Energies — Open Access Journal of Energy Research, Engineering and Policy

Hydraulic instability is a complex factor causing the vibration of hydro-turbine generator shafting system (HGSS), and the mechanism is the uneven distribution of flow along the circumference. The common reasons for this phenomenon include the inconsistency of the blade exit flow angle, the relay stroke and the guide vane opening. This paper mainly focuses on the research of the hydraulic instability caused by the inconsistency of the blade exit flow angle. Firstly, based on the Kutta-Joukowski theorem, the hydraulic unbalance force model is firstly presented. Then, considering the chain reaction among the hydraulic, mechanical and electrical instability, a combined nonlinear mathematical model of the HGSS is established. Finally, by using numerical simulation, the dynamic characteristics of the HGSS with the changing of the deviation of the blade exit flow angle, the blade exit diameter and the guide vane opening angle are analyzed. Moreover, it is found that the hydraulic instability determines the overall changing trend of the shafting dynamic behaviors. In addition, some stable ranges of the HGSS are distinguished. But above all, these results can efficiently provide a reference for the design and manufacture of hydro-turbine blades and the operation of hydropower stations. Full article

With the emergence of the smart grid, both consumers and electricity providing companies can benefit from real-time interaction and pricing methods. In this work, a smart power system is considered, where consumers share a common energy source. Each consumer is equipped with a home energy management controller (HEMC) as scheduler and a smart meter. The HEMC keeps updating the utility with the load profile of the home. The smart meter is connected to a power grid having an advanced metering infrastructure which is responsible for two-way communication. Genetic teaching-learning based optimization, flower pollination teaching learning based optimization, flower pollination BAT and flower pollination genetic algorithm based energy consumption scheduling algorithms are proposed. These algorithms schedule the loads in order to shave the peak formation without compromising user comfort. The proposed algorithms achieve optimal energy consumption profile for the home appliances equipped with sensors to maximize the consumer benefits in a fair and efficient manner by exchanging control messages. Control messages contain energy consumption of consumer and real-time pricing information. Simulation results show that proposed algorithms reduce the peak-to-average ratio by 34.56% and help the users to reduce their energy expenses by 42.41% without compromising the comfort. The daily discomfort is reduced by 28.18%. Full article

Evaluating the installation potential of ground source heat pump (GSHP) systems based on the hydrogeological condition of an area is important for the installation and sustainable use of the system. This work is the first to have compared the distributions of heat exchange rate in the Sendai Plain and Aizu Basin (Japan) in terms of topographical and hydrogeological conditions. A regional groundwater flow and heat transport model was constructed for the Sendai Plain. Suitability assessment was conducted for an identical closed-loop system by preparing the distribution maps of heat exchange rate for space heating for the plain and basin. For both locations, the upstream area showed a higher heat exchange rate than the downstream area. Multiple regression analysis was conducted using heat exchange rate as a response variable. Average groundwater flow velocity and average subsurface temperature were considered as explanatory variables. The heat exchange rate for the plain, whose Péclet number ranged from 3.5 × 10⁻³–7.3 × 10⁻², was affected by groundwater flow velocity and subsurface temperature. The exchange rate for the basin, whose Péclet number ranged from 8.5 × 10⁻²–5.8 × 10⁻¹, was affected by groundwater flow velocity. Inland basins are likely to be more suitable for GSHP system installation utilizing groundwater flow than coastal plains in terms of inclination of slope. This study showed that multiple regression analysis can reveal factors affecting the heat exchange rate as well as the degree to which they affect it. Full article

Granite is regarded as a good option of host rock for high-level radioactive waste (HLW) repositories. Despite of its creep strain is small, the creep damage of which, especially that in the accelerated creep stage, increase its permeability significantly. To investigate the relationship between the creep strain and permeability evolution in granite, the present paper conducted a set of creep-seepage experiments associated with acoustic emission (AE) technology. The analysis in terms of the evolution of creep strain and permeability, characters of AE hits, mechanism of creep strain and that of permeability convince us that, the permeability evolution of granite is related to the volumetric dilation and microcracks connectivity. According to this relationship, a three-dimensional damage-based creep model was deduced from a one-dimensional fractal derivative-based model, and a permeability evolution model was proposed as well in this paper. The experiment data suggest nonnegligible influence of creep damage on the permeability of granite, therefore this influence should be taken into consideration of the design work of HLW repositories. The calculated results of the proposed models match well the experiment data, suggesting good capability of the models in approaching the creep and hydraulic performance of granite. In addition, the permeability model is friendly in parameter identification due to its simple mathematic formulation. Full article

