and SoC estimation was evaluated with the federal urban driving sequence (FUDS) profile. The bias correction recursive least square (CRLS) and adaptive extended Kalman filter (AEKF) algorithm were adopted to estimate the model parameters and SoC jointly. Finally, the simulation results were compared and some insightful findings were concluded. For the given battery model and parameter estimation algorithm, the sampling period, and current/voltage sampling accuracy presented a non-negligible effect on the estimation results of model parameters. This research revealed the influence of the measurement uncertainty on the model parameter estimation, which will provide the guidelines to select a reasonable sampling period and the current/voltage sensor sampling precisions in engineering applications.

This paper proposes a new scheme to improve the standby efficiency of the high-power half-bridge line level control (LLC) resonant converter. This new circuit is applicable to improving the efficiency of the renewable energy generation system in distributed power systems. The main purpose is to achieve high-efficiency solar and wind power and stable output under different load conditions. In comparison with the traditional one, this novel method can improve standby efficiency at standby. The system characteristics of this proposed method have been analyzed through detailed simulations, which prove its feasibility.

Lignin is an aromatic biopolymer involved in providing structural support to plant cell walls. Compared to the other cell wall polymers, i.e., cellulose and hemicelluloses, lignin has been considered a hindrance in cellulosic bioethanol production due to the complexity involved in its separation from other polymers of various biomass feedstocks. Nevertheless, lignin is a potential source of valuable aromatic chemical compounds and upgradable building blocks. Though the biosynthetic pathway of lignin has been elucidated in great detail, the random nature of the polymerization (free radical coupling) process poses challenges for its depolymerization into valuable bioproducts. The absence of specific methodologies for lignin degradation represents an important opportunity for research and development. This review highlights research development in lignin biosynthesis, lignin genetic engineering and different biological and chemical means of depolymerization used to convert lignin into biofuels and bioproducts. yes

Policies to reduce household energy use usually target the individual customer. This is probably one explanation to the limited effect of many information policies, because two concepts with different meanings are confused: individual and household. In most contexts, an individual stands for what s/he does, but in the policy context, an individual is taken to represent the entire household. This is not problematic for a single-person household, but, in a multi-person household, activities performed by different household members influence the whole households energy use. This paper illuminates problems arising from confusing the concepts of household and individual when developing policies to reduce household energy use. Examples relate to indoor space heating and energy-intensive home-based activities. The results indicate that it is analytically simple to consider individuals at home, as well as their activities using electrical appliances contributing to heating, but much more complicated to take the whole household into consideration. Our model provides a basis for better-targeted information actions to reduce energy use. Also, empirically based models capturing variations between households with different activity patterns are important for developing policies resulting in reduced energy use for space heating in multi-person households. Funding Agencies|FORMAS-IQS; AB Stangastaden

We consider a monopolistic firm producing a good while polluting and using a fossil energy. This firm can adopt a clean technology by incurring an investment cost decreasing exponentially with the adoption date. This clean technology does not pollute and has a lower production cost because it uses a renewable energy. We determine the optimal adoption date for the firm in the case where it is not regulated at all, and in the case where it is regulated at each period of time i.e. the regulator looks for static social optimality. Interestingly, the regulated firm adopts the clean technology earlier than what is socially-optimal. However, the non-regulated firm adopts later than what is socially-optimal. The regulator can induce the firm to adopt at the socially-optimal date by a postpone adoption subsidy. Nevertheless, the regulator may be interested in the earlier adoption of the firm to encourage the diffusion of the use of clean technologies in other industries.

This article provides a comprehensive review of theory and research on the individual-level predictors of household energy usage. Drawing on literature from across the social sciences, we examine two broad categories of variables that have been identified as potentially important for explaining variability in energy consumption and conservation: socio-demographic factors (e.g., income, employment status, dwelling type/size, home ownership, household size, stage of family life cycle) and psychological factors (e.g., beliefs and attitudes, motives and intentions, perceived behavioral control, cost-benefit appraisals, personal and social norms). Despite an expanding literature, we find that empirical evidence of the impact of these variables has been far from consistent and conclusive to date. Such inconsistency poses challenges for drawing generalizable conclusions, and underscores the complexity of consumer behavior in this domain. In this article, we propose that a multitude of factors—whether directly, indirectly, or in interaction—influence how householders consume and conserve energy. Theory, research and practice can be greatly advanced by understanding what these factors are, and how, when, where, why and for whom they operate. We conclude by outlining some important practical implications for policymakers and directions for future research.

