Browsing by Subject "Energy Storage"

Now showing 1 - 4 of 4
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    Analysis of Optimal Dispatch of Energy Systems, Market Rules, and Market Power in Wholesale Electricity Markets
    (2021-08) Paine, Nathan
    The focus of this dissertation is on the operation of electric power systems, specifically on wholesale electricity markets and the potential for exercising market power in wholesale markets for electricity. Restructuring of the electric utility industry has encouraged Independent Power Producers (IPPs) to enter the industry and sell power in the wholesale electricity markets. However, as the United States continues the transition to restructured electricity markets, there are concerns about the market power that producers may exert. This dissertation is composed of three essays exploring these topics using dynamic optimization methods and empirical analysis. The first essay uses a framework to measure production costs and the component of price that is above marginal cost. I incorporate the start-up costs of generators. Using data from January 2016 to December 2018, I find evidence that market power was exercised, particularly in months having unseasonably cold temperatures and fuel price spikes as well as during the winter peak season. The results also suggest that the degree of market power increases during the peak hours of the day. The second essay utilizes a dynamic optimization model to illustrate how a low-temperature geothermal power plant can be flexibly dispatched to offer multiple different services in addition to base-load power to a utility customer. The utility industry still thinks of geothermal as a base-load resource, but I show that low temperature resource geothermal power plants offer more flexibility than other renewable energy technologies and thus can be operated as a variable energy resource to accommodate intermittent resources and alleviate transmission congestion. The third essay examines the interaction of policies, markets, and technologies that creates the modern electrical system. Integrating large amounts of electricity generated by variable renewable resources, such as from wind and solar, into electricity systems may require energy storage technologies to synchronize electricity production with electricity demand. Electricity markets compensate the performance of these energy storage technologies for the services they provide, and these markets are often operated by regional Independent System Operators (ISOs) that specify the market rules for this compensation. To examine how different ISO rules can affect the operation and profitability an energy storage technology, I develop a dynamic programming model of pumped hydroelectric storage (PHES) facility operation under the market rules from the Midcontinent ISO and ISO-New England. I show how differences in rules between these ISOs produce different operational strategies and profits and may not incentivize energy storage projects where they are most needed.
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    Carbon nanotube thin films for active noise cancellation, solar energy harvesting, and energy storage in building windows
    (2014-07) Hu, Shan
    This research explores the application of carbon nanotube (CNT) films for active noise cancellation, solar energy harvesting and energy storage in building windows. The CNT-based components developed herein can be integrated into a solar-powered active noise control system for a building window. First, the use of a transparent acoustic transducer as both an invisible speaker for auxiliary audio playback and for active noise cancellation is accomplished in this work. Several challenges related to active noise cancellation in the window are addressed. These include secondary path estimation and directional cancellation of noise so as to preserve auxiliary audio and internal sounds while preventing transmission of external noise into the building. Solar energy can be harvested at a low rate of power over long durations while acoustic sound cancellation requires short durations of high power. A supercapacitor based energy storage system is therefore considered for the window. Using CNTs as electrode materials, two generations of flexible, thin, and fully solid-state supercapacitors are developed that can be integrated into the window frame. Both generations consist of carbon nanotube films coated on supporting substrates as electrodes and a solid-state polymer gel layer for the electrolyte. The first generation is a single-cell parallel-plate supercapacitor with a working voltage of 3 Volts. Its energy density is competitive with commercially available supercapacitors (which use liquid electrolyte). For many applications that will require higher working voltage, the second-generation multi-cell supercapacitor is developed. A six-cell device with a working voltage as high as 12 Volts is demonstrated here. Unlike the first generation's 3D structure, the second generation has a novel planar (2D) architecture, which makes it easy to integrate multiple cells into a thin and flexible supercapacitor. The multi-cell planar supercapacitor has energy density exceeding that of other planar supercapacitors in literature by more than one order of magnitude. All-solution fabrication processes were developed for both generations to achieve economical and scalable production. In addition to carbon nanotubes, nickel/nickel oxide core-shell nanowires were also studied as electrode materials for supercapacitors, for which high specific capacitance but low working voltage were obtained. Semi-transparent solar cells with carbon nanotube counter electrodes are developed to power the active noise cancellation system. They can be directly mounted on the glass panes and become part of the home window. The 2.67% efficiency achieved is higher than the 1.8% efficiency required for harvesting adequate energy to cancel noise of 70dB Day-Night-Level, which impacts on a north-facing window. In summary, this project develops several fundamental technologies that together can contribute to a solar-powered active noise cancellation system for a building window. At the same time, since the component technologies being developed are fundamental, it is also likely that they will have wider applications in other domains beyond building windows.
