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12 pages, 207 KiB

Open AccessArticle

Sustainability Criteria and Indicators for the Bio-Based Economy in Europe: State of Discussion and Way Forward

by Uwe R. Fritsche and Leire Iriarte

Energies 2014, 7(11), 6825-6836; https://doi.org/10.3390/en7116825 - 24 Oct 2014

Cited by 62 | Viewed by 9030

Abstract

There is a strong interest in the EU to promote the bioeconomy sector within the EU 2020 strategy. It is thus necessary to assure a sound sustainability framework. This paper reviews international and European sustainability initiatives mainly for biomass for bioenergy. The basic [...] Read more.

There is a strong interest in the EU to promote the bioeconomy sector within the EU 2020 strategy. It is thus necessary to assure a sound sustainability framework. This paper reviews international and European sustainability initiatives mainly for biomass for bioenergy. The basic and advanced sustainability indicators are identified and described with particular attention to those points without agreement between stakeholders. Based on the state of the discussion, some suggestions to enhance the sustainable development of the bioeconomy sector are proposed. Full article

(This article belongs to the Special Issue Biomass Resource Efficiency for the Biobased Industries)

19 pages, 961 KiB

Open AccessArticle

A New System to Estimate and Reduce Electrical Energy Consumption of Domestic Hot Water in Spain

by Alberto Gutierrez-Escolar, Ana Castillo-Martinez, Jose M. Gomez-Pulido, Jose-Maria Gutierrez-Martinez and Zlatko Stapic

Energies 2014, 7(11), 6837-6855; https://doi.org/10.3390/en7116837 - 24 Oct 2014

Cited by 8 | Viewed by 8878

Abstract

Energy consumption rose about 28% over the 2001 to 2011 period in the Spanish residential sector. In this environment, domestic hot water (DHW) represents the second highest energy demand. There are several methodologies to estimate DHW consumption, but each methodology uses different inputs [...] Read more.

Energy consumption rose about 28% over the 2001 to 2011 period in the Spanish residential sector. In this environment, domestic hot water (DHW) represents the second highest energy demand. There are several methodologies to estimate DHW consumption, but each methodology uses different inputs and some of them are based on obsolete data. DHW energy consumption estimation is a key tool to plan modifications that could enhance this consumption and we decided to update the methodologies. We studied DHW consumption with data from 10 apartments in the same building during 18 months. As a result of the study, we updated one chosen methodology, adapting it to the current situation. One of the challenges to improve efficiency of DHW use is that most of people are not aware of how it is consumed in their homes. To help this information to reach consumers, we developed a website to allow users to estimate the final electrical energy needed for DHW. The site uses three estimation methodologies and chooses the best fit based on information given by the users. Finally, the application provides users with recommendations and tips to reduce their DHW consumption while still maintaining the desired comfort level. Full article

(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)

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30 pages, 2511 KiB

Open AccessArticle

Simplified Analysis of the Electric Power Losses for On-Shore Wind Farms Considering Weibull Distribution Parameters

by Antonio Colmenar-Santos, Severo Campíez-Romero, Lorenzo Alfredo Enríquez-Garcia and Clara Pérez-Molina

Energies 2014, 7(11), 6856-6885; https://doi.org/10.3390/en7116856 - 28 Oct 2014

Cited by 17 | Viewed by 12989

Abstract

Electric power losses are constantly present during the service life of wind farms and must be considered in the calculation of the income arising from selling the produced electricity. It is typical to estimate the electrical losses in the design stage as those [...] Read more.

Electric power losses are constantly present during the service life of wind farms and must be considered in the calculation of the income arising from selling the produced electricity. It is typical to estimate the electrical losses in the design stage as those occurring when the wind farm operates at rated power, nevertheless, it is necessary to determine a method for checking if the actual losses meet the design requirements during the operation period. In this paper, we prove that the electric losses at rated power should not be considered as a reference level and a simple methodology will be developed to analyse and foresee the actual losses in a set period as a function of the wind resource in such period, defined according to the Weibull distribution, and the characteristics of the wind farm electrical infrastructure. This methodology facilitates a simple way, to determine in the design phase and to check during operation, the actual electricity losses. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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11 pages, 493 KiB

Open AccessArticle

Ambiguity Reduction by Objective Model Selection, with an Application to the Costs of the EU 2030 Climate Targets

by Richard S. J. Tol

Energies 2014, 7(11), 6886-6896; https://doi.org/10.3390/en7116886 - 28 Oct 2014

Cited by 6 | Viewed by 6242

Abstract

I estimate the cost of meeting the EU 2030 targets for greenhouse gas emission reduction, using statistical emulators of ten alternative models. Assuming a first-best policy implementation, I find that total and marginal costs are modest. The statistical emulators allow me to compute [...] Read more.

I estimate the cost of meeting the EU 2030 targets for greenhouse gas emission reduction, using statistical emulators of ten alternative models. Assuming a first-best policy implementation, I find that total and marginal costs are modest. The statistical emulators allow me to compute the risk premiums, which are small, because the EU is rich and the policy impact is small. The ensemble of ten models allows me to compute the ambiguity premium, which is small for the same reason. I construct a counterfactual estimate of recent emissions without the climate policy and use that to test the predictive skill of the ten models. The models that show the lowest cost of emission reduction also have the lowest skill for Europe in recent times. Full article

(This article belongs to the Special Issue Energy Transitions and Economic Change)

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33 pages, 2500 KiB

Open AccessArticle

A Heuristic Rule-Based Passive Design Decision Model for Reducing Heating Energy Consumption of Korean Apartment Buildings

by Dongjun Suh and Seongju Chang

Energies 2014, 7(11), 6897-6929; https://doi.org/10.3390/en7116897 - 29 Oct 2014

Cited by 8 | Viewed by 7216

Abstract

This research presents an evaluative energy model for estimating the energy efficiency of the design choices of architects and engineers in the early design phase. We analyze the effects of various parameters with different characteristics in various combinations for building energy consumption. With [...] Read more.

This research presents an evaluative energy model for estimating the energy efficiency of the design choices of architects and engineers in the early design phase. We analyze the effects of various parameters with different characteristics in various combinations for building energy consumption. With this analysis, we build a database that identifies a set of heuristic rules for energy-efficient building design to facilitate the design of sustainable apartment housing. Perturbation studies are based on a sensitivity analysis used to identify the thermal influence of the input design parameters on various simulation outputs and compare the results to a reference case. Energy sensitivity weight factors are obtained from an extensive sensitivity study using building energy simulations. The results of the energy sensitivity study summarized in a set of heuristic rules for evaluating architectural features are estimated through case studies of Korean apartment buildings. This study offers valuable guidelines for developing energy-efficient residential housing in Korea and will help architects in considering appropriate design schemes and provide a ready reference to generalized test cases for both architects and engineers so that they can zero in on a set of effective design solutions. Full article

(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)

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24 pages, 1085 KiB

Open AccessArticle

A Model Predictive Control Approach for Fuel Economy Improvement of a Series Hydraulic Hybrid Vehicle

by Tri-Vien Vu, Chih-Keng Chen and Chih-Wei Hung

Energies 2014, 7(11), 7017-7040; https://doi.org/10.3390/en7117017 - 31 Oct 2014

Cited by 32 | Viewed by 9591

Abstract

This study applied a model predictive control (MPC) framework to solve the cruising control problem of a series hydraulic hybrid vehicle (SHHV). The controller not only regulates vehicle velocity, but also engine torque, engine speed, and accumulator pressure to their corresponding reference values. [...] Read more.

This study applied a model predictive control (MPC) framework to solve the cruising control problem of a series hydraulic hybrid vehicle (SHHV). The controller not only regulates vehicle velocity, but also engine torque, engine speed, and accumulator pressure to their corresponding reference values. At each time step, a quadratic programming problem is solved within a predictive horizon to obtain the optimal control inputs. The objective is to minimize the output error. This approach ensures that the components operate at high efficiency thereby improving the total efficiency of the system. The proposed SHHV control system was evaluated under urban and highway driving conditions. By handling constraints and input-output interactions, the MPC-based control system ensures that the system operates safely and efficiently. The fuel economy of the proposed control scheme shows a noticeable improvement in comparison with the PID-based system, in which three Proportional-Integral-Derivative (PID) controllers are used for cruising control. Full article

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26 pages, 784 KiB

Open AccessArticle

An Efficient, Scalable Time-Frequency Method for Tracking Energy Usage of Domestic Appliances Using a Two-Step Classification Algorithm

by Paula Meehan, Conor McArdle and Stephen Daniels

Energies 2014, 7(11), 7041-7066; https://doi.org/10.3390/en7117041 - 31 Oct 2014

Cited by 42 | Viewed by 7978

Abstract

Load monitoring is the practice of measuring electrical signals in a domestic environment in order to identify which electrical appliances are consuming power. One reason for developing a load monitoring system is to reduce power consumption by increasing consumers’ awareness of which appliances [...] Read more.

