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Energies, Volume 11, Issue 3 (March 2018)

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Cover Story (view full-size image) Microalgae have long been utilized as food and feed, and, more recently, fuel. When microalgae was [...] Read more.
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Open AccessCorrection Correction: Arshad A.; et al. An Analysis of Photo-Voltaic Hosting Capacity in Finnish Low Voltage Distribution Networks. Energies 2017, 10, 1702
Energies 2018, 11(3), 689; https://doi.org/10.3390/en11030689
Received: 1 February 2018 / Revised: 10 March 2018 / Accepted: 12 March 2018 / Published: 20 March 2018
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Abstract
The authors would like to correct following errors[...] Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle A Fast-Transient Output Capacitor-Less Low-Dropout Regulator Using Active-Feedback and Current-Reuse Feedforward Compensation
Energies 2018, 11(3), 688; https://doi.org/10.3390/en11030688
Received: 20 February 2018 / Revised: 10 March 2018 / Accepted: 15 March 2018 / Published: 19 March 2018
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Abstract
In this paper, output capacitor-less low-dropout (LDO) regulator using active-feedback and current-reuse feedforward compensation (AFCFC) is presented. The open-loop transfer function was obtained using small-signal modeling. The stability of the proposed LDO was analyzed using pole-zero plots, and it was confirmed by simulations
[...] Read more.
In this paper, output capacitor-less low-dropout (LDO) regulator using active-feedback and current-reuse feedforward compensation (AFCFC) is presented. The open-loop transfer function was obtained using small-signal modeling. The stability of the proposed LDO was analyzed using pole-zero plots, and it was confirmed by simulations that the stability was ensured under the load current of 50 mA. The proposed compensation method increases gain-bandwidth product (GBW) and reduces the on-chip compensation capacitor. The proposed AFCFC technique was applied to a three-stage output capacitor-less LDO. The LDO has a GBW of 5.6 MHz with a small on-chip capacitor of 2.6 pF. Fast-transient time of 450 ns with low quiescent current of 65.8 μA was achieved. The LDO was fabricated in 130 nm CMOS process consuming 180 × 140 μm2 of the silicon area. Full article
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Open AccessArticle The Energy Cost Analysis of Hybrid Systems and Diesel Generators in Powering Selected Base Transceiver Station Locations in Nigeria
Energies 2018, 11(3), 687; https://doi.org/10.3390/en11030687
Received: 29 November 2017 / Revised: 31 January 2018 / Accepted: 1 February 2018 / Published: 19 March 2018
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Abstract
As more locations gain access to telecommunication, there is a growing demand to provide energy in a reliable, efficient and environmentally friendly manner while effectively addressing growing energy needs. Erratic power supply and rising operation costs (OPEX) in Nigeria have increased the need
[...] Read more.
As more locations gain access to telecommunication, there is a growing demand to provide energy in a reliable, efficient and environmentally friendly manner while effectively addressing growing energy needs. Erratic power supply and rising operation costs (OPEX) in Nigeria have increased the need to harness local renewable energy sources. Thus, identifying the right generator schedule with the renewable system to reduce OPEX is a priority for operators and vendors. This study evaluates the energy costs of hybrid systems with different generator schedules in powering base transceiver stations in Nigeria using the Hybrid Optimization Model for Electric Renewable (HOMER). A load range of 4 kW to 8 kW was considered using: (i) an optimised generator schedule; (ii) forced-on generator schedule and (iii) the generator-only schedule. The results showed an optimal LCOE range between averages of USD 0.156/kWh to 0.172/kWh for the 8 kW load. The percent energy contribution by generator ranges from 52.80% to 60.90%, and by the solar PV system, 39.10% to 47.20%. Excess energy ranges from 0.03% to 14.98%. The optimised generator schedule has the highest solar PV penetration of 56.8%. The OPEX savings on fuel ranges from 41.68% to 47% for the different load schedules and carbon emission savings of 4222 kg to 31,428.36 kg. The simulation results shows that powering base stations using the optimised hybrid system schedule would be a better option for the telecom industry. Full article
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Open AccessArticle Research on Economic Comprehensive Control Strategies of Tractor-Planter Combinations in Planting, Including Gear-Shift and Cruise Control
Energies 2018, 11(3), 686; https://doi.org/10.3390/en11030686
Received: 27 January 2018 / Revised: 11 March 2018 / Accepted: 12 March 2018 / Published: 19 March 2018
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Abstract
An automatic control strategy for forward speed in the planting process is proposed to improve the fuel economy and reduce the labor intensity of drivers. Models of tractors with power-shift transmission (PST) and a precise pneumatic planter with an electric-driven seed metering device
[...] Read more.
