This study presents a simulation of low-carbon electricity supply for Australia, contributing new knowledge by demonstrating the benefits of load shifting in residential buildings for downsizing renewable electricity grids comprising wind, hydro, biomass, and solar resources. The load-shifting potential for the whole of Australia is estimated, based on air-conditioner load data and an insulation model for residential buildings. Load shifting is applied to enable transferring residential airconditioner load from peak to off-peak periods, assuming that air-conditioners can be turned-on a few hours ahead of need, during periods where demand is low and renewable resource availability is high, and turned-off during periods of high demand and low resource availability. Thus, load shifting can effectively reduce installed capacity requirements in renewable electricity grids. For 1 h load shifting of residential air-conditioners, Australian electricity demand can be met at the current reliability standards by 130 GW installed capacity, at cost around 12.5 ¢/kWh, and a capacity factor of 32%. The installed capacity can be further reduced by increasing the number of hours that loads can be shifted. The findings suggest that the application of load shifting in residential buildings can play a significant role for power networks with high renewable energy penetration.

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The ecology in the Murray-Darling Basin in Australia is threatened by water scarcity due to climate change and the over-extraction and over-use of natural water resources. Ensuring environmental flows and sustainable water resources management is urgently needed. Seawater desalination offers high potential to deliver water in virtually unlimited quantity. However, this technology is energyintensive. In order to prevent desalination becoming a driver of greenhouse gases, the operation of seawater desalination with renewables is increasingly being considered. Our study examines the optimisation of the operation of a 100% renewable energy grid by integrating seawater desalination plants and pipelines as a variable load. We use a GIS-based renewable energy load-shifting model and show how both technologies create synergy effects. First, we analyse what quantity of water is missing in the basin in the long run. We determine locations for seawater desalination plants and pipelines to distribute the water into existing storages in the Murray-Darling Basin. Second, we design a pipeline system and calculate the electricity needed to pump the water from the plants to the storages. Third, we use the combined renewable energy load-shifting model. We minimise the total cost of the energy system by shifting energy demand for water production to periods of high renewable energy availability. Our calculations show that in such a system, the unused spilt electricity can be reduced by at least 27 TWh. The electricity system's installed capacity and levelised cost of electricity can be reduced by up to 29%, and 43% respectively. This approach can provide an annual net economic benefit of $22.5 bn. The results illustrate that the expansion of seawater desalination capacity for loadshifting is economically beneficial. Abbreviations GISGeographic information system LCOE Levelised cost of electricity MDB Murray-Darling Basin MDBA Murray-Darling Basin Authority RE Renewable energies RO Reverse osmosis SDL Surface-water diversion limit SWRO Seawater reverse osmosis

Summary A low‐carbon electricity supply for Australia was simulated, and the installed capacity of the electrical grid was optimized by shifting the electricity demand of residential electric water heaters (EWHs). The load‐shifting potential of Australia was estimated for each hour of the simulation period using a nationwide aggregate EWH load model on a 90 × 110 raster grid. The electricity demand of water heaters was shifted from periods of low renewable resource and high demand to periods of high renewable resource and low demand, enabling us to effectively reduce the installed capacity requirements of a 100%‐renewable electricity grid. It was found that by shifting the EWH load by just 1 hour, the electricity demand of Australia could be met using purely renewable electricity at an installed capacity of 145 GW with a capacity factor of 30%, an electricity spillage of 20%, and a generation cost of 15.2 ¢/kWh. A breakdown of the primary energy sources used in our scenario is as follows: 43% wind, 29% concentrated solar thermal power, and 20% utility photovoltaic. Sensitivity analysis suggested that further reduction in installed capacity is possible by increasing the load‐shifting duration as well as the volume and insulation level of the EWH tank.