Energies

326 KiB

Open AccessArticle

A Multi-Criteria Methodology to Support Public Administration Decision Making Concerning Sustainable Energy Action Plans

by Giuliano Dall'O', Maria Franca Norese, Annalisa Galante and Chiara Novello

Energies 2013, 6(8), 4308-4330; https://doi.org/10.3390/en6084308 - 20 Aug 2013

Cited by 56 | Viewed by 8520

Abstract

For municipalities that have joined the Covenant of Mayors promoted by the European Commission, the Sustainable Energy Action Plan (SEAP) represents a strategic tool for achieving the greenhouse gas reductions required by 2020. So far as the energy retrofit actions in their residential [...] Read more.

For municipalities that have joined the Covenant of Mayors promoted by the European Commission, the Sustainable Energy Action Plan (SEAP) represents a strategic tool for achieving the greenhouse gas reductions required by 2020. So far as the energy retrofit actions in their residential building stock are concerned, which in the small-to-medium municipalities are responsible for more than 60% of CO₂ emissions, the scenarios for intervening are normally decided on the basis of an economic (cost/performance) analysis. This type of analysis, however, does not take into account important aspects for small and medium-sized communities such as social aspects, environmental impacts, local economic development and employment. A more comprehensive and effective tool to support the choices of public administrators is the multi-criteria analysis. This study proposes a methodology that integrates multi-criteria analysis in order to support Public Administration/Local Authorities in programming Sustainable Energy Action Plans with a more targeted approach to sustainability. The methodology, based on the ELECTRE III method, was applied to a medium-size municipality in the Lombardy region of Italy. The results obtained with this approach are discussed in this paper. Full article

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666 KiB

Open AccessArticle

A Dynamic Model for the Normal Impact of Fly Ash Particle with a Planar Surface

by Ming Dong, Jian Han, Sufen Li and Hang Pu

Energies 2013, 6(8), 4288-4307; https://doi.org/10.3390/en6084288 - 20 Aug 2013

Cited by 18 | Viewed by 5849

Abstract

The rebound behavior of fly ash particles normally impacting a planar surface is investigated by using a dynamic model. The three forms of soft sphere physical model are obtained using static/quasi-static contact mechanics and energy dissipation theory. The influences of the particle size, [...] Read more.

The rebound behavior of fly ash particles normally impacting a planar surface is investigated by using a dynamic model. The three forms of soft sphere physical model are obtained using static/quasi-static contact mechanics and energy dissipation theory. The influences of the particle size, the incident velocity of the particle on the damping coefficient and the impact contact time are all examined. We also predict the critical velocity for three particle sizes. It is found that the variation of the damping coefficient (η) with the normal incident velocity (v_in) can be roughly divided into the three parts. In the first part, η decreases with increasing v_in. In the second part, η is little changed with increasing v_in. In the third part, η rapidly increases with increasing v_in. For smaller impact velocities, the viscoelastic effect plays a dominant role in the impact process, while for higher incident velocities; the energy dissipation depends mainly on plastic deformation. In addition, the critical velocity shows a distinct dependence on the particle size. Finally, the contact displacement-contact time curves are examined. The work provides a solid basis for the development of a discrete-element-method approach to study ash deposition. Full article

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

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368 KiB

Open AccessArticle

A Vector-Controlled Distributed Generator Model for a Power Flow Based on a Three-Phase Current Injection Method

by Pyeong-Ik Hwang, Seung-Il Moon and Seon-Ju Ahn

Energies 2013, 6(8), 4269-4287; https://doi.org/10.3390/en6084269 - 20 Aug 2013

Cited by 7 | Viewed by 5602

Abstract

This paper proposes a vector-controlled distributed generator (DG) model for a power flow based on a three-phase current injection method (TCIM). In order to represent the DG models in the power flow, steady-state phase current output equations are formulated. Using these equations, the [...] Read more.

This paper proposes a vector-controlled distributed generator (DG) model for a power flow based on a three-phase current injection method (TCIM). In order to represent the DG models in the power flow, steady-state phase current output equations are formulated. Using these equations, the TCIM power flow formulation is modified to include the DG models. In the proposed power flow, a DG-connected bus is modeled as either a load bus (PQ bus) or a voltage-controlled bus (PV bus), depending on the control mode of the reactive power. However, unlike conventional bus models, the values of the DG-connected bus models are represented by three-phase quantities: three-phase active and reactive power output for a PQ bus, and three-phase active power and positive-sequence voltage for a PV bus. In addition, a method is proposed for representing the reactive power limit of a voltage-control-mode DG by using the q-axis current limit. Utilizing a modified IEEE 13-bus test system, the accuracy of the proposed method is verified by comparison to the power systems computer aided design (PSCAD) model. Furthermore, the effect of the number of DGs on the convergence rate is analyzed, using the IEEE 123-bus test system. Full article

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1245 KiB

Open AccessArticle

Analysis and Simulation of Fault Characteristics of Power Switch Failures in Distribution Electronic Power Transformers

by Zixia Sang, Chengxiong Mao, Jiming Lu and Dan Wang

Energies 2013, 6(8), 4246-4268; https://doi.org/10.3390/en6084246 - 19 Aug 2013

Cited by 32 | Viewed by 7832

Abstract

This paper presents research on the voltage and current distortion in the input stage, isolation stage and output stage of Distribution Electronic Power transformer (D-EPT) after the open-circuit and short-circuit faults of its power switches. In this paper, the operational principles and the [...] Read more.

