Thesis (master's)--Oregon State University, 1977. / Includes bibliographical references (p. 48-49). Also available on the World Wide Web.

A dynamic three-dimensional volume element model (VEM) of a parabolic trough solar collector (PTC) comprising an outer glass cover, annular space, absorber tube, and heat transfer fluid is studied with detail. The model is coupled with an existing semi-finite optical model for the purpose of simulation and optimization. The spatial domain in the VEM is discretized with lumped control volumes (i.e., volume elements) in cylindrical coordinates according to the predefined collector geometry. Therefore, the spatial dependency of the model is taken into account without the need to solve partial differential equations. The proposed model combines principles of thermodynamics and heat transfer as well as empirical heat transfer correlations, to simplify the modeling and expedite the computations. The resulting system of ordinary differential equations is integrated in time, yielding temperature fields which can be visualized and assessed with scientific visualization tools. The current model is validated with experimental data provided in the literature. The model was employed to evaluate the sensitivity of the collector performance described by the first and second law efficiencies to receiver length, annulus gap spacing, concentration ratio, incidence angle, inlet fluid temperature, and flow rate. This work also examined the effects of inlet fluid temperature and temperature differential on dynamic collector performance in the transient case study. Results showed that the first law efficiency was most sensitive to the inlet fluid temperature with the maximum variation of 30%, whereas the incidence angle and concentration ratio affected the second law efficiency the most with the maximum variations of 375% and 300%, respectively. The effect of the remaining parameters were trivial in all cases. In the transient analysis, higher temperature differential and lower inlet fluid temperature yielded higher total heat gain while the total exergy gain was insensitive to both parameters. The first law efficiency should therefore be of greater importance than the second law efficiency in the control of dynamic collector performance based on these two parameters. Furthermore, a sensitivity analysis of vemPTC is done with the Fourier amplitude sensitivity testing (FAST) for selected nine parameters. Cover transmittance shows a highly sensitive parameter within the rest of the selected parameters. After this sensitivity analysis, a multi-objective sensitivity analysis is studied for different heat transfer fluids such as synthetic oils, molten salts, liquid metals, nanofluids, and gases. Sobol sampling method is used for a multi-objective sensitivity analysis of different heat transfer fluids except for nanofluids, because it is more accurate to use a different methodology for sensitivity analysis of nanofluids, due to the effects of specific parameters on both first and second law efficiency. The fluid inlet temperature is a common sensitive parameter for almost all heat transfer fluids. Therefore, a multi-objective optimization study is done with four parameters and the results of it are presented in Chapter Four. Moreover, Chapter Five shows enhancement of the efficiency of both traditional parabolic trough solar collector (PTC) and transparent insulation material integrated PTC in both one and two dimensional model. Altering model types, operating conditions, or making an assumption for some used correlations is studied in the last chapter of this dissertation. After comparing the 1D and the 2D model, the results show that the most promising model type of PTC is the 2D model with TIM integrated one with correlation due to its stability for predicted efficiency. That approved that simplifying the model types may affect the results even though sufficiently accurate results are obtained with a simplified model. Temperature-dependent parameters should be selected for temperature sensitive variable in order to reach precise results. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2018. / October 18, 2018. / Optimization, Parabolic trough solar collector, Renewable energy, Solar energy, Sustainable energy / Includes bibliographical references. / Juan C. Ordóñez, Professor Directing Dissertation; Hui Li, University Representative; Wei Guo, Committee Member; Patrick J. Hollis, Committee Member.

