Energies

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Open AccessEditorial

Energies Best Paper Award 2013

by Ophelia Han

Energies 2013, 6(2), 1178-1180; https://doi.org/10.3390/en6021178 - 22 Feb 2013

Viewed by 6212

To better recognize the outstanding papers in the area of energy technologies and applications published in Energies, we announce the institution of an annual award. We are therefore pleased to announce the first “Energies Best Paper Award” for 2013. Nominations were [...] Read more.

To better recognize the outstanding papers in the area of energy technologies and applications published in Energies, we announce the institution of an annual award. We are therefore pleased to announce the first “Energies Best Paper Award” for 2013. Nominations were made by the Editor-in-Chief and Editorial Board members from all papers published in 2009. The awards are issued to reviews and full research articles separately. [...] Full article

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689 KiB

Open AccessArticle

Evaluation of Power Generation Efficiency of Cascade Hydropower Plants: A Case Study

by Ying Zheng, Xudong Fu and Jiahua Wei

Energies 2013, 6(2), 1165-1177; https://doi.org/10.3390/en6021165 - 22 Feb 2013

Cited by 11 | Viewed by 6846

Abstract

Effective utilization of scarce water resources has presented a significant challenge to respond to the needs created by rapid economic growth in China. In this study, the efficiency of the joint operation of the Three Gorges and Gezhouba cascade hydropower plants in terms [...] Read more.

Effective utilization of scarce water resources has presented a significant challenge to respond to the needs created by rapid economic growth in China. In this study, the efficiency of the joint operation of the Three Gorges and Gezhouba cascade hydropower plants in terms of power generation was evaluated on the basis of a precise simulation-optimization technique. The joint operation conditions of the Three Gorges and Gezhouba hydropower plants between 2004 and 2010 were utilized in this research in order to investigate the major factors that could affect power output of the cascade complex. The results showed that the current power output of the Three Gorges and Gezhouba cascade complex had already reached around 90% of the maximum theoretical value. Compared to other influencing factors evaluated in this study, the accuracy of hydrological forecasts and flood control levels can have significant impact on the power generating efficiency, whereas the navigation has a minor influence. This research provides a solid quantitative-based methodology to assess the operation efficiency of cascade hydropower plants, and more importantly, proposes potential methods that could improve the operation efficiency of cascade hydropower plants. Full article

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918 KiB

Open AccessArticle

Nonlinear Power-Level Control of the MHTGR Only with the Feedback Loop of Helium Temperature

by Zhe Dong

Energies 2013, 6(2), 1142-1164; https://doi.org/10.3390/en6021142 - 22 Feb 2013

Cited by 3 | Viewed by 5330

Abstract

Power-level control is a crucial technique for the safe, stable and efficient operation of modular high temperature gas-cooled nuclear reactors (MHTGRs), which have strong inherent safety features and high outlet temperatures. The current power-level controllers of the MHTGRs need measurements of both the [...] Read more.

Power-level control is a crucial technique for the safe, stable and efficient operation of modular high temperature gas-cooled nuclear reactors (MHTGRs), which have strong inherent safety features and high outlet temperatures. The current power-level controllers of the MHTGRs need measurements of both the nuclear power and the helium temperature, which cannot provide satisfactory control performance and can even induce large oscillations when the neutron sensors are in error. In order to improve the fault tolerance of the control system, it is important to develop a power-level control strategy that only requires the helium temperature. The basis for developing this kind of control law is to give a state-observer of the MHTGR a relationship that only needs the measurement of helium temperature. With this in mind, a novel nonlinear state observer which only needs the measurement of helium temperature is proposed. This observer is globally convergent if there is no disturbance, and has the L₂ disturbance attenuation performance if the disturbance is nonzero. The separation principle of this observer is also proven, which denotes that this observer can recover the performance of both globally asymptotic stabilizers and L₂ disturbance attenuators. Then, a new dynamic output feedback power-level control strategy is established, which is composed of this observer and the well-built static state-feedback power-level control based upon iterative dissipation assignment (IDA-PLC). Finally, numerical simulation results show the high performance and feasibility of this newly-built dynamic output feedback power-level controller. Full article

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Open AccessArticle

A Materials Life Cycle Assessment of a Net-Zero Energy Building

by Cassandra L. Thiel, Nicole Campion, Amy E. Landis, Alex K. Jones, Laura A. Schaefer and Melissa M. Bilec

Energies 2013, 6(2), 1125-1141; https://doi.org/10.3390/en6021125 - 21 Feb 2013

Cited by 94 | Viewed by 15353

Abstract

This study analyzed the environmental impacts of the materials phase of a net-zero energy building. The Center for Sustainable Landscapes (CSL) is a three-story, 24,350 square foot educational, research, and administrative office in Pittsburgh, PA, USA. This net-zero energy building is designed to [...] Read more.

This study analyzed the environmental impacts of the materials phase of a net-zero energy building. The Center for Sustainable Landscapes (CSL) is a three-story, 24,350 square foot educational, research, and administrative office in Pittsburgh, PA, USA. This net-zero energy building is designed to meet Living Building Challenge criteria. The largest environmental impacts from the production of building materials is from concrete, structural steel, photovoltaic (PV) panels, inverters, and gravel. Comparing the LCA results of the CSL to standard commercial structures reveals a 10% larger global warming potential and a nearly equal embodied energy per square feet, largely due to the CSL’s PV system. As a net-zero energy building, the environmental impacts associated with the use phase are expected to be very low relative to standard structures. Future studies will incorporate the construction and use phases of the CSL for a more comprehensive life cycle perspective. Full article

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Open AccessArticle

Game Optimization Theory and Application in Distribution System Expansion Planning, Including Distributed Generation

by Ran Li, Huizhuo Ma, Feifei Wang, Yihe Wang, Yang Liu and Zenghui Li

Energies 2013, 6(2), 1101-1124; https://doi.org/10.3390/en6021101 - 21 Feb 2013

Cited by 38 | Viewed by 8342 | Correction

Abstract

Based on Game Theory and Multi-objective optimization problems (MOP), Game Optimization Theory (GOT) is discussed in this paper. Optimization Stability Analysis (OSA), Distance Entropy Multi-Objective Particle Swarm Optimization (DEMPSO) and Fuzzy Multi-weights Decision-making Method (FMW) are proposed as well. Game Optimization Theory, which [...] Read more.