Load monitoring is the practice of measuring electrical signals in a domestic environment in order to identify which electrical appliances are consuming power. One reason for developing a load monitoring system is to reduce power consumption by increasing consumers’ awareness of which appliances consume the most energy. Another example of an application of load monitoring is activity sensing in the home for the provision of healthcare services. This paper outlines the development of a load disaggregation method that measures the aggregate electrical signals of a domestic environment and extracts features to identify each power consuming appliance. A single sensor is deployed at the main incoming power point, to sample the aggregate current signal. The method senses when an appliance switches ON or OFF and uses a two-step classification algorithm to identify which appliance has caused the event. Parameters from the current in the temporal and frequency domains are used as features to define each appliance. These parameters are the steady-state current harmonics and the rate of change of the transient signal. Each appliance’s electrical characteristics are distinguishable using these parameters. There are three Types of loads that an appliance can fall into, linear nonreactive, linear reactive or nonlinear reactive. It has been found that by identifying the load type first and then using a second classifier to identify individual appliances within these Types, the overall accuracy of the identification algorithm is improved. Full article

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27 pages, 3312 KiB

Open AccessArticle

Preliminary Design and Simulation of a Turbo Expander for Small Rated Power Organic Rankine Cycle (ORC)

by Roberto Capata and Gustavo Hernandez

Energies 2014, 7(11), 7067-7093; https://doi.org/10.3390/en7117067 - 3 Nov 2014

Cited by 34 | Viewed by 12604

Abstract

Nowadays, the Organic Rankine Cycle (ORC) system, which operates with organic fluids, is one of the leading technologies for “waste energy recovery”. It works as a conventional Rankine Cycle but, as mentioned, instead of steam/water, an organic fluid is used. This change allows [...] Read more.

Nowadays, the Organic Rankine Cycle (ORC) system, which operates with organic fluids, is one of the leading technologies for “waste energy recovery”. It works as a conventional Rankine Cycle but, as mentioned, instead of steam/water, an organic fluid is used. This change allows it to convert low temperature heat into electric energy where required. Large numbers of studies have been carried out to identify the most suitable fluids, system parameters and the various configurations. In the present market, most ORC systems are designed and manufactured for the recovery of thermal energy from various sources operating at “large power rating” (exhaust gas turbines, internal combustion engines, geothermal sources, large melting furnaces, biomass, solar, etc.); from which it is possible to produce a large amount of electric energy (30 kW ÷ 300 kW). Such applications for small nominal power sources, as well as the exhaust gases of internal combustion engines (car sedan or town, ships, etc.) or small heat exchangers, are very limited. The few systems that have been designed and built for small scale applications, have, on the other hand, different types of expander (screw, scroll, etc.). These devices are not adapted for placement in small and restricted places like the interior of a conventional car. The aim of this work is to perform the preliminary design of a turbo-expander that meets diverse system requirements such as low pressure, small size and low mass flow rates. The expander must be adaptable to a small ORC system utilizing gas of a diesel engine or small gas turbine as thermal source to produce 2–10 kW of electricity. The temperature and pressure of the exhaust gases, in this case study (400–600 °C and a pressure of 2 bar), imposes a limit on the use of an organic fluid and on the net power that can be produced. In addition to water, fluids such as CO₂, R134a and R245fa have been considered. Once the operating fluids has been chosen, the turbine characteristics (dimensions, input and output temperature, pressure ratio, etc.) have been calculated and an attempt to find the “nearly-optimal” combination has been carried out. The detailed design of a radial expander is presented and discussed. A thermo-mechanical performance study was carry out to verify structural tension and possible displacement. On the other hand, preliminary CFD analyses have been performed to verify the effectiveness of the design procedure. Full article

(This article belongs to the Special Issue Organic Rankine Cycle (ORC))

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11 pages, 711 KiB

Open AccessArticle

Experimental Investigation of Heat Transfer and Pressure Drop Characteristics of H-type Finned Tube Banks

by Heng Chen, Yungang Wang, Qinxin Zhao, Haidong Ma, Yuxin Li and Zhongya Chen

Energies 2014, 7(11), 7094-7104; https://doi.org/10.3390/en7117094 - 4 Nov 2014

Cited by 69 | Viewed by 9554

Abstract

H-type finned tube heat exchanger elements maintain a high capacity for heat transfer, possess superior self-cleaning properties and retain the ability to effect flue gas waste heat recovery in boiler renovations. In this paper, the heat transfer and pressure drop characteristics of H-type [...] Read more.

H-type finned tube heat exchanger elements maintain a high capacity for heat transfer, possess superior self-cleaning properties and retain the ability to effect flue gas waste heat recovery in boiler renovations. In this paper, the heat transfer and pressure drop characteristics of H-type finned tube banks are studied via an experimental open high-temperature wind tunnel system. The effects of fin width, fin height, fin pitch and air velocity on fin efficiency, convective heat transfer coefficient, integrated heat transfer capacity and pressure drop are examined. The results indicate that as air velocity, fin height and fin width increase, fin efficiency decreases. Convective heat transfer coefficient is proportional to fin pitch, but inversely proportional to fin height and fin width. Integrated heat transfer capacity is related to fin efficiency, convective heat transfer coefficient and finned ratio. Pressure drop increases with the increase of fin height and fin width. Finally, predictive correlations of fin efficiency, Nusselt number and Euler Number are developed based on the experimental data. Full article

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20 pages, 1661 KiB

Open AccessArticle

Design of High Performance Permanent-Magnet Synchronous Wind Generators

by Chun-Yu Hsiao, Sheng-Nian Yeh and Jonq-Chin Hwang

Energies 2014, 7(11), 7105-7124; https://doi.org/10.3390/en7117105 - 4 Nov 2014

Cited by 46 | Viewed by 12193

Abstract

This paper is devoted to the analysis and design of high performance permanent-magnet synchronous wind generators (PSWGs). A systematic and sequential methodology for the design of PMSGs is proposed with a high performance wind generator as a design model. Aiming at high induced [...] Read more.

This paper is devoted to the analysis and design of high performance permanent-magnet synchronous wind generators (PSWGs). A systematic and sequential methodology for the design of PMSGs is proposed with a high performance wind generator as a design model. Aiming at high induced voltage, low harmonic distortion as well as high generator efficiency, optimal generator parameters such as pole-arc to pole-pitch ratio and stator-slot-shoes dimension, etc. are determined with the proposed technique using Maxwell 2-D, Matlab software and the Taguchi method. The proposed double three-phase and six-phase winding configurations, which consist of six windings in the stator, can provide evenly distributed current for versatile applications regarding the voltage and current demands for practical consideration. Specifically, windings are connected in series to increase the output voltage at low wind speed, and in parallel during high wind speed to generate electricity even when either one winding fails, thereby enhancing the reliability as well. A PMSG is designed and implemented based on the proposed method. When the simulation is performed with a 6 Ω load, the output power for the double three-phase winding and six-phase winding are correspondingly 10.64 and 11.13 kW. In addition, 24 Ω load experiments show that the efficiencies of double three-phase winding and six-phase winding are 96.56% and 98.54%, respectively, verifying the proposed high performance operation. Full article

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22 pages, 1968 KiB

Open AccessArticle

Uncertainties in Life Cycle Greenhouse Gas Emissions from Advanced Biomass Feedstock Logistics Supply Chains in Kansas

by Long Nguyen, Kara G. Cafferty, Erin M. Searcy and Sabrina Spatari

Energies 2014, 7(11), 7125-7146; https://doi.org/10.3390/en7117125 - 4 Nov 2014

Cited by 42 | Viewed by 8363

Abstract

To meet Energy Independence and Security Act (EISA) cellulosic biofuel mandates, the United States will require an annual domestic supply of about 242 million Mg of biomass by 2022. To improve the feedstock logistics of lignocellulosic biofuels in order to access available biomass [...] Read more.

To meet Energy Independence and Security Act (EISA) cellulosic biofuel mandates, the United States will require an annual domestic supply of about 242 million Mg of biomass by 2022. To improve the feedstock logistics of lignocellulosic biofuels in order to access available biomass resources from areas with varying yields, commodity systems have been proposed and designed to deliver quality-controlled biomass feedstocks at preprocessing “depots”. Preprocessing depots densify and stabilize the biomass prior to long-distance transport and delivery to centralized biorefineries. The logistics of biomass commodity supply chains could introduce spatially variable environmental impacts into the biofuel life cycle due to needing to harvest, move, and preprocess biomass from multiple distances that have variable spatial density. This study examines the uncertainty in greenhouse gas (GHG) emissions of corn stover logistics within a bio-ethanol supply chain in the state of Kansas, where sustainable biomass supply varies spatially. Two scenarios were evaluated each having a different number of depots of varying capacity and location within Kansas relative to a central commodity-receiving biorefinery to test GHG emissions uncertainty. The first scenario sited four preprocessing depots evenly across the state of Kansas but within the vicinity of counties having high biomass supply density. The second scenario located five depots based on the shortest depot-to-biorefinery rail distance and biomass availability. The logistics supply chain consists of corn stover harvest, collection and storage, feedstock transport from field to biomass preprocessing depot, preprocessing depot operations, and commodity transport from the biomass preprocessing depot to the biorefinery. Monte Carlo simulation was used to estimate the spatial uncertainty in the feedstock logistics gate-to-gate sequence. Within the logistics supply chain GHG emissions are most sensitive to the transport of the densified biomass, which introduces the highest variability (0.2–13 g CO₂e/MJ) to life cycle GHG emissions. Moreover, depending upon the biomass availability and its spatial density and surrounding transportation infrastructure (road and rail), logistics can increase the variability in life cycle environmental impacts for lignocellulosic biofuels. Within Kansas, life cycle GHG emissions could range from 24 g CO₂e/MJ to 41 g CO₂e/MJ depending upon the location, size and number of preprocessing depots constructed. However, this range can be minimized through optimizing the siting of preprocessing depots where ample rail infrastructure exists to supply biomass commodity to a regional biorefinery supply system. Full article

(This article belongs to the Special Issue Biomass Resource Efficiency for the Biobased Industries)

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19 pages, 589 KiB

Open AccessArticle

Post Feed-in Scheme Photovoltaic System Feasibility Evaluation in Italy: Sicilian Case Studies

by Riccardo Squatrito, Filippo Sgroi, Salvatore Tudisca, Anna Maria Di Trapani and Riccardo Testa

Energies 2014, 7(11), 7147-7165; https://doi.org/10.3390/en7117147 - 5 Nov 2014

Cited by 43 | Viewed by 7098

Abstract

Thanks to national energy policies, over recent years the Italian photovoltaic (PV) sector has undergone an extraordinary growth, also affecting the primary sector. In this context, Mediterranean greenhouses are well-adapted to photovoltaic systems because they represent one of the most energy-intensive sectors in [...] Read more.

