The paper presents a new concept of a vertical axis wind turbine. The idea is focused on small wind turbines, and therefore, the dominating quality is safety. Another important necessary feature is efficient operation at small winds. This implies an application of the drag driven solution such as the Savonius rotor. The presented concept is aimed at reducing the rotor size and the cost of implementation. A new wind turbine solution, its efficiency, and functionality are described. The results of numerical simulations being a proof of the concept are reported. The simulations were followed by wind tunnel tests. Finally several prototypes were built and investigated for a longer period of time. The new wind turbine concept has undergone various testing and implementation efforts, making this idea matured, well proven and documented. A new feature, namely, the wind turbine size reduction at strong winds, or in other words, an increase in the wind turbine size at low winds is the reason wh... [more]

In this study, p-type amorphous silicon oxide (a-SiOx) films are deposited using a radio-frequency inductively-coupled plasma chemical vapor deposition system. Effects of the CO2 gas flow rate on film properties and crystalline silicon heterojunction (HJ) solar cell performance are investigated. The experimental results show that the band gap of the a-SiOx film can reach 2.1 eV at CO2 flow rate of 10 standard cubic centimeters per minute (sccm), but the conductivity of the film deteriorates. In the device simulation, the transparent conducting oxide and contact resistance are not taken into account. The electrodes are assumed to be perfectly conductive and transparent. The simulation result shows that there is a tradeoff between the increase in the band gap and the reduction in conductivity at increasing CO2 flow rate, and the balance occurs at the flow rate of six sccm, corresponding to a band gap of 1.95 eV, an oxygen content of 34%, and a conductivity of 3.3 S/cm. The best simulated... [more]

This study examines the effect of mixing on the performance of anaerobic digestion of cow manure in Chinese dome digesters (CDDs) at ambient temperatures (27−32 °C) in comparison with impeller mixed digesters (STRs) and unmixed digesters (UMDs) at the laboratory scale. The CDD is a type of household digester used in rural and pre-urban areas of developing countries for cooking. They are mixed by hydraulic variation during gas production and gas use. Six digesters (two of each type) were operated at two different influent total solids (TS) concentration, at a hydraulic retention time (HRT) of 30 days for 319 days. The STRs were mixed at 55 rpm, 10 min/hour; the unmixed digesters were not mixed, and the Chinese dome digesters were mixed once a day releasing the stored biogas under pressure. The reactors exhibited different specific biogas production and treatment efficiencies at steady state conditions. The STR 1 exhibited the highest methane (CH4) production and treatment efficiency (vo... [more]

This article describes an aging study of a foam-vacuum insulation panel (VIP) composite insulation board installed on a test wall in a natural exposure test facility through a 30-month period. Silica-based VIPs with a polymeric barrier film were used in this study. The study results showed the effectiveness of a VIP-based insulation to reduce the heat gains and losses through a wall compared to regular rigid foam insulation of the same thickness. However, the long-term performance monitoring indicated a gradual decline in the thermal performance of the foam-VIP composite. In addition, one-dimensional numerical models were created to simulate the in situ behavior of the foam-VIP composite. One model utilized constant thermal conductivities of the test wall components and another utilized temperature-dependent thermal conductivities; the latter used measurements of conductivity over temperatures ranging from −15 to 55 °C. The results of the simulations emphasized the need to use both tem... [more]

The intermittency of solar energy resources has brought a big challenge for the optimization and planning of a future smart grid. To reduce the intermittency, an accurate prediction of photovoltaic (PV) power generation is very important. Therefore, this paper proposes a new forecasting method based on the recurrent neural network (RNN). At first, the entire solar power time series data is divided into inter-day data and intra-day data. Then, we apply RNN to discover the nonlinear features and invariant structures exhibited in the adjacent days and intra-day data. After that, a new point prediction model is proposed, only by taking the previous PV power data as input without weather information. The forecasting horizons are set from 15 to 90 min. The proposed forecasting method is tested by using real solar power in Flanders, Belgium. The classical persistence method (Persistence), back propagation neural network (BPNN), radial basis function (RBF) neural network and support vector mac... [more]

Ceramic-coated materials used in different engineering sectors are the focus of world-wide interest and have generated a need for inspection techniques that detect very small structural anomalies. Non-destructive testing is increasingly being used to evaluate coating thickness and to test for coating flaws. The main pros of non-destructive testing is that the tested object remains intact and available for continued use afterward. This paper reports on an integrated, non-destructive testing approach that combines infrared thermography and acousto-ultrasonics to evaluate advanced aerospace sandwich structure materials with the aim of exploring any potential for detecting defects of more than one type. Combined, these two techniques successfully detected fabrication defects, including inclusions and material loss.