This paper presents research on the voltage and current distortion in the input stage, isolation stage and output stage of Distribution Electronic Power transformer (D-EPT) after the open-circuit and short-circuit faults of its power switches. In this paper, the operational principles and the control methods for input stage, isolation stage and output stage of D-EPT, which work as a cascaded H-bridge rectifier, DC-DC converter and inverter, respectively, are introduced. Based on conclusions derived from the performance analysis of D-EPT after the faults, this paper comes up with the effects from its topology design and control scheme on the current and voltage distortion. According to the EPT fault characteristics, since the waveforms of relevant components heavily depend on the location of the faulty switch, it is very easy to locate the exact position of the faulty switch. Finally, the fault characteristics peculiar to D-EPT are analyzed, and further discussed with simulation on the Saber platform, as well as a fault location diagnosis algorithm. Full article

(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)

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851 KiB

Open AccessArticle

Optimum Application of Thermal Factors to Artificial Neural Network Models for Improvement of Control Performance in Double Skin-Enveloped Buildings

by Jin Woo Moon, Kyung-Il Chin and Sooyoung Kim

Energies 2013, 6(8), 4223-4245; https://doi.org/10.3390/en6084223 - 19 Aug 2013

Cited by 10 | Viewed by 5690

Abstract

This study proposes an artificial neural network (ANN)-based thermal control method for buildings with double skin envelopes that has rational relationships between the ANN model input and output. The relationship between the indoor air temperature and surrounding environmental factors was investigated based on [...] Read more.

This study proposes an artificial neural network (ANN)-based thermal control method for buildings with double skin envelopes that has rational relationships between the ANN model input and output. The relationship between the indoor air temperature and surrounding environmental factors was investigated based on field measurement data from an actual building. The results imply that the indoor temperature was not significantly influenced by vertical solar irradiance, but by the outdoor and cavity temperature. Accordingly, a new ANN model developed in this study excluded solar irradiance as an input variable for predicting the future indoor temperature. The structure and learning method of this new ANN model was optimized, followed by the performance tests of a variety of internal and external envelope opening strategies for the heating and cooling seasons. The performance tests revealed that the optimized ANN-based logic yielded better temperature conditions than the non-ANN based logic. This ANN-based logic increased overall comfortable periods and decreased the frequency of overshoots and undershoots out of the thermal comfort range. The ANN model proved that it has the potential to be successfully applied in the temperature control logic for double skin-enveloped buildings. The ANN model, which was proposed in this study, effectively predicted future indoor temperatures for the diverse opening strategies. The ANN-based logic optimally determined the operation of heating and cooling systems as well as opening conditions for the double skin envelopes. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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573 KiB

Open AccessArticle

Effect of Mixing Driven by Siphon Flow: Parallel Experiments Using the Anaerobic Reactors with Different Mixing Modes

by Takuro Kobayashi, Ya-Peng Wu, Kai-Qin Xu and Yu-You Li

Energies 2013, 6(8), 4207-4222; https://doi.org/10.3390/en6084207 - 19 Aug 2013

Cited by 15 | Viewed by 7249

Abstract

The effect of mixing by siphon flow on anaerobic digestion, sludge distribution and microbial community were examined in parallel experiments using a siphon-mixed reactor (SMR), an unmixed reactor (UMR) and a continuously mixed reactor (CMR). The SMR performed well without the accumulation of [...] Read more.

The effect of mixing by siphon flow on anaerobic digestion, sludge distribution and microbial community were examined in parallel experiments using a siphon-mixed reactor (SMR), an unmixed reactor (UMR) and a continuously mixed reactor (CMR). The SMR performed well without the accumulation of fatty acids under COD loading rates varying from 3 to 18 kg/m³/day, while the UMR was totally acidified when the loading rate increased to 10 kg/m³/day. The methane yield of the SMR was at least 10% higher than that of the UMR, and comparable to that of the CMR. Furthermore, the SMR was found to markedly improve the dispersion of solids and reduce deposit formation compared to the UMR. Besides, during stable operation, the fatty acids level in the effluent of the SMR and UMR was lower than that in the CMR, and the archaeal community structure of the SMR was similar to that of the UMR. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2013)

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2213 KiB

Open AccessArticle

Thermal Efficiency Comparison of Borehole Heat Exchangers with Different Drillhole Diameters

by Jin Luo, Joachim Rohn, Manfred Bayer and Anna Priess

Energies 2013, 6(8), 4187-4206; https://doi.org/10.3390/en6084187 - 19 Aug 2013

Cited by 24 | Viewed by 6198

Abstract

Thermal efficiency of borehole heat exchangers (BHE) is of crucial importance for the design and optimization of ground source heat pump (GSHP) system. This paper investigates thermal efficiency of a BHE with three drillhole diameters: 121 mm, 165 mm and 180 mm. The [...] Read more.

Thermal efficiency of borehole heat exchangers (BHE) is of crucial importance for the design and optimization of ground source heat pump (GSHP) system. This paper investigates thermal efficiency of a BHE with three drillhole diameters: 121 mm, 165 mm and 180 mm. The BHE was installed in a GSHP system of an office building located in Nuremberg, Germany. Thermal properties and hydraulic properties of the ground where the BHE was installed have been measured by thermal response tests as well as pumping tests. Furthermore, the evaluation of thermal performance is made possible by monitoring operation of the GSHP system. Using the recorded data, thermal exchange rates have been calculated and compared in a daily period as well as a seasonal period. The daily statistics indicate that the thermal exchange rate of the BHE increases with larger drillhole diameter. For the seasonal cooling performance, the amount of thermal exchange of BHE with 165 mm and 180 mm diameters was found to be 3.2% and 7.1% larger than that of the BHE with 121 mm diameter, respectively. These findings provide helpful suggestions for the design of future GSHP systems to achieve higher energy-efficiency. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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240 KiB

Open AccessArticle

Energy Analysis of the Danish Food Production System: Food-EROI and Fossil Fuel Dependency

by Mads V. Markussen and Hanne Østergård

Energies 2013, 6(8), 4170-4186; https://doi.org/10.3390/en6084170 - 15 Aug 2013

Cited by 23 | Viewed by 8433

Abstract

Modern food production depends on limited natural resources for providing energy and fertilisers. We assess the fossil fuel dependency for the Danish food production system by means of Food Energy Returned on fossil Energy Invested (Food-EROI) and by the use of energy intensive [...] Read more.

