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- Genre: Masters Thesis
Description
Lithium titanium oxide (LTO), is a crystalline (spinel) anode material that has recently been considered as an alternative to carbon anodes in conventional lithium-ion batteries (LIB), mainly due to the inherent safety and durability of this material. In this paper commercial LTO anode 18650 cells with lithium cobalt oxide (LCO) cathodes have been cycled to simulate EV operating condition (temperature and drive profiles) in Arizona. The capacity fade of battery packs (pack #1 and pack#2), each consisting 6 such cells in parallel was studied. While capacity fades faster at the higher temperature (40°C), fading is significantly reduced at the lower temperature limit (0°C). Non-invasive techniques such as Electrochemical Impedance Spectroscopy (EIS) show a steady increase in the high-frequency resistance along with capacity fade indicating Loss of Active Material (LAM) and formation of co-intercalation products like Solid Electrolyte Interface (SEI). A two-stage capacity fade can be observed as previously reported and can be proved by differential voltage curves. The first stage is gradual and marks the slow degradation of the anode while the second stage is marked by a drastic capacity fade and can be attributed to the fading cathode. After an effective capacity fading of ~20%, the battery packs were disassembled, sorted and repackaged into smaller packs of 3 cells each for second-life testing. No major changes were seen in the crystal structure of LTO, establishing its electrochemical stability. However, the poor built of the 18650-cell appears to have resulted in failures like gradual electrolytic decomposition causing prominent swelling and failure in a few cells and LAM from the cathode along with cation dissolution. This result is important to understand how LTO batteries fail to better utilize the batteries for specific secondary-life applications.
ContributorsWadikar, Harshwardhan (Author) / Crozier, Peter (Thesis advisor) / Wang, Qing H (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2019
Description
Accurate forecasting of electricity prices has been a key factor for bidding strategies in the electricity markets. The increase in renewable generation due to large scale PV and wind deployment in California has led to an increase in day-ahead and real-time price volatility. This has also led to prices going negative due to the supply-demand imbalance caused by excess renewable generation during instances of low demand. This research focuses on applying machine learning models to analyze the impact of renewable generation on the hourly locational marginal prices (LMPs) for California Independent System Operator (CAISO). Historical data involving the load, renewable generation from solar and wind, fuel prices, aggregated generation outages is extracted and collected together in a dataset and used as features to train different machine learning models. Tree- based machine learning models such as Extra Trees, Gradient Boost, Extreme Gradient Boost (XGBoost) as well as models based on neural networks such as Long short term memory networks (LSTMs) are implemented for price forecasting. The focus is to capture the best relation between the features and the target LMP variable and determine the weight of every feature in determining the price.
The impact of renewable generation on LMP forecasting is determined for several different days in 2018. It is seen that the prices are impacted significantly by solar and wind generation and it ranks second in terms of impact after the electric load. The results of this research propose a method to evaluate the impact of several parameters on the day-ahead price forecast and would be useful for the grid operators to evaluate the parameters that could significantly impact the day-ahead price prediction and which parameters with low impact could be ignored to avoid an error in the forecast.
The impact of renewable generation on LMP forecasting is determined for several different days in 2018. It is seen that the prices are impacted significantly by solar and wind generation and it ranks second in terms of impact after the electric load. The results of this research propose a method to evaluate the impact of several parameters on the day-ahead price forecast and would be useful for the grid operators to evaluate the parameters that could significantly impact the day-ahead price prediction and which parameters with low impact could be ignored to avoid an error in the forecast.
ContributorsVad, Chinmay (Author) / Honsberg, C. (Christiana B.) (Thesis advisor) / King, Richard R. (Committee member) / Kurtz, Sarah (Committee member) / Arizona State University (Publisher)
Created2019
Description
Demand for green energy alternatives to provide stable and reliable energy
solutions has increased over the years which has led to the rapid expansion of global
markets in renewable energy sources such as solar photovoltaic (PV) technology. Newest
amongst these technologies is the Bifacial PV modules, which harvests incident radiation
from both sides of the module. The overall power generation can be significantly increased
by using these bifacial modules. The purpose of this research is to investigate and maximize
the effect of back reflectors, designed to increase the efficiency of the module by utilizing
the intercell light passing through the module to increase the incident irradiance, on the
energy output using different profiles placed at varied distances from the plane of the array
(POA). The optimum reflector profile and displacement of the reflector from the module
are determined experimentally.