Understanding of the transport phenomena in Li-air batteries is crucial for improving the performance and design of Li-air batteries. In this dissertation, the basic transport equations that govern the operation of Li-air batteries are derived by starting from the underlying mass and charge transport properties of the chemical species involved in the operation of the battery. Then, two approaches are presented to solve the transport equations. In the first approach, we use first-order approximations to derive a compact model for the discharge voltage of Li-air batteries with organic electrolyte. The model considers oxygen transport and volume change in the cathode, and Butler-Volmer kinetics at the anode and cathode electrodes, and is particularly useful to the fast prediction of the discharge voltage and specific capacities of Li-air batteries. In the second approach, we propose a finite-element model in which the basic transport equations are discretized over a finite space-time mesh and solved numerically to predict the battery characteristics under different discharge conditions and for different geometrical and physical parameters. Then, the transport equations are reexamined and improved to account for different pore microstructures, pore size distribution effects, and electron transport mechanisms through the discharge product. The different microstructures are simulated numerically and the performance of Li-air batteries is analyzed in each case. A novel hybrid model is introduced to explain the perceived transition from one microstructure to another. / A Dissertation submitted to the Department of Electrical and Computer Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester 2015. / July 13, 2015. / Cathode, Compact model, Energy density, Li-air, Microstrucuture, Nanofibers / Includes bibliographical references. / Petru Andrei, Professor Directing Dissertation; Anke Meyer-Baese, University Representative; Jim Zheng, Committee Member; Simon Foo, Committee Member.

This dissertation is mainly focused on the investigation of cathode in Li-air batteries using organic electrolyte and the development of high-rate rechargeable Li-air flow batteries. A Li-air battery using organic electrolyte with an air electrode made with a mixture of carbon nanotube (CNT) and carbon nanofiber (CNF) is utilized to investigate the capacity limitation effects of cathode using a multiple-discharge method. Scanning electron microscopy (SEM) images show that the discharge product mainly forms at the air side of cathode due to low oxygen solubility and diffusivity in the organic electrolyte. This inhomogeneous distribution of discharge product indicates that the Li-air cell falls short of the maximum capacity of air electrode. Electrochemical impedance spectra (EIS) demonstrated that during discharge at high current density (1 mA/cm2) pore blocking is the major factor that limits capacity; however, during discharge at low current density (0.2 mA/cm2) both pore blocking and impedance rise contribute to the capacity limitation. It's been confirmed that cathode is the dominant limitation to the discharge capacity. Also, the gradient porosity structure of cathode is able to increase the capacity based on the weight of carbon, but the electrolyte loading needs to be optimized to achieve high energy density of cell. A novel rechargeable Li-air flow battery is demonstrated. It consists of a lithium-ion conducting glass-ceramic membrane sandwiched by a Li-metal anode in organic electrolyte and a carbon nanofoam cathode through which oxygen-saturated aqueous electrolyte flows. It features a flow cell design in which aqueous electrolyte is bubbled with compressed air, and is continuously circulated between the cell and a storage reservoir to supply sufficient oxygen for high power output. It shows high rate capability (5 mA/cm²) and renders a power density of 7.64 mW/cm² at a constant discharge current density of 4 mA/cm². Adding RuO² as a catalyst in the cathode, the battery showed a high round-trip efficiency (ca. 83%), with the overpotentials of 0.67 V between charge and discharge at a current of 1 mA/cm². A Li-air flow battery using graphite as anode is also demonstrated for several cycles. / A Dissertation submitted to the Department of Electrical and Computer Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester, 2014. / October 10, 2014. / Li-air battery, Li-air flow battery / Includes bibliographical references. / Jim P. Zheng, Professor Directing Dissertation; Tao Liu, University Representative; Pedro Moss, Committee Member; Petru Andrei, Committee Member.