Understanding and modeling of coal and biomass pyrolysis assume particular importance being the first step occurring in both gasification and combustion processes. The complex chemical reaction network occurring in this step leads to a necessary effort in developing a suitable model framework capable of grasping the physics of the phenomenon and allowing a deeper comprehension of the sequence of events. The aim of this work is to show how the intrinsic flexibility of a model based on a double distribution of the activation energy is able to properly describe the two separate steps of primary and secondary pyrolysis, which characterize the thermochemical processing of most of the energetic materials. The model performance was tested by fitting the kinetic parameters from experimental data obtained by thermogravimetric analysis of two materials, which represent very different classes of energy source: a microalgae biomass and a sub-bituminous coal. The model reproduces with high accuracy the pyrolysis behavior of both the materials and adds important information about the relative occurring of the two pyrolysis steps.

Fatigue failure is one of the main failure modes for wind turbine drivetrain components made of cast iron. The wind turbine drivetrain consists of a variety of heavily loaded components, like the main shaft, the main bearings, the gearbox and the generator. The failure of each component will lead to substantial economic losses such as cost of lost energy production and cost of repairs. During the design lifetime, the drivetrain components are exposed to variable loads from winds and waves and other sources of loads that are uncertain and have to be modeled as stochastic variables. The types of loads are different for offshore and onshore wind turbines. Moreover, uncertainties about the fatigue strength play an important role in modeling and assessment of the reliability of the components. In this paper, a generic stochastic model for fatigue failure of cast iron components based on fatigue test data and a limit state equation for fatigue failure based on the SN-curve approach and Miner’s rule is presented. The statistical analysis of the fatigue data is performed using the Maximum Likelihood Method which also gives an estimate of the statistical uncertainties. Finally, illustrative examples are presented with reliability analyses depending on various stochastic models and partial safety factors.

Anion exchange membranes were synthesized from different compositions of glycidyl methacrylate (GMA) and vinylbenzyl chloride (VBC), with constant content of divinyl benzene (DVB) by radical polymerization using benzoyl peroxide (BPO) on non-woven polyethylene terephthalate (PET) substrate. Polymerized membranes were then quaternized by soaking in trimethylamine (TMA), triethylamine (TEA), tripropylamine (TPA), and 1,4-diazabicyclo [2.2.2] octane (DABCO). Characteristics of membranes were confirmed by Fourier transform infrared spectroscopy, water uptake, ion exchange capacity, ion conductivity, thermal, and alkaline stability. The results revealed that membranes quaternized by TPA and DABCO showed high affinity when GMA content was 15 wt% and 75 wt%, respectively. IEC and ion conductivity of membranes quaternized by TPA were 1.34 meq·g − 1 and 0.022 S·cm − 1 (at 60 °C), respectively. IEC and ion conductivity of membranes were quaternized by DABCO were 1.34 meq·g − 1 and 0.021 S·cm − 1 (at 60 °C), respectively. The results indicate that the membrane containing GMA 15 wt% quaternized by TPA showed the highest thermal stability among membranes and exhibited high ion conductivity compared to existing researches using GMA, VBC, and DVB monomers.

Single cell oils (SCOs) are considered potential raw material for the production of biodiesel. Rhodosporidium sp. and Lipomyces sp. are good candidates for SCO production. Lipid extractability differs according to yeast species and literature on the most suitable method for each oleaginous yeast species is scarce. This work aimed to investigate the efficiency of the most cited strategies for extracting lipids from intact and pretreated cells of Rhodosporidium toruloides and Lipomyces starkeyi . Lipid extractions were conducted using hexane or combinations of chloroform and methanol. The Folch method resulted in the highest lipid yields for both yeasts (42% for R. toruloides and 48% for L. starkeyi ). Also, this method eliminates the cell pretreatment step. The Bligh and Dyer method underestimated the lipid content in the tested strains (25% for R. toruloides and 34% for L. starkeyi ). Lipid extractability increased after acid pretreatment for the Pedersen, hexane, and Bligh and Dyer methods. For R. toruloides unexpected fatty acid methyl esters (FAME) composition were found for some lipid extraction strategies tested. Therefore, this work provides useful information for analytical and process development aiming at biodiesel production from the SCO of these two yeast species.

