ALBERT

Description: The present study aims to develop a thermoeconomic-based approach for optimization of steam levels in a steam production and distribution system by use of the specific exergy costing (SPECO) method for determining optimum steam levels to minimize the cost caused by exergy destruction. In the field of total site optimization, incremental cost of the utility system caused by exergy destruction has been selected as an objective function and the result is compared with the case that energy minimization has been selected as the prime objective. The steam levels are optimized considering steam demand at each level, output power generated by turbines, boiler duty, fuel and cold utility requirements as well as capital cost of equipments. The analysis showed that thermoeconomic (exergoeconomic) approach in optimization not only can change the optimum structure of steam levels but also may reduce the total cost of utility system up to 8%.

Description: In order to study the flashover mechanism of polluted insulators under AC voltage, a new arc propagation criterion which is based on an arc root voltage gradient is proposed. This criterion can explain the variation of the arc root voltage gradient in the arc propagation process. Based on this criterion, a new distributed parameter electrical circuit flashover model of polluted insulators is presented. The arc channel is considered as an equivalent distributed parameter circuit model instead of using the arc voltage-gradient equation. The parameters of the arc model are obtained from the electromagnetic field distribution of the arc and the gas discharge theories. The arc root is considered as parallel paths including the polluted layer. The variation of the voltage on the arc root is related to the capability of arc propagation. This model takes the microscopic mechanism of arc root ionization into consideration, which can improve the accuracy of the flashover model. The results obtained from the presented model are in good agreement with other mathematical and experimental results.

Description: Currently, hydropower accounts for close to 16% of the world’s total power supply and is the world’s most dominant (86%) source of renewable electrical energy. The key resource for hydropower generation is runoff, which is dependent on precipitation. The future global climate is uncertain and thus poses some risk for the hydropower generation sector. The crucial question and challenge then is what will be the impact of climate change on global hydropower generation and what are the resulting regional variations in hydropower generation potential? This paper is a study that aims to evaluate the changes in global hydropower generation resulting from predicted changes in climate. The study uses an ensemble of simulations of regional patterns of changes in runoff, computed from global circulation models (GCM) simulations with 12 different models. Based on these runoff changes, hydropower generation is estimated by relating the runoff changes to hydropower generation potential through geographical information system (GIS), based on 2005 hydropower generation. Hydropower data obtained from EIA (energy generation), national sites, FAO (water resources) and UNEP were used in the analysis. The countries/states were used as computational units to reduce the complexities of the analysis. The results indicate that there are large variations of changes (increases/decreases) in hydropower generation across regions and even within regions. Globally, hydropower generation is predicted to change very little by the year 2050 for the hydropower system in operation today. This change amounts to an increase of less than 1% of the current (2005) generation level although it is necessary to carry out basin level detailed assessment for local impacts which may differ from the country based values. There are many regions where runoff and hydropower generation will increase due to increasing precipitation, but also many regions where there will be a decrease. Based on this evaluation, it has been concluded that even if individual countries and regions may experience significant impacts, climate change will not lead to significant changes in the global hydropower generation, at least for the existing hydropower system.

Description: As part of its climate strategy, the EU aims at increasing the share of electricity from renewable energy sources (RES-E) in overall electricity generation. Attaining this target poses a considerable challenge as the electricity sector is “locked” into a carbon-intensive system, which hampers the adoption of RES-E technologies. Electricity generation, transmission and distribution grids as well as storage and demand response are subject to important path dependences, which put existing, non-renewable energy sources at an advantage. This paper examines how an EU framework for RES-E support policies should be designed to facilitate a carbon lock-out. For this purpose, we specify the major technological, economic and institutional barriers to RES-E. For each of the barriers, a policy review is carried out which assesses the performance of existing policy instruments and identifies needs for reform. The review reveals several shortcomings: while policies targeting generation are widely in place, measures to address barriers associated with electricity grids, storage and demand are still in their infancy and have to be extended. Moreover, the implementation of policies has been fragmented across EU Member States. In this respect, national policies should be embedded into an integrated EU-wide planning of the RES-E system with overarching energy scenarios and partially harmonized policy rules.

Description: Due to the movement and complexity of the carbon market, traditional monoscale forecasting approaches often fail to capture its nonstationary and nonlinear properties and accurately describe its moving tendencies. In this study, a multiscale ensemble forecasting model integrating empirical mode decomposition (EMD), genetic algorithm (GA) and artificial neural network (ANN) is proposed to forecast carbon price. Firstly, the proposed model uses EMD to decompose carbon price data into several intrinsic mode functions (IMFs) and one residue. Then, the IMFs and residue are composed into a high frequency component, a low frequency component and a trend component which have similar frequency characteristics, simple components and strong regularity using the fine-to-coarse reconstruction algorithm. Finally, those three components are predicted using an ANN trained by GA, i.e., a GAANN model, and the final forecasting results can be obtained by the sum of these three forecasting results. For verification and testing, two main carbon future prices with different maturity in the European Climate Exchange (ECX) are used to test the effectiveness of the proposed multiscale ensemble forecasting model. Empirical results obtained demonstrate that the proposed multiscale ensemble forecasting model can outperform the single random walk (RW), ARIMA, ANN and GAANN models without EMD preprocessing and the ensemble ARIMA model with EMD preprocessing.

Description: For achieving the European renewable electricity targets, a significant contribution is foreseen to come from offshore wind energy. Considering the large scale of the future planned offshore wind farms and the increasing distances to shore, grid integration through a transnational DC network is desirable for several reasons. This article investigates a nine-node DC grid connecting three northern European countries—namely UK, The Netherlands and Germany. The power-flow control inside the multi-terminal DC grid based on voltage-source converters is achieved through a novel method, called distributed voltage control (DVC). In this method, an optimal power flow (OPF) is solved in order to minimize the transmission losses in the network. The main contribution of the paper is the utilization of a genetic algorithm (GA) to solve the OPF problem while maintaining an N-1 security constraint. After describing main DC network component models, several case studies illustrate the dynamic behavior of the proposed control method.

Description: Municipal solid waste (MSW) is an important energy resource for combined heat and power (CHP) production. This study summarized an overview of CHP by MSW to energy (WtE) plants in South Korea and discussed the issues related to energy efficiency improvement. Given the dominant housing culture of apartment living in South Korea, the primary energy output of WtE plants has been for district heating. In 2010, approximately half of the 51 large WtE plants were CHP, while the rest produced heat. Power generation in the WtE CHP plants was estimated to be only 3.65% of the thermal input, while heat production was 60.79%. The R1 efficiency when compared to that in Europe was similar for the CHP plants and higher for heat-only plants. Improving power generation efficiency is required for new power plants producing steam at pressures higher than the current level of 20–30 bar. Over ten of the existing plants needed to increase their energy efficiency by installing new equipment such as steam turbines for excess steam. Finally, transboundary centralization of WtE plants between neighboring local authorities is essential for heat utilization since many existing small-scale plants (〈50 t/day capacity) do not recover heat.

Description: Among the non-linear loads used in household, Compact Fluorescent Lamps (CFLs) and LED lamps are becoming more widespread, while incandescent lamps are intended to be replaced by these types of lighting devices. LEDs and CFLs are significantly more efficient and economical than incandescent lamps, and are expected to be used in 100% of residential lighting in the future. As nonlinear loads, LEDs and CFLs produce highly distorted currents. A large number of customers using LEDs or CFLs for domestic, commercial and industrial lighting could determine important Power Quality problems. The paper reports experimental measurement results regarding Power Quality in indoor lighting systems. The harmonic absorptions of several types of luminaries are analyzed, highlighting the impact behavior of different lamps function of used luminaries’ technologies. The recorded harmonic absorption allows characterizing the harmonic spectrum variability of the investigated lamps.

Description:  In this research we have fabricated and tested Au/Dy2O3 composites for applications as Solid Oxide Fuel Cell (SOFC) electrocatalysts. The material was obtained by a process involving electrodeposition of a Au-Dy alloy from a urea/choline chloride ionic liquid electrolyte, followed by selective oxidation of Dy to Dy2O3 in air at high temperature. The electrochemical kinetics of the electrodeposition bath were studied by cyclic voltammetry, whence optimal electrodeposition conditions were identified. The heat-treated material was characterised from the morphological (scanning electron microscopy), compositional (X-ray fluorescence spectroscopy) and structural (X-ray diffractometry) points of view. The electrocatalytic activity towards H2 oxidation and O2 reduction was tested at 650 °C by electrochemical impedance spectrometry. Our composite electrodes exhibit an anodic activity that compares favourably with the only literature result available at the time of this writing for Dy2O3 and an even better cathodic performance.

Description: In this study, sewage sludge and mycelial waste from antibiotic production were pyrolyzed in a batch scale fixed-bed reactor as examples of two kinds of typical industrial biomass wastes with high nitrogen content. A series of experiments were conducted on the rapid pyrolysis and the slow pyrolysis of these wastes in the temperature range from 500–800 °C to investigate the Fuel-N transformation behavior among pyrolysis products. The results showed that Fuel-N conversion to Char-N intimately depended on the pyrolysis temperature and the yield of Char-N reduced with the increase of the pyrolysis temperature. Under the same pyrolysis conditions, Tar-N production mainly depended on complex properties of the different biomasses, including volatile matter, nitrogen content and biomass functional groups. HCN was the predominant NOx precursor in the rapid pyrolysis of biomass, whereas in the slow pyrolysis of mycelial waste, more NH3 was produced than HCN due to the additional NH3 formation through the hydrogenation reaction of Char-N, HCN and H radicals. At the same time, some part of the char was analyzed by Fourier Transform infrared spectroscopy (FTIR) to get more information on the nitrogen functionality changes and the tar was also characterized by Gas Chromatography and Mass Spectrometry (GCMS) to identify typical nitrogenous tar compounds. Finally, the whole nitrogen distribution in products was discussed.

Description: The objective of this paper was to provide a preliminary analysis of the utilization of energy derived from waste wood in Taiwan, a highly industrialized country with a high dependence (over 99%) on imported energy. The discussion focuses on the status of waste wood generation and its management over the past decade. Findings show that the quantities of biomass waste collected for reuse purposes in the industrial sectors of Taiwan has exhibited an increasing trend, from about 4000 tons in 2001 to over 52,000 tons in 2010. Although waste wood can be reused as a fuel and raw material for a variety of applications based on regulatory promotion, the most commonly used end use is to directly utilize it as an auxiliary fuel in industrial utilities (e.g., boilers, heaters and furnaces) for the purpose of co-firing with coal/fuel oil. The most progressive measure for promoting biomass-to-power is to introduce the feed-in tariff (FIT) mechanism according to the Renewable Energy Development Act passed in June 2009. The financial support for biomass power generation has been increasing over the years from 0.070 US$/kWh in 2010 to 0.094 US$/kWh in 2012. On the other hand, the environmental regulations in Taiwan regarding the hazard identification of wood-combusted ash (especially in filter fly-ash) and its options for disposal and utilization are further discussed in the paper, suggesting that waste wood impregnated with chromated copper arsenate (CCA) and other copper-based preservatives should be excluded from the wood-to-energy system. Finally, some recommendations for promoting wood-to-energy in the near future of Taiwan are addressed.

