Browsing by Subject "Energy storage"
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Item Charge Storage in Organic Electrodes for Energy & Electrochemical Applications(2014-10-15) Jeon, Ju WonEnergy storage has been emerging as an important research topic because of the lack of fossil fuels and growing energy consumption. This thesis focuses on synthesis and characterization of electrode materials such as polyaniline, graphene, and nitrogen-doped porous carbon for use in energy storage applications. Polyaniline (PANI), a conjugated polymer, has been widely investigated as an electrode material for energy storage. In order to enhance its oxidative stability, polyaniline:poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PANI:PAAMPSA) complex was synthesized using template polymerization. PANI:PAAMPSA possessed significantly increased oxidative stability up to 4.5 V (vs. Li/Li+) due to electrostatic and hydrogen bonding interactions between PANI and PAAMPSA. This polyacid-doped PANI showed a reversible capacity of 230 mAh/gPANI for over 800 cycles. Three different polyaniline-based layer-by-layer (LbL) electrodes, PANI/PAAMPSA, PANI/PANI:PAAMPSA, and linear poly(ethylenimine)/PANI:PAAMPSA were fabricated and their charge storage natures were assessed in non-aqueous energy storage systems. PANI:PAAMPSA retained its oxidative stability within LbL electrodes. The PANI/PAAMPSA LbL electrode did not show enhanced oxidative stability as compared to PANI:PAAMPSA complexes, which indicates that the interactions between PANI and PAAMPSA are not as strong as in PANI:PAAMPSA complexes. Porous PANI nanofiber/graphene hybrid electrodes were prepared by electrochemical reduction of PANI nanofiber/graphene oxide (PANI NF/GO) LbL assemblies at 1.5 V (vs. Li/Li+). The limited processibility of reduced graphene oxide was circumvented by using GO to build up PANI NF/GO LbL films followed by electrochemical reduction. PANI NF/electrochemically reduced graphene oxide (ERGO) LbL electrodes show high capacity and enhanced cycling stability. Its performance is strongly dependent on electrode thickness. Nitrogen-doped porous carbon was synthesized by one-step carbonization of isorecticular metal-organic frameworks (IRMOF-3). Porous IRMOF-3 itself acts as a self-sacrificial template to provide porous structure. Furthermore, additional carbon and nitrogen sources were not required. The nitrogen content can be easily controlled by varying carbonization temperature. Nitrogen-doped porous carbon possessed significantly higher capacitance due to additional pseudocapacitance originating from nitrogen as compared to analogous nitrogen-free porous carbons.Item Conducting polymer hydrogels for high-performance electrochemical devices(2014-05) Liu, Borui; Yu, Guihua (Assistant professor)Conducting polymer hydrogels (CPHs) is a class of unique materials that synergize the advantages of conducting polymers (CPs) and polymer hydrogels together. It has been employed in many high-performance electrochemical devices for years, such as energy storage and biosensors. However, large limitations of applying CPHs into the abovementioned areas have been facing the researcher for a long time, mainly due to the difficulties from complicated materials synthesis and untenable nanostructures for potential applications. The drawbacks of previously reported CPHs have put numerous disadvantages onto their applications, partially because they have, for example, high prices, untunable microscale or nanoscale architectures, environmentally hazardous properties, and unscalable and time-consuming synthesis processes. In this thesis, we proposed a novel route for carrying out CPHs by one-step organics synthesis at ambient conditions. The CPHs have hierarchically porous nanostructures crosslinked in a three-dimensional (3D) way, which enable its stable mechanical, unique chemical and physical properties, and outstanding electrochemical properties for potential applicability in long-term energy storage devices and highly sensitive biosensors. With highly controllable nanostructures of the CPHs, our novel concept and material system could possibly be utilized in a broad range of electrochemical applications, including but not limited to lithium-ion batteries (LIBs) electrodes, electrochemical capacitors (ECs), biofuel cells, medical electrodes, printable electronic devices, and biosensors.Item Coupling photovoltaics and grid-scale energy storage : performance and sitability(2015-05) Stoll, Brady Leigh; Deinert, Mark; Baldick, Ross; Edgar, Thomas; Howell, John; Shi, Li; Webber, MichaelThe Fifth Assessment of the International Panel on Climate Change has called for a four fold increase in the use of low-carbon sources of electricity to help stabilize climate change by mid century. Many people look to solar power systems to help reduce carbon intensity, but cost and variability have been significant obstacles to their widespread deployment. However, the cost of photovoltaics has dropped significantly in recent years, and grid-scale energy storage technologies are available to allow for production of dispatchable electricity from photovoltaics. In particular, compressed-air energy storage is both low-cost and can be built in a wide variety of geologies as well as above ground. I show that coupling large-scale photovoltaic arrays and grid-scale storage allows for dispatchable electricity production at costs that are comparable to other low carbon electricity sources. I examine four load curves: base-load generation, on-peak generation, and averaged load curves for the Electric Reliability Council of Texas (ERCOT) and PJM Independent