Coal blending is an effective way to organize and control coal ash fusibility to meet different requirements of Coal-fired power plants. This study investigates three different eutectic processes and explains the mechanism of how coal blending affects ash fusibility. The blended ashes were prepared by hand-mixing two raw coal ashes at five blending ratios, G:D = 10:90 (G10D90), G:D= 20:80 (G20D80), G:D = 30:70 (G30D70), G:D = 40:60 (G40D60), and G:D = 50:50 (G50D50). The samples were heated at 900 °C, 1000 °C, 1100 °C, 1200 °C, and 1300 °C in reducing atmosphere. XRD and SEM/EDX were used to identify mineral transformations and eutectic processes. The eutectic processes were finally simulated with FactSage. Results show that the fusion temperatures of the blended ashes initially decrease and then increase with the blending ratio, a trend that is typical of eutectic melting. Eutectic phenomena are observed in D100, G10D90, and G30D70 in different degrees, which do not appear in G100 and G50D50 for the lack of eutectic reactants. The main eutectic reactants are gehlenite, magnetite, merwinite, and diopside. The FactSage simulation results show that the content discrepancy of merwinite and diopside in the ashes causes the inconsistent eutectic temperatures and eutectic degrees, in turn decrease the fusion temperature of the blended ash and then increase them with the blending ratio.

In this study, the structures of external costs are built in line with coal-fired and biomass power plant life cycle activities in Northeast China. The external cost of coal-fired and biomass power plants was compared, using the lifecycle approach. In addition, the external costs of a biomass power plant are calculated for each stage for comparison with those of a coal-fired power plant. The results highlight that the external costs of a coal-fired plant are 0.072 US $/kWh, which are much higher than that of a biomass power plant, 0.00012 US$/kWh. The external cost of coal-fired power generation is as much as 90% of the current price of electricity generated by coal, while the external cost of a biomass power plant is 1/1000 of the current price of electricity generated by biomass. In addition, for a biomass power plant, the external cost associated with SO 2 , NO X , and PM 2.5 are particularly lower than those of a coal-fired power plant. The prospect of establishing precise estimations for external cost mechanisms and sustainable energy policies is discussed to show a possible direction for future energy schemes in China. The paper has significant value for supporting the biomass power industry and taxing or regulating coal-fired power industry to optimize the energy structure in China.

The development of new practical hydrogen storage materials with high volumetric and gravimetric hydrogen densities is necessary to implement fuel cell technology for both mobile and stationary applications. NaBH 4 , owing to its low cost and high hydrogen density (10.6 wt%), has received extensive attention as a promising hydrogen storage medium. However, its practical use is hampered by its high thermodynamic stability and slow hydrogen exchange kinetics. Recent developments have been made in promoting H 2 release and tuning the thermodynamics of the thermal decomposition of solid NaBH 4 . These conceptual advances offer a positive outlook for using NaBH 4 -based materials as viable hydrogen storage carriers for mobile applications. This review summarizes contemporary progress in this field with a focus on the fundamental dehydrogenation and rehydrogenation pathways and properties and on material design strategies towards improved kinetics and thermodynamics such as catalytic doping, nano-engineering, additive destabilization and chemical modification.

This paper presents a novel hybrid-flux magnetic gear, which integrates a transverse-flux magnetic gear and an axial-flux magnetic gear into a single unit. Compared to its conventional counterparts, the proposed magnetic gear transmits a relatively high torque density. When compared to the transverse-flux magnetic gear, this new structure employs an extra iron segment between the low-speed rotor and high-speed rotor to modulate the magnetic field and contribute to the transmission of additional torque. A three-dimensional (3-D) finite element method (FEM) is used for the analysis of the magnetic field. In the paper a variables-decoupling method based on the sensitivity analysis of the design parameters is also presented to accelerate the optimization process of the proposed machine.