The current method used for calculating societal aggregated exergy efficiencies is reviewed. Cooling is introduced as an end-use category; conversion efficiencies for heating processes are obtained for each energy carrier; and electricity shares per end-use are retrieved for each sector, improving the accuracy of the estimated values of aggregated exergy efficiencies. We show that: (1) cooling uses are a relevant end-use in Portugal and that their introduction decreased overall efficiency by 3.4% in 2009; and (2) disaggregating the heating second law efficiencies for each energy carrier has a significant effect on the aggregated efficiencies of the country, decreasing aggregated efficiency by 1.3% in 2009. We studied two other factors that showed no significant impact on aggregated exergy efficiency: a technological lag of 10 years in the efficiency of stationary mechanical drive devices and the use of a year-specific ambient temperature to compute exergy efficiencies of heating proces... [more]

A power transformer outage has a dramatic financial consequence not only for electric power systems utilities but also for interconnected customers. The service reliability of this important asset largely depends upon the condition of the oil-paper insulation. Therefore, by keeping the qualities of oil-paper insulation system in pristine condition, the maintenance planners can reduce the decline rate of internal faults. Accurate diagnostic methods for analyzing the condition of transformers are therefore essential. Currently, there are various electrical and physicochemical diagnostic techniques available for insulation condition monitoring of power transformers. This paper is aimed at the description, analysis and interpretation of modern physicochemical diagnostics techniques for assessing insulation condition in aged transformers. Since fields and laboratory experiences have shown that transformer oil contains about 70% of diagnostic information, the physicochemical analyses of oil... [more]

In a future sustainable energy vision, in which diversified conversion of renewable energies is essential, vertical axis wind turbines (VAWTs) exhibit some potential as a reliable means of wind energy extraction alongside conventional horizontal axis wind turbines (HAWTs). Nevertheless, there is currently a relative shortage of scientific, academic and technical investigations of VAWTs as compared to HAWTs. Having this in mind, in this work, we aim to, for the first time, study the wake of a single VAWT placed in the atmospheric boundary layer using large-eddy simulation (LES). To do this, we use a previously-validated LES framework in which an actuator line model (ALM) is incorporated. First, for a typical three- and straight-bladed 1-MW VAWT design, the variation of the power coefficient with both the chord length of the blades and the tip-speed ratio is analyzed by performing 117 simulations using LES-ALM. The optimum combination of solidity (defined as N c / R , where N is t... [more]

Passive solar elements for both direct and indirect gains, are systems used to maintain a comfortable living environment while saving energy, especially in the building energy retrofit and adaptation process. Sunspaces, thermal mass and glazing area and orientation have been often used in the past to guarantee adequate indoor conditions when mechanical devices were not available. After a period of neglect, nowadays they are again considered as appropriate systems to help face environmental issues in the building sector, and both international and national legislation takes into consideration the possibility of including them in the building planning tools, also providing economic incentives. Their proper design needs dynamic simulation, often difficult to perform and time consuming. Moreover, results generally suffer from several uncertainties, so quasi steady-state procedures are often used in everyday practice with good results, but some corrections are still needed. In this paper, a... [more]

The Korean government is fostering a renewable energy industry as a means of handling the energy crisis. Among the renewable energy systems available, geothermal energy has been highlighted as highly efficient, safely operable and relatively unaffected by outdoors air conditions. Despite the increasing use of renewable energy, the devices using renewables may not be operating appropriately. This study examined current problems in the operation of a geothermal heat pump (GHP) system. The efficiency of a geothermal heat pump system to studied to maximize the operation plan. Our study modelled the target building and analyzed the energy using TRNSYS, which is a dynamic energy simulation tool, to apply the coefficient of performance (COP) and evaluate the operation method. As a result, the GHP total energy consumption from the COP control method was reduced by 46% compared to the current operation. The proposed control method was evaluated after applying the system to a building. The resul... [more]

Climate change is altering hydrological processes with varying degrees in various regions of the world and remains a threat to water resources projects in southern Africa. The likely negative impacts of changes in Africa may be worse than in most other regions of the world. This study is an evaluation of the possible impacts of climate change on water resources and hydropower production potential in Kwanza River Basin, Angola. The regional climate data, the basis for future climate scenarios, is used in the hydrological model HBV to assess climate change impacts on water resources in the Kwanza River Basin. Evaluation of changes in hydropower production potential is carried out using an energy model. The simulations show that annual rainfall in 2080 would increase by approximately 16% with increasing inter-annual variability of rainfall and dry season river flow and later onset of the rainy season. The simulation results show that for the Kwanza River Basin the effects as a result of c... [more]