Description: The construction industry is a high-pollution and high-energy-consumption industry. Energy-saving designs for residential buildings not only reduce the energy consumed during construction, but also reduce long-term energy consumption in completed residential buildings. Because building design affects investment costs, designs are often influenced by investors’ decisions. A set of appropriate decision-support tools for residential buildings are required to examine how building design influences corporations externally and internally. From the perspective of energy savings and environmental protection, we combined three methods to develop a unique model for evaluating the energy-saving design of residential buildings. Among these methods, the Delphi group decision-making method provides a co-design feature, the analytical hierarchy process (AHP) includes multi-criteria decision-making techniques, and fuzzy logic theory can simplify complex internal and external factors into easy-to-understand numbers or ratios that facilitate decisions. The results of this study show that incorporating solar building materials, double-skin facades, and green roof designs can effectively provide high energy-saving building designs.

Description: The increasing presence of wind power in power systems will likely drive the integration of large wind farms with electrical networks that are series-compensated to sustain large power flows. This may potentially lead to subsynchronous resonance (SSR) issues. In this paper, a supplementary controller on the grid-side converter (GSC) control loop is designed to mitigate SSR for wind power systems based on doubly fed induction generators (DFIGs) with back-to-back converters. Different supplementary controller feedback signals and modulated-voltage injecting points are proposed and compared based on modal analysis and verified through root locus analysis to identify the optimal feedback signal and the most effective control location for SSR damping. The validity and effectiveness of the proposed supplemental control are demonstrated on the IEEE first benchmark model for computer simulations of SSR by means of time domain simulation analysis using Matlab/Simulink.

Description: This paper proposes and develops a residential energy and resource consumption estimation model in the context of multi-family residential housing in Korea using a multi-layer perceptron (MLP) neural network. Eight indicators are introduced which affect the energy and water resource usage characteristics of Korean residential complexes. The proposed model precisely estimated the electricity, gas energy and water consumption for each examined residential complex. In terms of validation, the results showed the highest level of agreement with actually collected datasets. The model shows promising prospects in providing necessary estimations, not only for optimally scaling and sizing energy- and water-related infrastructures, but also to promote reliable energy and resource savings through greenhouse gas (GHG) reduction planning in multi-family housing complexes. The model could also be of use in framing guidelines for the better planning of national or regional energy and resource policies and for forming a foundation of decision-making with definite references regarding the facility management of each apartment complex to enhance the energy and resource use efficiency at these locations.

Description: Recently the technology development and increasing amounts of investment in renewables has led to a growing interest towards design and optimization of green energy systems. In this context, advanced Computational Intelligence (CI) techniques can be applied by engineers to several technical problems in order to find out the best structure and to improve efficiency in energy recovery. This research promises to give new impulse to using innovative unconventional renewable sources and to develop the so-called Energy Harvesting Devices (EHDs). In this paper, the optimization of a Tubular Permanent Magnet-Linear Generator for energy harvesting from vehicles to grid is presented. The optimization process is developed by means of hybrid evolutionary algorithms to reach the best overall system efficiency and the impact on the environment and transportation systems. Finally, an experimental validation of the designed EHD prototype is presented. 

Description: Energy management systems strive to use energy resources efficiently, save energy, and reduce carbon output. This study proposes transient feature analyses of the transient response time and transient energy on the power signatures of non-intrusive demand monitoring and load identification to detect the power demand and load operation. This study uses the wavelet transform (WT) of the time-frequency domain to analyze and detect the transient physical behavior of loads during the load identification. The experimental results show the transient response time and transient energy are better than the steady-state features to improve the recognition accuracy and reduces computation requirements in non-intrusive load monitoring (NILM) systems. The discrete wavelet transform (DWT) is more suitable than short-time Fourier transform (STFT) for transient load analyses.

Description: A novel asymmetrical interleaved dc/dc switching converters family intended for photovoltaic and fuel cell applications is presented in this paper. The main requirements on such applications are small ripples in the generator and load, as well as high voltage conversion ratio. Therefore, interleaved structures and voltage multiplier cells have been asymmetrically combined to generate new converters, which inherently operate indiscontinuous conduction mode. The novel family is derived from boost, buck-boost and flyback-based structures. This converter family is analyzed to obtain the design equations and synthesize a design process based on the typical requirements of photovoltaic and fuel cell applications. Finally, the experimental results validate the characteristics and usefulness of the asymmetrical interleaved converter family. 

Description: PHEVs and BEVs make use of battery cells optimized for high energy rather than for high power. This means that the power abilities of these batteries are limited. In order to enhance their performance, a hybrid Rechargeable Energy Storage System (RESS) architecture can be used combining batteries with electrical-double layer capacitors (EDLCs). Such a hybridized architecture can be accomplished using passive or active systems. In this paper, the characteristics of these topologies have been analyzed and compared based on a newly developed hybridization simulation tool for association of lithium-ion batteries and EDLCs. The analysis shows that the beneficial impact of the EDLCs brings about enhanced battery performances in terms of energy efficiency and voltage drops, rather than extension of vehicle range. These issues have been particularly studied for the passive and active hybrid topologies. The classical passive and active topologies being expensive and less beneficial in term of cost, volume and weight, a new hybrid configuration based on the parallel combination of lithium-ion and EDLCs on cell level has been proposed in this article. This topology allows reducing cost, volume, and weight and system complexity in a significant way. Furthermore, a number of experimental setups have illustrated the power of the novel topology in terms of battery capacity increase and power capabilities during charging and discharging. Finally, a unique cycle life test campaign demonstrated that the lifetime of highly optimized lithium-ion batteries can be extended up to 30%–40%.

Description: A liquid electrolyte lithium/sulfur (Li/S) cell is a liquid electrochemical system. In discharge, sulfur is first reduced to highly soluble Li2S8, which dissolves into the organic electrolyte and serves as the liquid cathode. In solution, lithium polysulfide (PS) undergoes a series of complicated disproportionations, whose chemical equilibriums vary with the PS concentration and affect the cell’s performance. Since the PS concentration relates to a certain electrolyte/sulfur (E/S) ratio, there is an optimized E/S ratio for the cyclability of each Li/S cell system. In this work, we study the optimized E/S ratio by measuring the cycling performance of Li/S cells, and propose an empirical method for determination of the optimized E/S ratio. By employing an electrolyte of 0.25 m LiSO3CF3-0.25 m LiNO3 dissolved in a 1:1 (wt:wt) mixture of dimethyl ether (DME) and 1,3-dioxolane (DOL) in an optimized E/S ratio, we show that the Li/S cell with a cathode containing 72% sulfur and 2 mg cm−2 sulfur loading is able to retain a specific capacity of 780 mAh g−1 after 100 cycles at 0.5 mA cm−2 between 1.7 V and 2.8 V.

Description: This work thoroughly evaluates the electric power consumption of a full scale, 3 × 923 m3 complete stirred tank reactor (CSTR) research biogas plant with a production capacity of 186 kW of electric power. The plant was fed with a mixture of livestock manure and renewable energy crops and was operated under mesophilic conditions. This paper will provide an insight into precise electric energy consumption measurements of a full scale biogas plant over a period of two years. The results showed that a percentage of 8.5% (in 2010) and 8.7% (in 2011) of the produced electric energy was consumed by the combined heat and power unit (CHP), which was required to operate the biogas plant. The consumer unit agitators with 4.3% (in 2010) and 4.0% (in 2011) and CHP unit with 2.5% (in 2010 and 2011) accounted for the highest electrical power demand, in relation to the electric energy produced by the CHP unit. Calculations show that 51% (in 2010) and 46% (in 2011) of the total electric energy demand was due to the agitators. The results finally showed the need for permanent measurements to identify and quantify the electric energy saving potentials of full scale biogas plants.

Description: The reliable predictions of liquid holdup and pressure drop are essential for pipeline design in oil and gas industry. In this study, the drift-flux approach is utilized to calculate liquid holdups. This approach has been widely used in formulation of the basic equations for multiphase flow in pipelines. Most of the drift-flux models have been developed on an empirical basis from the experimental data. Even though, previous studies showed that these models can be applied to different flow pattern and pipe inclination, when the distribution parameter is flow pattern dependent. They are limited to a set of fluid properties, pipe geometries and operational conditions. The objective of this study is to develop a new drift-flux closure relationship for prediction of liquid holdups in pipes that can be easily applied to a wide range of flow conditions. The developed correlation is compared with nine available correlations from literatures, and validated using the TUFFP (Fluid Flow Projects of University of Tulsa) experimental datasets and OLGA (OiL and GAs simulator supplied by SPTgroup) steady-state synthetic data generated by OLGA Multiphase Toolkit. The developed correlation performs better in predicting liquid holdups than the available correlations for a wide range of flow conditions.

Description: In this paper, we develop a simple algorithm to determine the required number of generating units of wind-turbine generator and photovoltaic array, and the associated storage capacity for stand-alone hybrid microgrid. The algorithm is based on the observation that the state of charge of battery should be periodically invariant. The optimal sizing of hybrid microgrid is given in the sense that the life cycle cost of system is minimized while the given load power demand can be satisfied without load rejection. We also report a case study to show the efficacy of the developed algorithm.

Description: A numerical study of atmospheric turbulence effects on wind-turbine wakes is presented. Large-eddy simulations of neutrally-stratified atmospheric boundary layer flows through stand-alone wind turbines were performed over homogeneous flat surfaces with four different aerodynamic roughness lengths. Emphasis is placed on the structure and characteristics of turbine wakes in the cases where the incident flows to the turbine have the same mean velocity at the hub height but different mean wind shears and turbulence intensity levels. The simulation results show that the different turbulence intensity levels of the incoming flow lead to considerable influence on the spatial distribution of the mean velocity deficit, turbulence intensity, and turbulent shear stress in the wake region. In particular, when the turbulence intensity level of the incoming flow is higher, the turbine-induced wake (velocity deficit) recovers faster, and the locations of the maximum turbulence intensity and turbulent stress are closer to the turbine. A detailed analysis of the turbulence kinetic energy budget in the wakes reveals also an important effect of the incoming flow turbulence level on the magnitude and spatial distribution of the shear production and transport terms.

Description: This study attempted to address the existing urban design needs and computer-aided thermal engineering and explore the optimal green space layout to obtain an acceptable thermal environment at the neighborhood scale through a series of building energy and computational fluid dynamics (CFD) simulations. The building-energy analysis software eQUEST and weather database TMY2 were adopted to analyze the electric energy consumed by air conditioners and the analysis results were incorporated to derive the heat dissipated from air conditioners. Then, the PHOENICS CFD software was used to analyze how the green space layout influences outdoor thermal environment based on the heat dissipated from air conditioners and the solar heat reemitted from the built surfaces. The results show that a green space located in the center of this investigated area and at the far side of the downstream of a summer monsoon is the recommended layout. The layouts, with green space in the center, can decrease the highest temperature by 0.36 °C.