Based on Game Theory and Multi-objective optimization problems (MOP), Game Optimization Theory (GOT) is discussed in this paper. Optimization Stability Analysis (OSA), Distance Entropy Multi-Objective Particle Swarm Optimization (DEMPSO) and Fuzzy Multi-weights Decision-making Method (FMW) are proposed as well. Game Optimization Theory, which is a comprehensive system, could not only handle multi-objective optimization problems effectively, but also could offset the disadvantages of traditional optimization theories, such as lack of framework and the insufficient consideration of relevant elements. In this paper GOT is used for the first time in solving the distribution systems planning (DSP) issue by implementing distributed generation. The proposed model integrates costs, losses, and voltage index to achieve optimal size and site of distributed generation. The model allows minimizing total system costs, system power losses and maximizing voltage improvement. A detailed DSP example is used for verifying the effectiveness and reasonableness of GOT in this context. Full article

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Open AccessArticle

A Photovoltaic Power System Using a High Step-up Converter for DC Load Applications

by Sheng-Yu Tseng and Hung-Yuan Wang

Energies 2013, 6(2), 1068-1100; https://doi.org/10.3390/en6021068 - 21 Feb 2013

Cited by 43 | Viewed by 8321

Abstract

This paper presents a power system using a high step-up converter for dc load applications. The high step-up converter adopts a boost converter with interleaved mode and a coupled inductor to raise its powering ability and increase its step-up voltage ratio, respectively. In [...] Read more.

This paper presents a power system using a high step-up converter for dc load applications. The high step-up converter adopts a boost converter with interleaved mode and a coupled inductor to raise its powering ability and increase its step-up voltage ratio, respectively. In order to increase conversion efficiency, an active clamp circuit is introduced into the proposed one to provide soft-switching features to reduce switching losses. Moreover, switches in the converter and active clamp circuit are integrated with a synchronous switching technique to reduce circuit complexity and component counts, resulting in a lower cost and smaller volume. A perturb and observe method is adopted to extract the maximum power from photovoltaic (PV) arrays. Furthermore, a microchip associated with PWM IC is used to implement maximum power point tracking operation, voltage regulation and power management. Finally, a prototype PV power system with 400 V/6 A has been implemented for verifying the feasibility of the proposed PV power system. It is shown to be suitable for PV energy conversion applications when the duty ratios of switches in the dc/dc converter are less than 0.5. Full article

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Open AccessArticle

Exergy and Exergoeconomic Model of a Ground-Based CAES Plant for Peak-Load Energy Production

by Francesco Buffa, Simon Kemble, Giampaolo Manfrida and Adriano Milazzo

Energies 2013, 6(2), 1050-1067; https://doi.org/10.3390/en6021050 - 19 Feb 2013

Cited by 34 | Viewed by 7827

Abstract

Compressed Air Energy Storage is recognized as a promising technology for applying energy storage to grids which are more and more challenged by the increasing contribution of renewable such as solar or wind energy. The paper proposes a medium-size ground-based CAES system, based [...] Read more.

Compressed Air Energy Storage is recognized as a promising technology for applying energy storage to grids which are more and more challenged by the increasing contribution of renewable such as solar or wind energy. The paper proposes a medium-size ground-based CAES system, based on pressurized vessels and on a multiple-stage arrangement of compression and expansion machinery; the system includes recovery of heat from the intercoolers, and its storage as sensible heat in two separate (hot/cold) water reservoirs, and regenerative reheat of the expansions. The CAES plant parameters were adapted to the requirements of existing equipment (compressors, expanders and heat exchangers). A complete exergy analysis of the plant was performed. Most component cost data were procured from the market, asking specific quotations to the industrial providers. It is thus possible to calculate the final cost of the electricity unit (kWh) produced under peak-load mode, and to identify the relative contribution between the two relevant groups of capital and component inefficiencies costs. Full article

(This article belongs to the Special Issue Selected Papers from the 25th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems (ECOS2012))

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Open AccessArticle

Recycling of Waste Engine Oils Using a New Washing Agent

by Ihsan Hamawand, Talal Yusaf and Sardasht Rafat

Energies 2013, 6(2), 1023-1049; https://doi.org/10.3390/en6021023 - 19 Feb 2013

Cited by 103 | Viewed by 29471

Abstract

This paper addresses recycling of waste engine oils treated using acetic acid. A recycling process was developed which eventually led to comparable results with some of the conventional methods. This gives the recycled oil the potential to be reused in cars’ engines after [...] Read more.

This paper addresses recycling of waste engine oils treated using acetic acid. A recycling process was developed which eventually led to comparable results with some of the conventional methods. This gives the recycled oil the potential to be reused in cars’ engines after adding the required additives. The advantage of using the acetic acid is that it does not react or only reacts slightly with base oils. The recycling process takes place at room temperature. It has been shown that base oils and oils’ additives are slightly affected by the acetic acid. Upon adding 0.8 vol% of acetic acid to the used oil, two layers were separated, a transparent dark red colored oil and a black dark sludge at the bottom of the container. The base oils resulting from other recycling methods were compared to the results of this paper. The comparison showed that the recycled oil produced by acetic acid treatment is comparable to those recycled by the other conventional methods. Full article

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Open AccessArticle

Hydrate Formation/Dissociation in (Natural Gas + Water + Diesel Oil) Emulsion Systems

by Chang-Sheng Xiang, Bao-Zi Peng, Huang Liu, Chang-Yu Sun, Guang-Jin Chen and Bao-Jiang Sun

Energies 2013, 6(2), 1009-1022; https://doi.org/10.3390/en6021009 - 18 Feb 2013

Cited by 33 | Viewed by 7713

Abstract

Hydrate formation/dissociation of natural gas in (diesel oil + water) emulsion systems containing 3 wt% anti-agglomerant were performed for five water cuts: 5, 10, 15, 20, and 25 vol%. The natural gas solubilities in the emulsion systems were also examined. The experimental results [...] Read more.