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    Modeling, Control and Optimization of a Novel Compressed Air Energy Storage System for Off-Shore Wind Turbines
    (2016-08) Saadat, Mohsen
    Integrating wind and solar energy into the electric power grid is challenging due to variations in wind speed and solar intensity. Moreover, to maintain the stability of electric power grid, there must be always a balance between the energy production and consumption which is not easy since both of them undergo drastic variation over time. Large scale energy storage systems can solve these issues by storing the extra energy when supply exceeds demand power, and regenerating energy and send it to the electric grid when demand power surpasses the supply. This dissertation focuses on the optimal design and control of a new type of Com- pressed Air Energy Storage (CAES) system that is especially applicable to off-shore wind turbines. The system is designed such that it addresses the need for a compact and energy dense storage system with high roundtrip efficiency for large-scale energy storage applications. The contributions of this work are also beneficial for designing power dense gas compressors/expanders with high thermal efficiency. The material of this thesis can be divided into two parts: In the first part, different approaches and techniques are studied to increase the power density of a liquid piston air compressor/expander system without sacrificing its efficiency. These methods are then combined and optimized in the form of a single design to maximize the performance of an air compressor/expander unit which is the most critical component of the energy storage system under investigation. In the second part, component-level and supervisory-level controllers are designed and developed for the combined wind turbine and energy storage system such that both short-term and long-term objectives are achieved. Improvement of thermal efficiency of an air compressor/expander is achievable by increasing heat transfer between air under compression/expansion and its surrounding solid material in the compression/expansion chamber. This will prevent heat loss by reducing air temperature rise/drop during the compression/expansion phase. Here, liquid piston (instead of conventional solid piston) is used in the compression/expansion chamber where the chamber volume is filled with porous material that increases heat transfer area by an order of magnitude, and therefore improves the thermal efficiency. Since the liquid piston is driven by a variable displacement pump/motor, optimal compression/expansion trajectories are calculated and applied to further increase heat transfer and improve the performance of the system. This improvement is verified both analytically and experimentally. Based on numerical results, utilizing porous material in the compression/expansion chamber with optimized distribution, combined with the corresponding optimal compression/expansion trajectory has the potential to increase the power density by more than 20 folds, without reducing its thermal efficiency. An alternative method to increase heat transfer is to introduce micro-size water droplets (through water spray) in the chamber during air compression/expansion process. Since water has a high heat capacity, the generated heat during compression can be absorbed by water and therefore reduce the temperature rise of air during compression. The same phenomenon but in opposite direction happens in expansion case (heat transfer from water droplets to air) that prevents air from getting very cold which causes poor efficiency. A numerical model is developed and used to study the effect of water spray amount and timing on the thermal performance of air compressor/expander. The opti- mal timing of water spray is calculated to maximize the effectiveness of a given amount of water that is sprayed into the air. The optimally designed liquid piston air compressor/expander unit is then combined with the other components of energy storage system, as well as a wind turbine. Nonlinear techniques are used to design plant-level controllers in order to coordinate different parts in the system, and to achieve both short term objectives (maintaining the frequency of electric generator while capturing maximum wind power) and long term objectives (tracking the power demanded from electric grid and regulating the pressure in the storage vessel). Finally, the combined wind turbine and energy storage system is studied for maximizing the total achievable revenue by optimizing the storage/regeneration sequence according to varying electricity price and available wind power (given storage size and its nominal power). According to the results, an increase of up to 137% in total revenue is achievable by equipping a conventional wind turbine with a CAES system while tracking the calculated optimal storage/regeneration sequence. Additionally, by incorporating the price of different components of energy storage system, a study is conducted to find the effect of system size on maximum achievable revenue that can lead to the economical size selection of the energy storage system.
