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Pumped hydro energy storage: What are the opportunities for the water sector?

With the rapid growth in renewables, there is an increasing need for energy storage like pumped hydro. The water sector will need to keep up if it wants to make the most of the opportunities, writes Joshua Hoey.

Pumped hydro energy storage (PHES) is potential energy. It works like regular hydro-electricity: falling water spins a turbine and generator, producing electricity. But PHES closes the loop by pumping water uphill to be stored as potential energy, ready to flow down through a turbine and produce more electricity.

“Rather than just waiting for dams to fill up, what you can do is pump water from a low level to a high level to store, as we do in Snowy Hydro, and then release that water to produce electricity when we need it,” the Grattan Institute’s Energy Program director Tony Wood said.

Australia currently has three PHES plants (Snowy Hydro, Wivenhoe Dam and Shoalhaven – together generating 2.5 GW of electricity generating capacity) despite having over 22,000 potential PHES sites.

“It’s actually quite a bit of pumped hydro,” ANU Research Fellow at the College of Engineering and Computer Science Matthew Stocks said.

The three plants account for around 8% of Australia’s national energy mix and as renewable generation continues to grow, there will only be an increasing need for pumped hydro storage.

In 2017, with the prices for wind and solar continuing to drop, 155 GW of renewable generation capacity was added globally, outstripping new coal development.

“We’re now seeing more than 50% of the energy in South Australia coming from wind and PV [photovoltaic],” Stocks said.

The science behind pumped hydro energy storage (PHES). PHES closes the loop by pumping water uphill to be stored as potential energy, ready to flow down through a turbine and produce more electricity.

Victoria has committed to 40% renewable generation by 2025 and Queensland is looking at a 50% target by 2030. Nationally, the Clean Energy Regulator expects Australia will meet the energy target of 33,000 GWh of renewable generation by 2020, up from 17,500 GWh in 2016.

This significant growth in renewable generation means increasingly intermittent energy supplies and a need for storage like pumped hydro.

“As we put more wind and PV into the system, it’s going to be important that we store some of that energy to help smooth out the variation in the generation,” Stokes said.

Bolstering PHES

A report from Snowy Hydro Limited on Australia’s National Energy Market found that without large-scale pumped storage hydro, energy would be wasted on days with high renewable generation, and that increasing renewable generation capacity beyond the minimum targets wouldn’t be economical.

Snowy Hydro 2.0, with its addition of 2000 MW of generating capacity, has been the big pumped storage hydro announcement of late, but a number of other projects are also in the works.

Hydro Tasmania is conducting feasibility studies into its Battery of the Nation project, which it estimates would provide at least 2500 MW in pumped hydro capacity. Genex expects to begin construction later this year on its 250 MW Kidston pumped hydro project in North Queensland.

In South Australia, Tilt Renewables has announced its 300 MW Highbury project in South Australia is at the approvals phase, and feasibility studies are continuing at the 90 MW Iron Duchess project and the 225 MW Cultana pumped seawater project.

But all these projects are just a fraction of Australia’s PHES potential. A 2017 report from ANU identified over 22,000 potential pumped hydro sites around Australia, each with between 1-300 GWh of potential storage.

A 2017 report from ANU identified over 22,000 potential pumped hydro sites around Australia. A 2017 report from ANU identified over 22,000 potential pumped hydro sites around Australia. Image: ANU

ANU Professor Andrew Blakers led the research, working with Stocks and PhD candidate Bin Lu.

Blakers said the total capacity of the potential sites is over 100 times more than Australia’s estimated storage needs.

“South Australia is the state with the least potential sites, there’s only 10 times more than it actually needs. Most of the other states have got a 100 or 1000 times more sites than they need,” Blakers said.

The works

Comparing pumped storage hydro-electricity to other forms of renewable energy is misleading.

“Pumped hydro of itself doesn’t actually produce more electricity. You have to get the power from somewhere to pump the water up in the first place,” Wood said.