Hydrate formation/dissociation of natural gas in (diesel oil + water) emulsion systems containing 3 wt% anti-agglomerant were performed for five water cuts: 5, 10, 15, 20, and 25 vol%. The natural gas solubilities in the emulsion systems were also examined. The experimental results showed that the solubility of natural gas in emulsion systems increases almost linearly with the increase of pressure, and decreases with the increase of water cut. There exists an initial slow hydrate formation stage for systems with lower water cut, while rapid hydrate formation takes place and the process of the gas-liquid dissolution equilibrium at higher water cut does not appear in the pressure curve. The gas consumption amount due to hydrate formation at high water cut is significantly higher than that at low water cut. Fractional distillation for natural gas components also exists during the hydrate formation process. The experiments on hydrate dissociation showed that the dissociation rate and the amount of dissociated gas increase with the increase of water cut. The variations of temperature in the process of natural gas hydrate formation and dissociation in emulsion systems were also examined. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2013)

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Open AccessReview

A Generic Framework for the Evaluation of the Benefits Expected from the Smart Grid

by Spiros Livieratos, Vasiliki-Emmanouela Vogiatzaki and Panayotis G. Cottis

Energies 2013, 6(2), 988-1008; https://doi.org/10.3390/en6020988 - 13 Feb 2013

Cited by 27 | Viewed by 8406

Abstract

The Smart Grid has the potential to bring significant value to the various stakeholders of the electricity market. A methodology for the evaluation of the smart grid benefits is required to facilitate the decision making by quantifying the benefits expected from a smart [...] Read more.

The Smart Grid has the potential to bring significant value to the various stakeholders of the electricity market. A methodology for the evaluation of the smart grid benefits is required to facilitate the decision making by quantifying the benefits expected from a smart grid project. The present paper proposes a generic framework to assess these expected benefits taking into account the regulatory, business and technical challenges focusing particularly on Distributed Systems Operators (DSOs) and end users. An indicative study case is presented where the proposed cost-benefit approach assesses the expected value of DSOs from the Smart Grid and determines whether and under what conditions such an investment should be initiated. Full article

(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)

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Open AccessArticle

Evaluating the Economic Performance of High-Technology Industry and Energy Efficiency: A Case Study of Science Parks in Taiwan

by Min-Ren Yan and Kuo-Ming Chien

Energies 2013, 6(2), 973-987; https://doi.org/10.3390/en6020973 - 13 Feb 2013

Cited by 22 | Viewed by 9510

Abstract

High-technology industries provide opportunities for economic growth, but also raise concerns because of their energy-demanding nature. This paper provides an integrated evaluation of both economic benefits and energy efficiency of high-technology industries based on the real data from one of the globally recognized [...] Read more.

High-technology industries provide opportunities for economic growth, but also raise concerns because of their energy-demanding nature. This paper provides an integrated evaluation of both economic benefits and energy efficiency of high-technology industries based on the real data from one of the globally recognized high-technology industrial clusters, the national science parks in Taiwan. A nation-wide industrial Input-Output Analysis is conducted to demonstrate the positive effects of science parks on national economic developments and industrial upgrades. The concept of energy intensity and an energy-efficient economy index are applied to an integrated assessment of the relationship between economic growth and energy consumption. The proposed case study suggests that economic and energy efficiency objectives can be simultaneously achieved by the development of high-technology industries, while three energy policy implications are considered. First, a nation-wide macro viewpoint is needed and high-technology industries should be considered as parts of the national/regional economies by governmental agencies. Second, a proper industrial clustering mechanism and the shared environmental facilities supported by the government, such as planned land and road usage, electricity and water supply, telecommunications system, sewerage system and wastewater treatments, can improve energy efficiency of high-technology industries. Third, the governmental policies on the taxing and management system in science parks would also direct energy-efficient economy of high-technology industries. Full article

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Open AccessArticle

Retrofitting Conventional Electric Domestic Hot Water Heaters to Solar Water Heating Systems in Single-Family Houses—Model Validation and Optimization

by Luis R. Bernardo

Energies 2013, 6(2), 953-972; https://doi.org/10.3390/en6020953 - 12 Feb 2013

Cited by 9 | Viewed by 12128

Abstract

System cost reductions and development of standardised plug-and-function systems are some of the most important goals for solar heating technology development. Retrofitting hot water boilers in single-family houses when installing solar collectors has the potential to significantly reduce both material and installation costs. [...] Read more.