Description: We set out to determine the particle-size distribution, the fiber, the bark and the leaves content, the heating value, the CNH and the ash content of a wide sample of wood chips, collected from 10 forestry and 10 agroforestry production sources. This sampling focused on two main production types: forestry (Full Tree System—FTS—and logging residues—LR) and agroforestry (Short Rotation Coppice—SRC). For the forestry production wood chips from coniferous and broadleaf species were considered. For the agroforestry production wood chips from poplar plantations were examined (different clones with two different harvesting intervals). Overall, we collected 400 samples. Particle size distribution was determined with an automatic screening device on 200 samples. The higher heating value was determined on 200 subsamples using an adiabatic bomb calorimeter. The CNH and the ash content was ascertained on another 200 subsamples. FTS and SRC (with three year old sprouts) offered the best quality, with high fiber content (71%–80%), favorable particle-size distribution and good energetic parameters. On the contrary, both logging residues and SRC (with two year old sprouts) presented a high bark content (18%–27%) and occasionally a mediocre particle-size distribution, being often too rich in fines (6%–12%), but the energetic parameters are in the normal range.

Description: Global interest in stable energy resources coupled with growing demand for bio-oils in various conventional and arising industries has renewed the importance of vegetable oil production. To address this global interest, oilseed production has been increased in recent decades by different approaches, such as extending the cultivation area of oil crops, or breeding and growing genetically modified plants. In this study, pea (Pisum sativum L.) accessions were screened for lipid content using a rapid extraction method. This method quantifies lipid concentration in pea seeds and was developed by assessing and comparing the results of existing extraction methods used for canola and soybean, the top two Canadian oilseeds. Seeds of 151 field pea accessions were grown to maturity in 2009 and 2010 at McGill University (Quebec, Canada). Overall, lipid concentration in pea seeds ranged from 0.9 to 5.0%. Among several seed characteristics, only seed shape (wrinkled verses round) had a significant effect on the total lipid production in the seeds. Peas are a valuable source of protein and starch, but the lipid concentration in their seeds has been undervalued. This research supports the idea of developing a novel dual-purpose oilseed pea that emulates the protein and oil production in soybean seeds while being conveniently adapted to a colder climate.

Description: The hydrogen desorption/absorption behaviors of LiAlH4/LiBH4 with a focus on the effects of catalysts, namely TiCl3, TiO2, VCl3, and ZrCl4, were investigated using a thermal-volumetric apparatus. The hydrogen desorption was performed from room temperature to 300 °C with a heating rate of 2 °C min−1. The LiAlH4–LiBH4 mixture with a molar ratio of 2:1 decomposed between 100 and 220 °C, and the hydrogen desorption capacity reached up to 6.6 wt %. Doping 1 mol % of a catalyst to the mixture resulted in the two-step decomposition and a decrease in the hydrogen desorption temperature. All the doped samples provided lower amountz of desorbed hydrogen than that obtained from the undoped one. No hydrogen absorption was observed under 8.5 MPa of hydrogen pressure and 300 °C for 6 h. Despite the fact each of the catalysts may affect the hydrogen storage behaviors of the mixture differently, none resulted in a change in the sample reversibility.

Description: The paper presents a comparison of various CHP system configurations, such as Vapour Turbine, Gas Turbine, Internal Combustion Engine, External Combustion Engine (Stirling, Ericsson), when different thermodynamic criteria are considered, namely the first law efficiency and exergy efficiency. Thermodynamic optimization of these systems is performed intending to maximize the exergy, when various practical related constraints (imposed mechanical useful energy, imposed heat demand, imposed heat to power ratio) or main physical limitations (limited heat availability, maximum system temperature allowed, thermo-mechanical constraints) are taken into account. A sensitivity analysis to model parameters is given. The results have shown that the various added constraints were useful for the design allowing to precise the influence of the model main parameters on the system design. Future perspective of the work and recommendations are stated.

Description: In this paper, we analyze the Network and System Management (NSM) requirements and NSM data objects for the intrusion detection of power systems; NSM is an IEC 62351-7 standard. We analyze a SYN flood attack and a buffer overflow attack to cause the Denial of Service (DoS) attack described in NSM. After mounting the attack in our attack testbed, we collect a data set, which is based on attributes for the attack. We then run several data mining methods with the data set using the Waikato Environment for Knowledge Analysis (WEKA). In the results, we select the decision tree algorithms with high detection rates, and choose key attributes in high level components of the trees. When we run several data mining methods again with the data set of chosen key attributes, the detection rates of most data mining methods are higher than before. We prove that our selected attack attributes, and the proposed detection process, are efficient and suitable for intrusion detection in the smart grid environment.

Description: A constitutive model for marine sediments containing natural gas hydrate is essential for the simulation of the geomechanical response to gas extraction from a gas-hydrate reservoir. In this study, the triaxial compressive properties of artificial methane-hydrate-bearing sediment samples reported in an earlier work were analyzed to examine the applicability of a nonlinear elastic constitutive model based on the Duncan-Chang model. The presented model considered the dependences of the mechanical properties on methane hydrate saturation and effective confining pressure. Some parameters were decided depending on the type of sand forming a specimen. The behaviors of lateral strain versus axial strain were also formulated as a function of effective confining pressure. The constitutive model presented in this study will provide a basis for an elastic analysis of the geomechanical behaviors of the gas-hydrate reservoir in the future study, although it is currently available to a limited extent.

Description: We investigate the pricing formation of natural gas markets on three different continents (Europe, Asia and North America). We find that natural gas markets showed a strong relationship with the crude oil market between 1992 and 2001 and natural gas prices tended to thermal parity with crude oil prices. From 2002 natural gas markets exhibited a less pronounced relationship with the crude oil market and major natural gas markets were severely underpriced compared to crude oil. A globally integrated natural gas market, comparable to the global oil market, has not evolved. The main natural gas markets, however, exhibit some level of integration, especially over a longer time. The European market exhibits the strongest levels of integration, while the North American market exhibits the weakest.

Description: The radial-radial flux compound-structure permanent-magnet synchronous machine (CS-PMSM), integrated by two concentrically arranged permanent-magnet electric machines, is an electromagnetic power-splitting device for hybrid electric vehicles (HEVs). As the two electric machines share a rotor as structural and magnetic common part, their magnetic paths are coupled, leading to possible mutual magnetic-field interference and complex control. In this paper, a design method to ensure magnetic decoupling with minimum yoke thickness of the common rotor is investigated. A prototype machine is designed based on the proposed method, and the feasibility of magnetic decoupling and independent control is validated by experimental tests of mutual influence. The CS-PMSM is tested by a designed driving cycle, and functions to act as starter motor, generator and to help the internal combustion engine (ICE) operate at optimum efficiency are validated.

Description: Effects of reaction conditions on the production of alcohols (AOHs) and alkanes (Alk) from CO and H2, which can be obtained from the gasification of biomass, using a molybdenum sulfide (MoS2)-based catalyst of MoS2/γ-Al2O3 were studied. A high-pressure fixed packed bed (HPFPB) was employed to carry out the reaction. The results indicate that the conversion of CO (XCO) and specific production rates of alcohol (SPRAOH) and alkane (SPRAlk) are highly depended on temperature (T). In T = 423–573 K, maximum yield of alcohols (YAOH) and SPRAOH occur at T = 523 K. In the meantime, well performance gives the selectivity of ethanol (SEtOH) of 52.0 C%. For the studies on varying H2/CO mole ratio (MH/C) from 1 to 4 at 523 K, the appropriate MH/C to produce EtOH is 2, giving higher ratios of SPRAOH/SPRAlk and YAOH/YAlk than those with other MH/C. As for varying the total gas flow rates (QG) of 300, 450, 600 to 900 cm3 min−1 tested at T = 523 K and MH/C = 2, the lower QG provides longer reaction time (or gaseous retention time, tR) thus offering higher XCO, however lower productivity. For setting pressure (PST) = 225–540 psi, a supply of higher pressure is equivalent to providing a larger amount of reactants into the reaction system, this thus suggests the use of higher PST should give both higher XCO and productivity. The assessment of the above results indicates that the MoS2/γ-Al2O3 catalyst favors the production of alcohols over alkanes, especially for ethanol. The information obtained is useful for the proper utilization of biomass derived gases of CO and H2.

Description: One of the biggest obstacles to economic profitability of solar water heating systems is the investment cost. Retrofitting existing domestic hot water heaters when a new solar hot water system is installed can reduce both the installation and material costs. In this study, retrofitting existing water heaters for solar water heating systems in Swedish single-family houses was theoretically investigated using the TRNSYS software. Four simulation models using forced circulation flow with different system configurations and control strategies were simulated and analysed in the study. A comparison with a standard solar thermal system was also presented based on the annual solar fraction. The simulation results indicate that the retrofitting configuration achieving the highest annual performance consists of a system where the existing tank is used as storage for the solar heat and a smaller tank with a heater is added in series to make sure that the required outlet temperature can be met. An external heat exchanger is used between the collector circuit and the existing tank. For this retrofitted system an annual solar fraction of 50.5% was achieved. A conventional solar thermal system using a standard solar tank achieves a comparable performance for the same total storage volume, collector area and reference conditions.

Description: To reveal the inner mechanism of gas explosion dynamic behavior affected by gas equivalent concentration, a high speed Schlieren image system and flow field measurement technology was applied to record the gas explosion flame propagation and flame structure transition. The results show that a flame front structure transition occurs, followed by a flame accelerating propagation process. The laminar to turbulence transition was the essential cause of the flame structure changes. The laminar flame propagation behavior was influenced mainly by gas expansion and fore-compressive wave effect, while the turbulent flame speed mostly depended on turbulence intensity, which also played an important role in peak value of the explosive pressure and flame speed. On the condition that the laminar-turbulent transition was easier to form, the conclusion was drawn that, the lowest CH4 concentration for maximum overpressure can be obtained, which was the essential reason why the ideal explosive concentration differs under different test conditions.

Description: The porous microstructure of hydrates governs the mechanical strength of the hydrate-bearing sediment. To investigate the growth law and microstructure of hydrates in porous media, the growth process of tetrahydrofuran (THF) hydrate under different concentration of THF solution is directly observed using Magnetic Resonance Imaging (MRI). The images show that the THF hydrate grows as different models under different concentration of THF solution (19%, 11.4% and 5.7% by weight) at 1 °C. When the concentration is 19% (stoichiometric molar ratio of THF/H2O = 1:17), the THF hydrate grows as cementing model. However, with the decreasing concentration of THF, the growth model transfers from cementing model to floating model. The results show that the growth of the THF hydrate was influenced by the dissolved quantity of THF in the water. The extension of the observed behavior to methane hydrate could have implications in understanding their role in seafloor and permafrost stability.

Description: Evacuated tube solar water heater systems are widely used in China due to their high thermal efficiency, simple construction requirements, and low manufacturing costs. CPC evacuated tube solar water heaters with a geometrical concentration ratio C of less than one are rare. A comparison of the experimental rig of evacuated tube solar water heater systems with and without a mini-CPC reflector was set up, with a series of experiments done in Hefei (31°53'N, 117°15'E), China. The first and second laws of thermodynamics were used to analyze and contrast their thermal performance. The water in the tank was heated from 26.9 to 55, 65, 75, 85, and 95 °C. Two types of solar water heater systems were used, and the data gathered for two days were compared. The results show that when attaining low temperature water, the evacuated tube solar water heater system without a mini-CPC reflector has higher thermal and exergy efficiencies than the system with a mini-CPC reflector, including the average and immediate values. On the other hand, when attaining high temperature water, the system with a mini-CPC reflector has higher thermal and exergy efficiencies than the other one. The comparison presents the advantages of evacuated tube solar water heater systems with and without a mini-CPC reflector, which can be offered as a reference when choosing which solar water system to use for actual applications.