Thanks to national energy policies, over recent years the Italian photovoltaic (PV) sector has undergone an extraordinary growth, also affecting the primary sector. In this context, Mediterranean greenhouses are well-adapted to photovoltaic systems because they represent one of the most energy-intensive sectors in agriculture. The Italian feed-in scheme ended at the beginning of 2013, making it necessary to investigate the feasibility of photovoltaic systems devoid of any electricity production-related incentives. In this paper, production cost and profitability analyses of photovoltaic electricity have been conducted, considering Mediterranean solar greenhouses in which, thanks to net metering, all the electricity produced by photovoltaic panels is self-consumed. Our results showed that grid parity is already reached for Sicilian PV systems with a capacity greater than 50 kW. Moreover, net present value, internal rate of return and discounted payback time all demonstrate the high economic convenience of all the photovoltaic investments analyzed, due to the huge savings on energy expenditures. Full article

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12 pages, 724 KiB

Open AccessArticle

A Polygeneration System Based on Multi-Input Chemical Looping Combustion

by Xiaosong Zhang, Sheng Li and Hongguang Jin

Energies 2014, 7(11), 7166-7177; https://doi.org/10.3390/en7117166 - 6 Nov 2014

Cited by 13 | Viewed by 6887

Abstract

This paper proposes a polygeneration system based on a multi-input chemical looping combustion system, which generates methanol and electricity, through the use of natural gas and coal. In this system, the chemical looping hydrogen (CLH) production system and the coal-based methanol production system [...] Read more.

This paper proposes a polygeneration system based on a multi-input chemical looping combustion system, which generates methanol and electricity, through the use of natural gas and coal. In this system, the chemical looping hydrogen (CLH) production system and the coal-based methanol production system are integrated. A high quality fuel, natural gas, is used to improve the conversion ratio of coal. The Gibbs energy of the two kinds of fuels is fully used. Benefitting from the chemical looping process, 27% CO₂ can be captured without energy penalty. With the same outputs of methanol and electricity, the energy savings ratio of the new system is about 12%. Based on the exergy analyses, it is disclosed that the integration of synthetic utilization of natural gas and coal plays a significant role in reducing the exergy destruction of the new system. The promising results obtained in this paper may lead to a clean coal technology that will utilize natural gas and coal more efficiently and economically. Full article

(This article belongs to the Special Issue Selected Papers from ECOS 2014 — the 27st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems)

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16 pages, 805 KiB

Open AccessArticle

Lorenz Wind Disturbance Model Based on Grey Generated Components

by Yagang Zhang, Jingyun Yang, Kangcheng Wang and Yinding Wang

Energies 2014, 7(11), 7178-7193; https://doi.org/10.3390/en7117178 - 7 Nov 2014

Cited by 14 | Viewed by 6782

Abstract

In order to meet the needs of wind speed prediction in wind farms, we consider the influence of random atmospheric disturbances on wind variations. Considering a simplified fluid convection mode, a Lorenz system can be employed as an atmospheric disturbance model. Here Lorenz [...] Read more.

In order to meet the needs of wind speed prediction in wind farms, we consider the influence of random atmospheric disturbances on wind variations. Considering a simplified fluid convection mode, a Lorenz system can be employed as an atmospheric disturbance model. Here Lorenz disturbance is defined as the European norm of the solutions of the Lorenz equation. Grey generating and accumulated generating models are employed to explore the relationship between wind speed and its related disturbance series. We conclude that a linear or quadric polynomial generating model are optimal through the verification of short-term wind speed prediction in the Sotavento wind farm. The new proposed model not only greatly improves the precision of short-term wind speed prediction, but also has great significance for the maintenance and stability of wind power system operation. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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22 pages, 5448 KiB

Open AccessArticle

Naturally-Forced Slug Flow Expander for Application in a Waste-Heat Recovery Cycle

by Ben De Witt and Ron Hugo

Energies 2014, 7(11), 7223-7244; https://doi.org/10.3390/en7117223 - 10 Nov 2014

Cited by 2 | Viewed by 5916

Abstract

This paper investigates a slug-flow expander (SFE) for conversion of high-pressure gas/vapor into kinetic energy of liquid slugs. The energy transfer from high-pressure to kinetic energy is quantified using thrust plate measurements. Non-dimensional thrust data is used to quantify performance by normalizing measured [...] Read more.

This paper investigates a slug-flow expander (SFE) for conversion of high-pressure gas/vapor into kinetic energy of liquid slugs. The energy transfer from high-pressure to kinetic energy is quantified using thrust plate measurements. Non-dimensional thrust data is used to quantify performance by normalizing measured thrust by thrust for the same water flow rate at zero air flow rate. A total of 13 expander configurations are investigated and geometries with the shortest cavity length and the smallest exit diameter are found to result in the largest non-dimensional thrust increase. Results show that thrust augmentation increases with the initiation of slug flow in the SFE. The analysis performed on the normalized thrust readings suggested that as the water and air flow were increased to critical conditions, the liquid slugs produced by the SFE augmented the thrust measurements. The final performance evaluation was based on linear regression of the normalized thrust measurements where slug flow was generated for each SFE architecture. Greater magnitudes of the slope from the linear regression indicated the propensity of the SFE to augment thrust. This analysis confirmed that for the SFE configurations over the range of values investigated, the SFE increased thrust up to three times its original value at no air flow. Given the inherent multiphase nature of the slug-flow expander, application to systems involving expansion of wetting fluids (water as part of a waste-heat recovery system) or air with water droplet formation (as part of a compressed-air energy storage system) could be considered. Full article

(This article belongs to the Special Issue Waste Heat Recovery—Strategy and Practice)

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21 pages, 761 KiB

Open AccessArticle

Evaluation of Artificial Neural Network-Based Temperature Control for Optimum Operation of Building Envelopes

by Jin Woo Moon, Ji-Hyun Lee and Sooyoung Kim

Energies 2014, 7(11), 7245-7265; https://doi.org/10.3390/en7117245 - 12 Nov 2014

Cited by 12 | Viewed by 7240

Abstract

This study aims at developing an indoor temperature control method that could provide comfortable thermal conditions by integrating heating system control and the opening conditions of building envelopes. Artificial neural network (ANN)-based temperature control logic was developed for the control of heating systems [...] Read more.

This study aims at developing an indoor temperature control method that could provide comfortable thermal conditions by integrating heating system control and the opening conditions of building envelopes. Artificial neural network (ANN)-based temperature control logic was developed for the control of heating systems and openings at the building envelopes in a predictive and adaptive manner. Numerical comparative performance tests for the ANN-based temperature control logic and conventional non-ANN-based counterpart were conducted for single skin enveloped and double skin enveloped buildings after the simulation program was validated by comparing the simulation and the field measurement results. Analysis results revealed that the ANN-based control logic improved the indoor temperature environment with an increased comfortable temperature period and decreased overshoot and undershoot of temperatures outside of the operating range. The proposed logic did not show significant superiority in energy efficiency over the conventional logic. The ANN-based temperature control logic was able to maintain the indoor temperature more comfortably and with more stability within the operating range due to the predictive and adaptive features of ANN models. Full article

(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)

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16 pages, 693 KiB

Open AccessArticle

Performance Analysis of Cold Energy Recovery from CO₂ Injection in Ship-Based Carbon Capture and Storage (CCS)

by Hwalong You, Youngkyun Seo, Cheol Huh and Daejun Chang

Energies 2014, 7(11), 7266-7281; https://doi.org/10.3390/en7117266 - 12 Nov 2014

Cited by 13 | Viewed by 7718

Abstract

Carbon capture and storage (CCS) technology is one of the practical solutions for mitigating the effects of global warming. When captured CO₂ is injected into storage sites, the CO₂ is subjected to a heating process. In a conventional CO₂ injection [...] Read more.