System cost reductions and development of standardised plug-and-function systems are some of the most important goals for solar heating technology development. Retrofitting hot water boilers in single-family houses when installing solar collectors has the potential to significantly reduce both material and installation costs. In this study, the TRNSYS simulation models of the retrofitting solar thermal system were validated against measurements. Results show that the validated models are in good agreement with measurements. On an annual basis a deviation of 2.5% out of 1099 kWh was obtained between the auxiliary energy from results and from the simulation model for a complete system. Using the validated model a system optimization was carried out with respect to control strategies for auxiliary heating, heat losses and volume of auxiliary storage. A sensitivity analysis was carried out regarding different volumes of retrofitted hot water boiler, DHW profiles and climates. It was estimated that, with adequate improvements, extended annual solar fractions of 60%, 78% and 81% can be achieved for Lund (Sweden), Lisbon (Portugal) and Lusaka (Zambia), respectively. The correspondent collector area was 6, 4 and 3 m², respectively. The studied retrofitted system achieves a comparable performance with conventional solar thermal systems with the potential to reduce the investment cost. Full article

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Open AccessArticle

Modeling of the Partial Discharge Process in a Liquid Dielectric: Effect of Applied Voltage, Gap Distance, and Electrode Type

by Wenxia Sima, Chilong Jiang, Paul Lewin, Qing Yang and Tao Yuan

Energies 2013, 6(2), 934-952; https://doi.org/10.3390/en6020934 - 8 Feb 2013

Cited by 21 | Viewed by 7495

Abstract

The partial discharge (PD) process in liquid dielectrics is influenced by several factors. Although the PD current contains the information representing the discharge process during the PD event, it is difficult to determine the detailed dynamics of what is happening in the bulk [...] Read more.

The partial discharge (PD) process in liquid dielectrics is influenced by several factors. Although the PD current contains the information representing the discharge process during the PD event, it is difficult to determine the detailed dynamics of what is happening in the bulk of the liquid. In this paper, a microscopic model describing the dynamics of the charge carriers is implemented. The model consists of drift-diffusion equations of electrons, positive and negative ions coupled with Poisson’s equation. The stochastic feature of PD events is included in the equation. First the model is validated through comparison between the calculated PD current and experimental data. Then experiments are conducted to study the effects of the amplitude of the applied voltage, gap distance and electrode type on the PD process. The PD currents under each condition are recorded. Simulations based on the model have been conducted to analyze the dynamics of the PD events under each condition, and thus explain the mechanism of how these factors influence the PD events. The space charge generated in the PD process is revealed as the main reason affecting the microscopic process of the PD events. Full article

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Open AccessArticle

System Identification and Integration Design of an Air/Electric Motor

by Yean-Ren Hwang and Shih-Yao Huang

Energies 2013, 6(2), 921-933; https://doi.org/10.3390/en6020921 - 8 Feb 2013

Cited by 4 | Viewed by 6794

Abstract

This paper presents an integration design and implementation of an air motor and a DC servo motor which utilizes a magnetic powder brake to integrate these two motors together. The dynamic model of the air/electric hybrid system will be derived and eventually leads [...] Read more.

This paper presents an integration design and implementation of an air motor and a DC servo motor which utilizes a magnetic powder brake to integrate these two motors together. The dynamic model of the air/electric hybrid system will be derived and eventually leads to successful ECE-40 driving cycle tests with a FPGA-based speed controller. The testing results obtained by using the proposed experimental platform indicate that the total air consumption is about 256 L under air motor mode and the electric charge consumption is about 530 coulombs under DC servo motor mode. In a hybrid mode, the current reduction of the battery is about 18.5%, and then the service life of the battery can be improved. Furthermore, a prototype is built with a proportional-integral (PI) speed controller based on a field-programmable gate array (FPGA) in order to facilitate the entire analysis of the velocity switch experiment. Through the modular methodology of FPGA, the hybrid power platform can successfully operate under ECE-40 driving cycle with the PI speed controller. The experimental data shows that the chattering ranges of the air motor within ±1 km/h and ±0.2 km/h under DC servo motor drive. Therefore, the PI speed controller based on FPGA is successfully actualized. Full article

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Open AccessArticle

Modeling Supermarket Refrigeration Systems for Demand-Side Management

by S. Ehsan Shafiei, Henrik Rasmussen and Jakob Stoustrup

Energies 2013, 6(2), 900-920; https://doi.org/10.3390/en6020900 - 8 Feb 2013

Cited by 47 | Viewed by 10507

Abstract

Modeling of supermarket refrigeration systems for supervisory control in the smart grid is presented in this paper. A modular modeling approach is proposed in which each module is modeled and identified separately. The focus of the work is on estimating the power consumption [...] Read more.

Modeling of supermarket refrigeration systems for supervisory control in the smart grid is presented in this paper. A modular modeling approach is proposed in which each module is modeled and identified separately. The focus of the work is on estimating the power consumption of the system while estimating the cold reservoir temperatures as well. The models developed for each module as well as for the overall integrated system are validated by real data collected from a supermarket in Denmark. The results show that the model is able to estimate the actual electrical power consumption with a high fidelity. Moreover a simulation benchmark is introduced based on the produced model for demand-side management in smart grid. Finally, a potential application of the proposed benchmark in direct control of the power/energy consumption is presented by a simple simulation example. Full article

(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)

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Open AccessArticle

High Level Ethanol Production by Nitrogen and Osmoprotectant Supplementation under Very High Gravity Fermentation Conditions

by Pachaya Chan-u-tit, Lakkana Laopaiboon, Prasit Jaisil and Pattana Laopaiboon

Energies 2013, 6(2), 884-899; https://doi.org/10.3390/en6020884 - 8 Feb 2013

Cited by 33 | Viewed by 6386

Abstract

Optimization of nutrient supplements i.e., yeast extract (1, 3 and 5 g·L⁻¹), dried spent yeast (DSY: 4, 12 and 20 g·L⁻¹) and osmoprotectant (glycine: 1, 3 and 5 g·L⁻¹) to improve the efficiency of ethanol production [...] Read more.