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    The Performance of a Carbon-Dioxide Plume Geothermal Energy Storage System
    (2019-02) Fleming, Mark
    CO2-Plume Geothermal (CPG) is a system that can produce electricity from low-temperature heat from the subsurface of the earth, effectively combining geothermal energy and carbon capture and geologic storage; two technologies that have the potential to significantly reduce the amount of CO2 emitted into the atmosphere and limit the impacts of climate change. This system is different from other geothermal concepts as 1) the system uses CO2 as the heat extraction fluid in the subsurface reservoir, 2) the system does not rely shallow-natural hydrothermal locations or engineered (i.e. enhanced or fractured) reservoirs, instead using naturally permeably sedimentary basins, and 3) CPG systems utilize low-temperature resources which are currently undeveloped for geothermal energy. Therefore, CPG has significant potential to expand the geographic region where geothermal energy can operate, while providing an end used for captured CO2. This research demonstrates how the unique properties of the CPG system allow the system to be modified to operate as an energy storage system, which can increase the penetration of variable wind and solar resources on the grid, by using an additional shallow reservoir to separate the components that generate and consume power. To operate, the system generates power by extracting CO2 from the deeper-hotter reservoir and generates power in the turbine before the CO2 is slightly cooled and injected into the shallow reservoir, making use of the thermosiphon effect, where the thermal expansion of CO2 results in a density difference in each vertical well that can circulate CO2 without the need for pumps. To store power, the CO2 can be produced from the shallow reservoir, cooled and compressed, and then reinjected into the deep reservoir where it is heated. This research began by establishing the feasibility of the CPGES cycle for a single reservoir configuration and a mass flow rate near the optimum energy generation condition, demonstrating the effects of the intermittent injection and production of CO2 on the transient reservoir pressures and the power generated and consumed by the system over the first 10 years of operation (Chapter 2). The results demonstrated that the system was at a quasi-steady state condition at 10 years, and that the system could generate more energy to the grid than it consumed, providing both net energy generation of and energy storage. Using historical electrical price data, it was found that the CPGES system could use price arbitrage to be competitive with a CPG system, for the same geothermal heat extraction rate. Work was then expanded to illustrate how the CPGES system can operate over a range of time scales, with the cycle duration ranging from diurnal to seasonal (Chapter 3), and over a range of duty cycles (Chapter 5), demonstrating the versatility of this system. The CPGES system was compared to the CPG system for a range of geologic conditions, and it was determined that the trade-off of the flexible energy storage system was a reduction in the net energy generated per cycle (Chapter 4 & 5). However, these energy losses could be alleviated by operating the CPG and CPGES systems concurrently in the CPG+CPGES system. The addition of the second reservoir required for the energy storage operation increases the capital cost of the system, however, the increased cost of this flexible system could be alleviated by the value that the system adds to the grid as the amount of variable renewable energy increases (Chapter 5). Lastly, the effect of the co-production of water in solution with the CO2 is considered and found to increase the generation capacity of the CPG system, a result of the higher production temperature despite the reduced CO2 mass flow rate (Chapter 6). Overall, this research has demonstrated how the CPG system can be modified to operate as an energy storage system. The impact of this work is to establish the flexibility of the CPG technology and demonstrate that captured carbon can be used to increase the penetration of renewable energy technologies onto the grid, thereby further mitigating the emission of CO2 into the atmosphere. This will enable CPG to be integrated into future renewable energy portfolios.