System Operators. I found that on-peak and ERCOT loads typically required the lowest amount of storage, up to 2000 MWh [subscript e] less than that for base-load generation. However, in some regions, and for some storage amounts, baseload output actually provided the lowest cost of electricity. I also show that such coupled systems could provide base-load electricity for ≤ 0.08/kWh [subscript e] on more than 40% of global land surface, with a capacity factor equivalent to that of the US nuclear fleet. Importantly, this is below the projected cost of electricity from new nuclear power systems. While cost is a major factor, also of importance is where systems of photovoltaics and grid-scale storage would provide the most benefit. Locations expected to provide energy at the lowest cost do not necessarily correspond to load and population centers, where the electricity is most needed. I use multi-criteria decision analysis techniques to perform a global study of the optimal locations for siting these coupled systems to maximize their social benefit. I found that the most ideal locations are generally located in Africa, Iraq, and southeast Asia, as these locations have both high irradiance levels as well as expanding populations and low grid connectivity.Item Energy storage sizing for improved power supply availability during extreme events of a microgrid with renewable energy sources(2012-08) Song, Junseok; Kwasinski, Alexis; Grady, William M.; Driga, Mircea; Hallock, Gary; Son, Yoo SeokA new Markov chain based energy storage model to evaluate the power supply availability of microgrids with renewable energy generation for critical loads is proposed. Since critical loads require above-average availability to ensure reliable operation during extreme events, e.g., natural disasters, using renewable energy generation has been considered to diversify sources. However, the low availability and high variability of renewable energy sources bring a challenge in achieving the required availability for critical loads. Hence, adding energy storage systems to renewable energy generation becomes vital for ensuring the generation of enough power during natural disasters. Although adding energy storage systems would instantaneously increase power supply availability, there is another critical aspect that should be carefully considered; energy storage sizing to meet certain availability must be taken into account in order to avoid oversizing or undersizing capacity, which are two undesirable conditions leading to inadequate availability or increased system cost, respectively. This dissertation proposes to develop a power supply availability framework for renewable energy generation in a given location and to suggest the optimal size of energy storage for the required availability to power critical loads. In particular, a new Markov chain based energy storage model is presented in order to model energy states in energy storage system, which provides an understanding of the nature of charge and discharge rates for energy storage that affect the system's power output. Practical applications of the model are exemplified using electrical vehicles with photovoltaic roofs. Moreover, the minimal cut sets method is used to analyze the effects of microgrid architectures on availability characteristics of the microgrid power supply in the presence of renewable energy sources and energy storage. In addition, design considerations for energy storage power electronics interfaces and a comparison of various energy storage methods are also presented.Item Energy storage sizing for low-inertia microgrids, and lessons learned from a potential microgrid(2016-05) Toliyat, Amir; Baldick, Ross; Kwasinski, Alexis; Arapostathis, Aristotle; Hallock, Gary; Uriarte, FabianThe coordinated control of multiple distributed generators in a microgrid and the preservation of adequate system inertia in real-time operations are some of the principal technical challenges for stable microgrid operation. One issue in particular pertains to grid-tied inverters, which, as mandated by present standards, are only permitted to operate at unity power factor, thereby requiring the microgrid’s synchronous generators to operate at a low power factor. This behavior accordingly introduces ramifications by limiting the generator’s active power output, which would compromise frequency and voltage stability margins. Consideration is also given to the effect of line impedances, since interconnecting microgrid lines can be described by a variety of X/R ratios that affect the control and flow of active and reactive power. Moreover, the absence of a stiff grid presents control challenges for grid-tied inverters due to the inverters’ tendency to regulate the voltage at the point of common coupling. These same inverters also jeopardize microgrid stability due to their low equivalent inertia as traditional forms of generation (i.e., spinning sources) become displaced by inertia-less inverters. Because of this low microgrid inertia, fluctuations in the output power of renewable energy sources or changes in local load levels may lead to power quality or frequency/voltage stability concerns. Therefore, energy storage sizing is investigated in this dissertation, as it is closely related to the stability analysis of microgrids. Furthermore, an existing residential community (in Austin, TX) described by a moderate penetration of photovoltaic sources and electric vehicle charging is considered, and the implications of said community being retrofitted to a microgrid are examined.Item Energy storage-aware prediction/control for mobile systems with unstructured