Optimization of nutrient supplements i.e., yeast extract (1, 3 and 5 g·L⁻¹), dried spent yeast (DSY: 4, 12 and 20 g·L⁻¹) and osmoprotectant (glycine: 1, 3 and 5 g·L⁻¹) to improve the efficiency of ethanol production from a synthetic medium under very high gravity (VHG) fermentation by Saccharomyces cerevisiae NP 01 was performed using a statistical method, an L₉ (3⁴) orthogonal array design. The synthetic medium contained 280 g·L⁻¹ of sucrose as a sole carbon source. When the fermentation was carried out at 30 °C, the ethanol concentration (P), yield (Y_p/s) and productivity (Q_p) without supplementation were 95.3 g·L⁻¹, 0.49 g·g⁻¹ and 1.70 g·L⁻¹·h⁻¹, respectively. According to the orthogonal results, the order of influence on the P and Q_p values were yeast extract > glycine > DSY, and the optimum nutrient concentrations were yeast extract, 3; DSY, 4 and glycine, 5 g·L⁻¹, respectively. The verification experiment using these parameters found that the P, Y_p/s and Q_pvalues were 119.9 g·L⁻¹, 0.49 g g⁻¹ and 2.14 g·L⁻¹·h⁻¹, respectively. These values were not different from those of the synthetic medium supplemented with 9 g·L⁻¹ of yeast extract, indicating that DSY could be used to replace some amount of yeast extract. When sweet sorghum juice cv. KKU40 containing 280 g·L⁻¹ of total sugar supplemented with the three nutrients at the optimum concentrations was used as the ethanol production medium, the P value (120.0 g·L⁻¹) was not changed, but the Q_p value was increased to 2.50 g·L⁻¹·h⁻¹. Full article

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Open AccessArticle

Environmental Effects of Sewage Sludge Carbonization and Other Treatment Alternatives

by Ning-Yi Wang, Chun-Hao Shih, Pei-Te Chiueh and Yu-Fong Huang

Energies 2013, 6(2), 871-883; https://doi.org/10.3390/en6020871 - 7 Feb 2013

Cited by 47 | Viewed by 11052

Abstract

Carbonization is a newly developed process that converts sewage sludge to biocoal, a type of solid biomass that can partially substitute for coal during power generation. This study presents an assessment of the environmental effects of various sewage sludge treatment processes, including carbonization, [...] Read more.

Carbonization is a newly developed process that converts sewage sludge to biocoal, a type of solid biomass that can partially substitute for coal during power generation. This study presents an assessment of the environmental effects of various sewage sludge treatment processes, including carbonization, direct landfills, co-incineration with municipal solid waste, and mono-incineration in Taiwan. This assessment was conducted using the life cycle assessment software SimaPro 7.2 and the IMPACT2002+ model. Results show that carbonization is the best approach for sewage sludge treatment, followed in descending order by co-incineration with municipal solid waste, direct landfills, and mono-incineration. The carbonization process has noticeable positive effects in the environmental impact categories of terrestrial ecotoxicity, aquatic ecotoxicity, land occupation, ionizing radiation, aquatic eutrophication, non-renewable energy, and mineral extraction. For the emission quantity of greenhouse gases, landfilling has the greatest impact (296.9 kg CO₂eq./t sludge), followed by mono-incineration (232.2 kg CO₂eq./t sludge) and carbonization (146.1 kg CO₂eq./t sludge). Co-incineration with municipal solid waste has the benefit of reducing green house gas emission (–15.4 kg CO₂eq./t sludge). In the aspect of energy recovery, sewerage sludge that has been pretreated by thickening, digestion, and dewatering still retains a high moisture content, and thus requires a significant amount of energy use when used as a substitute solid fuel. Therefore, the carbonization of sewage sludge would be a more sustainable option if the energy delivery and integration processes are made more efficient. Full article

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Open AccessArticle

Numerical Model of a Variable-Combined-Cycle Engine for Dual Subsonic and Supersonic Cruise

by Victor Fernandez-Villace and Guillermo Paniagua

Energies 2013, 6(2), 839-870; https://doi.org/10.3390/en6020839 - 7 Feb 2013

Cited by 49 | Viewed by 11611

Abstract

Efficient high speed propulsion requires exploiting the cooling capability of the cryogenic fuel in the propulsion cycle. This paper presents the numerical model of a combined cycle engine while in air turbo-rocket configuration. Specific models of the various heat exchanger modules and the [...] Read more.

Efficient high speed propulsion requires exploiting the cooling capability of the cryogenic fuel in the propulsion cycle. This paper presents the numerical model of a combined cycle engine while in air turbo-rocket configuration. Specific models of the various heat exchanger modules and the turbomachinery elements were developed to represent the physical behavior at off-design operation. The dynamic nature of the model allows the introduction of the engine control logic that limits the operation of certain subcomponents and extends the overall engine operational envelope. The specific impulse and uninstalled thrust are detailed while flying a determined trajectory between Mach 2.5 and 5 for varying throttling levels throughout the operational envelope. Full article

(This article belongs to the Special Issue Combined Heat and Power – Strategy and Practice)

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Open AccessReview

Slag Behavior in Gasifiers. Part II: Constitutive Modeling of Slag

by Mehrdad Massoudi and Ping Wang

Energies 2013, 6(2), 807-838; https://doi.org/10.3390/en6020807 - 7 Feb 2013

Cited by 29 | Viewed by 7671

Abstract

The viscosity of slag and the thermal conductivity of ash deposits are among two of the most important constitutive parameters that need to be studied. The accurate formulation or representations of the (transport) properties of coal present a special challenge of modeling efforts [...] Read more.