An automatic control strategy for forward speed in the planting process is proposed to improve the fuel economy and reduce the labor intensity of drivers. Models of tractors with power-shift transmission (PST) and a precise pneumatic planter with an electric-driven seed metering device are built as research objects and simulated using Matlab with Simulink. The economic comprehensive control strategies for forward speed, including gear-shift schedule and cruise control strategy, are developed. Four levels control mode with different fuel economy performances are implemented to meet different driver or operation condition requirements. In addition, the control strategy is developed for the seed-metering device motor to maintain the required seed spacing in planting. Finally, the fuel economy and effectiveness of the control strategies for forward speed and planting quality are verified by simulations with Matlab/Simulink and Matlab/Stateflow. The simulation results verify the satisfactory performance of the proposed control strategies. The error of seed spacing is less than 3% when planting with speed fluctuation. Under the premise of ensuring planting quality and driver’s demands, the cruise control strategies for forward speed have more significant effects on the fuel economy than previous cruise control strategies. Furthermore, the control mode with higher level has better fuel economy and a larger speed deviation range. Full article
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Open AccessArticle Hydrodynamic Performance of an Array of Wave Energy Converters Integrated with a Pontoon-Type Breakwater
Energies 2018, 11(3), 685; https://doi.org/10.3390/en11030685
Received: 10 February 2018 / Revised: 13 March 2018 / Accepted: 15 March 2018 / Published: 18 March 2018
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Abstract
The cost of wave energy converters (WECs) can be reduced significantly by integrating WECs into other marine facilities, especially in sea areas with a mild wave climate. To reduce the cost and increase the efficiency, a hybrid WEC system, comprising a linear array
[...] Read more.
The cost of wave energy converters (WECs) can be reduced significantly by integrating WECs into other marine facilities, especially in sea areas with a mild wave climate. To reduce the cost and increase the efficiency, a hybrid WEC system, comprising a linear array (medium farm) of oscillating buoy-type WECs attached to the weather side of a fixed-type floating pontoon as the base structure is proposed. The performance of the WEC array is investigated numerically using a boundary element method (BEM) based on the linear potential flow theory. The linear power take-off (PTO) damping model is used to calculate the output power of the WEC array. The performance of the WEC array and each individual WEC device is balanced by using the mean interaction factor and the individual interaction factor. To quantify the effect of the pontoon, the hydrodynamic results of the WEC arrays with and without a pontoon are compared with each other. Detailed investigations on the influence of the structural and PTO parameters are performed in a wide wave frequency range. Results show that the energy conversion efficiency of a WEC array with a properly designed pontoon is much higher than that without a pontoon. This integration scheme can achieve the efficiency improvement and construction-cost reduction of the wave energy converters. Full article
(This article belongs to the Special Issue Wave Energy Potential, Behavior and Extraction)
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Open AccessArticle Assessment of the Induced Electric Fields in a Carbon-Fiber Electrical Vehicle Equipped with a Wireless Power Transfer System
Energies 2018, 11(3), 684; https://doi.org/10.3390/en11030684
Received: 13 February 2018 / Revised: 5 March 2018 / Accepted: 16 March 2018 / Published: 18 March 2018
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Abstract
In this study, the electric field induced inside two realistic anatomical models placed near or inside an electric vehicle made of carbon-fiber composite while charging its battery with a wireless power transfer (WPT) system has been investigated. The WPT source consists of two
[...] Read more.
In this study, the electric field induced inside two realistic anatomical models placed near or inside an electric vehicle made of carbon-fiber composite while charging its battery with a wireless power transfer (WPT) system has been investigated. The WPT source consists of two parallel inductive coils operating with a power output of 7.7 kW at two different frequencies of 85 and 150 kHz. Since a misalignment between the primary and the secondary coil creates higher induced fields, a misalignment of 20 cm is also considered as the worst-case exposure condition. The analysis of the obtained results shows that the International Commission on Non-Ionizing Radiation Protection (ICNIRP) basic restrictions are exceeded by 1.3 dB and 4.8 dB for the aligned and misaligned coil positions, respectively. This exceedance is however confined only in a small area of the driver’s foot. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Big Data Analytics for Discovering Electricity Consumption Patterns in Smart Cities
Energies 2018, 11(3), 683; https://doi.org/10.3390/en11030683
Received: 31 January 2018 / Revised: 5 March 2018 / Accepted: 13 March 2018 / Published: 18 March 2018
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Abstract
New technologies such as sensor networks have been incorporated into the management of buildings for organizations and cities. Sensor networks have led to an exponential increase in the volume of data available in recent years, which can be used to extract consumption patterns
[...] Read more.