Carbon capture and storage (CCS) technology is one of the practical solutions for mitigating the effects of global warming. When captured CO₂ is injected into storage sites, the CO₂ is subjected to a heating process. In a conventional CO₂ injection system, CO₂ cold energy is wasted during this heating process. This study proposes a new CO₂ injection system that takes advantage of the cold energy using the Rankine cycle. The study compared the conventional system with the new CO₂ injection system in terms of specific net power consumption, exergy efficiency, and life-cycle cost (LCC) to estimate the economic effects. The results showed that the new system reduced specific net power consumption and yielded higher exergy efficiency. The LCC of the new system was more economical. Several cases were examined corresponding to different conditions, specifically, discharge pressure and seawater temperature. This information may affect decision-making when CCS projects are implemented. Full article

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23 pages, 744 KiB

Open AccessArticle

An Optimization Model for Large–Scale Wind Power Grid Connection Considering Demand Response and Energy Storage Systems

by Zhongfu Tan, Huanhuan Li, Liwei Ju and Yihang Song

Energies 2014, 7(11), 7282-7304; https://doi.org/10.3390/en7117282 - 13 Nov 2014

Cited by 24 | Viewed by 7172

Abstract

To reduce the influence of wind power output uncertainty on power system stability, demand response (DRPs) and energy storage systems (ESSs) are introduced while solving scheduling optimization problems. To simulate wind power scenarios, this paper uses Latin Hypercube Sampling (LHS) to generate the [...] Read more.

To reduce the influence of wind power output uncertainty on power system stability, demand response (DRPs) and energy storage systems (ESSs) are introduced while solving scheduling optimization problems. To simulate wind power scenarios, this paper uses Latin Hypercube Sampling (LHS) to generate the initial scenario set and constructs a scenario reduction strategy based on Kantorovich distance. Since DRPs and ESSs can influence the distribution of demand load, this paper constructs a joint scheduling optimization model for wind power, ESSs and DRPs under the objective of minimizing total coal cost, and constraints of power demand and supply balance, users’ demand elasticity, thermal units’ startup-shutdown, thermal units’ output power climbing and wind power backup service. To analyze the influences of ESSs and DRPs on system wind power consumption capacity, example simulation is made in a 10 thermal units system with a 1000 MW wind farm and 400 MW energy storage systems under four simulation scenarios. The simulation results show that the introduction of DRPs and ESSs could promote system wind power consumption capacity with significantly economic and environment benefits, which include less coal consumption and less pollutant emission; and the optimization effect reaches the optimum when DRPs and ESSs are both introduced. Full article

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25 pages, 879 KiB

Open AccessArticle

An Integrated Energy-Efficient Operation Methodology for Metro Systems Based on a Real Case of Shanghai Metro Line One

by Cheng Gong, Shiwen Zhang, Feng Zhang, Jianguo Jiang and Xinheng Wang

Energies 2014, 7(11), 7305-7329; https://doi.org/10.3390/en7117305 - 13 Nov 2014

Cited by 45 | Viewed by 8385

Abstract

Metro systems are one of the most important transportation systems in people’s lives. Due to the huge amount of energy it consumes every day, highly-efficient operation of a metro system will lead to significant energy savings. In this paper, a new integrated Energy-efficient [...] Read more.

Metro systems are one of the most important transportation systems in people’s lives. Due to the huge amount of energy it consumes every day, highly-efficient operation of a metro system will lead to significant energy savings. In this paper, a new integrated Energy-efficient Operation Methodology (EOM) for metro systems is proposed and validated. Compared with other energy saving methods, EOM does not incur additional cost. In addition, it provides solutions to the frequent disturbance problems in the metro systems. EOM can be divided into two parts: Timetable Optimization (TO) and Compensational Driving Strategy Algorithm (CDSA). First, to get a basic energy-saving effect, a genetic algorithm is used to modify the dwell time of each stop to obtain the most optimal energy-efficient timetable. Then, in order to save additional energy when disturbances happen, a novel CDSA algorithm is formulated and proposed based on the foregoing method. To validate the correctness and effectiveness of the energy-savings possible with EOM, a real case of Shanghai Metro Line One (SMLO) is studied, where EOM was applied. The result shows that a significant amount of energy can be saved by using EOM. Full article

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18 pages, 1180 KiB

Open AccessArticle

Electronic Power Transformer Control Strategy in Wind Energy Conversion Systems for Low Voltage Ride-through Capability Enhancement of Directly Driven Wind Turbines with Permanent Magnet Synchronous Generators (D-PMSGs)

by Hui Huang, Chengxiong Mao, Jiming Lu and Dan Wang

Energies 2014, 7(11), 7330-7347; https://doi.org/10.3390/en7117330 - 14 Nov 2014

Cited by 16 | Viewed by 10774

Abstract

This paper investigates the use of an Electronic Power Transformer (EPT) incorporated with an energy storage system to smooth the wind power fluctuations and enhance the low voltage ride-through (LVRT) capability of directly driven wind turbines with permanent magnet synchronous generators (D-PMSGs). The [...] Read more.

This paper investigates the use of an Electronic Power Transformer (EPT) incorporated with an energy storage system to smooth the wind power fluctuations and enhance the low voltage ride-through (LVRT) capability of directly driven wind turbines with permanent magnet synchronous generators (D-PMSGs). The decoupled control schemes of the system, including the grid side converter control scheme, generator side converter control scheme and the control scheme of the energy storage system, are presented in detail. Under normal operating conditions, the energy storage system absorbs the high frequency component of the D-PMSG output power to smooth the wind power fluctuations. Under grid fault conditions, the energy storage system absorbs the redundant power, which could not be transferred to the grid by the EPT, to help the D-PMSG to ride through low voltage conditions. This coordinated control strategy is validated by simulation studies using MATLAB/Simulink. With the proposed control strategy, the output wind power quality is improved and the D-PMSG can ride through severe grid fault conditions. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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20 pages, 1745 KiB

Open AccessArticle

Design Optimization of Heat Wheels for Energy Recovery in HVAC Systems

by Stefano De Antonellis, Manuel Intini, Cesare Maria Joppolo and Calogero Leone

Energies 2014, 7(11), 7348-7367; https://doi.org/10.3390/en7117348 - 14 Nov 2014

Cited by 41 | Viewed by 12099

Abstract

Air to air heat exchangers play a crucial role in mechanical ventilation equipment, due to the potential primary energy savings both in case of refurbishment of existing buildings or in case of new ones. In particular, interest in heat wheels is increasing due [...] Read more.

Air to air heat exchangers play a crucial role in mechanical ventilation equipment, due to the potential primary energy savings both in case of refurbishment of existing buildings or in case of new ones. In particular, interest in heat wheels is increasing due to their low pressure drop and high effectiveness. In this paper a detailed optimization of design parameters of heat wheels is performed in order to maximize sensible effectiveness and to minimize pressure drop. The analysis is carried out through a one dimensional lumped parameters heat wheel model, which solves heat and mass transfer equations, and through appropriate correlations to estimate pressure drop. Simulation results have been compared with experimental data of a heat wheel tested in specific facilities, and good agreement is attained. The device optimization is performed through the variation of main design parameters, such as heat wheel length, channel base, height and thickness and for different operating conditions, namely the air face velocity and the revolution speed. It is shown that the best configurations are achieved with small channel thickness and, depending on the required sensible effectiveness, with appropriate values of wheel length and channel base and height. Full article

(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)

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27 pages, 656 KiB

Open AccessArticle

Thermodynamic Analysis of a Ship Power Plant Operating with Waste Heat Recovery through Combined Heat and Power Production

by Mirko Grljušić, Vladimir Medica and Nikola Račić

Energies 2014, 7(11), 7368-7394; https://doi.org/10.3390/en7117368 - 14 Nov 2014

Cited by 34 | Viewed by 13492

Abstract

The goal of this research is to study a cogeneration plant for combined heat & power (CHP) production that utilises the low-temperature waste energy in the power plant of a Suezmax-size oil tanker for all heating and electricity requirements during navigation. After considering [...] Read more.

The goal of this research is to study a cogeneration plant for combined heat & power (CHP) production that utilises the low-temperature waste energy in the power plant of a Suezmax-size oil tanker for all heating and electricity requirements during navigation. After considering various configurations, a standard propulsion engine operating at maximum efficiency and a CHP Plant with R245fa fluid using a supercritical organic Rankine cycle (ORC) is selected. All the ship heat requirements can be covered by energy of organic fluid after expansion in the turbine, except feeder-booster heating. Hence, an additional quantity of working fluid may be heated using an after Heat Recovery Steam Generator (HRSG) directed to the feeder-booster module. An analysis of the obtained results shows that the steam turbine plant does not yield significant fuel savings. However, a CHP plant with R245fa fluid using supercritical ORC meets all of the demands for electrical energy and heat while burning only a small amount of additional fuel in HRSG at the main engine off-design operation. Full article

(This article belongs to the Special Issue Organic Rankine Cycle (ORC))

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20 pages, 5403 KiB

Open AccessArticle

Dynamic Simulation of a CPV/T System Using the Finite Element Method

by Carlo Renno and Michele De Giacomo

Energies 2014, 7(11), 7395-7414; https://doi.org/10.3390/en7117395 - 14 Nov 2014

Cited by 33 | Viewed by 7031

Abstract

The aim of this paper is the determination of a concentrating thermo-photovoltaic (CPV/T) system dynamic model by means of the finite element method (FEM). The system consist of triple-junction InGaP/InGaAs/Ge (indium-gallium phosphide/indium-gallium-arsenide/germanium) solar cells connected to a metal core printed circuit board (MCPCB) [...] Read more.