By using excess electricity from the grid at times of low demand to pump water to a high reservoir, pumped storage hydro-electricity plants release water and energy at times of high demand. It’s why such plants work best in tandem with intermittent sources of energy like solar and wind.

Essentially, PHES functions as an energy warehouse or battery that stores and releases energy on demand, but on a much larger scale.

“Nobody’s building battery systems that are remotely close to the scale of a pumped hydro,” Blakers said.

“Batteries are very good for small scale energy storage, if you want a lot of power, but you don’t get a lot of time operating at that power.”

The Tesla battery facility in South Australia can generate around 100 MW over an hour and 17 minutes, storing 129 MWh of electricity. On the other hand, Snowy Hydro 2.0 would generate about 2000 MW over seven days and store 350,000 MWh.

Compared to batteries, PHES plants have longer lifespans and low-self discharge rates: when the water is stored, it can remain in a reservoir for a long time before releasing its potential energy.

Unlike fossil-fuel power plants, pumped storage hydro also has black-start capability.

“If the grid goes black, you just open a valve, the water runs through the turbine and you can get your system back up,” Blakers said.

Many energy experts agree that a combination of small scale battery and larger pumped hydro storage is needed to meet Australia’s energy demands.

“Batteries are much better at short-term requirements: the wind dies down, clouds go over the sun, a disruption causing a spike in the power system,” Wood added.

Batteries react in milliseconds, covering such spikes, whereas hydro storage can provide sustained output during peak demand at short notice.

Honing hydro projects

While pumped storage hydro-electricity is typically on the 100s to 1000s MW scale, Melbourne Water has built a network of 14 small-scale hydro-electric plants, with capacities ranging from 0.09 to 7.4 MW. The plants are traditional hydroelectric plants rather than pumped hydro, but cumulatively generate 65,900 MWh per year.

“Melbourne Water’s system is gravity-fed, so as we transfer water through the system, we’ve got hydro generating plants that harness the energy,” Melbourne Water Senior Project Manager Ian Royston said.

“Basically, hydraulic head and flow gives hydro power. It actually offset all of what we consumed from our water supply services in 2015-16.”

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The small hydro units cost Melbourne Water between $1 million and $3 million to install.

“Each site has some different constraints as to the hydraulic head and the flow," Royston said.

“Is there an electricity connection nearby? Are there other assets that we have to avoid? It differs on a case by case basis and is not a one-size-fits-all."

With the latest series of plants installed in 2017, Melbourne Water was able to reduce costs by relying on a containerised format that could be lifted into place ready for connection.

The hydro units are automatically controlled through Melbourne Water’s Supervisory control and data acquisition (SCADA) system.

“From the large perspective, they’re essentially just like valves that give us energy,” Royston said.

Another five to 10 additional sites are currently undergoing feasibility studies, and the utility has been approached by others about the project.

“We’ve had lots of inquiries. We’ve shown people around and explained how we do it, and every city supply system is different.”

Future energy mix

While some have expressed concern about ensuring water supply for PHES plants in Australia’s dry climate, Stokes said there are solutions.

"You don’t need very much evaporation suppression to ensure that rainfall exceeds evaporation across the vast majority of Australia," he said.

More importantly, by moving away from fossil fuel generation, there would be an overall reduction in the water demand for energy production with PHES, even including evaporation.

“It’s probably about three or four times less water required for electricity generation, if we have wind, PV and pumped hydro, than our existing coal and gas thermal plants,” Stokes said.

Rather than competing for water resources, Blakers and others see Australia’s pumped hydro storage as a natural fit for the water industry.

“Anyone who owns pipes and reservoirs will be looking to see whether they can have a second reservoir at the top of a hill somewhere and make use of their existing infrastructure,” Blakers said.

The Shoalhaven and Wivenhoe PHES plants are at reservoirs that supply municipal water to Sydney and Brisbane, so dual use isn’t without precedence.

“If a utility has a reservoir that they’re happy to have for dual use, then there’s an opportunity for them to have a head start in terms of the asset value,” Stocks added.

First published as 'Advanced energy storage' in Current magazine May 2018.