ALBERT

Description: This paper pays attention to magnetic flux linkage optimization of a direct-driven surface-mounted permanent magnet synchronous generator (D-SPMSG). A new compact representation of the D-SPMSG nonlinear dynamic differential equations to reduce system parameters is established. Furthermore, the nonlinear dynamic characteristics of new D-SPMSG equations in the process of varying magnetic flux linkage are considered, which are illustrated by Lyapunov exponent spectrums, phase orbits, Poincaré maps, time waveforms and bifurcation diagrams, and the magnetic flux linkage stable region of D-SPMSG is acquired concurrently. Based on the above modeling and analyses, a novel method of magnetic flux linkage optimization is presented. In addition, a 2 MW D-SPMSG 2D/3D model is designed by ANSYS software according to the practical design requirements. Finally, five cases of D-SPMSG models with different magnetic flux linkages are simulated by using the finite element analysis (FEA) method. The nephograms of magnetic flux density are agreement with theoretical analysis, which both confirm the correctness and effectiveness of the proposed approach.

Description: The construction of two marine bulk terminals in the Pacific Northwest region of the United States are currently under review and would open up additional thermal coal exports to Asia on the order of almost 100 million additional tonnes per year. The major exporters of coal to Asian markets include Indonesia and Australia. This life cycle analysis (LCA) seeks to understand the role of transportation and mining in the cradle-to-busbar environmental impacts of coal exports from the Powder River Basin (PRB) to Asian countries, when compared to the competitor countries. This LCA shows that: (1) the most significant greenhouse gas (GHG) impacts in the cradle-to-busbar life cycle of coal for power generation come from the combustion of coal in a power plant, even when 90% carbon capture is applied; (2) for non-GHG air impacts, power plant combustion impacts are less dominant and variations in upstream impacts (mining and transportation) are more important; and (3) when comparing impacts between countries, upstream impacts vary for both GHG and non-GHG results, but conclusions that rank countries cannot be made. Future research should include expansion to include non-air impacts, potential consequential effects of coal exports, and a better understanding around the characterization of non-GHG ocean transport impacts.

Description: Recently, Vernier permanent magnet (VPM) machines, one special case of magnetic flux-modulated (MFM) machines, benefiting from their compact, simple construction and low-speed/ high-torque characteristics, have been receiving increasing interest. In this paper, the Vernier structure is integrated with an axial-flux PM machine to obtain the magnetic gear effect and produce an improved torque density for direct-drive wind power generation application. Another advantage of the proposed machine is that the stator flux rotating speed can be relatively high when the shaft speed is low. With this benefit, sensorless control strategy can be easily implemented in a wide speed range. In this paper, an improved sliding mode observer (SMO) is proposed to estimate the rotor position and the speed of the proposed machine. With the estimated shaft speeds, the maximum power point tracking (MPPT) control strategy is applied to maximize the wind power extraction. The machine design and the sensorless MPPT control strategy are verified by finite element analysis and experimental verification.

Description: A fractional derivative system identification approach for modeling battery dynamics is presented in this paper, where fractional derivatives are applied to approximate non-linear dynamic behavior of a battery system. The least squares-based state-variable filter (LSSVF) method commonly used in the identification of continuous-time models is extended to allow the estimation of fractional derivative coefficents and parameters of the battery models by monitoring a charge/discharge demand signal and a power storage/delivery signal. In particular, the model is combined by individual fractional differential models (FDMs), where the parameters can be estimated by a least-squares algorithm. Based on experimental data, it is illustrated how the fractional derivative model can be utilized to predict the dynamics of the energy storage and delivery of a lithium iron phosphate battery (LiFePO 4 ) in real-time. The results indicate that a FDM can accurately capture the dynamics of the energy storage and delivery of the battery over a large operating range of the battery. It is also shown that the fractional derivative model exhibits improvements on prediction performance compared to standard integer derivative model, which in beneficial for a battery management system.

Description: In this paper, we present an energy optimization technique to schedule three types of household appliances (user dependent, interactive schedulable and unschedulable) in response to the dynamic behaviours of customers, electricity prices and weather conditions. Our optimization technique schedules household appliances in real time to optimally control their energy consumption, such that the electricity bills of end users are reduced while not compromising on user comfort. More specifically, we use the binary multiple knapsack problem formulation technique to design an objective function, which is solved via the constraint optimization technique. Simulation results show that average aggregated energy savings with and without considering the human presence control system are 11.77% and 5.91%, respectively.

Description: This study contributes to the realization of intended nationally determined contributions (INDCs) by analyzing their implications for the energy production system and the economy, and determines the role of renewable energies (RE) in reducing the challenge of committing to the INDCs. The Asia-Pacific Integrated Model/Computable General Equilibrium (AIM/CGE) model was used to assess seven scenarios having the same socioeconomic development but different shares of RE in power generation. By comparing different relative reductions caused by the emission constraints vis-a-vis the business-as-usual (BaU) scenario, the mitigation costs can be estimated. Results show that the economic impact could be reduced by around 55% in terms of welfare loss (from 6.0% to 2.7%) and by around 36% in terms of gross domestic product (GDP) loss (from 3.4% to 2.1%) through the incorporation of high levels of renewable energy. Furthermore, the additional double deployment of wind and SPV to 5.4% and 12.0%, respectively, which currently comprise 43.1% of the renewable energies used in electricity generation, could reduce the GDP loss from 2.1% to 1.9% and reduce the welfare loss from 2.7% to 1.5% in order to achieve a 25.0% GHG emissions reduction. These losses are less than those in the pricing-only scenario (2.1% and 2.3%, respectively).

Description: The axial magnetic-field-modulated brushless double-rotor machine (MFM-BDRM) is a novel possible alternative power-split device for hybrid electric vehicles (HEVs). This paper proposes a two-dimensional (2-D) analytical method to predict the performance of the axial MFM-BDRM to reduce computing time. The computation is based on the solution of Laplace’s or Poisson’s equation with boundary conditions for each elementary rectangular region. By taking account of the existence of modulating ring and the stator slotting effect, the proposed model is able to calculate magnetic-field distribution with high accuracy. In order to assess the proposed method, the 2-D analytical and three-dimensional (3-D) finite element analysis (FEA) results have been compared, and good agreements have been achieved. As the analytical computation is much faster and more flexible, the proposed method can be used in the preliminary design process of the axial MFM-BDRM.

Description: A microgrid is a micro-power system composed of local distributed generators, energy storage systems, loads, and other components in a local power network. Because renewable energy sources show relatively large output power variation, the integration of distributed generators in a microgrid often requires the installation of a large-scale energy storage system. The energy storage system is connected to a local AC bus via the DC/AC converter with an output inductor-capacitor (LC) filter. The energy storage system power converters generally form the local AC bus voltage. This grid-forming operation requires fast and robust voltage control to properly maintain a stable energy flow and high power quality in the local AC bus. In this paper, two major voltage control schemes—double-loop control and direct voltage control—are analytically compared, and their effects on the power quality of the microgrid are illustrated. The dynamic performance is compared through simulations and experimental results.

Description: The UK is currently suffering great overheating issues in summer, especially in residential buildings where no air-conditioning has been installed. This overheating will seriously affect people’s comfort and even health, especially for elderly people. Phase change materials (PCMs) have been considered as a useful passive method, which absorb excessive heat when the room is hot and release the stored heat when the room is cool. This research has adopted a simulation method in DesignBuilder to evaluate the effectiveness of using PCMs to reduce the overheating issues in UK residential applications and has analyzed potential factors that will influence the effectiveness of overheating. The factors include environment-related (location of the building, global warming/climate change) and construction-related (location of the PCM, insulation, heavyweight/lightweight construction). This research provides useful evidence about using PCMs in UK residential applications and the results are helpful for architects and engineers to decide when and where to use PCMs in buildings to maintain a low carbon lifestyle.

Description: Micro (0.5–10 kW) organic Rankine cycle (ORC) power systems are nowadays considered for domestic power generation. Selection of a suitable expander is one of the most important problems connected with the domestic ORC system design. Volumetric machines or micro-turbines can be adopted as an expander in domestic ORC systems. Scroll and screw expanders are a common choice and were successfully applied in different small- and micro-power applications. However, micro-turbines as well as scroll and screw expanders are mechanically complicated and expensive. An alternative are rotary-vane machines, which are simple and cheap compared to micro-turbines. This paper documents a study providing the experimental and numerical analyses on the rotary vane expander operating conditions in a micro-ORC system. A test-stand was designed and set up and a series of experiments was performed using the test-stand. Results of these experiments were further used as an input to numerical simulations of an expander operation. In order to simulate the expander operating conditions, a three-dimensional numerical model has been prepared. The analysis presented in this paper indicates that a properly designed multi-vane expander is a cheap and mechanically simple alternative to other expansion devices proposed for domestic ORC systems.

Description: Plate Fin Heat Sinks (PFHS) are among the simplest and most widespread devices for electronics cooling. Because of the many design parameters to be considered, developing both cost and thermal effective PFHS is a critical issue. Here, a novel thermal model of PFHS is presented. The model has a broad field of applicability, being comprehensive of the effects of flow bypass, developing boundary layers, fin efficiency and spreading resistance. Experiments are then carried out to validate the proposed thermal model, and its good accuracy is demonstrated. Finally, an optimization methodology based on genetic algorithms is proposed for a cost-effective selection of the design parameters of PFHS, which is particularly effective with semi-active configurations. Such an optimization methodology is then tested on a commercial heat sink, resulting in a possible 53% volume reduction at fixed thermal performances.

Description: Classification problems and their corresponding solving approaches constitute one of the fields of machine learning. The application of classification schemes in Renewable Energy (RE) has gained significant attention in the last few years, contributing to the deployment, management and optimization of RE systems. The main objective of this paper is to review the most important classification algorithms applied to RE problems, including both classical and novel algorithms. The paper also provides a comprehensive literature review and discussion on different classification techniques in specific RE problems, including wind speed/power prediction, fault diagnosis in RE systems, power quality disturbance classification and other applications in alternative RE systems. In this way, the paper describes classification techniques and metrics applied to RE problems, thus being useful both for researchers dealing with this kind of problem and for practitioners of the field.

Description: The day-ahead electricity market is closely related to other commodity markets such as the fuel and emission markets and is increasingly playing a significant role in human life. Thus, in the electricity markets, accurate electricity price forecasting plays significant role for power producers and consumers. Although many studies developing and proposing highly accurate forecasting models exist in the literature, there have been few investigations on improving the forecasting effectiveness of electricity price from the perspective of reducing the volatility of data with satisfactory accuracy. Based on reducing the volatility of the electricity price and the forecasting nature of the radial basis function network (RBFN), this paper successfully develops a two-stage model to forecast the day-ahead electricity price, of which the first stage is particle swarm optimization (PSO)-core mapping (CM) with self-organizing-map and fuzzy set (PCMwSF), and the second stage is selection rule (SR). The PCMwSF stage applies CM, fuzzy set and optimized weights to obtain the future price, and the SR stage is inspired by the forecasting nature of RBFN and effectively selects the best forecast during the test period. The proposed model, i.e., CM-PCMwSF-SR, not only overcomes the difficulty of reducing the high volatility of the electricity price but also leads to a superior forecasting effectiveness than benchmarks.

