Hydro energy is making again headlines in Australia - and not only because of the Government's planned expansion of the Snowy Hydro scheme. The public's attention is also increasingly set on the potential of other pumped hydro storage options across Australia.
In February, the South Australian Government announced grants worth $8.7 million for studies testing the feasibility of pumped hydro power plants in the state's Upper Spencer Gulf.
The projects by Altura Group, Rise Renewables, EnergyAustralia and GFG Alliance are based on reservoirs and disused mines near Whyalla, Port Augusta and Port Germein.
If progressed, their construction will together cost around $1.5 billion to then add 750 megawatt generation capacity to the South Australian electricity grid.
Pumped hydro storage of renewable energy could find more general use in Australia, according to a study from the Australian National University that identified 22,000 potential pumped hydro energy storage sites across the country.
The Atlas of Pumped Hydro Energy Storage Study indicates that the potential capacity of these sites could well exceed what is needed in Australia to support a 100% renewable electricity system (see our story Storage potential).
Pumped hydro storage systems are the most mature electrical energy storage systems available, chief scientist Dr Alan Finkel noted in his recent review of the National Electricity Market.
So far, the focus has been on inland freshwater systems, and there is indeed only one international example for a large-scale seawater system, a 30MW facility in Okinawa, Japan.
But a feasibility study released in September last year by the Australian Renewable Energy Agency (ARENA) has given a first green light to a seawater pumped hydro project by Energy Australia and consortium partners Arup Group and Melbourne Energy Institute at Cultana in South Australia's Spencer Gulf.
Compared to freshwater systems, there are significant challenges to be overcome, though. This includes biofouling, the potential for corrosion and additional construction costs associated with the marine environment.
While addressing these problems will result in higher capital cost, the project was found technically feasible, and economically viable under a range of plausible scenarios.
The study determined an optimal capacity of the project at 225 megawatt (MW) of electricity generation and 1770 MWh of power storage.
The plant could be constructed and operational by 2023 and is estimated to cost $477 million to build. With a capital cost of just over $2.1 million per megawatt capacity, storage would be around the third of the cost of batteries.
Importantly, the technology could also be widely deployed across Australia, the report says.
With the partial release of the Snowy 2.0 feasibility study last year, the Australian Government received some backing for its plan to expand the Snowy Hydro project, although, as with other mega infrastructure projects, such as the National Broadband Network, major cost blow-outs may be on the horizon.
If realised the Snowy 2.0 will have a capacity of generating 2000 megawatt of electricity, and storing the equivalent of 350,000 megawatt hours.
However, the project is now estimated to require investment of between $3.8 billion and $4.5 billion, more than twice the amount originally forecast by the Government. According to Snowy Hydro's $29 million feasibility study, the project's potential benefits would still far exceed its estimated costs.
The project "is expected to be economic, technically feasible and financeable".
But experts are already lining up warning that the real costs of the project could be much higher.
Monash University engineering lecturer Roger Dargaville told Fairfax Media that the all-in cost of the project could be as much as $6 billion or $7 billion, once transmission upgrades to transport the stored energy were taken into account.
The construction involves building an underground hydro-electric power station, and 27 kilometres of tunnels connecting two existing reservoirs in the Snowy Mountains, the Talbingo dam at 552 metres and the Tantangara reservoir at 1,233 metres.
The project is estimated to take around seven years to build, and then would use cheap off-peak energy to pump water into the upper Tantangara reservoir. Water flowing downhill and driving an electricity generator could then produce up to 2000 megawatts in additional power at times of peak demand.
This is meant to help the electricity network coping with volatility and intermittency that are associated with the increasing energy generated from renewable energy sources such as wind and solar.
Snowy 2.0 would have the capability to run for over seven days continuously, or 15 days during the peak period, before having to be 'recharged'.
The strengths of the project are its scale and centralised location, and that it can draw on existing infrastructure.
Importantly, the study concludes that if Snowy 2.0 is not built, the increased demand of energy storage would have to be met by alternative technologies, such as batteries at materially greater costs.