A study has found so many potential sites for pumped hydro storage that a 100% clean energy future is as certain as the sun will rise.

Batteries don’t get any bigger than pumped hydro – and the technology could hardly be more simple. Scoop out two reservoirs, one high above the other, connect them with a pipe, add a turbine and off you go.

It’s not a free ride, of course. Pumped hydro will only store about 80% of the energy it takes to push all that water uphill. But in a grid where the majority of generation is coming from renewables, a surplus of midday solar energy could be stored using pumped hydro for later in the day when the evening peak hits.

Around the world, pumped hydro accounts for 97% of stored energy systems. In Australia, we have three systems at work: Wivenhoe in Queensland and Tumut 3 and Kangaroo Valley in NSW.

We need more, says Australian National University professor of engineering Andrew Blakers.

Research from ANU is showing the cheapest way for Australia to solve its crisis of tearaway energy prices and patchy supply is to move to 100% renewables quite rapidly. At the moment Australia is adding about 3GW of wind and solar a year, Blakers says, which will get us to over 50% by 2030. If we push it up to 6GW a year, we’ll be 100% renewable by 2033.

Australian National University professor of engineering Andrew Blakers.

“Solar PV and wind generation are cheaper than gas, coal or nuclear, so it’s not very hard [to go 100% renewables],” Blakers says. But as renewables reach the tipping point of more than 50% of supply we’ll need more transmission, demand management and storage to stabilise the grid.

The good news is that Australia has a tonne of potential when it comes to pumped hydro. After looking over South Australia, Queensland, Tasmania and the ACT, Blakers’ team has found sites with a combined capacity of 15,000GWh, or more than 35 times what is needed to get to a 100% clean energy grid.

Estimates of capacity at the 5,000 sites range between 900MWh to more than 100,000MWh, which puts the 130MWh Tesla installation under construction in South Australia into perspective. The proposed Snowy Hydro 2.0 upgrade would boost capacity to 360GWh.

Queensland is host to 2,213 sites, Tasmania 2,075 sites, ACT and surrounds 871 sites, Alice Springs district 384 sites and South Australia 185 sites. The team slung the country into its modelling without any consideration for land ownership and nothing in the list of potential sites implies any rights for development. The researchers are now looking for sites in NSW, Victoria, Western Australia and the Northern Territory.

Stability and agility

Blakers says about 450GWh of storage is required to stabilise the NEM when renewables reach 100%, and his research has isolated sites with at least a 300-metre head, being the height difference between upper and lower reservoir. He’s particularly pleased the sites are mostly remote from running sources of the essential ingredient: water.

“Almost everything we’re turning up is nowhere near a river,” he tells EcoGeneration. “Ninety-nine percent of Australia is not near a river, so if you only look near rivers you’ll miss 99% of the sites. We avoid a large number of problems [such as flooding] by going off-river and multiplying by a factor of 100 the number of sites that we find.”

The things that would make a site look good are a big head, between 300 and 700 metres, a steep hill to the lower reservoir so the pipes or tunnels are short and steep, a large upper reservoir and geography that doesn’t require too much rock be moved.

“Because there are so many sites we are finding it’s reasonable to suppose you look at one site and if you run into a problem you go to the next one which could be over the ridge, just half a kilometre away.”

Pipes can be exposed but sometimes it’s cheaper to tunnel through, if an upper reservoir is on the other side of a ridge from a good lower reservoir site, he says. “The tunnel might only be 50 metres or 100 metres, but it makes the site very attractive – to tunnel through the ridge and go down the steep hill on the other side.”

The volume of water in a 20-hectare reservoir 20 metres deep would be enough to produce about 3GWh, or 300MW of power for 10 hours, the research says. “Roughly speaking, 1GWh of energy storage requires 1GL of stored water for a 400m head.”

Doubling the head doubles the power and energy available from an upper reservoir but usually does not double the capital cost, the research says.

Australia’s backbone

Virtually all of the sites the researchers have found run along the mountains from Cape York down to Melbourne and up the eastern side of the gulf in South Australia. That also happens to be where people live, the wind is strong and high voltage power lines are already built.

New transmission needs to be built west of the Great Dividing Range regardless of what storage is used, Blakers says, because storage and transmission support high penetration of wind and solar. “You can trade one for the other, in that if you have a lot of storage you can reduce the amount of transmission you need, or if you have a lot of transmission you can greatly reduce the amount of storage you need.”

An efficient National Energy Market is one where generation and storage assets are spread far and wide, he says. If you’re connecting North Queensland right through to South Australia, the chance that there’s poor weather for solar and wind generation becomes very low. If you go for high penetration of wind and solar and storage in one state, there’s a good chance the whole state has the same weather. “That’s why transmission is really important and it’s also why storage is important.”

The optimum is to spend a similar amount of money on more transmission and on more storage. “If you have too much of one and not enough of the other then you’re going to be spending more money than you have to.”

In sync

Blakers has spoken to a few of the major companies that build pumped hydro projects around the world and has been told it could take as little as three years to build plants, “if you get a bit of a production line going”. All the mechanical components and the electrical components go in parallel with the construction of the reservoirs and due diligence is simplified if you are not in river valleys and not exposed to floods.

“You need to build these things in sync with the PV and wind,” Blakers says. “If you build them too fast you’ll have quite a few of them sitting doing nothing because there’s not enough PV and wind variability to justify them. If you build them too slow you’ll have blackouts.”

The survey assumes earth and rock walls no more than 40m high, average water depth of 20m, minimum reservoir surface area of 10 hectares and a minimum volume of 2GL (very roughly equivalent to 2GWh storage). Pumped hydro plants have a lifetime around 50 years.

Once completed, the simplest way of filling a reservoir is to harvest water from a side gully. Most of the upper reservoirs identified are in high dry gullies that do run with water sometimes. Rainfall and evaporation are fairly similar. In some cases water may have to be trucked in.

Other than the attraction to investors of pumping when power is cheap and generating when it’s expensive the other important revenue component is from constant supply to a constrained powerline which otherwise may rely on intermittent solar or wind. “That means you make three times better use of that power line.” Equivalently you can put three times as many solar farms at the end of that powerline because you can squeeze that power down in the middle of the night if you’ve got local storage, he says.

The study received $449,000 in funding from the Australian Renewable Energy Agency.