Security of supply, energy spillage control and peaking options within a 100% renewable electricity system for New Zealand

In this paper, issues of security of supply, energy spillage control, and peaking options, within a fully renewable electricity system, are addressed. We show that a generation mix comprising 49% hydro, 23% wind, 13% geothermal, 14% pumped hydro energy storage peaking plant, and 1% biomass-fuelled generation on an installed capacity basis, was capable of ensuring security of supply over an historic 6-year period, which included the driest hydrological year on record in New Zealand since 1931. Hydro spillage was minimised, or eliminated, by curtailing a proportion of geothermal generation. Wind spillage was substantially reduced by utilising surplus generation for peaking purposes, resulting in up to 99.8% utilisation of wind energy. Peaking requirements were satisfied using 1550 MW of pumped hydro energy storage generation, with a capacity factor of 0.76% and an upper reservoir storage equivalent to 8% of existing hydro storage capacity. It is proposed that alternative peaking options, including biomass-fuelled gas turbines and demand-side measures, should be considered. As a transitional policy, the use of fossil-gas-fuelled gas turbines for peaking would result in a 99.8% renewable system on an energy basis. Further research into whether a market-based system is capable of delivering such a renewable electricity system is suggested.