New technologies such as sensor networks have been incorporated into the management of buildings for organizations and cities. Sensor networks have led to an exponential increase in the volume of data available in recent years, which can be used to extract consumption patterns for the purposes of energy and monetary savings. For this reason, new approaches and strategies are needed to analyze information in big data environments. This paper proposes a methodology to extract electric energy consumption patterns in big data time series, so that very valuable conclusions can be made for managers and governments. The methodology is based on the study of four clustering validity indices in their parallelized versions along with the application of a clustering technique. In particular, this work uses a voting system to choose an optimal number of clusters from the results of the indices, as well as the application of the distributed version of the k-means algorithm included in Apache Spark’s Machine Learning Library. The results, using electricity consumption for the years 2011–2017 for eight buildings of a public university, are presented and discussed. In addition, the performance of the proposed methodology is evaluated using synthetic big data, which cab represent thousands of buildings in a smart city. Finally, policies derived from the patterns discovered are proposed to optimize energy usage across the university campus. Full article
(This article belongs to the Special Issue Data Science and Big Data in Energy Forecasting)
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Open AccessArticle Experimental and Numerical Analyses of the Sloshing in a Fuel Tank
Energies 2018, 11(3), 682; https://doi.org/10.3390/en11030682
Received: 31 January 2018 / Revised: 8 March 2018 / Accepted: 15 March 2018 / Published: 17 March 2018
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Abstract
The sloshing of fuel inside the tank is an important issue in aerospace and automotive applications. This phenomenon, in fact, can cause various issues related to vehicle stability and safety, to component fatigue, audible noise, vibrations and to the level measurement of the
[...] Read more.
The sloshing of fuel inside the tank is an important issue in aerospace and automotive applications. This phenomenon, in fact, can cause various issues related to vehicle stability and safety, to component fatigue, audible noise, vibrations and to the level measurement of the fuel itself. The sloshing phenomenon can be defined as a highly nonlinear oscillatory movement of the free-surface of liquid inside a container, such as a fuel tank, under the effect of continuous or instantaneous forces. This paper is the result of a research collaboration between the Industrial Engineering Department of the University of Naples “Federico II” and the R&D department of Fiat Chrysler Automobiles (F.C.A.) The activity is focused on the study of the sloshing in the fuel tank of vehicles. The goal is the optimization of the tank geometry in order to allow, for example, the correct fuel suction under all driving conditions and to prevent undesired noise and vibrations. This paper shows results obtained on a reference tank filled by water tinted with a dark blue food colorant. The geometry has been tested on a test bench designed by Moog Inc. on specification from Fiat Chrysler Automobiles with harmonic excitation of a 2D tank slice along one degree of freedom. The test bench consists of a hexapod with six independent actuators connecting the base to the top platform, allowing all six Degrees of Freedom (DOFs). On the top platform there are other two additional actuators to extend pitch and roll envelope, thus the name of “8-DOF bench”. The designed tank has been studied with a three-dimensional Computational Fluid Dynamics (CFD) modeling approach, too. By the end, the numerical and experimental data have been compared with a post-processing analysis by means of Matlab® software. For this reason, the images have been reduced in two dimensions. In particular, the percentage gaps of the free surfaces and the center of gravity have been compared each other. The comparison, for the three different levels of liquid tested, has shown a good agreement with a discrepancy always less than 3%. Full article
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Open AccessArticle Algorithm for Fast and Efficient Detection and Reaction to Angle Instability Conditions Using Phasor Measurement Unit Data
Energies 2018, 11(3), 681; https://doi.org/10.3390/en11030681
Received: 15 February 2018 / Revised: 7 March 2018 / Accepted: 12 March 2018 / Published: 17 March 2018
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Abstract
In wide area monitoring, protection, and control (WAMPAC) systems, angle stability of transmission network is monitored using data from phasor measurement units (PMU) placed on transmission lines. Based on this PMU data stream advanced algorithm for out-of-step condition detection and early warning issuing
[...] Read more.