Description: CO2 hydrate formation and dissociation is crucial for hydrate-based CO2 capture and storage. Experimental and calculated phase equilibrium conditions of carbon dioxide (CO2) hydrate in porous medium were investigated in this study. Glass beads were used to form the porous medium. The experimental data were generated using a graphical method. The results indicated the decrease of pore size resulted in the increase of the equilibrium pressure of CO2 hydrate. Magnetic resonance imaging (MRI) was used to investigate the priority formation site of CO2 hydrate in different porous media, and the results showed that the hydrate form firstly in BZ-02 glass beads under the same pressure and temperature. An improved model was used to predict CO2 hydrate equilibrium conditions, and the predictions showed good agreement with experimental measurements.

Description: Optimization of four parameters, i.e., zinc (Zn2+), magnesium (Mg2+), manganese (Mn2+) and yeast extract for bioethanol production from sweet sorghum juice by Saccharomyces cerevisiae NP 01  under very high gravity (VHG, 270 g·L−1 of total sugar) conditions was performed using an L9 (34) orthogonal array design. The fermentation was carried out at 30 °C in 500-mL air-locked Erlenmeyer flasks at the agitation rate of 100 rpm and the initial yeast cell concentration in the juice was approximately 5 × 107 cells·mL−1. The results showed that the order of influence was yeast extract 〉 Mn2+ 〉 Zn2+ 〉 Mg2+ and the optimum nutrient concentrations for the ethanol fermentation were Zn2+, 0.01; Mg2+, 0.05; Mn2+, 0.04; and yeast extract, 9 g·L−1. The verification experiments under the optimum condition clearly indicated that the metals and nitrogen supplementation improved ethanol production efficiency under the VHG fermentation conditions. The ethanol concentration (P), yield (Yp/s) and productivity (Qp) were 120.58 ± 0.26 g·L−1, 0.49 ± 0.01 and 2.51 ± 0.01 g·L−1·h−1, respectively, while in the control treatment (without nutrient supplement) P, Yp/s and Qp were only 93.45 ± 0.45 g·L−1, 0.49 ± 0.00 and 1.30 ± 0.01 g·L−1·h−1, respectively.

Description: N2O emissions from coal fired fluidized-bed combustion are approximately 30–360 mg/Nm3, much higher than that from pulverized coal combustion (less than 30 mg/Nm3). One approach to reduce the N2O is to reburn the biomass gasification gas in the coal-fired fluidized bed. In this paper, the effects of gasified biomass reburning on the integrated boiler system were investigated by both simulation and experimental methods. The simulation as well as experimental results revealed that the increase of the reburning ratio would decrease the theoretical air volume and boiler efficiency, while it would increase the fuel gas volume, combustion and exhuast gas temperature. The experimental results also indicated that the N2O removal could reach as high as 99% when the heat ratio of biomass gas to coal is 10.5%.

Description: Driving patterns exert an important influence on the fuel economy of vehicles, especially hybrid electric vehicles. This paper aims to build a method to identify driving patterns with enough accuracy and less sampling time compared than other driving pattern recognition algorithms. Firstly a driving pattern identifier based on a Learning Vector Quantization neural network is established to analyze six selected representative standard driving cycles. Micro-trip extraction and Principal Component Analysis methods are applied to ensure the magnitude and diversity of the training samples. Then via Matlab/Simulink, sample training simulation is conducted to determine the minimum neuron number of the Learning Vector Quantization neural network and, as a result, to help simplify the identifier model structure and reduce the data convergence time. Simulation results have proved the feasibility of this method, which decreases the sampling window length from about 250–300 s to 120 s with an acceptable accuracy. The driving pattern identifier is further used in an optimized co-simulation together with a parallel hybrid vehicle model and improves the fuel economy by about 8%.

Description: In a conventional distribution system, protection algorithms are designed to operate on a unidirectional high fault-current level. In a microgrid, a fault current from distributed generation (DG) may bring about a relay malfunction because of the bidirectional and relatively small fault current. Therefore, the conventional protection scheme is not applicable to microgrids and a new protection method must be developed. In this paper, two protection coordination algorithms which can be applied for facility and secondary microgrids are proposed, respectively. The proposed protection algorithms eliminate faults not by the EMS signal but by directional relays. Moreover, this makes the algorithms flexible regardless of the types and numbers of DG. The proposed protection algorithms were simulated at the KEPCO RI Microgrid Demonstration Site.

Description: More than a single thermosyphon solar water heater may be employed in applications when considerable hot water consumption is required. In this experimental investigation, eight typical Taiwanese solar water heaters were connected in series. Degree of temperature stratification and thermosyphon flow rate in a horizontal tank were evaluated. The system was tested under no-load, intermittent and continuous load conditions. Results showed that there was stratification in tanks under the no-load condition. Temperature stratification also redeveloped after the draw-off. Analysis of thermal performance of the system was conducted for each condition.

Description: The performance analysis of a supercritical organic Rankine cycle system driven by exhaust heat using 18 organic working fluids is presented. Several parameters, such as the net power output, exergy efficiency, expander size parameter (SP), and heat exchanger requirement of evaporator and the condenser, were used to evaluate the performance of this recovery cycle and screen the working fluids. The results reveal that in most cases, raising the expander inlet temperature is helpful to improve the net power output and the exergy efficiency. However, the effect of the expander inlet pressure on those parameters is related to the expander inlet temperature and working fluid used. Either lower expander inlet temperature and pressure, or higher expander inlet temperature and pressure, generally makes the net power output more. Lower expander inlet temperature results in larger total heat transfer requirement and expander size. According to the screening criteria of both the higher output and the lower investment, the following working fluids for the supercritical ORC system are recommended: R152a and R143a.

Description: This paper describes a kinetic study of the decomposition of waste printed circuit boards (WPCB) under conventional and microwave-induced pyrolysis conditions. We discuss the heating rates and the influence of the pyrolysis on the thermal decomposition kinetics of WPCB. We find that the thermal degradation of WPCB in a controlled conventional thermogravimetric analyzer (TGA) occurred in the temperature range of 300 °C–600 °C, where the main pyrolysis of organic matter takes place along with an expulsion of volumetric volatiles. The corresponding activation energy is decreased from 267 kJ/mol to 168 kJ/mol with increased heating rates from 20 °C/min to 50 °C/min. Similarly, the process of microwave-induced pyrolysis of WPCB material manifests in only one stage, judging by experiments with a microwave power of 700 W. Here, the activation energy is determined to be only 49 kJ/mol, much lower than that found in a conventional TGA subject to a similar heating rate. The low activation energy found in microwave-induced pyrolysis suggests that the adoption of microwave technology for the disposal of WPCB material and even for waste electronic and electrical equipment (WEEE) could be an attractive option.

Description: A microgrid is an eco-friendly power system because renewable sources such as solar and wind power are used as the main power sources. For this reason, much research, development, and demonstration projects have recently taken place in many countries. Operation is one of the important research topics for microgrids. For efficient and economical microgrid operation, a human operator is required as in other power systems, but it is difficult because there are some restrictions related to operation costs and privacy issues. To overcome the restriction, autonomous operation for microgrids is required. Recently, an intelligent agent system for autonomous microgrid operation has been studied as a potential solution. This paper proposes a multiagent system for autonomous microgrid operation. To build the multiagent system, the functionalities of agents, interactions among agents, and an effective agent protocol have been designed. The proposed system has been implemented by using an ADIPS/DASH framework as an agent platform. The intelligent multiagent system for microgrid operation based on the proposed scheme is tested to show the functionality and feasibility on a distributed environment through the Internet.

Description: Many models have been developed to forecast wind farm power output. It is generally difficult to determine whether the performance of one model is consistently better than that of another model under all circumstances. Motivated by this finding, we aimed to integrate groups of models into an aggregated model using fuzzy theory to obtain further performance improvements. First, three groups of least squares support vector machine (LS-SVM) forecasting models were developed: univariate LS-SVM models, hybrid models using auto-regressive moving average (ARIMA) and LS-SVM and multivariate LS-SVM models. Each group of models is selected by a decorrelation maximisation method, and the remaining models can be regarded as experts in forecasting. Next, fuzzy aggregation and a defuzzification procedure are used to combine all of these forecasting results into the final forecast. For sample randomization, we statistically compare models. Results show that this group-forecasting model performs well in terms of accuracy and consistency.

Description: Animal wastes from high-density farming have severe impacts on the nitrogen cycle. According to current regulations, the disposal of manure on cropland is constrained by nitrogen content in the agricultural soils. On the contrary, anaerobic digestion (AD) of these wastes can produce energy and a digestate, which is easier to handle than manure and can be applied for agronomic uses. When herbaceous crops are co-digested with manure to increase the efficiency of biogas production, the nitrogen content in the digestate further increases, unless these larger plants are equipped with nitrogen stripping technologies. We propose a model to compare larger (cooperative) and smaller (single parcel) AD conversion plants. The whole process is modeled: from the collection of manures, to the cultivation of energy crops, to the disposal of the digestate. The model maximizes the energy produced on the basis of available biomass, road network, local heat demand and local availability of land for digestate disposal. Results are the optimal size and location of the plants, their technology and collection basins. The environmental performances of such plants are also evaluated. The study has been applied to the province of Forlì-Cesena, an Italian district where animal farming is particularly relevant.

Description: The impacts of ventilation ratio and vent balance on cooling load and air flow of naturally ventilated attics are studied in this paper using an unsteady computational fluid dynamics (CFD) model. Buoyancy-driven turbulent ventilations in attics of gable-roof residential buildings are simulated for typical summer conditions. Ventilation ratios from 1/400 to 1/25 combined with both balanced and unbalanced vent configurations are investigated. The modeling results show that the air flows in the attics are steady and exhibit a general streamline pattern that is qualitatively insensitive to the variations in ventilation ratio and vent configuration. The predicted temperature fields are characterized by thermal stratification, except for the soffit regions. It is demonstrated that an increase in ventilation ratio will reduce attic cooling load. Compared with unbalanced vent configurations, balanced attic ventilation is shown to be the optimal solution in both maximizing ventilating flow rate and minimizing cooling load for attics with ventilation ratio lower than 1/100. For attics with ventilation ratios greater than 1/67, a configuration of large ridge vent with small soffit vent favors ventilating air flow enhancement, while a configuration of small ridge vent with large soffit vent results in the lowest cooling energy consumption.

