A systems approach to assessing the sustainability of hybrid community energy systems.

Abstract

The goal to achieve a sustainable society that will endure over the long term is generally regarded as a positive evolutionary course. One of the challenges with this goal is developing a quantitative assessment of the sustainability of a system. Despite the different measures available in the literature, a standard and universally accepted index for assessing sustainability does not yet exist. This thesis develops a novel Integrated Sustainability Index (ISI) for energy systems that considers critical multidimensional sustainability criteria. The originality of this new index is that it incorporates fundamental thermodynamic, economic, and environmental constraints to combine indicators from multiple dimensions into a single-score evaluation of sustainability. The index is therefore unique because it can assess sustainability relative to an ideal reference state instead of being limited to ranking systems via relative assessments. The ISI of an energy system is determined by normalization, weighting, and aggregation of sustainability indicators. Indicators are normalized relative to sustainable threshold values and weighted based on time, space, and receptor (i.e., human or ecosystem impacts) criteria. Aggregation yields an ISI between zero and one, where one represents a sustainable system. The ISI is calculated for several different case studies spanning a range of fossil- and renewable-based energy systems. Each is designed as a stand-alone system to meet the energy needs of a small community in Southern Ontario. The analysis shows that of the various alternatives, a solar-photovoltaichydrogen system has the best ISI, which ranges from 0.65-0.90 and is a 4-25% improvement over the reference, gas-fired system. For the solar-photovoltaic-hydrogen system and many others, climate change and ozone layer depletion indicators have the strongest effect on ISI. Affordability, commercial viability, and land area indicators are also critical for other energy systems. The ISI is expected to prove useful as a high-level, multi-criteria decision analysis tool for understanding and fostering sustainable energy systems, alone or in concert with other approaches.