Many utility-scale solar farms use horizontal single axis tracking to follow the sun throughout the day and produce more energy. Solar farms on skewed topography produce complex shading patterns that require precise modeling techniques to determine the energy output. To accomplish this, MATLAB was used in conjunction with NREL weather predictions to predict shading shapes and energy outputs. The MATLAB models effectively predicted the sun’s position in the sky, panel tilt angle throughout the day, irradiance, cell temperature, and shading size. The Cal Poly Gold Tree Solar Farm was used to validate these models for various lengths of time. First, the models predicted the shading and power output for a single point in time. Four points of time measurements were taken; resulting in 6 to 32 percent difference in shade height, 5 to 60 percent difference for shade length, and 29 to 59 percent difference for power output. This shows the difficulty of predicting a point in time and suggests the sensitivity of numerous variables like solar position, torque tube position, panel tilt, and time itself. When predicting the power over an entire day, the power output curves for a single inverter matched almost exactly except for in the middle of the day due to possible inaccurate cell temperature modeling or the lack of considering degradation and soiling. Since the backtracking region of the power curve is modeled accurately, the optimization routine could be used to reduce interrow shading and maximize the energy output for a single zone of the solar field. By assuming every day is sunny, the optimization routine adjusted the onset of backtracking to improve the energy output by 117,695 kilowatt hours for the year or 8.14 percent compared to the nominal settings. The actual solar farm will likely never see this increase in energy due to cloudy days but should improve by a similar percentage. Further optimization of other zones can be analyzed to optimize the entire solar field.

Phase change material (PCM)-based ocean thermal energy harvesting is a relatively new method, which extracts the thermal energy from the temperature gradient in the ocean thermocline. Its basic idea is to utilize the temperature variation along the ocean water depth to cyclically freeze and melt a specific kind of PCM. The volume expansion, which happens in the melting process, is used to do useful work (e.g., drive a turbine generator), thereby converting a fraction of the absorbed thermal energy into mechanical energy or electrical energy. Compared to other ocean energy technologies (e.g., wave energy converters, tidal current turbines, and ocean thermal energy conversion), the proposed PCM-based approach can be easily implemented at a small scale with a relatively simple structural system, which makes it a promising method to extend the range and service life of battery-powered devices, e.g, autonomous underwater vehicles (AUVs). This dissertation presents a combined theoretical and experimental study of the PCM-based ocean thermal energy harvesting approach, which aims at demonstrating the feasibility of the proposed approach and investigating possible methods to improve the overall performance of prototypical systems. First, a solid/liquid phase change thermodynamic model is developed, based on which a specific upperbound of the thermal efficiency is derived for the PCM-based approach. Next, a prototypical PCM-based ocean thermal energy harvesting system is designed, fabricated, and tested. To predict the performance of specific systems, a thermo-mechanical model, which couples the thermodynamic behaviors of the fluid materials and the elastic behavior of the structural system, is developed and validated based on the comparison with the experimental measurement. For the purpose of design optimization, the validated thermo-mechanical model is employed to conduct a parametric study. Based on the results of the parametric study, a new scalable and portable PCM-based ocean thermal energy harvesting system is developed and tested. In addition, the thermo-mechanical model is modified to account for the design changes. However, a combined analysis of the results from both the prototypical system and the model reveals that achieving a good performance requires maintaining a high internal pressure, which will complicate the structural design. To mitigate this issue, the idea of using a hydraulic accumulator to regulate the internal pressure is proposed, and experimentally and theoretically examined. Finally, a spatial-varying Robin transmission condition for fluid-structure coupled problems with strong added-mass effect is proposed and investigated using fluid structure interaction (FSI) model problems. This can be a potential method for the future research on the fluid-structure coupled numerical analysis of AUVs, which are integrated with and powered by the PCM-based thermal energy harvesting devices. / Doctor of Philosophy / The global ocean, which covers about 71% of the Earth’s surface, absorbs a great amount of heat from the sunshine everyday, making it a reliable and renewable source of thermal energy. Also, the temperature of the ocean water varies with depth, which provides a necessary condition (i.e, a temperature gradient) to extract the thermal energy. If harvested and converted into electrical energy using small scale portable devices, the ocean thermal energy can be a potential energy resource to provide power for autonomous underwater vehicles (AUVs), which are conventionally powered by on-board rechargeable batteries. To this end, this dissertation presents a study of using solid/liquid phase change materials (PCMs) to extract thermal energy from the temperature gradient in the ocean. The basic idea is to use the warm surface water and deep cold water to melt and freeze the PCM cyclically. In the meantime, the volume of PCM will expand and contract accordingly. Therefore, a turbine generator can be driven by the volume expansion in the melting process, thereby converting a fraction of the absorbed thermal energy into electrical energy. This study includes four key aspects. First, to evaluate the theoretical full potential of the PCM-based approach, a solid/liquid phase change thermodynamic model – which represents an idealized energy harvester – is developed. Based on the thermodynamic model, an upperbound of the thermal efficiency is derived. Secondly, two prototypical systems, as well as a thermo-mechanical model which can predict the performance of specific designs, are developed. Third, for the purposes of performance improvement and pressure regulation, the latter of which is associated with the structural safety, a hydraulic accumulator is added to the existing system and its effects are examined using both experimental and theoretical methods. Finally, a computational method is proposed and demonstrated, which can be a potential tool for the design of PCM-based ocean thermal energy harvesting systems when they are integrated with exiting AUVs.