The 2nd generation plants producing ethanol from lignocelluloses demand risky and high investment costs. This paper presents the energy- and economical evaluations for integrating lignocellulose in current 1st generation dry mill ethanol processes, using filamentous fungi. Dry mills use grains and have mills, liquefactions, saccharifications, fermentation, and distillation to produce ethanol, while their stillage passes centrifugation, and evaporation to recycle the water and dry the cake and evaporated syrup into animal feed. In this work, a bioreactor was considered to cultivate fungi on the stillage either before or after the centrifugation step together with pretreated lignocellulosic wheat bran. The results showed that the integrated 1st and 2nd generation ethanol process requires a capital investment of 77 million USD, which could yield NPV of 162 million USD after 20 years. Compared to the fungal cultivation on thin stillage modified 1st generation process, the integrated proces... [more]

At present, the common practice in the power system of China is to represent the small and medium hydropower generator group as a negative load. This paper presents a method to build a dynamic equivalent model of the hydropower generator group using a 3rd order generator model and a static characteristic load model. Based on phasor measurements in the tie line which connects to the modeled hydropower generator group, the dynamic multi-swarm particle swarm optimizer (DMS-PSO) algorithm is used to obtain parameters of the equivalent model. The proposed method is verified in the small and medium hydropower generator group of Sichuan power grid with both simulation and actual data. The results show that the dynamic responses and the transient stability are consistent before and after the equivalence. The proposed method can be used for modeling a group of small and medium hydropower generators whose structures and parameters are unknown.

In this paper, advanced equivalent circuit models (ECMs) were developed to model large format and high energy nickel manganese cobalt (NMC) lithium-ion 20 Ah battery cells. Different temperatures conditions, cell characterization test (Normal and Advanced Tests), ECM topologies (1st and 2nd Order Thévenin model), state of charge (SoC) estimation techniques (Coulomb counting and extended Kalman filtering) and validation profiles (dynamic discharge pulse test (DDPT) and world harmonized light vehicle profiles) have been incorporated in the analysis. A concise state-of-the-art of different lithium-ion battery models existing in the academia and industry is presented providing information about model classification and information about electrical models. Moreover, an overview of the different steps and information needed to be able to create an ECM model is provided. A comparison between begin of life (BoL) and aged (95%, 90% state of health) ECM parameters (internal resistance (Ro), pola... [more]

The high contents of disadvantageous elements contained in non-woody biomass are known to cause problems during small and large scale combustion, typically resulting in a higher risk of slagging, corrosion, and increased emissions. Mechanically leaching the respective elements from the biomass through a sequence of process steps has proven to be a promising solution.The florafuel process used here is comprised of size reduction followed by washing and subsequent mechanical dewatering of the biomass. Densification of the upgraded biomass into standardized pellets (Ø 6mm) enables an application in existing small-scale boilers. The presented combustion trials investigated the performance of pellets made from leached grass, foliage and a mixture of both in two small-scale boilers (<100 kWth) with slightly different technology (moving grate versus water-cooled burner tube) during a 4-h measurement period. Emissions were in accordance with German emissions standards except for NOx (thresh... [more]

Light-emitting diode (LED) road lighting has been widely implemented in recent years, but few studies have evaluated its performance after installation. This study investigated whether LED road lighting complies with minimum regulations in terms of traffic safety and whether improvements for energy efficiency are possible. Average road surface luminance (L), overall luminance uniformity (Uo), longitudinal luminance uniformity (UI), power density (PD) and normalised power density (PN) were evaluated for 14 roads (seven designed for vehicular traffic and seven for pedestrians and bicycles). Energy savings were calculated as the percentage reduction to the minimum level of the existing lighting class or a lower lighting class and by applying a dimming schedule. The results showed that LED road lighting for vehicular traffic roads generally fulfilled the requirements, whereas that for pedestrian and bicycle roads generally corresponded to the lowest lighting class for L, and often did not... [more]

When drilling coal-bearing sequences to enhance coal seam permeability by hydraulic fracturing (HF), the location where fractures are initiated is important. To date, most research on fracture initiation has studied the problem in two dimensions. In this study, a three-dimensional model to assess initiation location is developed. The model analyzes the stress state of both the borehole wall and the coal-rock interface and the model shows that the fracture initiation location is affected by in situ stress, the dip of the coal seam, and the angle between the borehole and the coal seam. How the initiation location changes near different types of geological faults is calculated by assuming typical in situ stresses for the faults. Following these calculations, physical experiments were carried out to emulate cross-measure hydraulic fracturing under stress conditions equivalent to those in the Chongqing Tonghua coal mine, China. Fracture initiation during the experiments was monitored by an... [more]

This paper proposes a fault detection and the improved fault-tolerant control for an open fault in the five-phase inverter driving system. The five-phase induction machine has a merit of fault-tolerant control due to its increased number of phases. This paper analyzes an open fault pattern of one switch and proposes an effective fault detection method based upon this analysis. The proposed fault detection method using the analyzed patterns is applied in the power inverter. In addition, when the open fault occurs in the one switch of the induction machine driving system, the proposed fault-tolerant control method is used to operate the induction machine using the remaining healthy phases, after performing the fault detection method. Simulation and experiment results are provided to validate the proposed technique.