Modern food production depends on limited natural resources for providing energy and fertilisers. We assess the fossil fuel dependency for the Danish food production system by means of Food Energy Returned on fossil Energy Invested (Food-EROI) and by the use of energy intensive nutrients from imported livestock feed and commercial fertilisers. The analysis shows that the system requires 221 PJ of fossil energy per year and that for each joule of fossil energy invested in farming, processing and transportation, 0.25 J of food energy is produced; 0.28 when crediting for produced bioenergy. Furthermore, nutrients in commercial fertiliser and imported feed account for 84%, 90% and 90% of total supply of N, P and K, respectively. We conclude that the system is unsustainable because it is embedded in a highly fossil fuel dependent system based on a non-circular flow of nutrients. As energy and thus nutrient constraints may develop in the coming decades, the current system may need to adapt by reducing use of fossil energy at the farm and for transportation of food and feed. An operational strategy may be to relocalise the supply of energy, nutrients, feed and food. Full article

1100 KiB

Open AccessArticle

Islanding Detection Method of a Photovoltaic Power Generation System Based on a CMAC Neural Network

by Kuei-Hsiang Chao, Min-Sen Yang and Chin-Pao Hung

Energies 2013, 6(8), 4152-4169; https://doi.org/10.3390/en6084152 - 15 Aug 2013

Cited by 11 | Viewed by 5383

Abstract

This study proposes an islanding detection method for photovoltaic power generation systems based on a cerebellar model articulation controller (CMAC) neural network. First, islanding phenomenon test data were used as training samples to train the CMAC neural network. Then, a photovoltaic power generation [...] Read more.

This study proposes an islanding detection method for photovoltaic power generation systems based on a cerebellar model articulation controller (CMAC) neural network. First, islanding phenomenon test data were used as training samples to train the CMAC neural network. Then, a photovoltaic power generation system was tested with the islanding phenomena. Because the CMAC neural network possesses association and induction abilities and characteristics that activate similar input signals in approximate memory during training process, the CMAC only requires that the weight values of the excited memory addresses be adjusted, thereby reducing the training time. Furthermore, quantification of the input signals enhanced the detection tolerance of the proposed method. Finally, the simulative and experimental data verified the feasibility of adopting the proposed detection method for islanding phenomena. Full article

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882 KiB

Open AccessArticle

Adaptive State of Charge Estimation for Li-Ion Batteries Based on an Unscented Kalman Filter with an Enhanced Battery Model

by Zhiwei He, Mingyu Gao, Caisheng Wang, Leyi Wang and Yuanyuan Liu

Energies 2013, 6(8), 4134-4151; https://doi.org/10.3390/en6084134 - 12 Aug 2013

Cited by 87 | Viewed by 9292

Abstract

Accurate estimation of the state of charge (SOC) of batteries is one of the key problems in a battery management system. This paper proposes an adaptive SOC estimation method based on unscented Kalman filter algorithms for lithium (Li)-ion batteries. First, an enhanced battery [...] Read more.

Accurate estimation of the state of charge (SOC) of batteries is one of the key problems in a battery management system. This paper proposes an adaptive SOC estimation method based on unscented Kalman filter algorithms for lithium (Li)-ion batteries. First, an enhanced battery model is proposed to include the impacts due to different discharge rates and temperatures. An adaptive joint estimation of the battery SOC and battery internal resistance is then presented to enhance system robustness with battery aging. The SOC estimation algorithm has been developed and verified through experiments on different types of Li-ion batteries. The results indicate that the proposed method provides an accurate SOC estimation and is computationally efficient, making it suitable for embedded system implementation. Full article

(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)

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1609 KiB

Open AccessArticle

Design of a Novel Experimental Facility for Testing of Tidal Arrays

by Matevz Pintar and Athanasios J. Kolios

Energies 2013, 6(8), 4117-4133; https://doi.org/10.3390/en6084117 - 12 Aug 2013

Cited by 6 | Viewed by 5723

Abstract

In order to obtain the maximum amount of energy from tidal stream extraction devices, deployment in large arrays should be studied. The area of seabed with favorable conditions is fairly limited; therefore layout spacing has to be optimized. In this paper a feasibility [...] Read more.

In order to obtain the maximum amount of energy from tidal stream extraction devices, deployment in large arrays should be studied. The area of seabed with favorable conditions is fairly limited; therefore layout spacing has to be optimized. In this paper a feasibility study for a novel experimental facility, suitable for the testing of an array of tidal devices, is presented. To avoid space and scale limitations of towing tanks, testing is proposed to be performed in large lakes or calm seas using a self-propelled vessel, which will carry an array of devices with variable spacing, creating relevant speed differences and measuring their performance and loading. Using hydrodynamic scaling laws, an appropriate size for test turbines and the range of vessel speed was determined to fulfill experimental requirements. Computational fluid dynamic simulations, using the actuator disc method, have suggested a suitable turbine array configuration to resemble real application conditions. A simplified model of the vessel was analyzed using the finite elements method to determine the main scantlings. The hull resistance calculated by empirical formulae was found to be negligible compared to the resistance of the tested turbine. It was confirmed that turbine size and speed determined by scaling laws are also reasonable from a propulsion point of view. Full article

(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)

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686 KiB

Open AccessArticle

Damping Wind and Wave Loads on a Floating Wind Turbine

by Søren Christiansen, Thomas Bak and Torben Knudsen

Energies 2013, 6(8), 4097-4116; https://doi.org/10.3390/en6084097 - 9 Aug 2013

Cited by 36 | Viewed by 10042

Abstract

Offshore wind energy capitalizes on the higher and less turbulent wind speeds at sea. To enable deployment of wind turbines in deep-water locations, structures are being explored, where wind turbines are placed on a floating platform. This combined structure presents a new control [...] Read more.