Standardized communication plays an important role in substation automation system (SAS). IEC 61850 is a de-facto standard in SAS. It facilitates smooth communication between different devices located in the substation by achieving interoperability. Generic Object-Oriented Substation Event (GOOSE) and Sample Value (SV) messages developed according to IEC 61850 enable efficient monitoring and operation control of SAS. IEC 61850 is very popular due to its flexible and robust modeling. As the number of critical infrastructures that employed IEC 61850 increases, it is important to study cybersecurity aspects as well. To this end, this paper develops a software framework, S-GoSV (Secure GOOSE and SV), that generates custom GOOSE and Sample Value messages. Furthermore, security features are added to protect them from different security attacks within a substation. IEC 62351-6 specifies digital signatures to achieve node authentication and messages integrity. Therefore, S-GoSV implements RSAS... [more]

In Europe, ethanol is blended with gasoline fuel in 5 or 10% volume (E5 or E10). In USA the blend is 15% in volume (E15) and there are also pumps that provide E85. In Brazil, the conventional gasoline is E27 and there are pumps that offer E100, due to the growing market of flex fuel vehicles. Bioethanol production is usually by means of biological conversion of several biomass feedstocks (first generation sugar cane in Brazil, corn in the USA, sugar beet in Europe, or second-generation bagasse of sugarcane or lignocellulosic materials from crop wastes). The environmental sustainability of the bioethanol is usually measured by the global warming potential metric (GWP in CO2eq), 100 years time horizon. Reviewed values could range from 0.31 to 5.55 gCO2eq/LETOH. A biomass-to-ethanol industrial scenario was used to evaluate the impact of methodological choices on CO2eq: conventional versus dynamic Life Cycle Assessment; different impact assessment methods (TRACI, IPCC, ILCD, IMPACT, EDIP,... [more]

Germany has experienced rapid growth in onshore wind capacities over the past two decades. Substantial capacities of offshore wind turbines have been added since 2013. On a local, highly-resolved level, this analysis evaluated if differences in wind speed forecast errors exist for offshore and onshore locations regarding magnitude and variation. A model based on the Extra Trees algorithm is proposed and found to be a viable method to transform local wind speeds and capacities into aggregated wind energy feed-in. This model was used to analyze if offshore and onshore wind power expansion lead to different distributions of day-ahead wind energy forecast errors in Germany. The Extra Trees model results indicate that offshore wind capacity expansion entails an energy forecast error distribution with more frequent medium to high deviations, stemming from larger and more variable wind speed deviations of offshore locations combined with greater geographical concentration of offshore wind tur... [more]

Under the European Union (EU) energy efficiency targets that Romania has assumed, increasing the share of solar energy has been one of the main points to be considered. The most important solar energy resources are found in the lowlands and low hills in southern and south-eastern parts of the country. The current paper is focused on the Romanian Plain, which has the best environmental conditions to support the development of photovoltaic (PV) farms. One hundred and ten PV farms have been identified and mapped which cover a total area of 1393 hectares. Although it provides a clean and sustainable energy source, the related environmental implications of PV farms could be either positive or negative. In this study, some of the main categories of impacts have been selected for identification and analysis of their environmental consequences. Several indicators have been computed: the share of PV farms from the main land use/cover categories and main soil types, and the distance of PV farms... [more]

Currently, in most countries, the electricity sector is liberalized, and electricity is traded in deregulated electricity markets. In these markets, electricity demand is determined the day before the physical delivery through (semi-)hourly concurrent auctions. Hence, accurate forecasts are essential for efficient and effective management of power systems. The electricity demand and prices, however, exhibit specific features, including non-constant mean and variance, calendar effects, multiple periodicities, high volatility, jumps, and so on, which complicate the forecasting problem. In this work, we compare different modeling techniques able to capture the specific dynamics of the demand time series. To this end, the electricity demand time series is divided into two major components: deterministic and stochastic. Both components are estimated using different regression and time series methods with parametric and nonparametric estimation techniques. Specifically, we use linear regress... [more]

According to the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report in 2013 (IPCC, 2013) [...]