Wind energy has become one of the most important and thriving renewable energy resources in the world. Transforming the kinetic energy of wind into electric power is more environmentally friendly than traditional processes such as the combustion of fossil fuels. It provides independence from the limited fossil fuels reserves by using an unlimited resource. In order to develop a wind power facility, it is important to develop an initial wind resource assessment to guarantee the selected site will be profitable in terms of electric energy output. Several countries lack developed wind atlases that indicate a rough estimate of wind resource in their territories, which is an obstacle for inexpensive wind resource evaluations. In order to perform site evaluations generally an anemometer must be put in place to take wind measurements. This process is costly and time consuming since at least a year of data must be observed. The quality of wind resource depends on several geographic and atmospheric characteristics such as: air density, site location, site topography, wind speed and direction. This study was conducted to provide an initial wind resource assessment on three locations in Venezuela which do not have previous evaluations: Cerro Copey, Punta de Piedras and Los Roques. The assessment was done remotely based on the national meteorological service meteorological observations; wind resource and turbine power output uncertainties were taken into account. The wind assessment was done through Monte Carlo simulations mathematically considering several uncertainties with emphasis on surface roughness for vertical extrapolation. The results exhibit wind energy potential of the three sites and a throughout wind resource characterization of the site with the most potential: Cerro Copey. / A Thesis submitted to the Department of Civil and Environmental Engineering in partial fulfillment of the Master of Science. / Spring Semester 2016. / April 8, 2016. / Assessment, Energy, Venezuela, Wind / Includes bibliographical references. / Sungmoon Jung, Professor Directing Thesis; Eren Erman Ozguven, Committee Member; Kamal Tawfiq, Committee Member; Raphael Kampmann, Committee Member.

Renewable energy sources are fundamental alternatives to supply the rising energy demand in the world and to reduce or replace fossil fuel technologies. In order to make renewable-based technologies suitable for commercial and industrial applications, two main challenges need to be solved: the design and manufacture of highly efficient devices and reliable systems to operate under intermittent energy supply conditions. In particular, power generation technologies based on solar energy are one of the most promising alternatives to supply the world energy demand and reduce the dependence on fossil fuel technologies. In this dissertation, the dynamic behavior of a Concentrated Solar Power (CSP) supercritical CO2 cycle is studied under different seasonal conditions. The system analyzed is composed of a central receiver, hot and cold thermal energy storage units, a heat exchanger, a recuperator, and multi-stage compression-expansion subsystems with intercoolers and reheaters between compressors and turbines respectively. The effects of operating and design parameters on the system performance are analyzed. Some of these parameters are the mass flow rate, intermediate pressures, number of compression-expansion stages, heat exchangers' effectiveness, multi-tank thermal energy storage, overall heat transfer coefficient between the solar receiver and the environment and the effective area of the recuperator. Energy and exergy models for each component of the system are developed to optimize operating parameters in order to lead to maximum efficiency. From the exergy analysis, the components with high contribution to exergy destruction were identified. These components, which represent an important potential of improvement, are the recuperator, the hot thermal energy storage tank and the solar receiver. Two complementary alternatives to improve the efficiency of concentrated solar thermal systems are proposed in this dissertation: the optimization of the system's operating parameters and optimization of less efficient components. The parametric optimization is developed for a 1MW reference CSP system with CO2 as the working fluid. The component optimization, focused on the less efficient components, comprises some design modifications to the traditional component configuration for the recuperator, the hot thermal energy storage tank and the solar receiver. The proposed optimization alternatives include the heat exchanger's effectiveness enhancement by optimizing fins shapes, multi-tank thermal energy storage configurations for the hot thermal energy storage tank and the incorporation of a transparent insulation material into the solar receiver. Some of the optimizations are conducted in a generalized way, using dimensionless models to be applicable no only to the CSP but also to other thermal systems. This project is therefore an effort to improve the efficiency of power generation systems based on solar energy in order to make them competitive with conventional fossil fuel power generation devices. The results show that the parametric optimization leads the system to an efficiency of about 21% and a maximum power output close to 1.5 MW. The process efficiencies obtained in this work, of more than 21%, are relatively good for a solar-thermal conversion system and are also comparable with efficiencies of conversion of high performance PV panels. The thermal energy storage allows the system to operate for several hours after sunset. This operating time is approximately increased from 220 to 480 minutes after optimization. The hot and cold thermal energy storage also lessens the temperature fluctuations by providing smooth changes of temperatures at the turbines' and compressors' inlets. Additional improvements in the overall system efficiency are possible by optimizing the less efficient components. In particular, the fin's effectiveness can be improved in more than 5% after its shape is optimized, increments in the efficiency of the thermal energy storage of about 5.7% are possible when the mass is divided into four tanks, and solar receiver efficiencies up to 70% can be maintained for high operating temperatures (~ 1200°C) when a transparent insulation material is incorporated to the receiver. The results obtained in this dissertation indicate that concentrated solar systems using supercritical CO2 could be a viable alternative to satisfying energy needs in desert areas with scarce water and fossil fuel resources. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2016. / February 26, 2016. / Concentrated Solar Power (CSP), Efficiency, Optimization, Supercritical CO2 (sCO2), Thermodynamic Analysis / Includes bibliographical references. / Juan C. Ordonez, Professor Co-Directing Dissertation; Alejandro Rivera-Alvarez, Professor Co-Directing Dissertation; Hui Li, University Representative; Kunihiko Taira, Committee Member; Carl Moore, Committee Member; Rob Hovsapian, Committee Member.