Offshore wind energy capitalizes on the higher and less turbulent wind speeds at sea. To enable deployment of wind turbines in deep-water locations, structures are being explored, where wind turbines are placed on a floating platform. This combined structure presents a new control problem, due to the partly unconstrained movement of the platform and ocean wave excitation. If this additional complexity is not dealt with properly, this may lead to a significant increase in the structural loads and, potentially, instability of the controlled system. In this paper, the wave excitation is investigated, and we show the influence that both wind speed, wave frequencies and misalignment between wind and waves have on the system dynamics. A new control model is derived that extends standard turbine models to include the hydrodynamics, additional platform degrees of freedom, the platform mooring system and tower side-side motion, including gyroscopic effects. The models support a model-based design that includes estimators for wind speed and wave frequency. The design is applied to a number of examples representing different wind and wave conditions and successfully demonstrates a reduction in the structural oscillations, while improving power performance. Full article

(This article belongs to the Special Issue Wind Turbines 2013)

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1748 KiB

Open AccessArticle

Effects of Impermeable Boundaries on Gas Production from Hydrate Accumulations in the Shenhu Area of the South China Sea

by Gang Li, Xiao-Sen Li, Keni Zhang, Bo Li and Yu Zhang

Energies 2013, 6(8), 4078-4096; https://doi.org/10.3390/en6084078 - 8 Aug 2013

Cited by 61 | Viewed by 7061

Abstract

Based on currently available data from site measurements and the preliminary estimates of the gas production potential from the hydrate accumulations at the SH7 site in the Shenhu Area using the depressurization method with a single horizontal well placed in the middle of [...] Read more.

Based on currently available data from site measurements and the preliminary estimates of the gas production potential from the hydrate accumulations at the SH7 site in the Shenhu Area using the depressurization method with a single horizontal well placed in the middle of the Hydrate-Bearing Layer (HBL), the dependence of production performance on the permeabilities of the overburden (OB) and underburden (UB) layers was investigated in this modeling study. The simulation results indicated that the temperature and the pressure of the HBL were affected by the permeabilities of OB and UB and the effect of depressurization with impermeable OB and UB was significantly stronger than that with permeable boundaries. Considering the percentage of hydrate dissociation, the gas production rate and the gas-to-water ratio, the hydrate deposit with impermeable OB and UB was expected to be the potential gas production target. Full article

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

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12498 KiB

Open AccessArticle

Comparison of the Experimental and Numerical Results of Modelling a 32-Oscillating Water Column (OWC), V-Shaped Floating Wave Energy Converter

by Thomas Kelly, Thomas Dooley, John Campbell and John V. Ringwood

Energies 2013, 6(8), 4045-4077; https://doi.org/10.3390/en6084045 - 8 Aug 2013

Cited by 38 | Viewed by 9486

Abstract

Combining offshore wind and wave energy converting apparatuses presents a number of potentially advantageous synergies. To facilitate the development of a proposed floating platform combining these two technologies, proof of concept scale model testing on the wave energy converting component of this platform [...] Read more.

Combining offshore wind and wave energy converting apparatuses presents a number of potentially advantageous synergies. To facilitate the development of a proposed floating platform combining these two technologies, proof of concept scale model testing on the wave energy converting component of this platform has been conducted. The wave energy component is based on the well-established concept of the oscillating water column. A numerical model of this component has been developed in the frequency domain, and the work presented here concerns the results of this modelling and testing. The results of both are compared to assess the validity and usefulness of the numerical model. Full article

(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)

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5365 KiB

Open AccessArticle

Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter

by Rico H. Hansen, Morten M. Kramer and Enrique Vidal

Energies 2013, 6(8), 4001-4044; https://doi.org/10.3390/en6084001 - 7 Aug 2013

Cited by 149 | Viewed by 17306

Abstract

The Wavestar Wave Energy Converter (WEC) is a multiple absorber concept, consisting of 20 hemisphere shaped floats attached to a single platform. The heart of the Wavestar WEC is the Power Take-Off (PTO) system, converting the wave induced motion of the floats into [...] Read more.

The Wavestar Wave Energy Converter (WEC) is a multiple absorber concept, consisting of 20 hemisphere shaped floats attached to a single platform. The heart of the Wavestar WEC is the Power Take-Off (PTO) system, converting the wave induced motion of the floats into a steady power output to the grid. In the present work, a PTO based on a novel discrete displacement fluid power technology is explored for the Wavestar WEC. Absorption of power from the floats is performed by hydraulic cylinders, supplying power to a common fixed pressure system with accumulators for energy smoothing. The stored pressure energy is converted into electricity at a steady pace by hydraulic motors and generators. The storage, thereby, decouples the complicated process of wave power absorption from power generation. The core for enabling this PTO technology is implementing a near loss-free force control of the energy absorbing cylinders. This is achieved by using special multi-chambered cylinders, where the different chambers may be connected to the available system pressures using fast on/off valves. Resultantly, a Discrete Displacement Cylinder (DDC) is created, allowing near loss free discrete force control. This paper presents a complete PTO system for a 20 float Wavestar based on the DDC. The WEC and PTO is rigorously modeled from incident waves to the electric output to the grid. The resulting model of +600 states is simulated in different irregular seas, showing that power conversion efficiencies above 70% from input power to electrical power is achievable for all relevant sea conditions. Full article

(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)

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444 KiB

Open AccessArticle

A Two-Stage Continuous Fermentation System for Conversion of Syngas into Ethanol

by Hanno Richter, Michael E. Martin and Largus T. Angenent

Energies 2013, 6(8), 3987-4000; https://doi.org/10.3390/en6083987 - 7 Aug 2013

Cited by 137 | Viewed by 14566

Abstract

We have established a two-stage continuous fermentation process for production of ethanol from synthesis gas (syngas) with Clostridium ljungdahlii. The system consists of a 1-L continuously stirred tank reactor as a growth stage and a 4-L bubble column equipped with a cell [...] Read more.