loads(2013-08) LeSage, Jonathan Robert, 1985-; Longoria, Raul G.Mobile systems, such as ground robots and electric vehicles, inherently operate in stochastic environments where load demands are largely unknown. Onboard energy storage, most commonly an electrochemical battery system, can significantly constrain operation. As such, mission planning and control of mobile systems can benefit from a priori knowledge about battery dynamics and constraints, especially the rate-capacity and recovery effects. To help overcome overly conservative predictions common with most existing battery remaining run-time algorithms, a prediction scheme was proposed. For characterization of a priori unknown power loads, an unsupervised Gaussian mixture routine identifies/clusters the measured power loads, and a jump-Markov chain characterizes the load transients. With the jump-Markov load forecasts, a model-based particle filter scheme predicts battery remaining run-time. Monte Carlo simulation studies demonstrate the marked improvement of the proposed technique. It was found that the increase in computational complexity from using a particle filter was justified for power load transient jumps greater than 13.4% of total system power. A multivariable reliability method was developed to assess the feasibility of a planned mission. The probability of mission completion is computed as the reliability integral of mission time exceeding the battery run-time. Because these random variables are inherently dependent, a bivariate characterization was necessary and a method is presented for online estimation of the process correlation via Bayesian updating. Finally, to abate transient shutdown of mobile systems, a model predictive control scheme is proposed that enforces battery terminal voltage constraints under stochastic loading conditions. A Monte Carlo simulation study of a small ground vehicle indicated significant improvement in both time and distance traveled as a result. For evaluation of the proposed methodologies, a laboratory terrain environment was designed and constructed for repeated mobile system discharge studies. The test environment consists of three distinct terrains. For each discharge study, a small unmanned ground vehicle traversed the stochastic terrain environment until battery exhaustion. Results from field tests with a Packbot ground vehicle in generic desert terrain were also used. Evaluation of the proposed prediction algorithms using the experimental studies, via relative accuracy and [alpha]-[lambda] prognostic metrics, indicated significant gains over existing methods.Item Fast real-time monitoring of rotating machines(Texas Tech University, 2003-08) McHale, Gary BrentThis project involves the application of methods and techniques that have been developed for high performance control of relatively slow turning industrial machines and extends these techniques to the more demanding regime of AC-machines used for kinetic energy storage and fast AC-servos for military applications. In particular, techniques for fast monitoring of the output voltage of AC-generators will be discussed. To accomplish fast monitoring, the (sinusoidal) AC output voltage is converted to a DC quantity that represents the instantaneous amplitude. This is achieved through the use of a rotational transformation. This transformation, also called 'Vector Rotation," can be used for very fast observation of the momentary amplitudes of electrical machine quantities. The hardware that was designed to control the machines will also be discussed in extreme detail. The procedure is implemented by tightly integrating a digital motion control co-processor into the memory map of a 16-bit microcontroller.Item A framework to model and optimize the operation of lithium-ion energy storage in electricity markets, and an assessment of lithium-ion energy storage in Texas(2015-08) Fares, Robert Leo; Webber, Michael E., 1971-; Baldick, Ross; Bickel, James E.; Chen, Dongmei; Edgar, Thomas FThe lithium-ion (Li-ion) battery has become an established technology in portable electronics and electric vehicle applications. At the same time, there is rising interest in grid-based battery energy storage to improve the flexibility of the electric grid and integrate intermittent sources of renewable energy. To provide information for energy storage developers, battery system operators, state policymakers, and the general public, this research develops a framework to characterize, operate, and evaluate Li-ion battery energy storage that is connected to the electric grid and participates in a wholesale electricity market. Methods are developed to characterize and model the voltage, temperature, and capacity degradation behavior of a Li-ion battery system. Then, an optimization program is developed to schedule Li-ion storage in an electricity market while modeling and controlling its operating state and rate of capacity loss. The optimization framework is used to simulate operation of Li-ion storage in Texas’s Electric Reliability Council of Texas (ERCOT) electricity from 2002–2014, and the market revenue potential and operating lifetime of Li-ion storage are approximated. It is shown that controlling capacity degradation in operational management can extend the lifetime of Li-ion battery modules by approximately 30–60% without significantly reducing market revenue potential. To test the reliability impact of distributed Li-ion storage, residential electricity data are used to approximate how long a battery system could isolate downstream electricity customers during an outage. Thousands of outage events are simulated to show the