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Energies, Volume 11, Issue 12 (December 2018)

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Cover Story (view full-size image) Fault diagnosis of PMSM in safety critical applications can be ensured by monitoring the variations [...] Read more.
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Open AccessArticle
Development and Test of Solutions to Enlarge the Power of PV Irrigation and Application to a 140 kW PV-Diesel Representative Case
Energies 2018, 11(12), 3538; https://doi.org/10.3390/en11123538 - 19 Dec 2018
Cited by 1 | Viewed by 707
Abstract
The current state of the art of photovoltaic (PV) irrigation systems is limited to PV peak powers below 40 kWp, which does not cover the irrigation needs of farmers, co-operatives, irrigator communities, and agro-industries. This limitation of power is due to two main [...] Read more.
The current state of the art of photovoltaic (PV) irrigation systems is limited to PV peak powers below 40 kWp, which does not cover the irrigation needs of farmers, co-operatives, irrigator communities, and agro-industries. This limitation of power is due to two main technical barriers: The quick intermittence of PV power due to the passing of clouds, and the maladjustment between PV production and water needs. This paper presents new solutions that have been developed to overcome these barriers and their application to the design and performance of a 140 kWp hybrid PV-diesel system for the drip irrigation of 195 ha of olive trees in Alter do Chão, Portugal. The performance of the solutions was analysed during two years of real operation. As the performance of the PV system is not only affected by intrinsic-to-design characteristics, but also by circumstances external to the system, new performance indices were developed. As an example, the percentage of use of PV electricity, PVSH, was 78% and 82% in 2017 and 2018, respectively, and the performance ratio of the PV part, PRPV, was 0.79 and 0.80. The economic feasibility was also analysed based on experimental data, resulting in savings in the levelized cost of electricity of 61%. Full article
(This article belongs to the Section Sustainable Energy)
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Open AccessArticle
Experimental Comparison of Three Real-Time Optimization Strategies Applied to Renewable/FC-Based Hybrid Power Systems Based on Load-Following Control
Energies 2018, 11(12), 3537; https://doi.org/10.3390/en11123537 - 19 Dec 2018
Cited by 4 | Viewed by 706
Abstract
Besides three different real-time optimization strategies analyzed for the Renewable/Fuel Cell Hybrid Power Systems (REW/FC-HPS) based on load-following (LFW) control, a short but critical assessment of the Real-Time Optimization (RTO) strategies is presented in this paper. The advantage of power flow balance on [...] Read more.
Besides three different real-time optimization strategies analyzed for the Renewable/Fuel Cell Hybrid Power Systems (REW/FC-HPS) based on load-following (LFW) control, a short but critical assessment of the Real-Time Optimization (RTO) strategies is presented in this paper. The advantage of power flow balance on the DC bus through the FC net power generated using the LFW control instead of using the batteries’ stack is highlighted in this study. As LFW control consequence, the battery operates in charge-sustained mode and many advantages can be exploited in practice such as: reducing the size of the battery and maintenance cost, canceling the monitoring condition of the battery state-of-charge etc. The optimization of three FC-HPSs topologies based on appropriate RTO strategy is performed here using indicators such as fuel economy, fuel consumption efficiency, and FC electrical efficiency. The challenging task to optimize operation of the FC-HPS under unknown profile of the load demand is approached using an optimization function based on linear mix of the FC net power and the fuel consumption through the weighting coefficients knet and kfuel. If optimum values are chosen, then a RTO switching strategy can improve even further the fuel economy over the entire range of load. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle
Experimental Study for the Assessment of the Measurement Uncertainty Associated with Electric Powertrain Efficiency Using the Back-to-Back Direct Method
Energies 2018, 11(12), 3536; https://doi.org/10.3390/en11123536 - 19 Dec 2018
Cited by 1 | Viewed by 676
Abstract
Brushless electric motors are used intensively in the industrial automation sector due to the motors low inertia and fast response. According to the International Electrotechnical Commission, IEC 60034-2-1, the efficiency of a three-phase electric machine (excluding machines for traction vehicles) can be determined [...] Read more.
Brushless electric motors are used intensively in the industrial automation sector due to the motors low inertia and fast response. According to the International Electrotechnical Commission, IEC 60034-2-1, the efficiency of a three-phase electric machine (excluding machines for traction vehicles) can be determined by direct or indirect techniques. In the case of small traction motors (<10 kW), direct methods are used extensively by manufacturers, even if no standard has been published or scheduled by the IEC. In this paper, we evaluated the accuracy of the (direct) back-to-back method for the estimation of the energy performance of a 3 kW brushless AC electric motor used in a light electric vehicle. We measured the efficiencies of a pair of motors and inverters, as well as the overall efficiency of the entire power train. The results showed that the methodology was sufficiently accurate and comparable with other indirect methods available in existing literature. Moreover, we developed a Simulink model that used the powertrain efficiency map as the input to perform the simulation of a standard urban driving cycle. The simulation was run 500 times to calculate the probability density function associated with the total range of the vehicle, considering the uncertainty of the efficiency that was determined experimentally. The simulation results confirmed the low deviation of the distribution standard compared to the average value of the range of the vehicle. Full article
(This article belongs to the Special Issue Analysis for Electrical Machines Monitoring)
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Open AccessArticle
Effects of Mooring Compliancy on the Mooring Forces, Power Production, and Dynamics of a Floating Wave Activated Body Energy Converter
Energies 2018, 11(12), 3535; https://doi.org/10.3390/en11123535 - 19 Dec 2018
Cited by 1 | Viewed by 562
Abstract
The paper aims at investigating the interactions between a floating wave energy device (WEC) and its mooring system under a variety of wave conditions (regular and irregular, perpendicular and oblique, ordinary and extreme). The analyzed WEC is the DEXA, a wave activated body [...] Read more.