We have established a two-stage continuous fermentation process for production of ethanol from synthesis gas (syngas) with Clostridium ljungdahlii. The system consists of a 1-L continuously stirred tank reactor as a growth stage and a 4-L bubble column equipped with a cell recycle module as an ethanol production stage. Operating conditions in both stages were optimized for the respective purpose (growth in stage one and alcohol formation in stage two). The system was fed with an artificial syngas mixture, mimicking the composition of syngas derived from lignocellulosic biomass (60% CO, 35% H₂, and 5% CO₂). Gas recycling was used to increase the contact area and retention time of gas in the liquid phase, improving mass transfer and metabolic rates. In stage two, the biocatalyst was maintained at high cell densities of up to 10 g DW/L. Ethanol was continuously produced at concentrations of up to 450 mM (2.1%) and ethanol production rates of up to 0.37 g/(L·h). Foam control was essential to maintain reactor stability. A stoichiometric evaluation of the optimized process revealed that the recovery of carbon and hydrogen from the provided carbon monoxide and hydrogen in the produced ethanol was 28% and 74%, respectively. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2013)

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880 KiB

Open AccessArticle

Effects of Biomass Feedstocks and Gasification Conditions on the Physiochemical Properties of Char

by Kezhen Qian, Ajay Kumar, Krushna Patil, Danielle Bellmer, Donghai Wang, Wenqiao Yuan and Raymond L. Huhnke

Energies 2013, 6(8), 3972-3986; https://doi.org/10.3390/en6083972 - 6 Aug 2013

Cited by 175 | Viewed by 10886

Abstract

Char is a low-value byproduct of biomass gasification and pyrolysis with many potential applications, such as soil amendment and the synthesis of activated carbon and carbon-based catalysts. Considering these high-value applications, char could provide economic benefits to a biorefinery utilizing gasification or pyrolysis [...] Read more.

Char is a low-value byproduct of biomass gasification and pyrolysis with many potential applications, such as soil amendment and the synthesis of activated carbon and carbon-based catalysts. Considering these high-value applications, char could provide economic benefits to a biorefinery utilizing gasification or pyrolysis technologies. However, the properties of char depend heavily on biomass feedstock, gasifier design and operating conditions. This paper reports the effects of biomass type (switchgrass, sorghum straw and red cedar) and equivalence ratio (0.20, 0.25 and 0.28), i.e., the ratio of air supply relative to the air that is required for stoichiometric combustion of biomass, on the physiochemical properties of char derived from gasification. Results show that the Brunauer-Emmett-Teller (BET) surface areas of most of the char were 1–10 m²/g and increased as the equivalence ratio increased. Char moisture and fixed carbon contents decreased while ash content increased as equivalence ratio increased. The corresponding Fourier Transform Infrared spectra showed that the surface functional groups of char differed between biomass types but remained similar with change in equivalence ratio. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2013)

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661 KiB

Open AccessArticle

Cooperative Control to Enhance the Frequency Stability of Islanded Microgrids with DFIG-SMES

by Wei Gu, Wei Liu, Zhi Wu, Bo Zhao and Wu Chen

Energies 2013, 6(8), 3951-3971; https://doi.org/10.3390/en6083951 - 6 Aug 2013

Cited by 48 | Viewed by 6968

Abstract

The issue of frequency stability of microgrids under islanded operation mode and mode transfer has attracted particular attention recently. In this paper, a cooperative frequency control method, which consists of a microgrid central control (MGCC) and microgrid local control (MGLC), is proposed to [...] Read more.

The issue of frequency stability of microgrids under islanded operation mode and mode transfer has attracted particular attention recently. In this paper, a cooperative frequency control method, which consists of a microgrid central control (MGCC) and microgrid local control (MGLC), is proposed to achieve a seamless transfer from grid-connected to islanded mode, and hence increase the frequency stability of islanded microgrids during both primary and secondary frequency control. A power deficiency prediction and distribution method is proposed in MGCC to effectively distribute and utilize the power and loads, and accomplish the cooperative control of all microgrid units. With regards to MGLC, a Hopfield fuzzy neural network control (HFNNC) is applied to make the corresponding frequency control of DFIG-SMES more adaptive. Meanwhile a state of capacity (SOC) control is utilized in battery energy storage (BES) to extend battery life. Simulation results indicate that the proposed frequency control approach can maintain the frequency stability of islanded microgrids even in emergency conditions. Full article

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299 KiB

Open AccessArticle

Bioethanol Production by Carbohydrate-Enriched Biomass of Arthrospira (Spirulina) platensis

by Giorgos Markou, Irini Angelidaki, Elias Nerantzis and Dimitris Georgakakis

Energies 2013, 6(8), 3937-3950; https://doi.org/10.3390/en6083937 - 6 Aug 2013

Cited by 162 | Viewed by 10961

Abstract

In the present study the potential of bioethanol production using carbohydrate-enriched biomass of the cyanobacterium Arthrospira platensis was studied. For the saccharification of the carbohydrate-enriched biomass, four acids (H₂SO₄, HNO₃, HCl and H₃PO₄) [...] Read more.

In the present study the potential of bioethanol production using carbohydrate-enriched biomass of the cyanobacterium Arthrospira platensis was studied. For the saccharification of the carbohydrate-enriched biomass, four acids (H₂SO₄, HNO₃, HCl and H₃PO₄) were investigated. Each acid were used at four concentrations, 2.5 N, 1 N, 0.5 N and 0.25 N, and for each acid concentration the saccharification was conducted under four temperatures (40 °C, 60 °C, 80 °C and 100 °C). Higher acid concentrations gave in general higher reducing sugars (RS) yields (%, g_RS/g_{Total sugars}) with higher rates, while the increase in temperature lead to higher rates at lower acid concentration. The hydrolysates then were used as substrate for ethanolic fermentation by a salt stress-adapted Saccharomyces cerevisiae strain. The bioethanol yield (%, g_EtOH/g_Biomass) was significantly affected by the acid concentration used for the saccharification of the carbohydrates. The highest bioethanol yields of 16.32% ± 0.90% (g_EtOH/g_Biomass) and 16.27% ± 0.97% (g_EtOH/g_Biomass) were obtained in hydrolysates produced with HNO₃ 0.5 N and H₂SO₄ 0.5 N, respectively. Full article

(This article belongs to the Special Issue Algae Fuel 2013)

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466 KiB

Open AccessArticle

Numerical Investigation of the Thermal Management Performance of MEPCM Modules for PV Applications

by Abednego Oscar Tanuwijava, Ching Jenq Ho, Chi-Ming Lai and Chao-Yang Huang

Energies 2013, 6(8), 3922-3936; https://doi.org/10.3390/en6083922 - 6 Aug 2013

Cited by 31 | Viewed by 6199

Abstract

The efficiency of photovoltaic modules decreases as the cell temperature increases. It is necessary to have an adequate thermal management mechanism for a photovoltaic module, especially when combined with a building construction system. This study aims to investigate via computational fluid dynamics simulations [...] Read more.