The aim of this paper is the determination of a concentrating thermo-photovoltaic (CPV/T) system dynamic model by means of the finite element method (FEM). The system consist of triple-junction InGaP/InGaAs/Ge (indium-gallium phosphide/indium-gallium-arsenide/germanium) solar cells connected to a metal core printed circuit board (MCPCB) placed on a coil circuit used for the thermal energy recovery. In particular, the main aim is to determine the fluid outlet temperature. It is evaluated corresponding both to a constant cell temperature equal to 120 °C, generally representing the maximum operating temperature, and to cell temperature values instantly variable with the direct normal irradiation (DNI). Hence, an accurate DNI analysis is realized adopting the Gordon-Reddy statistical model. Using an accurate electric model, the cell temperature and efficiency are determined together with the CPV/T module electric and thermal powers. Generally, the CPV system size is realized according to the user electric load demand and, then, it is important to evaluate the necessary minimum concentration ratio (C_min), the limit of CPV system applicability, in order to determine the energy convenience profile. The fluid outlet temperature can be then obtained by the FEM analysis to verify if a CPV/T system can be used in solar heating and cooling applications. Full article

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19 pages, 955 KiB

Open AccessArticle

Operation of Steam Turbines under Blade Failures during the Summer Peak Load Periods

by Chien-Hsing Lee, Shih-Cheng Huang, Chia-An Chang and Bin-Kwie Chen

Energies 2014, 7(11), 7415-7433; https://doi.org/10.3390/en7117415 - 17 Nov 2014

Cited by 6 | Viewed by 6273

Abstract

This paper presents a discussion of practical experience related to the study of a cogeneration system where one of the four steam units occurs a failure of the low-pressure blades during peak load times of the summer months in Taiwan in the year [...] Read more.

This paper presents a discussion of practical experience related to the study of a cogeneration system where one of the four steam units occurs a failure of the low-pressure blades during peak load times of the summer months in Taiwan in the year 2007. This study investigates various scenarios consisting of shutting down the damaged unit for repairs and having continued operation of the unit by removing the low-pressure blades and replacing the stationary blade ring with buffer boards. Based on the simulation results, the numerical model has reflected strong agreement with the critical decisions made to operate the damaged unit continuously in a time of the blade failure. Full article

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20 pages, 2298 KiB

Open AccessArticle

3D Geothermal Modelling of the Mount Amiata Hydrothermal System in Italy

by Paolo Fulignati, Paola Marianelli, Alessandro Sbrana and Valentina Ciani

Energies 2014, 7(11), 7434-7453; https://doi.org/10.3390/en7117434 - 17 Nov 2014

Cited by 22 | Viewed by 10654

Abstract

In this paper we build a subsurface model that helps in visualizing and understanding the structural framework, geology and their interactions with the Mt. Amiata geothermal system. Modelling in 3D provides the possibility to interpolate the geometry of structures and is an effective [...] Read more.

In this paper we build a subsurface model that helps in visualizing and understanding the structural framework, geology and their interactions with the Mt. Amiata geothermal system. Modelling in 3D provides the possibility to interpolate the geometry of structures and is an effective way of understanding geological features. The 3D modelling approach appears to be crucial for further progress in the reconstruction of the assessment of the geothermal model of Mt. Amiata. Furthermore, this model is used as the basis of a 3D numerical thermo-fluid-dynamic model of the existing reservoir(s). The integration between borehole data and numerical modelling results allows reconstructing the temperature distribution in the subsoil of the Mt. Amiata area. Full article

(This article belongs to the Special Issue Geothermal Energy: Delivering on the Global Potential)

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29 pages, 1279 KiB

Open AccessArticle

Analysis of Future Vehicle Energy Demand in China Based on a Gompertz Function Method and Computable General Equilibrium Model

by Tian Wu, Mengbo Zhang and Xunmin Ou

Energies 2014, 7(11), 7454-7482; https://doi.org/10.3390/en7117454 - 18 Nov 2014

Cited by 41 | Viewed by 10264

Abstract

This paper presents a model for the projection of Chinese vehicle stocks and road vehicle energy demand through 2050 based on low-, medium-, and high-growth scenarios. To derive a gross-domestic product (GDP)-dependent Gompertz function, Chinese GDP is estimated using a recursive dynamic Computable [...] Read more.

This paper presents a model for the projection of Chinese vehicle stocks and road vehicle energy demand through 2050 based on low-, medium-, and high-growth scenarios. To derive a gross-domestic product (GDP)-dependent Gompertz function, Chinese GDP is estimated using a recursive dynamic Computable General Equilibrium (CGE) model. The Gompertz function is estimated using historical data on vehicle development trends in North America, Pacific Rim and Europe to overcome the problem of insufficient long-running data on Chinese vehicle ownership. Results indicate that the number of projected vehicle stocks for 2050 is 300, 455 and 463 million for low-, medium-, and high-growth scenarios respectively. Furthermore, the growth in China’s vehicle stock will increase beyond the inflection point of Gompertz curve by 2020, but will not reach saturation point during the period 2014–2050. Of major road vehicle categories, cars are the largest energy consumers, followed by trucks and buses. Growth in Chinese vehicle demand is primarily determined by per capita GDP. Vehicle saturation levels solely influence the shape of the Gompertz curve and population growth weakly affects vehicle demand. Projected total energy consumption of road vehicles in 2050 is 380, 575 and 586 million tonnes of oil equivalent for each scenario. Full article

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16 pages, 1788 KiB

Open AccessArticle

CFD Study on Aerodynamic Power Output Changes with Inter-Turbine Spacing Variation for a 6 MW Offshore Wind Farm

by Nak Joon Choi, Sang Hyun Nam, Jong Hyun Jeong and Kyung Chun Kim

Energies 2014, 7(11), 7483-7498; https://doi.org/10.3390/en7117483 - 18 Nov 2014

Cited by 15 | Viewed by 9928

Abstract

This study examined the aerodynamic power output change of wind turbines with inter-turbine spacing variation for a 6 MW wind farm composed of three sets of 2 MW wind turbines using computational fluid dynamics (CFD). The wind farm layout design is becoming increasingly [...] Read more.

This study examined the aerodynamic power output change of wind turbines with inter-turbine spacing variation for a 6 MW wind farm composed of three sets of 2 MW wind turbines using computational fluid dynamics (CFD). The wind farm layout design is becoming increasingly important as the use of wind energy is steadily increasing. Among the many wind farm layout design parameters, the inter-turbine spacing is a key factor in the initial investment cost, annual energy production and maintenance cost. The inter-turbine spacing should be determined to maximize the annual energy production and minimize the wake effect, turbulence effect and fatigue load during the service lifetime of wind turbines. Therefore, some compromise between the aerodynamic power output of wind turbines and the inter-turbine spacing is needed. An actuator disc model with the addition of a momentum source was not used, and instead, a full 3-dimensional model with a tower and nacelle was used for CFD analysis because of its great technical significance. The CFD analysis results, such as the aerodynamic power output, axial direction wind speed change, pressure drop across the rotor of wind turbine, and wind speed deficit due to the wake effect with inter-turbine spacing variation, were studied. The results of this study can be applied effectively to wind farm layout design and evaluation. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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20 pages, 772 KiB

Open AccessArticle

Game-Theoretic Energy Management for Residential Users with Dischargeable Plug-in Electric Vehicles

by Bingtuan Gao, Wenhu Zhang, Yi Tang, Mingjin Hu, Mingcheng Zhu and Huiyu Zhan

Energies 2014, 7(11), 7499-7518; https://doi.org/10.3390/en7117499 - 18 Nov 2014

Cited by 65 | Viewed by 7643

Abstract

The plug-in electric vehicle (PEV) has attracted more and more attention because of the energy crisis and environmental pollution, which is also the main shiftable load of the residential users’ demand side management (DSM) system in the future smart grid (SG). In this [...] Read more.

The plug-in electric vehicle (PEV) has attracted more and more attention because of the energy crisis and environmental pollution, which is also the main shiftable load of the residential users’ demand side management (DSM) system in the future smart grid (SG). In this paper, we employ game theory to provide an autonomous energy management system among residential users considering selling energy back to the utility company by discharging the PEV’s battery. By assuming all users are equipped with smart meters to execute automatic energy consumption scheduling (ECS) and the energy company can adopt adequate pricing tariffs relating to time and level of energy usage, we formulate an energy management game, where the players are the residential users and the strategies are their daily schedules of household appliance use. We will show that the Nash equilibrium of the formulated energy management game can guarantee the global optimization in terms of minimizing the energy costs, where the depreciation cost of PEV’s battery because of discharging and selling energy back is also considered. Simulation results verify that the proposed game-theoretic approach can reduce the total energy cost and individual daily electricity payment. Moreover, since plug-in electric bicycles (PEBs) are currently widely used in China, simulation results of residential users owing household appliances and bidirectional energy trading of PEBs are also provided and discussed. Full article

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16 pages, 1496 KiB

Open AccessArticle

A Recursive Solution for Power-Transmission Loss in DC-Powered Networks

by Sehwan Kim and Pai H. Chou

Energies 2014, 7(11), 7519-7534; https://doi.org/10.3390/en7117519 - 18 Nov 2014

Viewed by 5824

Abstract

This article presents a recursive solution to the power-transmission loss in DC-powered networks. In such a network, the load cannot be modeled as a fixed equivalent resistance value, since the switching regulator may draw more or less current based on the actual supply [...] Read more.