The paper aims at investigating the interactions between a floating wave energy device (WEC) and its mooring system under a variety of wave conditions (regular and irregular, perpendicular and oblique, ordinary and extreme). The analyzed WEC is the DEXA, a wave activated body point absorber, of the type that performs better when aligned to the incident wave direction. Two typologies of mooring systems were studied: for limited depths, the spread system, with a disposition of the lines that do not constrain the yaw movements; for large depths, the catenary anchor leg mooring (CALM) system. The spread system was experimentally investigated, including a realistic power take-off system, to capture non-linear behaviors and assess device motions, power production, and forces on mooring lines. The CALM system was numerically simulated, as mooring modelling is more reliable in deep waters and allows testing of a number of different configurations, by changing the number of the mooring lines and the mooring layout. The experiments showed that a reduction of the mooring compliancy increases the power production. The numerical simulations showed that a redundancy on the number of chains allows a better distribution of the loads, with advantages on reliability and costs. Full article
(This article belongs to the Section Sustainable Energy)
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Open AccessArticle
Influences of Fracturing Fluid Injection on Mechanical Integrity of Cement Sheath under Four Failure Modes
Energies 2018, 11(12), 3534; https://doi.org/10.3390/en11123534 - 19 Dec 2018
Cited by 2 | Viewed by 589
Abstract
The significant decreased wellbore temperature and increased casing pressure during fracturing fluid injection present a big challenge for the mechanical integrity of cement sheath in fracturing wells. Based on the theories of elastic mechanics, thermodynamics, and a multi-layer composed thick-wall cylinder, this paper [...] Read more.
The significant decreased wellbore temperature and increased casing pressure during fracturing fluid injection present a big challenge for the mechanical integrity of cement sheath in fracturing wells. Based on the theories of elastic mechanics, thermodynamics, and a multi-layer composed thick-wall cylinder, this paper proposed a new mechanical model of cement sheath for fracturing wells, coupling pressure, and thermal loads, which consider the failure modes of de-bonding, radial cracking, disking, and shear failure. The radial nonuniform temperature change and the continuous radial stress and radial displacement at two interfaces have been considered. With the proposed model, the radial distributions of failure stress and the corresponding safety factor for cement sheath during fracturing fluid injection have been analyzed and compared under four failure modes. Results show that the decreased wellbore temperature will produce significant tri-axial tensile stress and induce cement failure of de-bonding, radial cracking, and disking. The increased casing pressure will significantly lower the risk of de-bonding but also aggravate radial cracking and shear failure. For integrity protection of cement sheath, increasing the injected fluid temperature, maintaining higher circulation pumping pressures, and adopting cement sheath with a low elasticity modulus have been suggested for fracturing wells. Full article
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Open AccessArticle
AC Breakdown Characteristics of c-C4F8/N2 Gas Mixtures in an Extremely Non-Uniform Electric Field
Energies 2018, 11(12), 3533; https://doi.org/10.3390/en11123533 - 19 Dec 2018
Viewed by 605
Abstract
Octafluorocyclobutane (c-C4F8) is one of the environmentally friendly gases with the potential to replace SF6. In this paper, the AC breakdown characteristics of c-C4F8/N2 mixture in an extremely non-uniform electric field were [...] Read more.
Octafluorocyclobutane (c-C4F8) is one of the environmentally friendly gases with the potential to replace SF6. In this paper, the AC breakdown characteristics of c-C4F8/N2 mixture in an extremely non-uniform electric field were studied; the effects of the gas pressure, electrode distance, and c-C4F8 volume fraction on the breakdown voltage were analyzed; and the feasibility of replacing SF6 with c-C4F8/N2 was verified. The results show that the breakdown voltage of c-C4F8 /N2 increases with an increase in pressure, electrode spacing, and volume fraction of c-C4F8 in an extremely non-uniform electric field. Under the same conditions, the breakdown voltage of 20%c-C4F8/80%N2 is 46–90% that of 20%SF6/80%N2. When the pressure is 0.3 MPa, the 20%c-C4F8/80%N2 breakdown voltage can reach over 57% that of SF6. Taking into consideration the environment, liquefaction temperature, and insulation strength, 20%c-C4F8/80%N2 may replace SF6 used for medium- and low-voltage equipment. Full article
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Open AccessArticle
Key Development Factors of Hydrothermal Processes in Germany by 2030: A Fuzzy Logic Analysis
Energies 2018, 11(12), 3532; https://doi.org/10.3390/en11123532 - 19 Dec 2018
Viewed by 642
Abstract
To increase resource efficiency, it is necessary to use biogenic residues in the most efficient and value-enhancing manner. For high water-containing biomass, hydrothermal processes (HTP) are particularly promising as they require wet conditions for optimal processing anyway. In Germany, however, HTP have not [...] Read more.
To increase resource efficiency, it is necessary to use biogenic residues in the most efficient and value-enhancing manner. For high water-containing biomass, hydrothermal processes (HTP) are particularly promising as they require wet conditions for optimal processing anyway. In Germany, however, HTP have not yet reached the industrial level, although suitable substrates are available and technological progress has been made in previous years. This study aims to determine why this is by identifying key factors that need to occur HTP development in Germany until 2030. By using results of previous analyses within this context (i.e., literature review, SWOT analysis, expert survey, and focus group workshop) and combining them with the results of an expert workshop and Delphi-survey executed during this analysis, a comprehensive information basis on important development factors is created. Fuzzy logic is used to analyze these factors in terms of interconnections, relevance, and probability of occurrence by 2030. The results show that technological factors, such as a cost-efficient process water treatment and increased system integration of HTP into bio-waste and wastewater treatment plants, are given high relevance and probability of occurrence. The adaptation of the legal framework, for example, the approval of end products from HTP as standard fuels, has very high relevance but such adaptions are considered relatively unlikely. Full article
(This article belongs to the Special Issue Hydrothermal Technology in Biomass Utilization & Conversion)
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Open AccessArticle
New DC Grid Power Line Communication Technology Used in Networked LED Driver
Energies 2018, 11(12), 3531; https://doi.org/10.3390/en11123531 - 18 Dec 2018
Viewed by 902
Abstract
In order to reduce the cost and improve the reliability, real-time performance, and installation convenience of remote-controlled light-emitting diode (LED) lighting systems, a networked LED driving technology based on the direct current (DC) grid power line carrier is proposed. In this system, an [...] Read more.