The efficiency of photovoltaic modules decreases as the cell temperature increases. It is necessary to have an adequate thermal management mechanism for a photovoltaic module, especially when combined with a building construction system. This study aims to investigate via computational fluid dynamics simulations the heat transfer characteristics and thermal management performance of microencapsulated phase change material modules for photovoltaic applications under temporal variations of daily solar irradiation. The results show that the aspect ratio of the microencapsulated phase change material layer has significant effects on the heat transfer characteristics and the overall thermal performance of the two cases examined with different melting points (26 °C and 34 °C) are approximately the same. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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452 KiB

Open AccessArticle

Use of LCA as a Tool for Building Ecodesign. A Case Study of a Low Energy Building in Spain

by Ignacio Zabalza, Sabina Scarpellini, Alfonso Aranda, Eva Llera and Alberto Jáñez

Energies 2013, 6(8), 3901-3921; https://doi.org/10.3390/en6083901 - 2 Aug 2013

Cited by 52 | Viewed by 9295

Abstract

This paper demonstrates how to achieve energy savings in the construction and operation of buildings by promoting the use of life cycle assessment techniques in the design for new buildings and for refurbishment. The paper aims to draw on the application of a [...] Read more.

This paper demonstrates how to achieve energy savings in the construction and operation of buildings by promoting the use of life cycle assessment techniques in the design for new buildings and for refurbishment. The paper aims to draw on the application of a specific methodology for low energy consumption, integrated planning, environmental performance evaluation of buildings, and design for sustainability and LCA techniques applied to buildings. The ENergy Saving through promotion of LIfe Cycle assessment in buildings (ENSLIC) methodology based on LCA for use in an integral planning process has been promoted to stakeholders who require a means to optimize the environmental performance of buildings. Feedback from the stakeholders has facilitated the creation of simplified LCA guidelines, a systematic approach guiding the user through the alternative options regarding software choices, their strengths and weaknesses, the databases available, the usefulness of different indicators, aggregation, definition of limits and options for simplifying the process. As a result, this paper presents the applied results of a case study where this methodology is implemented serving as an energy savings evaluation tool for decision makers, end-users, professionals involved in the different stages of construction, etc. Finally, it is demonstrated how LCA can facilitate comparisons between different buildings, showing the influence of all variables on a building’s life cycle environmental impact and showing the potential for energy savings. Removing market barriers to sustainable construction is actually stricter and this is good news for promoting higher energy efficiency in buildings. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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529 KiB

Open AccessArticle

Biofuel that Keeps Glycerol as Monoglyceride by 1,3-Selective Ethanolysis with Pig Pancreatic Lipase Covalently Immobilized on AlPO₄ Support

by Carlos Luna, Enrique Sancho, Diego Luna, Verónica Caballero, Juan Calero, Alejandro Posadillo, Cristóbal Verdugo, Felipa M. Bautista and Antonio A. Romero

Energies 2013, 6(8), 3879-3900; https://doi.org/10.3390/en6083879 - 30 Jul 2013

Cited by 27 | Viewed by 8037

Abstract

By using pig pancreatic lipase (EC 3.1.1.3 or PPL) as a biocatalyst, covalently immobilized on amorphous AlPO₄ support, a new second generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol. The resulting biofuel is composed of fatty acid [...] Read more.

By using pig pancreatic lipase (EC 3.1.1.3 or PPL) as a biocatalyst, covalently immobilized on amorphous AlPO₄ support, a new second generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol. The resulting biofuel is composed of fatty acid ethyl esters and monoglycerides (FAEE/MG) blended in a 2:1 molar ratio. This novel product, which integrates glycerol as monoacylglycerols (MG) into the biofuels composition, has similar physicochemical properties as conventional biodiesel and also avoids the removal step of the by-product by washing of the biodiesel with water. Immobilization of PPL was achieved by covalent attachment of the ε-amino group of the lysine residues of PPL with the aldehyde groups of p-hydroxybenzaldehyde linked on a hybrid organic-inorganic functionalized AlPO₄ surface. With this procedure, the PPL biocatalyst was strongly fixed to the inorganic support surface (94.3%). Nevertheless, the efficiency of the immobilized enzyme was relatively lower compared to that of the free PPL, but it showed a remarkable stability as well as a great capacity of reutilization (25 reuses) without a significant loss of its initial catalytic activity. Therefore, this enzymatic method allows the production of a biodiesel which integrates the glycerol, allows a more efficient fabrication method and minimizes the waste production as compared to the conventional alkali-catalyzed process. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2013)

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577 KiB

Open AccessArticle

Infrared Screening of Residential Buildings for Energy Audit Purposes: Results of a Field Test

by Giuliano Dall'O', Luca Sarto and Angela Panza

Energies 2013, 6(8), 3859-3878; https://doi.org/10.3390/en6083859 - 30 Jul 2013

Cited by 109 | Viewed by 9376

Abstract

In the European Union (EU), the building sector is responsible for approximately 40% of total energy consumption. The existing building stock is inefficient and can, and indeed must be retrofitted to address this issue. The practical implementation of the European strategies requires knowledge [...] Read more.

