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Abstract When developers are building wind farms offshore or onshore, are there notable characteristics that differentiate these projects? If so, what does this tell us about the nature of wind power development patterns? This study makes use of industry data from 44 wind farms, including 11 offshore wind farms, 19 onshore wind farms located in farmland and 14 wind farms located in forested areas with a total capacity of 1190 MW installed actual wind farms to test four hypotheses based on preconceptions identified in a literature review. Testing the validity of these preconceptions is important because if policymakers are to design policy to facilitate specific development patterns in a given nation, they need to be clear on what is working in the market. Our data suggest that, contrary to popular belief, offshore wind farms do not produce more energy per installed MW when compared to onshore wind farms. However, our data confirm that offshore wind farms produce more energy than onshore wind farms. We contend that this has less to do with superior wind quality in offshore sites than with scale differences. It appears that developers construct far larger offshore wind farms in order to presumably counteract the proportionally higher development costs associated with marine environments. One other remarkable finding associated with this study is that onshore wind turbines that are located in forested areas might be capable of matching the power production of offshore wind farms without incurring the additional costs associated with offshore projects.

Abstract When developers are building wind farms offshore or onshore, are there notable characteristics that differentiate these projects? If so, what does this tell us about the nature of wind power development patterns? This study makes use of industry data from 44 wind farms, including 11 offshore wind farms, 19 onshore wind farms located in farmland and 14 wind farms located in forested areas with a total capacity of 1190 MW installed actual wind farms to test four hypotheses based on preconceptions identified in a literature review. Testing the validity of these preconceptions is important because if policymakers are to design policy to facilitate specific development patterns in a given nation, they need to be clear on what is working in the market. Our data suggest that, contrary to popular belief, offshore wind farms do not produce more energy per installed MW when compared to onshore wind farms. However, our data confirm that offshore wind farms produce more energy than onshore wind farms. We contend that this has less to do with superior wind quality in offshore sites than with scale differences. It appears that developers construct far larger offshore wind farms in order to presumably counteract the proportionally higher development costs associated with marine environments. One other remarkable finding associated with this study is that onshore wind turbines that are located in forested areas might be capable of matching the power production of offshore wind farms without incurring the additional costs associated with offshore projects.

This paper presents a control method based on active disturbance rejection control (ADRC) for both the primary and secondary control layers in a hybrid DC/AC microgrid (MG). A DC bus inside MG includes a wind turbine generator, photovoltaic panels, a fuel cell and battery energy storage. Maintaining the DC link voltage under various scenarios is made possible by applying an energy management system (EMS) based on the deviation in the state of charge of the battery and using a fuel cell as a backup. Through a voltage source inverter, the DC bus of the MG is connected to the AC side, which supplies AC loads. Using the proposed ADRC-based control strategy for the inverter, the voltage, frequency, and power flow within the MG would be effectively controlled. In order to demonstrate the effectiveness of the proposed method, a comparison between the ADRC and PI controller has also been implemented in different scenarios, proving the superiority of the suggested controller over classical approaches.

This paper presents a control method based on active disturbance rejection control (ADRC) for both the primary and secondary control layers in a hybrid DC/AC microgrid (MG). A DC bus inside MG includes a wind turbine generator, photovoltaic panels, a fuel cell and battery energy storage. Maintaining the DC link voltage under various scenarios is made possible by applying an energy management system (EMS) based on the deviation in the state of charge of the battery and using a fuel cell as a backup. Through a voltage source inverter, the DC bus of the MG is connected to the AC side, which supplies AC loads. Using the proposed ADRC-based control strategy for the inverter, the voltage, frequency, and power flow within the MG would be effectively controlled. In order to demonstrate the effectiveness of the proposed method, a comparison between the ADRC and PI controller has also been implemented in different scenarios, proving the superiority of the suggested controller over classical approaches.