Cu(In,Ga)Se₂ (CIGS)/CdS thin-film solar cells have reached, at laboratory scale, an efficiency higher than 22.3%, which is one of the highest efficiencies ever obtained for thin-film solar cells. The research focus has now shifted onto fabrication processes, which have to be easily scalable at an industrial level. For this reason, a process is highlighted here which uses only the sputtering technique for both the absorber preparation and the deposition of all the other materials that make up the cell. Particular emphasis is placed on the comparison between different precursors obtained with either In₂Se₃ and Ga₂Se₃ or InSe and GaSe as starting materials. In both cases, the precursor does not require any heat treatment, and it is immediately ready to be selenized. The selenization is performed in a pure-selenium atmosphere and only lasts a few minutes at a temperature of about 803 K. Energy conversion efficiencies in the range of 15%⁻16% are reproducibly obtained on soda-lime glass (SLG... [more]

All-vanadium redox flow batteries (VRBs) are potential energy storage systems for renewable power sources because of their flexible design, deep discharge capacity, quick response time, and long cycle life. To minimize the energy loss due to the shunt current, in a traditional design, a flow field is machined on two electrically insulated frames with a graphite plate in between. A traditional bipolar plate (BP) of a VRB consists of many components, and thus, the assembly process is time consuming. In this study, an integrally molded BP is designed and fabricated to minimize the manufacturing cost. First, the effects of the mold design and injection parameters on frame formability were analyzed by simulation. Second, a new graphite plate design for integral molding was proposed, and finally, two integrally molded BPs were fabricated and compared. Results show that gate position significantly affects air traps and the maximum volume shrinkage occurs at the corners of a BP. The volume shr... [more]

The present work is to design a passive pitch-control mechanism for small horizontal axis wind turbine (HAWT) to generate stable power at high wind speeds. The mechanism uses a disk pulley as an actuator to passively adjust the pitch angle of blades by centrifugal force. For this design, aerodynamic braking is caused by the adjustment of pitch angles at high wind speeds. As a marked advantage, this does not require mechanical brakes that would incur electrical burn-out and structural failure under high speed rotation. This can ensure the survival of blades and generator in sever operation environments. In this paper, the analysis uses blade element momentum theory (BEMT) to develop graphical user interface software to facilitate the performance assessment of the small-scale HAWT using passive pitch control (PPC). For verification, the HAWT system was tested in a full-scale wind tunnel for its aerodynamic performance. At low wind speeds, this system performed the same as usual, yet at h... [more]

The suitability of turbine configurations to different wind resources has been traditionally restricted to considering turbines operating as standalone entities. In this paper, a framework is thus developed to investigate turbine suitability in terms of the minimum cost of energy offered when operating as a group of optimally-micro-sited turbines. The four major steps include: (i) characterizing the geographical variation of wind regimes in the onshore U.S. market; (ii) determining the best performing turbines for different wind regimes through wind farm layout optimization; (iii) developing a metric to quantify the expected market suitability of available turbine configurations; and (iv) exploring the best tradeoffs between the cost and capacity factor yielded by these turbines. One hundred thirty one types of commercial turbines offered by major global manufacturers in 2012 are considered for selection. It is found that, in general, higher rated power turbines with medium tower heigh... [more]

The permeability of coal is a critical parameter in estimating the performance of coal reservoirs. Darcy’s law describes the flow pattern that the permeability has a linear relationship with the flow velocity. However, the stress induced deformation and damage can significantly influence the gas flow pattern and permeability of coal. Coals from Songzao coalfield in Chongqing, southwest China were collected for the study. The gas flow velocities under different injection gas pressures and effective stresses in the intact coal and damaged coal were tested using helium, incorporating the role of gas flow pattern on the permeability of coal. The relationships between the flow velocity and square of gas pressure gradient were discussed, which can help us to investigate the transformation conditions of gas linear flow and gas nonlinear flow in the coal. The results showed that the gas flow in the intact coal existed pseudo-initial flow rate under low effective stress. The low-velocity non-Da... [more]

In the actual era of smart homes and smart grids, advanced technological systems that allow the automation of domestic tasks are developing rapidly. There are numerous technologies and applications that can be installed in smart homes today. They enable communication between home appliances and users, and enhance home appliances’ automation, monitoring and remote control capabilities. This review article, by introducing the concept of the smart home and the advent of the smart grid, investigates technologies for smart homes. The technical descriptions of the systems are presented and point out advantages and disadvantages of each technology and product today available on the market. Barriers, challenges, benefits and future trends regarding the technologies and the role of users have also been discussed.