This dissertation examines the employment impacts of investments in renewable energy and energy efficiency in the U.S. A broad expansion of the use of renewable energy in place of carbon-based energy, in addition to investments in energy efficiency, comprise a prominent strategy to slow or reverse the effects of anthropogenic climate change. This study first explores the literature on the employment impacts of these investments. This literature to date consists mainly of input-output (I-O) studies or case studies of renewable energy and energy efficiency (REEE). Researchers are constrained, however, by their ability to use the I-O model to study REEE, since currently industrial codes do not recognize this industry as such. I develop and present two methods to use the I-O framework to overcome this constraint: the synthetic and integrated approaches. In the former, I proxy the REEE industry by creating a vector of final demand based on the industrial spending patterns of REEE firms as found in the secondary literature. In the integrated approach, I collect primary data through a nationwide survey of REEE firms and integrate these data into the existing I-O tables to explicitly identify the REEE industry and estimate the employment impacts resulting from both upstream and downstream linkages with other industries. The size of the REEE employment multiplier is sensitive to the choice of method, and is higher using the synthetic approach than using the integrated approach. I find that using both methods, the employment level per $1 million demand is approximately three times greater for the REEE industry than for fossil fuel (FF) industries. This implies that a shift to clean energy will result in positive net employment impacts. The positive effects stem mainly from the higher labor intensity of REEE in relation to FF, as well as from higher domestic content and lower average wages. The findings suggest that as we transition away from a carbon-based energy system to more sustainable and low-carbon energy sources, approximately three jobs will be created in clean energy sectors for each job lost in the fossil fuel sector.

The increasing frequency of extreme weather events is a consequence of changing climate. The direct physical causes are carbon dioxide emissions from the intensive use of fossil fuels and accelerated soil and plant decomposition from alterations in land use. Efforts to avoid a global environmental calamity and engineer a shift towards a more sustainable path are at the forefront of global agenda. However, beyond all the commitments and good intentions, there is no consensus on what constitutes sustainability, the requirements for a power transition towards a post-carbon era, or the energy resources available to achieve economic goals. This dissertation aims to clarify the relationship between energy and sustainability. We begin with a review of capacity factors for the leading power technologies at a global and regional scale to understand performance of these technologies and their potential. To address the challenge of evaluating sustainability, we propose a new approach, the eight-dimensional sustainability octagon. This approach broadens the fundamental pillars of sustainability (social, environmental, and economic), and provides a simple yet robust tool for comparing the sustainability of countries on the Earth. This analysis shows that the world is performing at one-third of achievable sustainability levels. Afterwards, we assess current global energy mix from a primary power perspective and estimate energy savings from- and limitations of electrification. We evaluate the power requirements, nominal power to be installed, infrastructure needs, and carbon dioxide emissions associated with replacing current fossil electricity generation mix with renewables. This evaluation indicates that complete decarbonization of the global power mix is impossible by 2050, and electrification could further delay decarbonization. At a single country level (case study), we analyze connections between the ongoing energy-environmental crisis and population growth to assess the feasibility of achieving the government of Rwanda’s developmental goals, given available power resources. We evaluate Lake Kivu in Rwanda as a complex methane source and energy system. We assess the implicit risks and environmental impacts of large-scale methane production to generate electricity. From our analysis, Rwanda is overpopulated, and the available energy resources can only secure low incomes for the population.