Solar photovoltaic (PV) energy integration in distribution networks is one of the fastest growing sectors of distributed energy integration. The growth in solar PV integration is incentivized by various clean power policies, global interest in solar energy, and reduction in manufacturing and installation costs of solar energy systems. The increase in solar PV integration has raised a number of concerns regarding the potential impacts that might arise as a result of high PV penetration. Some impacts have already been recorded in networks with high PV penetration such as in China, Germany, and USA (Hawaii and California). Therefore, network planning is becoming more intricate as new technologies are integrated into the existing electric grid. The integrated new technologies pose certain compatibility concerns regarding the existing electric grid infrastructure. Therefore, PV integration impact studies are becoming more essential in order to have a better understanding of how to advance the solar PV integration efforts without introducing adverse impacts into the network. PV impact studies are important for understanding the nature of the new introduced phenomena. Understanding the nature of the potential impacts is a key factor for mitigating and accommodating for said impacts. Traditionally, electric power utilities relied on phasor-based power flow simulations for planning their electric networks. However, the conventional, commercially available, phasor-based simulation tools do not provide proper visibility across a wide spectrum of electric phenomena. Moreover, different types of simulation approaches are suitable for specific types of studies. For instance, power flow software cannot be used for studying time varying phenomena. At the same time, it is not practical to use electromagnetic transient (EMT) tools to perform power flow solutions. Therefore, some electric phenomena caused by the variability of PV generation are not visible using the conventional utility simulation software. On the other hand, EMT simulation tools provide high accuracy and visibility over a wide bandwidth of frequencies at the expense of larger processing and memory requirements, limited network size, and long simulation time. Therefore, there is a gap in simulation tools and techniques that can efficiently and effectively identify potential PV impact. New planning simulation tools are needed in order to accommodate for the simulation requirements of new integrated technologies in the electric grid. The dissertation at hand starts by identifying some of the potential impacts that are caused by high PV penetration. A phasor-based quasi-static time series (QSTS) analysis tool is developed in order to study the slow dynamics that are caused by the variations in the PV generation that lead to voltage fluctuations. Moreover, some EMT simulations are performed in order to study the impacts of PV systems on the electric network harmonic levels. These studies provide insights into the type and duration of certain impacts, as well as the conditions that may lead to adverse phenomena. In addition these studies present an idea about the type of simulation tools that are sufficient for each type of study. After identifying some of the potential impacts, certain planning tools and techniques are proposed. The potential PV impacts may cause certain utilities to refrain from integrating PV systems into their networks. However, each electric network has a certain limit beyond which the impacts become substantial and may adversely interfere with the system operation and the equipment along the feeder; this limit is referred to as the hosting limit (or hosting capacity). Therefore, it is important for utilities to identify the PV hosting limit on a specific electric network in order to safely and confidently integrate the maximum possible PV systems. In the following dissertation, two approaches have been proposed for identifying the hosing limit: 1. Analytical approach: this is a theoretical mathematical approach that demonstrated the understanding of the fundamentals of electric power system operation. It provides an easy way to estimate the maximum amount of PV power that can be injected at each node in the network. This approach has been tested and validated. 