In order to reduce the cost and improve the reliability, real-time performance, and installation convenience of remote-controlled light-emitting diode (LED) lighting systems, a networked LED driving technology based on the direct current (DC) grid power line carrier is proposed. In this system, an alternating current (AC)/DC bus converter converts the mains into a DC bus with multiple distributed LED drive powers on the DC bus. The AC/DC bus converter receives the user’s control command and modulates it into the DC bus voltage. The DC bus waveform changes to a square wave containing the high and low changes of the address information and command information. The LED drive power of the corresponding address receives energy from the DC bus and demodulates the commands, such as turning the lights on and off, dimming, etc., and performs the action. In order to make the waveform of the AC/DC bus converter have better rising and falling edge, this paper adopts the half-bridge topology with variable modal control. In the modulation process, the circuit works in buck mode and boost mode. Distributed LED drivers have DC/DC circuits and very simple demodulation circuits that dissipate energy and information from the DC bus. Through experiments, the technology not only simplifies the use of communication technology in application, but also reduces the application difficulty. Full article
(This article belongs to the Special Issue Design and Control of Power Converters)
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Open AccessArticle
Computational Fluid Dynamic Modelling and Optimisation of Wastewater Treatment Plant Bioreactor Mixer
Energies 2018, 11(12), 3530; https://doi.org/10.3390/en11123530 - 18 Dec 2018
Viewed by 628
Abstract
This study aims to determine the optimal configuration (position and operation duration) for wall mounted mechanical mixers based on the comparison of three-dimensional computational fluid dynamics (CFD) modelling results and physical data collected from the treatment plant. A three dimensional model of anoxic [...] Read more.
This study aims to determine the optimal configuration (position and operation duration) for wall mounted mechanical mixers based on the comparison of three-dimensional computational fluid dynamics (CFD) modelling results and physical data collected from the treatment plant. A three dimensional model of anoxic zone in 1, 2 and 3 of Northern Wastewater Treatment Plant (NWWTP) located at Cairns Regional Council, Cairns, Queensland, Australia was developed and validated. The model was used to simulate the flow pattern of the WWTP and the simulation results are in good agreement with the physical data varying between 0% to 15% in key locations. The anoxic zones were subject to velocities less than the desired 0.3 m per second however results for mixed liquor suspended solids (MLSS) concentration indicate that good mixing is being achieved. Results for suspended solids concentrations suggest that the anoxic zones are towards the upper limits recommended by literature for specific power dissipation. The duration for operation of mechanical mixers was investigated and identified that the duration could be reduced from 900 s down to 150 s. Alternative mixer positioning was also investigated and identified positioning which would increase the average flow velocity with decreased duration (150 s). The study identified that Council may achieve savings of $28,500 per year through optimisation of the mechanical mixers and would be expected to extend the operational life of the mixers. Full article
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Open AccessArticle
Evaluation of the Adaptability of the Ukrainian Economy to Changes in Prices for Energy Carriers and to Energy Market Risks
Energies 2018, 11(12), 3529; https://doi.org/10.3390/en11123529 - 18 Dec 2018
Viewed by 1584
Abstract
The methodological framework for assessing adaptability of the economy to changes in energy prices and risks to energy markets was developed. The study proposes indicators for assessing the level of adaptability of the economic sectors to changes in prices for energy carriers and [...] Read more.
The methodological framework for assessing adaptability of the economy to changes in energy prices and risks to energy markets was developed. The study proposes indicators for assessing the level of adaptability of the economic sectors to changes in prices for energy carriers and to risks of energy markets. The model of decomposition of adaptability level of the economy sectors to changes in energy prices has been developed. The theoretical and empirical analysis of the influence of energy prices on adaptability level of enterprises and households is carried out. Based on the empirical analysis, it was found that adaptability level of the sectors of Ukrainian economy significantly differs both in the years of the investigated period and in sectors of the economy. At the same time, most indicators of the level of adaptability vary from 0.4 to 0.7. Consequently, the actual decline in the profit of enterprises was 40–70% lower than the potentially possible decrease in the profit of these enterprises due to the prices rising for energy carriers. Moreover sectors which are less vulnerable to the growth of prices show higher adaptability level.The possibility of using the obtained results in developing a state energy saving strategy is substantiated. Full article
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Open AccessArticle
Adaptive Backstepping Control with Online Parameter Estimator for a Plug-and-Play Parallel Converter System in a Power Switcher
Energies 2018, 11(12), 3528; https://doi.org/10.3390/en11123528 - 18 Dec 2018
Cited by 1 | Viewed by 605
Abstract
This study aims to address the inherent uncertainty in plug loads and load extraction, distributed generation, and the inevitable circulating current in a parallel structure. Therefore, in this paper, an adaptive backstepping control scheme with an online parameter estimator (OPE) for a plug-and-play [...] Read more.
This study aims to address the inherent uncertainty in plug loads and load extraction, distributed generation, and the inevitable circulating current in a parallel structure. Therefore, in this paper, an adaptive backstepping control scheme with an online parameter estimator (OPE) for a plug-and-play parallel converter system in a four-port power switcher is proposed. The adaptive backstepping control method was designed in the dq0 coordinate system to suppress the circulating current in the zero-component; the circulating current can be suppressed by using an embedded algorithm and omitting the extra controller. An adaptive update law was designed to weaken the influence of the arbitrary plug and extraction operations in the DC and AC buses to realize the plug-and-play function. The transient tracking performance is governed by the limitation of maximum total errors in the voltage and current. As a result, the settling times of the voltage, current, and power decreased. Additionally, to further improve the system robustness, an online inductance and resistance estimator was established using an optimal algorithm that solves the weighted least squares problem. In the estimator, there are no additional voltage and current sensors needed, and the mean squared error (MSE) of the estimation can be minimized. Simulation studies on a two-converter parallel system with a plug-and-play function were conducted using MATLAB/SIMULINK (R2018b, MathWorks, Natick, MA, USA) to verify the effectiveness of the proposed adaptive backstepping control strategy. The results show that this strategy improves system performance over that of a system with unbalanced parameters among a parallel structure with AC and DC system disturbances caused by arbitrary plug and extraction operations. Full article
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Open AccessArticle
Two-Stage Stochastic Optimization for the Strategic Bidding of a Generation Company Considering Wind Power Uncertainty
Energies 2018, 11(12), 3527; https://doi.org/10.3390/en11123527 - 18 Dec 2018
Cited by 1 | Viewed by 533
Abstract
With the deregulation of electricity market, generation companies must take part in strategic bidding by offering its bidding quantity and bidding price in a day-ahead electricity wholesale market to sell their electricity. This paper studies the strategic bidding of a generation company with [...] Read more.