Texas is the leading producer of renewable energy in the U.S, and Dallas-Fort Worth (DFW) is the largest metropolitan area in the state. Texas has a deregulated energy market, with three types of providers: privatized, public-owned, and co-operatives. Privatized providers compete in the deregulated market, and consumers choose between hundreds of electricity retailers. Public-owned providers are owned by the municipality, and electricity consumers that live within the city limits must use the municipal provider. Electric co-operatives operate similarly where customers within the region must use the co-operative, but instead of being owned by the city, co-ops are owned by the members (customers). To date, the availability, cost, accessibility, and outreach of renewable electricity among these provider types remains unclear. For this reason, my research examines the renewable energy market in DFW by asking: (1) Who has access to renewable energy and how do they understand it? (2) How do electricity retailers distribute and make renewable energy available? and (3) If consumers can choose their provider, why do they select certain electricity plans over others? My findings suggest that while many consumers want or are open to using renewable energy, uncertainties surrounding how to find or choose a provider, price, and lack of information about renewables are obstacles for consumers to access renewable energy. Additionally, while renewable energy is widely distributed in the region, there are disparities in renewable energy options.

In several areas around the world, clean water is a precious asset that at anytime, and mainly due to circumstances of weather and climate, can become scarce. Mainly in the dry and remote places, people suffer with lack of water. A solution for this suffering can be a water desalination system, which makes water potable and usable for industry. That solution inherently, brings the problem of power requirement, which is sometimes arduous to accomplish in such remote areas of difficult access and long distances to overcome to build the infrastructure required to operate an electric power plant. Texas and the USA also face this scenario for many regions, for which the government has been creating some programs and driving forward incentives, looking for solutions to support water desalination. Water desalination has future applications for municipalities water-consuming or for arid and remote regions, as well as for industries that rely on heavy water usage, such as natural gas drilling operations, for which millions of gallons are trucked overland to the site and also hauled away afterwards, when the waste water produced must be treated. This thesis created the concept of autonomy for water desalination plants replacing the actual power supply from fossil fuel to a renewable source from wind or sun, giving capacity to them to produce its own electricity to operate as an autonomous unit, as demonstrated in the business case done for the Brownsville water desalination facility.

学位プログラム名: 京都大学大学院思修館 / 京都大学 / 0048 / 新制・課程博士 / 博士(総合学術) / 甲第21232号 / 総総博第4号 / 新制||総総||1(附属図書館) / 京都大学大学院総合生存学館総合生存学専攻 / (主査)教授 池田 裕一, 教授 IALNAZOV Dimiter Savov, 教授 諸富 徹 / 学位規則第4条第1項該当 / Doctor of Philosophy / Kyoto University / DFAM

学位プログラム名: 京都大学大学院思修館 / 京都大学 / 0048 / 新制・課程博士 / 博士(総合学術) / 甲第22611号 / 総総博第11号 / 新制||総総||2(附属図書館) / 京都大学大学院総合生存学館総合生存学専攻 / (主査)教授 IALNAZOV Dimiter Savov, 教授 山敷 庸亮, 特定教授 高島 宏明, 教授 大垣 英明 / 学位規則第4条第1項該当 / Doctor of Philosophy / Kyoto University / DFAM

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