Description: In Northern China, due to the high penetration of coal-fired cogeneration facilities, which are generally equipped with extraction-condensing steam turbines, lots of wind power resources may be wasted during the heating season. In contrast, considerable coal is consumed in the power generation sector. In this article, firstly it is revealed that there exists a serious divergence in the ratio of electrical to thermal energy between end users’ demand and the cogenerations’ production during off-peak load at night, which may negate active power-balancing of the electric power grid. Secondly, with respect to this divergence only occurring during off-peak load at night, a temporary proposal is given so as to enable the integration of more wind power. The authors suggest that if the energy carrier for part of the end users’ space heating is switched from heating water to electricity (e.g., electric heat pumps (EHPs) can provide space heating in the domestic sector), the ratio of electricity to heating water load should be adjusted to optimize the power dispatch between cogeneration units and wind turbines, resulting in fuel conservation. With this proposal, existing infrastructures are made full use of, and no additional ones are required. Finally a numerical simulation is performed in order to illustrate both the technical and economic feasibility of the aforementioned proposal, under ongoing infrastructures as well as electricity and space heating tariff conditions without changing participants’ benefits. The authors aim to persuade Chinese policy makers to enable EHPs to provide space heating to enable the integration of more wind power.

Description: Ground heat is a renewable resource that is readily available for buildings in cool climates, but its relatively low temperature requires the use of a heat pump to extract it for heating. We developed a system that uses low temperature ground heat directly in a building wall to reduce transmission heat losses. The Active Low Exergy Geothermal Insulation Systems (ALEGIS) minimizes exergy demand and maximizes the use of renewable geothermal heat from the ground. A fluid is pumped into a small pipe network in an external layer of a wall construction that is linked to a ground heat source. This decouples the building from the outside temperature, therefore eliminating large peak demands and reducing the primary energy demand. Our steady-state analysis shows that at a design temperature of −10 °C the 6 cm thick active insulation system has equivalent performance to 11 cm of passive insulation. Our comparison of heating performance of a building with our active insulation system versus a building with static insulation of the same thickness shows a 15% reduction in annual electricity demand, and thus exergy input. We present an overview of the operation and analysis of our low exergy concept and its modeled performance.

Description: On the basis of the shifting process of automated mechanical transmissions (AMTs) for traditional hybrid electric vehicles (HEVs), and by combining the features of electric machines with fast response speed, the dynamic model of the hybrid electric AMT vehicle powertrain is built up, the dynamic characteristics of each phase of shifting process are analyzed, and a control strategy in which torque and speed of the engine and electric machine are coordinatively controlled to achieve AMT shifting control for a plug-in hybrid electric vehicle (PHEV) without clutch is proposed. In the shifting process, the engine and electric machine are well controlled, and the shift jerk and power interruption and restoration time are reduced. Simulation and real car test results show that the proposed control strategy can more efficiently improve the shift quality for PHEVs equipped with AMTs.

Description: Microgrids can increase power penetration from distributed generation (DG) in the power system. The interface (i.e., the point of common coupling, PCC) between the microgrid and the power utility must satisfy certain standards, such as IEEE Sd. 1547. Energy monitoring of the microgrid at the PCC by the power utility is crucial if the utility cannot install advanced meters at different locations in the microgrid (e.g., a factory). This paper presents a new nonintrusive energy monitoring method using a hybrid self-organizing feature-mapping neural network (SOFMNN). The components of the FFT spectra for voltage, current, kW and kVAR, measured at the PCC, serve as the signatures for the hybrid SOFMNN inputs. The nonintrusive energy monitoring at the PCC identifies different load levels for individual linear/nonlinear loads and output levels for wind power generators in the microgrid. Using this energy monitoring result, the power utility can establish an energy management policy. The simulation results from a microgrid, consisting of a diesel generator, a wind-turbine-generator, a rectifier and a cyclo-converter, show the practicability of the proposed method.

Description: In this paper, an artificial pollution test is carried out to study the leakage current of porcelain insulators. Fractal theory is adopted to extract the characteristics hidden in leakage current waveforms. Fractal dimensions of the leakage current for the security, forecast and danger zones are analyzed under four types of degrees of contamination. The mean value and the standard deviation of the fractal dimension in the forecast zone are calculated to characterize the differences. The analysis reveals large differences in the fractal dimension of leakage current under different contamination discharge stages and degrees. The experimental and calculation results suggest that the fractal dimension of a leakage current waveform can be used as a new indicator of the discharge process and contamination degree of insulators. The results provide new methods and valid indicators for forecasting contamination flashovers.

Description: Oils with high content of free fatty acid (FFA) can be treated by acid esterification where an alcohol reacts with the given oil in the presence of acid catalyst. The investigated parameters include methanol to oil ratio, temperature and amount of catalyst. The optimum conditions for acid esterification which could reduce FFA content in the feedstock to less than 1.88% (acid value 3.76 mg KOH/g waste cooking oil) were 50 °C, 20% methanol to oil ratio (by volume) and 0.4 vol.% H2SO4 after 5 h. However, oil with an acid value of more than 1 mg KOH/g oil cannot meet the alkaline catalyzed transesterification conditions. Under the conditions of NaOH concentration 0.5 N, excess alkali 15%, 60 °C, 40 min, the FFA removal rate for deacidification reached 77.11% (acid value 0.86 mg KOH/g esterified oil). The acid value of deacidification product was reduced below 0.86 mg KOH/g esterified oil, thus meeting the base-catalyzed trans-esterification conditions.

Description: The imbalance between energy resource availability, demand, and production capacity, coupled with inherent economic and environmental uncertainties make strategic energy resources planning, management, and decision-making a challenging process. In this paper, a descriptive approach has been taken to synthesize the world’s energy portfolio and the global energy balance outlook in order to provide insights into the role of Organization of Petroleum Exporting Countries (OPEC) in maintaining “stability” and “balance” of the world’s energy market. This synthesis illustrates that in the absence of stringent policies, i.e., if historical trends of the global energy production and consumption hold into the future, it is unlikely that non-conventional liquid fuels and renewable energy sources will play a dominant role in meeting global energy demand by 2030. This should be a source of major global concern as the world may be unprepared for an ultimate shift to other energy sources when the imminent peak oil production is reached. OPEC’s potential to impact the supply and price of oil could enable this organization to act as a facilitator or a barrier for energy transition policies, and to play a key role in the global energy security through cooperative or non-cooperative strategies. It is argued that, as the global energy portfolio becomes more balanced in the long run, OPEC may change its typical high oil price strategies to drive the market prices to lower equilibria, making alternative energy sources less competitive. Alternatively, OPEC can contribute to a cooperative portfolio management approach to help mitigate the gradually emerging energy crisis and global warming, facilitating a less turbulent energy transition path while there is time.

Description: As the wind turbine size has been increasing and their mechanical components are built lighter, the reduction of the structural loads becomes a very important task of wind turbine control in addition to maximum wind power capture. In this paper, we present a separate set of collective and individual pitch control algorithms. Both pitch control algorithms use the LQR control technique with integral action (LQRI), and utilize Kalman filters to estimate system states and wind speed. Compared to previous works in this area, our pitch control algorithms can control rotor speed and blade bending moments at the same time to improve the trade-off between rotor speed regulation and load reduction, while both collective and individual pitch controls can be designed separately. Simulation results show that the proposed collective and individual pitch controllers achieve very good rotor speed regulation and significant reduction of blade bending moments.

Description: The Velenje Coal Mine (VCM) is one of the largest and the most modern underground coal mines in Europe. Although the coal mining industry produces coal as an energy source, it is also uses a lot of energy for its own operation and support processes. At this time of volatile energy prices and more and more strict environmental emission requirements, optimizing energy consumption plays an important role in good business performance. To track the consumption of electricity, district heating, drinking water and compressed air at the VCM a detailed energy monitoring methodology was developed and established in July 2010. The essential element of the presented monitoring system is a software application named “Central System for Regulation of Energy” (CSRE). The purpose of the CSRE is to control energy processes from a distance, take measures for economical and efficient use of energy, as well as to assist in maintenance. Such monitoring allows extensive comparisons between different energy sources consumption and enables correct measures to be taken to reduce the difference between the target and actual consumption of energy in VCM. With established real-time monitoring system, it is possible to look at mining processes and see where energy is being used inefficiently.

Description: In this paper, a double-linear approximation algorithm (DLAA) to achieve maximum-power-point tracking (MPPT) for photovoltaic (PV) arrays is proposed. The DLAA is based on the approximation that the maximum power point varies linearly with irradiation and temperature. With the DLAA, a maximum power point can be determined instantaneously. Moreover, complicated calculations and perturbations about an optimal point can be avoided. The paper also proposes a corresponding circuit to realize the DLAA. The configuration of the DLAA circuit is simple such that it is cost-effective and can be embedded into PV arrays easily. An example of implementation of a PV power supply system with the proposed MPPT is designed and the DLAA is compared with the perturb-and-observe method. Simulated and experimental results have demonstrated the feasibility of the PV power system and verified the advantages of the proposed DLAA.

Description: Worldwide, algal biofuel research and development efforts have focused on increasing the competitiveness of algal biofuels by increasing the energy and financial return on investments, reducing water intensity and resource requirements, and increasing algal productivity. In this study, analyses are presented in each of these areas—costs, resource needs, and productivity—for two cases: (1) an Experimental Case, using mostly measured data for a lab-scale system, and (2) a theorized Highly Productive Case that represents an optimized commercial-scale production system, albeit one that relies on full-price water, nutrients, and carbon dioxide. For both cases, the analysis described herein concludes that the energy and financial return on investments are less than 1, the water intensity is greater than that for conventional fuels, and the amounts of required resources at a meaningful scale of production amount to significant fractions of current consumption (e.g., nitrogen). The analysis and presentation of results highlight critical areas for advancement and innovation that must occur for sustainable and profitable algal biofuel production can occur at a scale that yields significant petroleum displacement. To this end, targets for energy consumption, production cost, water consumption, and nutrient consumption are presented that would promote sustainable algal biofuel production. Furthermore, this work demonstrates a procedure and method by which subsequent advances in technology and biotechnology can be framed to track progress.

Description: This paper presents the construction, mathematical modeling and testing of a scaled universal hydraulic Power Take-Off (PTO) device for Wave Energy Converters (WECs). A specific prototype and test bench were designed and built to carry out the tests. The results obtained from these tests were used to adjust an in-house mathematical model. The PTO was initially designed to be coupled to a scaled wave energy capture device with a low speed and high torque oscillating motion and high power fluctuations. Any Energy Capture Device (ECD) that fulfils these requirements can be coupled to this PTO, provided that its scale is adequately defined depending on the rated power of the full scale prototype. The initial calibration included estimation of the pressure drops in the different components, the pressurization time of the oil inside the hydraulic cylinders and the volumetric efficiency of the complete circuit. Since the overall efficiency measured during the tests ranged from 0.69 to 0.8 and the dynamic performance of the PTO was satisfactory, the results are really promising and it is believed that this solution might prove effective in real devices.