This paper proposes a real-time pricing scheme for the demand response management between one energy provider and multiple energy hub operators. A promising energy trading scenario has been designed for the near future integrated energy system. The Stackelberg game approach was employed to capture the interactions between the energy provider (leader) and energy consumers (follower). A distributed algorithm was proposed to derive the Stackelberg equilibrium, then, the best strategies for the energy provider and each energy hub operator were explored in order to maximize their benefits. Simulation results showed that the proposed method can balance the energy supply and demand, improve the payoffs for all players, as well as smooth the aggregated load profiles of all energy consumers. Full article

This work is located in a growing sector within the field of renewable energies, wave energy converters (WECs). Specifically, it focuses on one of the point absorber waves (PAWs) of the hybrid platform W2POWER. With the aim of maximizing the mechanical power extracted from the waves by these WECs and reducing their mechanical fatigue, the design of five different model predictive controllers (MPCs) with hard and soft constraints has been carried out. As a contribution of this paper, two of the MPCs have been designed with the addition of an embedded integrator. In order to analyze and compare the MPCs with conventional PI type control, an exhaustive study about performance and robustness is realized through the computer simulations carried out, in which uncertainties in the WEC dynamics and JONSWAP spectrum are considered. The results obtained show how the MPCs with embedded integrator improve power production of the WEC system studied in this work. Full article

At present, a variety of standardized 18650 commercial cylindrical lithium-ion batteries are widely used in new energy automotive industries. In this paper, the Panasonic NCR18650PF cylindrical lithium-ion batteries were studied. The NEWWARE BTS4000 battery test platform is used to test the electrical performances under temperature, vibration and temperature-vibration coupling conditions. Under the temperature conditions, the discharge capacity of the same battery at the low temperature was only 85.9% of that at the high temperature. Under the vibration condition, mathematical statistics methods (the Wilcoxon Rank-Sum test and the Kruskal-Wallis test) were used to analyze changes of the battery capacity and the internal resistance. Changes at a confidence level of 95% in the capacity and the internal resistance were considered to be significantly different between the vibration conditions at 5 Hz, 10 Hz, 20 Hz and 30 Hz versus the non-vibration condition. The internal resistance of the battery under the Y-direction vibration was the largest, and the difference was significant. Under the temperature-vibration coupling conditions, the orthogonal table L₉ (3⁴) was designed. It was found out that three factors were arranged in order of temperature, vibration frequency and vibration direction. Among them, the temperature factor is the main influencing factor affecting the performance of lithium-ion batteries. Full article

In this paper, we propose a multi-dimensional sparse-coded ambient backscatter communication (MSC-AmBC) system for long-range and high-rate massive Internet of things (IoT) networks. We utilize the characteristics of the ambient sources employing orthogonal frequency division multiplexing (OFDM) modulation to mitigate strong direct-link interference and improve signal detection of AmBC at the reader. Also, utilization of the sparsity originated from the duty-cycling operation of batteryless RF tags is proposed to increase the dimension of signal space of backscatter signals to achieve either diversity or multiplexing gains in AmBC. We propose optimal constellation mapping and reflection coefficient projection and expansion methods to effectively construct multi-dimensional constellation for high-order backscatter modulation while guaranteeing sufficient energy harvesting opportunities at these tags. Simulation results confirm the feasibility of the long-range and high-rate AmBC in massive IoT networks where a huge number of active ambient sources and passive RF tags coexist. Full article

This contribution outlines the design of electric vehicle direct-current (DC) bus control system supplied by a battery/ultracapacitor hybrid energy storage system, and its coordination with the fully electrified vehicle driveline control system. The control strategy features an upper-level DC bus voltage feedback controller and a direct load compensator for stiff tracking of variable (speed-dependent) voltage target. The inner control level, comprising dedicated battery and ultracapacitor current controllers, is commanded by an intermediate-level control scheme which dynamically distributes the upper-level current command between the ultracapacitor and the battery energy storage systems. The feedback control system is designed and analytical expressions for feedback controller parameters are obtained by using the damping optimum criterion. The proposed methodology is verified by means of simulations and experimentally for different realistic operating regimes, including electric vehicle DC bus load step change, hybrid energy storage system charging/discharging, and electric vehicle driveline subject to New European Driving Cycle (NEDC), Urban Driving Dynamometer Schedule (UDDS), New York Certification Cycle (NYCC) and California Unified Cycle (LA92), as well as for abrupt acceleration/deceleration regimes. Full article

The waste of coal resources, a complicated production process and slow mining speed seriously restrict the rapid development of longwall mining. To achieve effective mining, an innovative noncoal pillar mining approach (i.e., Gob-side Entry Retaining by Roof Cutting (GERRC)) was introduced. The mechanism of the GERRC approach and its three key technologies (i.e., roof support technology, directional presplit cumulative blasting technology and surrounding rock control technology) were studied by theoretical analysis, numerical simulation, laboratory and field experiments. The new approach was finally tested under medium-thick coal seam and compound roof conditions. The results show that the directional presplit cumulative blasting technology can effectively control the damage evolution in the roof rock, maintain the integrity of the entry roof and contribute the gob roof to the cave in time. The support technologies in different roof movement stages can control the entry surroundings, and the final section of the retained entry met the safety production requirements. The test results suggested that the proposed approach for coal effective mining is feasible, and the introduced key technologies and design methods potentially produce reasonable values for applications of pillarless mining in similar projects. Full article