In wide area monitoring, protection, and control (WAMPAC) systems, angle stability of transmission network is monitored using data from phasor measurement units (PMU) placed on transmission lines. Based on this PMU data stream advanced algorithm for out-of-step condition detection and early warning issuing is developed. The algorithm based on theoretical background described in this paper is backed up by the data and results from corresponding simulations done in Matlab environment. Presented results aim to provide the insights of the potential benefits, such as fast and efficient detection and reaction to angle instability, this algorithm can have on the improvement of the power system protection. Accordingly, suggestion is given how the developed algorithm can be implemented in protection segments of the WAMPAC systems in the transmission system operator control centers. Full article
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Open AccessArticle An Artificially Intelligent Technique to Generate Synthetic Geomechanical Well Logs for the Bakken Formation
Energies 2018, 11(3), 680; https://doi.org/10.3390/en11030680
Received: 4 February 2018 / Revised: 12 March 2018 / Accepted: 14 March 2018 / Published: 17 March 2018
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Abstract
Artificially intelligent and predictive modelling of geomechanical properties is performed by creating supervised machine learning data models utilizing artificial neural networks (ANN) and will predict geomechanical properties from basic and commonly used conventional well logs such as gamma ray, and bulk density. The
[...] Read more.
Artificially intelligent and predictive modelling of geomechanical properties is performed by creating supervised machine learning data models utilizing artificial neural networks (ANN) and will predict geomechanical properties from basic and commonly used conventional well logs such as gamma ray, and bulk density. The predictive models were created by following the approach on a large volume of data acquired from 112 wells containing the Bakken Formation in North Dakota. The studied wells cover a large surface area of the formation containing the five main producing counties in North Dakota: Burke, Mountrail, McKenzie, Dunn, and Williams. Thus, with a large surface area being analyzed in this research, there is confidence with a high degree of certainty that an extensive representation of the Bakken Formation is modelled, by training neural networks to work on varying properties from the different counties containing the Bakken Formation in North Dakota. Shear wave velocity of 112 wells is also analyzed by regression methods and neural networks, and a new correlation is proposed for the Bakken Formation. The final goal of the research is to achieve supervised artificial neural network models that predict geomechanical properties of future wells with an accuracy of at least 90% for the Upper and Middle Bakken Formation. Thus, obtaining these logs by generating it from statistical and artificially intelligent methods shows a potential for significant improvements in performance, efficiency, and profitability for oil and gas operators. Full article
(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries 2018)
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Open AccessArticle Thermal Performance of Microencapsulated Phase Change Material (mPCM) in Roof Modules during Daily Operation
Energies 2018, 11(3), 679; https://doi.org/10.3390/en11030679
Received: 18 February 2018 / Revised: 13 March 2018 / Accepted: 15 March 2018 / Published: 17 March 2018
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Abstract
This study combines microencapsulated phase change materials (mPCMs) (core material: paraffin; melting points: 37 and 43 °C) and aluminum honeycomb boards (8 mm core cell) to form mPCM roof modules and investigates their heat absorption and release performances, as well as their impact
[...] Read more.
This study combines microencapsulated phase change materials (mPCMs) (core material: paraffin; melting points: 37 and 43 °C) and aluminum honeycomb boards (8 mm core cell) to form mPCM roof modules and investigates their heat absorption and release performances, as well as their impact on indoor heat gain by conducting experiments over a 24-h period, subject to representative weather. The outdoor boundary conditions of the module are hourly sunlight and nighttime natural cooling; on the indoor side of the module, the conditions are daytime air conditioning and nighttime natural cooling. The results indicate that compared to a roof module with a 43 °C melting point mPCM, the roof module with a 37 °C melting point mPCM had improved peak load-shifting capacity, but had a slightly increased indoor heat gain. The mPCMs in both roof modules were successfully cooled during the night, returning to their initial state, to begin a new thermal cycle the next day. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle Stochastic Stability Analysis of the Power System with Losses
Energies 2018, 11(3), 678; https://doi.org/10.3390/en11030678
Received: 17 January 2018 / Revised: 13 March 2018 / Accepted: 13 March 2018 / Published: 17 March 2018
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Abstract
Renewable energy and electric vehicles have become involved in power systems, which has attracted researchers to stochastic continuous disturbances (SDEs). This paper addresses stochastic analysis issues for the stability of a power system with losses under SDEs. Firstly, the quasi-Hamiltonian models of power
[...] Read more.