Description: In order to evaluate and control the seismic effect of blasting, as well as its planning, it is required to determine the soil oscillation law, with the strike/mining facilities to be protected. One of the most commonly used equations is that of M.A. Sadovskii, defining the law of alteration in the oscillation velocity of the soil depending on distance, the explosive amount, and conditions of blasting and geologic characteristics of the soil; all of this being determined on the basis of test blasting for the specific work environment. In the Sadovskii equation two parameters, K and n appear and they are conditioned both by rock mass characteristics and blasting conditions. The practical part of this study includes experimental investigations performed in the Veliki Krivelj Open Pit in the Bor District located in Eastern Serbia and investigations carried out during mass mining in the Kovilovača Open Pit near Despotovac, Eastern Serbia. Thus this paper offers several modes for determination of parameters K and n in the Sadovskii equation. To determine the parameters in the Sadovskii formula, in addition to the usual least square method, two more new models were applied. In the models the parameters K and n were determined by applying the quotient of the relative growth of oscillation velocities and reduced distances for Model 2. The link between the parameters K and n is determined by applying the trapezoidal formula for finding the value of definite integral for Model 3. In doing so, it was noted that all three models can be used to calculate the oscillation velocity of the rock mass.

Description: Carbon emissions are the major cause of the global warming; therefore, the exploration of carbon emissions reduction potential is of great significance to reduce carbon emissions. This paper explores the potential of carbon intensity reduction in Beijing in 2020. Based on factors including economic growth, resident population growth, energy structure adjustment, industrial structure adjustment and technical progress, the paper sets 48 development scenarios during the years 2015–2020. Then, the back propagation (BP) neural network optimized by improved particle swarm optimization algorithm (IPSO) is used to calculate the carbon emissions and carbon intensity reduction potential under various scenarios for 2016 and 2020. Finally, the contribution of different factors to carbon intensity reduction is compared. The results indicate that Beijing could more than fulfill the 40%–45% reduction target for carbon intensity in 2020 in all of the scenarios. Furthermore, energy structure adjustment, industrial structure adjustment and technical progress can drive the decline in carbon intensity. However, the increase in the resident population hinders the decline in carbon intensity, and there is no clear relationship between economy and carbon intensity. On the basis of these findings, this paper puts forward relevant policy recommendations.

Description: There is considerable interest recently in by-products for application in green buildings. These materials are widely used as building envelope insulators or blocks. In this study, an experimental study was conducted to test stranded driftwood residues as raw material for possible thermo-acoustic insulation panel and environmentally sustainable brick. The thermal and acoustic characteristics of such a natural by-product were examined. Part of samples were mineralized by means of cement-based additive to reinforce the material and enhance its durability as well as fire resistance. Several mixtures with different sizes of ground wood chips and different quantities of cement were investigated. The thermo-acoustic in-lab characterization was aimed at investigating the thermal conductivity, thermal diffusivity, volumetric specific heat, and acoustic transmission loss. All samples were tested before and after mineralization. Results from this study indicate that it is possible to use stranded driftwood residues as building materials with competitive thermo-acoustic properties. In fact, the thermal conductivity was shown to be always around 0.07 W/mK in the unbound samples, and around double that value for the mineralized samples, which present a much higher volumetric specific heat (1.6 MJ/m3K) and transmission loss capability. The lignin powder showed a sort of intermediate behavior between the unbound and the mineralized samples.

Description: Micro energy grids have many merits and promising applications under the smart grid vision. There are demanding procedures for their optimal planning and performance enhancement. One of the key features of a micro energy grid is its ability to separate and isolate itself from the main electrical network to continue feeding its own islanded portion. In this paper, an optimal sizing and operation strategy for micro energy grids equipped with renewable and non-renewable based distributed generation (DG) and storage are presented. The general optimization objective is to define the best DG mix and energy storage units for self-sufficient micro energy grids. A multi-objective genetic algorithm (GA) was applied to solve the planning problem at a minimum optimization goal of overall cost (including investment cost, operation and maintenance cost, and fuel cost) and carbon dioxide emission. The constraints include power and heat demands constraints, and DGs capacity limits. The candidate technologies include CHPs (combined heat and power) with different characteristics, boilers, thermal and electrical storages, and renewable generators (wind and photovoltaic). In order to assess different configuration options and components sizes, several case studies for a typical micro energy grid have been presented.

Description: The hump feature is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations can be observed, which are harmful to their safe and stable operation and can even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening conditions. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), characteristic hysteresis was found in the hump region. The analysis of performance characteristics reveals that the hump instability is the result of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to the hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of the corresponding fast Fourier transform confirms that the hump characteristic is related to low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cessation of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis feature. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

Description: In day-ahead electricity price forecasting (EPF) variable selection is a crucial issue. Conducting an empirical study involving state-of-the-art parsimonious expert models as benchmarks, datasets from three major power markets and five classes of automated selection and shrinkage procedures (single-step elimination, stepwise regression, ridge regression, lasso and elastic nets), we show that using the latter two classes can bring significant accuracy gains compared to commonly-used EPF models. In particular, one of the elastic nets, a class that has not been considered in EPF before, stands out as the best performing model overall.

Description: It is a common practice for storage batteries to be connected to DC microgrid buses through DC-DC converters for voltage support on islanded operation mode. A feed-forward control based dual-loop constant voltage PI control for three-branch interleaved DC-DC converters (TIDC) is proposed for storage batteries in DC microgrids. The working principle of TIDC is analyzed, and the factors influencing the response rate based on the dual-loop constant voltage control for TIDC are discussed, and then the method of feed-forward control for TIDC is studied to improve the response rate for load changing. A prototype of the TIDC is developed and an experimental platform is built. The experiment results show that DC bus voltage sags or swells caused by load changing can be reduced and the time for voltage recovery can be decreased significantly with the proposed feed-forward control.

Description: Increasingly complex air path concepts are investigated to achieve a substantial reduction in fuel consumption while improving the vehicle dynamics. One promising technology is the two-stage turbocharging for gasoline engines, where a high pressure and a low pressure turbocharger are placed in series. For exploiting the high potential, a control concept has to be developed that allows for coordinated management of the two turbocharger stages. In this paper, the control strategy is investigated. Therefore, the effect of the actuated values on transient response and pumping losses is analyzed. Based on these findings, an optimization-based control algorithm is developed that allows taking both requirements into account. The developed new controller allows achieving a fast transient response, while at the same time reducing pumping losses in stationary operation.

Description: Due to the rapid growth in the amount of wind energy connected to distribution grids, they are exposed to higher network constraints, which poses additional challenges to system operation. Based on regulation, the system operator has the right to curtail wind energy in order to avoid any violation of system constraints. Energy storage systems (ESS) are considered to be a viable solution to solve this problem. The aim of this paper is to provide the best locations of both ESS and wind power by optimizing distribution system costs taking into account network constraints and the uncertainty associated to the nature of wind, load and price. To do that, we use a mixed integer linear programming (MILP) approach consisting of loss reduction, voltage improvement and minimization of generation costs. An alternative current (AC) linear optimal power flow (OPF), which employs binary variables to define the location of the generation, is implemented. The proposed stochastic MILP approach has been applied to the IEEE 69-bus distribution network and the results show the performance of the model under different values of installed capacities of ESS and wind power.

Description: To achieve the carbon free electricity generation target for 2050, the penetration of renewable energy sources should further increase. To address the impacts of their unpredictable and intermittent characteristics on the future electricity grid, Pumped Hydro Energy Storage (PHES) plants should enhance their regulation capability by extending their continuous operating range far beyond the optimal normal working range. However, for the time being, the regulation capability of the new generation of PHES, equipped with reversible pump-turbines due to their cost-effectiveness, is limited at part load by instability problems. The aim of this paper is to analyse, during a pumping power reduction scenario, the onset and development of unsteady phenomena leading to unstable behaviour. A 3D transient numerical simulation was carried out on the first stage of a variable-speed two-stage pump-turbine from full load to the unstable operating zone by progressively reducing the speed from 100% to 88% rpm corresponding to a power reduction from full load to about 60% with a ramp rate of 1.5% per s. Two three-dimensional unsteady flow structures affecting the return channel and the wicket gates at the end of the first stage were identified and their evolution in the power regulation scenario was fluid-dynamically and spectrally characterized to determine the fluid-dynamical conditions causing the head drop in the hump zone.

Description: A new control technique known as inverted error deviation (IED) control is incorporated into the main DC-link capacitor voltage regulation algorithm of a three-level neutral-point diode clamped (NPC) inverter-based shunt active power filter (SAPF) to enhance its performance in overall DC-link voltage regulation so as to improve its harmonics mitigation performances. In the SAPF controller, DC-link capacitor voltage regulation algorithms with either the proportional-integral (PI) or fuzzy logic control (FLC) technique have played a significant role in maintaining a constant DC-link voltage across the DC-link capacitors. However, both techniques are mostly operated based on a direct voltage error manipulation approach which is insufficient to address the severe DC-link voltage deviation that occurs during dynamic-state conditions. As a result, the conventional algorithms perform poorly with large overshoot, undershoot, and slow response time. Therefore, the IED control technique is proposed to precisely address the DC-link voltage deviation. To validate effectiveness and feasibility of the proposed algorithm, simulation work in MATLAB-Simulink and experimental implementation utilizing a TMS320F28335 Digital Signal Processor (DSP) are performed. Moreover, conventional algorithms with PI and FLC techniques are tested too for comparison purposes. Both simulation and experimental results are presented, confirming the improvement achieved by the proposed algorithm in terms of accuracy and dynamic response in comparison to the conventional algorithms.

Description: This paper presents a Monte Carlo approach for reliability assessment of distribution systems with distributed generation using parallel computing. The calculations are carried out with a royalty-free power flow simulator, OpenDSS (Open Distribution System Simulator). The procedure has been implemented in an environment in which OpenDSS is driven from MATLAB. The test system is an overhead distribution system represented by means of a three-phase model that includes protective devices. The paper details the implemented procedure, which can be applied to systems with or without distributed generation, includes an illustrative case study and summarizes the results derived from the analysis of the test system during one year. The goal is to evaluate the test system performance considering different scenarios with different level of system automation and reconfiguration, and assess the impact that distributed photovoltaic generation can have on that performance. Several reliability indices, including those related to the impact of distributed generation, are obtained for every scenario.