The viscosity of slag and the thermal conductivity of ash deposits are among two of the most important constitutive parameters that need to be studied. The accurate formulation or representations of the (transport) properties of coal present a special challenge of modeling efforts in computational fluid dynamics applications. Studies have indicated that slag viscosity must be within a certain range of temperatures for tapping and the membrane wall to be accessible, for example, between 1,300 °C and 1,500 °C, the viscosity is approximately 25 Pa·s. As the operating temperature decreases, the slag cools and solid crystals begin to form. Since slag behaves as a non-linear fluid, we discuss the constitutive modeling of slag and the important parameters that must be studied. We propose a new constitutive model, where the stress tensor not only has a yield stress part, but it also has a viscous part with a shear rate dependency of the viscosity, along with temperature and concentration dependency, while allowing for the possibility of the normal stress effects. In Part I, we reviewed, identify and discuss the key coal ash properties and the operating conditions impacting slag behavior. Full article

(This article belongs to the Special Issue Coal Combustion and Gasification)

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Open AccessReview

Slag Behavior in Gasifiers. Part I: Influence of Coal Properties and Gasification Conditions

by Ping Wang and Mehrdad Massoudi

Energies 2013, 6(2), 784-806; https://doi.org/10.3390/en6020784 - 7 Feb 2013

Cited by 124 | Viewed by 12931

Abstract

In the entrained-flow gasifiers used in integrated gasification combined cycle (IGCC) plants, the majority of mineral matter transforms to liquid slag on the wall of the gasifier and flows out the bottom. However, a small fraction of the mineral matter is entrained (as [...] Read more.

In the entrained-flow gasifiers used in integrated gasification combined cycle (IGCC) plants, the majority of mineral matter transforms to liquid slag on the wall of the gasifier and flows out the bottom. However, a small fraction of the mineral matter is entrained (as fly ash) with the raw syngas out of the gasifier to downstream processing. This molten/sticky fly ash could cause fouling of the syngas cooler. To improve gasification availability through better design and operation of the gasification process, a better understanding of slag behavior and the characteristics of the slagging process is needed. Char/ash properties, gas compositions in the gasifier, the gasifier wall structure, fluid dynamics, and plant operating conditions (mainly temperature and oxygen/carbon ratio) all affect slagging behavior. Because coal has varying ash content and composition, different operating conditions are required to maintain the slag flow and limit problems downstream. In Part I, we review the main types and the operating conditions of entrained-flow gasifiers and coal properties used in IGCC plants; we identify and discuss the key coal ash properties and the operating conditions impacting slag behavior; finally, we summarize the coal quality criteria and the operating conditions in entrained-flow gasifiers. In Part II, we discuss the constitutive modeling related to the rheological studies of slag flow. Full article

(This article belongs to the Special Issue Coal Combustion and Gasification)

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Open AccessArticle

Chlorella protothecoides Microalgae as an Alternative Fuel for Tractor Diesel Engines

by Saddam H. Al-lwayzy and Talal Yusaf

Energies 2013, 6(2), 766-783; https://doi.org/10.3390/en6020766 - 6 Feb 2013

Cited by 54 | Viewed by 8776

Abstract

Biodiesel has attracted a great deal attention recently as an alternative fuel due to increasing fuel prices and the imperative to reduce emissions. Among a wide range of biodiesel resources, microalgae are a promising alternative fuel source because of the high biomass, lipid [...] Read more.

Biodiesel has attracted a great deal attention recently as an alternative fuel due to increasing fuel prices and the imperative to reduce emissions. Among a wide range of biodiesel resources, microalgae are a promising alternative fuel source because of the high biomass, lipid productivity and environmentally friendliness. Microalgae is also a non-edible food, therefore, there will be no impact on the human food supply chain. In this work, petroleum diesel (PD) and biodiesel from the microalgae Chlorella protothecoides (MCP-B20) blend have been used to examine the performance and the emission of a 25.8 kW agriculture tractor engine. Two engine speeds at maximum power take off (PTO) power and torque have been selected for analysis using analysis of variance (ANOVA). The results showed that there is no significant difference between the engine performance when microalgae biodiesel blend (MCP-B20) and PD were used. However, a significant reduction in CO, CO₂ and NO emissions was found when MCP-B20 was used. These outcomes give strong indication that microalgae can be successfully used in tractors as alternative fuel. Full article

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512 KiB

Open AccessArticle

Economic Feasibility of V2G Frequency Regulation in Consideration of Battery Wear

by Sekyung Han and Soohee Han

Energies 2013, 6(2), 748-765; https://doi.org/10.3390/en6020748 - 6 Feb 2013

Cited by 68 | Viewed by 8458

Abstract

An economic feasibility study of vehicle-to-grid (V2G) frequency regulation is performed in consideration of battery wear. Usually, a transaction for frequency regulation is made in terms of power capacity while the battery-wear proceeds in proportion to the absolute amount of energy transferred. In [...] Read more.

An economic feasibility study of vehicle-to-grid (V2G) frequency regulation is performed in consideration of battery wear. Usually, a transaction for frequency regulation is made in terms of power capacity while the battery-wear proceeds in proportion to the absolute amount of energy transferred. In order to relate the two quantities, we first estimate the amount of transferred energy in terms of contracted power capacity, and hence regulation income, by analyzing actual regulation signals and transactions. On the other hand, the amount of transferrable energy during the life cycle of a battery is estimated analyzing some pervasive specifications for electric vehicle (EV) batteries. The expected V2G income is then estimated and compared with battery prices to judge the economic feasibility of V2G regulation. In the latter part of the paper, the assessment result is validated with actual cycle life data of an EV battery cell. As a result, it is concluded that the estimated profit exceeds current market price of EV batteries, indicating that V2G regulation is an economically feasible service. Full article

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Open AccessArticle

A Bayesian Method for Short-Term Probabilistic Forecasting of Photovoltaic Generation in Smart Grid Operation and Control

by Antonio Bracale, Pierluigi Caramia, Guido Carpinelli, Anna Rita Di Fazio and Gabriella Ferruzzi

Energies 2013, 6(2), 733-747; https://doi.org/10.3390/en6020733 - 6 Feb 2013

Cited by 119 | Viewed by 9779

Abstract

A new short-term probabilistic forecasting method is proposed to predict the probability density function of the hourly active power generated by a photovoltaic system. Firstly, the probability density function of the hourly clearness index is forecasted making use of a Bayesian auto regressive [...] Read more.

