From abandoned mine to pump storage station

Using gravitational potential energy as a storage solution...
13 June 2022

Interview with 

Ashley Grohn, Mott MacDonald


A coal mine


Another way to store energy is to use gravity. If you use electricity to push something up a hill, you’ve given it gravitational potential energy and you can get that energy back by letting the thing roll back down the hill. If you do this with water, you’ve got the basis of what’s called a “pump storage hydroelectric system”, and this is what engineers have been able to do in one part of Queensland in Australia. In a world first, they’ve turned a flooded abandoned mine pit at Kidston into a system that uses solar energy to pump water out of the mine pit during the day to provide power for the nearby town at night. Mott MacDonald’s Ashley Grohn told me how it works…

Ashley - The Kidston project converts a 100 year old gold mine and repurposes it into a gravity hydro pump storage project. It's a fascinating project because the mine workings left a 300 metre pit in the ground which, for reference, now that I'm sitting in London, is about the height of the Shard. Over time, it has filled with water and what the project does is it uses that 300 metre height differential to store energy in a top reservoir and generates energy through turbines, dumping the water into the lower reservoir. Then, it recycles the water back up to the top reservoir to store it so that it can be used on a daily basis.

Chris - Is this an open-cast pit, or are we talking old mine workings, tunnels, etc.?

Ashley - It is an open-cast pit and the spoil left from the mine workings has created the upper reservoir and the 300 metre deep pit is the lower reservoir for the pump storage scheme.

Chris - And how big is that pit then?

Ashley - If you were a golfer, it's about a driver, approximately 300 or 400 metres - depending on how good you are at golf -across. If you can, imagine a conical shaped pit in the ground.

Chris - How much water is in there?

Ashley - It's in excess of 3000 Olympic swimming pools and the pump storage scheme basically pumps 2000 Olympic swimming pools up the hill over an eight hour period. Then, it can flow the same quantity of water down through the turbines to generate the power in an eight hour period.

Chris - I presume that the rationale for doing this is you could use electricity that you've produced in a green way to power those pumps. So, you're basically using renewables to push the water uphill and store that energy as gravity. Then, you can turn the taps on when you want that energy back when the sun isn't shining or the wind isn't blowing?

Ashley - That's absolutely correct, Chris. In Australia in particular, we have excess solar power generated during the day, so there is excess and very cheap solar energy to pump the water up the hill. Then, when everybody comes home of an evening and switches on their air conditioning in Australia, or boils their kettle in the morning, we can generate power from that water stored during the day to meet the needs of consumers during the night and the morning peaks.

Chris - How much energy will this thing put out? How powerful is it?

Ashley - In technical terms, it's a 250 megawatt scheme and can generate for eight hours. As a point of reference, that's basically enough to power 100,000 homes.

Chris - Right. When those people come home from work, this thing just basically turns on and runs all night. And so they've got power coming from this project all night?

Ashley - It has the potential to run all night. That's correct. Really, its primary purpose is, as we are retiring conventional coal fired power plants, there is potential for pump storage and even bigger projects than this in Australia, basically to keep the lights on and keep industry moving that works on a 24 hour cycle.

Chris - I suppose one other benefit here, you mentioned coal, is that traditionally when people have turned the TV on and then the adverts have come on and they've put the kettle on, or their favourite programme finishes and they put the kettle on, or there's just anticipation of people coming home in the evening and putting the air con on, they have to turn the coal fired power stations on an hour or more before they want that surge because it takes that long to heat things up. Presumably, yours, because the water is sitting there ready to go, it's just a press of a button and you're up to full output instantly?

Ashley - That's a good analogy, Chris. Whereas a coal fired plant will take hours to heat up, a pumped hydro scheme can basically go from zero to full output in one to two minutes.

Chris - How much does it cost to implement? Is this something which is a realistic prospect or do you need very specific conditions to make something like this work?

Ashley - Yes. At the moment, when we look at the energy trilemma - that balance between sustainability, energy security, but also importantly price - especially in the Australian market, you really do need a pump storage scheme that works in your favour economically, for it to be comparable with other technologies. That was the beauty of the Kidston project because, essentially, the big holes were already in the ground and there was already significant infrastructure at site including actually a solar farm that had already been built. It economically stacked up and it is the first project in 40 years built in Australia in terms of hydro and it is the first project that has actually been privately financed.

Chris - I presume one could now take the blueprint for doing this because you must have data to die for in terms of how to implement this, how it works, what the pitfalls are, literally as well as metaphorically, in terms of being able to extrapolate this, upscale it, downscale it and distribute it across the world. There must be lots of places where this would be an ideal fit.

Ashley - Absolutely. There are a lot of learnings, especially when you are looking at repurposing an old mine workings. Certainly, the international hydro association has been looking at this, as well as most countries globally, looking at the opportunities. There is absolutely no shortage. In Australia alone, there are literally thousands of potential opportunities for pump storage that have been identified.


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