Description: Because of their simplicity and dynamic response, current pulse series are often used to extract parameters for equivalent electrical circuit modeling of Li-ion batteries. These models are then applied for performance simulation, state estimation, and thermal analysis in electric vehicles. However, these methods have two problems: The assumption of linear dependence of the matrix columns and negative parameters estimated from discrete-time equations and least-squares methods. In this paper, continuous-time equations are exploited to construct a linearly independent data matrix and parameterize the circuit model by the combination of non-negative least squares and genetic algorithm, which constrains the model parameters to be positive. Trigonometric functions are then developed to fit the parameter curves. The developed model parameterization methodology was applied and assessed by a standard driving cycle.

Description: Environmental radiation in space (from the Sun, etc.) and operational thermal loads result in heat flows inside the structure of satellites. Today these heat flows remain unused and are collected, transported to a radiator and emitted to space to prevent the satellite from overheating, but they hold a huge potential to generate electrical power independently of solar panels. Thermoelectric generators are a promising approach for such applications because of their solid state characteristics. As they do not have any moving parts, they do not cause any vibrations in the satellite. They are said to be maintenance-free and highly reliable. Due to the expected small heat flows modern devices based on BiTe have to be considered, but these devices have no flight heritage. Furthermore, energy harvesting on space systems is a new approach for increasing the efficiency and reliability. In this paper, different systems studies and applications are discussed based some experimental characterisation of the electrical behaviour and their dependence on thermal cycles and vibration.

Description: This paper presents real time information based energy management algorithms to reduce electricity cost and peak to average ratio (PAR) while preserving user comfort in a smart home. We categorize household appliances into thermostatically controlled (tc), user aware (ua), elastic (el), inelastic (iel) and regular (r) appliances/loads. An optimization problem is formulated to reduce electricity cost by determining the optimal use of household appliances. The operational schedules of these appliances are optimized in response to the electricity price signals and customer preferences to maximize electricity cost saving and user comfort while minimizing curtailed energy. Mathematical optimization models of tc appliances, i.e., air-conditioner and refrigerator, are proposed which are solved by using intelligent programmable communication thermostat ( iPCT). We add extra intelligence to conventional programmable communication thermostat (CPCT) by using genetic algorithm (GA) to control tc appliances under comfort constraints. The optimization models for ua, el, and iel appliances are solved subject to electricity cost minimization and PAR reduction. Considering user comfort, el appliances are considered where users can adjust appliance waiting time to increase or decrease their comfort level. Furthermore, energy demand of r appliances is fulfilled via local supply where the major objective is to reduce the fuel cost of various generators by proper scheduling. Simulation results show that the proposed algorithms efficiently schedule the energy demand of all types of appliances by considering identified constraints (i.e., PAR, variable prices, temperature, capacity limit and waiting time).

Description: Energy is considered as a main influence on urban configurations. However, there is a difficulty on translating the city models based on theoretical renewable energy concepts into practical applications. This study considers the possibility of understanding this future model as a transformation of the existing urban centres. With this objective, a methodology to intervene in existing cities based on the study of solar access is developed. Therefore, an analysis of solar potential in relation with urban morphology is carried on through a simulation software in l’Eixample, a neighbourhood of Barcelona. The distribution of the sun factor in the different areas of the building blocks envelope displays possible morphological modifications that would facilitate solar energy collection. Consequently, the analytical method presented could be applied to regulate urban interventions with the aim of obtaining more solar energy based cities.

Description: Local electricity generation and sharing has been given considerable attention recently for its disaster resilience and other reasons. However, the process of designing local sharing communities (or local grids) is still unclear. Thus, this study empirically compares algorithms for electricity sharing community clustering in terms of self-sufficiency, sharing cost, and stability. The comparison is performed for all 12 months of a typical year in Yokohama, Japan. The analysis results indicate that, while each individual algorithm has some advantages, an exhaustive algorithm provides clusters that are highly self-sufficient. The exhaustive algorithm further demonstrates that a clustering result optimized for one month is available across many months without losing self-sufficiency. In fact, the clusters achieve complete self-sufficiency for five months in spring and autumn, when electricity demands are lower.

Description: This book contains the successful invited submissions [1–25] to a Special Issue of Energies on the subject area of “Electrical Power and Energy Systems for Transportation Applications”.

Description: In this paper, we develop and investigate the optimal control of a group of 104 heat pumps and a central Combined Heat and Power unit (CHP). The heat pumps supply space heating and domestic hot water to households. Each house has a buffer for domestic hot water and a floor heating system for space heating. Electricity for the heat pumps is generated by a central CHP unit, which also provides thermal energy to a district heating system. The paper reviews recent smart grid control approaches for central and distributed levels. An online algorithm is described based on the earliest deadline first theory that can be used on the aggregator level to control the CHP and to give signals to the heat pump controllers if they should start or should wait. The central controller requires only a limited amount of privacy-insensitive information from the heat pump controllers about their deadlines, which the heat pump controllers calculate for themselves by model predictions. In this way, a robust heat pump and CHP control is obtained, which is able to minimize energy demand and results in the desired thermal comfort for the households. The simulations demonstrate fast computation times due to minor computational and communication overheads.

Description: Outdoor thermal comfort is an essential factor of people’s everyday life and deeply affects the habitability of outdoor spaces. However the indices used for its evaluation were usually developed for indoor environments assuming still air conditions and absence of solar radiation and were only later adapted to outdoor spaces. For this reason, in a previous study the Mediterranean Outdoor Comfort Index (MOCI) was developed, which is an empirical index able to estimate the thermal perception of people living in the Mediterranean area. In this study it was compared numerically (by using the data obtained through a field survey) with other selected thermal indices. This comparison, performed in terms of Spearman’s rho correlation coefficient, association Gamma, percentage of correct predictions and cross-tabulation analysis, led to identify the MOCI as the most suitable index to examine outdoor thermal comfort in the interested area. As a matter of fact it showed a total percentage of correct predictions of 35.5%. Good performances were reported even in thermophysiological indices as the Physiological Equivalent Temperature (PET) and Predicted Mean Vote (PMV). Moreover it was revealed that adaptation and acclimatization phenomena tend to have a certain influence as well.

Description: Although Permanent Magnet Synchronous Generator (PMSG) wind turbines (WTs) mitigate gearbox impacts, they requires high reliability of generators and converters. Statistical analysis shows that the failure rate of direct-drive PMSG wind turbines’ generators and inverters are high. Intelligent fault diagnosis algorithms to detect inverters faults is a premise for the condition monitoring system aimed at improving wind turbines’ reliability and availability. The influences of random wind speed and diversified control strategies lead to challenges for developing intelligent fault diagnosis algorithms for converters. This paper studies open-circuit fault features of wind turbine converters in variable wind speed situations through systematic simulation and experiment. A new fault diagnosis algorithm named Wind Speed Based Normalized Current Trajectory is proposed and used to accurately detect and locate faulted IGBT in the circuit arms. It is compared to direct current monitoring and current vector trajectory pattern approaches. The results show that the proposed method has advantages in the accuracy of fault diagnosis and has superior anti-noise capability in variable wind speed situations. The impact of the control strategy is also identified. Experimental results demonstrate its applicability on practical WT condition monitoring system which is used to improve wind turbine reliability and reduce their maintenance cost.

Description: While previous studies have examined China’s changing industrial energy consumption at the national level, this study argues that it is more useful, from a policy standpoint, to conduct a regional-level analysis owing to the significant regional disparity in industrialisation in the country. This study focuses particularly on Northeast China, where the implementation of the Northeast Revitalisation Strategy in 2003 has contributed to rapid reindustrialisation, which has a serious implication for industrial energy consumption. We decompose the region’s energy consumption changes into activity, structure, and intensity effects. Our results show that the intensity effect is not the only negative factor impacting industrial energy consumption during 2003–2012. The structure effect also has a negative impact on industrial energy consumption between 2005 and 2012. However, the negative impact of the two factors is weakening and not strong enough to counter the positive impact of the activity effect. This result highlights the problem of uncoordinated policy-making in Northeast China. The development strategy, which still depends highly on traditional heavy industries, is in conflict with the national strategy of energy conservation. The two conflicting objectives of industrial revitalization and energy conservation must be reconciled for sustainability in the long term. The study concludes with policy recommendations on how to achieve such reconciliation.

Description: In order to determine the most cost effective alternative among hardening options of power systems, the direct monetary benefits should be evaluated above all other things. Therefore, this paper presents a life-cycle cost model which describes total monetary costs experienced in annual time increments during the project with consideration for the time value of money. In addition, to minimize the risks associated with estimated cost errors due to uncertainties of input data, the stochastic input data are considered. Using the Monte Carlo method, the probabilities and cost ranges in the case studies can be predicted, in turn resulting in better decisions in the selection of hardening options which are cost effective.

Description: The realization of the Smart Grid vision will change the way of producing and distributing electrical energy. It paves the road for end-users to become pro-active in the distribution system and, equipped with renewable energy generators such as a photovoltaic panel, to become a so called “prosumer”. The prosumer is engaged in both energy production and consumption. Prosumers’ energy can be transmitted and exchanged as a commodity between end-users, disrupting the traditional utility model. The appeal of such scenario lies in the engagement of the end user, in facilitating the introduction and optimization of renewables, and in engaging the end-user in its energy management. To facilitate the transition to a prosumers’ governed grid, we propose a novel strategy for optimizing decentralized energy exchange in digitalized power grids, i.e., the Smart Grid. The strategy considers prosumer’s involvement, energy loss of delivery, network topology, and physical constraints of distribution networks. To evaluate the solution, we build a simulation program and design three meaningful evaluation cases according to different energy flow patterns. The simulation results indicate that, compared to traditional power distribution system, the maximum reduction of energy loss, energy costs, energy provided by the electric utility based using the proposed strategy can reach 51 % , 66 % , 97.5 % , depending on the strategy. Moreover, the proportion of energy self-satisfaction approaches reaches 98 % .

Description: In electric power systems, there are always power quality disturbances (PQDs). Usually, noise contamination interferes with their detection and classification. Common methods perform frequency or time-frequency analyses on the power distribution signal for detecting and classifying a limited number of PQDs with some difficulties at low signal-to-noise ratio (SNR). In this regard, recently proposed methodologies for PQD detection estimate several parameters and apply distinct signal processing techniques to improve the detection of PQD. In this work, a novel methodology that merges empirical mode decomposition (EMD), the moments of a random variable, and an artificial neural network (ANN) is proposed for detecting and classifying different PQD. The proposed method estimates skewness, kurtosis, and Shannon entropy from the EMD of one-phase voltage/current signal. Then, an ANN is in charge of classifying the input signal into one of nine different classes for PQD, receiving these parameters as inputs. The effectiveness of the proposed method was verified through computer simulations and experimentation with real data. Obtained results demonstrate its high effectiveness reaching an outstanding 100% of accuracy in detecting and classifying all treated PQD through a few number of parameters, outperforming most of previously proposed approaches.

