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Energies, Volume 8, Issue 7 (July 2015) , Pages 6249-7521

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Open AccessArticle Screening and Evaluation of Some Green Algal Strains (Chlorophyceae) Isolated from Freshwater and Soda Lakes for Biofuel Production
Energies 2015, 8(7), 7502-7521; https://doi.org/10.3390/en8077502
Received: 13 May 2015 / Revised: 10 June 2015 / Accepted: 23 June 2015 / Published: 22 July 2015
Cited by 17 | Viewed by 2266 | PDF Full-text (875 KB) | HTML Full-text | XML Full-text
Abstract
Microalgae are photosynthetic microorganisms that can produce lipids, proteins and carbohydrates in large amounts and within short periods of time and these can be processed into both biofuels and other useful commercial products. Due to this reason microalgae are considered as a potential [...] Read more.
Microalgae are photosynthetic microorganisms that can produce lipids, proteins and carbohydrates in large amounts and within short periods of time and these can be processed into both biofuels and other useful commercial products. Due to this reason microalgae are considered as a potential source of renewable energy; and one of the most important decisions in obtaining oil from microalgae is the choice of species. In this study, the potential of Chlorophyceae species isolated from freshwater and soda lakes in Hungary and Romania (Central Europe) were characterized and evaluated by determining their biomass accumulation, lipid productivity, fatty acid profiles, and biodiesel properties besides protein and carbohydrate productivity. Out of nine strains tested, three accumulated more than 40% dry weight of protein, four accumulated more than 30% dry weight of carbohydrate and the strain Chlorella vulgaris LC8 accumulated high lipid content (42.1% ± 2.6%) with a favorable C16-C18 fatty acid profile (77.4%) as well as suitable biodiesel properties of high cetane number (57.3), low viscosity (4.7 mm2/s), lower iodine number (75.18 g I2/100 g), relative cloud point (8.8 °C) and negative cold filter plugging point (−6.5 °C). Hence the new strain, Chlorella vulgaris LC8 has potential as a feedstock for the production of excellent quality biodiesel. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle Flow Regime Changes: From Impounding a Temperate Lowland River to Small Hydropower Operations
Energies 2015, 8(7), 7478-7501; https://doi.org/10.3390/en8077478
Received: 19 May 2015 / Revised: 14 July 2015 / Accepted: 16 July 2015 / Published: 22 July 2015
Cited by 6 | Viewed by 2120 | PDF Full-text (2326 KB) | HTML Full-text | XML Full-text
Abstract
This article discusses the environmental issues facing small hydropower plants (SHPs) operating in temperate lowland rivers of Lithuania. The research subjects are two medium head reservoir type hydro schemes considered within a context of the global fleet of SHPs in the country. This [...] Read more.
This article discusses the environmental issues facing small hydropower plants (SHPs) operating in temperate lowland rivers of Lithuania. The research subjects are two medium head reservoir type hydro schemes considered within a context of the global fleet of SHPs in the country. This research considers general abiotic indicators (flow, level, water retention time in the reservoirs) of the stream that may affect the aquatic systems. The main idea was to test whether the hydrologic regime has been altered by small hydropower dams. The analysis of changes in abiotic indicators is a complex process, including both pre- and post-reservoir construction and post commissioning of the SHPs under operation. Downstream hydrograph (flow and stage) ramping is also an issue for operating SHPs that can result in temporary rapid changes in flow and consequently negatively impact aquatic resources. This ramping has been quantitatively evaluated. To avoid the risk of excessive flow ramping, the types of turbines available were evaluated and the most suitable types for the natural river flow regime were identified. The results of this study are to allow for new hydro schemes or upgrades to use water resources in a more sustainable way. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change) Printed Edition available
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Open AccessArticle Study on Pyroelectric Harvesters Integrating Solar Radiation with Wind Power
Energies 2015, 8(7), 7465-7477; https://doi.org/10.3390/en8077465
Received: 6 June 2015 / Revised: 1 July 2015 / Accepted: 16 July 2015 / Published: 22 July 2015
Cited by 15 | Viewed by 1890 | PDF Full-text (3775 KB) | HTML Full-text | XML Full-text
Abstract
Pyroelectric harvesters use temperature fluctuations to generate electrical outputs. Solar radiation and waste heat are rich energy sources that can be harvested. Pyroelectric energy converters offer a novel and direct energy-conversion technology by transforming time-dependent temperatures directly into electricity. Moreover, the great challenge [...] Read more.
Pyroelectric harvesters use temperature fluctuations to generate electrical outputs. Solar radiation and waste heat are rich energy sources that can be harvested. Pyroelectric energy converters offer a novel and direct energy-conversion technology by transforming time-dependent temperatures directly into electricity. Moreover, the great challenge for pyroelectric energy harvesting lies in finding promising temperature variations or an alternating thermal loading in real situations. Hence, in this article, a novel pyroelectric harvester integrating solar radiation with wind power by the pyroelectric effect is proposed. Solar radiation is a thermal source, and wind is a dynamic potential. A disk generator is used for harvesting wind power. A mechanism is considered to convert the rotary energy of the disk generator to drive a shutter for generating temperature variations in pyroelectric cells using a planetary gear system. The optimal period of the pyroelectric cells is 35 s to harvest the stored energy, about 70 μJ, while the rotary velocity of the disk generator is about 31 RPM and the wind speed is about 1 m/s. In this state, the stored energy acquired from the pyroelectric harvester is about 75% more than that from the disk generator. Although the generated energy of the proposed pyroelectric harvester is less than that of the disk generator, the pyroelectric harvester plays a complementary role when the disk generator is inactive in situations of low wind speed. Full article
(This article belongs to the Special Issue Thermoelectric Energy Harvesting)
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Open AccessArticle Characteristic Analysis and Control of a Hybrid Excitation Linear Eddy Current Brake
Energies 2015, 8(7), 7441-7464; https://doi.org/10.3390/en8077441
Received: 31 March 2015 / Revised: 22 June 2015 / Accepted: 17 July 2015 / Published: 22 July 2015
Cited by 3 | Viewed by 2501 | PDF Full-text (1466 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a novel hybrid excitation linear eddy current brake is presented as a braking system for high-speed road and rail vehicles. The presence of the permanent magnets (PMs), whose flux lines in the primary core are oppositely directed with respect to [...] Read more.