Theoretically, a 60-cell bifacial module can produce 26% additional energy in
comparison to a 48-cell bifacial module due to the 12 excess cells found in the 60-cell
module. It was determined that bifacial modules have the capacity to produce additional
energy when optimized back reflectors are utilized. The inverted U reflector produced
higher energy gain when placed at farther distances from the module, indicating direct
dependent proportionality between the placement distance of the reflector from the module
and the output energy gain. It performed the best out of all current construction geometries
with reflective coatings, generating more than half of the additional energy produced by a
densely-spaced 60-cell benchmark module compared to a sparsely-spaced 48-cell reference
module.ii
A gain of 11 and 14% was recorded on cloudy and sunny days respectively for the
inverted U reflector. This implies a reduction in the additional cells of the 60-cell module
by 50% can produce the same amount of energy of the 60-cell module by a 48-cell module
with an inverted U reflector. The use of the back reflectors does not only affect the
additional energy gain but structural and land costs. Row to row spacing for bifacial
systems(arrays) is reduced nearly by half as the ground height clearance is largely
minimized, thus almost 50% of height constraints for mounting bifacial modules, using
back reflectors resulting in reduced structural costs for mounting of bifacial modules
solutions has increased over the years which has led to the rapid expansion of global
markets in renewable energy sources such as solar photovoltaic (PV) technology. Newest
amongst these technologies is the Bifacial PV modules, which harvests incident radiation
from both sides of the module. The overall power generation can be significantly increased
by using these bifacial modules. The purpose of this research is to investigate and maximize
the effect of back reflectors, designed to increase the efficiency of the module by utilizing
the intercell light passing through the module to increase the incident irradiance, on the
energy output using different profiles placed at varied distances from the plane of the array
(POA). The optimum reflector profile and displacement of the reflector from the module
are determined experimentally.
Theoretically, a 60-cell bifacial module can produce 26% additional energy in
comparison to a 48-cell bifacial module due to the 12 excess cells found in the 60-cell
module. It was determined that bifacial modules have the capacity to produce additional
energy when optimized back reflectors are utilized. The inverted U reflector produced
higher energy gain when placed at farther distances from the module, indicating direct
dependent proportionality between the placement distance of the reflector from the module
and the output energy gain. It performed the best out of all current construction geometries
with reflective coatings, generating more than half of the additional energy produced by a
densely-spaced 60-cell benchmark module compared to a sparsely-spaced 48-cell reference
module.ii
A gain of 11 and 14% was recorded on cloudy and sunny days respectively for the
inverted U reflector. This implies a reduction in the additional cells of the 60-cell module
by 50% can produce the same amount of energy of the 60-cell module by a 48-cell module
with an inverted U reflector. The use of the back reflectors does not only affect the
additional energy gain but structural and land costs. Row to row spacing for bifacial
systems(arrays) is reduced nearly by half as the ground height clearance is largely
minimized, thus almost 50% of height constraints for mounting bifacial modules, using
back reflectors resulting in reduced structural costs for mounting of bifacial modules
ContributorsMARTIN, PEDRO JESSE (Author) / Tamizhmani, Govindasamy (Thesis advisor) / Phelan, Patrick (Committee member) / Wang, Liping (Committee member) / Arizona State University (Publisher)
Created2019
Description
This is a two part thesis:
Part 1 of this thesis determines the most dominant failure modes of field aged photovoltaic (PV) modules using experimental data and statistical analysis, FMECA (Failure Mode, Effect, and Criticality Analysis). The failure and degradation modes of about 5900 crystalline-Si glass/polymer modules fielded for 6 to 16 years in three different photovoltaic (PV) power plants with different mounting systems under the hot-dry desert climate of Arizona are evaluated. A statistical reliability tool, FMECA that uses Risk Priority Number (RPN) is performed for each PV power plant to determine the dominant failure modes in the modules by means of ranking and prioritizing the modes. This study on PV power plants considers all the failure and degradation modes from both safety and performance perspectives, and thus, comes to the conclusion that solder bond fatigue/failure with/without gridline/metallization contact fatigue/failure is the most dominant failure mode for these module types in the hot-dry desert climate of Arizona.
Part 2 of this thesis determines the best method to compute degradation rates of PV modules. Three different PV systems were evaluated to compute degradation rates using four methods and they are: I-V measurement, metered kWh, performance ratio (PR) and performance index (PI). I-V method, being an ideal method for degradation rate computation, were compared to the results from other three methods. The median degradation rates computed from kWh method were within ±0.15% from I-V measured degradation rates (0.9-1.37 %/year of three models). Degradation rates from the PI method were within ±0.05% from the I-V measured rates for two systems but the calculated degradation rate was remarkably different (±1%) from the I-V method for the third system. The degradation rate from the PR method was within ±0.16% from the I-V measured rate for only one system but were remarkably different (±1%) from the I-V measured rate for the other two systems. Thus, it was concluded that metered raw kWh method is the best practical method, after I-V method and PI method (if ground mounted POA insolation and other weather data are available) for degradation computation as this method was found to be fairly accurate, easy, inexpensive, fast and convenient.
