Assessment of the life cycle-based environmental impacts of New Zealand electricity : a thesis presented in partial fulfilment of the requirements for the degree of Master in Environmental Management at Massey University, Palmerston North, New Zealand

Abstract

The life cycle-based environmental impacts of New Zealand electricity arise from the different energy generation systems used to provide electricity to the national grid, and construction, maintenance and operation of the national electricity transmission and distribution system. Due to the high share of hydropower in the New Zealand electricity mix, base load electricity is rainfall dependent and its variable supply is balanced by generation from fossil fuelled power plants, geothermal, and to a lesser extent from wind, biogas and biomass power. This temporal variability of energy sources in the mix changes the Life Cycle Assessment (LCA) results for New Zealand electricity when the environmental impacts are assessed over different time periods. Therefore, this research had two main objectives: to conduct an LCA of electricity generation, and to assess the influence of temporal variation in the electricity mix on LCA results. Using the ecoinvent v 3.1 database and New Zealand-specific data, an LCA model of electricity generation and use was developed for the year 2013. The LCA results, using the CML 2001 – Apr. 2013 impact assessment method, showed that coal and natural gas power plants contributed 10 to 90 % in all impact categories. Electricity transmission and distribution (T&D) infrastructure contributed more than 50 % of the result for Abiotic Depletion Potential (ADP), Terrestrial Ecotoxicity Potential (TETP) and Human Toxicity Potential (HTP) impact categories. The Climate Change Potential (CCP) for 1 kWh of low-voltage electricity was 186 g CO2-eq; for high and medium-voltage electricity, the CCP results were 172 and 176 g CO2-eq per kWh respectively. To investigate the variability in LCA results over different time periods 3, 5 and 10 year moving averages (MAVG) were calculated; as expected, the variability decreased as the time period increased. The analysis showed that the 10 MAVG was associated with the lowest variability in LCA results. However a 10 MAVG will not reflect changes in installed power plant capacity. Therefore for attributional LCA studies of products using electricity over a year-to-year time frame, a representative average of the electricity mix or a 3, 5, or 10 year MAVG can be used as long as there are no changes in installed power plant capacity. This information aids New Zealand´s electricity industries understand environmental impacts associated with transitions to renewable energy technologies and meet greenhouse gas reduction targets.