In this paper, a novel hybrid excitation linear eddy current brake is presented as a braking system for high-speed road and rail vehicles. The presence of the permanent magnets (PMs), whose flux lines in the primary core are oppositely directed with respect to the flux lines by the excitation windings, has the effect of mitigating the saturation of the iron in the teeth of the primary core. This allows the brake to be fed with more intense currents, improving the braking force. First, using the magnetic equivalent circuit method and the layer theory approach, the analytical model of the hybrid excitation linear eddy current brake was developed, which can account for the saturation effects occurring in the iron parts. The saturation effects make the design and control of eddy current brakes more difficult. Second, the relationship between the braking force characteristics and the design parameters were analyzed to provide useful information to the designers of eddy current brakes. Then, the controller of the hybrid excitation linear eddy current brake was designed to control the amplitude of the braking force. Finally, experimental measurements were conducted to verify the validity of the theoretical analysis. Full article
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Open AccessArticle Facile and Economical Preparation of SiAlON-Based Composites Using Coal Gangue: From Fundamental to Industrial Application
Energies 2015, 8(7), 7428-7440; https://doi.org/10.3390/en8077428
Received: 21 May 2015 / Revised: 11 July 2015 / Accepted: 13 July 2015 / Published: 22 July 2015
Cited by 2 | Viewed by 1831 | PDF Full-text (2790 KB) | HTML Full-text | XML Full-text
Abstract
The present study aims to synthesize SiAlON-based composites utilizing coal gangue. Different types of SiAlON-based composites were synthesized using coal gangue by carbothermal reduction nitridation method through control of different reaction atmospheres. The experimental results indicate that the oxygen partial pressure was an [...] Read more.
The present study aims to synthesize SiAlON-based composites utilizing coal gangue. Different types of SiAlON-based composites were synthesized using coal gangue by carbothermal reduction nitridation method through control of different reaction atmospheres. The experimental results indicate that the oxygen partial pressure was an essential factor in the manufacture of SiAlON-based composites and under proper control of the atmospheres, SiAlON-based composites with different crystal structures could be synthesized. The optimum conditions of synthesis of different SiAlON-based composites were respectively determined. Based on the laboratory results, a prototype plant was proposed and constructed, and β-SiAlON composite was successfully produced using coal gangue. The synthesized β-SiAlON composite was applied in preparation of iron ladle brick instead of SiC, which showed that the compression strength, refractoriness under load and high temperature bending strength were increased from 44.5 ± 6.7 MPa, 1618 ± 21 °C and 5.4 ± 1.2 MPa to 64.1 ± 2.5 MPa, 1700 ± 28 °C and 7.1 ± 1.6 MPa, respectively. Compared with the traditional synthesis method, the present technique is expected to save energy both in raw materials and technical process. Full article
(This article belongs to the Special Issue Recent Advances in Coal Combustion and Gasification)
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Open AccessArticle Data Mining Techniques for Detecting Household Characteristics Based on Smart Meter Data
Energies 2015, 8(7), 7407-7427; https://doi.org/10.3390/en8077407
Received: 16 April 2015 / Revised: 3 June 2015 / Accepted: 6 July 2015 / Published: 22 July 2015
Cited by 17 | Viewed by 2328 | PDF Full-text (1603 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The main goal of this research is to discover the structure of home appliances usage patterns, hence providing more intelligence in smart metering systems by taking into account the usage of selected home appliances and the time of their usage. In particular, we [...] Read more.
The main goal of this research is to discover the structure of home appliances usage patterns, hence providing more intelligence in smart metering systems by taking into account the usage of selected home appliances and the time of their usage. In particular, we present and apply a set of unsupervised machine learning techniques to reveal specific usage patterns observed at an individual household. The work delivers the solutions applicable in smart metering systems that might: (1) contribute to higher energy awareness; (2) support accurate usage forecasting; and (3) provide the input for demand response systems in homes with timely energy saving recommendations for users. The results provided in this paper show that determining household characteristics from smart meter data is feasible and allows for quickly grasping general trends in data. Full article
(This article belongs to the Special Issue Smart Metering)
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Open AccessArticle Automated Linear Function Submission-Based Double Auction as Bottom-up Real-Time Pricing in a Regional Prosumers’ Electricity Network
Energies 2015, 8(7), 7381-7406; https://doi.org/10.3390/en8077381
Received: 9 June 2015 / Revised: 11 July 2015 / Accepted: 14 July 2015 / Published: 22 July 2015
Cited by 6 | Viewed by 3372 | PDF Full-text (1102 KB) | HTML Full-text | XML Full-text
Abstract
A linear function submission-based double auction (LFS-DA) mechanism for a regional electricity network is proposed in this paper. Each agent in the network is equipped with a battery and a generator. Each agent simultaneously becomes a producer and consumer of electricity, i.e., a [...] Read more.
A linear function submission-based double auction (LFS-DA) mechanism for a regional electricity network is proposed in this paper. Each agent in the network is equipped with a battery and a generator. Each agent simultaneously becomes a producer and consumer of electricity, i.e., a prosumer, and trades electricity in the regional market at a variable price. In the LFS-DA, each agent uses linear demand and supply functions when they submit bids and asks to an auctioneer in the regional market. The LFS-DA can achieve an exact balance between electricity demand and supply for each time slot throughout the learning phase and was shown capable of solving the primal problem of maximizing the social welfare of the network without any central price setter, e.g., a utility or a large electricity company, in contrast with conventional real-time pricing (RTP). This paper presents a clarification of the relationship between the RTP algorithm derived on the basis of a dual decomposition framework and LFS-DA. Specifically, we proved that the changes in the price profile of the LFS-DA mechanism are equal to those achieved by the RTP mechanism derived from the dual decomposition framework, except for a constant factor. Full article
(This article belongs to the collection Smart Grid)
Open AccessArticle A Solar Automatic Tracking System that Generates Power for Lighting Greenhouses
Energies 2015, 8(7), 7367-7380; https://doi.org/10.3390/en8077367
Received: 25 April 2015 / Revised: 3 July 2015 / Accepted: 15 July 2015 / Published: 21 July 2015
Cited by 6 | Viewed by 1971 | PDF Full-text (883 KB) | HTML Full-text | XML Full-text
Abstract
In this study we design and test a novel solar tracking generation system. Moreover, we show that this system could be successfully used as an advanced solar power source to generate power in greenhouses. The system was developed after taking into consideration the [...] Read more.