A new short-term probabilistic forecasting method is proposed to predict the probability density function of the hourly active power generated by a photovoltaic system. Firstly, the probability density function of the hourly clearness index is forecasted making use of a Bayesian auto regressive time series model; the model takes into account the dependence of the solar radiation on some meteorological variables, such as the cloud cover and humidity. Then, a Monte Carlo simulation procedure is used to evaluate the predictive probability density function of the hourly active power by applying the photovoltaic system model to the random sampling of the clearness index distribution. A numerical application demonstrates the effectiveness and advantages of the proposed forecasting method. Full article

(This article belongs to the Special Issue Hybrid Advanced Techniques for Forecasting in Energy Sector)

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Open AccessArticle

Application Model for a Stirling Engine Micro-Generation System in Caravans in Different European Locations

by Carlos Ulloa, Jacobo Porteiro, Pablo Eguía and José M. Pousada-Carballo

Energies 2013, 6(2), 717-732; https://doi.org/10.3390/en6020717 - 6 Feb 2013

Cited by 19 | Viewed by 8066

Abstract

This article describes a simple model obtained from a commercial Stirling engine and used for heating a caravan. The Stirling engine has been tested in the lab under different electrical load conditions, and the operating points obtained are presented. As an application of [...] Read more.

This article describes a simple model obtained from a commercial Stirling engine and used for heating a caravan. The Stirling engine has been tested in the lab under different electrical load conditions, and the operating points obtained are presented. As an application of the model, a series of transient simulations was performed using TRNSYS. During these simulations, the caravan is traveling throughout the day and is stationary at night. Therefore, during the night-time hours, the heating system is turned on by means of the Stirling engine. The study was performed for each month of the year in different European cities. The different heating demand profiles for different cities induce variation in the electricity production, as it has been assumed that electricity is only generated when the thermal demand requires the operation of the Stirling system. As a result, a comparison of the expected power generation in different European cities is presented. Full article

(This article belongs to the Special Issue Combined Heat and Power – Strategy and Practice)

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999 KiB

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Wind Farm Wake: The Horns Rev Photo Case

by Charlotte Bay Hasager, Leif Rasmussen, Alfredo Peña, Leo E. Jensen and Pierre-Elouan Réthoré

Energies 2013, 6(2), 696-716; https://doi.org/10.3390/en6020696 - 5 Feb 2013

Cited by 46 | Viewed by 19892

Abstract

The aim of the paper is to examine the nowadays well-known wind farm wake photographs taken on 12 February 2008 at the offshore Horns Rev 1 wind farm. The meteorological conditions are described from observations from several satellite sensors quantifying clouds, surface wind [...] Read more.

The aim of the paper is to examine the nowadays well-known wind farm wake photographs taken on 12 February 2008 at the offshore Horns Rev 1 wind farm. The meteorological conditions are described from observations from several satellite sensors quantifying clouds, surface wind vectors and sea surface temperature as well as ground-based information at and near the wind farm, including Supervisory Control and Data Acquisition (SCADA) data. The SCADA data reveal that the case of fog formation occurred 12 February 2008 on the 10:10 UTC. The fog formation is due to very special atmospheric conditions where a layer of cold humid air above a warmer sea surface re-condensates to fog in the wake of the turbines. The process is fed by warm humid air up-drafted from below in the counter-rotating swirl generated by the clock-wise rotating rotors. The condensation appears to take place primarily in the wake regions with relatively high axial velocities and high turbulent kinetic energy. The wind speed is near cut-in and most turbines produce very little power. The rotational pattern of spiraling bands produces the large-scale structure of the wake fog. Full article

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Quantile Forecasting of Wind Power Using Variability Indices

by Georgios Anastasiades and Patrick McSharry

Energies 2013, 6(2), 662-695; https://doi.org/10.3390/en6020662 - 5 Feb 2013

Cited by 26 | Viewed by 7442

Abstract

Wind power forecasting techniques have received substantial attention recently due to the increasing penetration of wind energy in national power systems. While the initial focus has been on point forecasts, the need to quantify forecast uncertainty and communicate the risk of extreme ramp [...] Read more.

Wind power forecasting techniques have received substantial attention recently due to the increasing penetration of wind energy in national power systems. While the initial focus has been on point forecasts, the need to quantify forecast uncertainty and communicate the risk of extreme ramp events has led to an interest in producing probabilistic forecasts. Using four years of wind power data from three wind farms in Denmark, we develop quantile regression models to generate short-term probabilistic forecasts from 15 min up to six hours ahead. More specifically, we investigate the potential of using various variability indices as explanatory variables in order to include the influence of changing weather regimes. These indices are extracted from the same wind power series and optimized specifically for each quantile. The forecasting performance of this approach is compared with that of appropriate benchmark models. Our results demonstrate that variability indices can increase the overall skill of the forecasts and that the level of improvement depends on the specific quantile. Full article

(This article belongs to the Special Issue Hybrid Advanced Techniques for Forecasting in Energy Sector)

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767 KiB

Open AccessArticle

Integrating Building Energy Efficiency with Land Use and Transportation Planning in Jinan, China

by Manish Shirgaokar, Elizabeth Deakin and Nicolae Duduta

Energies 2013, 6(2), 646-661; https://doi.org/10.3390/en6020646 - 5 Feb 2013

Cited by 6 | Viewed by 7375

Abstract

With the rapid growth occurring in the urban regions of China, it is critical to address issues of sustainability through practices that engender holistic energy efficient solutions. In this paper, we present results from a collaborative design project carried out with planning officials [...] Read more.