expected islanding duration for outages occurring at different times of day. The potential reliability benefit from avoided residential electric outages is calculated and found to be much smaller than the revenue potential from the electricity market, indicating that market applications should be prioritized over residential reliability applications in siting and operating a battery system. It is found that the net-present value (NPV) of a Li-ion battery system providing wholesale energy arbitrage in the ERCOT market is negative across a range of cost and benefit parameters. However, controlling capacity degradation in operational management of the battery system is found to increase its value by approximately $100/kWh of rated energy capacity. The NPV of a battery system providing a combination of energy and Fast Responding Regulation Service (FRRS) is found to be positive across a wide range of cost and benefit parameters, indicating a Li-ion battery system could most likely provide a combination of energy and FRRS service to the ERCOT electricity market at a profit. Controlling capacity degradation in operational management of the battery system for energy and FRRS is found to have little impact on its NPV. However, controlling capacity loss makes the NPV less sensitive to variation in the lifetime of the battery modules, reducing the risks associated with premature battery cell failure.Item A grid-level assessment of compressed air energy storage in ERCOT(2013-05) Townsend, Aaron Keith; Webber, Michael E., 1971-In the Electric Reliability Council of Texas (ERCOT) compressed air energy storage (CAES) is currently viewed as the most promising energy storage technology due to Texas having suitable geology for CAES and few locations suitable for pumped-hydro storage. CAES is a proven technology but the economics for new facilities are uncertain. This work quantified the economic prospects for CAES in ERCOT as a function of installed wind capacity, natural gas price, and CAES capital cost. Two types of models were developed and used in this work. The first type of model was a CAES dispatch optimization model, which determined the maximum operating profits a CAES facility could earn given a set of electricity and ancillary services market prices. These models were used to examine several separate research questions relating to the maximum potential for CAES and the impact of uncertainty and other real-world complications. The models determined that the maximum operating profit from 2002-2010 varied widely from year to year and averaged $120-140/kW-year, which is likely below the operating profits required to justify investing in CAES. The models also determined that current price forecasting methods are sufficient to earn approximately 95% of the operating profits achievable with perfect knowledge of all prices in the year. The second type of model was a unit commitment model of ERCOT, which determined the least-cost operation of all the generators in the generation fleet to meet given load. The unit commitment model was used to determine electricity and ancillary service market prices under different assumptions about natural gas price, installed wind capacity, and installed CAES capacity. The CAES dispatch optimization model was then used to determine the operating profits of a CAES facility under these scenarios. CAES operating profits were found to increase with increasing natural gas price and installed wind capacity and to decrease with increasing installed CAES capacity. CAES operating profits were estimated to support installed CAES capacities from zero to more than 6 GW, depending on the natural gas price, installed wind capacity, installed CAES capacity, and the CAES capital costs. The strongest determinant of the maximum CAES capacity that would be profitable is the natural gas price, followed by the CAES capital costs.Item A grid-level unit commitment assessment of high wind penetration and utilization of compressed air energy storage in ERCOT(2014-12) Garrison, Jared Brett; Webber, Michael E., 1971-Emerging integration of renewable energy has prompted a wide range of research on the use of energy storage to compensate for the added uncertainty that accompanies these resources. In the Electric Reliability Council of Texas (ERCOT), compressed air energy storage (CAES) has drawn particular attention because Texas has suitable geology and also lacks appropriate resources and locations for pumped hydroelectric storage (PHS). While there have been studies on incorporation of renewable energy, utilization of energy storage, and dispatch optimization, this is the first body of work to integrate all these subjects along with the proven ability to recreate historical dispatch and price conditions. To quantify the operational behavior, economic feasibility, and environmental impacts of CAES, this work utilized sophisticated unit commitment and dispatch (UC&D) models that determine the least-cost dispatch for meeting a set of grid and generator constraints. This work first addressed the ability of these models to recreate historical dispatch and price conditions through a calibration analysis that incorporated major model improvements such as capacity availability and sophisticated treatment of combined heat and power (CHP) plants. These additions appreciably improved the consistency of the model results when compared to historical ERCOT conditions. An initial UC&D model was used to investigate the impacts on the dispatch of a future high wind generation scenario with the potential to utilize numerous CAES facilities. For all future natural gas prices considered, the addition