In this study we design and test a novel solar tracking generation system. Moreover, we show that this system could be successfully used as an advanced solar power source to generate power in greenhouses. The system was developed after taking into consideration the geography, climate, and other environmental factors of northeast China. The experimental design of this study included the following steps: (i) the novel solar tracking generation system was measured, and its performance was analyzed; (ii) the system configuration and operation principles were evaluated; (iii) the performance of this power generation system and the solar irradiance were measured according to local time and conditions; (iv) the main factors affecting system performance were analyzed; and (v) the amount of power generated by the solar tracking system was compared with the power generated by fixed solar panels. The experimental results indicated that compared to the power generated by fixed solar panels, the solar tracking system generated about 20% to 25% more power. In addition, the performance of this novel power generating system was found to be closely associated with solar irradiance. Therefore, the solar tracking system provides a new approach to power generation in greenhouses. Full article
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Open AccessReview Enhancing Wave Energy Competitiveness through Co-Located Wind and Wave Energy Farms. A Review on the Shadow Effect
Energies 2015, 8(7), 7344-7366; https://doi.org/10.3390/en8077344
Received: 30 April 2015 / Revised: 25 June 2015 / Accepted: 13 July 2015 / Published: 21 July 2015
Cited by 22 | Viewed by 2303 | PDF Full-text (801 KB) | HTML Full-text | XML Full-text
Abstract
Wave energy is one of the most promising alternatives to fossil fuels due to the enormous available resource; however, its development may be slowed as it is often regarded as uneconomical. The largest cost reductions are expected to be obtained through economies of [...] Read more.
Wave energy is one of the most promising alternatives to fossil fuels due to the enormous available resource; however, its development may be slowed as it is often regarded as uneconomical. The largest cost reductions are expected to be obtained through economies of scale and technological progress. In this sense, the incorporation of wave energy systems into offshore wind energy farms is an opportunity to foster the development of wave energy. The synergies between both renewables can be realised through these co-located energy farms and, thus, some challenges of offshore wind energy can be met. Among them, this paper focuses on the longer non-operational periods of offshore wind turbines—relative to their onshore counterparts—typically caused by delays in maintenance due to the harsh marine conditions. Co-located wave energy converters would act as a barrier extracting energy from the waves and resulting in a shielding effect over the wind farm. On this basis, the aim of this paper is to analyse wave energy economics in a holistic way, as well as the synergies between wave and offshore wind energy, focusing on the shadow effect and the associated increase in the accessibility to the wind turbines. Full article
(This article belongs to the Special Issue Tools and Techniques for Economic Delivery of Ocean Energy)
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Open AccessArticle Autonomous Household Energy Management Based on a Double Cooperative Game Approach in the Smart Grid
Energies 2015, 8(7), 7326-7343; https://doi.org/10.3390/en8077326
Received: 28 May 2015 / Revised: 1 July 2015 / Accepted: 14 July 2015 / Published: 20 July 2015
Cited by 13 | Viewed by 2005 | PDF Full-text (509 KB) | HTML Full-text | XML Full-text
Abstract
Taking advantage of two-way communication infrastructure and bidirectional energy trading between utility companies and customers in the future smart grid (SG), autonomous energy management programs become crucial to the demand-side management (DSM). Most of the existing autonomous energy management schemes are for the [...] Read more.
Taking advantage of two-way communication infrastructure and bidirectional energy trading between utility companies and customers in the future smart grid (SG), autonomous energy management programs become crucial to the demand-side management (DSM). Most of the existing autonomous energy management schemes are for the scenario with a single utility company or the scenario with one-way energy trading. In this paper, an autonomous household energy management system with multiple utility companies and multiple residential customers is studied by considering the bidirectional energy trading. To minimize the overall costs of both the utility companies and the residential customers, the energy management system is formulated as a double cooperative game. That is, the interaction among the residential users is formulated as a cooperative game, where the players are the customers and the strategies are the daily schedules of their household appliances; and the interaction among the utility companies is also formulated as a cooperative game, where the players are the suppliers and the strategies are the proportions of the daily total energy they provide for the customers. Without loss of generality, the bidirectional energy trading in the double cooperative game is formulated by allowing plug-in electric vehicles (PEVs) to discharge and sell energy back. Two distributed algorithms will be provided to realize the global optimal performance in terms of minimizing the energy costs, which can be guaranteed at the Nash equilibriums of the formulated cooperative games. Finally, simulation results illustrated that the proposed double cooperative game can benefit both the utility companies and residential users significantly. Full article
(This article belongs to the collection Smart Grid)
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Open AccessArticle Effects of Pilot Injection Timing and EGR on Combustion, Performance and Exhaust Emissions in a Common Rail Diesel Engine Fueled with a Canola Oil Biodiesel-Diesel Blend
Energies 2015, 8(7), 7312-7325; https://doi.org/10.3390/en8077312
Received: 16 April 2015 / Revised: 19 June 2015 / Accepted: 13 July 2015 / Published: 20 July 2015
Cited by 18 | Viewed by 3062 | PDF Full-text (860 KB) | HTML Full-text | XML Full-text
Abstract
Biodiesel as a clean energy source could reduce environmental pollution compared to fossil fuel, so it is becoming increasingly important. In this study, we investigated the effects of different pilot injection timings from before top dead center (BTDC) and exhaust gas recirculation (EGR) [...] Read more.
Biodiesel as a clean energy source could reduce environmental pollution compared to fossil fuel, so it is becoming increasingly important. In this study, we investigated the effects of different pilot injection timings from before top dead center (BTDC) and exhaust gas recirculation (EGR) on combustion, engine performance, and exhaust emission characteristics in a common rail diesel engine fueled with canola oil biodiesel-diesel (BD) blend. The pilot injection timing and EGR rate were changed at an engine speed of 2000 rpm fueled with BD20 (20 vol % canola oil and 80 vol % diesel fuel blend). As the injection timing advanced, the combustion pressure, brake specific fuel consumption (BSFC), and peak combustion pressure (Pmax) changed slightly. Carbon monoxide (CO) and particulate matter (PM) emissions clearly decreased at BTDC 20° compared with BTDC 5°, but nitrogen oxide (NOx) emissions increased slightly. With an increasing EGR rate, the combustion pressure and indicated mean effective pressure (IMEP) decreased slightly at BTDC 20° compared to other injection timings. However, the Pmax showed a remarkable decrease. The BSFC and PM emissions increased slightly, but the NOx emission decreased considerably. Full article
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Open AccessReview Smart Home Communication Technologies and Applications: Wireless Protocol Assessment for Home Area Network Resources
Energies 2015, 8(7), 7279-7311; https://doi.org/10.3390/en8077279
Received: 13 March 2015 / Revised: 21 June 2015 / Accepted: 6 July 2015 / Published: 20 July 2015
Cited by 33 | Viewed by 4263 | PDF Full-text (1046 KB) | HTML Full-text | XML Full-text
Abstract
The paper discusses Home Area Networks (HAN) communication technologies for smart home and domestic application integration. The work is initiated by identifying the application areas that can benefit from this integration. A broad and inclusive home communication interface is analysed utilizing as a [...] Read more.