With the deregulation of electricity market, generation companies must take part in strategic bidding by offering its bidding quantity and bidding price in a day-ahead electricity wholesale market to sell their electricity. This paper studies the strategic bidding of a generation company with thermal power units and wind farms. This company is assumed to be a price-maker, which indicates that its installed capacity is high enough to affect the market-clearing price in the electricity wholesale market. The relationship between the bidding quantity of the generation company and market-clearing price is then studied. The uncertainty of wind power is considered and modeled through a set of discrete scenarios. A scenario-based two-stage stochastic bidding model is then provided. In the first stage, the decision-maker determines the bidding quantity in each time period. In the second stage, the decision-maker optimizes the unit commitment in each wind power scenario based on the bidding quantity in the first stage. The proposed two-stage stochastic optimization model is an NP-hard problem with high dimensions. To tackle the problem of “curses-of-dimensionality” caused by the coupling scenarios and improve the computation efficiency, a modified Benders decomposition algorithm is used to solve the model. The computational results show the following: (1) When wind power uncertainty is considered, generation companies prefer higher bidding quantities since the loss of wind power curtailment is much higher than the cost of additional power purchases in the current policy environment. (2) The wind power volatility has a strong negative effect on generation companies. The higher the power volatility is, the lower the profits, the bidding quantities, and the wind power curtailment of generation companies are. (3) The thermal power units play an important role in dealing with the wind power uncertainty in the strategic bidding problem, by shaving peak and filling valley probabilistic scheduling. Full article
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Open AccessArticle
Solving the Energy Efficient Coverage Problem in Wireless Sensor Networks: A Distributed Genetic Algorithm Approach with Hierarchical Fitness Evaluation
Energies 2018, 11(12), 3526; https://doi.org/10.3390/en11123526 - 18 Dec 2018
Cited by 3 | Viewed by 618
Abstract
This paper proposed a distributed genetic algorithm (DGA) to solve the energy efficient coverage (EEC) problem in the wireless sensor networks (WSN). Due to the fact that the EEC problem is Non-deterministic Polynomial-Complete (NPC) and time-consuming, it is wise to use a nature-inspired [...] Read more.
This paper proposed a distributed genetic algorithm (DGA) to solve the energy efficient coverage (EEC) problem in the wireless sensor networks (WSN). Due to the fact that the EEC problem is Non-deterministic Polynomial-Complete (NPC) and time-consuming, it is wise to use a nature-inspired meta-heuristic DGA approach to tackle this problem. The novelties and advantages in designing our approach and in modeling the EEC problems are as the following two aspects. Firstly, in the algorithm design, we realized DGA in the multi-processor distributed environment, where a set of processors run distributed to evaluate the fitness values in parallel to reduce the computational cost. Secondly, when we evaluate a chromosome, different from the traditional model of EEC problem in WSN that only calculates the number of disjoint sets, we proposed a hierarchical fitness evaluation and constructed a two-level fitness function to count the number of disjoint sets and the coverage performance of all the disjoint sets. Therefore, not only do we have the innovations in algorithm, but also have the contributions on the model of EEC problem in WSN. The experimental results show that our proposed DGA performs better than other state-of-the-art approaches in maximizing the number of disjoin sets. Full article
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Open AccessArticle
Wind Power Monitoring and Control Based on Synchrophasor Measurement Data Mining
Energies 2018, 11(12), 3525; https://doi.org/10.3390/en11123525 - 18 Dec 2018
Cited by 4 | Viewed by 647
Abstract
More and more countries and utilities are trying to develop smart grid projects to make transformation of their power infrastructure towards future grids with increased share of renewable energy production and near zero emissions. The intermittent nature of solar and wind power can [...] Read more.
More and more countries and utilities are trying to develop smart grid projects to make transformation of their power infrastructure towards future grids with increased share of renewable energy production and near zero emissions. The intermittent nature of solar and wind power can in general cause large problems for power system control. Parallel to this process, the aging of existing infrastructure also imposes requirements to utility budgets in the form of a need for large capital investments in reconstruction or maintenance of key equipment. Synchrophasor and other synchronized measurement technologies are setting themselves as one of the solutions for larger wind power integration. With that aim, in this paper one possible solution for wind power control through data mining algorithms used on a large quantity of data gathered from phasor measurement units (PMU) is described. Developed model and algorithm are tested on an IEEE 14 bus test system as well as on real measurements made on wind power plants currently in operation. One such wind power plant is connected to the distribution grid and the other one to the transmission grid. Results are analyzed and compared. Full article
(This article belongs to the Special Issue Methods and Concepts for Designing and Validating Smart Grid Systems)
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Open AccessArticle
A Highly Efficient Single-Phase Three-Level Neutral Point Clamped (NPC) Converter Based on Predictive Control with Reduced Number of Commutations
Energies 2018, 11(12), 3524; https://doi.org/10.3390/en11123524 - 18 Dec 2018
Cited by 3 | Viewed by 820
Abstract
This paper proposes a highly efficient single-phase three-level neutral point clamped (NPC) converter operated by a model predictive control (MPC) method with reduced commutations of switches. The proposed method only allows switching states with none or a single commutation at the next step [...] Read more.
This paper proposes a highly efficient single-phase three-level neutral point clamped (NPC) converter operated by a model predictive control (MPC) method with reduced commutations of switches. The proposed method only allows switching states with none or a single commutation at the next step as candidates for future switching states for the MPC method. Because the proposed method preselects switching states with reduced commutations when selecting an optimal state at a future step, the proposed method can reduce the number of switchings and the corresponding switching losses. Although the proposed method slightly increases the peak-to-peak variations of the two dc capacitor voltages, the developed method does not deteriorate the input current quality and input power factor despite the reduced number of switching numbers and losses. Thus, the proposed method can reduce the number of switching losses and lead to high efficiency, in comparison with the conventional MPC method. Full article
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Open AccessArticle
Renewable and Sustainable Energy Transitions for Countries with Different Climates and Renewable Energy Sources Potentials
Energies 2018, 11(12), 3523; https://doi.org/10.3390/en11123523 - 18 Dec 2018
Cited by 2 | Viewed by 647
Abstract
Renewable energy sources (RES) are playing an increasingly important role in energy markets around the world. It is necessary to evaluate the benefits from a higher level of RES integration with respect to a more active cross-border transmission system. In particular, this paper [...] Read more.