Machine learning has been applied successfully for faulty wafer detection tasks in semiconductor manufacturing. For the tasks, prediction models are built with prior data to predict the quality of future wafers as a function of their precedent process parameters and measurements. In real-world problems, it is common for the data to have a portion of input variables that are irrelevant to the prediction of an output variable. The inclusion of many irrelevant variables negatively affects the performance of prediction models. Typically, prediction models learned by different learning algorithms exhibit different sensitivities with regard to irrelevant variables. Algorithms with low sensitivities are preferred as a first trial for building prediction models, whereas a variable selection procedure is necessarily considered for highly sensitive algorithms. In this study, we investigate the effect of irrelevant variables on three well-known representative learning algorithms that can be appli... [more]

This paper reports on the optimum conditions for simultaneous hydrogen and butyric acid production from microalgae (Chlorella sp.) using enriched anaerobic mixed cultures as inoculum. The fermentation was objectively carried out under acidogenic conditions to achieve butyric acid for further ABE fermentation in solventogenesis stage. The main effects of initial pH (5 and 7), temperature (35 °C and 55 °C), and substrate concentration (40, 60, 80, and 100 g-VS/L) for hydrogen and butyric acid production were evaluated by using batch fermentation experiment. The major effects on hydrogen and butyric acid production are pH and temperature. The highest production of hydrogen and butyric acid was observed at pH 7 and temperature 35 °C. Using initial Chlorella sp. concentration of 80 g-VS/L or 100 g-VS/L at pH 7 and temperature 35 °C could produce hydrogen with an average yield of 22 mL-H2/g-VS along with high butyric acid production yield of 0.05 g/g-VS, suggesting that microalgae (Chlorella... [more]

The discharge resistor is only used in case of electrical trip to reduce the field current as fast as possible and to minimize the damages produced by the short-circuit current supplied by the synchronous machine. The connection of the discharge resistor is done by opening the field breaker and it implies a large negative voltage in the field winding. This negative voltage is limited to 80% of the winding insulation voltage. On the other hand, in case of a transient de-excitation, at the first moment, the automatic voltage regulator (AVR) reduces the field voltage to the minimum. In case of one-quadrant rectifier type AVR, the minimum voltage is zero and in case of two-quadrant rectifier AVR, the minimum voltage is close to the ceiling voltage with negative polarity. In both cases, the minimum voltages are much smaller than the negative voltage produced by the connection of the discharge resistor. This paper presents a new system that improves the transient de-excitation of synchronous... [more]

The water hammer can cause great risks in water supply pipe systems. A surge tank is a kind of general water hammer control device. In order to improve the behavior of the surge tank, a self-adaptive auxiliary control (SAC) system was proposed in this paper. The system can optimize the response of the surge tank according to the transient pressure. The numerical model and the matched boundary conditions were established to simulate the improved surge tank and optimize the SAC system. Then, various transient responses were simulated by the proposed model with different parameters set. The proposed system is validated by comparing the water hammer process in a river-pipe-valve (RLV) system with and without SAC. The results show that the SAC can greatly improve the water hammer control of the pipeline and the water level oscillation of the surge tank. With the SAC system, the required vertical size of the surge tank can be significantly reduced with the desired water hammer control functi... [more]

In order to improve the performance of switched reluctance motor (SRM) systems for photovoltaic (PV) pumps, this paper introduces a new converter topology for SRM with controllable multiple power sources. Only simple switching components need to be added at the front end of the asymmetric half-bridge converter in this topology, which enables the control of multiple power sources. The new PV pump system has four operating modes, which are the PV panel driven mode, battery bank driven mode, dual-source driven mode, and battery charging mode. By adjusting the state of the front-end converter switch, the voltage tracking of PV panel can be achieved, providing a stable bus voltage for the SRM system. By controlling the battery bypass switch, the bus voltage of SRM system can be increased, thereby increasing the system power level. Simulations and experiments based on a four-phase 8/6 SRM demonstrate the effect of the novel converter proposed in this paper.

At this time, there are plans to develop offshore wind projects in the Caspian Sea. The aim of the present work was to estimate the possible benefits coming from such a project. As a first step, the wind profile of this region was established by considering reanalysis data coming from the ERA-Interim project, the time interval covered being between January 1999 and December 2018. According to these results, significant resources have been noticed in the northern part where the wind speed frequently reached 8 m/s, being identified also as a hot-spot south of Olya site. In the second part, the performances of some offshore wind turbines were established. These were defined by rated capacities ranging from 3 MW to 8.8 MW. The downtime period of some generators can reach 90% in the central and southern sectors, while for the capacity factor, the authors expected a maximum of 33.07% for a turbine rated at 4.2 MW. From a financial point of view, the values of the levelized cost of energy (LC... [more]

As different types of lithium batteries are increasingly employed in various devices, it is crucial to predict the state of health (SOH) of lithium batteries. There are plenty of methods for SOH estimation of a lithium-ion battery. However, existing technologies often have computational complexity. Furthermore, it is difficult to use least the previous 30% of data of the battery degradation process to predict the SOH variation of the entire degradation process. To address this problem, in this paper, the SOH of the target battery is estimated based on the transfer of different battery data sets. Firstly, according to importance sampling (IS), valid features are extracted from cycles of charging voltage in both the source and target battery. Secondly, transfer component analysis (TCA) is used to map the source data set to the target data set. Moreover, an extreme learning machine (ELM) algorithm is employed to train a single hidden layer feed forward neural network (SLFN) for its fast t... [more]

