Date of Award

Spring 1-1-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical, Computer & Energy Engineering

First Advisor

Alan Mickelson

Second Advisor

Frank Barnes

Third Advisor

Sean Shaheen

Abstract

Deterioration and capacity fade, i.e. ageing, of Lithium Ferro Phosphate(LFP) cells, a thermally stable Lithium chemistry with promise for Energy Storage System (ESS) applications, is typically protracted through laboratory measurements such as Electrochemical Impedance Spectroscopy or full charge and discharge cycles with accompanying Coulomb counting. When installed in remote microgrid stations such as intermediary sites of a communications system, these measurements are often not possible, which makes the identification and quantification of deterioration challenging for LFP batteries deployed in real world settings. Herein lies the impetus to identify and extract other metrics indicating ageing from the operational profiles of remote LFP installations.

The University of Colorado testbed is a Wifi Long Distance network funded by the IEEE Smart Villages group and located on the front range of Colorado. Each station is outfitted with an isolated microgrid consisting of LFP batteries and Solar PV panels, as well as a microcontroller system taking current, voltage, and temperature measurements at a five second resolution. After a collection period spanning 7 months (April - October, 2017), this data is analyzed and Schedule Points representing 100 % State of Charge are identified. The Coulombic and Battery Energy efficiency, that is, the ratio of charge delivered verse charge recovered and the ratio of energy delivered verse energy recovered, respectively, of each cycle is then derived and further analysis is performed to identify any ageing trends. While a quantiable amount of ageing and further statements about the State of Health are not possible without further analysis, a clear decline in efficiencies representing ageing is indentified, establishing a basis for further work to quantify these metrics.

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