Description: Since the evolution of the electric and hybrid vehicle, the analysis of batteries’ characteristics and influence on driving range has become essential. This fact advocates the necessity of accurate simulation modeling for batteries. Different models for the Li-ion battery cell are reviewed in this paper and a group of the highly dynamic models is selected for comparison. A new open circuit voltage (OCV) model is proposed. The new model can simulate the OCV curves of lithium iron magnesium phosphate (LiFeMgPO4) battery type at different temperatures. It also considers both charging and discharging cases. The most remarkable features from different models, in addition to the proposed OCV model, are integrated in a single hybrid electrical model. A lumped thermal model is implemented to simulate the temperature development in the battery cell. The synthesized electro-thermal battery cell model is extended to model a battery pack of an actual electric vehicle. Experimental tests on the battery, as well as drive tests on the vehicle are performed. The proposed model demonstrates a higher modeling accuracy, for the battery pack voltage, than the constituent models under extreme maneuver drive tests.

Description: This article presents heat transfer and fluid flow characteristics in a solar air heater (SAH) channel with multi V-type perforated baffles. The flow passage has an aspect ratio of 10. The relative baffle height, relative pitch, relative baffle hole position, flow attack angle, and baffle open area ratio are 0.6, 8.0, 0.42, 60°, and 12%, respectively. The Reynolds numbers considered in the study was in the range of 3000–10,000. The re-normalization group (RNG) k-ε turbulence model has been used for numerical analysis, and the optimum relative baffle width has been investigated considering relative baffle widths of 1.0–7.0.The numerical results are in good agreement with the experimental data for the range considered in the study. Multi V-type perforated baffles are shown to have better thermal performance as compared to other baffle shapes in a rectangular passage. The overall thermal hydraulic performance shows the maximum value at the relative baffle width of 5.0.

Description: The introduction of uncontrollable renewable energy is having a positive impact on our health, the climate, and the economy, but it is also pushing the limits of the power system. The main reason for this is that, in any power system, the generation and consumption must match each other at all times. Thus, if we want to further introduce uncontrollable generation, we need a large ability to manage the demand. However, the ability to control the power consumption of existing demand management approaches is limited, and most of these approaches cannot contribute to the introduction of reneweables, because they do not consider distributed uncontrolled consumption and generation in the control. Furthermore, these methods do not allow users to exchange or jointly manage their power generation and consumption. In this context, we propose an augmented energy management model for prosumers (i.e., producer and consumer). This model considers controlled and uncontrolled generation and consumption, as well as the prosumer’s ability (i) to plan the intended power consumption; and (ii) to manage real-time deviations from the intended consumption. We apply this model to the energy management of prosumer communities, by allowing the prosumers to coordinate their power consumption plan, to manage the deviations from the intended consumption, and to help each other by compensating deviations. The proposed approach seeks to enhance the power system, and to enable a prosumer society that takes account social and environmental issues, as well as each prosumer’s quality of life.

Description: The objective of this paper is to numerically investigate the effects of the atmospheric boundary layer on the aerodynamic performance and loads of a novel dual-rotor wind turbine (DRWT). Large eddy simulations are carried out with the turbines operating in the atmospheric boundary layer (ABL) and in a uniform inflow. Two stability conditions corresponding to neutral and slightly stable atmospheres are investigated. The turbines are modeled using the actuator line method where the rotor blades are modeled as body forces. Comparisons are drawn between the DRWT and a comparable conventional single-rotor wind turbine (SRWT) to assess changes in aerodynamic efficiency and loads, as well as wake mixing and momentum and kinetic energy entrainment into the turbine wake layer. The results show that the DRWT improves isolated turbine aerodynamic performance by about 5%–6%. The DRWT also enhances turbulent axial momentum entrainment by about 3.3 %. The highest entrainment is observed in the neutral stability case when the turbulence in the ABL is moderately high. Aerodynamic loads for the DRWT, measured as out-of-plane blade root bending moment, are marginally reduced. Spectral analyses of ABL cases show peaks in unsteady loads at the rotor passing frequency and its harmonics for both rotors of the DRWT.

Description: In cognitive radio (CR), the spectrum sensing of the primary user (PU) may consume some electrical power from the battery capacity of the secondary user (SU), resulting in a decrease in the transmission power of the SU. In this paper, a multislot simultaneous spectrum sensing and energy harvesting model is proposed, which uses the harvested radio frequency (RF) energy of the PU signal to supply the spectrum sensing. In the proposed model, the sensing duration is divided into multiple sensing slots consisting of one local-sensing subslot and one energy-harvesting subslot. If the PU is detected to be present in the local-sensing subslot, the SU will harvest RF energy of the PU signal in the energy-harvesting slot, otherwise, the SU will continue spectrum sensing. The global decision on the presence of the PU is obtained through combining local sensing results from all the sensing slots by adopting “Or-logic Rule”. A joint optimization problem of sensing time and time splitter factor is proposed to maximize the throughput of the SU under the constraints of probabilities of false alarm and detection and energy harvesting. The simulation results have shown that the proposed model can clearly improve the maximal throughput of the SU compared to the traditional sensing-throughput tradeoff model.

Description: Advanced metering infrastructure (AMI) subsystems monitor and control energy distribution through exchange of information between smart meters and utility networks. A key challenge is how to select a cost-effective communication system without compromising the performance of the applications. Current communication technologies were developed for conventional data networks with different requirements. It is therefore necessary to investigate how much of existing communication technologies can be retrofitted into the new energy infrastructure to cost-effectively deliver acceptable level of service. This paper investigates broadband power line communications (BPLC) as a backhaul solution in AMI. By applying the disparate traffic characteristics of selected AMI applications, the network performance is evaluated. This study also examines the communication network response to changes in application configurations in terms of packet sizes. In each case, the network is stress-tested and performance is assessed against acceptable thresholds documented in the literature. Results show that, like every other communication technology, BPLC has certain limitations; however, with some modifications in the network topology, it indeed can fulfill most AMI traffic requirements for flexible and time-bounded applications. These opportunities, if tapped, can significantly improve fiscal and operational efficiencies in AMI services. Simulation results also reveal that BPLC as a backhaul can support flat and clustered AMI structures with cluster size ranging from 1 to 150 smart meters.

Description: This paper presents an application and extension of multiple-criteria decision-making (MCDM) methods to account for stochastic input variables. More in particular, a comparative study is carried out among well-known and widely-applied methods in MCDM, when applied to the reference problem of the selection of wind turbine support structures for a given deployment location. Along with data from industrial experts, six deterministic MCDM methods are studied, so as to determine the best alternative among the available options, assessed against selected criteria with a view toward assigning confidence levels to each option. Following an overview of the literature around MCDM problems, the best practice implementation of each method is presented aiming to assist stakeholders and decision-makers to support decisions in real-world applications, where many and often conflicting criteria are present within uncertain environments. The outcomes of this research highlight that more sophisticated methods, such as technique for the order of preference by similarity to the ideal solution (TOPSIS) and Preference Ranking Organization method for enrichment evaluation (PROMETHEE), better predict the optimum design alternative.

Description: This paper presents the development of a WebGIS application aimed at providing safe and reliable data needed for reclamation of abandoned mines in national parks and other protected areas in Vojvodina in compliance with existing legal regulations. The geodatabase model for this application has been developed using UML and the CASE tool Microsoft Visio featuring an interface with ArcGIS. The WebGIS application was developed using GeoServer, an open source tool in the Java programming language, with integrated PostgreSQL DB and the possibility of generating and publishing WMS, WFS and KML services. The WebGIS application is publicly available, based on an appropriate central database, which for the first time encompasses all available data on abandoned mines in Vojvodina, and as such may serve as a model for similar databases on the territory of the Republic of Serbia.

Description: This paper presents a review of over a decade of research on Vertical Axis Wind Turbines (VAWTs) conducted at Uppsala University. The paper presents, among others, an overview of the 200 kW VAWT located in Falkenberg, Sweden, as well as a description of the work done on the 12 kW prototype VAWT in Marsta, Sweden. Several key aspects have been tested and successfully demonstrated at our two experimental research sites. The effort of the VAWT research has been aimed at developing a robust large scale VAWT technology based on an electrical control system with a direct driven energy converter. This approach allows for a simplification where most or all of the control of the turbines can be managed by the electrical converter system, reducing investment cost and need for maintenance. The concept features an H-rotor that is omnidirectional in regards to wind direction, meaning that it can extract energy from all wind directions without the need for a yaw system. The turbine is connected to a direct driven permanent magnet synchronous generator (PMSG), located at ground level, that is specifically developed to control and extract power from the turbine. The research is ongoing and aims for a multi-megawatt VAWT in the near future.

Description: As safety and reliability critical components, lithium-ion batteries always require real-time diagnosis and prognosis. This often involves a large amount of computation, which makes diagnosis and prognosis difficult to implement, especially in embedded or mobile applications. To address this issue, this paper proposes a run-time Reconfigurable Computing (RC) system on Field Programmable Gate Array (FPGA) for Relevance Vector Machine (RVM) to realize real-time Remaining Useful Life (RUL) estimation. The system leverages state-of-the-art run-time dynamic partial reconfiguration technology and customized computing circuits to balance the hardware occupation and computing efficiency. Optimal hardware resource consumption is achieved by partitioning the RVM algorithm according to a multi-objective optimization. Moreover, pipelined and parallel computation circuits for kernel function and matrix inverse are proposed on FPGA to further accelerate the computation. Experimental results with two different battery data sets show that, without sacrificing the RUL prediction performance, the embedded RC platform significantly reduces the computation time and the requirement of hardware resources. This demonstrates that complex prognostic tasks can be implemented and deployed on the proposed system, and it can be extended to the embedded computation of other machine learning algorithms.

Description: Interior permanent magnet (IPM) motors are widely used in electric vehicles (EVs), benefiting from the excellent advantages of a more rational use of energy. For further improvement of energy utilization, this paper presents an analytical method of d- and q-axis inductance calculation for IPM motors with V-shaped rotor in no-load condition. A lumped parameter magnetic circuit model (LPMCM) is adopted to investigate the saturation and nonlinearity of the bridge. Taking into account the influence of magnetic field distribution on inductance, the winding function theory (WFT) is employed to accurately calculate the armature reaction airgap magnetic field and d- and q-axis inductances. The validity of the analytical technique is verified by the finite element method (FEM).

Description: A building integrated holographic concentrating photovoltaic-thermal system has been optically and energetically simulated. The system has been designed to be superimposed into a solar shading louvre; in this way the concentrating unit takes profit of the solar altitude tracking, which the shading blinds already have, to increase system performance. A dynamic energy simulation has been conducted in two different locations—Sde Boker (Israel) and Avignon (France)—both with adequate annual irradiances for solar applications, but with different weather and energy demand characteristics. The simulation engine utilized has been TRNSYS, coupled with MATLAB (where the ray-tracing algorithm to simulate the holographic optical performance has been implemented). The concentrator achieves annual mean optical efficiencies of 30.3% for Sde Boker and 43.0% for the case of Avignon. Regarding the energy production, in both locations the thermal energy produced meets almost 100% of the domestic hot water demand as this has been considered a priority in the system control. On the other hand, the space heating demands are covered by a percentage ranging from 15% (Avignon) to 20% (Sde Boker). Finally, the electricity produced in both places covers 7.4% of the electrical demand profile for Sde Boker and 9.1% for Avignon.