Assessing the tidal stream energy resource, its intermittency and likely environmental feedbacks due to energy extraction, relies on the ability to accurately represent kinetic losses in ocean models. Energy conversion has often been implemented in ocean models with enhanced turbine stress terms formulated using an array-averaging approach, rather than implementing extraction at device-scale. In depth-averaged models, an additional drag term in the momentum equations is usually applied. However, such array-averaging simulations neglect intra-array device wake interactions, providing unrealistic energy extraction dynamics. Any induced simulation error will increase with array size. For this study, an idealized channel is discretized at sub 10 m resolution, resolving individual device wake profiles of tidal turbines in the domain. Sensitivity analysis is conducted on the applied turbulence closure scheme, validating results against published data from empirical scaled turbine studies. We test the fine scale model performance of several mesh densities, which produce a centerline velocity wake deficit accuracy (R²) of 0.58–0.69 (RMSE = 7.16–8.28%) using a k-Ɛ turbulence closure scheme. Various array configurations at device scale are simulated and compared with an equivalent array-averaging approach by analyzing channel flux differential. Parametrization of array-averaging energy extraction techniques can misrepresent simulated energy transfer and removal. The potential peak error in channel flux exceeds 0.5% when the number of turbines n_TECs ≈ 25 devices. This error exceeds 2% when simulating commercial-scale turbine array farms (i.e., >100 devices). Full article

In the modern electric power industry, Flexible AC Transmission Systems (FACTS) have a special place. In connection with the increased interest in the development of “smart energy”, the use of such devices is becoming especially urgent. Their main function is the ability to manage modes in real time: maintain the necessary level of voltage in the grids, control the power flow, increase the capacity of power lines and increase the static and dynamic stability of the power grid. The problem of system reliability and stability is related to the task of definitions and optimizations and planning indicators, design and exploitation. The main aim of this article is the definition of the best placement of the STATCOM compensator in case to provide stability and reliability of the grid with the minimization of the power losses, using Particle Swarm Optimization algorithms. All calculations were performed in MATLAB. Full article

To date, Korea has built four 1000 MW gross-power ultra-critical coal-fired power plants. With the introduction of this new power plant type, there is a need for the development of best practices and lessons learned associated with its construction. One such need identified as a gap in literature is the early project planning estimation of project duration. To fill this research gap, this study utilized the Program Evaluation and Review Technique/Critical Path Method (PERT/CPM) and Monte Carlo simulations for estimating the appropriate construction duration at the planning stage of a new 1000 MW class coal-fired power plant project. Through the case study of the four Korean ultra-critical coal-fired power plants in operation, there was found an 85% likelihood of construction duration to be between 64 and 68 months. From interviews with subject matter experts, the most significant risk factors were found to be labor strikes and construction safety incidents. The findings within aid early planning decision makers by providing a replicable and accurate schedule estimation process. While the findings are based on Korean power plants, the results of this research can be used as a tool for coal-fired power plant construction schedule estimation worldwide. Full article

Graphite/poly(3,4-ethyenedioxythiophene) (PEDOT) nanocomposites were prepared by an in-situ oxidative polymerization process. The electrical conductivity and Seebeck coefficient of the graphite/PEDOT nanocomposites with different content of graphite were measured in the temperature range from 300 K to 380 K. The results show that as the content of graphite increased from 0 to 37.2 wt %, the electrical conductivity of the nanocomposites increased sharply from 3.6 S/cm to 80.1 S/cm, while the Seebeck coefficient kept almost the same value (in the range between 12.0 μV/K to 15.1 μV/K) at 300 K, which lead to an increased power factor. The Seebeck coefficient of the nanocomposites increased from 300 K to 380 K, while the electrical conductivity did not substantially depend on the measurement temperature. As a result, a power factor of 3.2 μWm⁻¹ K⁻² at 380 K was obtained for the nanocomposites with 37.2 wt % graphite. Full article