This article presents a recursive solution to the power-transmission loss in DC-powered networks. In such a network, the load cannot be modeled as a fixed equivalent resistance value, since the switching regulator may draw more or less current based on the actual supply voltage to meet the power demand. Although the power-transmission loss itself is simply I2 RL, I, in turn, depends on the load’s supply voltage, which, in turn, depends on I, making it impossible to derive a closed-form solution by classical resistive network analysis in general. The proposed approach is to first derive a closed-form solution to I in the one-node topology using the quadratic formula. Next, we extend our solution to a locally daisy-chained (LDC) network, where the network is readily decomposable into stages, such that the solution combines the closed-form formula for the current stage with the recursive solution for the subsequent stages. We then generalize the LDC topology to trees. In practice, the solution converges quickly after a small number of iterations. It has been validated on real-life networks, such as power over controller area network (PoCAN). Full article

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20 pages, 2053 KiB

Open AccessArticle

Numerical Study on Heat Transfer Deterioration of Supercritical n-Decane in Horizontal Circular Tubes

by Yanhong Wang, Sufen Li and Ming Dong

Energies 2014, 7(11), 7535-7554; https://doi.org/10.3390/en7117535 - 18 Nov 2014

Cited by 36 | Viewed by 7136

Abstract

In order to obtain a deeper understanding of the regenerative cooling process of scramjet engines, in this paper, a numerical investigation on the supercritical convective heat transfer of n-decane in horizontal circular tubes was conducted, based on a complete set of conservation equations [...] Read more.

In order to obtain a deeper understanding of the regenerative cooling process of scramjet engines, in this paper, a numerical investigation on the supercritical convective heat transfer of n-decane in horizontal circular tubes was conducted, based on a complete set of conservation equations and the Renormalization group (RNG) k–ε turbulence model with enhanced wall treatment. The present study mainly focuses on the heat transfer deterioration (HTD) phenomenon, including the mechanism and critical conditions for the onset of HTD. Moreover, the applicability of some conventional heat transfer empirical correlations was analyzed and compared, thus providing guidance for the Nusselt number predictions in the cooling channels. Results indicate that under the compositive conditions of low pressure and high heat flux, two types of HTD phenomena could occur when the wall and bulk fluid temperatures are near the pseudo-critical temperature, owing to the abnormal distributions of near-wall turbulent kinetic energy and radial velocity, respectively. Increasing the pressure would effectively alleviate and eliminate the HTD. A comparison of numerical results with those obtained with different empirical expressions shows that the Bae-Kim expression provides the best agreement, especially when HTD occurs. Furthermore, a new correction for critical heat flux of HTD has been successfully developed. Full article

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13 pages, 432 KiB

Open AccessArticle

Introducing Textiles as Material of Construction of Ethanol Bioreactors

by Osagie A. Osadolor, Patrik R. Lennartsson and Mohammad J. Taherzadeh

Energies 2014, 7(11), 7555-7567; https://doi.org/10.3390/en7117555 - 18 Nov 2014

Cited by 11 | Viewed by 9494

Abstract

The conventional materials for constructing bioreactors for ethanol production are stainless and cladded carbon steel because of the corrosive behaviour of the fermenting media. As an alternative and cheaper material of construction, a novel textile bioreactor was developed and examined. The textile, coated [...] Read more.

The conventional materials for constructing bioreactors for ethanol production are stainless and cladded carbon steel because of the corrosive behaviour of the fermenting media. As an alternative and cheaper material of construction, a novel textile bioreactor was developed and examined. The textile, coated with several layers to withstand the pressure, resist the chemicals inside the reactor and to be gas-proof was welded to form a 30 L lab reactor. The reactor had excellent performance for fermentative production of bioethanol from sugar using baker’s yeast. Experiments with temperature and mixing as process parameters were performed. No bacterial contamination was observed. Bioethanol was produced for all conditions considered with the optimum fermentation time of 15 h and ethanol yield of 0.48 g/g sucrose. The need for mixing and temperature control can be eliminated. Using a textile bioreactor at room temperature of 22 °C without mixing required 2.5 times longer retention time to produce bioethanol than at 30 °C with mixing. This will reduce the fermentation investment cost by 26% for an ethanol plant with capacity of 100,000 m³ ethanol/y. Also, replacing one 1300 m³ stainless steel reactor with 1300 m³ of the textile bioreactor in this plant will reduce the fermentation investment cost by 19%. Full article

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18 pages, 646 KiB

Open AccessArticle

Recycle Effect on Device Performance of Wire Mesh Packed Double-Pass Solar Air Heaters

by Chii-Dong Ho, Chun-Sheng Lin, Tz-Jin Yang and Chun-Chieh Chao

Energies 2014, 7(11), 7568-7585; https://doi.org/10.3390/en7117568 - 18 Nov 2014

Viewed by 5574

Abstract

A new device for inserting an absorber plate to divide a flat-plate channel into two subchannels to conduct double-pass wire mesh packed operations was developed. The proposed wire mesh packed device improves the heat transfer efficiency substantially as compared that to flat-plate single-pass [...] Read more.

A new device for inserting an absorber plate to divide a flat-plate channel into two subchannels to conduct double-pass wire mesh packed operations was developed. The proposed wire mesh packed device improves the heat transfer efficiency substantially as compared that to flat-plate single-pass and double-pass operations using the same working dimensions, and the improvement of device performance was investigated experimentally and theoretically. Good agreement between the theoretical prediction and the measured values from the experimental results was achieved. Considerable heat transfer improvement was obtained employing wire mesh packed double-pass operations under the absorber plate with external recycle. The influences of recycle ratio on the heat transfer efficiency and the power consumption increase were also discussed. Full article

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16 pages, 1762 KiB

Open AccessArticle

Three-Dimensional Modeling of the Thermal Behavior of a Lithium-Ion Battery Module for Hybrid Electric Vehicle Applications

by Jaeshin Yi, Boram Koo and Chee Burm Shin

Energies 2014, 7(11), 7586-7601; https://doi.org/10.3390/en7117586 - 18 Nov 2014

Cited by 22 | Viewed by 8487

Abstract

This paper reports a modeling methodology to predict the effects of operating conditions on the thermal behavior of a lithium-ion battery (LIB) module. The potential and current density distributions on the electrodes of an LIB cell are predicted as a function of discharge [...] Read more.

This paper reports a modeling methodology to predict the effects of operating conditions on the thermal behavior of a lithium-ion battery (LIB) module. The potential and current density distributions on the electrodes of an LIB cell are predicted as a function of discharge time based on the principle of charge conservation. By using the modeling results of the potential and current density distributions of the LIB cell, the non-uniform distribution of the heat generation rate in a single LIB cell within the module is calculated. Based on the heat generation rate in the single LIB cell determined as a function of the position on the electrode and time, a three-dimensional thermal modeling of an LIB module is performed to calculate the three-dimensional velocity, pressure, and temperature distributions within the LIB module as a function of time at various operating conditions. Thermal modeling of an LIB module is validated by the comparison between the experimental measurements and the modeling results. The effect of the cooling condition of the LIB module on the temperature rise of the LIB cells within the module and the uniformity of the distribution of the cell temperatures are analyzed quantitatively based on the modeling results. Full article

(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)

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18 pages, 1449 KiB

Open AccessArticle

Exergy Destruction in Pipeline Flow of Surfactant-Stabilized Oil-in-Water Emulsions

by Rajinder Pal

Energies 2014, 7(11), 7602-7619; https://doi.org/10.3390/en7117602 - 18 Nov 2014

Cited by 10 | Viewed by 6424

Abstract

Exergy destruction in adiabatic pipeline flow of surfactant-stabilized oil-in-water emulsions is investigated in five different diameter pipes. The dispersed-phase (oil droplets) concentration of the emulsions is varied from 0% to 55.14% vol. The emulsions are Newtonian in that the viscosity is independent of [...] Read more.

Exergy destruction in adiabatic pipeline flow of surfactant-stabilized oil-in-water emulsions is investigated in five different diameter pipes. The dispersed-phase (oil droplets) concentration of the emulsions is varied from 0% to 55.14% vol. The emulsions are Newtonian in that the viscosity is independent of the shear rate. For a given emulsion and pipe diameter, the exergy destruction rate per unit pipe length increases linearly with the increase in the Reynolds number on a log-log scale in both laminar and turbulent regimes. However the slope in the turbulent regime is higher. The exergy destruction rate increases with the increase in the dispersed-phase concentration of emulsion and decreases with the increase in the pipe diameter. New models are developed for the prediction of exergy destruction rate in pipeline flow of surfactant-stabilized oil-in-water emulsions. The models are based on the single-phase flow equations. The experimental data on exergy destruction in pipeline flow of emulsions shows excellent agreement with the predictions of the proposed models. Full article

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20 pages, 724 KiB

Open AccessArticle

Saturated Adaptive Output-Feedback Power-Level Control for Modular High Temperature Gas-Cooled Reactors

by Zhe Dong

Energies 2014, 7(11), 7620-7639; https://doi.org/10.3390/en7117620 - 19 Nov 2014

Cited by 6 | Viewed by 7575

Abstract

Small modular reactors (SMRs) are those nuclear fission reactors with electrical output powers of less than 300 MW_e. Due to its inherent safety features, the modular high temperature gas-cooled reactor (MHTGR) has been seen as one of the best candidates for [...] Read more.