Description: Some microalgae are particularly attractive as a renewable feedstock for biodiesel production due to their rapid growth, high content of triacylglycerols, and ability to be grown on non-arable land. Unfortunately, obtaining oil from algae is currently cost prohibitive in part due to the need to pump and process large volumes of dilute algal suspensions. In an effort to circumvent this problem, we have explored the use of anion exchange resins for simplifying the processing of algae to biofuel. Anion exchange resins can bind and accumulate the algal cells out of suspension to form a dewatered concentrate. Treatment of the resin-bound algae with sulfuric acid/methanol elutes the algae and regenerates the resin while converting algal lipids to biodiesel. Hydrophobic polymers can remove biodiesel from the sulfuric acid/methanol, allowing the transesterification reagent to be reused. We show that in situ transesterification of algal lipids can efficiently convert algal lipids to fatty acid methyl esters while allowing the resin and transesterification reagent to be recycled numerous times without loss of effectiveness.

Description: Microalgae represent a sustainable energy source because of their high biomass productivity and ability to remove air and water born pollutants. This paper reviews the current status of production and conversion of microalgae, including the advantages of microalgae biodiesel, high density cultivation of microalgae, high-lipid content microalgae selection and metabolic control, and innovative harvesting and processing technologies. The key barriers to commercial production of microalgae biodiesel and future perspective of the technologies are also discussed.

Description: The paper adapts the Newton-like Extremum-Seeking Control technique to extract the maximum power from photovoltaic panels. This technique uses the gradient and Hessian of the panel characteristic in order to approximate the operating point to its optimum. The paper describes in detail the gradient and Hessian estimations carried out by means of sinusoidal dithering signals. Furthermore, we compare the proposed technique with the common Extremum Seeking Control that only uses the gradient. The comparison is done by means of PSIM simulations and it shows the different transient behaviors and the faster response of the Newton-like Extremum-Seeking Control solution.

Description: The collector efficiency in a downward-type double-pass external-recycle solar air heater with fins attached on the absorbing plate has been investigated theoretically. Considerable improvement in collector efficiency is obtainable if the collector is equipped with fins and the operation is carried out with an external recycle. Due to the recycling, the desirable effect of increasing the heat transfer coefficient compensates for the undesirable effect of decreasing the driving force (temperature difference) of heat transfer, while the attached fins provide an enlarged heat transfer area. The order of performances in the devices of same size is: double pass with recycle and fins 〉 double pass with recycle but without fins 〉 single pass without recycle and fins.

Description: Within the German integrated project SUGAR, aiming for the development of new technologies for the exploration and exploitation of submarine gas hydrates, the option of gas transport by gas hydrate pellets has been comprehensively re-investigated. A series of pVT dissociation experiments, combined with analytical tools such as x-ray diffraction and cryo-SEM, were used to gather an additional level of understanding on effects controlling ice formation. Based on these new findings and the accessible literature, knowns and unknowns of the self-preservation effect important for the technology are summarized. A conceptual process design for methane hydrate production and pelletisation has been developed. For the major steps identified, comprising (i) hydrate formation; (ii) dewatering; (iii) pelletisation; (iv) pellet cooling; and (v) pressure relief, available technologies have been evaluated, and modifications and amendments included where needed. A hydrate carrier has been designed, featuring amongst other technical solutions a pivoted cargo system with the potential to mitigate sintering, an actively cooled containment and cargo distribution system, and a dual fuel engine allowing the use of the boil-off gas. The design was constrained by the properties of gas hydrate pellets, the expected operation on continental slopes in areas with rough seas, a scenario-defined loading capacity of 20,000 m3 methane hydrate pellets, and safety as well as environmental considerations. A risk analysis for the transport at sea has been carried out in this early stage of development, and the safety level of the new concept was compared to the safety level of other ship types with similar scopes, i.e., LNG carriers and crude oil tankers. Based on the results of the technological part of this study, and with best knowledge available on the alternative technologies, i.e., pipeline, LNG and CNG transportation, an evaluation of the economic competitiveness of the methane hydrate transport technology has been performed. The analysis considers capital investment as well as operational costs and comprises a wide set of scenarios with production rates from 20 to 800 103 Nm3·h−1 and transport distances from 200 to 10,000 km. In contrast to previous studies, the model calculations in this study reveal no economic benefit of methane hydrate transportation versus competing technologies.

Description: The accumulation of methane hydrate in marine sediments is controlled by a number of physical and biogeochemical parameters including the thickness of the gas hydrate stability zone (GHSZ), the solubility of methane in pore fluids, the accumulation of particulate organic carbon at the seafloor, the kinetics of microbial organic matter degradation and methane generation in marine sediments, sediment compaction and the ascent of deep-seated pore fluids and methane gas into the GHSZ. Our present knowledge on these controlling factors is discussed and new estimates of global sediment and methane fluxes are provided applying a transport-reaction model at global scale. The modeling and the data evaluation yield improved and better constrained estimates of the global pore volume within the modern GHSZ ( ≥ 44 × 1015 m3), the Holocene POC accumulation rate at the seabed (~1.4 × 1014 g yr−1), the global rate of microbial methane production in the deep biosphere (4−25 × 1012 g C yr−1) and the inventory of methane hydrates in marine sediments ( ≥ 455 Gt of methane-bound carbon).

Description: Power semiconductor switching devices play an important role in the performance of high power wind energy generation systems. The state-of-the-art device choices in the wind power application as reported in the industry include IGBT modules, IGBT press-pack and IGCT press-pack. Because of significant deviation in the packaging structure, electrical characteristics, as well as thermal impedance, these available power switching devices may have various thermal cycling behaviors, which will lead to converter solutions with very different cost, size and reliability performance. As a result, this paper aimed to investigate the thermal related characteristics of some important power switching devices. Their impact on the thermal cycling of a 10 MW three-level Neutral-Point-Clamped wind power converter is then evaluated under various operating conditions; the main focus will be on the grid connected inverter. It is concluded that the thermal performances of the 3L-NPC wind power converter can be significantly changed by the power device technology as well as their parallel configurations.

Description: This paper is concerned with the protection of wind energy systems against the direct effects of lightning. As wind power generation undergoes rapid growth, lightning damages involving wind turbines have come to be regarded as a serious problem. Nevertheless, very few studies exist yet in Portugal regarding lightning protection of wind energy systems using numerical codes. A new case study is presented in this paper, based on a wind turbine with an interconnecting transformer, for the analysis of transient phenomena due to a direct lightning strike to the blade. Comprehensive simulation results are provided by using models of the Restructured Version of the Electro-Magnetic Transients Program (EMTP), and conclusions are duly drawn.

Description: The working principle of enzyme-based biofuel cells (EBFCs) is the same as that of conventional fuel cells. In an EBFC system, the electricity-production process is very intricate. Analysis requires a mathematical model that can adequately describe the EBFC and predict its performance. This paper develops a dynamic model simulating the discharge performance of the anode for which supported glucose oxidase and mediator immobilize in the EBFC. The dynamic transport behavior of substrate, redox state (ROS) of enzyme, enzyme-substrate complex, and the mediator creates different potential changes inside the anode. The potential-step method illustrates the dynamic phenomena of substrate diffusion, ROS of enzyme, production of enzyme-substrate complex, and reduction of the mediator with different potential changes.

Description: Cheese whey utilization is of major concern nowadays. Its high organic matter content, in combination with the high volumes produced and limited treatment options make cheese whey a serious environmental problem. However, the potential production of biogas (methane), hydrogen or other marketable products with a simultaneous high COD reduction through appropriate treatment proves that cheese whey must be considered as an energy resource rather than a pollutant. The presence of biodegradable components in the cheese whey coupled with the advantages of anaerobic digestion processes over other treatment methods makes anaerobic digestion an attractive and suitable treatment option. This paper intends to review the most representative applications of anaerobic treatment of cheese whey currently being exploited and under research. Moreover, an effort has been made to categorize the common characteristics of the various research efforts and find a comparative basis, as far as their results are concerned. In addition, a number of dairy industries already using such anaerobic digestion systems are presented.

Description: Classical equilibrium molecular dynamics (MD) simulations have been performed to investigate the computational performance of the Simple Point Charge (SPC) and TIP4P water models applied to simulation of methane hydrates, and also of liquid water, on a variety of specialised hardware platforms, in addition to estimation of various equilibrium properties of clathrate hydrates. The FPGA-based accelerator MD-GRAPE 3 was used to accelerate substantially the computation of non-bonded forces, while GPU-based platforms were also used in conjunction with CUDA-enabled versions of the LAMMPS MD software packages to reduce computational time dramatically. The dependence of molecular system size and scaling with number of processors was also investigated. Considering performance relative to power consumption, it is seen that GPU-based computing is quite attractive.

Description: This paper investigates the optimization of the performance of a solar powered Stirling engine based on finite-time thermodynamics. Heat transference in the heat exchangers between a concentrating solar collector and the Stirling engine is studied. The irreversibility of a Stirling engine is considered with the heat transfer following Newton's law. The power generated by a Stirling engine is used as an objective function for maximum power output design with the concentrating solar collector temperature and the engine thermal efficiency as the optimization parameters. The maximum output power of engine and its corresponding system parameters are determined using a genetic algorithm.

Description: When a three-phase induction generator (IG) supplies unbalanced loads, its terminal voltages and line currents are also unbalanced, which may cause the IG to overheat and need to be derated. A single-phase loaded self-excited induction generator (SEIG) works under most unfavorable load unbalance conditions. This paper proposes a three-capacitor circuit scheme and a method to find the values of the self-excitation capacitors that allow the SEIG to be balanced. The SEIG is modeled by a two-port network equivalent circuit that resolves the SEIG into its positive- and negative-sequence circuits associated with the self-excitation capacitors and the load. The network can then be analyzed by common AC circuit analysis techniques. Successful results for balancing the SEIG supplying a single-phase load have been achieved by properly choosing the values of the excitation capacitors. The proposed method has also been validated by experiments on a 0.37 kW SEIG.

Description: The objective of this study was to provide experimental data that could be used to predict frost growth and frost performance of a round plate fin-tube heat exchanger for low temperature heat pumps used in zero emission vehicles under cold weather conditions. In this study, round plate fin-tube heat exchangers were tested with variation of the fin space, air flow rate, relative humidity, and inlet air temperature. Frost height was measured and considered with the boundary layer interruption between fins. Frost height for 8.0 mm of fin space was increased by approximately 91.9% with an increase of relative humidity from 50.0% to 80.0%. The growth rate of frost height at 1.2 m3/min was observed to be 13.0% greater than that at 0.8 m3/min. Finally, the variation of the blockage ratio with fin space would be an important reference for designing advanced heat exchangers that operate under cold weather conditions.

Description: Industrial energy efficiency has received increasing attention in many countries because of its importance in the pursuit of energy supply security, increased economic competitiveness and in the mitigation of greenhouse gases emissions. This paper aimed to evaluate the energy consumption development of the Brazilian pulp and paper industry through an energy decomposition analysis and an energy efficiency index approach over a 30 years period. An international comparison with other important paper-producing countries (i.e., Canada, United States of America, Finland and Sweden) was carried out. It was concluded that despite a significant increase in the energy efficiency levels, responsible for 5.6 PJ savings in electricity consumption and for 38.6 PJ savings in fuels consumption between 1979 and 2009, a saving potential of 7.8 PJ and 146.2 PJ related to the annual consumption of electricity and fuels, respectively, could be identified in the Brazilian pulp and paper industry. Among the countries evolved in the international comparison, both the Swedish and Finnish industries were the most efficient, followed by the Brazilian, American and Canadian, the latter being the only one where there was a reduction in the energy efficiency levels from 1979 to 2009.