Renewable energy and electric vehicles have become involved in power systems, which has attracted researchers to stochastic continuous disturbances (SDEs). This paper addresses stochastic analysis issues for the stability of a power system with losses under SDEs. Firstly, the quasi-Hamiltonian models of power systems with losses under SDEs are given. Secondly, a novel analytical method is proposed to analyze the stability of the power system with losses under SDEs based on the stochastic averaging method. Thirdly, comparisons of stability probability under different parameters are performed, from which insights to improve the stability probability of power systems with losses under SDEs can be obtained. Even though it is challenging to assess the stability of a power system with losses under SDEs, the proposed method in this paper could serve well in this regard. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Research on Improved VSG Control Algorithm Based on Capacity-Limited Energy Storage System
Energies 2018, 11(3), 677; https://doi.org/10.3390/en11030677
Received: 15 February 2018 / Revised: 13 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
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Abstract
A large scale of renewable energy employing grid connected electronic inverters fail to contribute inertia or damping to power systems, and, therefore, may bring negative effects to the stability of power system. As a solution, an advanced Virtual Synchronous Generator (VSG) control technology
[...] Read more.
A large scale of renewable energy employing grid connected electronic inverters fail to contribute inertia or damping to power systems, and, therefore, may bring negative effects to the stability of power system. As a solution, an advanced Virtual Synchronous Generator (VSG) control technology based on Hamilton approach is introduced in this paper firstly to support the frequency and enhance the suitability and robustness of the system. The charge and discharge process of power storage devices forms the virtual inertia and damping of VSG, and, therefore, limits on storage capacity may change the coefficients of VSG. To provide a method in keeping system output in an acceptable level with the capacity restriction in a transient period, an energy control algorithm is designed for VSG adaptive control. Finally, simulations are conducted in DIgSILENT to demonstrate the correctness of the algorithm. The demonstration shows: (1) the proposed control model aims at better system robustness and stability; and (2) the model performs in the environment closer to practical engineering by fitting the operation state of storage system. Full article
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Open AccessArticle A Hybrid Excited Machine with Flux Barriers and Magnetic Bridges
Energies 2018, 11(3), 676; https://doi.org/10.3390/en11030676
Received: 23 January 2018 / Revised: 11 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
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Abstract
In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic
[...] Read more.
In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic torque, no-load magnetic flux linkage, rotor iron losses and back electromotive force is shown. Three different rotor designs are analyzed. Furthermore, the field control characteristics depending on additional DC control coil currents are shown. Full article
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Open AccessArticle Life Cycle Performance of Hydrogen Production via Agro-Industrial Residue Gasification—A Small Scale Power Plant Study
Energies 2018, 11(3), 675; https://doi.org/10.3390/en11030675
Received: 28 January 2018 / Revised: 13 March 2018 / Accepted: 13 March 2018 / Published: 16 March 2018
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This study evaluates the environmental profile of a real biomass-based hydrogen production small-scale (1 MWth) system composed of catalytic candle indirectly heated steam gasifier coupled with zinc oxide (ZnO) guard bed, water gas shift (WGS) and pressure swing absorber (PSA) reactors.
[...] Read more.
This study evaluates the environmental profile of a real biomass-based hydrogen production small-scale (1 MWth) system composed of catalytic candle indirectly heated steam gasifier coupled with zinc oxide (ZnO) guard bed, water gas shift (WGS) and pressure swing absorber (PSA) reactors. Environmental performance from cradle-to-gate was investigated by life cycle assessment (LCA) methodology. Biomass production shows high influence over all impact categories. In the syngas production process, the main impacts observed are global warming potential (GWP) and acidification potential (AP). Flue gas emission from gasifier burner has the largest proportion of total GWP. The residual off gas use in internal combustion engine (ICE) leads to important environmental savings for all categories. Hydrogen renewability score is computed as 90% due to over 100% decline in non-renewable energy demand. Sensitivity analysis shows that increase in hydrogen production efficiency does not necessarily result in decrease in environmental impacts. In addition, economic allocation of environmental charges increases all impact categories, especially AP and photochemical oxidation (POFP). Full article
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