If there is one takeaway from Queensland government's renewable energy plan, it is that the state is committed to pumped hydro technology.
It's the centrepiece of the state's new renewables target, coming in the form of two new pumped hydro facilities, one of which will be the largest of its kind worldwide.
The announcement was made by Queensland Premier Annastacia Palaszczuk in her State of the State speech on Wednesday in which she outlined the 10-year energy plan.
One pumped hydro plant will be built at the Borumba Dam in south-east Queensland west of Gympie.
The second and larger facility will be called the Pioneer-Burdekin pumped hydro project and will be situated 70 kilometres west of Mackay.
So, what is pumped hydro?
It's an energy storage system that moves water between two dams, one at the top of a hill and another at the bottom, through a turbine.
It's a simple concept of using excess renewable energy to pump water up a hill and hold it there until it's needed.
Stephen Wilson, energy advisor and an adjunct professor at the University of Queensland, said pumped hydropower works similar to rechargeable batteries but with water and gravity.
"You are basically turning gravitational energy into electrical energy by running water down through a turbine," he said.
How does pumped hydro work?
Professor Wilson said pumped hydro plants pump and store energy for times when more power is needed.
Water is stored in an upper reservoir and run through a turbine to a lower reservoir when electricity is needed, such as when the sun is not shining or the wind is not blowing.
The water can then be pumped back uphill when electricity from renewables and other sources is abundant and cheaper (the sun is shining, wind is blowing).
"At time when you might have a lot of power available, more power available than you need, you use that to drive a pump and push the water back from the lower dam, back up to the upper dam so that can then use it again later to generate power again," Professor Wilson said.
Where do pumped hydro plants source power from?
Pumped hydro plants source electricity from a grid or nearby renewables to pump and store energy for later.
Professor Wilson said pumped hydro's role cannot be looked at in isolation.
"Wind, solar, hydro, pumped hydro, gas, coal, nuclear, all these technologies have to be looked at in the context of the whole system," he said.
Deputy Premier Steven Miles told ABC Brisbane Radio, solar and wind energy from across the network, will feed into the new pumped hydro plants.
He also said the upgrade to the grid, dubbed the "SuperGrid" in the energy plan, would provide the links needed to connect the energy sources to the pumped hydro plants.
Is any energy lost to power the pumped hydro plant?
Professor Wilson said there would be energy lost to power the pumped hydro plants, just like any energy storage system.
"Over the course of the year, you will definitely use more energy driving the pumps to push the water uphill," he said.
Professor Wilson said the energy lost in each round trip is approximately 30 per cent
"You get around 70 per cent of the pumping energy back when you are running the generators to generate power," he said.
How many pumped hydro plants are there in Queensland?
Wivenhoe Pumped Storage Hydroelectric Power Station, west of Brisbane, is the only currently working pumped hydro plant in Queensland.
It was first commissioned in 1984 and has the capacity to store 570 megawatts.
The power station at Wivenhoe pumps waters uphill from Wivenhoe Dam, into and stores it in Splityard Creek Dam until energy is needed.
The Kidston Pumped Storage Hydro Project, approximately 280 kilometres north-west of Townsville, is still under construction.
The old gold mine turned pumped hydro plant is set to feed into the National Electricity Market in early 2025.
"The project's upper reservoir will be able to deliver up to 4.5 gigalitres of water to spin the project's 2-by-125 [megawatts] turbines for up to eight hours," Minister for Energy, Mick de Brenni said in April.
The Borumba pumped hydro plant is set to be completed by 2030 and will be able to store two gigawatts of power at all times — enough to provide power for 2 million homes.
Stage one of the Pioneer-Burdekin pumped hydro project, announced on Wednesday, is estimated to be completed in 2032, with the final stage operational by 2035.
By then Queensland plans to be using 80 per cent renewable energy.
Premier Annastacia Palaszczuk said the facility in Pioneer Creek will be "the largest pumped hydro energy storage in the world with five gigawatts of 24-hour storage".
Can droughts impact pumped hydro?
Professor Wilson said evaporation needs to be considered, so pumped hydro could be impacted by droughts.
"If there are very long periods with no rainfall, then you might have a problem where you do not have enough water," he said.
"But generally speaking, because you are using the water multiple times, the physical water is being cycled between the upper dam and the lower dam.
"So, you are not letting the water run away down the river and towards the sea."