Description: In order to investigate how artificial neural networks (ANNs) have been applied for partial discharge (PD) pattern recognition, this paper reviews recent progress made on ANN development for PD classification by a literature survey. Contributions from several authors have been presented and discussed. High recognition rate has been recorded for several PD faults, but there are still many factors that hinder correct recognition of PD by the ANN, such as high-amplitude noise or wide spectral content typical from industrial environments, trial and error approaches in determining an optimum ANN, multiple PD sources acting simultaneously, lack of comprehensive and up to date databank of PD faults, and the appropriate selection of the characteristics that allow a correct recognition of the type of source which are currently being addressed by researchers. Several suggestions for improvement are proposed by the authors include: (1) determining the optimum weights in training the ANN; (2) using PD data captured over long stressing period in training the ANN; (3) ANN recognizing different PD degradation levels; (4) using the same resolution sizes of the PD patterns when training and testing the ANN with different PD dataset; (5) understanding the characteristics of multiple concurrent PD faults and effectively recognizing them; and (6) developing techniques in order to shorten the training time for the ANN as applied for PD recognition Finally, this paper critically assesses the suitability of ANNs for both online and offline PD detections outlining the advantages to the practitioners in the field. It is possible for the ANNs to determine the stage of degradation of the PD, thereby giving an indication of the seriousness of the fault.

Description: Attributing to the advantages of high efficiency, low electromagnetic interference (EMI) noise and closest to the pulse-width-modulation (PWM) converter counterpart, zero-voltage-transition (ZVT) PWM soft-switching inverters are very suitable for high-performance applications. However, the conventional control algorithms intended for high efficiency generally results in voltage distortion. Thus, this paper, for the first time, proposes a high-precision control method to eliminate the dead-time effect through controlling the auxiliary current in the auxiliary resonant snubber inverter (ARSI), which is a typical ZVT PWM inverter. The dead-time effect of ARSI is analyzed, which is distinguished from hard-switching inverters. The proposed high-precision control is introduced based on the investigation of dead-time effect. A prototype was developed to verify the effectiveness of the proposed control. The experimental results shows that the total harmonic distortion (THD) of the output current of the ARSI can be reduced compared with that of the hard-switching inverter, because the blanking delay error is eliminated. The quality of the output current and voltage can be further improved by utilizing the proposed control method.

Description: Trigeneration plants can use different types of chillers in the same plant, typically single effect and double effect absorption chillers, vapour compression chillers and also cooling storage systems. The highly variable cooling demand of the buildings connected to a district heating and cooling (DHC) network has to be distributed among these chillers to achieve lower operating costs and higher energy efficiencies. This problem is difficult to solve due to the different partial load behaviour of each chiller and the different chiller combinations that can cover a certain cooling demand using an appropriate sizing of the cooling storage. The objective of this paper is to optimize the daily plant operation of an existing trigeneration plant based on cogeneration engines and to study the optimal cooling load sharing between different types of absorption chillers using a mixed integer linear programming (MILP) model. Real data from a trigeneration plant connected to a DHC close to Barcelona (Spain) is used for the development of this model. The cooling load distribution among the different units is heavily influenced by the price of the electricity sold to the grid which rules the duration of the operation time of the engines. The main parameter to compare load distribution configurations is the primary energy saving indicator. Cooling load distribution among the different chillers changes also with the load of the whole plant because the chiller performance changes with load.

Description: This study describes the environmental impact of the material production, transportation, and construction phases from the construction site perspective. CO2 emissions for each process were determined using the Korea Life Cycle Inventory Database (LCI DB) in the material production phase, and the actual amounts of oil consumption for transportation equipment were identified in the material transportation phase. Generally, the oil and electric energy consumed during the construction was evaluated by direct monitoring. Through the construction period and cost according to work type, a correlation with CO2 emissions was also investigated. In addition, CO2 emissions were examined through the system capacity and gross floor area for each work type. The calculations have shown that CO2 emissions from the material production phase constitute 93.4% of the total CO2 emissions. In addition, CO2 emissions from the material transportation and on-site construction account for 2.4% and 4.2% of the total CO2 emissions, respectively. This paper concludes that it is important to select appropriate input materials and resources for the reduction of CO2 emissions. Furthermore, the amount of CO2 emissions arising from the construction site was reduced by finding and practicing measures to reduce CO2 emissions for each process.

Description: In the context of the liberalization of electricity markets, forecasting prices is essential. With this aim, research has evolved to model the particularities of electricity prices. In particular, dynamic factor models have been quite successful in the task, both in the short and long run. However, specifying a single model for the unobserved factors is difficult, and it cannot be guaranteed that such a model exists. In this paper, model averaging is employed to overcome this difficulty, with the expectation that electricity prices would be better forecast by a combination of models for the factors than by a single model. Although our procedure is applicable in other markets, it is illustrated with an application to forecasting spot prices of the Iberian Market, MIBEL (The Iberian Electricity Market). Three combinations of forecasts are successful in providing improved results for alternative forecasting horizons.

Description: Demand Side Management (DSM) is a popular approach for grid-aware peak-shaving. The most commonly used DSM methods either have no look ahead feature and risk deploying flexibility too early, or they plan ahead using predictions, which are in general not very reliable. To counter this, a DSM approach is presented that does not rely on detailed power predictions, but only uses a few easy to predict characteristics. By using these characteristics alone, near optimal results can be achieved for electric vehicle (EV) charging, and a bound on the maximal relative deviation is given. This result is extended to an algorithm that controls a group of EVs such that a transformer peak is avoided, while simultaneously keeping the individual house profiles as flat as possible to avoid cable overloading and for improved power quality. This approach is evaluated using different data sets to compare the results with the state-of-the-art research. The evaluation shows that the presented approach is capable of peak-shaving at the transformer level, while keeping the voltages well within legal bounds, keeping the cable load low and obtaining low losses. Further advantages of the methodology are a low communication overhead, low computational requirements and ease of implementation.

Description: The objective of this work was to monitor and analyse temperature changes in the ground with installed linear and Slinky-type horizontal ground heat exchangers (HGHEs), used as low-potential heat pump energy sources. Specific heat flows and specific energies extracted from the ground during the heating season were also measured and compared. The verification results showed that the average daily ground temperatures with the two HGHEs are primarily affected by the temperature of the ambient environment. The ground temperatures were higher than ambient temperature during most of the heating season, were only seldom below zero, and were higher by an average 1.97 ± 0.77 K in the ground with the linear HGHE than in the ground with the Slinky-type HGHE. Additionally, the specific thermal output extracted from the ground by the HGHE was higher by 8.45 ± 16.57 W/m2 with the linear system than with the Slinky system. The specific energies extracted from the ground over the whole heating season were 110.15 kWh/m2 and 57.85 kWh/m2 for the linear and Slinky-type HGHEs, respectively.

Description: Integrating natural resources and ecological services in the production process is crucial to implement sustainable agriculture. However, the measurement of natural resource efficiency remains difficult. This paper aims at contributing to this issue, by investigating French farms’ use and excess (slack) of energy resources through Data Envelopment Analyses (DEA). Results show that disentangling energy resources from the rest of intermediate consumption highlights energy use excess which is masked when considering intermediate consumption as a whole. The analysis of the determinants of energy use excess and of intermediate consumption shows a discrepancy in results, which policy-makers should take into account when designing energy policies. In addition, results show that large and highly capital intensive farms perform better in terms of energy use excess, while the dependence on public subsidies is a constraint.

Description: Fuel cells are the most clean and efficient power source for vehicles. In particular, proton exchange membrane fuel cells (PEMFCs) are the most promising candidate for automobile applications due to their rapid start-up and low-temperature operation. Through extensive global research efforts in the latest decade, the performance of PEMFCs, including energy efficiency, volumetric and mass power density, and low temperature startup ability, have achieved significant breakthroughs. In 2014, fuel cell powered vehicles were introduced into the market by several prominent vehicle companies. However, the low durability and high cost of PEMFC systems are still the main obstacles for large-scale industrialization of this technology. The key materials and components used in PEMFCs greatly affect their durability and cost. In this review, the technical progress of key materials and components for PEMFCs has been summarized and critically discussed, including topics such as the membrane, catalyst layer, gas diffusion layer, and bipolar plate. The development of high-durability processing technologies is also introduced. Finally, this review is concluded with personal perspectives on the future research directions of this area.

Description: In this paper, a photovoltaic (PV)-based single ended primary-inductor converter (SEPIC) is developed with introduction of dual-fuzzy logic controller (FLC) maximum power point tracking (MPPT) algorithm. Separate FLC parts, for the first time used for MPPT, are configured for optimal operations of both buck and boost operations. During buck operation, a high overshoot voltage exists, and during boost operation, an undershoot voltage occurs, both during the initial rising period. Definitely, a single-FLC MPPT could not be able to minimize both problems, which on the other hand can be handled by the proposed MPPT algorithm. For evaluation purposes, buck operation has been conducted during high irradiance, while during low irradiance, boost operation has been conducted. The dual-FLC MPPT with SEPIC was simulated in MATLAB-Simulink, and further a laboratory prototype was implemented with a TMS320F28335 eZdsp board. Both simulation and experimental results and comparison analysis (with the single-FLC MPPT) have been presented. From the results and analysis, the dual-FLC MPPT performs better than the single-FLC MPPT in terms of faster response time, lower overshoot and undershoot, and further significant reduction of power losses.

Description: The development of renewable energy is one of the aspirations of the European Union energy policy, being generated by the struggle against climatic changes and by the intention of achieving a high rate of energy autonomy. In this context, geothermal energy is a viable solution which has been little exploited so far. Analysing the EU’s dependence on imported energy, the paper provides a short review of the utilization of geothermal energy, of the advantages and of the problems raised by the exploitation of this resource. It also analyzes the availability of this resource in Romania and the contribution it can have towards the energy autonomy of local communities. The paper presents a particular methodology for calculating the energy autonomy. Using this methodology, one can obtain an energetic overview of the community or the area analyzed, can calculate the degree of energy autonomy and, based on the results achieved, a sustainable development strategy can be designed. The low enthalpy case study used emphasizes the way this methodology can be deployed and, moreover, allows an analysis of the contribution of geothermal energy to the degree of autonomy of the Romanian community.

Description: Heat dissipation per unit volume has grown rapidly, as the size of modern electronic devices has continued to decrease. The air flow induced by an oscillating cantilever blade enhances the heat transfer performance of high heat density devices. The heat transfer improvement mainly depends on the velocity magnitude and distribution of air streams induced by the vibrating blade. Accordingly, this study numerically and experimentally examines the time-varying flow characteristics of a vibrating cantilever for five blade types. The blades are rectangular or trapezoidal with various widths and actuated at various frequencies. The fluid domain is numerically discretized using a dynamic meshing scheme to model the three-dimensional time-varying vibrating blade. The experiment utilizes nine hot-wire velocity meters to measure the average velocities. The flow structure with streamlines and velocity contours of the induced air flow are determined at various section planes. The results show that a major maximum-velocity region appears around the blade tip and that four minor local-maximum-velocity regions appear at the four corners. In addition, the width and width ratio of the blade significantly affects the velocity distribution of the flow induced by the vibrating cantilever blade.