of CAES led to reduced use of high marginal cost generator types, increased use of base-load generator types, and average reductions in the total operating costs of 3.7 million dollars per week. Additional analyses demonstrated the importance of allowing CAES to participate in all available energy and ancillary services (AS) markets and that a reduction in future thermal capacity would increase the use of CAES. A second UC&D model, which incorporated advanced features like variable marginal heat rates, was used to analyze the influence of future wind generation variability on the dispatch and resulting environmental impacts. This analysis revealed that higher amounts of wind variability led to an increase in the daily net load ramping requirements which resulted in less use of coal and nuclear generators in favor of faster ramping units along with reductions in emissions and water use. The changes to the net load also resulted in increased volatility of the energy and AS prices between daily minimum and maximum levels. These impacts were also found to increase with compounding intensity as higher levels of wind variability were reached. Lastly, the advanced UC&D model was also used to evaluate the operational behavior and potential economic feasibility of a first entrant conventional or adiabatic CAES system. Both storage systems were found to operate in a single mode that enabled very high utilization of their capacity indicating both systems have highly desirable characteristics. The results suggest that there is a positive case for the investment in a first entrant CAES facility in the ERCOT market.Item Grid-scale battery energy storage systems(2013-05) Hill, Cody Aaron; Kwasinski, AlexisThis report presents an overview of the engineering considerations involved in the design of grid-scale battery energy storage systems. Grid-scale is defined here as systems over 1 MW in rated power, typically operated by a utility, independent power producer, or Independent System Operator (ISO). The physical components of a BESS are presented and explained, including power electronics, an introduction to various commercially available battery technologies, necessary control systems, and balance of plant hardware. Also presented are a variety of real-world applications of battery energy storage systems, showing how the specific application determines what mix of technology will be selected when designing the system, as well as explaining the foundation for the control algorithms.Item An integrated energy storage scheme for a dispatchable wind and solar powered energy system(2009-12) Garrison, Jared Brett; Webber, Michael E., 1971-; Schmidt, PhilipWind and solar technologies have experienced rapid market growth recently as a result of the growing interest for implementation of renewable energy. However, the intermittency of wind and solar power is a major obstacle to their broader use. The additional risks of unexpected interruptions and mismatch with demand have hindered the expansion of these two primary renewable resources. The goal of this research is to analyze an integrated energy system that includes a novel configuration of wind and solar coupled with two storage methods to make both wind and solar sources dispatchable during peak demand, thereby enabling their broader use. Named DSWiSS for Dispatchable Solar Wind Storage System, the proposed system utilizes compressed air energy storage (CAES) that is driven from wind energy and thermal storage supplied by concentrating solar thermal power in order to achieve this desired dispatchability. Although DSWiSS mimics the operation of a typical CAES facility, the replacement of energy derived from fossil fuels with energy generated from renewable resources makes this system unique. While current CAES facilities use off peak electricity to power their compressors, this system uses power from wind turbines. Also, rather than using natural gas for heating of the compressed air before its expansion through a turbine, DSWiSS uses solar thermal energy and thermal storage. For this research, two models were created; the first is a dynamic model of a 1.5 MW variable speed wind turbine, programmed in PSCAD/EMTDC, that utilizes rotor resistive control to maintain rated power output. This model simulates the dynamic response of the wind turbine to changing wind conditions as well as the nominal performance parameters at all wind speeds. The second model is a steady state thermodynamic simulation of the turbomachinery power unit in the DSWiSS facility. By assuming conditions similar to those of a currently operating CAES facility in McIntosh, Alabama, the model calculates the performance parameters of DSWiSS and estimates the relative energy input requirements. By combining these models with a levelized lifetime cost analysis estimates of the power system performance and the cost of energy for the DSWiSS facility were estimated. The combination of these components yielded an efficiency greater than 46% for the main power block and a nearly equal utilization of both renewable resources. It was also estimated that the overall system is only slightly more expensive per unit of electricity generated than the current technologies employed today, namely coal, nuclear, and natural gas, but is comparable to a stand-alone solar thermal facility. However, this economic analysis, though accurate with regard to the technologies chosen, will not be complete until cost values can be placed on some of the externalities associated with power generation such as fuel cost volatility, national security, and emissions.Item Low-temperature synthesis and electrochemical