Small modular reactors (SMRs) are those nuclear fission reactors with electrical output powers of less than 300 MW_e. Due to its inherent safety features, the modular high temperature gas-cooled reactor (MHTGR) has been seen as one of the best candidates for building SMR-based nuclear plants with high safety-level and economical competitive power. Power-level control is crucial in providing grid-appropriation for all types of SMRs. Usually, there exists nonlinearity, parameter uncertainty and control input saturation in the SMR-based plant dynamics. Motivated by this, a novel saturated adaptive output-feedback power-level control of the MHTGR is proposed in this paper. This newly-built control law has the virtues of having relatively neat form, of being strong adaptive to parameter uncertainty and of being able to compensate control input saturation, which are given by constructing Lyapunov functions based upon the shifted-ectropies of neutron kinetics and reactor thermal-hydraulics, giving an online tuning algorithm for the controller parameters and proposing a control input saturation compensator respectively. It is proved theoretically that input-to-state stability (ISS) can be guaranteed for the corresponding closed-loop system. In order to verify the theoretical results, this new control strategy is then applied to the large-range power maneuvering control for the MHTGR of the HTR-PM plant. Numerical simulation results show not only the relationship between regulating performance and control input saturation bound but also the feasibility of applying this saturated adaptive control law practically. Full article

(This article belongs to the Special Issue Advances in Nuclear Reactor and Fuel Cycle Technologies)

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21 pages, 857 KiB

Open AccessArticle

A Mine-Based Uranium Market Clearing Model

by Aris Auzans, Erich A. Schneider, Robert Flanagan and Alan H. Tkaczyk

Energies 2014, 7(11), 7673-7693; https://doi.org/10.3390/en7117673 - 19 Nov 2014

Cited by 5 | Viewed by 6942

Abstract

Economic analysis and market simulation tools are used to evaluate uranium (U) supply shocks, sale or purchase of uranium stockpiles, or market effects of new uranium mines or enrichment technologies. This work expands on an existing U market model that couples the market [...] Read more.

Economic analysis and market simulation tools are used to evaluate uranium (U) supply shocks, sale or purchase of uranium stockpiles, or market effects of new uranium mines or enrichment technologies. This work expands on an existing U market model that couples the market for primary U from uranium mines with those of secondary uranium, e.g., depleted uranium (DU) upgrading or highly enriched uranium (HEU) down blending, and enrichment services. This model accounts for the interdependence between the primary U supply on the U market price, the economic characteristics of each individual U mine, sources of secondary supply, and the U enrichment market. This work defines a procedure for developing an aggregate supply curve for primary uranium from marginal cost curves for individual firms (Uranium mines). Under this model, market conditions drive individual mines’ startup and short- and long-term shutdown decisions. It is applied to the uranium industry for the period 2010–2030 in order to illustrate the evolution of the front end markets under conditions of moderate growth in demand for nuclear fuel. The approach is applicable not only to uranium mines but also other facilities and reactors within the nuclear economy that may be modeled as independent, decision-making entities inside a nuclear fuel cycle simulator. Full article

(This article belongs to the Special Issue Advances in Nuclear Reactor and Fuel Cycle Technologies)

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23 pages, 1096 KiB

Open AccessArticle

High Performance Reduced Order Models for Wind Turbines with Full-Scale Converters Applied on Grid Interconnection Studies

by Heverton A. Pereira, Allan F. Cupertino, Remus Teodorescu and Selênio R. Silva

Energies 2014, 7(11), 7694-7716; https://doi.org/10.3390/en7117694 - 20 Nov 2014

Cited by 19 | Viewed by 9391

Abstract

Wind power has achieved technological evolution, and Grid Code (GC) requirements forced wind industry consolidation in the last three decades. However, more studies are necessary to understand how the dynamics inherent in this energy source interact with the power system. Traditional energy production [...] Read more.

Wind power has achieved technological evolution, and Grid Code (GC) requirements forced wind industry consolidation in the last three decades. However, more studies are necessary to understand how the dynamics inherent in this energy source interact with the power system. Traditional energy production usually contains few high power unit generators; however, Wind Power Plants (WPPs) consist of dozens or hundreds of low-power units. Time domain simulations of WPPs may take too much time if detailed models are considered in such studies. This work discusses reduced order models used in interconnection studies of synchronous machines with full converter technology. The performance of all models is evaluated based on time domain simulations in the Simulink/MATLAB environment. A detailed model is described, and four reduced order models are compared using the performance index, Normalized Integral of Absolute Error (NIAE). Models are analyzed during wind speed variations and balanced voltage dip. During faults, WPPs must be able to supply reactive power to the grid, and this characteristic is analyzed. Using the proposed performance index, it is possible to conclude if a reduced order model is suitable to represent the WPPs dynamics on grid studies. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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15 pages, 773 KiB

Open AccessArticle

Point Estimate Method for Voltage Unbalance Evaluation in Residential Distribution Networks with High Penetration of Small Wind Turbines

by Chao Long, Mohamed Emad A. Farrag, Donald M. Hepburn and Chengke Zhou

Energies 2014, 7(11), 7717-7731; https://doi.org/10.3390/en7117717 - 20 Nov 2014

Cited by 6 | Viewed by 5292

Abstract

Voltage unbalance (VU) in residential distribution networks (RDNs) is mainly caused by load unbalance in three phases, resulting from network configuration and load-variations. The increasing penetration of distributed generation devices, such as small wind turbines (SWTs), and their uneven distribution over the three [...] Read more.

Voltage unbalance (VU) in residential distribution networks (RDNs) is mainly caused by load unbalance in three phases, resulting from network configuration and load-variations. The increasing penetration of distributed generation devices, such as small wind turbines (SWTs), and their uneven distribution over the three phases have introduced difficulties in evaluating possible VU. This paper aims to provide a three-phase probabilistic power flow method, point estimate method to evaluate the VU. This method, considering the randomness of load switching in customers’ homes and time-variation in wind speed, is shown to be capable of providing a global picture of a network’s VU degree so that it can be used for fast evaluation. Applying the 2m + 1 scheme of the proposed method to a generic UK distribution network shows that a balanced SWT penetration over three phases reduces the VU of a RDN. Greater unbalance in SWT penetration results in higher voltage unbalance factor (VUF), and cause VUF in excess of the UK statutory limit of 1.3%. Full article

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14 pages, 694 KiB

Open AccessArticle

A Grid Voltage Measurement Method for Wind Power Systems during Grid Fault Conditions

by Cheol-Hee Yoo, Il-Yop Chung, Hyun-Jae Yoo and Sung-Soo Hong

Energies 2014, 7(11), 7732-7745; https://doi.org/10.3390/en7117732 - 20 Nov 2014

Cited by 7 | Viewed by 8561

Abstract

Grid codes in many countries require low-voltage ride-through (LVRT) capability to maintain power system stability and reliability during grid fault conditions. To meet the LVRT requirement, wind power systems must stay connected to the grid and also supply reactive currents to the grid [...] Read more.

Grid codes in many countries require low-voltage ride-through (LVRT) capability to maintain power system stability and reliability during grid fault conditions. To meet the LVRT requirement, wind power systems must stay connected to the grid and also supply reactive currents to the grid to support the recovery from fault voltages. This paper presents a new fault detection method and inverter control scheme to improve the LVRT capability for full-scale permanent magnet synchronous generator (PMSG) wind power systems. Fast fault detection can help the wind power systems maintain the DC-link voltage in a safe region. The proposed fault detection method is based on on-line adaptive parameter estimation. The performance of the proposed method is verified in comparison to the conventional voltage measurement method defined in the IEC 61400-21 standard. Full article

(This article belongs to the Collection Wind Turbines)

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27 pages, 2916 KiB

Open AccessArticle

Dynamics and Control of Lateral Tower Vibrations in Offshore Wind Turbines by Means of Active Generator Torque

by Zili Zhang, Søren R. K. Nielsen, Frede Blaabjerg and Dao Zhou

Energies 2014, 7(11), 7746-7772; https://doi.org/10.3390/en7117746 - 21 Nov 2014

Cited by 94 | Viewed by 14792

Abstract

Lateral tower vibrations of offshore wind turbines are normally lightly damped, and large amplitude vibrations induced by wind and wave loads in this direction may significantly shorten the fatigue life of the tower. This paper proposes the modeling and control of lateral tower [...] Read more.