Part 1 of this thesis determines the most dominant failure modes of field aged photovoltaic (PV) modules using experimental data and statistical analysis, FMECA (Failure Mode, Effect, and Criticality Analysis). The failure and degradation modes of about 5900 crystalline-Si glass/polymer modules fielded for 6 to 16 years in three different photovoltaic (PV) power plants with different mounting systems under the hot-dry desert climate of Arizona are evaluated. A statistical reliability tool, FMECA that uses Risk Priority Number (RPN) is performed for each PV power plant to determine the dominant failure modes in the modules by means of ranking and prioritizing the modes. This study on PV power plants considers all the failure and degradation modes from both safety and performance perspectives, and thus, comes to the conclusion that solder bond fatigue/failure with/without gridline/metallization contact fatigue/failure is the most dominant failure mode for these module types in the hot-dry desert climate of Arizona.
Part 2 of this thesis determines the best method to compute degradation rates of PV modules. Three different PV systems were evaluated to compute degradation rates using four methods and they are: I-V measurement, metered kWh, performance ratio (PR) and performance index (PI). I-V method, being an ideal method for degradation rate computation, were compared to the results from other three methods. The median degradation rates computed from kWh method were within ±0.15% from I-V measured degradation rates (0.9-1.37 %/year of three models). Degradation rates from the PI method were within ±0.05% from the I-V measured rates for two systems but the calculated degradation rate was remarkably different (±1%) from the I-V method for the third system. The degradation rate from the PR method was within ±0.16% from the I-V measured rate for only one system but were remarkably different (±1%) from the I-V measured rate for the other two systems. Thus, it was concluded that metered raw kWh method is the best practical method, after I-V method and PI method (if ground mounted POA insolation and other weather data are available) for degradation computation as this method was found to be fairly accurate, easy, inexpensive, fast and convenient.
ContributorsShrestha, Sanjay (Author) / Tamizhmani, Govindsamy (Thesis advisor) / Srinivasan, Devrajan (Committee member) / Rogers, Bradley (Committee member) / Arizona State University (Publisher)
Created2014
Description
Energy can be harvested from wastewater using microbial fuel cells (MFC). In order to increase power generation, MFCs can be scaled-up. The MFCs are designed with two air cathodes and two anode electrodes. The limiting electrode for power generation is the cathode and in order to maximize power, the cathodes were made out of a C-N-Fe catalyst and a polytetrafluoroethylene binder which had a higher current production at -3.2 mA/cm2 than previous carbon felt cathodes at -0.15 mA/cm2 at a potential of -0.29 V. Commercial microbial fuel cells from Aquacycl were tested for their power production while operating with simulated blackwater achieved an average of 5.67 mW per cell. The small MFC with the C-N-Fe catalyst and one cathode was able to generate 8.7 mW. Imitating the Aquacycl cells, the new MFC was a scaled-up version of the small MFC where the cathode surface area increased from 81 cm2 to 200 cm2. While the MFC was operating with simulated blackwater, the peak power produced was 14.8 mW, more than the smaller MFC, but only increasing in the scaled-up MFC by 1.7 when the surface area of the cathode increased by 2.46. Further long-term application can be done, as well as operating multiple MFCs in series to generate more power and improve the design.
ContributorsRussell, Andrea (Author) / Torres, Cesar (Thesis advisor) / Garcia Segura, Sergio (Committee member) / Fraser, Matthew (Committee member) / Arizona State University (Publisher)
Created2022
Description
This study deals with various flow field designs for anode, cathode, and coolant plates for optimizing the performance of proton exchange membrane fuel cell using H2 and air. In particular, the 3D models with various flow field patterns such as single parallel serpentine (anode), multi parallel (anode), multi-parallel serpentine (cathode), multi serpentine (cathode) have been evaluated for enhancing the fuel cell performance at 60 oC, with three different coolant flow designs (mirror serpentine, multi serpentine and parallel serpentine). Both the peak power and limiting current density are considered based on the parameters such as temperature distribution, pressure distribution, reactants/species distribution and the membrane water content on the active area (50 cm2) region. It is interesting to note that the coolant channel also has a significant effect in regulating the fuel cell performance at high current densities, in addition to reactant gas flow channels. The simulated single cell with Nafion (thickness: 18 m) demonstrates a peak power density of 0.97 W.cm-2 with single parallel serpentine (anode), multi parallel serpentine (cathode) and serpentine (coolant) and 0.91 W.cm-2 with multi parallel (anode), multi serpentine (cathode), and parallel serpentine (coolant) flow field designs. The simulated fuel cell performance is also experimentally validated with four cells at 60 oC using H2 fuel and air as the oxidant.
ContributorsAhmed, Rafiq (Author) / Mada Kannan, Arunachala (Thesis advisor) / Torres, Cesar (Committee member) / Lin, Jerry (Committee member) / Arizona State University (Publisher)
Created2023