Description: This paper deals with a fault-tolerant semi-12-phase permanent-magnet synchronous machine (PMSM) used for electric vehicles. High fault-tolerant and low toque ripple features are achieved by employing fractional slot concentrated windings (FSCWs) and open windings. Excessive magnetomotive force (MMF) harmonic components can lead to thermal demagnetization of rotor magnets as well as high core loss. An improved all-teeth-wound winding disposition that changes the winding factor of each harmonic is applied to suppress harmonics. A relatively large slot leakage inductance that limits the short-circuit current (SCC) induced in the short-circuited winding is proposed to deal with short-circuit fault. Fault-tolerant controls up to two phases open circuited are investigated in this paper based on keeping the same torque-producing MMF. The fault-tolerant control strategies corresponding to each faulty mode are studied and compared to ensure high performance operation.

Description: Blends of biodiesels produced from soapnut oil and high-oleic free fatty acids (FFAs), which are potential non-edible oil feedstocks, were investigated with respect to their fuel properties. The soapnut oil methyl esters (SNME) had satisfactory fuel properties with the exception of its high cold filter plugging point. In contrast, the biodiesel from the FFAs had favorable fuel properties such as a low cold filter plugging point of −6 °C; however, it exhibits poor oxidation stability with an induction period (IP) of 0.2 h. The complementary blend of the SNME and the FFA-based biodiesel at various weight ratios was studied to improve the fuel properties. As a result, the biodiesel blend at a weight ratio of 70:30 can successfully meet all the biodiesel specifications, except the marginal oxidation stability. Furthermore, the effectiveness of N,N’-di-sec-butyl-p-phenylenediamine at the concentration between 100 and 500 ppm on the improvement in the oxidation stability of the biodiesel blend was examined. The relationship between the IP values associated with the consumption of antioxidants in the biodiesel blends was described by first-order reaction rate kinetics. In addition, the natural logarithm of IP (ln IP) at various concentrations of antioxidant presented a linear relation with the test temperature. The IP at ambient temperature can be predicted based on the extrapolation of the temperature dependence relation.

Description: The increasing demand for high energy density fuels and the concern for their safety have propelled research in the field of gelled propellants, where understanding the combustion of single gelled fuel droplets is the first stage to predict the spray combustion characteristics. The experiments utilized single-isolated freely falling gelled unsymmetrical dimethylhydrazine (UDMH) droplets instead of the conventional suspended droplet approach, in order to eliminate the perturbation associated with the suspension mechanism. Morphological transformations of the gelled droplet involved in the combustion processes were monitored by employing a high-speed digital camera, while the effects of ambient pressure and oxygen concentration on burning rate constants were also studied. The experimental results show that four main phenomena (droplet deformation, bubble formation and growth, vapor jetting and luminous jetting flame with “horn” shape) and three distinct phases were identified in the droplet combustion process; the high yield stress and polymer chain structure of polymer gellant are responsible for the appearance of bubbles with almost the same order of magnitude as the droplets. Increasing the ambient pressure can increase the burning rate, postpone the appearance of microexplosions, and weaken microexplosion intensity; while increasing the ambient oxygen concentration can promote the appearance of microexplosions, strengthen microexplosion intensity and increase the burning rate.

Description: The core objective of this paper is to analyze the energy and CO2 reduction potentials as well as the market prospects of biofuels in EU-15 in a dynamic framework till 2050. The most important result of this analysis is that 2nd generation biofuels might become economically competitive between 2020 and 2030, yet this can only be achieved if the following preconditions are fulfilled: (1) achievement of significant learning effects leading to considerably lower plant costs; (2) significant improvement of conversion efficiency from feedstock to fuel leading to lower feedstock costs and better ecological performance; (3) increases in conventional diesel and gasoline prices, e.g., due to CO2 based taxes.

Description: Because of its strong inherent safety features and high outlet temperature, the modular high temperature gas-cooled nuclear reactor (MHTGR) is already seen as the central part of the next generation of nuclear plants. Such power plants are being considered for industrial applications with a wide range of power levels, and thus power-level control is an important technique for their efficient and stable operation. Stimulated by the high regulation performance provided by nonlinear controllers, a novel dynamic output-feedback nonlinear power-level regulator is developed in this paper based on the technique of iterative damping assignment (IDA). This control strategy can provide the L2 disturbance attenuation performance under modeling uncertainty or exterior disturbance, and can also guarantee the globally asymptotic closed-loop stability without uncertainty and disturbance. This newly built control strategy is then applied to the power-level regulation of the HTR-PM plant, and numerical simulation results show both the feasibility and high performance of this newly-built control strategy. Furthermore, the relationship between the values of the parameters and the performance of this controller is not only illustrated numerically but also analyzed theoretically.

Description: This paper presents modeling approaches for step-up grid-connected photovoltaic systems intended to provide analytical tools for control design. The first approach is based on a voltage source representation of the bulk capacitor interacting with the grid-connected inverter, which is a common model for large DC buses and closed-loop inverters. The second approach considers the inverter of a double-stage PV system as a Norton equivalent, which is widely accepted for open-loop inverters. In addition, the paper considers both ideal and realistic models for the DC/DC converter that interacts with the PV module, providing four mathematical models to cover a wide range of applications. The models are expressed in state space representation to simplify its use in analysis and control design, and also to be easily implemented in simulation software, e.g., Matlab. The PV system was analyzed to demonstrate the non-minimum phase condition for all the models, which is an important aspect to select the control technique. Moreover, the system observability and controllability were studied to define design criteria. Finally, the analytical results are illustrated by means of detailed simulations, and the paper results are validated in an experimental test bench.

Description: The purpose of this study was to reveal the energy use and indoor environment characteristics of twelve households located in six cities in China, including daily use of gas and electricity, temperature and humidity throughout a year. The energy uses for district heating and hot water were not included. The investigated houses were separated into two groups, namely Group 1 with domestic heating, and Group 2 with district heating. The analysis showed that the energy use of Lighting and Audio visual & information for each house is not very different during the four seasons. Annual energy use varied from 13.3 to 32.4 GJ in Group 1. The energy use of House 05 was 32.4 GJ/year, which is the highest in Group 1, the space heating reached 18.5 GJ/year, accounting for 57% of the total. Energy use of House 01 increased in winter and summer, which is attributed to the use of heating in winter and cooling in summer, respectively. Annual energy use varied from 2.9 to 17.0 GJ in Group 2. Almost no change of energy use was found for the houses in Group 2 during the four seasons, but a big difference of average indoor temperature was found in the coldest days between the houses in Group 1 (around 10 °C) and Group 2 (around 20 °C), while the difference was small in summer.

Description: In the energy realm there is a pressing need to make decisions in a complex world characterized by biophysical limits. Exergy has been promoted as a preferred means of characterizing the impacts of resource consumption and waste production for the purpose of improving decision-making. This paper provides a unique and critical analysis of universal and comprehensive formulations of the chemical exergy reference environment, for the purpose of better understanding how exergy can inform decision-making. Four related insights emerged from the analysis, notably: (1) standard and universal chemical exergy reference environments necessarily encounter internal inconsistencies and even contradictions in their very formulations; (2) these inconsistencies are a result of incompatibility between the exergy reference environment and natural environment, and the desire to model the exergy reference environment after the natural environment so as to maintain analytical relevance; (3) the topics for which exergy is most appropriate as an analytical tool are not well served by comprehensive reference environments, and (4) the inconsistencies point to a need for deeper reflection of whether it is appropriate to adopt a thermodynamic frame of analysis for situations whose relevant characteristics are non-thermodynamic (e.g., to characterize scarcity). The use of comprehensive reference environments may lead to incorrect recommendations and ultimately reduce its appeal for informing decision-making. Exergy may better inform decision-making by returning to process dependent reference states that model specific processes and situations for the purpose of engineering optimization.

Description: Sequestration of carbon dioxide (CO2) in the form of its hydrates in natural methane (CH4) hydrate reservoirs, via CO2/CH4 exchange, is an attractive pathway that also yields valuable CH4 gas as product. In this paper, we describe a macroscale experiment to form CO2 and CH4-CO2 hydrates, under seafloor-mimic conditions, in a vessel fitted with glass windows that provides visualization of hydrates throughout formation and dissociation processes. Time resolved pressure and temperature data as well as images of hydrates are presented. Quantitative gas conversions with pure CO2, calculated from gas chromatographic measurements yielded values that range from 23 – 59% that correspond to the extent of formed hydrates. In CH4-rich CH4-CO2 mixed gas systems, CH4 hydrates were found to form preferentially.

Description: This work evaluates the potential for the reduction of energy demand in residential buildings by acting on the exterior envelope, both in newly constructed buildings and in the retrofitting of existing stock. It focuses on analysing social housing buildings in Mediterranean areas and on quantifying the scope of that reduction in the application of different envelope design strategies, with the purpose of prioritizing their application based on their energy efficiency. The analyses and quantifications were made by means of the generation of energy models with the TRNSYS tool for simple or combined solutions, identifying possible potentials for reduction of the energy demand from 20% to 25%, basically by acting on the windows. The case study was a newly built social housing building of a closed block type located in Seville (Spain). Its constructive techniques and the insulation level of its envelope are standardized for current buildings widespread across Mediterranean Europe.

Description: The current global conditions provide the pulp mill new opportunities beyond the traditional production of cellulose. Due to stricter environmental regulations, volatility of oil price, energy policies and also the global competitiveness, the challenges for the pulp industry are many. They range from replacing fossil fuels with renewable energy sources to the export of biofuels, chemicals and biomaterials through the implementation of biorefineries. In spite of the enhanced maturity of various bio and thermo-chemical conversion processes, the economic viability becomes an impediment when considering the effective implementation on an industrial scale. In the case of kraft pulp mills, favorable conditions for biofuels production can be created due to the availability of wood residues and generation of black liquor. The objective of this article is to give an overview of the technologies related to the production of alternative biofuels in the kraft pulp mills and discuss their potential and prospects in the present and future scenario.

Description: Distributed generation with a combustion engine prime mover is still widely used to supply electric power in a variety of applications. These applications range from backup power supply systems and combined wind-diesel generation to providing power in places where grid connection is either technically impractical or financially uneconomic. Modelling of such systems as a whole is extremely difficult due to the long-time load profiles needed and the computational difficulty of including small time-constant electrical dynamics with large time-constant mechanical dynamics. This paper presents the development of accelerated, reduced-order models of a distributed internal combustions engine generator unit. Overall these models are shown to achieve a massive improvement in the computational time required for long-time simulations while also achieving an extremely high level of dynamic accuracy. It is demonstrated how these models are derived, used and verified against benchmark models created using established techniques. Throughout the paper the modelling set as a whole, including multi level detail, is presented, detailed and finally summarised into a crucial tool for general system investigation and multiple target optimisation.