The paper discusses Home Area Networks (HAN) communication technologies for smart home and domestic application integration. The work is initiated by identifying the application areas that can benefit from this integration. A broad and inclusive home communication interface is analysed utilizing as a key piece a Gateway based on machine-to-machine (M2M) communications that interacts with the surrounding environment. Then, the main wireless networks are thoroughly assessed, and later, their suitability to the requirements of HAN considering the application area is analysed. Finally, a qualitative analysis is portrayed. Full article
(This article belongs to the Special Issue Smart Metering)
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Open AccessArticle Energy Performance Database of Building Heritage in the Region of Umbria, Central Italy
Energies 2015, 8(7), 7261-7278; https://doi.org/10.3390/en8077261
Received: 26 March 2015 / Revised: 12 June 2015 / Accepted: 13 July 2015 / Published: 17 July 2015
Cited by 9 | Viewed by 1871 | PDF Full-text (524 KB) | HTML Full-text | XML Full-text
Abstract
Household energy consumption has been increasing in the last decades; the residential sector is responsible for about 40% of the total final energy use in Europe. Energy efficiency measures can both reduce energy needs of buildings and energy-related CO2 emissions. For this [...] Read more.
Household energy consumption has been increasing in the last decades; the residential sector is responsible for about 40% of the total final energy use in Europe. Energy efficiency measures can both reduce energy needs of buildings and energy-related CO2 emissions. For this reason, in recent years, the European Union has been making efforts to enhance energy saving in buildings by introducing various policies and strategies; in this context, a common methodology was developed to assess and to certify energy performance of buildings. The positive effects obtained by energy efficiency measures need to be verified, but measuring and monitoring building energy performance is time consuming and financially demanding. Alternatively, energy efficiency can also be evaluated by specific indicators based on energy consumption. In this work, a methodology to investigate the level of energy efficiency reached in the Umbria Region (Central Italy) is described, based on data collected by energy certificates. In fact, energy certificates, which are the outcomes of simulation models, represent a useful and available tool to collect data related to the energy use of dwellings. A database of building energy performance was developed, in which about 6500 energy certificates of residential buildings supplied by Umbria region were inserted. On the basis of this data collection, average energy and CO2 indicators related to the building heritage in Umbria were estimated and compared to national and international indicators derived from official sources. Results showed that the adopted methodology in this work can be an alternative method for the evaluation of energy indicators; in fact, the ones calculated considering simulation data were similar to the ones reported in national and international sources. This allowed to validate the adopted methodology and the efficiency of European policies. Full article
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Open AccessArticle Reinforcement Learning–Based Energy Management Strategy for a Hybrid Electric Tracked Vehicle
Energies 2015, 8(7), 7243-7260; https://doi.org/10.3390/en8077243
Received: 14 January 2015 / Revised: 16 June 2015 / Accepted: 29 June 2015 / Published: 16 July 2015
Cited by 10 | Viewed by 2830 | PDF Full-text (783 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a reinforcement learning (RL)–based energy management strategy for a hybrid electric tracked vehicle. A control-oriented model of the powertrain and vehicle dynamics is first established. According to the sample information of the experimental driving schedule, statistical characteristics at various velocities [...] Read more.
This paper presents a reinforcement learning (RL)–based energy management strategy for a hybrid electric tracked vehicle. A control-oriented model of the powertrain and vehicle dynamics is first established. According to the sample information of the experimental driving schedule, statistical characteristics at various velocities are determined by extracting the transition probability matrix of the power request. Two RL-based algorithms, namely Q-learning and Dyna algorithms, are applied to generate optimal control solutions. The two algorithms are simulated on the same driving schedule, and the simulation results are compared to clarify the merits and demerits of these algorithms. Although the Q-learning algorithm is faster (3 h) than the Dyna algorithm (7 h), its fuel consumption is 1.7% higher than that of the Dyna algorithm. Furthermore, the Dyna algorithm registers approximately the same fuel consumption as the dynamic programming–based global optimal solution. The computational cost of the Dyna algorithm is substantially lower than that of the stochastic dynamic programming. Full article
(This article belongs to the Special Issue Advances in Plug-in Hybrid Vehicles and Hybrid Vehicles)
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Open AccessArticle Coordinated Control Strategies of VSC-HVDC-Based Wind Power Systems for Low Voltage Ride Through
Energies 2015, 8(7), 7224-7242; https://doi.org/10.3390/en8077224
Received: 23 April 2015 / Revised: 7 June 2015 / Accepted: 13 July 2015 / Published: 16 July 2015
Cited by 11 | Viewed by 2571 | PDF Full-text (867 KB) | HTML Full-text | XML Full-text
Abstract
The Voltage Source Converter-HVDC (VSC-HVDC) system applied to wind power generation can solve large scale wind farm grid-connection and long distance transmission problems. However, the low voltage ride through (LVRT) of the VSC-HVDC connected wind farm is a key technology issue that must [...] Read more.
The Voltage Source Converter-HVDC (VSC-HVDC) system applied to wind power generation can solve large scale wind farm grid-connection and long distance transmission problems. However, the low voltage ride through (LVRT) of the VSC-HVDC connected wind farm is a key technology issue that must be solved, and it is currently lacking an economic and effective solution. In this paper, a LVRT coordinated control strategy is proposed for the VSC-HVDC-based wind power system. In this strategy, the operation and control of VSC-HVDC and wind farm during the grid fault period is improved. The VSC-HVDC system not only provides reactive power support to the grid, but also effectively maintains the power balance and DC voltage stability by reducing wind-farm power output, without increasing the equipment investment. Correspondingly, to eliminate the influence on permanent magnet synchronous generator (PMSG)-based wind turbine (WT) systems, a hierarchical control strategy is designed. The speed and validity of the proposed LVRT coordinated control strategy and hierarchical control strategy were verified by MATLAB/Simulink simulations. Full article
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Open AccessArticle Investigation of Fault Permeability in Sands with Different Mineral Compositions (Evaluation of Gas Hydrate Reservoir)
Energies 2015, 8(7), 7202-7223; https://doi.org/10.3390/en8077202
Received: 26 March 2015 / Revised: 4 July 2015 / Accepted: 7 July 2015 / Published: 16 July 2015
Cited by 5 | Viewed by 1911 | PDF Full-text (3361 KB) | HTML Full-text | XML Full-text
Abstract
We used a ring-shear apparatus to examine the perpendicular permeability of sands with different mineral compositions to evaluate fault behavior around gas hydrate reservoirs. The effect of effective normal stress on the permeability of two sand types was investigated under constant effective normal [...] Read more.
