Green energy: a new life for an old mine

The 100% Renewable Energy Group at the Australian National University (ANU) in Canberra has used satellite imagery to identify sites where off-river pumped hydro energy storage (PHES) schemes could be developed. Among these sites are what are known as brownfields: areas previously used for mining or some other activity that could be repurposed. It identified 904 disused mines across the globe with the potential of becoming PHES schemes with a combined storage capacity of 30 terawatt-hours (30 TWh). Australia is home to 37 of them, with the potential of supporting the country’s energy transition. They include the Coppabella coal mine in Queensland, the Cadia Hill gold mine in New South Wales, the Leigh Creek coal mine in South Australia, and iron-ore mines in Western Australia. By converting these sites into PHES, they would have a combined storage capacity of 540 gigawatt-hours (540 GWh). In an interview with We Build Value magazine, ANU Research Officer Timothy Weber explains how such schemes not only require less water than coal-fired power stations but also recycle what they use to turn their turbines. They are a sustainable way to supporting the country’s transition to renewable energy sources.

WHY SHOULD OLD MINES BE CONVERTED INTO PUMPED HYDRO ENERGY STORAGE SCHEMES?

One of the big bottlenecks for Australia’s energy transition at the moment has been building new transmission (lines). Part of the challenge is that you have to negotiate with lots and lots of private landholders to pass the new transmission through their lands. So if you have a mine site where you’ve already got electricity transmission infrastructure set up… a water licence or a water source nearby with pumping infrastructure… nearby accommodation, perhaps major road access… it is a lot easier to get through the decision (-making) process to build a pumped hydro system and not having to negotiate with too many different stakeholders. Examples of brownfield PHES already exist. There is the Dinorwig Power Station, located in a slate quarry in northern Wales (United Kingdom). It has been operating for more than 30 years.

THESE 37 SITES COULD DELIVER A COMBINED 540 GWH OF STORED ENERGY POTENTIAL? 

For Australia, we would need roughly 550 to 950 GWh worth of energy storage for 100-percent renewables (based on industry and university analyses). It sort of depends on how big our hydrogen economy will be. And Snowy 2.0 (Editor’s Note: being built by Webuild and its local subsidiary Clough in the Future Generation Joint Venture for integrated energy provider Snowy Hydro Limited) is already going to be 350 GWh of that. And so that is going to be a big chunk of seasonal storage. But then, from our brownfield atlas, we’ve got those 37 sites giving 540 GWh of energy storage potential.

WHAT ARE THE CHALLENGES OF CONVERTING OLD MINES INTO PHES?

One of the challenges with mines in particular compared to – say – a greenfield site with a brand-new reservoir is that mines are particularly dug with quite steep sides. If you have very rapid pressure fluctuations from the water changing height in the reservoir as you pump it and drop it back down, it can put a strain on the steep slopes and create problems within the reservoir. They are sort of conically shaped and so towards the bottom of the reservoir as you drop a small volume of water, you can have a rapid change in the head for the pumped hydro system, and that significant pressure change can impact the turbines, so you are sort of mostly constrained to the top volume of the reservoir and you can’t use the very steep conical bottom quite as much unless you shape it at the end of a mine’s life.

There is also the challenge of contamination. If there are sulphides from the mining process, they can form sulphuric acid when mixing with water and that can lead to contamination for ground water or the local environment. So you might need some other measures like a reservoir lining to protect against seepage through the ground of those contaminants.

WHERE DO YOU GET THE WATER TO TURN THEM INTO RESERVOIRS?

The benefit of a mining site is that they might have an existing water licence and pumping infrastructure. But it just depends on the nearby water sources, which might be from groundwater, an aquifer, or nearby reservoir, nearby river flows. It would be the same process where you acquire a water licence and pumping rights, and you can take a certain amount of that water off for a given period of time. But the benefit of the pumped hydro is that if you had a 100-percent renewable energy grid supported by pumped hydro, that is going to use far less water than the existing fossil fuel power stations because you have no cooling towers and you have no fuel processing which also uses a lot of water for processing coal. And then the pumped hydro – because we look at off-river sites which are closed loop …just recycle the water backwards and forwards for a hundred years. So after your initial fill, you only really need to top up little bits for evaporation and seepage and that’s it.