Award Date

May 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering and Construction

First Committee Member

Sajjad Ahmad

Second Committee Member

Jacimaria Batista

Third Committee Member

Yahia Baghzouz

Fourth Committee Member

Haroon Stephen

Fifth Committee Member

Ashok Singh

Number of Pages

265

Abstract

Water is crucial for energy production and conversion, and energy is crucial for various water related processes including water conveyance, treatment and distribution. Sustainability of water and energy are inextricably linked with each other. Over-utilization/ degradation of these resources may occur due to limited availability of water under the changing climate scenario, growing population, and increasing pollution due to the burning of fossil fuels. The goal of the current research was to study the water-energy nexus of the Southwestern U.S. and develop approaches for solar development and treatment of drinking water. To achieve the overall objective, the work was divided into two main research tasks.

Research task 1 addressed the water demands and availability issues for utility-scale solar development in six southwestern states to meet the target goals of their renewable portfolio standards (RPS) between the years of 2015-2030. Solar energy-water nexus was analyzed for the southwestern states of Arizona, California, Nevada, Colorado, New Mexico and Utah. Estimates were gathered for water withdrawal and consumption (related to plant construction, operations, and dismantling) and land use (direct and total) for solar technologies of concentrated solar power and solar photovoltaics (PV), and harmonized through review and screening of relevant literature. Next, the estimates were incorporated into a system dynamics model to analyze water availability and usage, land availability and usage, and associated reductions in carbon emissions for utility-scale solar development in the nineteen solar energy zones (SEZs) of six southwestern states based upon the RPS during 2015-2030. Results showed that solar PV was the most appropriate technology for water-limited regions. Sufficient land was available within the 19 SEZs to meet the RPS requirements. Available water was adequate to meet RPS solar carve-out water requirements for Nevada and New Mexico. Further, solar development led to tremendous reduction in carbon emissions in the region. Contributions of this study include a greater understanding of solar energy-water nexus, especially on a local scale, which is crucial for successful implementation of energy policies, by quantifying the effects of solar land and water demands on the resources of southwestern region. The generated model may be used as a screening tool for a crude assessment of future energy planning, solar project applications, and permit approvals. For future work, the generated model can be modified to analyze the performances of renewables in addition to solar.

Research task 2 involved the application of water-energy nexus approach for treatment of drinking water, which is an energy-intensive process and essential for safeguarding public health. Environmental impacts of the nexus are carbon emissions, which were reduced by using distributed solar to fulfill the energy requirements of three drinking water treatment plants (DWTPs), located in southwestern United States. The three plants differed by capacity (10 MGD, 90 MGD, 300 MGD), raw water source (groundwater, river, lake), and unit processes involved for treatment of raw water (in-line filtration, conventional filtration, direct filtration). Energy consumption was determined for various energy driving units. This, along with the existing acreage of the plant and economic feasibility; the DWTP was sized for solar photovoltaics. System Advisor Model was used for the performance and economic analysis of the solar system. Associated reduction in carbon emissions was also estimated. Energy intensity was determined as 153.7, 165.4, and 508.1 Wh m-3 for the small, medium and large DWTP, respectively. Pumping operation was determined to be the largest consumer of electricity for all three plants and utilized about 98%, 95%, and 90% of the total energy consumption for the 10 MGD, 90 MGD and 300 MGD plant, respectively. The development of solar PV for the three treatment plants was found to be economically feasible with positive NPV, with and without battery-storage systems. However, standalone solar PV development was not profitable for the 300 MGD DWTP for offsetting the total energy consumption. Further, the economic assessment was sensitive to changes in governmental incentives and financial parameters. Existing landholdings of the plants were sufficient for solar development. Moreover, change in geographic location from the southwest to east coast US, identified governmental incentives to affect the economic feasibility of PV systems. Contributions of this study include a successful application of the water-energy nexus approach for sustainable treatment of drinking water, by offsetting the fossil-fuel based energy consumption of three existing DWTPs by means of solar development. The design equations and results for the energy consumption can be applied to other plants utilizing similar processes. With the aim of incorporating sustainability in DWTPs in the southwestern U.S., the study provides a roadmap for using solar PV for DWTPs, leading to reduction in carbon emissions, energy costs and achieving energy independence.

Keywords

Energy consumption of drinking water treatment; Energy water land nexus; Solar development in United States; Technical economic feasibility of photovoltaics; Water and land demands for utility scale solar development

Disciplines

Civil Engineering

Language

English


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