We used a ring-shear apparatus to examine the perpendicular permeability of sands with different mineral compositions to evaluate fault behavior around gas hydrate reservoirs. The effect of effective normal stress on the permeability of two sand types was investigated under constant effective normal stresses of 0.5–8.0 MPa. Although Toyoura sand and silica sand No. 7 mainly comprise quartz, silica sand No. 7 contains small amounts of feldspar. For Toyoura sand, the permeability after ring-shearing dramatically decreased with increasing effective normal stress up to 3.0 MPa, then gradually decreased for stresses over 3.0 MPa, whereas the permeability after ring-shearing of silica sand No. 7 rapidly decreased with increasing effective normal stress up to 2.0 MPa. Although the relationships between the permeability after ring-shearing and effective normal stress for both sands could be expressed by exponential equations up to 3.0 MPa, a more gradual change in slope was shown for Toyoura sand. The permeabilities of both sands were almost equal for effective normal stresses over 3.0 MPa. The mineralogical properties of the small amount of feldspar in the sample indicate that both mineralogy and original grain size distribution affect the fault permeability and shear zone formation. Full article
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Open AccessArticle Development of Optical Fiber-Based Daylighting System and Its Comparison
Energies 2015, 8(7), 7185-7201; https://doi.org/10.3390/en8077185
Received: 7 June 2015 / Revised: 6 July 2015 / Accepted: 7 July 2015 / Published: 15 July 2015
Cited by 11 | Viewed by 2481 | PDF Full-text (4493 KB) | HTML Full-text | XML Full-text
Abstract
Fiber-optic daylighting systems have been shown to be a promising and effective way to transmit sunlight in the interior space whilst reducing electric lighting energy consumption. To increase efficiency in terms of providing uniform illumination in the interior, the current need is to [...] Read more.
Fiber-optic daylighting systems have been shown to be a promising and effective way to transmit sunlight in the interior space whilst reducing electric lighting energy consumption. To increase efficiency in terms of providing uniform illumination in the interior, the current need is to illuminate optical fiber-bundle with uniform light flux. To this end, we propose a method for achieving collimated light, which illuminates the fiber-bundle uniformly. Light is collected through a parabolic concentrator and focused toward a collimating lens, which distributes the light over each optical fiber. An optics diffusing structure is utilized at the end side of the fiber bundle to spread light in the interior. The results clearly reveal that the efficiency in terms of uniform illumination, which also reduces the heat problem for optical fibers, is improved. Furthermore, a comparison study is conducted between current and previous approaches. As a result, the proposed daylighting system turns out convenient in terms of energy saving and reduction in greenhouse gas emissions. Full article
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Open AccessArticle Effects of Low-Carbon Technologies and End-Use Electrification on Energy-Related Greenhouse Gases Mitigation in China by 2050
Energies 2015, 8(7), 7161-7184; https://doi.org/10.3390/en8077161
Received: 3 June 2015 / Revised: 4 July 2015 / Accepted: 6 July 2015 / Published: 15 July 2015
Cited by 6 | Viewed by 1826 | PDF Full-text (1134 KB) | HTML Full-text | XML Full-text
Abstract
Greenhouse gas emissions in China have been increasing in line with its energy consumption and economic growth. Major means for energy-related greenhouse gases mitigation in the foreseeable future are transition to less carbon intensive energy supplies and structural changes in energy consumption. In [...] Read more.
Greenhouse gas emissions in China have been increasing in line with its energy consumption and economic growth. Major means for energy-related greenhouse gases mitigation in the foreseeable future are transition to less carbon intensive energy supplies and structural changes in energy consumption. In this paper, a bottom-up model is built to examine typical projected scenarios for energy supply and demand, with which trends of energy-related carbon dioxide emissions by 2050 can be analyzed. Results show that low-carbon technologies remain essential contributors to reducing emissions and altering emissions trends up to 2050. By pushing the limit of current practicality, emissions reduction can reach 20 to 28 percent and the advent of carbon peaking could shift from 2040 to 2030. In addition, the effect of electrification at end-use sectors is studied. Results show that electrifying transport could reduce emissions and bring the advent of carbon peaking forward, but the effect is less significant compared with low-carbon technologies. Moreover, it implies the importance of decarbonizing power supply before electrifying end-use sectors. Full article
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Open AccessArticle Online Fault Identification Based on an Adaptive Observer for Modular Multilevel Converters Applied to Wind Power Generation Systems
Energies 2015, 8(7), 7140-7160; https://doi.org/10.3390/en8077140
Received: 4 May 2015 / Revised: 12 June 2015 / Accepted: 6 July 2015 / Published: 15 July 2015
Cited by 10 | Viewed by 2318 | PDF Full-text (898 KB) | HTML Full-text | XML Full-text
Abstract
Due to the possibility of putting a large number of modules consisting of switches and capacitors connected in series, the modular multilevel converter (MMC) can easily be scaled to high power and high voltage power conversion, which is an attractive feature for filter-less [...] Read more.
