It makes up the vast majority of all energy storage worldwide, and it’s set to play a key role in the Queensland Energy and Jobs Plan that will provide power for generations to come. So how does pumped hydro actually work, and why is it so important to Queensland’s energy future?

With more and more wind and solar power in the electricity generation mix, there’s a growing need for energy storage. That’s certainly the case in Queensland, where three gigawatts (GW) of large-scale wind and solar generation are already connected to the grid, and another 22GW are set to be connected by 2035 under the newly announced Queensland Energy and Jobs Plan.

Electricity generation from wind and solar power is variable, because these generators are dependent on the weather. But in order for power grids to function, operators need to be able to manage supply and demand in real time, with a continuous flow of electricity, in order to avoid shortages, overloads and outages.

This means that, as variable renewable energy makes up an increasingly large percentage of the electricity in Australia’s generation mix, there’s a growing need for large-scale storage to store excess power at times when wind and solar output exceeds demand, and inject that power into the grid at times when wind and solar output can’t meet demand, to provide 24/7 reliable power.

Whereas coal can be stockpiled, electricity itself cannot be stored – but it can be converted into other forms of energy, which can be stored and later reconverted to electricity when required. Batteries, for instance, don’t actually store electricity, but they do store chemicals that can be converted into electricity, through a process known as electrochemistry.

Similarly, excess wind and solar energy can be used to power the production of renewable hydrogen. This can be stored for long periods of time and converted back into electricity that can be dispatched when the market needs it, helping to firm the grid and smooth out peaks and troughs in supply.

With renewables now expected to make up 70 per cent of Queensland’s generation by 2032, and almost 100 per cent of total annual generation in the National Electricity Market (NEM) by 2050, unprecedented levels of investment in dispatchable energy storage are required. This will include utility-scale batteries, renewable hydrogen and virtual power plants, as well as pumped hydro.

What is pumped hydro?

Hydropower, which converts the energy of moving water into electricity, is one of the oldest energy technologies in existence.

Hydropower works by passing water from an upper reservoir down to a lower reservoir, usually a dam. On the way down, the water flows through a turbine. The force of the water causes the turbine’s blades to rotate. The spinning turbine, in turn, drives a generator connected to it, which converts the motion into electrical energy, or hydroelectricity.

Pumped hydro takes this process a step further. A plant using pumped hydro technology won’t just pass water down through a turbine. It’ll then pump that water back up to the upper reservoir through a pipe or tunnel, where it can be stored and used to generate energy again.

Pumped hydro storage consumes more electricity than it produces – it requires about 20 per cent more electricity to pump water uphill than is generated when the water comes back down. But timing is everything, and the key to pumped hydro’s usefulness is in when it consumes and produces energy.

At times when supply is plentiful and demand is low, electricity – either from the grid or from a nearby renewable energy source – is used to pump water from the lower reservoir into the upper reservoir.

The water is then held in the upper reservoir until energy is needed, either because wind and solar production has reduced or stopped or because demand has increased (or both). The water is then passed back through the turbine into the lower reservoir to produce hydroelectricity.

This essentially turns the upper reservoir into a giant battery, storing surplus energy until the grid requires it.

Pumped hydro generators are capable of fast response times (from idle to full capacity in one or two minutes), so their hydroelectricity can be dispatched into the grid almost immediately whenever the operator requires it. Their generators can also be operated as synchronous condensers, providing grid stability services without consuming any significant quantity of water.

Today’s lithium-ion batteries are ideal for storing and releasing energy over short periods of time – say, for storing energy while the sun is shining during the day and releasing it when demand peaks in the early evening.

But pumped hydro is generally capable of storing larger amounts of energy for longer periods of time, making it a more cost-effective option for overnight and long-term storage – at least until bigger and better batteries are more economical.

Because of their heavy rotating generators, pumped hydro plants provide the grid with inertia. Inertia acts as a shock absorber, maintaining consistent frequency across the grid and preventing surges that can cause damage to connected electrical systems and equipment.

Presently, this inertia is provided by coal-fired and gas-fired power stations. But it’s not provided by generators that are connected to the grid via inverters, including solar panels, wind turbines and batteries, although new developments in grid-forming inverters may address this issue.

What’s the status of pumped hydro in Australia?

Pumped hydro accounts for about 97 per cent of all energy storage worldwide, but there are only three major pumped hydro systems connected to the grid in Australia at the moment.

The 1.6 gigawatt (GW) national pumped hydro fleet includes the Wivenhoe Power Station in Queensland, and the Tumut and Shoalhaven stations in New South Wales. In May 2021, the Wivenhoe pumped hydro station ramped up quickly to generate 530MW over a four-hour period, helping to meet demand after an unexpected outage.

There are another two projects currently under construction. The Snowy 2.0 project in New South Wales will link the Tantangara and Talbingo dams via 27 kilometres of tunnels, while construction has also begun on the Kidston Pumped Storage Hydro Project in North Queensland, about 270 kilometres northwest of Townsville.

The recent Queensland Energy and Jobs Plan included details about two new world-class pumped hydro projects for Queensland that could deliver up to 7GW of long duration storage. The Queensland Government is investigating two sites:

• Borumba pumped hydro – Located near Imbil in the Gympie region, this site has been undergoing detailed design and cost analysis, and consultation with the local community.

• Pioneer-Burdekin pumped hydro – Initial studies are underway for this site near Mackay, referred to by Premier Annastacia Palaszczuk as ‘The Battery of the North’, which has the potential to be the largest pumped hydro station in the world. At 5GW, its potential generation capacity is 2.5 times that of Snowy 2.0.

The Queensland Government has set aside $273.5 million, including $203.5 million in new funding announced as part of the Queensland Energy and Jobs Plan, to advance consideration of the Borumba and Pioneer-Burdekin projects. The funding will support detailed engineering and environmental investigations, community engagement, and some early access works.

If the projects proceed, they are expected to become pillars of the Queensland SuperGrid – the collective name for all of the poles, wires, solar, wind and storage that will provide Queenslanders with clean, reliable and affordable power for generations.

Ultimately, the more energy storage is connected to the grid – whether it’s in the form of pumped hydro, renewable hydrogen, batteries, or other emerging technologies – the more renewable energy resources will be unlocked, ensuring a steady and secure supply of power for homes and businesses around Queensland and Australia as our energy system evolves.