This study examines the Granger-causal relationships between oil price movements and global stock returns by using time-varying Granger-causality tests in mean and in variance. We use the daily returns from Morgan Stanley Capital International (MSCI) G7 and the MSCI Emerging Stock Market Indexes to distinguish between the effects of daily oil price movements on G7 countries’ and emerging market countries’ stock markets. We further divide the emerging markets into two groups as oil-exporting and oil-importing countries. For the oil market, we use both the West Texas Intermediate (WTI) and Brent oil daily price movements. While the Granger-causality-in-mean tests indicate a causal link from WTI oil prices and G7 countries’ stock returns to MSCI emerging countries’ stock returns, the Granger-causality-in-variance tests suggest no causal link from global oil market prices to stock market returns. Nonetheless, a causal link from the G7 countries’ stock returns to the MSCI emerging countries’ stock returns is detected. In addition, G7 countries’ stock market volatility is found to Granger-cause Brent oil price volatility. The time-varying Granger-causality-in-mean and Granger-causality-in-variance tests present new and further insights. A causal relationship between oil price changes and G7 countries’ stock returns is found for some periods during and after the global financial crisis. Time-varying Granger-causality-in-variance test results indicate evidence of causal linkages among oil prices and global stock market returns that are specific only to certain time periods. We also find that there might be a difference between the movements in Brent and WTI oil prices with respect to their Granger-causal effects on oil-importing emerging markets’ stock returns—especially after the global financial crisis. Our results provide further evidence that the effects of oil price movements on stock returns might be different depending on the volatility in the stock markets. Full article

The adequacy of legal and regulatory framework relating to nuclear energy in Bangladesh has sparked many questions since the government took the formal decision to establish a nuclear power plant (NPP) at Rooppur. Consequently, the government has taken some measures to make a comprehensive and robust framework to ensure safe and secure nuclear energy production in the country. Even though these initiatives are highly appreciable, there remain certain regulatory concerns which this paper has attempted to reflect. Therefore, the objective of this paper is to showcase the recent legal and regulatory development of Bangladesh in relation to nuclear energy and to recommend further developments. The study was based on secondary sources where a doctrinal research was carried out to solve particular research questions. The safety and security of the Rooppur Nuclear Power Plant will frankly rely on how the government of Bangladesh plans and learns to implement, design, safeguard, exchange and further develop nuclear energy related knowledge and talent around the country. Full article

The technical and economic features of a patented V-shape roof guide vane (VRGV) with a solar and wind power generation system mounted on an eco-roof system are presented in this paper. Moreover, this innovative VRGV was investigated on for the purpose of improving the performance of a vertical axis wind turbine (VAWT), which was installed on an eco-roof system to solve the low-efficiency power generation problem of the wind turbines under the condition of a low wind speed. This paper proposes a preliminary study for the performance of the VAWT with the VRGV on a building. This research used a mock-up building with a double slope roof, where a five straight-bladed VAWT was mounted and tested under two conditions, with and without the VRGV. From the comparative experiments, the self-starting performance and rotational speed of the VAWT mounted above a double slope roof with the VRGV have been significantly improved compared to the VAWT without the VRGV. Further, the power coefficient (C_p) of the VAWT can be augmented to about 71.2% increment due to the VRGV design. In addition, numerical simulations by computational fluid dynamics (CFD) were proposed to verify the augmented effect of the C_p of the VAWT under the influence of the VRGV in the experiment. Besides, economic estimation of the VRGV was conducted. Full article

This research aims to develop an optimal continuous process to produce fatty acid methyl esters (biodiesel) from waste cooking oil using a series of shockwave power reactors. Response surface methodology (RSM) based on central composite design (CCD) was used to design the experiment and to analyze five operating parameters: ratio of rotor diameter to stator diameter (Dr/Ds), ratio of cavity diameter to rotor diameter (Dc/Dr), ratio of cavity depth to gap between rotor and stator (dc/∆r), rotational speed of rotor (N), and Residence time (Tr). The optimum conditions were determined to be Dr/Ds = 0.73, Dc/Dr = 0.06, dc/∆r = 0.50, 25,510.55 rpm rotational speed of rotor, and 30.10 s residence times under this condition. Regarding the results, the most important parameter in shockwave power reactor (SPR) reactors was ratio of rotor diameter to stator diameter (Dr/Ds). The optimum predicted and actual FAME yield was 98.53% and 96.62%, respectively, which demonstrates that RSM is a reliable method for modeling the current procedure. Full article

Users are increasing their demands on the home appliances they utilize by requiring them to be powered anywhere and anytime. In order to satisfy this need, wireless power transfer helps transfer energy between objects without conductors. For domestic scenarios, strongly magnetic resonant technology offers a method to enable wireless power transfer, even when there exist intermediate non-metallic objects between the wireless power source and the load. This paper reviews this technology with a comprehensive explanation about its fundamentals and physical principles. Some practical issues are also analyzed in this work. Particularly, how the control can be designed and how the coils are built. Finally, this paper also addresses the study about the features of other technologies to power home appliances without conductors. They can be foreseen as the technological competitors of strongly coupled magnetic resonant systems. Full article