Due to the possibility of putting a large number of modules consisting of switches and capacitors connected in series, the modular multilevel converter (MMC) can easily be scaled to high power and high voltage power conversion, which is an attractive feature for filter-less and transformer-less design and helpful to achieve high efficiency. However, a significantly increased amount of sub-modules in a MMC may increase the requirements for sensors and also increase the risk of failures. As a result, fault detection and diagnosis of MMC sub-modules are of great importance for continuous operation and post-fault maintenance. Therefore, in this paper, an effective fault diagnosis technique for real-time diagnosis of the switching device faults covering both the open-circuit faults and the short-circuit faults in MMC sub-modules is proposed, in which the faulty phase and the fault type is detected by analyzing the difference among the three output load currents, while the localization of the faulty switches is achieved by comparing the estimation results by the adaptive observer. In contrast to other methods that use additional sensors or devices, the presented technique uses the measured phase currents only, which are already available for MMC control. In additional, its operation, effectiveness and robustness are confirmed by simulation results under different operating conditions and load conditions. Full article
(This article belongs to the collection Wind Turbines) Printed Edition available
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Open AccessReview A Supply-Chain Analysis Framework for Assessing Densified Biomass Solid Fuel Utilization Policies in China
Energies 2015, 8(7), 7122-7139; https://doi.org/10.3390/en8077122
Received: 6 January 2015 / Revised: 28 May 2015 / Accepted: 24 June 2015 / Published: 14 July 2015
Cited by 10 | Viewed by 2645 | PDF Full-text (4318 KB) | HTML Full-text | XML Full-text
Abstract
Densified Biomass Solid Fuel (DBSF) is a typical solid form of biomass, using agricultural and forestry residues as raw materials. DBSF utilization is considered to be an alternative to fossil energy, like coal in China, associated with a reduction of environmental pollution. China [...] Read more.
Densified Biomass Solid Fuel (DBSF) is a typical solid form of biomass, using agricultural and forestry residues as raw materials. DBSF utilization is considered to be an alternative to fossil energy, like coal in China, associated with a reduction of environmental pollution. China has abundant biomass resources and is suitable to develop DBSF. Until now, a number of policies aimed at fostering DBSF industry have been proliferated by policy makers in China. However, considering the seasonality and instability of biomass resources, these inefficiencies could trigger future scarcities of biomass feedstocks, baffling the resilience of biomass supply chains. Therefore, this review paper focuses on DBSF policies and strategies in China, based on the supply chain framework. We analyzed the current developing situation of DBSF industry in China and developed a framework for policy instruments based on the supply chain steps, which can be used to identify and assess the deficiencies of current DBSF industry policies, and we proposed some suggestions. These findings may inform policy development and identify synergies at different steps in the supply chain to enhance the development of DBSF industry. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change) Printed Edition available
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Open AccessArticle Improved Adaptive Droop Control Design for Optimal Power Sharing in VSC-MTDC Integrating Wind Farms
Energies 2015, 8(7), 7100-7121; https://doi.org/10.3390/en8077100
Received: 28 April 2015 / Revised: 24 June 2015 / Accepted: 7 July 2015 / Published: 14 July 2015
Cited by 7 | Viewed by 2615 | PDF Full-text (480 KB) | HTML Full-text | XML Full-text
Abstract
With the advance of insulated gate bipolar transistor (IGBT) converters, Multi-Terminal DC (MTDC) based on the voltage-source converter (VSC) has developed rapidly in renewable and electric power systems. To reduce the copper loss of large capacity and long distance DC transmission line, an [...] Read more.
With the advance of insulated gate bipolar transistor (IGBT) converters, Multi-Terminal DC (MTDC) based on the voltage-source converter (VSC) has developed rapidly in renewable and electric power systems. To reduce the copper loss of large capacity and long distance DC transmission line, an improved droop control design based on optimal power sharing in VSC-MTDC integrating offshore wind farm is proposed. The proposed approach provided a calculation method for power-voltage droop coefficients under two different scenarios either considering local load or not. The available headroom of each converter station was considered as a converter outage, to participate in the power adjustment according to their ability. A four-terminal MTDC model system including two large scale wind farms was set up in PSCAD/EMTDC. Then, the proposed control strategy was verified through simulation under the various conditions, including wind speed variation, rectifier outage and inverter outage, and a three-phase short-circuit of the converter. Full article
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Open AccessArticle Characterization of Anion Exchange Membrane Containing Epoxy Ring and C–Cl Bond Quaternized by Various Amine Groups for Application in Fuel Cells
Energies 2015, 8(7), 7084-7099; https://doi.org/10.3390/en8077084
Received: 26 May 2015 / Revised: 22 June 2015 / Accepted: 7 July 2015 / Published: 14 July 2015
Cited by 9 | Viewed by 2569 | PDF Full-text (1430 KB) | HTML Full-text | XML Full-text
Abstract
Anion exchange membranes were synthesized from different compositions of glycidyl methacrylate (GMA) and vinylbenzyl chloride (VBC), with constant content of divinyl benzene (DVB) by radical polymerization using benzoyl peroxide (BPO) on non-woven polyethylene terephthalate (PET) substrate. Polymerized membranes were then quaternized by soaking [...] Read more.
Anion exchange membranes were synthesized from different compositions of glycidyl methacrylate (GMA) and vinylbenzyl chloride (VBC), with constant content of divinyl benzene (DVB) by radical polymerization using benzoyl peroxide (BPO) on non-woven polyethylene terephthalate (PET) substrate. Polymerized membranes were then quaternized by soaking in trimethylamine (TMA), triethylamine (TEA), tripropylamine (TPA), and 1,4-diazabicyclo [2.2.2] octane (DABCO). Characteristics of membranes were confirmed by Fourier transform infrared spectroscopy, water uptake, ion exchange capacity, ion conductivity, thermal, and alkaline stability. The results revealed that membranes quaternized by TPA and DABCO showed high affinity when GMA content was 15 wt% and 75 wt%, respectively. IEC and ion conductivity of membranes quaternized by TPA were 1.34 meq·g1 and 0.022 S·cm1 (at 60 °C), respectively. IEC and ion conductivity of membranes were quaternized by DABCO were 1.34 meq·g1 and 0.021 S·cm1 (at 60 °C), respectively. The results indicate that the membrane containing GMA 15 wt% quaternized by TPA showed the highest thermal stability among membranes and exhibited high ion conductivity compared to existing researches using GMA, VBC, and DVB monomers. Full article
(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells 2015)
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Open AccessArticle Development and Characterization of Non-Conventional Micro-Porous Layers for PEM Fuel Cells
Energies 2015, 8(7), 7070-7083; https://doi.org/10.3390/en8077070
Received: 16 June 2015 / Revised: 2 July 2015 / Accepted: 6 July 2015 / Published: 13 July 2015
Cited by 4 | Viewed by 1776 | PDF Full-text (2212 KB) | HTML Full-text | XML Full-text
Abstract
Gas diffusion medium (GDM) is a crucial component in proton exchange membrane fuel cells (PEMFCs). Being composed of a gas diffusion layer (GDL) with a micro-porous layer (MPL) coated onto it, it ensures a proper water management due to the highly hydrophobic materials [...] Read more.
