Prime Minister Malcolm Turnbull makes a return visit to Snowy Hydro in August. Credit:Alex Ellinghausen The Prime Minister such a favourable response in March when he revealed uncosted plans to increase the storage capacity of the Snowy Mountains Hydro-Electricity Scheme by 2000 megawatts – almost a 50 per cent expansion of its 4100 MW total – that he's been back for more photo opportunities since. And no wonder. Few of the Turnbull's announcements have drawn such praise. Building on the "romantic memories" of the "iconic" Snowy scheme, it was applauded as "the kind of plan the whole country could get behind". The "2.0" upgrade is supposed to exploit untapped potential for pumped hydro storage, a concept seemingly so simple, it begs the question why it hadn't been done before. Pumped hydro is effectively a recycling loop. Water is released from a higher reservoir through a turbine to generate electricity during times of high demand and high prices, before being collected in a lower dam.

The Snowy Hydro Scheme at Talbingo Reservoir, potentially part of Snowy 2.0. Credit:Alex Ellinghausen When prices are low, such as overnight or during periods of surplus wind energy, water is pumped back to the top dam. The core drilling in the Snowy Mountains is part of a $29 million feasibility study led by Snowy Hydro's former engineering unit, SMEC, due for completion by the year's end. SMEC is now owned by Singapore-based Surbana Jurong. Part of the existing and hydro scheme in the Snowy Mountains. Snowy Hydro is certainly bullish about the project, noting how pumped hydro is well understood. Indeed, its own Tumut 3 power station has been partly running on it for four decades.

Snowy 2.0 could store as much as 350 gigawatt-hours of electricity at a hundredth the cost of present-day lithium batteries, its website states. Construction – rather optimistically – "has been estimated at a minimum of four years". The huge storage could be used as the vital "firming" capacity that the national electricity grid will need if there is to be a much greater penetration by variable renewable energy sources such as wind and solar. But as promising as the technology is, Snowy's own geography and geology could render the project uncompetitive. For one thing, Snowy 2.0 would have a lot of competition, even in pumped hydro. The nation is blessed with as many as 22,000 suitable sites, as the Australian National University revealed last week, including several sites from Tasmania to Queensland nearing fruition. Engineering, too, will be a huge challenge. The proposed scheme will require boring a 27-kilometre tunnel linking the existing Tantangara reservoir in the east to Talbingo dam, and a power plant would be built about one kilometre underground.

"It's a very, very long tunnel," says Nick West, senior hydro power engineer at Entura, the consulting arm of Hydro Tasmania. "There would be other projects that could be developed quicker and easier." Should the drilling rigs prospecting potential paths find granite at least the tunnel might not need a lot of expensive shoring up, such as with steel, and construction would be simpler. "If there's weak rock, it could prove to be an issue," West says. The viability of pumped hydro also hinges on its "return efficiency" – how much energy is lost by pumping the water, or from the friction of water plunging down the tunnel. Snowy Hydro says its study is modelling a tunnel with a 10 to 12-metre diameter in a bid to limit the loss from the latter. Dylan McConnell, a research fellow at Melbourne University's Australian German Climate and Energy College, says that for a 2000 MW plant and a 10m-diameter tunnel, "the velocity of the water would have to be quite fast, ending up with significant efficiency losses".

The monumental size of the tunnel is shown by its comparison with other projects. The Chunnell between Britain and France under the English Channel, for instance, has a 7.6m diameter, Melbourne's Metro Tunnel now being built is 7m in diameter, and Sydney's Harbour Tunnel is 10.5m. Turnbull initially floated the cost of Snowy 2.0 at $2 billion. The project's bill would, though, has already swollen to double that once the cost of building extra transmission lines is taken into account. Entura's West says the industry's rule of thumb is $2m per MW of capacity for pumped storage to be viable: "Any more than that will be hard to make a case for." Environment and Energy Minister Josh Frydenberg downplayed estimates Snowy 2.0 would cost as much as $5 billion, saying the feasibility study will determine its tab. The NSW and Victorian governments – which own 58 per cent and 28 per cent of Snowy Hydro, respectively, with the Commonwealth holding the rest – are also reserving judgement on Snowy 2.0, as is the federal opposition.