The main function of an airport is to provide access to air transport both for passengers and cargo. The number of air operations over the past 20 years has increased rapidly, and this has led to a rise in the energy needs of airports to satisfy this demand. As a consequence, the cost of energy supply for airport managers has escalated. At the same time, global energy consumption has soared due to the needs of emerging countries like China and India, with the consequent environmental impact. This complex scenario of environmental and economic factors has made airport managers become aware of the need to reduce energy consumption as well as a more efficient use of it. The aim of this article is to analyze the main behaviors and energy trends at airports in more recent research, starting with the description of the main energy sources and consumers, the application of energy conservation and energy efficiency measures, the establishment of energy indicators and benchmarking between airpo... [more]

With the increasing age of the primary equipment of the electrical grids there exists also an increasing need to know its internal condition. For this purpose, off- and online diagnostic methods and systems for power transformers have been developed in recent years. Online monitoring is used continuously during operation and offers possibilities to record the relevant stresses which can affect the lifetime. The evaluation of these data offers the possibility of detecting oncoming faults early. In comparison to this, offline methods require disconnecting the transformer from the electrical grid and are used during planned inspections or when the transformer is already failure suspicious. This contribution presents the status and current trends of different diagnostic techniques of power transformers. It provides significant tutorial elements, backed up by case studies, results and some analysis. The broadness and improvements of the presented diagnostic techniques show that the power tr... [more]

Recovering energy from exhaust air systems of building cooling towers is an innovative idea. A specific wind turbine generator was designed in order to achieve this goal. This device consists of two Giromill vertical axis wind turbines (VAWT) combined with four guide vanes and two diffuser plates. It was clear from previous literatures that no comprehensive flow behavior study had been carried out on this innovative device. Therefore, the working principle of this design was simulated using the Analysis System (ANSYS) Fluent computational fluid dynamics (CFD) package and the results were compared to experimental ones. It was perceived from the results that by introducing the diffusers and then the guide vanes, the overall power output of the wind turbine was improved by approximately 5% and 34%, respectively, compared to using VAWT alone. In the case of the diffusers, the optimum angle was found to be 7°, while for guide vanes A and B, it was 70° and 60° respectively. These results wer... [more]

In order to overcome the shortcoming of magnetic bearings whereby general mathematical models of the radial suspension forces cannot be accurately established, a mathematical model considering the edge effect is set up. The configuration, operation principle and flux distribution features of a three-pole radial hybrid magnetic bearing (HMB) are analyzed in this paper. The magnetic field division method is employed to calculate the permeance of different regions around the end portion of poles. The total permeance of a single pole is composed of the permeance of the regions. Then, an accurate mathematical model of the radial suspension forces considering the edge effect is deduced by the equivalent magnetic circuit method. From the modeling procedures, it can be seen that the edge effect calculation is only related to the configuration and parameters of the magnetic poles, and is isolated with the other configurations and parameters of the three-pole radial HMB, therefore, the mathemati... [more]

In this paper a methodology is presented that can be used to model the annual wind energy yield (AEYmod) on a high spatial resolution (50 m × 50 m) grid based on long-term (1979⁻2010) near-surface wind speed (US) time series measured at 58 stations of the German Weather Service (DWD). The study area for which AEYmod is quantified is the German federal state of Baden-Wuerttemberg. Comparability of the wind speed time series was ensured by gap filling, homogenization and detrending. The US values were extrapolated to the height 100 m (U100m,emp) above ground level (AGL) by the Hellman power law. All U100m,emp time series were then converted to empirical cumulative distribution functions (CDFemp). 67 theoretical cumulative distribution functions (CDF) were fitted to all CDFemp and their goodness of fit (GoF) was evaluated. It turned out that the five-parameter Wakeby distribution (WK5) is universally applicable in the study area. Prior to the least squares boosting (LSBoost)-based modelin... [more]

Since driving cycle greatly affects load power demand, driving cycle identification (DCI) is proposed to predict power demand that can be expected to prepare for the power distribution between battery and supercapacitor. The DCI is developed based on a learning vector quantization (LVQ) neural network method, which is assessed in both training and validation based on the statistical data obtained from six standard driving cycles. In order to ensure network accuracy, characteristic parameter and slide time window, which are two important factors ensuring the network accuracy for onboard hybrid energy storage system (HESS) applications in electric vehicles, are discussed and designed. Based on the identification results, Multi-level Haar wavelet transform (Haar-WT) is proposed for allocating the high frequency components of power demand into the supercapacitor which could damage battery lifetime and the corresponding low frequency components into the battery system. The proposed energy m... [more]