Smart production as one of the key issues for the world to advance toward Industry 4.0 has been a research focus in recent years. In a smart factory, hundreds or even thousands of sensors and smart devices are often deployed to enhance product quality. Generally, sensor data provides abundant information for artificial intelligence (AI) engines to make decisions for these smart devices to collect more data or activate some required activities. However, this also consumes a lot of energy to transmit the sensor data via networks and store them in data centers. Data compression is a common approach to reduce the sensor data size so as to lower transmission energies. Literature indicates that many Bounded-Error Piecewise Linear Approximation (BEPLA) methods have been proposed to achieve this. Given an error bound, they make efforts on how to approximate to the original sensor data with fewer line segments. In this paper, we furthermore consider resolution reduction, which sets a new restri... [more]

Line loss rate plays an essential role in evaluating the economic operation of power systems. However, in a low voltage (LV) distribution network, calculating line loss rate has become more cumbersome due to poor configuration of the measuring and detecting device, the difficulty in collecting operational data, and the excessive number of components and nodes. Most previous studies mainly focused on the approaches to calculate or predict line loss rate, but rarely involve the evaluation of the prediction results. In this paper, we propose an approach based on a gradient boosting decision tree (GBDT), to predict line loss rate. GBDT inherits the advantages of both statistical models and AI approaches, and can identify the complex and nonlinear relationship while computing the relative importance among variables. An empirical study on a data set in a city demonstrates that our proposed approach performs well in predicting line loss rate, given a large number of unlabeled examples. Experi... [more]

The thermal energy storage properties of a working fluid can be modified by the exothermic and endothermic adsorption and desorption of fluid molecules in the micro/nanoporous materials. In this study, thermogravimetric (TG) analysis experiments and molecular simulations (molecular dynamics, MD, and grand canonical Monte Carlo, GCMC) were employed to examine the thermal energy storage properties of the UIO-66 metal organic framework material, UIO-66/H2O nanofluids and pure water. Our results showed that the molecular simulation calculations were, in principle, consistent with the obtained experimental data. The thermal energy storage performance of UIO-66/H2O nanofluids was enhanced with the increase in the UIO-66 mass fraction. In addition, the differences between the simulation calculations and experimental results could be mainly ascribed to the different structures of UIO-66 and the evaporation of fluid samples. Furthermore, this work indicated that molecular simulations contribute... [more]

Considering that the European Directive has imposed that at least 20% of the total energy should come from renewable energy sources (RES) by 2020 already and the specific targets for each European Union Member State, this paper attempts to assess the importance of GDP per capita in realizing these targets and also the effects of the RES share in electricity. Contrary to previous research, this paper does not consider the connection between economic growth and RES, but rather the potential connection between the share of RES in electricity and the real GDP per capita. The panel data models indicated to a positive, but very low impact of GDP per capita on the share of RES in electricity in the period of 2007−2017 in the case of the EU countries, except Luxembourg that has outlier values of GDP per capita. However, causality between the two variables was not identified. Some groups of countries were described according to these variables using cluster analysis. Future research should focu... [more]

In the present study, a numerical framework for predicting the aerodynamic performance and the aeroelastic behavior of floating offshore wind turbine rotor blades involving platform motion was developed. For this purpose, the aerodynamic and structural analyses were conducted simultaneously in a tightly coupled manner by exchanging the information about the aerodynamic loads and the elastic blade deformations at every time step. The elastic behavior of the turbine rotor blades was described by adopting a structural model based on the Euler-Bernoulli beam. The aerodynamic loads by the rotor blades were evaluated by adopting a blade element momentum theory. The numerical simulations were conducted when the platform of the wind turbine independently moves in each of the six degrees-of-freedom directions consisting of heave, sway, surge, roll, pitch, and yaw. It was observed that flexible blades exhibit complicated vibratory behaviors when they are excited by the aerodynamic, inertia, and... [more]

Train operation strategy optimization is a multi-objective optimization problem affected by multiple conditions and parameters, and it is difficult to solve it by using general optimization methods. In this paper, the parallel structure and double-population strategy are used to improve the general optimization algorithm. One population evolves by genetic algorithm (GA), and the other population evolves by particle swarm optimization (PSO). In order to make these two populations complement each other, an immigrant strategy is proposed, which can give full play to the overall advantages of parallel structure. In addition, GA and PSO is also improved, respectively. For GA, its convergence speed is improved by adjusting the selection pressure adaptively based on the current iteration number. Elite retention strategy (ERS) is introduced into GA, so that the best individual in each iteration can be saved and enter the next iteration process. In addition, the opposition-based learning (OBL)... [more]