A 100 per cent renewable grid of solar and wind backed up by pumped hydro energy storage will eliminate the need for coal and gas, according to ANU researchers – and it will be “decisively cheaper”.

With hydro power energy storage, water is pumped uphill when energy supply is plentiful and stored to generate electricity on demand.

Lead researcher Professor Andrew Blakers from ANU said most existing coal and gas stations would retire over the next 15 years, and it would be cheaper to replace them with wind and solar PV.

Thanks to falling costs, nearly all new generation capacity in Australia is now solar and wind power, and half the world’s new generation capacity is made up of renewables. In Europe new research shows renewables were 90 per cent of all new power generation.

Wind is now cheaper than supercritical black coal and gas, and solar PV is expected to fall below the cost of fossil fuels in the next few years.

However, due to issues with intermittency, back-up power needs to be available for when the sun isn’t shining and wind isn’t blowing.

The researchers found that the cost of a 100 per cent renewable electricity system stabilised by high voltage interconnectors and pumped hydro storage would be around AU$75/MWh at 2020s prices – cheaper than gas-fuelled power, and without the emissions.

Graph: The cost of electricity ($/Megawatt-hour) from single new-build generators is approximately:

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This would eliminate Australia’s need for coal and gas-fired power, the researchers said.

“With Australia wrestling with how to secure its energy supply, we’ve found we can make the switch to affordable and reliable clean power,” Professor Blakers said.

ANU is now leading a study to map potential short-term off-river pumped hydro energy storage (STORES) sites that could help get more renewables into the grid.

STORES sites are pairs of reservoirs usually around 10 hectares in size that are separated by an altitude difference of between 300-900 metres and joined by a pipe with a pump and turbine.

ANU Research School of Engineering’s Dr Matthew Stocks said STORES needed much less water than that produced by fossil fuels and had limited impact on the environment because water was recycled between the small reservoirs.

“This hydro power doesn’t need a river and can go from zero to full power in minutes, providing an effective method to stabilise the grid,” he said.

“The water is pumped up from the low reservoir to the high reservoir when the sun shines and wind blows and electricity is abundant, and then the water can run down through the turbine at night and when electricity is expensive.”

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