Renewable energy sources (RES) are playing an increasingly important role in energy markets around the world. It is necessary to evaluate the benefits from a higher level of RES integration with respect to a more active cross-border transmission system. In particular, this paper focuses on the sustainable energy transitions for Finland and Italy, since they have two extreme climate conditions in Europe and quite different profiles in terms of energy production and demand. We developed a comprehensive energy system model using EnergyPLAN with hourly resolution for a reference year for both countries. The models include electricity, heat and transportation sectors. According to the current base models, new scenarios reflecting an RES increase in total fuel consumption have been proposed. The future shares of renewables are based on each nation’s potential. The outcomes of the new scenarios support the future national plans, showing how decarburization in an energy system can occur in relation to the European Roadmap 2030 and 2050. In addition, possible power transmission between Italy and Finland were investigated according to the vision of an integrated European energy system with more efficient cross-border activities. Full article
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Open AccessArticle
Optimization of Wave Energy Converter Arrays by an Improved Differential Evolution Algorithm
Energies 2018, 11(12), 3522; https://doi.org/10.3390/en11123522 - 18 Dec 2018
Viewed by 606
Abstract
Since different incident waves will cause the same array to perform differently with respect to the wave energy converter (WEC), the parameters of the incident wave, including the incident angle and the incident wave number, are taken into account for optimizing the [...] Read more.
Since different incident waves will cause the same array to perform differently with respect to the wave energy converter (WEC), the parameters of the incident wave, including the incident angle and the incident wave number, are taken into account for optimizing the wave energy converter array. Then, the differential evolution (DE) algorithm, which has the advantages of simple operation procedures and a strong global search ability, is used to optimize the wave energy converter array. However, the traditional differential evolution algorithm cannot satisfy the convergence precision and speed simultaneously. In order to make the optimization results more accurate, the concept of an adaptive mutation operator is presented to improve the performance of differential evolution algorithm. It gives the improved algorithm a faster convergence and a higher precision ability. The three-float, five-float, and eight-float arrays were optimized, respectively. It can be concluded that the larger the size of the array is, the greater the interaction between the floats is. Hence, a higher efficiency of wave energy extraction for wave energy converter arrays is achieved by the layout optimization of the array of wave energy converters. The results also show that the optimal layout of the array system is inhomogeneously distributed and that the improved DE algorithm used on array optimization is superior to the traditional DE algorithm. Full article
(This article belongs to the Section Sustainable Energy)
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Open AccessFeature PaperArticle
Comprehensive Thermodynamic Analysis of the Humphrey Cycle for Gas Turbines with Pressure Gain Combustion
Energies 2018, 11(12), 3521; https://doi.org/10.3390/en11123521 - 18 Dec 2018
Cited by 3 | Viewed by 1020
Abstract
Conventional gas turbines are approaching their efficiency limits and performance gains are becoming increasingly difficult to achieve. Pressure Gain Combustion (PGC) has emerged as a very promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine [...] Read more.
Conventional gas turbines are approaching their efficiency limits and performance gains are becoming increasingly difficult to achieve. Pressure Gain Combustion (PGC) has emerged as a very promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine thermodynamic cycles. Up to date, only very simplified models of open cycle gas turbines with pressure gain combustion have been considered. However, the integration of a fundamentally different combustion technology will be inherently connected with additional losses. Entropy generation in the combustion process, combustor inlet pressure loss (a central issue for pressure gain combustors), and the impact of PGC on the secondary air system (especially blade cooling) are all very important parameters that have been neglected. The current work uses the Humphrey cycle in an attempt to address all these issues in order to provide gas turbine component designers with benchmark efficiency values for individual components of gas turbines with PGC. The analysis concludes with some recommendations for the best strategy to integrate turbine expanders with PGC combustors. This is done from a purely thermodynamic point of view, again with the goal to deliver design benchmark values for a more realistic interpretation of the cycle. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle
Smart Meter Forecasting from One Minute to One Year Horizons
Energies 2018, 11(12), 3520; https://doi.org/10.3390/en11123520 - 18 Dec 2018
Cited by 3 | Viewed by 669
Abstract
The ability to predict consumption is an essential tool for the management of a power distribution network. The availability of an advanced metering infrastructure through smart meters makes it possible to produce consumption forecasts down to the level of the individual user and [...] Read more.
The ability to predict consumption is an essential tool for the management of a power distribution network. The availability of an advanced metering infrastructure through smart meters makes it possible to produce consumption forecasts down to the level of the individual user and to introduce intelligence and control at every level of the grid. While aggregate load forecasting is a mature technology, single user forecasting is a more difficult problem to address due to the multiple factors affecting consumption, which are not always easily predictable. This work presents a hybrid machine learning methodology based on random forest (RF) and linear regression (LR) for the deterministic and probabilistic forecast of household consumption at different time horizons and resolutions. The approach is based on the separation of long term effects (RF) from short term ones (LR), producing deterministic and probabilistic forecasts. The proposed procedure is applied to a public dataset, achieving a deterministic forecast accuracy much higher than other methodologies, in all scenarios analyzed. This covers horizons of forecast from one minute to one year, and highlights the great added value provided by probabilistic forecasting. Full article
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Open AccessArticle
An Adaptive Approach for Voltage Sag Automatic Segmentation
Energies 2018, 11(12), 3519; https://doi.org/10.3390/en11123519 - 17 Dec 2018
Cited by 1 | Viewed by 522
Abstract
Voltage sag characterization is essential for extracting information about a sag event’s origin and how sag events impact sensitive equipment. In response to such needs, more characteristics are required, such as the phase-angle jump, point-on-wave, unbalance, and sag type. However, the absence of [...] Read more.