Pumped hydro at a larger scale at Snowy "was not proceeded with at the time Snowy was built as it was not economical", Frydenberg says. "The economics of storage have since changed dramatically as renewables have made electricity prices far more volatile." Oddly enough, power prices may not yet be volatile enough. Tumut 3, which operates with about 70 per cent efficiency once lost energy is tallied, "scarcely" uses its pumped hydro capacity, says Hugh Saddler, an honorary associate professor at ANU. "The arbitrage gap has not been big enough for long enough," Saddler says, referring to the ability of Snowy to capture high prices by quick release of hydro power, and then tap low prices to pump the water back up the hill. Andrew Blakers, the ANU professor leading research into pumped hydro, says if Snowy 2.0 turns out to be cheap "why wouldn't they build it?"

Its advantages include its size – which could provide crucial back up for the occasional "cold wet windless weeks in winter" when energy demand is high but solar and wind power may be low. The two reservoirs – albeit massively bigger than needed – are also already in place. In a paper published this year in Energy journal, Blakers said pumped hydro already accounted for 97 per cent of the world's existing electricity storage. A station with twin reservoirs 20 metres deep with a surface of just 10 hectares – 1/200th Tantangara's size – separated by 700 metres of height and 80 per cent efficiency could deliver 500 MW of electricity for six hours. It "would be a piece of cake to build 6 GW [capacity] of pumped hydro by 2030," Blakers says, allowing for the share of renewable energy to soar to 55 per cent by then. The available hydro capacity, for instance, is already supporting electricity-hungry industries as aluminium and steel, despite claims by opponents of renewable energy, such as Tony Abbott.

Abbott told the steel industry in 2011 during his campaign against the carbon tax that "there's no way on God's earth you can have a solar-powered steel mill," reheated such claims last week. Hydro Tasmania also begs to differ, noting how about 70 per cent of its electricity – almost all of its hydro-powered – is used by four customers, including aluminium, zinc and manganese smelters. "The idea you can't integrate renewables into the grid is not true," says Chris Gwynne, a Hydro Tasmania spokesman. Hydro Tasmania, in fact, has identified massive pumped storage opportunities of its own. On Friday, it released details of potential sites that could total 2500 MW, or double its existing capacity, for a cost Hydro Tasmania has previously estimated at about $5 billion.

As part of the Battery of the Nation plan supported by the Australian Renewable Energy Agency, feasibility studies costing $5 million will examine redeveloping two existing hydro-electric plants, examine 10-15 prospective pumped hydro sites, and the role Tasmania could play in bolstering the National Electricity Market via Bass Strait links. "Our assets are always going to be more valuable in the future," Gwynne says. "There's only upside for us." The revamp of existing turbines to allow them to operate for pumped hydro could happen "certainly a lot quicker than what would need to occur at Snowy," he says. With the cost of new solar and wind now far cheaper than coal or gas, Australia could use pumped hydro to swiftly move to 100 per cent clean energy as aging "legacy" coal-fired plants drop out, Blakers says. (See AGL Energy's estimates of the relative cost of new generation, showing renewables are cheaper even with "firming" included.)

The total storage capacity needed would be about 20 GW with an average of 25 hours' supply. That total could be achieved by developing just two dozen, or 0.1 per cent, of the 22,000 suitable pumped storage sites Blakers' team identified – even without Snowy 2.0. Loading Blakers is generally supportive of the Snowy project, saying "every PM has one or two little schemes, and Malcolm Turnbull has picked a good one". Still, he says that even if Snowy 2.0 doesn't get up, wind and solar prices will keep falling and pumped storage will finally come into its own, meaning "it's really game over for coal".