properties of aliovalently-doped phosphates and spinel oxides(2014-05) Gutierrez, Arturo, 1978-; Manthiram, ArumugamLithium-ion batteries are being intensely pursued as energy storage devices because they provide higher energy and power densities compared to other battery systems such as lead-acid and nickel-metal hydride batteries. This dissertation (i) explores the use of a low-temperature microwave-assisted synthesis process to obtain aliovalently-doped lithium transition-metal phosphates and lower-valent vanadium oxide spinels, some of which are difficult to obtain by conventional high-temperature processes, and (ii) presents an investigation of the electrochemical properties of the aliovantly-doped phosphate cathodes and doped lithium manganese oxide and oxyfluoride spinel cathodes in lithium-ion batteries. Following the introduction and general experimental procedures, respectively, in Chapters 1 and 2, Chapter 3 first focuses on understanding of how the inductive effect and structural features in lithium transition-metal borate, silicate, and phosphate cathodes affect the M²⁺ʹ³⁺redox energies. It is found that the magnitude of the voltages delivered by the polyanion cathodes can be predicted based simply on the coordination of the transition-metal ion. Furthermore, the differences in the voltages delivered by the phosphates and pyrophosphates are explained by considering the resonance structures and their contribution to the covalency of the polyanion. Chapter 4 presents a low-temperature microwave-assisted solvothermal process to substitute 20 atom % V³⁺ for Mn²⁺ in LiMnPO₄. It is shown that the solubility of vanadium in LiMnPO₄ decreases upon heating the doped samples to ≥ 575 °C, demonstrating the importance of employing a low-temperature process to achieve aliovalent doping in LiMnPO₄. It is further demonstrated that by increasing the vanadium content in the material, the discharge capacity in the first cycle could be increased without any additional carbon coating. Subsequent X-ray absorption spectroscopy data reveal that the better performance is facilitated by enhanced Mn-O hybridization upon incorporating vanadium into the lattice. Chapter 5 explores the influence of various factors, such as the oxidation state of Mn, electronegativity of the dopant cation Mn+, and the dissociation energy of M-O bond, on the electrochemical properties of cation-doped oxide and oxyfluoride spinel cathodes. As an extension, Chapter 6 presents the effect of processing conditions on the surface concentration of the dopant cation Mn+. Chapter 7 presents an extension of the low-temperature microwave-assisted synthesis process to obtain AV₂O₄ (Mg, Fe, Mn, and Co) spinel oxides. The method is remarkably effective in reducing the synthesis time and energy use due to the efficiency of dielectric heating compared to conventional heating. The ability to access V³⁺ is facilitated by the relative positions of the energy levels of the cations in solution, which is lower than that in the solid, and the use of a strong reducing solvent like TEG. Finally, Chapter 8 provides a summary of the salient findings in this dissertation.Item Microwave-assisted synthesis and characterization of inorganic materials for energy applications(2012-08) Harrison, Katharine Lee; Manthiram, ArumugamLithium-ion batteries play a crucial role in portable electronics, but require further innovation for electric vehicle and grid storage applications. To meet this demand, significant emphasis has been placed on developing safe, inexpensive, high energy density cathode materials. LiFePO₄ is a candidate cathode material for electric vehicle and grid storage applications. Vanadium-doped LiFePO₄ cathodes of the form [chemical formula] (0 ≤ x ≤ 0.25) were synthesized here by a facile, low-temperature microwave-assisted solvothermal (MW-ST) method. Such an approach offers manufacturing-energy and cost savings compared to conventional synthesis. Additionally, although [chemical formula] has been synthesized previously by conventional methods, it is shown here that the MW-ST method allows much higher doping levels than can be achieved at conventional temperatures, indicating that metastable phases can be isolated through the low-temperature microwave-assisted synthesis. LiFePO₄ suffers from poor ionic conductivity, but this limitation can be minimized by microwave-assisted synthesis through a tuning of the particle size, allowing for decreased Li⁺ diffusion paths. LiVOPO₄ is another polyanion material with higher energy density than LiFePO₄, but similar ionic conductivity limitations. It has not been previously synthesized by MW-ST. Thus, a MW-ST method was developed here to prepare LiVOPO₄. By varying reaction conditions, three polymorphic modifications of LiVOPO₄ were accessed and the electrochemical performance was optimized. LiVOPO₄ can be further discharged to Li₂VOPO₄, which has been suggested in the literature, but the structural transformation that accompanies this process has not been detailed. To this end, the delithiation process was studied by ex situ XRD measurements to better understand how the second lithium is accommodated. Finally, MW-ST has also been exploited to grow thin films of anatase TiO₂ phase on indium tin oxide (ITO)-coated glass substrates. The microwave field is selectively absorbed by the conductive ITO layer on the glass substrates, leading to ohmic heating. The resulting heated ITO layer acts as a favorable site for nucleation and growth. TiO₂ thin films have widespread applications in the energy and electronics sectors. Such selective microwave-assisted ohmic heating of solid materials