Voltage sag characterization is essential for extracting information about a sag event’s origin and how sag events impact sensitive equipment. In response to such needs, more characteristics are required, such as the phase-angle jump, point-on-wave, unbalance, and sag type. However, the absence of an effective automatic segmentation method is a barrier to obtaining these characteristics. In this paper, an automatic segmentation method is proposed to improve this situation. Firstly, an extended voltage sag characterization method is described, in which segmentation plays an important role. Then, a multi-resolution singular value decomposition method is introduced to detect the boundaries of each segment. Further, the unsolved problem of how to set a threshold adaptively for different waveforms is addressed, in which the sag depth, the mean square error, and the entropy of the sag waveform are considered. Simulation data and field measurements are utilized to validate the effectiveness and reliability of the proposed method. The results show that the accuracies of both boundary detection and segmentation obtained using the proposed method are higher than those obtained using existing methods. In general, the proposed method can be implemented into a power quality monitoring system as a preprocess to support related research activities. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle
An Experimental Study of Combustion of a Methane Hydrate Layer Using Thermal Imaging and Particle Tracking Velocimetry Methods
Energies 2018, 11(12), 3518; https://doi.org/10.3390/en11123518 - 17 Dec 2018
Cited by 2 | Viewed by 702
Abstract
In this paper, the combustion of methane hydrate over a powder layer is experimentally studied using thermal imaging and Particle Tracking Velocimetry (PTV) methods. The experiments are carried out at different velocities of the external laminar air-flow from zero to 0.6 m/s. Usually, [...] Read more.
In this paper, the combustion of methane hydrate over a powder layer is experimentally studied using thermal imaging and Particle Tracking Velocimetry (PTV) methods. The experiments are carried out at different velocities of the external laminar air-flow from zero to 0.6 m/s. Usually, simulation of methane hydrate combustion is carried out without taking into account free convection. A standard laminar boundary layer is often considered for simplification, and the temperature measurements are carried out only on the axis of the powder tank. Measurements of the powder temperature field have shown that there is a highly uneven temperature field on the layer surface, and inside the layer the transverse temperature profiles are nonlinear. The maximum temperature always corresponds to the powder near the side-walls, which is more than 10 °C higher than the average volumetric temperature in the layer. Thermal imager measurements have shown the inhomogeneous nature of combustion over the powder surface and the highly variable velocity of methane above the surface layer. The novelty of the research follows from the measurement of the velocity field using the PTV method and the measurement of methane velocity, which show that the nature of velocity at combustion is determined by the gas buoyancy rather than by the forced convection. The maximum gas velocity in the combustion region exceeds 3 m/s, and the excess of the oxidizer over the fuel leads to more than tenfold violation of the stoichiometric ratio. Despite that, the velocity profile in the combustion region is formed mainly due to free convection, it is also necessary to take into account the external flow of the forced gas U0. Even at low velocities U0, the velocity direction lines significantly deviate under the forced air-flow. Full article
(This article belongs to the Special Issue Sustainability of Fossil Fuels) Printed Edition available
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Open AccessArticle
Position Sensorless Control of Switched Reluctance Motor with Consideration of Magnetic Saturation Based on Phase-Inductance Intersection Points Information
Energies 2018, 11(12), 3517; https://doi.org/10.3390/en11123517 - 17 Dec 2018
Viewed by 570
Abstract
The precise estimation of position is an essential concern for the control of a switched reluctance motor (SRM). Given the prominent role of position, the promising sensorless control approach for an SRM drive should be capable of providing accurate position. An inductance-based approach [...] Read more.
The precise estimation of position is an essential concern for the control of a switched reluctance motor (SRM). Given the prominent role of position, the promising sensorless control approach for an SRM drive should be capable of providing accurate position. An inductance-based approach has been widely applied in the position estimation. However, the estimated accuracy suffers from the magnetic saturation effect, resulting in the poor performance of sensorless operation. This paper presents a reversible synchronization of commutation with the corresponding rotor position for SRM. With the consideration of magnetic saturation, the proposed approach is taken as a suitable candidate and plays an essential role in accommodating the requirement of optimal control. The relationship between a typical inductance position and magnetic circuit saturation is investigated. The instant of the intersections is sensed by comparing the instantaneous inductance of adjacent phases. Thus, the predicted position is obtained with the information of the special point and the calculated average speed. Compared with other existing methods, the proposed approach has the certain advantages, such as the ability to update the estimated speed and position six times per electrical period, which guarantees the estimated accuracy. The proposed approach is also valid even when the motor is operated at an acceleration state and heavy load operation. In addition, the requirement of the educated inductance structure is not unnecessary, less memory space is needed in the chip, and the accumulated error is eliminated. The simulation and experimental findings demonstrate the feasibility and practicality of the proposed position estimation approach with carrying out the inertial operation, load mutation, and high-speed test. Full article
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Open AccessArticle
Real-Time Implementation of High Performance Control Scheme for Grid-Tied PV System for Power Quality Enhancement Based on MPPC-SVM Optimized by PSO Algorithm
Energies 2018, 11(12), 3516; https://doi.org/10.3390/en11123516 - 17 Dec 2018
Cited by 2 | Viewed by 772
Abstract
This paper proposes a high performance control scheme for a double function grid-tied double-stage PV system. It is based on model predictive power control with space vector modulation. This strategy uses a discrete model of the system based on the time domain to [...] Read more.
This paper proposes a high performance control scheme for a double function grid-tied double-stage PV system. It is based on model predictive power control with space vector modulation. This strategy uses a discrete model of the system based on the time domain to generate the average voltage vector at each sampling period, with the aim of canceling the errors between the estimated active and reactive power values and their references. Also, it imposes a sinusoidal waveform of the current at the grid side, which allows active power filtering without a harmonic currents identification phase. The latter attempts to reduce the size and cost of the system as well as providing better performance. In addition, it can be implemented in a low-cost control platform due to its simplicity. A double-stage PV system is selected due to its flexibility in control, unlike single-stage strategies. Sliding mode control-based particle swarm optimization (PSO) is used to track the maximum power of the PV system. It offers high accuracy and good robustness. Concerning DC bus voltage of the inverter, the anti-windup PI controller is tuned offline using the particle swarm optimization algorithm to deliver optimal performance in DC bus voltage regulation. The overall system has been designed and validated in an experimental prototype; the obtained results in different phases demonstrate the higher performance and the better efficiency of the proposed system in terms of power quality enhancement and PV power injection. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle
Hydrodynamic Conjunction of Textured Journal Surface—Bearing for Improved Frictional Response during Warm-Up of an Internal Combustion Engine
Energies 2018, 11(12), 3515; https://doi.org/10.3390/en11123515 - 17 Dec 2018
Viewed by 559
Abstract
Considerable prime global energy is used in the transport sector. Significant energy is lost to overcome the internal friction of engines in transport vehicles. Journal bearings are crucial tribo-pairs and passive components that cause energy loss. Frictional losses increase extensively during the warm-up [...] Read more.