Description: A supercritical methanol transesterification method was applied to produce biodiesel from the high-acid oil of soybean soapstock. The fuel properties of biodiesel produced with various molar ratios of methanol to raw oil were analyzed and compared in this experimental study. Oleic acid (C18:1), linoleic acid (C18:2), and palmitic acid (C16:0) were the three main compounds in the high-acid oil-biodiesel. The saturated fatty acid content of the high-acid oil increased significantly due to the supercritical-methanol transesterification reaction. The fuel characteristics of the resulting high-acid oil, including the specific gravity and kinematic viscosity, were also greatly improved. The saturated fatty acid content of the biodiesel produced from the high-acid oil was higher than that of biodiesel from waste cooking oil produced by the subcritical transesterification using a strongly alkaline catalyst. The high-acid oil-biodiesel that was produced with a molar ratio of methanol to raw oil of 42 had the best fuel properties, including a higher distillation temperature and cetane index and a lower kinematic viscosity and water content, among the biodiesels with different molar ratios.

Description: A 2D unsteady computational fluid dynamics (CFD) model is employed to simulate buoyancy-driven turbulent ventilation in attics with different pitch values and ceiling insulation levels under summer conditions. The impacts of roof pitch and ceiling insulation on the cooling load of gable-roof residential buildings are investigated based on the simulation of turbulent air flow and natural convection heat transfer in attic spaces with roof pitches from 3/12 to 18/12 combined with ceiling insulation levels from R-1.2 to R-40. The modeling results show that the air flows in the attics are steady and exhibit a general streamline pattern that is qualitatively insensitive to the investigated variations of roof pitch and ceiling insulation. Furthermore, it is predicted that the ceiling insulation plays a control role on the attic cooling load and that an increase of roof pitch from 3/12 to 8/12 results in a decrease in the cooling load by around 9% in the investigated cases. The results suggest that the increase of roof pitch alone, without changing other design parameters, has limited impact on attics cooling load and airflow pattern. The research results also suggest both the predicted ventilating mass flow rate and attic cooling load can be satisfactorily correlated by simple relationships in terms of appropriately defined Rayleigh and Nusselt numbers.

Description: Traditionally, people in the Mediterranean region knew that the temperatures in their courtyards were cooler in summer than outside temperature. This paper provides a quantitative study on the usefulness of Mediterranean courtyards as passive energy saving systems. This work is based on the creation of a Computational Fluid Dynamics (CFD) numerical model developed using the open source Freefem++ language. In this work, first the numerical model is tested using simplified-shape courtyards which have been previously studied both physically under controlled parameters, and mathematically through numerical simulations. We also study the most appropriate depth ratio for a courtyard, based on these simplified shapes, depending on the climate. Secondly, we apply the numerical model in a real geometry, the Monte Málaga hotel. We compare the numerical results with the monitored data of the temperature in the courtyard of the hotel. The numerical model takes into account precomputed solar radiation in the walls of the courtyard, the predominant wind and buoyancy effects.

Description: Switching overvoltages (SOV) are considered a possible source of component failures experienced in existing offshore wind farms (OWFs). The inclusion of sufficiently accurate and validated models of the main electrical components in the OWF in the simulation tool is therefore an important issue in order to ensure reliable switching operations. Transient measurement results in an OWF are compared with simulation results in PSCAD EMTDC and DigSILENT Power Factory. A user-defined model of the vacuum circuit breaker (VCB) is included in both tools, capable of simulating multiple prestrikes during the closing operation. An analysis of the switching transients that might occur in OWFs will be made on the basis of the validated model, and the importance of the inclusion of a sufficiently accurate representation of the VCB in the simulation tool will be described. The inclusion of the VCB model in PSCAD greatly improves the simulation results, whereas little improvement is found in DigSILENT. Based on the transient study it is found that the simulated SOV can be up to 60% higher at the sending end when using the detailed VCB representation compared to the built-in switch, which emphasises the need for accurate representation of the VCB for energisation studies.

Description: Massive integration of renewable energy sources in electrical power systems of remote islands is a subject of current interest. The increasing cost of fossil fuels, transport costs to isolated sites and environmental concerns constitute a serious drawback to the use of conventional fossil fuel plants. In a weak electrical grid, as it is typical on an island, if a large amount of conventional generation is substituted by renewable energy sources, power system safety and stability can be compromised, in the case of large grid disturbances. In this work, a model for transient stability analysis of an isolated electrical grid exclusively fed from a combination of renewable energy sources has been studied. This new generation model will be installed in El Hierro Island, in Spain. Additionally, an operation strategy to coordinate the generation units (wind, hydro) is also established. Attention is given to the assessment of inertial energy and reactive current to guarantee power system stability against large disturbances. The effectiveness of the proposed strategy is shown by means of simulation results.

Description: In this paper, an energy storage system with voltage equalization strategy for wind energy conversion is presented. The proposed energy storage system provides a voltage equalization strategy for series-connected lead-acid batteries to increase their total storage capacity and lifecycle. In order to draw the maximum power from the wind energy, a perturbation-and-observation method and digital signal processor (DSP) are incorporated to implement maximum power point tracking (MPPT) algorithm and power regulating scheme. In the proposed energy storage system, all power switches have zero-voltage-switching (ZVS) feature at turn-on transition. Therefore, the conversion efficiency can be increased. Finally, a prototype energy storage system for wind energy conversion is built and implemented. Experimental results have verified the performance and feasibility of the proposed energy storage system for wind energy conversion.

Description: The efficiency of the wind power conversions systems can be greatly improved using an appropriate control algorithm. In this work, a sliding mode control for variable speed wind turbine that incorporates a doubly fed induction generator is described. The electrical system incorporates a wound rotor induction machine with back-to-back three phase power converter bridges between its rotor and the grid. In the presented design the so-called vector control theory is applied, in order to simplify the electrical equations. The proposed control scheme uses stator flux-oriented vector control for the rotor side converter bridge control and grid voltage vector control for the grid side converter bridge control. The stability analysis of the proposed sliding mode controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. Finally simulated results show, on the one hand, that the proposed controller provides high-performance dynamic characteristics, and on the other hand, that this scheme is robust with respect to the uncertainties that usually appear in the real systems.

Description: This study describes the first general optimization model for complex systems with uncertain parameters and decision variables represented as intervals in CDM forestry projects. We work through a specific example of the optimization method developed for a Clean Development Mechanism (CDM) forestry project in Inner Mongolia, China. This model is designed to optimize the carbon sink capacity of the new forests, and can deal with uncertainties in the carbon sink capacity, average annual rainfall, ecological parameters, and biological characteristics of tree species. The uncertain inputs are presented in the form of intervals, as are several of the optimized output variables. Compared with the project’s originally recommended scheme, the optimized model will absorb and fix between 1,142 and 885,762 tonnes of extra carbon dioxide. Moreover, the ecological and environmental benefits of the project are also raised to various extents.

Description: This paper presents the construction, mathematical modeling and testing of a scaled universal hydraulic Power Take-Off (PTO) device for Wave Energy Converters (WECs). A specific prototype and test bench were designed and built to carry out the tests. The results obtained from these tests were used to adjust an in-house mathematical model. The PTO was initially designed to be coupled to a scaled wave energy capture device with a low speed and high torque oscillating motion and high power fluctuations. Any Energy Capture Device (ECD) that fulfils these requirements can be coupled to this PTO, provided that its scale is adequately defined depending on the rated power of the full scale prototype. The initial calibration included estimation of the pressure drops in the different components, the pressurization time of the oil inside the hydraulic cylinders and the volumetric efficiency of the complete circuit. Since the overall efficiency measured during the tests ranged from 0.69 to 0.8 and the dynamic performance of the PTO was satisfactory, the results are really promising and it is believed that this solution might prove effective in real devices.

Description: Electric vehicles (EVs) and the related infrastructure are being developed rapidly. In order to evaluate the impact of factors on the aggregated EV load and to coordinate charging, a model is established to capture the relationship between the charging load and important factors based on data mining. The factors can be categorized as internal and external. The internal factors include the EV battery size, charging rate at different places, penetration of the charging infrastructure, and charging habits. The external factor is the time-of-use pricing (TOU) policy. As a massive input data is necessary for data mining, an algorithm is implemented to generate a massive sample as input data which considers real-world travel patterns based on a historical travel dataset. With the input data, linear regression was used to build a linear model whose inputs were the internal factors. The impact of the internal factors on the EV load can be quantified by analyzing the sign, value, and temporal distribution of the model coefficients. The results showed that when no TOU policy is implemented, the rate of charging at home and range anxiety exerts the greatest influence on EV load. For the external factor, a support vector regression technique was used to build a relationship between the TOU policy and EV load. Then, an optimization model based on the relationship was proposed to devise a TOU policy that levels the load. The results suggest that implementing a TOU policy reduces the difference between the peak and valley loads remarkably.

Description: Bioenergy is currently regarded as a renewable energy source with a high growth potential. Forest-based biodiesel, with the significant advantage of not competing with grain production on cultivated land, has been considered as a promising substitute for diesel fuel by many countries, including China. Consequently, extracting biodiesel from Jatropha curcas has become a growing industry. However, many key issues related to the development of this industry are still not fully resolved and the prospects for this industry are complicated. The aim of this paper is to evaluate the net energy, CO2 emission, and cost efficiency of Jatropha biodiesel as a substitute fuel in China to help resolve some of the key issues by studying data from this region of China that is well suited to growing Jatropha. Our results show that: (1) Jatropha biodiesel is preferable for global warming mitigation over diesel fuel in terms of the carbon sink during Jatropha tree growth. (2) The net energy yield of Jatropha biodiesel is much lower than that of fossil fuel, induced by the high energy consumption during Jatropha plantation establishment and the conversion from seed oil to diesel fuel step. Therefore, the energy efficiencies of the production of Jatropha and its conversion to biodiesel need to be improved. (3) Due to current low profit and high risk in the study area, farmers have little incentive to continue or increase Jatropha production. (4) It is necessary to provide more subsidies and preferential policies for Jatropha plantations if this industry is to grow. It is also necessary for local government to set realistic objectives and make rational plans to choose proper sites for Jatropha biodiesel development and the work reported here should assist that effort. Future research focused on breading high-yield varieties, development of efficient field management systems, and detailed studies lifecycle environmental impacts analysis is required to promote biologically and economically sustainable development of Jatropha biodiesel and to assist government agencies in setting realistic objectives and appropriate and advantageous policies for the regions and the country.

Description: Among solar passive systems integrated in buildings, sunspaces or solar greenhouses represent a very interesting solution. A sunspace is a closed, southbound volume, constituted by transparent surfaces, adjacent to a building, which reduces winter energy demand thanks to the use of solar gains. The effect of a typical solar greenhouse on the energy balance of a building was evaluated during the heating period with two stationary procedures (Method 5000 and EN ISO 13790) and with a dynamic tool (TRNSYS). After the analysis of the greenhouse alone, the behavior of an entire house was simulated; a flat equipped with a sunspace, recently built thanks to public contributions provided by the Umbria Region in Italy to widespread bio-climatic architecture, was used as case-study. Simulations were carried out for the examined flat, both with a steady-state tool and with a dynamic one; the contribution of the sunspace was estimated thanks to the various methods previously mentioned. Finally, the simulated data were satisfactorily compared with the real energy consumptions (natural gas for heating) of the flat; the sunspace allows a reduction of winter energy demand of the flat of about 20%.