In the European Union (EU), the building sector is responsible for approximately 40% of total energy consumption. The existing building stock is inefficient and can, and indeed must be retrofitted to address this issue. The practical implementation of the European strategies requires knowledge of the energy performance of existing buildings through energy audit techniques. Application of thermography in the fields of energy are very widespread, since, through such a non-invasive investigation, and through correct interpretation of infrared images, it is possible to highlight inefficiencies in buildings and related facilities. The paper shows and discusses the results of an infrared audit campaign on 14 existing buildings located in Milan Province (Italy) made in different construction periods and characterised, therefore, by different building technologies. The U-values obtained in an indirect way through the thermography of the opaque walls of the buildings investigated, were compared with the actual known values in order to verify the reliability of the method and the possible margin of error. The study indicated that the category of buildings in which the application of this method is sufficiently reliable is that of solid-mass structure buildings, the most widespread in Italy, whereas in the case of buildings whose external walls are insulated, the percentage of deviation is very high. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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538 KiB

Open AccessArticle

Results of Current Density Distribution Mapping in PEM Fuel Cells Dependent on Operation Parameters

by Maik Heuer, Paul A. Bernstein, Michael Wenske and Zbigniew A. Styczynski

Energies 2013, 6(8), 3841-3858; https://doi.org/10.3390/en6083841 - 29 Jul 2013

Cited by 10 | Viewed by 7184

Abstract

This paper presents in situ measurements of a newly developed current density measurement system for proton exchange membrane fuel cells (PEMFC). While the functional principle and technical evaluation of the measurement system were presented in a previous paper, this paper analyzes the influence [...] Read more.

This paper presents in situ measurements of a newly developed current density measurement system for proton exchange membrane fuel cells (PEMFC). While the functional principle and technical evaluation of the measurement system were presented in a previous paper, this paper analyzes the influence of various operation parameters, including multiple start-stop operation, at the anode, cathode and cooling locations on the distribution and long-term development of the current density. The system was operated for 500 h over two years with long periods of inactivity between measurements. The measurement results are evaluated and provide additional information on how to optimize the operation modes of fuel cells, including the start and stop of such systems as well as the water balance. Full article

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574 KiB

Open AccessArticle

A Virtual Tool for Minimum Cost Design of a Wind Turbine Tower with Ring Stiffeners

by Fatih Karpat

Energies 2013, 6(8), 3822-3840; https://doi.org/10.3390/en6083822 - 29 Jul 2013

Cited by 19 | Viewed by 8561

Abstract

Currently, renewable energy resources are becoming more important to reduce greenhouse gas emissions and increase energy efficiency. Researchers have focused on all components of wind turbines to increase reliability and minimize cost. In this paper, a procedure including a cost analysis method and [...] Read more.

Currently, renewable energy resources are becoming more important to reduce greenhouse gas emissions and increase energy efficiency. Researchers have focused on all components of wind turbines to increase reliability and minimize cost. In this paper, a procedure including a cost analysis method and a particle swarm optimization algorithm has been presented to efficiently design low cost steel wind turbine towers. A virtual tool is developed in MATLAB for the cost optimization of wind turbine steel towers with ring stiffeners using a particle swarm optimization algorithm. A wind turbine tower optimization problem in the literature is solved using the developed computer program. In the optimization procedure the optimization results match very well with the optimization results obtained previously. The wall thickness of the shell segments and the dimensions of the ring stiffeners are selected as the design variables, and the limits of the local buckling for the flat ring stiffeners, the local shell buckling limit, the panel ring buckling limit and the limitation of the frequency are considered the design constraints. Numerical examples are presented to understand the impacts of the design variables on the total cost of the wind turbine tower. Full article

(This article belongs to the Special Issue Wind Turbines 2013)

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653 KiB

Open AccessArticle

Flicker Mitigation by Speed Control of Permanent Magnet Synchronous Generator Variable-Speed Wind Turbines

by Weihao Hu, Yunqian Zhang, Zhe Chen and Yanting Hu

Energies 2013, 6(8), 3807-3821; https://doi.org/10.3390/en6083807 - 29 Jul 2013

Cited by 23 | Viewed by 8218

Abstract

Grid-connected wind turbines are fluctuating power sources that may produce flicker during continuous operation. This paper presents a simulation model of a MW-level variable speed wind turbine with a full-scale back-to-back power converter and permanent magnet synchronous generator (PMSG) developed in the simulation [...] Read more.

Grid-connected wind turbines are fluctuating power sources that may produce flicker during continuous operation. This paper presents a simulation model of a MW-level variable speed wind turbine with a full-scale back-to-back power converter and permanent magnet synchronous generator (PMSG) developed in the simulation tool of PSCAD/EMTDC. Flicker emission of this system is investigated. The 3p (three times per revolution) power oscillation due to wind shear and tower shadow effects is the significant part in the flicker emission of variable speed wind turbines with PMSG during continuous operation. A new method of flicker mitigation by controlling the rotational speed is proposed. It smoothes the 3p active power oscillations from wind shear and tower shadow effects of the wind turbine by varying the rotational speed of the PMSG. Simulation results show that damping the 3p active power oscillation by using the flicker mitigation speed controller is an effective means for flicker mitigation of variable speed wind turbines with full-scale back-to-back power converters and PMSG during continuous operation. Full article

(This article belongs to the Special Issue Wind Turbines 2013)

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840 KiB

Open AccessReview

The Use of Artificial Neural Networks for Identifying Sustainable Biodiesel Feedstocks

by Mohammed I. Jahirul, Richard J. Brown, Wijitha Senadeera, Ian M. O'Hara and Zoran D. Ristovski

Energies 2013, 6(8), 3764-3806; https://doi.org/10.3390/en6083764 - 29 Jul 2013

Cited by 55 | Viewed by 10860

Abstract

Over the past few decades, biodiesel produced from oilseed crops and animal fat is receiving much attention as a renewable and sustainable alternative for automobile engine fuels, and particularly petroleum diesel. However, current biodiesel production is heavily dependent on edible oil feedstocks which [...] Read more.

