Just weeks after spruiking the merits of "clean coal" generation, there is surprise at the scale of the Prime Minister's pumped hydro plans among academics who study reducing emissions in the electricity industry.

Tim Forcey, a 35-year veteran of the power sector, warned the new Snowy Mountains scheme could turn out to be "the most expensive pumped hydro that anyone could conceive" unless its real objective is actually to support a fully-renewable electricity grid.

And Professor Andrew Blakers from the Australian National University said the $2 billion idea would be cost-effective because it would effectively make solar and wind a "baseload" source by ironing out shortfalls and providing power at peak times.

Professor Blakers, who last month published an analysis on the move to 100 per cent renewables, said Mr Turnbull's 2000 megawatt pumped hydro energy storage scheme would need to be replicated nine times across Australia to preclude the need for any fossil fuel-based power generation, including gas.

Two-thirds of Australia's fossil fuel-powered electricity generators are due to be decommissioned by 2036 and he said the move to a mix of photovoltaic systems - known as solar PV - and wind generation can replace them without any disruption.

"I don't think people realise just how advanced the solar and wind revolution is. Half the new generation capacity around the world is solar PV and wind and in Australia the only new generation is solar PV and wind," he said.

The output of new renewable power due to commence in 2017 will more than replace the loss to the grid of the Hazelwood brown coal power station in Victoria's La Trobe Valley.

Mr Turnbull has not suggested any shift in the government's timetable towards a green grid, with the Renewable Energy Target set at reducing emissions to 26-28 per cent on 2005 levels by 2030.

Mr Forcey, who is an adviser at Melbourne University's Energy Institute, said Mr Turnbull's Snowy Hydro scheme only makes sense if it is intended to support a renewable-only grid.

Most new pumped hydro systems use two closely located ponds to provide a short burst of power for peak demand but the Snowy system will move water as far as 25-30 kilometres between dams and have enough storage for a week's power generation - the type of back-up needed for renewables when weather conditions let generators down.

"I'm concerned this Snowy Hydro thing could end up being the most expensive pumped hydro that anyone could conceive," said Mr Forcey who used to work for industry regulator, the Australian Energy Market Operator.

"That said, when you eventually move to high-penetration of renewables, it looks like it makes perfect sense."

Mr Turnbull has not confirmed any plans to speed the transformation to green power.

"I'm not interested in ideology or politics on this. What I want is economics and engineering to deliver secure and affordable power for Australian families, keep downward pressure on prices, make sure the lights stay on and deliver the power that we need for businesses that supports millions of jobs," he said.

The sense in proceeding with new pumped hydro in the Snowy Mountains appeared to be called into question by a 2013 AEMO report but on Friday the regulator did an about-face on its findings.

The 2013 report backed concentrated solar thermal as the best renewable option and said pumped hydro was "uneconomic".

"The modelling included existing pumped hydro, but no additional pumped hydro was added to the mix as the modelling found it to be an uneconomic option," AEMO said in 2013.

But a spokesman said things had moved on significantly from that time.

"Given the significant transformation of the energy sector since the publication of our 2013 report, it is AEMO's view that there can be no correlation made between our statements relating to pumped hydro in the 2013 report, and the recent announcement by the federal government relating to Snowy Hydro 2.0," he said.

Solar thermal, geothermal and biogas, identified in the report as playing a role, had not attracted the investment anticipated, he said.

"The modelling in the 2013 report only looked at the development of new hydro facilities - not the extension of existing, such as what has been proposed by the federal government," he said.

Mr Turnbull's office rejected comparisons with the 2013 report because it was based on the premise of a 100 per cent renewable energy target.

The Australian Energy Council, which represents electricity generators, welcomed the Snowy Hydro 2.0 announcement.

"As more intermittent renewable generation is built the importance of power storage and backup energy supply systems will only increase", said chief executive Matthew Warren.

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