With the rapid growth occurring in the urban regions of China, it is critical to address issues of sustainability through practices that engender holistic energy efficient solutions. In this paper, we present results from a collaborative design project carried out with planning officials from the city of Jinan (population 3.4 million), for the Luokou district, a 3.1 km² (1.2 mi²) area to the north of the CBD that is expected to house 100,000–130,000 people by 2020. By integrating sustainable building design, land use, urban design, and transportation, our proposal identified opportunities for improving energy efficiency that might have been overlooked by considering buildings and transportation separately. Mixed land uses and walkable neighborhoods were proposed along with highly differentiated street designs, intended to carry different traffic loads and prioritize diverse travel modes. Street widths and building heights were adjusted to maximize the potential for passive solar heating and daylight use within buildings. The district’s environmental performance, analyzed using building energy evaluation and traffic micro simulation models, showed that the design would reduce energy loads by over 25% compared to business as usual. While the proposal complied with national and local policies, and had far better energy performance than conventional designs, the proposal ultimately was not accepted by local officials because initial costs to the developers were higher than for conventional designs. Full article

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411 KiB

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Power Quality Assessment in Small Scale Renewable Energy Sources Supplying Distribution Systems

by Nicolae Golovanov, George Cristian Lazaroiu, Mariacristina Roscia and Dario Zaninelli

Energies 2013, 6(2), 634-645; https://doi.org/10.3390/en6020634 - 29 Jan 2013

Cited by 73 | Viewed by 7537

Abstract

The impact of wind turbines and photovoltaic systems on network operation and power quality (harmonics, and voltage fluctuations) is very important. The capability of the power system to absorb this perturbation is dependent on the fault level at the point of common coupling. [...] Read more.

The impact of wind turbines and photovoltaic systems on network operation and power quality (harmonics, and voltage fluctuations) is very important. The capability of the power system to absorb this perturbation is dependent on the fault level at the point of common coupling. The paper deals with power quality case studies conducted on existing renewable resources-based systems. Voltage fluctuations determined by a 0.65 MVA wind turbine are analyzed. The impact of photovoltaic systems on steady state voltage variations and current harmonics is investigated. The correlation between the generated power and the main power quality indices is highlighted. Full article

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250 KiB

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Use of Isomerization and Hydroisomerization Reactions to Improve the Cold Flow Properties of Vegetable Oil Based Biodiesel

by Stephen J. Reaume and Naoko Ellis

Energies 2013, 6(2), 619-633; https://doi.org/10.3390/en6020619 - 28 Jan 2013

Cited by 34 | Viewed by 7031

Abstract

Biodiesel is a promising alternative to petroleum diesel with the potential to reduce overall net CO₂ emissions. However, the high cloud point of biodiesel must be reduced when used in cold climates. We report on the use of isomerization and hydroisomerization reactions [...] Read more.

Biodiesel is a promising alternative to petroleum diesel with the potential to reduce overall net CO₂ emissions. However, the high cloud point of biodiesel must be reduced when used in cold climates. We report on the use of isomerization and hydroisomerization reactions to reduce the cloud point of eight different fats and oils. Isomerization was carried out at 260 °C and 1.5 MPa H₂ pressure utilizing beta zeolite catalyst, while hydroisomerization was carried out at 300 °C and 4.0 MPa H₂ pressure utilizing 0.5 wt % Pt-doped beta zeolite catalyst. Reaction products were tested for cloud point and flow properties, in addition to catalyst reusability and energy requirements. Results showed that high unsaturated fatty acid biodiesels increased in cloud point, due to the hydrogenation side reaction. In contrast, low unsaturated fatty acid biodiesels yielded cloud point reductions and overall improvement in the flow properties. A maximum cloud point reduction of 12.9 °C was observed with coconut oil as the starting material. Results of the study have shown that branching can reduce the cloud point of low unsaturated fatty acid content biodiesel. Full article

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Open AccessArticle

Green-Roof Effects on Neighborhood Microclimate and Human Thermal Sensation

by Lilliana L.H. Peng and C. Y. Jim

Energies 2013, 6(2), 598-618; https://doi.org/10.3390/en6020598 - 25 Jan 2013

Cited by 179 | Viewed by 16313

Abstract

Green roofs have been recognized as an effective sustainable design tool to mitigate urban heat island (UHI) effects. Previous studies have identified green-roof benefits in cooling and energy-conservation at the building scale, with limited exploration of the wider influence on neighborhood microclimate and [...] Read more.

Green roofs have been recognized as an effective sustainable design tool to mitigate urban heat island (UHI) effects. Previous studies have identified green-roof benefits in cooling and energy-conservation at the building scale, with limited exploration of the wider influence on neighborhood microclimate and human thermal comfort (HTC). This paper investigated the impacts of community-scale green-roof installation on air temperature and HTC in five typical residential neighborhoods of subtropical Hong Kong. The microclimate models ENVI-met and RayMan permitted studies of two main green-roof scenarios, namely extensive (EGR) and intensive (IGR). Microclimatic monitoring data from a local experimental green-roof site validated the modeling methods. The results verified that green-roof cooling effects were not restricted to rooftops, but extended to the ground to improve neighborhood microclimate. EGR reduced pedestrian-level air temperature by 0.4–0.7 °C, and IGR by 0.5–1.7 °C, with maximum effect in open-set low rise sites. Coverage by building footprints and building height dampened lateral and vertical advection of cool air generated by green roofs. Roof greening also improved notably the rooftop-podium level HTC. Diurnal duration of high heat stress was reduced by 6–9 h for EGR scenarios, and 9–11 h for IGR. The findings indicated that large-scale green-roof installation could bring neighborhood-wide cooling, mitigate urban heat island effect, and furnish more comfortable thermal environment for urban residents. Full article

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Energies, Volume 6, Issue 2 (February 2013) – 32 articles , Pages 566-1180

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