Over the past few decades, biodiesel produced from oilseed crops and animal fat is receiving much attention as a renewable and sustainable alternative for automobile engine fuels, and particularly petroleum diesel. However, current biodiesel production is heavily dependent on edible oil feedstocks which are unlikely to be sustainable in the longer term due to the rising food prices and the concerns about automobile engine durability. Therefore, there is an urgent need for researchers to identify and develop sustainable biodiesel feedstocks which overcome the disadvantages of current ones. On the other hand, artificial neural network (ANN) modeling has been successfully used in recent years to gain new knowledge in various disciplines. The main goal of this article is to review recent literatures and assess the state of the art on the use of ANN as a modeling tool for future generation biodiesel feedstocks. Biodiesel feedstocks, production processes, chemical compositions, standards, physio-chemical properties and in-use performance are discussed. Limitations of current biodiesel feedstocks over future generation biodiesel feedstock have been identified. The application of ANN in modeling key biodiesel quality parameters and combustion performance in automobile engines is also discussed. This review has determined that ANN modeling has a high potential to contribute to the development of renewable energy systems by accelerating biodiesel research. Full article

(This article belongs to the Special Issue Alternative Fuels for the Internal Combustion Engines (ICE) 2013)

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1237 KiB

Open AccessArticle

Application of Circulation Controlled Blades for Vertical Axis Wind Turbines

by Andrew Shires and Velissarios Kourkoulis

Energies 2013, 6(8), 3744-3763; https://doi.org/10.3390/en6083744 - 26 Jul 2013

Cited by 33 | Viewed by 9904

Abstract

The blades of a vertical axis wind turbine (VAWT) rotor see an inconsistent angle of attack through its rotation. Consequently, VAWT blades generally use symmetrical aerofoils with a lower lift-to-drag ratio than cambered aerofoils tailored to maximise horizontal axis wind turbine rotor performance. [...] Read more.

The blades of a vertical axis wind turbine (VAWT) rotor see an inconsistent angle of attack through its rotation. Consequently, VAWT blades generally use symmetrical aerofoils with a lower lift-to-drag ratio than cambered aerofoils tailored to maximise horizontal axis wind turbine rotor performance. This paper considers the feasibility of circulation controlled (CC) VAWT blades, using a tangential air jet to provide lift and therefore power augmentation. However CC blade sections require a higher trailing-edge thickness than conventional sections giving rise to additional base drag. The choice of design parameters is a compromise between lift augmentation, additional base drag as well as the power required to pump the air jet. Although CC technology has been investigated for many years, particularly for aerospace applications, few researchers have considered VAWT applications. This paper considers the feasibility of the technology, using Computational Fluid Dynamics to evaluate a baseline CC aerofoil with different trailing-edge ellipse shapes. Lift and drag increments due to CC are considered within a momentum based turbine model to determine net power production. The study found that for modest momentum coefficients significant net power augmentation can be achieved with a relatively simple aerofoil geometry if blowing is controlled through the blades rotation. Full article

(This article belongs to the Special Issue Wind Turbines 2013)

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1684 KiB

Open AccessReview

A Literature Review on Heating of Ventilation Air with Large Diameter Earth Tubes in Cold Climates

by Lili Tan and James A. Love

Energies 2013, 6(8), 3734-3743; https://doi.org/10.3390/en6083734 - 25 Jul 2013

Cited by 15 | Viewed by 7562

Abstract

Earth-air heat exchange (EAHE) systems offer the possibility of reducing use of nonrenewable energy for heating ventilation air in cold climates. The number of installations of large diameter (greater than 900 mm) EAHE systems reported for cold climates is small. Even less has [...] Read more.

Earth-air heat exchange (EAHE) systems offer the possibility of reducing use of nonrenewable energy for heating ventilation air in cold climates. The number of installations of large diameter (greater than 900 mm) EAHE systems reported for cold climates is small. Even less has been reported on their heating performance, but the available information suggests that further rigorous assessment is warranted to determine whether the reported better than expected temperature rise is supported and, if so, the reasons for this. Another concern is the possibility of long-term heat depletion in the surrounding soil, which would affect performance. Only a couple of short-term experimental studies of ground temperature effects of heating with EAHE were found for cool climates. Four articles that addressed ground temperature effects with horizontal ground source heat pump exchangers had conflicting findings regarding heat depletion in the soil. Full article

(This article belongs to the Special Issue Energy Efficient Building Design 2013)

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2798 KiB

Open AccessArticle

Exploring the Potential for Increased Production from the Wave Energy Converter Lifesaver by Reactive Control

by Jonas Sjolte, Christian McLisky Sandvik, Elisabetta Tedeschi and Marta Molinas

Energies 2013, 6(8), 3706-3733; https://doi.org/10.3390/en6083706 - 25 Jul 2013

Cited by 45 | Viewed by 7979

Abstract

Fred Olsen is currently testing their latest wave energy converter (WEC), Lifesaver, outside of Falmouth Bay in England, preparing it for commercial operation at the Wavehub test site. Previous studies, mostly focusing on hydrodynamics and peak to average power reduction, have shown that [...] Read more.

Fred Olsen is currently testing their latest wave energy converter (WEC), Lifesaver, outside of Falmouth Bay in England, preparing it for commercial operation at the Wavehub test site. Previous studies, mostly focusing on hydrodynamics and peak to average power reduction, have shown that this device has potential for increased power extraction using reactive control. This article extends those analyses, adding a detailed model of the all-electric power take-off (PTO) system, consisting of a permanent magnet synchronous generator, inverter and DC-link. Time domain simulations are performed to evaluate the PTO capabilities of the modeled WEC. However, when tuned towards reactive control, the generator losses become large, giving a very low overall system efficiency. Optimal control with respect to electrical output power is found to occur with low added mass, and when compared to pure passive loading, a 1% increase in annual energy production is estimated. The main factor reducing the effect of reactive control is found to be the minimum load-force constraint of the device. These results suggest that the Lifesaver has limited potential for increased production by reactive control. This analysis is nevertheless valuable, as it demonstrates how a wave-to-wire model can be used for investigation of PTO potential, annual energy production estimations and evaluations of different control techniques for a given WEC device. Full article

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Energies, Volume 6, Issue 8 (August 2013) – 34 articles , Pages 3637-4330

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