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

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Open AccessArticle A Multi-Criteria Methodology to Support Public Administration Decision Making Concerning Sustainable Energy Action Plans
Energies 2013, 6(8), 4308-4330; https://doi.org/10.3390/en6084308
Received: 2 July 2013 / Revised: 31 July 2013 / Accepted: 7 August 2013 / Published: 20 August 2013
Cited by 23 | PDF Full-text (326 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle A Dynamic Model for the Normal Impact of Fly Ash Particle with a Planar Surface
Energies 2013, 6(8), 4288-4307; https://doi.org/10.3390/en6084288
Received: 16 May 2013 / Revised: 3 July 2013 / Accepted: 31 July 2013 / Published: 20 August 2013
Cited by 5 | PDF Full-text (666 KB) | HTML Full-text | XML Full-text
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,
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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 (vin) can be roughly divided into the three parts. In the first part, η decreases with increasing vin. In the second part, η is little changed with increasing vin. In the third part, η rapidly increases with increasing vin. 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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Open AccessArticle A Vector-Controlled Distributed Generator Model for a Power Flow Based on a Three-Phase Current Injection Method
Energies 2013, 6(8), 4269-4287; https://doi.org/10.3390/en6084269
Received: 27 June 2013 / Revised: 3 August 2013 / Accepted: 6 August 2013 / Published: 20 August 2013
Cited by 3 | PDF Full-text (368 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Analysis and Simulation of Fault Characteristics of Power Switch Failures in Distribution Electronic Power Transformers
Energies 2013, 6(8), 4246-4268; https://doi.org/10.3390/en6084246
Received: 5 June 2013 / Revised: 17 July 2013 / Accepted: 9 August 2013 / Published: 19 August 2013
Cited by 7 | PDF Full-text (1245 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Optimum Application of Thermal Factors to Artificial Neural Network Models for Improvement of Control Performance in Double Skin-Enveloped Buildings
Energies 2013, 6(8), 4223-4245; https://doi.org/10.3390/en6084223
Received: 4 June 2013 / Revised: 4 August 2013 / Accepted: 5 August 2013 / Published: 19 August 2013
Cited by 7 | PDF Full-text (851 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Effect of Mixing Driven by Siphon Flow: Parallel Experiments Using the Anaerobic Reactors with Different Mixing Modes
Energies 2013, 6(8), 4207-4222; https://doi.org/10.3390/en6084207
Received: 8 June 2013 / Revised: 25 July 2013 / Accepted: 5 August 2013 / Published: 19 August 2013
Cited by 6 | PDF Full-text (573 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Thermal Efficiency Comparison of Borehole Heat Exchangers with Different Drillhole Diameters
Energies 2013, 6(8), 4187-4206; https://doi.org/10.3390/en6084187
Received: 10 May 2013 / Revised: 8 July 2013 / Accepted: 22 July 2013 / Published: 19 August 2013
Cited by 9 | PDF Full-text (2213 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Energy Analysis of the Danish Food Production System: Food-EROI and Fossil Fuel Dependency
Energies 2013, 6(8), 4170-4186; https://doi.org/10.3390/en6084170
Received: 29 May 2013 / Revised: 18 July 2013 / Accepted: 18 July 2013 / Published: 15 August 2013
Cited by 9 | PDF Full-text (240 KB) | HTML Full-text | XML Full-text
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
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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
Open AccessArticle Islanding Detection Method of a Photovoltaic Power Generation System Based on a CMAC Neural Network
Energies 2013, 6(8), 4152-4169; https://doi.org/10.3390/en6084152
Received: 19 March 2013 / Revised: 24 July 2013 / Accepted: 29 July 2013 / Published: 15 August 2013
Cited by 3 | PDF Full-text (1100 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Adaptive State of Charge Estimation for Li-Ion Batteries Based on an Unscented Kalman Filter with an Enhanced Battery Model
Energies 2013, 6(8), 4134-4151; https://doi.org/10.3390/en6084134
Received: 28 May 2013 / Revised: 30 July 2013 / Accepted: 6 August 2013 / Published: 12 August 2013
Cited by 42 | PDF Full-text (882 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Design of a Novel Experimental Facility for Testing of Tidal Arrays
Energies 2013, 6(8), 4117-4133; https://doi.org/10.3390/en6084117
Received: 2 May 2013 / Revised: 11 July 2013 / Accepted: 22 July 2013 / Published: 12 August 2013
Cited by 1 | PDF Full-text (1609 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Damping Wind and Wave Loads on a Floating Wind Turbine
Energies 2013, 6(8), 4097-4116; https://doi.org/10.3390/en6084097
Received: 22 April 2013 / Revised: 11 July 2013 / Accepted: 23 July 2013 / Published: 9 August 2013
Cited by 15 | PDF Full-text (686 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Effects of Impermeable Boundaries on Gas Production from Hydrate Accumulations in the Shenhu Area of the South China Sea
Energies 2013, 6(8), 4078-4096; https://doi.org/10.3390/en6084078
Received: 6 May 2013 / Revised: 2 July 2013 / Accepted: 15 July 2013 / Published: 8 August 2013
Cited by 9 | PDF Full-text (1748 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Comparison of the Experimental and Numerical Results of Modelling a 32-Oscillating Water Column (OWC), V-Shaped Floating Wave Energy Converter
Energies 2013, 6(8), 4045-4077; https://doi.org/10.3390/en6084045
Received: 11 March 2013 / Revised: 1 July 2013 / Accepted: 8 July 2013 / Published: 8 August 2013
Cited by 7 | PDF Full-text (12498 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle Discrete Displacement Hydraulic Power Take-Off System for the Wavestar Wave Energy Converter
Energies 2013, 6(8), 4001-4044; https://doi.org/10.3390/en6084001
Received: 14 May 2013 / Revised: 28 June 2013 / Accepted: 15 July 2013 / Published: 7 August 2013
Cited by 43 | PDF Full-text (5365 KB) | HTML Full-text | XML Full-text
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
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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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