Description: The critical problem arising from the depletion of fossil fuels has stimulated recent interests in alternative sources for petroleum-based fuel. An alternative fuel should be technically feasible, readily available, sustainable, and techno-economically competitive. Biodiesel is considered as a potential replacement of conventional diesel fuel, which is prepared from non-edible and high-acid feedstock via transesterification technology. The focus of this study is to investigate the catalytic activity of mixed metal oxides (MMOs) as catalysts for biodiesel production by using non-edible jatropha oil as feedstock. Various types of MMOs (CaO-MgO, CaO-ZnO, CaO-La2O3, and MgO-ZnO) were synthesized via a co-precipitation method. In this study, transesterification activities are closely related to the physicochemical properties of catalysts. The presence of different active metals in the binary system greatly influenced the surface area, basicity, and the stability of catalysts. The catalytic activity of MMO catalysts was increased in the order of CaO-ZnO (94% ± 1%) > CaO ~ CaO-MgO ~ CaO-La2O3 (~90% ± 2%) > MgO-ZnO (83% ± 2%) > MgO (64% ± 1%) > ZnO (41% ± 2%) > La2O3 (23% ± 1%). In addition, the MMO catalysts, especially CaO-ZnO, demonstrated high reusability and catalyst stability for four cycles of transesterification reaction of jatropha oil.

Description: Super typhoon activity is likely to make the electric power network fail, or blow the wind-measuring device off, which all lead to the yaw control system of wind turbine being inactive. Under this condition, blades can be blown by the violent side wind from unfavorable directions, and the aerodynamic loads on the wind turbine will be increased by a large amount, which can lead to low-cycle fatigue damage and other catastrophic collapses. So far, not enough consideration has been given to the above problems in wind turbine design. Using the transient computational fluid dynamics (CFD), this study investigates the wind load characteristics of offshore wind turbines under typhoon condition with 360-degree full wind directions. Two primary influence factors of the aerodynamic characteristics of wind turbines are clarified: variation of the wind direction and different parking positions of the wind rotor. Using 3D-numerical simulation results, this study provides detailed references for the ultimate strength and fatigue life in wind turbine design, and presents the best parking position of the wind turbine with a free yawing strategy.

Description: Plasma stability is one of the obstacles in the path to the successful operation of fusion devices. Numerical control-oriented codes as it is the case of the widely accepted RZIp may be used within Tokamak simulations. The novelty of this article relies in the hierarchical development of a dynamic control loop. It is based on a current profile Model Predictive Control (MPC) algorithm within a multiloop structure, where a MPC is developed at each step so as to improve the Proportional Integral Derivative (PID) global scheme. The inner control loop is composed of a PID-based controller that acts over the Multiple Input Multiple Output (MIMO) system resulting from the RZIp plasma model of the Tokamak à Configuration Variable (TCV). The coefficients of this PID controller are initially tuned using an eigenmode reduction over the passive structure model. The control action corresponding to the state of interest is then optimized in the outer MPC loop. For the sake of comparison, both the traditionally used PID global controller as well as the multiloop enhanced MPC are applied to the same TCV shot. The results show that the proposed control algorithm presents a superior performance over the conventional PID algorithm in terms of convergence. Furthermore, this enhanced MPC algorithm contributes to extend the discharge length and to overcome the limited power availability restrictions that hinder the performance of advanced tokamaks.

Description: A multi-variable optimization program has been developed to investigate the performance of Organic Rankine Cycles (ORCs) for low temperature heat recovery applications using both turbine and twin-screw expanders when account is taken of performance variation due to changes in ambient conditions. The cycle simulation contains thermodynamic models of both types of expander. In the case of the twin-screw machine, the methods used to match the operation of the expander to the requirements of the cycle are described. The performance of turbine expanders in a superheated ORC has been modelled using correlations derived from operational data for single stage reaction turbines to predict the turbine efficiency at “off-design” conditions. Several turbine configurations have been considered including variable nozzle area and variable speed. The capability of the cycle model has been demonstrated for the case of heat recovery from a steady source of pressurized hot water at 120 °C. The system parameters are optimised for a typical operating condition, which determines the required size of heat exchangers and the expander characteristics. Performance at off-design conditions can then be optimized within these constraints. This allows a rigorous investigation of the effect of air temperature variation on the system performance, and the seasonal variation in net power output for the turbine and twin-screw ORC systems. A case study is presented for a low temperature heat recovery application with system electrical power output of around 100 kWe at design conditions. The results indicate that similar overall performance can be achieved for ORC systems using either type of expander.

Description: An experimental study was performed to investigate the effect of subcritical carbon dioxide (CO2) adsorption on mechanical properties of shales with different coring directions. Uniaxial compressive strength (UCS) tests were conducted on shale samples with different CO2 adsorption time at a pressure of 7 MPa and a temperature of 40 °C. The crack propagation and the failure mechanism of shale samples were recorded by using acoustic emission (AE) sensors together with ARAMIS technology. According to the results, samples with parallel and normal bedding angles present reductions of 26.7% and 3.0% in UCS, 30.7% and 36.7% in Young’s modulus after 10 days’ adsorption of CO2, and 30.3% and 18.4% in UCS, 13.8% and 22.6% in Young’s modulus after 20 days’ adsorption of CO2. Samples with a normal bedding angle presented higher brittleness index than that with a parallel bedding angle. The strain distributions show that longer CO2 adsorption will cause higher axial strains and lateral strains. The AE results show that samples with a parallel angle have higher AE energy release than the samples with a normal angle. Finally, samples with longer CO2 adsorption times present higher cumulative AE energy release.

Description: In this paper, a generic coordinated control method for wave energy converters is proposed, and the constraints on motion amplitudes and the hydrodynamic interaction between converters are considered. The objective of the control problem is to maximize the energy converted from ocean waves, and this is achieved by coordinating the power take-off (PTO) damping of each wave energy converter in the frequency domain in each sea state. In a case study, a wave energy farm consisting of four converters based on the concept developed by Uppsala University is studied. In the solution, motion constraints, including constraints on the amplitudes of displacement and velocity, are included. Twelve months of sea states, based on measured wave data at the Lysekil test site on the Swedish west coast, are used in the simulation to evaluate the performance of the wave energy farm using the new method. Results from the new coordinated control method and traditional control method are compared, indicating that the coordinated control of wave energy converters is an effective way to improve the energy production of wave energy farm in harmonic waves.

Description: In the field of state of charge (SOC) estimation, the Kalman filter has been widely used for many years, although its performance strongly depends on the accuracy of the battery model as well as the noise covariance. The Kalman gain determines the confidence coefficient of the battery model by adjusting the weight of open circuit voltage (OCV) correction, and has a strong correlation with the measurement noise covariance (R). In this paper, the online identification method is applied to acquire the real model parameters under different operation conditions. A criterion based on the OCV error is proposed to evaluate the reliability of online parameters. Besides, the equivalent circuit model produces an intrinsic model error which is dependent on the load current, and the property that a high battery current or a large current change induces a large model error can be observed. Based on the above prior knowledge, a fuzzy model is established to compensate the model error through updating R. Combining the positive strategy (i.e., online identification) and negative strategy (i.e., fuzzy model), a more reliable and robust SOC estimation algorithm is proposed. The experiment results verify the proposed reliability criterion and SOC estimation method under various conditions for LiFePO4 batteries.

Description: The authors wish to make the following corrections to the published paper [1].[...]

Description: Standalone microgrids, which are mainly constructed on island areas have low system inertia, may result large frequency deviations even for small load change. Moreover, increasing penetration level of renewable energy sources (RESs) into standalone microgrids makes the frequency stability problem even worse. To overcome this problem, this paper proposes an active power sharing method with zero frequency deviations. To this end, a battery energy storage system (BESS) is operated as constant frequency (CF) control mode, whereas the other distributed generations (DGs) are operated as an active and reactive power (PQ) control mode. As a result, a state of charge (SOC) of the BESS is changed as the system load varies. Based on the SOC deviation, DGs share the load change. The SOC data is assumed to be sent via communication system, hence the communication time delay is considered. To enhance reliability, controllers of DGs are designed to take account of the failure of communication system. The simulation results show that active power can be shared among DGs according to desired ratio without frequency deviations even for large variation of output power of RESs.

Description: We propose an optimal electric and heat energy management for a cooperative multi-microgrid community. The sequentially-coordinated operation for heat energy is proposed in order to distribute the computational burden as an extension of “Optimal Energy Management of Multi-Microgrids with Sequentially Coordinated Operations” and is following the sequentially-coordinated operations for electric energy in it. This sequentially-coordinated operation for heat energy is mathematically modeled and how to obtain the global heat energy optimization solution in the cooperative multi-microgrid community is presented. The global heat energy optimization is achieved for the cooperative community by adjusting the combined electric and heat energy production amounts of combined heat and power (CHP) generators and the heat energy production amount of heat only boilers (HOBs) which satisfy all heat loads, as well as optimize the external electric energy trading in order to minimize the unnecessary cost from the external electric trading, and/or maximize the profit from the external electric trading. To validate the proposed mathematical energy management models, a simulation study is also conducted.

Description: In this paper, we investigate the energy problem of monitoring sensors on high-voltage power transmission lines and propose a wireless charging scheme for a Radio Frequency IDentification (RFID) sensor tag to solve a commercial efficiency problem: the maintenance-caused power outage. Considering the environmental influences on power transmission lines, a self-powered wireless energy relay is designed to meet the energy requirement of the passive RFID sensor tag. The relay can obtain the electric field energy from the transmission lines and wirelessly power the RFID sensor tags around for longer operating distance. A prototype of the energy relay is built and tested on a 110 kv line. The measurement results show that the energy relay can provide stable energy even with the influences of wind, noise and power outage. To our knowledge, it is the first work to power the RFID sensor tags on power transmission lines.

Description: In order to achieve a greater light absorption in the near-infrared (NIR) region with a panchromatic spectral response and to suppress the photo-isomerisation phenomenon, we herein report the design, synthesis, spectroscopic and electrochemical characterization of novel centrally functionalized symmetric benzoindolenine squaraine dyes. These molecules have shown different photoelectrical conversion properties, depending on the dicyanovinyl and cyano-ester group substitution on the squaric core unit and on the extension of the π-conjugation.

