Renewable-powered desalination as an optimisation pathway for renewable energy systems: the case of Australia's Murray-Darling Basin

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 ofwater 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.