Investigations show that most simulations on solar parabolic trough collectors reported in the literature are one-dimensional or at least with a variety of simplifications. Indeed, for this collector type, due to the complex heat transfer elements as well as two-phase flow through the tubes, etc., such simplifications make the model fail to give an acceptable estimation of the circumferential temperature distribution of the walls, thermal stresses, heat losses, vapor volume fraction, etc. In this article, a detailed three-dimensional numerical modeling of solar parabolic trough collectors is presented. The results of this model are also compared to those given by an axisymmetric model and a one-dimensional nodal model to highlight the impacts of such a rigorous model on the accuracy of the final results. The results demonstrated that although the axisymmetric and nodal models show acceptable accuracy in predicting the temperature and enthalpy for the flow, they are quite incapable of precisely calculating the vapor volume fraction and heat loss rates. The discrepancy in the distribution of vapor volume fraction in different sections of the absorber tube causes significant temperature heterogeneity in the solid walls.

Investigations show that most simulations on solar parabolic trough collectors reported in the literature are one-dimensional or at least with a variety of simplifications. Indeed, for this collector type, due to the complex heat transfer elements as well as two-phase flow through the tubes, etc., such simplifications make the model fail to give an acceptable estimation of the circumferential temperature distribution of the walls, thermal stresses, heat losses, vapor volume fraction, etc. In this article, a detailed three-dimensional numerical modeling of solar parabolic trough collectors is presented. The results of this model are also compared to those given by an axisymmetric model and a one-dimensional nodal model to highlight the impacts of such a rigorous model on the accuracy of the final results. The results demonstrated that although the axisymmetric and nodal models show acceptable accuracy in predicting the temperature and enthalpy for the flow, they are quite incapable of precisely calculating the vapor volume fraction and heat loss rates. The discrepancy in the distribution of vapor volume fraction in different sections of the absorber tube causes significant temperature heterogeneity in the solid walls.

A control technique of multilevel converter topologies based on Direct Lyapunov Control method is presented in this paper for integration of Distributed Generation (DG) resources into the power grid. The compensation of instantaneous variations in the reference current components in ac-side and dc-voltage variations of cascaded capacitors in dc-side of the interfacing system are considered properly, which is the main contribution and novelty of this work in comparison with other control strategies. The proposed control technique provides the continuous injection of active power in fundamental frequency from DG sources to the grid. In addition, reactive power and harmonic current components of loads are provided with a fast dynamic response; thereby, achieving sinusoidal grid currents in phase with load voltages, while the required power from load side is more than the maximum capacity of interfaced converter, is possible. Simulation results confirm the effectiveness of the proposed control strategy in DG technology during dynamic and steady-state operating conditions.

A control technique of multilevel converter topologies based on Direct Lyapunov Control method is presented in this paper for integration of Distributed Generation (DG) resources into the power grid. The compensation of instantaneous variations in the reference current components in ac-side and dc-voltage variations of cascaded capacitors in dc-side of the interfacing system are considered properly, which is the main contribution and novelty of this work in comparison with other control strategies. The proposed control technique provides the continuous injection of active power in fundamental frequency from DG sources to the grid. In addition, reactive power and harmonic current components of loads are provided with a fast dynamic response; thereby, achieving sinusoidal grid currents in phase with load voltages, while the required power from load side is more than the maximum capacity of interfaced converter, is possible. Simulation results confirm the effectiveness of the proposed control strategy in DG technology during dynamic and steady-state operating conditions.

The recommended power quality (PQ) indices in electric power systems are defined based on the discrete Fourier transform (DFT). DFT is mostly evaluated applying fast Fourier transform (FFT) algorithm which requires signals to be periodic in nature. Hence, it evaluates PQ indices accurately for stationary PQ disturbances only. However, in case of nonstationary PQ disturbances signal is aperiodic and FFT results in erroneous assessment due to spectral leakage phenomena. Furthermore, FFT cannot provide time information of the PQ indices as computation is performed in frequency domain only. Which is significant shortcoming of the FFT when dealing with time-varying PQ disturbances to extract dynamic signature of the signal. Thereby, this paper presents a framework of redefining PQ indices for stationary and nonstationary PQ disturbances employing time-frequency distribution (TFD) method. Among all TFDs, reduced interference distribution (RID) represents the most suitable properties for analyzing time-varying PQ disturbances. Hence, in this work, it is employed to reformulate PQ indices typically used in electric power systems. The results of two synthetic examples considering stationary and nonstationary PQ disturbances imply that the RID-based redefined PQ indices are closer to the actual values. Also, they provide more accurate results than the existing transient PQ indices and traditional FFT-based method.