Description: The Up-THERM heat converter is an unsteady, two-phase thermofluidic oscillator that employs an organic working fluid, which is currently being considered as a prime-mover in small- to medium-scale combined heat and power (CHP) applications. In this paper, the Up-THERM heat converter is compared to a basic (sub-critical, non-regenerative) organic Rankine cycle (ORC) heat engine with respect to their power outputs, thermal efficiencies and exergy efficiencies, as well as their capital and specific costs. The study focuses on a pre-specified Up-THERM design in a selected application, a heat-source temperature range from 210 °C to 500 °C and five different working fluids (three n-alkanes and two refrigerants). A modeling methodology is developed that allows the above thermo-economic performance indicators to be estimated for the two power-generation systems. For the chosen applications, the power output of the ORC engine is generally higher than that of the Up-THERM heat converter. However, the capital costs of the Up-THERM heat converter are lower than those of the ORC engine. Although the specific costs (£/kW) of the ORC engine are lower than those of the Up-THERM converter at low heat-source temperatures, the two systems become progressively comparable at higher temperatures, with the Up-THERM heat converter attaining a considerably lower specific cost at the highest heat-source temperatures considered.

Description: Recent growth in the renewable energy industry has increased government support for alternative energy. In the United States, hydropower is the largest source of renewable energy and also one of the most efficient. Currently, there are 30,000 megawatts of potential energy capacity through small- and micro-hydro projects throughout the United States. Increased development of micro-hydro could double America’s hydropower energy generation, but micro-hydro is not being developed at the same rate as other renewable sources. Micro-hydro is regulated by the Federal Energy Regulatory Commission and subject to the same regulation as large hydroelectric projects despite its minimal environmental impact. We studied two cases of micro-hydro projects in Logan, Utah, and Afton, Wyoming, which are both small rural communities. Both cases showed that the web of federal regulation is likely discouraging the development of micro-hydro in the United States by increasing the costs in time and funds for developers. Federal environmental regulation like the National Environmental Policy Act, the Endangered Species Act, and others are likely discouraging the development of clean renewable energy through micro-hydro technology.

Description: This paper presents an initial investment cost analysis of public transportation systems operating with wireless charging electric vehicles (EVs). There are three different types of wireless charging systems, namely, stationary wireless charging (SWC), in which charging happens only when the vehicle is parked or idle, quasi-dynamic wireless charging (QWC), in which power is transferred when a vehicle is moving slowly or in stop-and-go mode, and dynamic wireless charging (DWC), in which power can be supplied even when the vehicle is in motion. This analysis compares the initial investment costs for these three types of charging systems for a wireless charging-based public transportation system. In particular, this analysis is focused on the energy logistics cost in transportation, which is defined as the cost of transferring and storing the energy needed to operate the transportation system. Performing this initial investment analysis is complicated, because it involves considerable tradeoffs between the costs of batteries in the EV fleet and different kinds of battery-charging infrastructure. Mathematical optimization models for each type of EV and infrastructure system are used to analyze the initial costs. The optimization methods evaluate the minimum initial investment needed to deploy the public transportation system for each type of EV charging solution. To deal with the variable cost estimates for batteries and infrastructure equipment in the current market, a cost-sensitivity analysis is performed. The goal of this analysis is to identify the market cost conditions that are most favorable for each type of wireless charging solution. Furthermore, the cost analysis quantitatively verifies the qualitative comparison of the three different wireless charging types conducted in the previous research.

Description: The potential of organic Rankine cycle (ORC) systems is acknowledged by both considerable research and development efforts and an increasing number of applications. Most research aims at improving ORC systems through technical performance optimization of various cycle architectures and working fluids. The assessment and optimization of technical feasibility is at the core of ORC development. Nonetheless, economic feasibility is often decisive when it comes down to considering practical instalments, and therefore an increasing number of publications include an estimate of the costs of the designed ORC system. Various methods are used to estimate ORC costs but the resulting values are rarely discussed with respect to accuracy and validity. The aim of this paper is to provide insight into the methods used to estimate these costs and open the discussion about the interpretation of these results. A review of cost engineering practices shows there has been a long tradition of industrial cost estimation. Several techniques have been developed, but the expected accuracy range of the best techniques used in research varies between 10% and 30%. The quality of the estimates could be improved by establishing up-to-date correlations for the ORC industry in particular. Secondly, the rapidly growing ORC cost literature is briefly reviewed. A graph summarizing the estimated ORC investment costs displays a pattern of decreasing costs for increasing power output. Knowledge on the actual costs of real ORC modules and projects remains scarce. Finally, the investment costs of a known heat recovery ORC system are discussed and the methodologies and accuracies of several approaches are demonstrated using this case as benchmark. The best results are obtained with factorial estimation techniques such as the module costing technique, but the accuracies may diverge by up to +30%. Development of correlations and multiplication factors for ORC technology in particular is likely to improve the quality of the estimates.

Description: The provision of energy infrastructure is essential for economic growth, social cohesion, and environmental sustainability. Understanding the multiple functions and services it provides us requires firstly a deeper understanding of the factors that influence energy infrastructure itself. This paper focusses on the factors that influence the evolution of energy infrastructure in Nigeria. By studying different eras of energy use according to the technologies that were being implemented, resources that were available, and the political practice of the time it is possible to better frame the drivers of energy infrastructure. The paper explores the transitions of how Nigerians managed to obtain the vast majority of energy from food calories and traditional biomass, to the broad portfolio of energy sources that is in use today.

Description: This paper reports on a comprehensive study of the CO2-EOR (Enhanced oil recovery) process, a detailed literature review and a numerical modelling study. According to past studies, CO2 injection can recover additional oil from reservoirs by reservoir pressure increment, oil swelling, the reduction of oil viscosity and density and the vaporization of oil hydrocarbons. Therefore, CO2-EOR can be used to enhance the two major oil recovery mechanisms in the field: miscible and immiscible oil recovery, which can be further increased by increasing the amount of CO2 injected, applying innovative flood design and well placement, improving the mobility ratio, extending miscibility, and controlling reservoir depth and temperature. A 3-D numerical model was developed using the CO2-Prophet simulator to examine the effective factors in the CO2-EOR process. According to that, in pure CO2 injection, oil production generally exhibits increasing trends with increasing CO2 injection rate and volume (in HCPV (Hydrocarbon pore volume)) and reservoir temperature. In the WAG (Water alternating gas) process, oil production generally increases with increasing CO2 and water injection rates, the total amount of flood injected in HCPV and the distance between the injection wells, and reduces with WAG flood ratio and initial reservoir pressure. Compared to other factors, the water injection rate creates the minimum influence on oil production, and the CO2 injection rate, flood volume and distance between the flood wells have almost equally important influence on oil production.

Description: Bidirectional power converters for electric vehicles (EVs) have received much attention recently, due to either grid-supporting requirements or emergent power supplies. This paper proposes a hybrid modulation of the three-phase dual-active bridge (3ΦDAB) converter for EV charging systems. The designed hybrid modulation allows the converter to switch its modulation between phase-shifted and trapezoidal modes to increase the conversion efficiency, even under light-load conditions. The mode transition is realized in a real-time manner according to the charging or discharging current. The operation principle of the converter is analyzed in different modes and thus design considerations of the modulation are derived. A lab-scaled prototype circuit with a 48V/20Ah LiFePO4 battery is established to validate the feasibility and effectiveness.

Description: This paper aims to focus on the smooth output of DC-DC buck converters in wireless power transfer systems under input perturbations and load disturbances using the high-order sliding mode controller (HOSM) and HOSM with super-twisting differentiator (HOSM + STD). The proposed control approach needs only measurement of converter output voltage. Theoretical analysis and design procedures, as well as the super-twisting differentiator of the proposed controller are presented in detail with the prescribed convergence law of high-order sliding modes. Comparisons of both simulation and experimental results among conventional proportional-integral (PI) control, traditional sliding mode control (SMC), HOSM and HOSM + STD under various test conditions such as steady state, input voltage perturbations and output load disturbances, are presented and discussed. The results demonstrate and validate the effectiveness and robustness of the proposed control method.

Description: Energy efficiency is an important criterion in the design of next generation networks for both economic and environmental concerns. This paper presents an energy-efficient router that is able to dynamically adapt its routing capability in response to real-time traffic load, achieving energy proportional routing. The NetFPGA reference router, which operates at one of two frequencies (125 MHz or 62.5 MHz), requires a board reset to switch frequencies. We have modified the reference router to allow dynamic switching among five operating frequencies. Experiments with real traces indicate that, compared to the reference router, a 10% power reduction can be achieved through dynamic frequency scaling. When the router is further modified to support green traffic engineering and Ethernet port shut-down, power consumption can be reduced by 46% while maintaining the required quality of service. This allows the router to meet the instantaneous performance requirements while minimizing power dissipation. Similar results can be expected when these general power-saving principles are applied in future commercial routers.

Description: In this paper, first the operating principles of a non-isolated universal bidirectional DC-DC converter are studied and analyzed. The presented power converter is capable of operating in all power transferring directions in buck/boost modes. Zero voltage switching can be achieved for all the power switches through proper modulation strategy design, therefore, the presented converter can achieve high efficiency. To further improve the efficiency, the relationship between the phase-shift angle and the overall system efficiency is analyzed in detail, an adaptive phase-shift (APS) control method which determines the phase-shift value between gating signals according to the load level is then proposed. As the modulation strategy is a software-based solution, there is no requirement for additional circuits, therefore, it can be implemented easily and instability and noise susceptibility problems can be reduced. To validate the correctness and the effectiveness of the proposed method, a 300 W prototyping circuit is implemented and tested. A low cost dsPIC33FJ16GS502 digital signal controller is adopted in this paper to realize the power flow control, DC-bus voltage regulation and APS control. According to the experimental results, a 12.2% efficiency improvement at light load and 4.0% efficiency improvement at half load can be achieved.

Description: This paper presents numerical and experimental analyses aimed at evaluating the technical and economic feasibility of photovoltaic/thermal (PVT) collectors. An experimental setup was purposely designed and constructed in order to compare the electrical performance of a PVT solar field with the one achieved by an identical solar field consisting of conventional photovoltaic (PV) panels. The experimental analysis also aims at evaluating the potential advantages of PVT vs. PV in terms of enhancement of electrical efficiency and thermal energy production. The installed experimental set-up includes four flat polycrystalline silicon PV panels and four flat unglazed polycrystalline silicon PVT collectors. The total electrical power and area of the solar field are 2 kWe and 13 m2, respectively. The experimental set-up is currently installed at the company AV Project Ltd., located in Avellino (Italy). This study also analyzes the system from a numerical point of view, including a thermo-economic dynamic simulation model for the design and the assessment of energy performance and economic profitability of the solar systems consisting of glazed PVT and PV collectors. The experimental setup was modelled and partly simulated in TRNSYS environment. The simulation model was useful to analyze efficiencies and temperatures reached by such solar technologies, by taking into account the reference technology of PVTs (consisting of glazed collectors) as well as to compare the numerical data obtained by dynamic simulations with the gathered experimental results for the PV technology. The numerical analysis shows that the PVT global efficiency is about 26%. Conversely, from the experimental point of view, the average thermal efficiency of PVT collectors is around 13% and the electrical efficiencies of both technologies are almost coincident and equal to 15%.