within a growth solution represents a promising new avenue for microwave synthesis, which has been minimally explored in the literature.Item A mixed-integer model for optimal grid-scale energy storage allocation(2010-08) Harris, Chioke Bem; Meyers, Jeremy P.; Webber, Michael E., 1971-To meet ambitious upcoming state renewable portfolio standards (RPSs), respond to customer demand for “green” electricity choices and to move towards more renewable, domestic and clean sources of energy, many utilities and power producers are accelerating deployment of wind, solar photovoltaic and solar thermal generating facilities. These sources of electricity, particularly wind power, are highly variable and difficult to forecast. To manage this variability, utilities can increase availability of fossil fuel-dependent backup generation, but this approach will eliminate some of the emissions benefits associated with renewable energy. Alternately, energy storage could provide needed ancillary services for renewables. Energy storage could also support other operational needs for utilities, providing greater system resiliency, zero emission ancillary services for other generators, faster responses than current backup generation and lower marginal costs than some fossil fueled alternatives. These benefits might justify the high capital cost associated with energy storage. Quantitative analysis of the role energy storage can have in improving economic dispatch, however, is limited. To examine the potential benefits of energy storage availability, a generalized unit commitment model of thermal generating units and energy storage facilities is developed. Initial study will focus on the city of Austin, Texas. While Austin Energy’s proximity to and collaborative partnerships with The University of Texas at Austin facilitated collaboration, their ambitious goal to produce 30-35% of their power from renewable sources by 2020, as well as their continued leadership in smart grid technology implementation makes them an excellent initial test case. The model developed here will be sufficiently flexible that it can be used to study other utilities or coherent regions. Results from the energy storage deployment scenarios studied here show that if all costs are ignored, large quantities of seasonal storage are preferred, enabling storage of plentiful wind generation during winter months to be dispatched during high cost peak periods in the summer. Such an arrangement can yield as much as $94 million in yearly operational cost savings, but might cost hundreds of billions to implement. Conversely, yearly cost reductions of $40 million can be achieved with one CAES facility and a small fleet of electrochemical storage devices. These results indicate that small quantities of storage could have significant operational benefit, as they manage only the highest cost hours of the year, avoiding the most expensive generators while improving utilization of renewable generation throughout the year. Further study using a modified unit commitment model can help to narrow the performance requirements of storage, clarify optimal storage portfolios and determine the optimal siting of this storage within the grid.Item Modeling and control of directly connected and inverter interfaced sources in a microgrid(2011-08) Chamana, Manohar; Bayne, Stephen B.; Mohsenian-Rad, HamedThere has been a keen interest on Distributed Generation (DG) due to their restricted goals of meeting local loads and improving reliability of the overall system. Microgrids (MGs) are connected to the main grid through a Point of Common Coupling which separates the former from the latter. At the time of an intentional islanding or fault at the grid level, a microgrid is able to disconnect itself from the rest of the grid and operate by itself. A microgrid may contain both directly connected and inverter interfaced sources with different control configurations. When disconnected or islanded from the main grid there are various approaches to share the load, one of them being master-slave control where a storage device may become the reference DG to set the nominal voltage and frequency. When the main grid is brought back to normal operation, the microgrid is able to resynchronize itself to the main grid only when it meets certain conditions so as to avoid transients. All the microsources, power electronics and their control with power management were developed in Matlab/Simulink.Item Modeling and simulation of distribution system components in anticipation of a smarter electric power grid(2011-05) Toliyat, Amir; Kwasinski, Alexis; Grady, WiliamSuccessful development of the electric power grid of the future, hereinafter referred to as a smart grid, implicitly demands the capability to model the behavior, performance, and cost of distribution-level smart grid components. The modeling and simulation of such individual components, together with their overall interaction, will provide a foundation for the design and configuration of a smart grid. It is the primary intent of this thesis, to provide a basic insight into the energy transfer of various distribution-level components by modeling and simulating their dynamic behavior. The principal operations of a smart grid must be considered, including variable renewable generation, energy storage, power electronic interfaces, variable load, and plug-in electric vehicles. The methodology involves deriving the mathematical equations of components, and, using the MATLAB/Simulink environment, creating modules for each component. Ultimately, these individual modules may be connected together via a voltage interface to perform