Considerable prime global energy is used in the transport sector. Significant energy is lost to overcome the internal friction of engines in transport vehicles. Journal bearings are crucial tribo-pairs and passive components that cause energy loss. Frictional losses increase extensively during the warm-up period of an engine due to high lubricant viscosity. Recent tribological developments have shown that surface textures can be a potential solution to reduce friction. A numerical investigation is performed to evaluate the effect of surface texture on the frictional and lubrication performance of a journal bearing at varying thermal operating conditions in an internal combustion engine. Temperature variations during engine warm-up are considered with oil rheology to observe texture-based improvements. Surface texture substantially reduces frictional energy loss during engine warm-up. Eight different monograde and multigrade engine oils are considered, and consistency is observed in texture-based improved outcomes. Full article
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Open AccessArticle
Effect of Accelerated High Temperature on Oxidation and Polymerization of Biodiesel from Vegetable Oils
Energies 2018, 11(12), 3514; https://doi.org/10.3390/en11123514 - 17 Dec 2018
Cited by 1 | Viewed by 725
Abstract
Oxidation of biodiesel (BD) obtained from the decomposition of biomass can damage the fuel injection and engine parts during its use as a fuel. The excess heating of vegetable oils can also cause polymerization of the biodiesel. The extent of BD oxidation depends [...] Read more.
Oxidation of biodiesel (BD) obtained from the decomposition of biomass can damage the fuel injection and engine parts during its use as a fuel. The excess heating of vegetable oils can also cause polymerization of the biodiesel. The extent of BD oxidation depends on its fatty acid composition. In this study, an accelerated oxidation test of BDs at 95 °C was investigated according to ASTM D 2274 by applying a long-term storage test for 16 weeks. The density, viscosity, and total acid number (TAN) of BDs increased because of the accelerated oxidation. Furthermore, the contents of unsaturated fatty acid methyl esters (FAMEs), C18:2 ME, and C18:3 ME in BDs decreased due to the accelerated oxidation. The 1H-nuclear magnetic resonance spectrum of BDs that were obtained from the accelerated high temperature oxidation at 180 °C for 72 h differed from that of fresh BDs. The mass spectrum obtained from the analysis of the model FAME, linoleic acid (C18:2) methyl ester, which was oxidized at high temperature, indicated the formation of dimers and epoxy dimers of linoleic acid (C18:2) methyl ester by a Diels-Alder reaction. Full article
(This article belongs to the Special Issue Biomass Processing for Biofuels, Bioenergy and Chemicals)
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Open AccessArticle
Luminescent Electrochromic Devices for Smart Windows of Energy-Efficient Buildings
Energies 2018, 11(12), 3513; https://doi.org/10.3390/en11123513 - 17 Dec 2018
Cited by 2 | Viewed by 792
Abstract
To address the challenges of the next generation of smart windows for energy-efficient buildings, new electrochromic devices (ECDs) are introduced. These include indium molybdenum oxide (IMO), a conducting oxide transparent in the near-infrared (NIR) region, and a NIR-emitting electrolyte. The novel electrolytes are [...] Read more.
To address the challenges of the next generation of smart windows for energy-efficient buildings, new electrochromic devices (ECDs) are introduced. These include indium molybdenum oxide (IMO), a conducting oxide transparent in the near-infrared (NIR) region, and a NIR-emitting electrolyte. The novel electrolytes are based on a sol-gel-derived di-urethane cross-linked siloxane-based host structure, including short chains of poly (ε-caprolactone) (PCL(530) (where 530 represents the average molecular weight in g mol−1). This hybrid framework was doped with a combination of either, lithium triflate (LiTrif) and erbium triflate (ErTrif3), or LiTrif and bisaquatris (thenoyltrifluoroacetonate) erbium (III) ([Er(tta)3(H2O)2]). The [email protected][Er(tta)3(H2O)2] device presents a typical Er3+ NIR emission around 1550 nm. The figures of merit of these devices are high cycling stability, good reversibility, and unusually high coloration efficiency (CE = ΔOD/ΔQ, where Q is the inserted/de-inserted charge density). CE values of −8824/+6569 cm2 C−1 and −8243/+5200 cm2 C−1 were achieved at 555 nm on the 400th cycle, for [email protected]3 and [email protected][Er(tta)3(H2O)2], respectively. Full article
(This article belongs to the Special Issue Building-Integrated Photovoltaics/Luminescent Solar Concentrators)
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Open AccessFeature PaperArticle
A Decentralized, Hybrid Photovoltaic-Solid Oxide Fuel Cell System for Application to a Commercial Building
Energies 2018, 11(12), 3512; https://doi.org/10.3390/en11123512 - 16 Dec 2018
Cited by 2 | Viewed by 1030
Abstract
New energy solutions are needed to decrease the currently high electricity costs from conventional electricity-only central power plants in Cyprus. A promising solution is a decentralized, hybrid photovoltaic-solid oxide fuel cell (PV-SOFC) system. In this study a decentralized, hybrid PV-SOFC system is investigated [...] Read more.