Gas diffusion medium (GDM) is a crucial component in proton exchange membrane fuel cells (PEMFCs). Being composed of a gas diffusion layer (GDL) with a micro-porous layer (MPL) coated onto it, it ensures a proper water management due to the highly hydrophobic materials employed in cell assembly. In current commercial applications, the desired water repellent behaviour is usually obtained by using polytetrafluoroethylene (PTFE). In this work, Fluorolink® P56 (Solvay Specialty Polymers, Milan, Italy), a commercially available, anionic, segmented high molecular weight polyfluorourethane with perfluoropolyether groups was extensively evaluated as an alternative to PTFE for micro-porous layer hydrophobization. A change in polymer used is desirable in order to simplify the production process, both in terms of ink formulation and thermal treatment, as well as to get a higher hydrophobicity and, consequently, more efficient water management. Innovative prepared samples were compared to a PTFE-based GDM, in order to assess differences both from morphological and from an electrochemical point of view. Full article
(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells 2015)
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Open AccessArticle A Mathematical Model of Hourly Solar Radiation in Varying Weather Conditions for a Dynamic Simulation of the Solar Organic Rankine Cycle
Energies 2015, 8(7), 7058-7069; https://doi.org/10.3390/en8077058
Received: 7 May 2015 / Revised: 2 July 2015 / Accepted: 6 July 2015 / Published: 13 July 2015
Cited by 5 | Viewed by 2118 | PDF Full-text (872 KB) | HTML Full-text | XML Full-text
Abstract
A mathematical model of hourly solar radiation with weather variability is proposed based on the simple sky model. The model uses a superposition of trigonometric functions with short and long periods. We investigate the effects of the model variables on the clearness ( [...] Read more.
A mathematical model of hourly solar radiation with weather variability is proposed based on the simple sky model. The model uses a superposition of trigonometric functions with short and long periods. We investigate the effects of the model variables on the clearness (kD) and the probability of persistence (POPD) indices and also evaluate the proposed model for all of the kD-POPD weather classes. A simple solar organic Rankine cycle (SORC) system with thermal storage is simulated using the actual weather conditions, and then, the results are compared with the simulation results using the proposed model and the simple sky model. The simulation results show that the proposed model provides more accurate system operation characteristics than the simple sky model. Full article
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Open AccessArticle Ejin Oasis Land Use and Vegetation Change between 2000 and 2011: The Role of the Ecological Water Diversion Project
Energies 2015, 8(7), 7040-7057; https://doi.org/10.3390/en8077040
Received: 6 May 2015 / Revised: 30 June 2015 / Accepted: 6 July 2015 / Published: 13 July 2015
Cited by 12 | Viewed by 1861 | PDF Full-text (4685 KB) | HTML Full-text | XML Full-text
Abstract
Ejin Oasis, located in the lower reaches of the Heihe River Basin (HRB), has experienced severe ecosystem decline between the 1960s and 1990s. In response, the Chinese Government implemented the Ecological Water Diversion Project (EWDP) in 2000. To evaluate the effects of the [...] Read more.
Ejin Oasis, located in the lower reaches of the Heihe River Basin (HRB), has experienced severe ecosystem decline between the 1960s and 1990s. In response, the Chinese Government implemented the Ecological Water Diversion Project (EWDP) in 2000. To evaluate the effects of the EWDP, this study monitored changes in land use and vegetation in the Ejin Oasis since 2000 and examined driving factors behind such changes. Results demonstrated that the Ejin Oasis ecosystem generally improved between 2000 and 2011. Water body area significantly increased. Lake area of once dried-up Sogo Nuur increased to 45 km2. Accordingly, vegetation cover restoration has also significantly increased. For example, the Seasonally Integrated Normalized Difference Vegetation Index (SINDVI) has shown that 31.18% of the entire study area experienced an increase in vegetation area. On the other hand, even though the EWDP has been successful in driving vegetation recovery and lake restoration, farmland reclamation has counteracted such restoration initiatives. Farmland area almost doubled between 2000 and 2011. Thus, farmland expansion management is necessary for the full restoration of the Ejin Oasis ecosystems as well as HRB sustainable development. The results of this study can provide a reference for the management of the HRB. Full article
(This article belongs to the Special Issue Large Scale LUCC, Ecosystem Service, Water Balance and Energy Use)
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Open AccessArticle A Novel Ground Fault Identification Method for 2 × 5 kV Railway Power Supply Systems
Energies 2015, 8(7), 7020-7039; https://doi.org/10.3390/en8077020
Received: 21 April 2015 / Revised: 17 June 2015 / Accepted: 6 July 2015 / Published: 13 July 2015
Cited by 6 | Viewed by 2292 | PDF Full-text (4522 KB) | HTML Full-text | XML Full-text | Correction
Abstract
The location of ground faults in railway electric lines in 2 × 5 kV railway power supply systems is a difficult task. In both 1 × 25 kV and transmission power systems it is common practice to use distance protection relays to clear [...] Read more.
The location of ground faults in railway electric lines in 2 × 5 kV railway power supply systems is a difficult task. In both 1 × 25 kV and transmission power systems it is common practice to use distance protection relays to clear ground faults and localize their positions. However, in the particular case of this 2 × 25 kV system, due to the widespread use of autotransformers, the relation between the distance and the impedance seen by the distance protection relays is not linear and therefore the location is not accurate enough. This paper presents a simple and economical method to identify the subsection between autotransformers and the conductor (catenary or feeder) where the ground fault is happening. This method is based on the comparison of the angle between the current and the voltage of the positive terminal in each autotransformer. Consequently, after the identification of the subsection and the conductor with the ground defect, only the subsection where the ground fault is present will be quickly removed from service, with the minimum effect on rail traffic. This method has been validated through computer simulations and laboratory tests with positive results. Full article
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Open AccessArticle Transformation toward a Secure and Precaution-Oriented Energy System with the Guiding Concept of Resilience—Implementation of Low-Exergy Solutions in Northwestern Germany
Energies 2015, 8(7), 6995-7019; https://doi.org/10.3390/en8076995
Received: 1 June 2015 / Revised: 1 July 2015 / Accepted: 3 July 2015 / Published: 10 July 2015
Cited by 4 | Viewed by 2394 | PDF Full-text (2722 KB) | HTML Full-text | XML Full-text
Abstract
Climate changes, incidents like nuclear disasters, and associated political objectives call for significant changes to the current energy system. Despite these far-reaching transformation processes, within the intended changes security of supply and precautions against the possible consequences of climate change must be ensured. [...] Read more.