2. Stochastic simulation software approach: this approach provides a comprehensive simulation software that can be used in order to identify the PV hosting limit. The software performs a large number of stochastic simulation while varying the PV system size and location. The collected data is then analyzed for violations in the voltage levels, voltage fluctuations and reverse power flow. It is important to note that there are multiple factors that affect the hosting limits in a distribution network. Moreover, the limit can be assessed based on different parameters; however, it will be shown in this dissertation that in most cases the voltage level is the first parameter to be violated under high PV penetration conditions. Therefore, in both approaches, the voltage is considered the main factor to be monitored for violations for PV hosting limit identification. The work presented hereinafter focuses on providing novel, innovative and practical solutions for fulfilling certain gaps in power system simulation. A novel hybrid simulation tool is presented in this dissertation as a solution for some of the issues facing the simulation of distribution networks with high PV penetration. Hybrid simulation is a relatively new concept in power system simulation and has not yet been applied for studying PV impacts in distribution networks. The presented hybrid tool offers accurate results and fast simulations. It can be used for various applications regarding the study of PV impacts as will be shown in this dissertation. It interfaces an EMT model of a grid-tied PV system with a phasor-domain model of a distribution network. The presented hybrid simulation tool incorporates a phasor-domain QSTS simulation with a time-domain EMT simulation which allows for a wide range of frequency visibility. The tool offers full EMT-level visibility at the point of common coupling (PCC), as well as slow dynamic visibility through the QSTS simulation. The tool is validated and tested by comparing the results with a full EMT simulation. It is used for studying the impacts of PV systems on the distribution network during fault conditions, islanding situation, solar irrandiance variation, among many other applications. The developed tool is made completely open-source in order to promote the hybrid simulation concept in power systems simulations as a viable solution for many of the conventional simulation tool limitations. Moreover, the work presented hereinafter proposes a novel co-simulation architecture with power hardware-in-the-loop (PHIL) simulation. The proposed architecture is the first of its kind developed at the National Renewable Energy Laboratory (NREL). The co-simulation testbed is developed in order to allow for wider range of hardware testing before deploying new technologies into the field. The testbed is composed of: 1. A full phasor model of the distribution network developed using a commercial distribution management software (DMS) environment. 2. A reduced form of the full network model developed in a real-time EMT environment using Opal-RT real-time simulator. 3. A hardware setup tested in a PHIL simulation environment. The hardware setup represents a grid-tied PV system at the PCC composed of a grid simulator, PV simulator, and a PV inverter. The co-simulation allows a slow QSTS simulation to be performed using the DMS model where slow variations are simulated, such as voltage regulator operations and slow variations in loads and solar irradiance. The QSTS simulation updates the EMT model components (loads, generators, voltage sources, and voltage regulators). The reduced EMT model is solved in real-time which allows for detailed and accurate visibility of the transient phenomena occurring in the network. Finally, the EMT model communicates with the physical hardware device at the PCC in order to close the PHIL loop. This architecture expands the capabilities of conventional PHIL testing and allows for more tests and scenarios to be implemented. The co-simulation testbed is tested by solving a real feeder network model in the DMS using historic load and solar irradiance data. The phasor model updates the EMT model's loads, voltage sources, and voltage regulator status at every QSTS time-step. The EMT model communicates through the hardware interface of the real-time simulator with the hardware setup by sending command control signals to the grid simulator and the PV simulator in order to replicate the simulated conditions in the real physical hardware. The inverter is tested under different operation modes, and its capabilities to use advanced algorithms for voltage regulation are put to test. The co-simulation architecture also addresses the stability and accuracy concerns of the PHIL experiments. A detailed stability and accuracy analysis is discussed in Chapter 6. / A Dissertation submitted to the Department of Electrical and Computer Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2017. / April 7, 2017. / Distribution Network Planning, Hardware-in-the-Loop, Photovoltaic Systems, Power System Simulation, PV Impact Studies, Simulation Tool / Includes bibliographical references. / Juan Ordonez, University Representative; Simon Y. Foo, Committee Member; Chris S. Edrington, Committee Member.

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Call number: LD2668 .T4 1966 H436 / Master of Science

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