New energy solutions are needed to decrease the currently high electricity costs from conventional electricity-only central power plants in Cyprus. A promising solution is a decentralized, hybrid photovoltaic-solid oxide fuel cell (PV-SOFC) system. In this study a decentralized, hybrid PV-SOFC system is investigated as a solution for useful energy supply to a commercial building (small hotel). An actual load profile and solar/weather data are fed to the system model to determine the thermoeconomic characteristics of the proposed system. The maximum power outputs for the PV and SOFC subsystems are 70 and 152 kWe, respectively. The average net electrical and total efficiencies for the SOFC subsystem are 0.303 and 0.700, respectively. Maximum net electrical and total efficiencies reach up to 0.375 and 0.756, respectively. The lifecycle cost for the system is 1.24 million USD, with a unit cost of electricity at 0.1057 USD/kWh. In comparison to the conventional case, the unit cost of electricity is about 50% lower, while the reduction in CO2 emissions is about 36%. The proposed system is capable of power and heat generation at a lower cost, owing to the recent progress in both PV and fuel cell technologies, namely longer lifetime and lower specific cost. Full article
(This article belongs to the Special Issue Alternative Sources of Energy Modeling and Automation)
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Open AccessArticle
Life-Cycle Cost Minimization of Gas Turbine Power Cycles for Distributed Power Generation Using Sequential Quadratic Programming Method
Energies 2018, 11(12), 3511; https://doi.org/10.3390/en11123511 - 16 Dec 2018
Viewed by 749
Abstract
The life-cycle cost reduction of medium-class gas turbine power plants was investigated using the mathematical optimization technique. Three different types of gas turbine power cycles—a simple cycle, a regenerative cycle, and a combined cycle—were examined, and their optimal design conditions were determined using [...] Read more.
The life-cycle cost reduction of medium-class gas turbine power plants was investigated using the mathematical optimization technique. Three different types of gas turbine power cycles—a simple cycle, a regenerative cycle, and a combined cycle—were examined, and their optimal design conditions were determined using the sequential quadratic programming (SQP) technique. As a modeling reference, the Siemens SGT-700 gas turbine was chosen and its technical data were used for system simulation and validation. Through optimization using the SQP method, the overall costs of the simple cycle, regenerative cycle, and combined cycle were reduced by 7.4%, 12.0%, and 3.9%, respectively, compared to the cost of the base cases. To examine the effect of economic parameters on the optimal design condition and cost, different values of fuel costs, interest rates, and discount rates were applied to the cost calculation, and the optimization results were analyzed and compared. The values were chosen to reflect different countries’ economic situations: South Korea, China, India, and Indonesia. For South Korea and China, the optimal design condition is proposed near the upper bound of the variation range, implying that the efficiency improvement plays an important role in cost reduction. For India and Indonesia, the optimal condition is proposed in the middle of the variation ranges. Even for India and Indonesia, the fuel cost has the largest contribution to the total cost, accounting for more than 60%. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle
An LM-BP Neural Network Approach to Estimate Monthly-Mean Daily Global Solar Radiation Using MODIS Atmospheric Products
Energies 2018, 11(12), 3510; https://doi.org/10.3390/en11123510 - 16 Dec 2018
Cited by 2 | Viewed by 806
Abstract
Solar energy is one of the most widely used renewable energy sources in the world and its development and utilization are being integrated into people’s lives. Therefore, accurate solar radiation data are of great significance for site-selection of photovoltaic (PV) power generation, design [...] Read more.
Solar energy is one of the most widely used renewable energy sources in the world and its development and utilization are being integrated into people’s lives. Therefore, accurate solar radiation data are of great significance for site-selection of photovoltaic (PV) power generation, design of solar furnaces and energy-efficient buildings. Practically, it is challenging to get accurate solar radiation data because of scarce and uneven distribution of ground-based observation sites throughout the country. Many artificial neural network (ANN) estimation models are therefore developed to estimate solar radiation, but the existing ANN models are mostly based on conventional meteorological data; clouds, aerosols, and water vapor are rarely considered because of a lack of instrumental observations at the conventional meteorological stations. Based on clouds, aerosols, and precipitable water-vapor data from Moderate Resolution Imaging Spectroradiometer (MODIS), along with conventional meteorological data, back-propagation (BP) neural network method was developed in this work with Levenberg-Marquardt (LM) algorithm (referred to as LM-BP) to simulate monthly-mean daily global solar radiation (M-GSR). Comparisons were carried out among three M-GSR estimates, including the one presented in this study, the multiple linear regression (MLR) model, and remotely-sensed radiation products by Cloud and the Earth’s radiation energy system (CERES). The validation results indicate that the accuracy of the ANN model is better than that of the MLR model and CERES radiation products, with a root mean squared error (RMSE) of 1.34 MJ·m−2 (ANN), 2.46 MJ·m−2 (MLR), 2.11 MJ·m−2 (CERES), respectively. Finally, according to the established ANN-based method, the M-GSR of 36 conventional meteorological stations for 12 months was estimated in 2012 in the study area. Solar radiation data based on the LM-BP method of this study can provide some reference for the utilization of solar and heat energy. Full article
(This article belongs to the Special Issue Solar and Wind Energy Forecasting)
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Open AccessArticle
On a Roadmap for Future Industrial Nuclear Reactor Core Simulation in the U.K. to Support the Nuclear Renaissance
Energies 2018, 11(12), 3509; https://doi.org/10.3390/en11123509 - 16 Dec 2018
Viewed by 815
Abstract
The U.K. has initiated the nuclear renaissance by contracting for the first two new plants and announcing further new build projects. The U.K. government has recently started to support this development with the announcement of a national programme of nuclear innovation. The aim [...] Read more.
The U.K. has initiated the nuclear renaissance by contracting for the first two new plants and announcing further new build projects. The U.K. government has recently started to support this development with the announcement of a national programme of nuclear innovation. The aim of this programme with respect to modelling and simulation is foreseen to fulfil the demand in education and the build-up of a reasonably qualified workforce, as well as the development and application of a new state-of-the-art software environment for improved economics and safety. This document supports the ambition to define a new approach to the structured development of nuclear reactor core simulation that is based on oversight instead of looking at detail problems and the development of single tools for these specific detail problems. It is based on studying the industrial demand to bridge the gap in technical innovation that can be derived from basic research in order to create a tailored industry solution to set the new standard for reactor core modelling and simulation for the U.K. However, finally, a technical requirements specification has to be developed alongside the strategic approach to give code developers a functional specification that they can use to develop the tools for the future. Key points for a culture change to the application of modern technologies are identified in the use of DevOps in a double-strata approach to academic and industrial code development. The document provides a novel, strategic approach to achieve the most promising final product for industry, and to identify the most important points for improvement. Full article
(This article belongs to the Section Energy Economics and Policy)
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