Pumped hydroelectricity storage (PHES) using freshwater is the most common form of grid connected energy storage in the world, accounting for around 97% of the total. Due to fresh water constraints Arup in collaboration with Melbourne Energy Institute (MEI) undertook research into using seawater instead, funded by Arup’s Global Research Challenge in 2014.
The study found that as an alternative to using natural valleys, there is potential in Australia to construct artificial reservoirs, known as “turkey-nest” type dams, for PHES service. Further, the study found that coastal seawater PHES, which uses the ocean as the lower reservoir, may have economic application in Australia.
The study identified a number of example sites in South Australia and scoping-level capital cost estimates for seawater “turkey-nest” type PHES facilities could be as low as A$100,000/MWh to A$200,000/MWh.
The right solution at the right time
South Australia has been experiencing energy storage and grid stability problems with state-wide black-outs in late 2016/17. Having seen the research, EnergyAustralia, one of Australia’s largest and oldest gas and electricity supply companies, recognised the potential for this new technology to help solve South Australia’s energy issues. A consortium, including Arup, MEI and EnergyAustralia are now undertaking a feasibility study for a PHES project with the support of State and Federal Government, including the Prime Minister’s office.
If the results of the feasibility study are positive, a 100-250 MW PHES may be built on a site near the tip of the Spencer Gulf in South Australia. It would help the South Australian electricity market vary their output in response to changes in demand. Having it connected to PHES allows storage during low demand and additional generation during high demand, allowing the combination of technologies to provide flexible, reliable and cost effective electricity.
It could also mean that more of the ideal renewable wind and solar generation resources can be deployed and tapped to provide renewable energy for the pumping cycle of this grid scale storage technology, further reducing the states carbon footprint.
Australia already has a three PHES facilities, but the market that is most in need of grid-scale energy storage at the moment in South Australia. However, South Australia lacks the rainfall, rivers and mountains that are required to run a typical hydro system, with or without storage.
Arup suggested that a novel way to use this technology when you don’t have access to fresh water rivers is to use the ocean as the lower reservoir.
An upper reservoir needs to be built, but it doesn’t require a river to fill it with fresh water, it just needs to have an upper reservoir at a significantly higher level than the coast.
To date, globally only one example of this seawater PHES technology has been built, in Okinawa, Japan. The storage system proved to be a perfect partner for the islands requirements, providing peak power above the capacity of generators during the evening periods. However the proposed South Australian PHES project will be significantly larger and use a combination of renewable energy from wind and solar farms to provide low cost, reliable base load renewable power to the grid.