Description: The exhaust gas in an internal combustion engine provides favorable conditions for a waste-heat recovery (WHR) system. The highest potential is achieved by the Rankine cycle as a heat recovery technology. There are only few experimental studies that investigate full-scale systems using water-based working fluids and their effects on the performance and operation of a Rankine cycle heat recovery system. This paper discusses experimental results and practical challenges with a WHR system when utilizing heat from the exhaust gas recirculation system of a truck engine. The results showed that the boiler’s pinch point necessitated trade-offs between maintaining adequate boiling pressure while achieving acceptable cooling of the EGR and superheating of the water. The expander used in the system had a geometric compression ratio of 21 together with a steam outlet timing that caused high re-compression. Inlet pressures of up to 30 bar were therefore required for a stable expander power output. Such high pressures increased the pump power, and reduced the EGR cooling in the boiler because of pinch-point effects. Simulations indicated that reducing the expander’s compression ratio from 21 to 13 would allow 30% lower steam supply pressures without adversely affecting the expander’s power output.

Description: This paper presents the results of the implementation of a self-consumption maximization strategy tested in a real-scale Vanadium Redox Flow Battery (VRFB) (5 kW, 60 kWh) and Building Integrated Photovoltaics (BIPV) demonstrator (6.74 kWp). The tested energy management strategy aims to maximize the consumption of energy generated by a BIPV system through the usage of a battery. Whenever possible, the residual load is either stored in the battery to be used later or is supplied by the energy stored previously. The strategy was tested over seven days in a real-scale VRF battery to assess the validity of this battery to implement BIPV-focused energy management strategies. The results show that it was possible to obtain a self-consumption ratio of 100.0%, and that 75.6% of the energy consumed was provided by PV power. The VRFB was able to perform the strategy, although it was noticed that the available power (either to charge or discharge) varied with the state of charge.

Description: This paper fully describes the working principle of slide valves in single-screw expanders (SSEs). A geometric analysis of suction and volume ratio slide valves is presented to determine the relations between volume ratio, suction closure volume, discharge opening volume and slide valves displacement. An organic Rankine cycle (ORC) thermodynamic model with SSE integrated with slide valves is developed to analyze the power output of SSE and the net power output of ORC system and variation law of slide valves displacement. Analysis of a typical ORC system under changing operating conditions shows that the power output of the expander and the net output power of the ORC system with slide valves are much better than those without slide valves. When the condensing temperature is 40 °C and the waste availability is 80 kW, the increase in output power and net output power are approximately 3.4 kW and 5 kW, respectively. The presented geometric analysis of slide valves and the thermodynamic model integrated with slide valves can be used to provide a theoretical and technical basis for designing the slide valves of SSEs and the control strategies of slide valves under varied operating conditions.

Description: Wind power has achieved great development in Northern China, but abundant wind power is dissipated, rather than utilized, due to inflexible electricity production of combined heat and power (CHP) units. In this paper, an integrated CHP system consisting of CHP units, wind power plants, and condensing power plants is investigated to decouple the power and heat production on both the power supply side and heat supply side, by incorporating electrical energy storage (EES) and thermal energy storage (TES). Then the integrated CHP system dispatch (ICHPSD) model is formulated to reach the target of reducing wind power curtailment and primary energy consumption. Finally, the feasibility and effectiveness of the proposed ICHPSD model are verified by the six-bus system, and the simulation results show that EES has a better effect on wind power integration than TES. The annual net benefits by incorporating EES and TES increase with increasing wind penetration, but they gradually approach saturation. Introducing both EES and TES can largely increase the amount of wind power integration and improve the operation efficiency of the system.

Description: This paper reviews the most recent and relevant research into the variability characteristics of wind and solar power resources in Europe. The background for this study is that wind and solar resources will probably constitute major components of the future European power system. Such resources are variable, and EU plans to balance the variability with more grids and demand response. Thus, planning for the future power system requires an in-depth understanding of the variability. Resource variability is a multi-faceted concept best described using a range of distinct characteristics, and this review is structured on the basis of seven of these: Distribution Long-Term (hours to years), Distribution Short-Term (less than one hour), Step Changes, Autocorrelation, Spatial Correlation, Cross Correlation and Predictable Patterns. The review presents simulations and empirical results related to resource variability for each of these characteristics. Results to date reveal that the variability characteristics of the future power system is limited understood. This study recommends the development of a scheme for greater systematic assessment of variability. Such a scheme will contribute to the understanding of the impacts of variability and will make it possible to compare alternative power production portfolios and impacts of grid expansions, demand response and storage technologies.

Description: In this paper, the optimal operation of a stationary sub-critical 11 kW el organic Rankine cycle (ORC) unit for waste heat recovery (WHR) applications is investigated, both in terms of energy production and safety conditions. Simulation results of a validated dynamic model of the ORC power unit are used to derive a correlation for the evaporating temperature, which maximizes the power generation for a range of operating conditions. This idea is further extended using a perturbation-based extremum seeking (ES) algorithm to identify online the optimal evaporating temperature. Regarding safety conditions, we propose the use of the extended prediction self-adaptive control (EPSAC) approach to constrained model predictive control (MPC). Since it uses input/output models for prediction, it avoids the need for state estimators, making it a suitable tool for industrial applications. The performance of the proposed control strategy is compared to PID-like schemes. Results show that EPSAC-MPC is a more effective control strategy, as it allows a safer and more efficient operation of the ORC unit, as it can handle constraints in a natural way, operating close to the boundary conditions where power generation is maximized.

Description: As the result of climate change and deteriorating global environmental quality, nations are under pressure to reduce their emissions of greenhouse gases per unit of GDP. China has announced that it is aiming not only to reduce carbon emission per unit of GDP, but also to consume increased amounts of non-fossil energy. The carbon emission allowance is a new type of financial asset in each Chinese province and city that also affects individual firms. This paper attempts to examine the allocative efficiency of carbon emission reduction and non-fossil energy consumption by employing a zero sum gains data envelopment analysis (ZSG-DEA) model, given the premise of fixed CO2 emissions as well as non-fossil energy consumption. In making its forecasts, the paper optimizes allocative efficiency in 2020 using 2010 economic and carbon emission data from 30 provinces and cities across China as its baseline. An efficient allocation scheme is achieved for all the provinces and cities using the ZSG-DEA model through five iterative calculations.

Description: Lithium-ion batteries are shipped worldwide with many limitations implemented to ensure safety and to prevent loss of cargo. Many of the transportation guidelines focus on new batteries; however, the shipment requirements for used or degraded batteries are less clear. Current international regulations regarding the air transport of lithium-ion batteries are critically reviewed. The pre-shipping tests are outlined and evaluated to assess their ability to fully mitigate risks during battery transport. In particular, the guidelines for shipping second-use batteries are considered. Because the electrochemical state of previously used batteries is inherently different from that of new batteries, additional considerations must be made to evaluate these types of cells. Additional tests are suggested that evaluate the risks of second-use batteries, which may or may not contain incipient faults.

Description: 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.

Description: 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) substrates. Similar results are achieved if commercial ceramic tiles are used as a substrate instead of glass. This result is especially useful for the so-called building integrated photovoltaic. Cu(In,Ga)Se2-based solar cells grown directly on ceramic tiles are ideal for the fabrication of ventilated façades in low impact buildings.

Description: The concept of the Misselhorn cycle is introduced as a power cycle that aims for efficient waste heat recovery of temperature sources below 100 °C. The basic idea shows advantages over a standard Organic Rankine Cycle (ORC) in overall efficiency and utilization of the heat source. The main characteristic of this cycle is the use of at least three parallel batch evaporators instead of continuous heat exchangers. The operational phases of the evaporators are shifted so that there is always one vaporizer in discharge mode. A transient MATLAB® model (The MathWorks: Natick, MA, USA) is used to simulate the achievable performance of the Misselhorn cycle. The calculations of the thermodynamic states of the system are based on the heat flux, the equations for energy conservation and the equations of state found in the NIST Standard Reference Database 23 (Reference Fluid Thermodynamic and Transport Properties - REFPROP, National Institute of Standards and Technology: Gaithersburg, MD, USA). In the isochoric batch evaporation, the pressure and the corresponding boiling temperature rise over time. With a gradually increasing boiling temperature, no pinch point limitation occurs. Furthermore, the heat source medium is passed through the evaporators in serial order to obtain a quasi-counter flow setup. It could be shown that these features offer the possibility to gain both high thermal efficiencies and an enhanced utilization of the heat source at the same time. A basic model with a fixed estimated heat transfer coefficient promises a possible system exergy efficiency of 44.4%, which is an increase of over 60% compared to a basic ORC with a system exergy efficiency of only 26.8%.

Description: Because of their low cost, photovoltaic (PV) cells made from upgraded metallurgical grade silicon (UMG-Si) are a promising alternative to conventional solar grade silicon-based PV cells. This study investigates the outdoor performance of a 1.26 kW grid-connected UMG-Si PV system over five years, reporting the energy yields and performance ratio and estimating the long-term performance degradation rate. To make this investigation more meaningful, the performance of a mono-Si PV system installed at the same place and studied during the same period of time is presented for reference. Furthermore, this study systematizes and rationalizes the necessity of a data selection and filtering process to improve the accuracy of degradation rate estimation. The impact of plane-of-array irradiation threshold for data filtering on performance ratio and degradation rate is also studied. The UMG-Si PV system’s monthly performance ratio after data filtering ranged from 84% to 93% over the observation period. The annual degradation rate was 0.44% derived from time series of monthly performance ratio using the classical decomposition method. A comparison of performance ratio and degradation rate to conventional crystalline silicon-based PV systems suggests that performance of the UMG-Si PV system is comparable to that of conventional systems.

Description: When modeling low capacity energy systems, such as a small size (5–150 kWel) organic Rankine cycle unit, the governing dynamics are mainly concentrated in the heat exchangers. As a consequence, the accuracy and simulation speed of the higher level system model mainly depend on the heat exchanger model formulation. In particular, the modeling of thermo-flow systems characterized by evaporation or condensation requires heat exchanger models capable of handling phase transitions. To this aim, the finite volume (FV) and the moving boundary (MB) approaches are the most widely used. The two models are developed and included in the open-source ThermoCycle Modelica library. In this contribution, a comparison between the two approaches is presented. An integrity and accuracy test is designed to evaluate the performance of the FV and MB models during transient conditions. In order to analyze how the two modeling approaches perform when integrated at a system level, two organic Rankine cycle (ORC) system models are built using the FV and the MB evaporator model, and their responses are compared against experimental data collected on an 11 kWel ORC power unit. Additionally, the effect of the void fraction value in the MB evaporator model and of the number of control volumes (CVs) in the FV one is investigated. The results allow drawing general guidelines for the development of heat exchanger dynamic models involving two-phase flows.

Description: 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 shrinkage can be reduced using a large graphite plate embedded within the frame.

Description: 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 high wind speeds, the equipped PPC system can effectively reduce the rotational speed to generate stable power.