Climate changes, incidents like nuclear disasters, and associated political objectives call for significant changes to the current energy system. Despite these far-reaching transformation processes, within the intended changes security of supply and precautions against the possible consequences of climate change must be ensured. Consequently, the question arises how to direct energy systems. In this context the processes of guiding orientations with the help of the guiding concept of “resilient systems” and feasible and addressee-oriented guiding design principles can be an option to provide guidance in transformation processes. However, it is questionable whether and how such processes are effective in the long term and if they are able to give direction by doing so. Within the framework of empirical studies of a regional guiding orientation process for the energy system of Northwestern Germany, the long-term effectiveness of the process and its spread resilient guiding design principles of “low-exergy solutions” and “climate-adapted and energy-efficient refrigeration” has been confirmed. Such effectiveness requires the implementation of a four-phase guiding orientation process which takes content-related and process-related effectiveness factors into account. Therefore, the study shows how regional energy systems can be designed toward the major challenges of ensuring security and precaution. Full article
(This article belongs to the Special Issue Resilience of Energy Systems)
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Open AccessArticle Analysis on the Initial Cracking Parameters of Cross-Measure Hydraulic Fracture in Underground Coal Mines
Energies 2015, 8(7), 6977-6994; https://doi.org/10.3390/en8076977
Received: 27 May 2015 / Revised: 1 July 2015 / Accepted: 2 July 2015 / Published: 10 July 2015
Cited by 13 | Viewed by 2007 | PDF Full-text (2609 KB) | HTML Full-text | XML Full-text
Abstract
Initial cracking pressure and locations are important parameters in conducting cross-measure hydraulic fracturing to enhance coal seam permeability in underground coalmines, which are significantly influenced by in-situ stress and occurrence of coal seam. In this study, stress state around cross-measure fracturing boreholes was [...] Read more.
Initial cracking pressure and locations are important parameters in conducting cross-measure hydraulic fracturing to enhance coal seam permeability in underground coalmines, which are significantly influenced by in-situ stress and occurrence of coal seam. In this study, stress state around cross-measure fracturing boreholes was analyzed using in-situ stress coordinate transformation, then a mathematical model was developed to evaluate initial cracking parameters of borehole assuming the maximum tensile stress criterion. Subsequently, the influences of in-situ stress and occurrence of coal seams on initial cracking pressure and locations in underground coalmines were analyzed using the proposed model. Finally, the proposed model was verified with field test data. The results suggest that the initial cracking pressure increases with the depth cover and coal seam dip angle. However, it decreases with the increase in azimuth of major principle stress. The results also indicate that the initial cracking locations concentrated in the second and fourth quadrant in polar coordinate, and shifted direction to the strike of coal seam as coal seam dip angle and azimuth of maximum principle stress increase. Field investigation revealed consistent rule with the developed model that the initial cracking pressure increases with the coal seam dip angle. Therefore, the proposed mathematical model provides theoretical insight to analyze the initial cracking parameters during cross-measure hydraulic fracturing for underground coalmines. Full article
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Open AccessArticle Multi-Objective Reservoir Optimization Balancing Energy Generation and Firm Power
Energies 2015, 8(7), 6962-6976; https://doi.org/10.3390/en8076962
Received: 14 April 2015 / Revised: 12 June 2015 / Accepted: 23 June 2015 / Published: 10 July 2015
Cited by 10 | Viewed by 1688 | PDF Full-text (968 KB) | HTML Full-text | XML Full-text
Abstract
To maximize annual power generation and to improve firm power are important but competing goals for hydropower stations. The firm power output is decisive for the installed capacity in design, and represents the reliability of the power generation when the power plant is [...] Read more.
To maximize annual power generation and to improve firm power are important but competing goals for hydropower stations. The firm power output is decisive for the installed capacity in design, and represents the reliability of the power generation when the power plant is put into operation. To improve the firm power, the whole generation process needs to be as stable as possible, while the maximization of power generation requires a rapid rise of the water level at the beginning of the storage period. Taking the minimal power output as the firm power, both the total amount and the reliability of the hydropower generation are considered simultaneously in this study. A multi-objective model to improve the comprehensive benefits of hydropower stations are established, which is optimized by Non-dominated Sorting Genetic Algorithm-II (NSGA-II). The Three Gorges Cascade Hydropower System (TGCHS) is taken as the study case, and the Pareto Fronts in different search spaces are obtained. The results not only prove the effectiveness of the proposed method, but also provide operational references for the TGCHS, indicating that there is room of improvement for both the annual power generation and the firm power. Full article
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Open AccessArticle An Environmentally-Friendly Tourist Village in Egypt Based on a Hybrid Renewable Energy System––Part Two: A Net Zero Energy Tourist Village
Energies 2015, 8(7), 6945-6961; https://doi.org/10.3390/en8076945
Received: 23 April 2015 / Revised: 17 June 2015 / Accepted: 18 June 2015 / Published: 10 July 2015
Cited by 8 | Viewed by 2073 | PDF Full-text (4609 KB) | HTML Full-text | XML Full-text
Abstract
The main objective of this study is to discuss the economical and the environmental analysis of a net zero energy (NZE) tourist village in Alexandria, Egypt, by maximizing the renewable energy fraction and minimizing the greenhouse gases (GHG) emissions. The hybrid photovoltaics (PV)/wind/diesel/battery [...] Read more.
The main objective of this study is to discuss the economical and the environmental analysis of a net zero energy (NZE) tourist village in Alexandria, Egypt, by maximizing the renewable energy fraction and minimizing the greenhouse gases (GHG) emissions. The hybrid photovoltaics (PV)/wind/diesel/battery system is found to be the optimum hybrid renewable energy system (HRES) for the proposed tourist village under the study. The optimum HRES consists of 1600 kW of PV panels (58.09% solar energy penetration), 1000 kW of wind turbines (41.34% wind energy penetration), 1000 kW of power converters, 200 kW diesel generator (only 0.57% diesel generator penetration) in addition to 2000 batteries with the capacity of 589 Ah each. The levelized cost of energy (COE) from the optimum HRES is $0.17/kWh and the total net present cost (NPC) of this system is $15,383,360. Additionally, the maximum renewable energy fraction is 99.1% and the amount of GHG emitted from the optimum HRES is only 31,289 kg/year, which is negligible in comparison with the other system configurations, therefore the optimum HRES can be considered as a green system. In addition to this, the achieved percentage of the capacity shortage and the unmet load in the optimal HRES is only 0% for both. Full article
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