An Exergy Analysis of the New Zealand Energy System

Abstract

Exergy analysis has been shown to be a valuable method of assessing energy use on a national scale. Exergy analysis measures the work potential of mass and energy flows, and therefore more accurately identifies areas with potential for improvement. This thesis presents an exergy analysis of the New Zealand energy system. Exergy flows, from resource inputs through transformation to output end-use, are calculated and presented in Sankey diagrams. Exergy flows for the total energy system, each resource category and each sector of the economy are presented. Exergy efficiencies are calculated from these flows. Energy flows and energy efficiencies are also presented for comparison. The total exergy efficiency for NZ is 22% and energy efficiency is 38%. Results show the transportation, residential, and commercial end-use sectors have the largest exergy losses. In transportation, the losses arise from the inefficiency of the conversion of chemical fuels to motive force in internal combustion engines. In the commercial and residential sectors the losses arise from the use of high exergy sources for low temperature space and water heating. This second loss would not be captured in an energy analysis. Another significant finding is the large impact of geothermal energy resources on the analysis. Geothermal energy currently makes up 26% of NZ total primary energy resources. Energy analysis does not account for the work potential in geothermal resources used for electricity generation, and therefore over estimates the potential of the geothermal resource. Due to the large percentage of geothermal in New Zealand’s energy system, this has a significant impact on overall results. Policy implications of these finding are discussed including a proposal to evaluate New Zealand’s energy productivity, the ratio of economic outputs to energy inputs, based on exergy rather than energy inputs to more accurately account for geothermal resources.