Lateral tower vibrations of offshore wind turbines are normally lightly damped, and large amplitude vibrations induced by wind and wave loads in this direction may significantly shorten the fatigue life of the tower. This paper proposes the modeling and control of lateral tower vibrations in offshore wind turbines using active generator torque. To implement the active control algorithm, both the mechanical and power electronic aspects have been taken into consideration. A 13-degrees-of-freedom aeroelastic wind turbine model with generator and pitch controllers is derived using the Euler–Lagrangian approach. The model displays important features of wind turbines, such as mixed moving frame and fixed frame-defined degrees-of-freedom, couplings of the tower-blade-drivetrain vibrations, as well as aerodynamic damping present in different modes of motions. The load transfer mechanisms from the drivetrain and the generator to the nacelle are derived, and the interaction between the generator torque and the lateral tower vibration are presented in a generalized manner. A three-dimensional rotational sampled turbulence field is generated and applied to the rotor, and the tower is excited by a first order wave load in the lateral direction. Next, a simple active control algorithm is proposed based on active generator torques with feedback from the measured lateral tower vibrations. A full-scale power converter configuration with a cascaded loop control structure is also introduced to produce the feedback control torque in real time. Numerical simulations have been carried out using data calibrated to the referential 5-MW NREL (National Renewable Energy Laboratory) offshore wind turbine. Cases of drivetrains with a gearbox and direct drive to the generator are considered using the same time series for the wave and turbulence loadings. Results show that by using active generator torque control, lateral tower vibrations can be significantly mitigated for both gear-driven and direct-driven wind turbines, with modest influence on the smoothness of the power output from the generator. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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21 pages, 1369 KiB

Open AccessArticle

System Integration of the Horizontal-Axis Wind Turbine: The Design of Turbine Blades with an Axial-Flux Permanent Magnet Generator

by Chi-Jeng Bai, Wei-Cheng Wang, Po-Wei Chen and Wen-Tong Chong

Energies 2014, 7(11), 7773-7793; https://doi.org/10.3390/en7117773 - 21 Nov 2014

Cited by 26 | Viewed by 11525

Abstract

In designing a horizontal-axis wind turbine (HAWT) blade, system integration between the blade design and the performance test of the generator is important. This study shows the aerodynamic design of a HAWT blade operating with an axial-flux permanent magnet (AFPM) generator. An experimental [...] Read more.

In designing a horizontal-axis wind turbine (HAWT) blade, system integration between the blade design and the performance test of the generator is important. This study shows the aerodynamic design of a HAWT blade operating with an axial-flux permanent magnet (AFPM) generator. An experimental platform was built to measure the performance curves of the AFPM generator for the purpose of designing the turbine blade. An in-house simulation code was developed based on the blade element momentum (BEM) theory and was used to lay out the geometric shape of the turbine blade, including the pitch angle and chord length at each section. This simulation code was combined with the two-dimensional (2D) airfoil data for predicting the aerodynamic performance of the designed blades. In addition, wind tunnel experiments were performed to verify the simulation results for the various operating conditions. By varying the rotational speeds at four wind speeds, the experimental and simulation results for the mechanical torques and powers presented good agreement. The mechanical power of the system, which maximizes at the best operating region, provided significant information for designing the HAWT blade. Full article

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22 pages, 2975 KiB

Open AccessArticle

Analyzing the Performance of a Dual Loop Organic Rankine Cycle System for Waste Heat Recovery of a Heavy-Duty Compressed Natural Gas Engine

by Baofeng Yao, Fubin Yang, Hongguang Zhang, Enhua Wang and Kai Yang

Energies 2014, 7(11), 7794-7815; https://doi.org/10.3390/en7117794 - 21 Nov 2014

Cited by 24 | Viewed by 9352

Abstract

A dual loop organic Rankine cycle (DORC) system is designed to recover waste heat from a heavy-duty compressed natural gas engine (CNGE), and the performance of the DORC–CNGE combined system is simulated and discussed. The DORC system includes high-temperature (HT) and low-temperature (LT) [...] Read more.

A dual loop organic Rankine cycle (DORC) system is designed to recover waste heat from a heavy-duty compressed natural gas engine (CNGE), and the performance of the DORC–CNGE combined system is simulated and discussed. The DORC system includes high-temperature (HT) and low-temperature (LT) cycles. The HT cycle recovers energy from the exhaust gas emitted by the engine, whereas the LT cycle recovers energy from intake air, engine coolant, and the HT cycle working fluid in the preheater. The mathematical model of the system is established based on the first and second laws of thermodynamics. The characteristics of waste heat energy from the CNGE are calculated according to engine test data under various operating conditions. Moreover, the performance of the DORC–CNGE combined system is simulated and analyzed using R245fa as the working fluid. Results show that the maximum net power output and the maximum thermal efficiency of the DORC system are 29.37 kW and 10.81%, respectively, under the rated power output condition of the engine. Compared with the original CNG engine, the maximum power output increase ratio and the maximum brake specific fuel consumption improvement ratio are 33.73% and 25%, respectively, in the DORC–CNGE combined system. Full article

(This article belongs to the Special Issue Organic Rankine Cycle (ORC))

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Review

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87 pages, 1259 KiB

Open AccessReview

A Review of Methodological Approaches for the Design and Optimization of Wind Farms

by José F. Herbert-Acero, Oliver Probst, Pierre-Elouan Réthoré, Gunner Chr. Larsen and Krystel K. Castillo-Villar

Energies 2014, 7(11), 6930-7016; https://doi.org/10.3390/en7116930 - 29 Oct 2014

Cited by 234 | Viewed by 21384

Abstract

This article presents a review of the state of the art of the Wind Farm Design and Optimization (WFDO) problem. The WFDO problem refers to a set of advanced planning actions needed to extremize the performance of wind farms, which may be composed [...] Read more.

This article presents a review of the state of the art of the Wind Farm Design and Optimization (WFDO) problem. The WFDO problem refers to a set of advanced planning actions needed to extremize the performance of wind farms, which may be composed of a few individual Wind Turbines (WTs) up to thousands of WTs. The WFDO problem has been investigated in different scenarios, with substantial differences in main objectives, modelling assumptions, constraints, and numerical solution methods. The aim of this paper is: (1) to present an exhaustive survey of the literature covering the full span of the subject, an analysis of the state-of-the-art models describing the performance of wind farms as well as its extensions, and the numerical approaches used to solve the problem; (2) to provide an overview of the available knowledge and recent progress in the application of such strategies to real onshore and offshore wind farms; and (3) to propose a comprehensive agenda for future research. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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29 pages, 294 KiB

Open AccessReview

Macroalgae-Derived Biofuel: A Review of Methods of Energy Extraction from Seaweed Biomass

by John J. Milledge, Benjamin Smith, Philip W. Dyer and Patricia Harvey

Energies 2014, 7(11), 7194-7222; https://doi.org/10.3390/en7117194 - 7 Nov 2014

Cited by 262 | Viewed by 29609

Abstract

The potential of algal biomass as a source of liquid and gaseous biofuels is a highly topical theme, but as yet there is no successful economically viable commercial system producing biofuel. However, the majority of the research has focused on producing fuels from [...] Read more.

The potential of algal biomass as a source of liquid and gaseous biofuels is a highly topical theme, but as yet there is no successful economically viable commercial system producing biofuel. However, the majority of the research has focused on producing fuels from microalgae rather than from macroalgae. This article briefly reviews the methods by which useful energy may be extracted from macroalgae biomass including: direct combustion, pyrolysis, gasification, trans-esterification to biodiesel, hydrothermal liquefaction, fermentation to bioethanol, fermentation to biobutanol and anaerobic digestion, and explores technical and engineering difficulties that remain to be resolved. Full article

(This article belongs to the Special Issue Algae Based Technologies)

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33 pages, 891 KiB

Open AccessReview

Metaheuristic Algorithms Applied to Bioenergy Supply Chain Problems: Theory, Review, Challenges, and Future

by Krystel K. Castillo-Villar

Energies 2014, 7(11), 7640-7672; https://doi.org/10.3390/en7117640 - 19 Nov 2014

Cited by 38 | Viewed by 9346

Abstract

Bioenergy is a new source of energy that accounts for a substantial portion of the renewable energy production in many countries. The production of bioenergy is expected to increase due to its unique advantages, such as no harmful emissions and abundance. Supply-related problems [...] Read more.

Bioenergy is a new source of energy that accounts for a substantial portion of the renewable energy production in many countries. The production of bioenergy is expected to increase due to its unique advantages, such as no harmful emissions and abundance. Supply-related problems are the main obstacles precluding the increase of use of biomass (which is bulky and has low energy density) to produce bioenergy. To overcome this challenge, large-scale optimization models are needed to be solved to enable decision makers to plan, design, and manage bioenergy supply chains. Therefore, the use of effective optimization approaches is of great importance. The traditional mathematical methods (such as linear, integer, and mixed-integer programming) frequently fail to find optimal solutions for non-convex and/or large-scale models whereas metaheuristics are efficient approaches for finding near-optimal solutions that use less computational resources. This paper presents a comprehensive review by studying and analyzing the application of metaheuristics to solve bioenergy supply chain models as well as the exclusive challenges of the mathematical problems applied in the bioenergy supply chain field. The reviewed metaheuristics include: (1) population approaches, such as ant colony optimization (ACO), the genetic algorithm (GA), particle swarm optimization (PSO), and bee colony algorithm (BCA); and (2) trajectory approaches, such as the tabu search (TS) and simulated annealing (SA). Based on the outcomes of this literature review, the integrated design and planning of bioenergy supply chains problem has been solved primarily by implementing the GA. The production process optimization was addressed primarily by using both the GA and PSO. The supply chain network design problem was treated by utilizing the GA and ACO. The truck and task scheduling problem was solved using the SA and the TS, where the trajectory-based methods proved to outperform the population-based methods. Full article

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Energies, Volume 7, Issue 11 (November 2014) – 45 articles , Pages 6825-7815

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