Date of Award

8-3-2017

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

First Advisor

Carriveau, Rupp

Second Advisor

Ting, David

Keywords

Buoyancy, Energy Storage, Offshore, Renewable Integration

Abstract

The present document is a manuscript-based dissertation covering Kyle Bassett’s PhD research from January, 2015 to January 2017. The research was particularly focused on studying and developing an emerging energy storage technique known as Buoyancy Battery Energy Storage (BBES). The buoyancy energy storage technique is presented and primary components are described and discussed. An idealized system was analyzed to determine governing equations of operation as well as ideal energy storage density. Experimental analysis was conducted to confirm properties of constant discharge force with respect to both float position and storage duration. Discharge testing was conducted with a developed scale system installed in the offshore testing tank and the University of Windsor. To evaluate the scalability of the technique, a utility scale BBES system was designed with power output capacity of 1 MW and energy storage capacity of 1MWh. Several commercially available marine lift bags were considered and evaluated for volume requirements and drag effects at various float speeds. Theoretical roundtrip efficiency for this designed system was found to be 83% based on results from drag calculations, pulley losses and electrical efficiency losses. Numerical simulations of system performance were completed to determine the revenue generation of the designed system based on 2015 Ontario market energy prices. To validate system operation in a marine environment, open water testing was conducted in Lake Huron. Testing validated surface deploy ability and steady state float motion was achieved. To further investigate the market opportunities and challenges facing the grid scale integration of energy storage, an analysis of market conditions was performed using Ontario, Canada as a case study. Ten years of Hourly Ontario Energy Price was analyzed using Fourier transform to reveal periodic trends within the data. It was found that the introduction of Time-of-use billing for electricity was effective in changing energy consumption behavior, improving balance for the electricity grid. Revenue generation simulations were completed for utility scale energy storage systems of various technologies (and thus various roundtrip efficiencies) using historic 2015 energy price data. Simulations included single and multi-cycle storage programs. It was determined that energy storage facilities are not currently financially viable, due to the minimal revenue produced through energy arbitrage transactions. The development of energy storage in Ontario will depend greatly on governmental subsidies and additional revenue-generating ancillary services such as regulation and black start capability. Additional experimental analysis was performed using a modified BBES system designed to convert input energy into mechanical work such that each quantity could be controlled and measured. Three float shapes of interest were tested including a horizontally configured cylinder, a vertically configured cylinder as well as a sphere. Discharge efficiencies greater than 90% were achieved. Roundtrip efficiencies of 78% were recorded. Results suggest that with improved conversion pulleys and component scaling, experimental roundtrip efficiencies should approach the theoretical efficiency used in the 1 MW BBES system designed.

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