various analyses, such as the treatment of harmonics, or to acquire an understanding of design parameters such as capacity, runtime, and optimal asset utilization.Item Nanoparticles in mesoporous materials : optical and electrochemical properties for energy storage applications(2009-08) Patel, Mehul Naginbhai; Johnston, Keith P., 1955-The design of nanoparticles in mesoporous supports is explored through synthetic strategies of electrophoretic deposition and electroless deposition with application towards energy storage. Electrophoretic deposition of nanoparticles into a mesoporous thin film is examined using charged nanocrystals in a low-permittivity solvent. To provide a basis for the deposition, the mechanism of particle charging in a low-permittivity solvent was studied. Dispersions of carbon black particles in toluene with an anionic surfactant were characterized using differential-phase optical coherence tomography with close electrode spacing to measure the electrophoretic mobility. The particle charge in concentrated dispersions was found to decrease as a function of increasing surfactant concentration. Partitioning of cations between the surfactant-laden particle surface and micelle cores in the double-layer was found to govern the dynamics of particle charging. Subsequently, charged Au nanocrystals were deposited by electrophoresis within perpendicular mesochannels of a TiO2 support. High loadings of 21 wt% Au with good dispersion were achieved within the mesoporous TiO2 support using electrophoretic deposition, which would otherwise be inhibited by the weak nanocrystal-support interaction. According to a modified Fokker-Planck equation, the mean penetration depth of a single nanocrystal inside of the perpendicular pores was found to be dependent on the electric field strength, electrophoretic mobility, pore diameter, nanocrystal size, and local deposition rate constant. Nanocomposites for electrochemical capacitors were designed via electroless deposition of redox-active MnO2 in a high surface area mesoporous carbon support. Disordered mesoporous carbon supports with a pore size of ~8 nm were used both in amorphous (AMC) and graphitic (GMC) form, with a ~1000-fold larger conductivity for GMC. High loadings of 30 wt% MnO2 were achieved in the AMC in the form of ~1 nm thick domains, which were highly dispersed throughout the support. Oxidation of the GMC was necessary to facilitate wetting and deposition of the MnO2 precursor in order to achieve high loadings of 35 wt% MnO2 with ~1 nm thickness. High gravimetric MnO2 pseudocapacitances of >500 F/gMnO2 were achieved at low loadings and low scan rate of 2 mV/s for both carbon supports. However, at high scan rates ≥100 mV/s, the MnO2 pseudocapacitance is twofold larger for MnO2/GMC, relative to MnO2/AMC. Sodium ion diffusion throughout both MnO2/AMC and MnO2/GMC was shown to be facile. For the GMC versus AMC support, the higher MnO2 pseudocapacitance is attributed to the higher electronic conductivity, which facilitates electron transport to the MnO2 domains.Item Nanostructured anode materials for Li-ion and Na-ion batteries(2013-08) Lin, Yong-Mao; Mullins, C. B.; Heller, AdamThe demand for electrical energy storage has increased tremendously in recent years, especially in the applications of portable electronic devices, transportation and renewable energy. The performances of lithium-ion and sodium-ion batteries depend on their electrode materials. In commercial Li-ion batteries with graphite anodes the intercalation potential of lithium in graphite is close to the reversible Li/Li⁺ half-cell potential. The proximity of the potentials can result in unintended electroplating of metallic instead of intercalation of lithium in the graphite anode and frequently leads to internal shorting and overheating, which constitute unacceptable hazards, especially when the batteries are large, as they are in cars and airplanes. Moreover, graphite cannot be readily used as the anode material of Na-ion batteries, because electroplating of metallic sodium on graphite is kinetically favored over sodium intercalation in graphite. This dissertation examines safer Li-ion and Na-ion battery anode materials.Item Optically enhanced attachment processes in diffuse discharges(Texas Tech University, 1987-05) Holmberg, Courtney DoyalDuring the last several years, interest In high voltage switches for pulsed power applications has increased significantly. One main concern in the field of pulsed power Is that of energy storage. While inductive energy storage systems have space and weight savings when compared with capacitive energy storage systems, they also require the use of a high power opening switch. Therefore, opening switch technology has started to be developed, and several concepts for opening switches are currently being studied. One particular concept is that of the diffuse discharge opening switch, which has several advantages over other types of opening switches. A significant advantage of the diffuse discharge opening switch is that it may be externally controlled by optical means or by an electron beam. In this paper, three experiments are presented which study the use of optically enhanced attachment as a discharge control mechanism in diffuse discharges. The first experiment demonstrates the effect of UV enhanced attachment in an externally sustained discharge. The second experiment shows the effect of IR illumination in a self sustained discharge. The last experiment demonstrates the effect of IR enhanced attachment in an externally sustained discharge. Future experiments in optically enhanced attachment are also discussed.